Crustal Structure, Deformational History, and Tectonic Origin of the Bahamas Carbonate Platform

The 2–10‐km‐thick, mainly carbonate cap of the 14,000 km2 Bahamas carbonate platform (BCP) has impeded imaging of its underlying crustal structure. The deeper structure of the BCP records both its Mesozoic rift and hotspot history and its later deformation related to its Paleogene collision with the Great Arc of the Caribbean (GAC). We use regional gravity data to model the crustal structure, type, and deformational processes of the BCP by: (a) integrating publicly available seismic data; (b) inverting the Moho along 2D regional gravity transects across the collisional zone; (c) modeling flexural uplift of a forebulge that reflects the attempted subduction of the BCP beneath the GAC; and (d) using downhole temperatures and radiogenic heat production in 1D basin models to differentiate crustal types related to the Mesozoic rift history. We interpret three crustal domains underlying the BCP: (a) 27–12‐km‐thick, rifted, and thinned continental crust of the northern Bahamas between the Blake Plateau and Exuma Sound; (b) 24–12‐km‐thick, volcanically‐thickened oceanic crust related to the Triassic‐Jurassic Bahamas hotspot in the central Bahamas southeast of Long Island; and (c) 20–12‐km‐thick, thickened oceanic crust north of Hispaniola. We propose that these crustal types reflect northwest‐southeastward, Triassic‐Jurassic rifting of the Bahamas region during the breakup of Pangea and accompanying magmatic activity related to the Triassic‐Jurassic Bahamas hotspot and early oceanic spreading. Growth of the BCP during the Cretaceous in this area was followed by Late Cretaceous‐Paleogene subduction‐related flexure and terminal Paleogene collision between the GAC and the BCP.


Challenges for Understanding the Crustal Structure of the Cuba-Bahamas Collisional Zone
The largely submarine Bahamas carbonate platform (BCP) formed during late Triassic to early Jurassic continental rifting between Guyana in South America and Mauritania in West Africa (Basile et al., 2020;Erlich & Pindell, 2020;Reuber et al., 2016) (Figure 1a).Following the Triassic-Jurassic rifting event, the Cretaceous-Paleogene development of the Bahamas passive margin is recorded by the deposition of the 2-10-km-thick BCP (Pindell & Kennan, 2009).The Great Arc of the Caribbean (GAC) diachronously collided with the ramped, southwestern margin of the Bahamas margin from the Paleocene to the early Miocene (Massaferro & Eberli, 1999;Montheil et al., 2023) with the main collision between the Cuban sector of the GAC occurring during the period from the latest Paleocene to early Eocene (Bralower & Iturralde-Vinent, 1997) (Figure 1a).
There are three different hypotheses for the Mesozoic, rift-related crustal structure underlying the BCP: (a) thinned continental crust related to the Mesozoic rifting of the North American, African, and South American plates (Ball, 1967;Mattson, 1972;Mullins & Lynts, 1977) (Figure 1b); (b) volcanically-thickened oceanic crust related to hotspot activity associated with the breakup of Pangea (Dietz et al., 1970;Newell, 1955) (Figure 1c); and (c) the early formation of oceanic crust in the Central Atlantic Ocean (Klitgord et al., 1984;Uchupi et al., 1971) (Figure 1d).The interpretation of continental crust beneath the Bahamas was also proposed from stratigraphic correlations between continental rocks in Cuba and the Bahamas (Ball, 1967) and from the presence of continental crust beneath the BCP that was inferred from seismic reflection and potential fields data (Mullins & Lynts, 1977) (Figure 1b).Newell (1955) inferred volcanic activity within the Bahamas and suggested that the Cretaceous-Cenozoic BCP nucleated on volcanically-thickened oceanic crust and seamounts (Figure 1c).Dietz (1973) correlated Late Triassic-Early Jurassic volcanic rocks now known collectively as the Central Atlantic Magmatic Province (CAMP) (Marzoli et al., 2018) with thickened, oceanic crust beneath the BCP.Rhyolite samples of latest Triassicearliest Jurassic CAMP age have been recovered from deep wells drilled into the basal sedimentary sections of the BCP (Erlich & Pindell, 2020).Becker et al. (2009) showing the location of the study area of the Bahamas-Great Arc collisional zone of Paleogene age.The dashed yellow line indicates the extent of the Bahamas carbonate platform (BCP) and the black dotted line indicates the location of the schematic, along-strike cross-sections of 1b, 1c, and 1d.(b) Cross-sectional view of thinned continental crust underlying the BCP as proposed by Ball (1967), Mattson (1972), and Mullins and Lynts (1977) along the dashed, regional, cross-sectional line extending 1,500 km from the Straits of Florida to Puerto Rico.(c) Cross-sectional view of volcanically-thickened oceanic crust reflecting hotspot activity underlying the BCP proposed by Newell (1955) and Dietz et al. (1970).(d) Cross-sectional view of normal oceanic crust underlying the BCP proposed by Uchupi et al. (1971) and Klitgord et al. (1984).BCP, Bahamas Carbonate Platform; CB, Ciao Basin; ES, Exuma Sound; PRT, Puerto Rico Trench; TC, Turks and Caicos; TOT, Tongue of the Ocean.

SHIPPER AND MANN
The objective of this paper is to carry out 3D integrated modeling of potential fields, seismic reflection, and refraction data to test the three hypotheses for the crustal structure beneath the BCP (Figures 1b-1d).These studies of the subsurface crustal structure of the BCP are an important step for: (a) improving Triassic-Jurassic plate reconstructions of the BCP and its conjugate margins in Guyana and Mauritania (Basile et al., 2020;Erlich & Pindell, 2020;Kneller & Johnson, 2011;Pindell & Heyn, 2022;Reuber et al., 2016); and (b) for understanding the regional deformation induced by the early Cenozoic collision of the GAC with the BCP (Bralower & Iturralde-Vinent, 1997;Román et al., 2021).In this study, we use the earliest Jurassic (200 Ma) reconstruction of Müller et al. (2019) to propose that the Bahamas hotspot was located near the tip of the present-day Florida Peninsula and formed the center of a large, radial dike swarm (Figure 2).The orientation of Triassic-Jurassic mafic dikes of the reconstructed, pre-rift continental blocks of North America, South America, and Africa are radial about this Bahamas hotspot (Marzoli et al., 2018), and have been inferred to be the center of its plume head (Mann, 2022) (Figures 2b-2e).

Tectonic
The tectonic origin and age of Mesozoic, rift-related volcanic rocks in this region remains poorly known because of their deep burial beneath the BCP and beneath the conjugate Demerara and Guinea oceanic plateaus (Figures 2a-2d).Both these conjugate, oceanic plateaus exhibit layers of seaward-dipping reflectors (SDRs), which are up to 25 km in thickness and dip in the restored position of the conjugate BCP (Reuber et al., 2016) (Figures 2a-2d).Basile et al. (2020) dated volcanic rocks in the uppermost SDRs of the Demerara Plateau as Middle Jurassic (173.4Ma), with the thick, underlying SDR sequence remaining undated.This regional pattern of Late Triassic to Early Jurassic magmatic activity collectively forms the CAMP along the three arms of the Proto-Central Atlantic Ocean, Proto-Bahamas and Gulf of Mexico (GOM), and the Proto-Equatorial Atlantic Ocean at the Triassic-Jurassic boundary (200)(201)(202) (Marzoli et al., 2018;Mann, 2022).The volcanic rocks underlying the BCP may have formed either as a northwestern branch of CAMP (Erlich & Pindell, 2020;Pindell et al., 2021) or were related to a more localized hotspot that included the conjugate Demerara and Guinea volcanic plateaus (Figure 2b).In this study, we follow the plate reconstruction from Müller et al. (2019) that shows the sequential locations of the Bahamas hotspot, that became sub-divided into three parts that now underlie the BCP and the Demerara and Guinea plateaus (Figures 2b-2j).Much of the volcanicallythickened Early Cretaceous oceanic crust related to the Bahamas hotspot track in the southeastern BCP has either been subducted beneath Hispaniola and Puerto Rico.

Paleogene Collision of the GAC With the BCP
The formation of the GAC collision can be described in seven phases as shown on the plate reconstructions in Figures 2e-2g: (a) creation of oceanic crust within the proto-Caribbean seaway formed by the separation of the North and South American plates (Levander et al., 2006;Pindell, 1985;Pindell & Kennan, 2009); (b) Jurassic opening and seafloor spreading in the central GOM and its resulting, counter-clockwise rotation of the Yucatan block (Lin et al., 2019;Pindell & Dewey, 1982); (c) Cretaceous formation of the Caribbean large igneous province (CLIP) (Pindell & Kennan, 2009;Romito & Mann, 2021); (d) late Cretaceous collision of the Chortis block with island arc terrane north of the CLIP (Pindell, et al., 1988;Rosenfeld, 1993;Sanchez et al., 2016); (e) eastward transport of the CLIP and Caribbean Plate as the western GAC collides and translates past the Bahamas margin and into the Central Atlantic Ocean (Gordon et al., 1997;Mann et al., 1995); (f) large-scale counterclockwise rotation of the eastern GAC collisional zone related to its indentation by the BCP (Erikson et al., 1990;Montheil et al., 2023); and (g) Eocene to recent formation of the Cayman Trough that records the steady, eastward motion of the Caribbean Plate (Rosencrantz et al., 1988) (Figures 2e-2g).
The top crystalline basement and Moho were interpreted from vintage seismic reflection and refraction controls and were gridded to a cell size of 55 km that was then used to constrain gravity models (Figures 4a and 4b).Interpretation of seismic refraction and reflection in the central BCP indicates a 3-7 km depth to the top basement in the northwestern Bahamas and a 7-10 km depth to the top basement in the southeastern BCP (Figure 4a).Only one refraction station is present within the central Bahamas and indicates a depth to the top basement of 11 km that is related to a rift with Mesozoic salt diapirs known in the Exuma Sound area (Spector et al., 2016) (Figure 4a).We infer that salt deposits beneath the Exuma Sound are the southernmost occurrence of a discontinuous salt belt associated with rifts along the east coast of the USA (Mann, 2022).
The best expression of a suture-parallel, flexural bulge is observed as a northwest-trending high below the Cay Sal Bank with the top of basement at a depth of 5-6 km.Massaferro et al. (2002) dated the uplift of the Santaren anticline that parallels this structural high by analyzing its Cenozoic growth stratigraphy.Their results indicate folding continued throughout the Oligocene-Early Miocene, which records the waning collisional phase of the Cuban segment of the GAC with the BCP that began during the Paleocene-Eocene (Bralower & Iturralde-Vinent, 1997;Cruz-Orosa et al., 2012;Gordon et al., 1997).
The original structure of the intraoceanic GAC (García-Gasco et al., 2008) combined with the convergent crustal deformation of the GAC and areas within the Caribbean Plate form an irregular top basement surface for the collided, intraoceanic arc crust of the GAC (Figure 4a).The 4 km transition from top crystalline basement in northwestern Cuba to much shallower and deeply-eroded basement in Hispaniola reflects the active transpressional deformation of Hispaniola along the Septentrional (SFZ) and Enriquillo-Plantain-Garden fault zones (EPGFZ) (Román et al., 2021;Sun et al., 2020).

Previous Onland and Oceanic Drilling
From the 1970s-1990s, the petroleum industry drilled five onland exploration wells, which yielded three successful shows of live oil and gas condensate from early Cretaceous and late Jurassic limestone.These wells include: (a) Cay Sal-1, which was drilled to a depth of 5,762 m into Late Jurassic evaporites; (b) Long Island-1, which was drilled 5,351 m into Barremian dolomite; (c) Doubloon Saxon-1, which was drilled 6,626 m into Late Jurassic evaporites and carbonates; and (d) Great Isaac-1, which was drilled 5,439 m through a thick carbonate   Becker et al. (2009) showing the location of wells and vintage seismic reflection data compiled for our study area indicated by the dashed, white line.(b) Regional well correlation along a 1,200-km transect crossing the northwestern Bahamas carbonate platform modified from Dale (2013).The oldest rocks penetrated by deep wells are Triassic volcaniclastic rocks in Great Isaac-1.Sedimentary sections within most of these wells consist of dolomitic limestone with interbedded anhydrite (Jacobs, 1977).Oil and gas shows are documented from all of the wells and are indicated on the well logs.Well abbreviations are: CS, Cay Sal-1; CC, Cayo Coco-2; LI, Long Island-1; DS, Doubloon Saxon-1; and GI, Great Isaac-1.section into a basal Triassic volcaniclastic rock related to continental rifting.A summary of these well logs is shown in Figure 3.
Ten Oceanic Drilling Program (ODP) sites have been drilled for academic objectives in the northwestern Bahamas along the southern Blake Plateau, in the northwestern Tongue of the Ocean and in the Exuma Sound, and along the boundary on the edges of the Great Bahama Bank (Austin et al., 1998;Eberli et al., 1997).Drilling reports document the presence of Miocene-recent shallow-water carbonate and evaporite rocks.Schlager et al. (1988) described a transition from Cretaceous shallow-water deposits to Late Cretaceous-Miocene deepwater chalks, which reached a maximum paleowater depth of 660 m (Figure 3b).Biostratigraphy for these deep-water chalks deposited during the Eocene-Oligocene (Schlager et al., 1988) and shallow-water depths near Mesozoic salt diapirs in the Exuma Sound (Spector et al., 2016).

2D Gravity Modeling
Bathymetric and topographic data used as input for the gravity modeling transects of the BCP were compiled from Becker et al. (2009).The boundaries of the BCP were taken from Sun et al. (2020).Publicly-available gravity data from Liang et al. (2020) were also used in this study for forward modeling.Sources for the gravity data include the GOCE, GRACE, satellite altimetry, and EGM2008 datasets.The total horizontal derivative (THD) filter was applied to these gravity data to identify major structural and crustal boundaries throughout the study area following the methods of Yuan and Geng (2014).Magnetic data from Zietz (1982) was used to constrain alternative forward models for the modeled gravity transects.
We produced 2D gravity models for nine regional transects across the BCP using the GM-SYS module in Oasis Montaj.Each model calculates free-air gravity from interpreted blocks with the standard crustal, upper mantle, and oceanic densities compiled from previous studies.Densities for deeper sediments were calculated by comparing velocities from refraction data with the Nafe-Drake curve (Ludwig et al., 1971).
Each gravity transect distinguishes individual blocks whose boundaries were determined from seismic refraction, seismic reflection, and well log information.The total error tolerated between observed and calculated gravity is ±15 mGal.

2D Flexural Modeling
To assess the deformational effects of the Paleogene collision between the BCP and the GAC, we applied an analytical solution for the deflection of an infinite plate affected by a line load (Turcotte & Schubert, 1982).Flexural modeling was completed along all nine transects using the MATLAB Toolbox for Analysis of Flexural Isostasy (TAFI) script (Jha et al., 2017).

Basin Modeling
Genesis and Trinity modeling software from Zetaware, Inc. was used to model thermal stress for each 1D basin model.Thermal stress is defined as the standard temperature that a source rock must attain at a standardized heating rate of 2°C/Myr to achieve approximately the same extent of kerogen degradation as when heated to the real temperature at the real rate within a sedimentary basin (Pepper & Corvi, 1995).

Regional Crustal Structure From Potential Fields
Gravimetric and magnetic data were used to map the top of the crystalline basement that underlies the BCP.We applied a THD filter to Bouguer gravimetric data from Liang et al. (2020) to image lateral changes in gravity anomalies and to identify primary structural domains throughout the broader study area of the northeastern Caribbean (Figure 5).Most of the gravimetric data for the BCP are low resolution because of the 2-10-km thickness of its Cretaceous-Cenozoic carbonate cap.Positive anomalies throughout the Bahamas are associated with larger carbonate platforms, including the Cay Sal Bank, Blake Ridge, and Turks and Caicos Islands.Negative gravity anomalies correspond to the Tongue of the Ocean, Exuma Sound basin, Colombian basin, Puerto Rico Trench (PRT), and the GAC-Bahamas suture zone (Figure 5).The Bahamas fracture zone described by Le Pichon and Fox (1971), Klitgord et al. (1984), andPindell (1985) was renamed the "Florida Transfer Fault" by Pindell and Heyn (2022), as much of this linear fault traverses continental crust of south Florida known from deep drilling.We interpreted a co-linear fracture zone in the BCP using elongated positive THD anomalies and truncated free-air anomalies extending along the northwestern edge of the Turks and Caicos Islands, Long Island, southwestern Exuma Sound, and northern Andros Island (Figure 5).Oliviera de Sá et al. ( 2024) describe the "Cuba fracture zone" extending along the length of the Cuba-BCP suture zone.They proposed that the fracture zone was an older oceanic feature that was reactivated during the Paleogene Cuba-BCP collisional event.

Northwestern Area of the Cuban Arc and BCP
Gravity transects A, B, and C extend 1,000-1,500 km to the northwest across the northwestern Pinar Del Rio and Santa Clara areas of western Cuba to the Camaguey area of central Cuba and extending across to the northwestern BCP in the area of the Cay Sal Bank and to the Great Bahamas Bank in the central BCP (Figure 6).The variation in crustal thickness is supported by previous interpretations of the Moho and top of crystalline basement (Barrera-Lopez et al., 2022;Moreno Toiran, 2003;Rosencrantz, 1993).

Crustal Structure of the Yucatan Back-Arc Basin
Transect A crosses the Yucatan back-arc basin and shows the transition from a 12-km-thick crust within the Cayman Ridge along the southern margin of the Yucatan basin to 3-km-thick oceanic crust of the northeastern Yucatan basin (Ramos & Mann, 2023).From northwest to southeast, three dip-oriented transects cross the Cayman Ridge and show a lower crustal thickness of 6 km.
The Cayman Ridge formed as the thickest part of the volcanic arc of the GAC, resulting in a dense, 8-km-thick, 2.9 g/cc lower crust in transects B and C. Toward the SE and along transect C, the sedimentary section thickens  Zietz (1982) show sparse anomalies in the southeastern Bahamas and broad wavelength positive anomalies throughout the northeastern Bahamas.The broad, magnetic anomalies indicate deeper magnetic sources likely related to continental crust.Interpretations for crustal boundaries are consistent with previous interpretations by Dale (2013) and Romito and Mann (2021).from 1.5 to 6.5 km, the sedimentary densities increase by 0.16 g/cc, and the top basement surface becomes more rugose.Along the southwestern edge of transect C, a transition of 4-14 km of crust reveals the thin oceanic crust of Eocene to recent age formed within the Cayman Trough pull-apart basin.

Crustal Structure of the Northwestern Cuban Arc
Metamorphic and volcanic outcrops throughout the GAC are modeled with a density of 2.75 g/cc as shown in the modeled gravity transects in Figure 6.The width of the Cuban volcanic arc increases by 170 km between gravity transect A across the Pinel Del Rio region in Cuba to transects B and C across southeastern Cuba.The change in the width of the volcanic arc may reflect the variable mode of back-arc opening with the formation of localized areas of oceanic crust in the Yucatan basin and the formation of strike-slip faults that crosscut the GAC in Cuba (Ramos & Mann, 2023).

Crustal Structure of the Northwestern Suture Zone
The 1,000-km-long suture between the Cuban segment of the GAC and the BCP changes in its cross-sectional width from 182 km along transect A near the Cay Sal Bank to a width of 89 km along transects B and C near the Great Bahamas Bank (Figure 6).The oblique orientation of transect A relative to the trend of the GAC explains part of this large, cross-sectional variation in the width of the suture zone.Crustal thickness across the GAC-BCP suture zone varies from 7 km on transect A to 21 km on transect B.

Crustal Structure of the Northwestern Bahamas Platform
The modeled crustal thickness across the northwestern Bahamas margin and Great Bahamas Bank varies from 19 to 22 km.Along transects A-D, the average thickness of the Cretaceous oceanic crust seaward of the BCP is 7.5 km but varies locally along the linear Bahamas and Jacksonville fracture zones (Figure 6).
Transects A-G reveal a flexural bulge southeast of the Cuba arc-Bahamas suture zone.Modeled flexural uplift, elastic thickness, and loading effects increase from northwest to southeast with an especially large increase between transects A and B (Figure 6).

Crustal Structure of the Cayman Trough and Eastern Nicaraguan Rise
The thicker crust south of Hispaniola is thickened oceanic plateau crust of the Late Cretaceous CLIP.The thinner, 18-km-thick, island arc crust in the eastern Cayman Trough pull-apart basin reflects Eocene thinning of the GAC and the CLIP terrane underlying the eastern Nicaraguan Rise and the Cayman Trough as observed from the elevated Moho observed along transect E. The 18-km-deep Moho of the Cayman Ridge and the southeastern tip of Cuba thins to normal oceanic crust within the eastern Cayman Trough (Basile, 2015;de Lépinay et al., 2016).Toward the southwestern corner of transect E, the modeled Moho rises by 4 km near the central part of the Nicaraguan Rise.

Crustal Structure of the Central Cuban Arc
On transect D, the southeastern tip of the Cuban GAC narrows to a width of 80 km against the southwestern Cayman Trough and northeastern Cuba-Bahamas suture zone.There is an abrupt change in the depth of the Moho coinciding with the main strike-slip plate boundary (Oriente FZ) that separates the North American Plate from the Gonave microplate.This southern area of the GAC in Cuba has been elevated both by its Paleogene collision against the Bahamas margin and its post-collisional deformation along the Oriente strike-slip fault zone (Oliviera de Sá et al., 2024).
On transect E, the Oriente and Enriquillo-Plantain Garden strike-slip fault zones elevate the GAC and CLIP basement and upper-lower mantle boundary that underlies the Gonave microplate.These rapid variations in Moho depth are commonly observed along transform margins (Basile, 2015;de Lépinay et al., 2016).

Crustal Structure of the Central Suture Zone
Outcrops of ophiolites parallel the length of the GAC-BCP suture zone in Cuba and Hispaniola.On transects D and E, the crustal thickness of the suture zone varies from 16.5 to 11 km and its width varies from 40 to 80 km (Oliviera de Sá et al., 2024).

Crustal Structure of the Central BCP
The crustal structure beneath the central BCP is characterized by several abrupt truncations in the top basement surface and an elevated Moho near Acklins Island.Elongate basement highs align with the locations of the northwest-trending Bahamas and Jacksonville fracture zones.In transect F, the rugose top basement surface is disrupted by an 84-km-wide, 11-km-long basement low.Our flexural models show that 12-15 km elastic thickness dominates the central area of the BCP.Flexural uplift and loading continue to increase in the southeastern BCP.The east-west-trending EPGFZ bounds the Haiti sub-basin to the north, the Nicaraguan Rise to the west, and the Beata Ridge to the east (Mann et al., 1995).The late Cretaceous CLIP crustal thickness along transects F and G varies from a thickened lower crust of 10 km with a thin upper crust of 4.5 km along the Beata Ridge (transect F) to a thickened upper crust of 10 km and a thin lower crust of 4 km along the Beata Ridge (transect G) (Figure 6).We interpret the thickened upper crust along the Beata Ridge as a result of basaltic flows related to the development of the thickest area of the Late Cretaceous CLIP (Diebold et al., 1999;Nerlich et al., 2015).The modeled crustal thickness for the CLIP along transects F and G is consistent with the crustal thickness range proposed by Barrera-Lopez et al. (2022).

Crustal Structure of the Hispaniola Arc
Two microplates formed by the oblique collision of the CLIP terrane and the BCP characterize the Hispaniola island arc: the northern Hispaniola microplate bounded on the south by the Septentrional-Oriente fault zone, and the Gonave microplate juxtaposed between the EPGFZ and the northern Hispaniola microplate (Liu et al., 2024;Mann et al., 1995Mann et al., , 2002;;Sun et al., 2020).
Our results show a thicker crust and an increase in width of the GAC volcanically-and tectonically-thickened crust of Hispaniola and the southeastern Bahamas along transects F and G (Figure 6).Widening and thickening of the GAC in this area may reflect both its original width as an intra-oceanic arc and its transpressional deformation during the Eocene to recent, eastward translation of the Caribbean Plate and its oblique collision with the southeastern BCP.The Gonave microplate in western Hispaniola is deformed by transpressional thrust belts and synclinal basins that contain as much as 5 km of clastic sedimentary rocks (Mann et al., 2002).
To the southeast, the Hispaniola microplate is bounded by the Muertos Trough formed by the northward subduction of CLIP-related crust of the Caribbean Plate.Multiple refraction controls from J. I. Ewing et al. (1960) and Houtz and Ewing (1964) constrain the crustal structure of subducted slabs beneath eastern Hispaniola (Mann et al., 2002).

Crustal Structure of the Hispaniola and BCP Suture Zone
The crustal structure resulting from the combined deformation between the Septentrional-Oriente transpression, Atlantic-Bahamas subduction, and oblique Caribbean collision have resulted in a 6.5-12.5 km deep and elongate low in the top basement surface that trends parallel to the North Hispaniola subduction zone as seen on transects E, F, and G (Liu et al., 2024;Rodríguez-Zurrunero et al., 2020;Sun et al., 2020) (Figure 6).

Crustal Structure of the Southeastern Bahamas Platform
Crustal thickness ranges from 14 to 16 km south of the Turks and Caicos Islands.An increase in sedimentary thickness of 7 km north of the North Hispaniola Trench is modeled with decreasing sedimentary density that reflects variations of carbonate thickness of the southeastern Bahamas.Elastic thickness increases to an average of 19.2 km between transects F and G. Flexural modeling of the GAC collision shows a large 3.3 km and 8.39e + 13 N decrease in uplift and loading from northwest to southeast (Sun et al., 2020).

Results on the Crustal Structure of the Bahamas-Cuban Arc Collisional Zone in the Along-Strike Transects
Transect I extends from the northwest to southeast in a strike-parallel direction along the trend of the GAC and transect H extends along the adjacent 1,400-km-long BCP (Figure 7).These along-strike transects highlight the variations in crustal structure between the ∼20-km-thick intraoceanic island arc of the GAC that is sutured against the 18-km-thick crust of the Bahamas margin.On transect H, the overall modeled crustal thickness of the BCP tapers from thicker crust in the northwest to thinner crust in the southeast.

Along-Strike Crustal Structure of the Northwestern Cuban Arc
The northwestern area of transect H exhibits an abrupt 13-25 km thickening of thin continental crust in the GOM and Florida Straits to the thicker GAC crust in western Cuba.We interpret this abrupt transition to northeaststriking, left-lateral strike-slip faults (Hondo and Pinar fault zones) that extend to the southwest and juxtaposes continental rocks in the Yucatan Peninsula with oceanic crust in the Yucatan basin (Ramos & Mann, 2023) (Figure 7).Modeled sedimentary sections within the Florida Straits and GOM show a 6-km-thick clastic, foreland wedge that thickens along the Upper Cretaceous fold-thrust belt in the Pinar Del Rio region of Cuba (Gordon et al., 1997;Rosencrantz, 1993).
The Golfo de Batabano in northwestern Cuba shows a 2-km-thick, sedimentary section overlying a transition of 19.5-13-km-thick upper crust.This decrease in upper crust thickness and thickening of denser lower crust can be correlated with adjacent outcrops of rocks of the Escambray massif that are adjacent to the southeastern Golfo de Batabano.

Along-Strike Crustal Structure of the Northwestern BCP
The crustal structure of the area from Andros Island to the southeastern edge of the Great Bahamas Bank shows a tapered crustal profile 22-19-km-thick at the 122 km distance along transect H with basement lows separated by basement highs exhibiting up to 8 km of relief.Sedimentary thickness increases to 7.8 km beneath Andros Island where the Moho elevates by 3 km.This increase in basement depth over a distance of 134 km coincides with an area of proposed, deeply-buried Mesozoic rifts (Sheridan et al., 1981).
We interpret the increase in 2.3 g/cc modeled sediments as indicative of underlying syn-rift Triassic-Jurassic volcaniclastic or clastic rocks similar to those documented in the Great Isaac-1 well.The southern edge of Andros Island bounds this basement low with an adjacent basement high.A second basement high separates the deep 10.8 km of the Ocean and Columbus basin.This rugose crustal structure tapers to the southeast from 11 to 7.5 km.

Along-Strike Crustal Structure of the Central Cuban Arc
On transect I, the 23.5-km-thick and 30-km-wide Escambray metamorphic massif of central Cuba is bounded to the southeast by an elevated granitic pluton with an upper crustal thickness of 20 km.The La Trocha left-lateral strike-slip fault elevates the Moho by 5 km and depresses the top basement to 3 km (Cruz-Orosa et al., 2012) (Figure 7).
To the southeast, transect I passes through the Camaguey area and traverses an area of granitic, GAC basement with a 28-km-thick crust.Gravity modeling throughout Cuba ends with the 3.7-km-thick Cauto basin bounded by the left-lateral Oriente strike-slip fault zone, which truncates the Moho by 3 km (Figure 7).

Along-Strike Crustal Structure of the Central Bahamas Platform
From Long Island on the BCP to the northwestern Turks and Caicos Islands, the top basement structure of the BCP exhibits minor variations with an average depth of 7.8 km and sedimentary thickness of 6.3 km.This smooth, flat-topped basement is typical of volcanic rifted margins (Reuber et al., 2019;Sapin et al., 2021) and oceanic plateaus as observed on the CLIP in the Caribbean Sea (Diebold et al., 1999) (Figure 7b).Northwest of the Columbus basin in the Tongue of the Ocean, the top basement surface is more rugose than seen to the south in the area of Turks and Caicos.We propose the northeast-trending, continent-ocean boundary (COB) underlies the Columbus basin as shown on transect I in Figure 7c.

Along-Strike Structure of the Hispaniola Arc
On transect I, the Cayman Trough and Windward Passage deepen to 3 km near Cuba and Hispaniola and show a 22-km-thick crust (Figure 7c).The EPGFZ is south of the eastern boundary of the Cayman Trough throughout transect I.The Trans-Haitian thrust belt exhibits a deepening sedimentary section along-strike and is faulted against the Central Cordillera with a 30-km-thick crust.
Throughout eastern Hispaniola, crustal thickness averages around 25 km with a slight thickening of the lower crust 10 km east of the Central Cordillera.Gravity modeling of transect I terminates at the Muertos Trough.The Muertos Trough exhibits a 27.7-12 km tapered Moho and an increase in sedimentary thickness of 1.5 km from northwest to southeast.

Along-Strike Structure of the Southeastern Bahamas Platform
The Turks and Caicos Islands to Caicos basin zones traversed by transect H exhibit a crustal thickness of 15.6 km and a maximum sedimentary thickness of 10 km (Figure 7c).A narrow, 2-km-deep basement depression separates the thick carbonate of the southern Turks and Caicos Islands from thinner crust of the adjacent Caicos basin.The modeled Moho and basement exhibit a 2.5 km rise throughout the Caicos basin.Multiple short wavelength folds define the Moho and lower-upper crust boundary.
Water depth increases to a maximum of 6.1 km along the Hispaniola Trench north of Hispaniola, and the modeled basement increases to 10 km (Rodríguez-Zurrunero et al., 2020).The lower crust thickens by 12 km beneath the elevated Puerto Rico basement possibly in response to late Paleocene-early Eocene transpressional deformation related to the collision of the BCP with this segment of the GAC (Mann et al., 2002;Sun et al., 2020).

Alternative Solutions to Gravity Models
Because forward modeling of gravity data is non-unique, other geological constraints are necessary to show which gravity solutions are the most geologically reasonable.We created three forward gravity models with equal error to test the proposed hypothesis for crustal type and structure beneath the BCP.These modes were calibrated with depth estimates of the top of magnetic basement using Werner deconvolution using the compilation of shipbased magnetic data compiled by Zietz (1982).Werner deconvolution of magnetic data applies algorithms to linearize a 2D inverse problem of a magnetic dike or contact parameters by clearing the denominators of the rational functions that describe the associated anomalies (Hansen & Simmonds, 1993).
We used Montaj software to apply a sliding scale that solves for the 2D inverse problem of magnetic dikes and contacts.Because of limited ship-based magnetic data in the areas outside of northwestern Bahamas, the resulting modeled depth to basement identified two possibilities along transect H in Figure 7b: (a) an 11-km-thick upper crust with a 5.3 km thick lower crust; or (b) a 13-km-thick lower crust with a 3.3-km-thick upper crust.

Theory and Methods for Flexural Modeling
Flexural theory proposes that a continuous lithosphere acts as a solid beam overlying the upper mantle and responds isostatically to tectonic loads such as large seamounts and oceanic crust entering subduction zones.To calculate the degree of flexural uplift from the deflection of the plate, we solved the following fourth-order differential equation with the flexural modeling software TAFI (Turcotte & Schubert, 1982): where q a is the vertical displacement of the lithosphere along strike, calculated from the flexural rigidity of the lithosphere D, the acceleration due to gravity g, the mantle density ρ m , the overburden density ρ s, and the alongstrike displacement of the lithosphere w(x).The model integrates computed uplift with flexural rigidity and load and yields a best-fit estimate of elastic thickness and load as summarized on the transects across the BCP shown in Figure 8.

Crustal Structure of the Collided Western Cuban Arc and the Northwestern Bahamas
Transects A, B, and C shown in Figure 8 exhibit less flexural uplift consistent with the greater flexural rigidity that is consistent with our interpretation that continental crust underlies the northwestern area of the BCP.

Crustal Structure of the Collided Eastern Cuban Arc and the Central Bahamas
Flexural rigidity correlates with stiffness of the crust while loading is dependent on the surrounding tectonics and paleodeposition.The loading and resulting flexural uplift of transect D bracket the lower values in the northwestern BCP and higher values in the southeastern BCP as shown in Figure 8.We interpret the low flexural rigidity in the central BCP to indicate the presence of an underlying, weak oceanic crust.

Crustal Structure of the Collided Hispaniola Arc and the Southeastern Bahamas
Flexural modeling of the collided Hispaniola island arc is separated by a 5.8 km maximum bulge north of a thrust belts in western Hispaniola to a 2.5 km bulge from eastern Hispaniola north of the PRT (Figure 8).Modeled slab subduction extends 10-30 km deeper than that indicated by the distribution of earthquake hypocenters in the crust (Barrera-Lopez et al., 2022;Rodríguez-Zurrunero et al., 2020).
The modeled elastic thickness of the lithosphere in the Bahamas increases by an average of 5.8 km from central Bahamas to both transects F and G in the southeastern Bahamas (Figure 8).We interpret the lack of variation in elastic thickness from transects F and G and high variation in flexural uplift and loading to indicate that a uniform and thickened area of Cretaceous oceanic crust underlies the southeastern Bahamas.Subsidence histories for Cay Sal-1 and Great Isaac-1 modified after Schlager et al. (1988) and Walles (1993).
formation of a subduction-collision-related forebulge that led to swallowing and subaerial exposure of the foreland area; (f) Paleocene-Eocene (60-45 Ma) abrupt deepening to depths of 2000-3000 m related to the previously formed forebulge entering the foredeep area, submerging and drowning of the platform carbonates.
On Figure 9c, we compare five Jurassic-to-Cenozoic tectonic phases proposed by Escalona and Yang (2013) in the Straits of Florida and northwestern Cuba with the subsidence histories of the three deepest exploration wells from the BCP: Great Isaac-1 on the northernmost BCP and ~400 km north of the BCP-GAC suture zone, and Cay Sal-1 and Doubloon Saxon-1, which are both 50 km north of the suture zone (well locations shown in Figure 9b) (Erlich & Pindell, 2020;Schenk, 2009;Walles, 1993).Some similarities in the subsidence of the DSDP wells and these three wells include: (a) all four areas exhibit rapid subsidence in the late Cretaceous which may also reflect rising eustatic sea level during this time as discussed by Escalona and Yang (2013).The least rapid subsidence during this period is the Cay Sal-1 well, which is the most distant from the GAC-BCP suture zone; (b) Uplift events and inflection occurring in the Paleogene in Cay Sal-1, Doubloon Saxon-1, and Great Isaac-1 wells shown as stars on Figure 9c approximately correlate with the more precisely known, onland Paleogene deformation related to the GAC-BCP in Cuba as reviewed by Bralower and Iturralde-Vinent (1997) and Cruz-Orosa et al. (2012).These uplifts on the BCP may record the flexure related to the terminal collision event.

Basin Modeling of the BCP
Three publicly-available calibration wells with lithologic descriptions and downhole temperature measurements were used to calculate the radiogenic heat production (RHP) of the crust (Walles, 1993) (Figure 9).Relatively higher RHP values can be used as an indicator for granitic crust of continental origin with internal RHP, whereas relatively lower or negligible RHP values are indicative of basaltic crust of oceanic origin with much less internal RHP.Crustal thickness values used for basin modeling were taken from gravity models created in this study.A range of lithospheric thicknesses from 120 to 205 km was used in the basin model at the three well locations (González et al., 2012).
For each 1D basin model, a lower boundary condition with a fixed temperature of 1,330°C was applied to the base of the lithosphere.These models take into account the effects of changing sedimentation rates through time.The RHP was calculated by matching each well's resulting geothermal gradient to published temperature data (Walles, 1993).
The resulting RHP values that best fit these temperature constraints vary from 0.21 to 1.04 μW/m 3 for the Doubloon Saxon-1 well, from 0.1 to 0.75 μW/m 3 for the Cay Sal-1 well, and 0.45 μW/m 3 for the Great Isaac well.These relatively higher RHP values are consistent with our proposal that all three wells are underlain by rifted continental crust.

Summary of Crustal Provinces Underlying the BCP
The map in Figure 10 summarizes our interpretation of the origin and deformation of the main crustal provinces of the Paleogene collisional zone between the BCP and the GAC in Cuba and Hispaniola.Our results for crustal thickness variations across the collisional zone are consistent with previous 2D crustal models (Dale, 2013;Sun et al., 2020).
From the three previous hypotheses of thinned continental crust, volcanically-thickened oceanic crust, and oceanic crust as summarized in Figures 1b-1d, we propose a thinned and rifted continental crust beneath the northwestern Bahamas, which transitions across a northeast-trending, continent-oceanic boundary to a volcanically-thickened oceanic crust on the southeastern edge of the Great Bahamas Bank (Figures 10a and 10b).
Four key observations that support the location of this interpreted continent-ocean transition at the southeastern edge of the Great Bahama Bank include the following, shown in Figures 8-10: 1.Our models yielded a range of RHP values from 0.75 μW/m 3 for the minimum lithospheric thickness of 100 km to 0.1 μW/m 3 for the maximum lithospheric thickness of 205 km (Figure 10c).This range of lithospheric thickness is similar to the lithospheric thickness of arc-continent collisional zones in other areas (González et al., 2012).
Geochemistry, Geophysics, Geosystems 10.1029/2023GC011300 2. The modeled upper crust thickness varies from 22 to 19 km with a density of 2.75 g/cc (Figure 10c).This density value would correspond to lithologies that range from granites to volcaniclastic sedimentary rocks as recovered in the lowermost section of the 5,439-m-deep Great Isaac-1 well (Jacobs, 1977).3. Mesozoic salt diapirs on the seafloor of the southern Exuma Sound basin (Spector et al., 2016) and described in onland areas of central Cuba are consistent with our proposed COB and area of rifted and thinned continental crust (Figures 10a and 10b).The presence of Mesozoic salt in these areas is consistent with depressed rift blocks created during continental rifting and forming restricted shallow-water environments favorable for the deposition and preservation of thick salt.The presence of salt in exposed and shallowly-buried salt diapirs in central Cuba adjacent to the BCP and the seafloor salt diapirism in Exuma Sound form a northeast-trending line that is parallel to our proposed continent-ocean transition (Figures 10a and 10b).4. The low, modeled elastic thickness (13.45 km) present in central Bahamas indicates a weaker crust than typical continental crust which commonly varies from 35 to 100 km in elastic thickness (Tassara et al., 2007;Tesauro et al., 2012).We propose the low elastic thickness of the central Bahamas crust reflects a weaker crust due to mantle upwelling and intrusions (Figure 8).

Summary of Crustal Provinces in the Great Arc of the Caribbean
The GAC in Cuba, Hispaniola, and Puerto Rico consists of a variety of plutonic, volcanic, and metamorphic lithologies that commonly characterize intraoceanic island arcs (Cruz-Orosa et al., 2012;Sommer, 2009) whose segments and crustal levels are juxtaposed along left-lateral, strike-slip faults in Cuba and in the Yucatan and Hispaniola back-arc basins (Ramos & Mann, 2023) (Figure 7c).We interpret an average 25-km-deep Moho along the volcanic arc of the GAC in Cuba.Abrupt truncations of the GAC trends occur along left-lateral faults that include the Pinar, Matanzas, La Trocha, Cauto, and Oriente fault zones.

Tectonic History and Timing of the Closure Between the Cuban Arc and the Central Bahamas
Multiple tectonic phases shaped the evolution of the GAC collision, as shown in Figure 11 and include this proposed sequence of Late Cretaceous to recent tectonic events: 1. Subduction of the Proto-Caribbean crust by the GAC and subsequent collision of the GAC with the Maya Block of southern Mexico starting in the Late Cretaceous (Mann, 1997;Mann et al., 1995;Pindell et al., 1988Pindell et al., , 2012Pindell et al., , 2023;;Schenk, 2009) (Figures 2e and 2f). 2. Formation of the Pinar and Varadero left lateral, strike-slip faults and opening of the Yucatan back-arc basin during the Paleocene and Early Eocene as the Cuban segment of the GAC moved northeastward along the eastern margin of the Yucatan block (Ramos & Mann, 2023) (Figures 2g and 2h). 3. Collision of the GAC in northwestern Cuba with the BCP was accompanied by a more eastward migration of the GAC in the unopposed, or "escape" direction of Atlantic oceanic crust.We interpret this migration to be the primary cause of a depressed basement with less flexural uplift when comparing transect A of northwestern Cuba to transects B and C. Eastward migrating deformation of the La Trocha fault resulted in the creation of the Central basin and additional loading along central and southeastern Cuba in the Early Eocene (Cruz-Orosa et al., 2012;Gordon et al., 1997;Rosencrantz, 1993) (Figures 2g-2i).4. Opening of the Cayman Trough pull-apart basin along the left-lateral Oriente fault zone and the Middle Eocene transition from BCP collision with the GAC in Cuba to Hispaniola occurred due to Late Eocene to recent, leftlateral strike-slip faulting (Kysar-Mattietti, 2001;Mann et al., 1995;Pardo, 2009;Pindell & Barrett, 1991).
The transition from the Early Paleocene maximum uplift in Great Isaac-1 to the Middle Eocene maximum uplift of Doubloon Saxon-1 reflects this eastward migration of deformation (Figures 2i and 2j). 5. Formation of the Septentrional fault zone resulted from the highly oblique southeastern Bahamas subduction and formation of the Muertos Trough, which defines the Late Eocene-Oligocene GAC collision (Román et al., 2021) (Figures 2k and 2l).6. Oblique collision and shallow subduction of the southeastern BCP beneath northern Hispaniola has produced uplift and regional shortening.

Large-Scale, Paleomagnetic Rotations Related to the Closure and Indentation of the Bahamas Platform
Recent thermochronologic dating and paleomagnetic data constrain a 45°counterclockwise rotation of the northern Lesser Antilles and Puerto Rico since the Late Eocene (Montheil et al., 2023;Noury et al., 2021).This large rotation is not observed in the southern Lesser Antilles which remained stable during this period.Montheil et al. (2023) proposed that the rotation was produced by one of these two tectonic processes: (a) arc-parallel motion of a forearc sliver that included the northern Lesser Antilles and Puerto Rico that occurred along a known, left-lateral, strike-slip fault in the northern Lesser Antilles (Montserrrat-Harvers FZ); and (b) a major tectonic indentation of the northern GAC during the collisional and post-collisional period with backthrusting along the Muertos Trough and accompanying large-scale rotations in the indented area of Puerto Rico and the northern Lesser Antilles.
We prefer the latter model for eastward-directed convergence and accompanying counterclockwise rotation as a result of the indentation of the BCP into the GAC and Caribbean Plate for these reasons: (a) the Montserrat-Harvers FZ exhibits minor offset and the structural character of an immature and recently formed strike-slip fault; and (b) the magnitude of regional-scale Paleogene collisional effects on crustal structure (Figures 6 and  7), Paleogene flexure of the BCP and its adjacent oceanic crust (Figure 8), and sedimentary effects including changes in paleo-water depths (Figure 9).

Implications of the Well and Maturity Data for the Hydrocarbon Potential of the BCP
Assessments of petroleum and geothermal potential rely on an accurate understanding of the relationship between tectonic deformation, burial, and heat generated from the underlying lithosphere.In the Bahamas, the lack of commercial petroleum discoveries has been previously attributed to: (a) seal failure induced by uplift and erosional effects during the GAC collision; (b) lack of migration pathways from deeper Jurassic source rocks to overlying Cretaceous reservoirs; (c) poor reservoir quality in tight carbonate lithologies; and (d) low source rock maturity due to either low overburden or inadequate basal heat flow (Walles, 1993).
In this study, we show on the regional transects the areas of most intensive deformation within the BCP-GAC collisional zone.Due to these structural complexities within the collisional zone, there are large uncertainties regarding the geographic variations in heat generated from the lithosphere.Based on our estimate of the crustal RHP from publicly-available temperature data, the RHP for the 172-km-wide suture zone between the GAC and BCP averaged 0.62 μW/m 3 .The resulting basal heat flow would be too low to generate hydrocarbons to explain the observed oil and gas shows in the three modeled wells (Figure 12).One explanation for oil shows in some wells is that source rocks have matured in the deeper basins around Andros Island, offshore of northwestern Cuba and at Exuma Sound, and have migrated updip on the basement highs where the three wells shown in Figure 12 were drilled.

Conclusions
The difficult-to-image crustal types and deformational structures of the BCP were modeled using a variety of diverse data types that include: gravity, magnetic, seismic reflection, seismic refraction, on-land geology, radiometric age dating of crystalline rocks, paleo-water depths of sedimentary rocks from biostratigraphy, and  (Klitgord et al., 1984), the Straits of Florida (Dallmeyer, 1984), and in the northernmost Bahamas at the Great Isaac-1 well (Jacobs, 1977) all penetrated volcanic rocks that range in age from the earliest Jurassic (199 Ma) to the late Jurassic (160 Ma).We propose this as the site of the Bahamas hotspot, which tracked southeast with the opening of the Central Atlantic Ocean.Abbreviations: CS, Cay Sal-1; DS, Doubloon Saxon-1; GI, Great Isaac-1.

Figure 1 .
Figure 1.(a) Bathymetric-topographic map of the Caribbean and Florida Peninsula compiled by Becker et al. (2009) showing the location of the study area of the Bahamas-Great Arc collisional zone of Paleogene age.The dashed yellow line indicates the extent of the Bahamas carbonate platform (BCP) and the black dotted line indicates the location of the schematic, along-strike cross-sections of 1b, 1c, and 1d.(b) Cross-sectional view of thinned continental crust underlying the BCP as proposed byBall (1967),Mattson (1972), andMullins and Lynts (1977) along the dashed, regional, cross-sectional line extending 1,500 km from the Straits of Florida to Puerto Rico.(c) Cross-sectional view of volcanically-thickened oceanic crust reflecting hotspot activity underlying the BCP proposed byNewell (1955) andDietz et al. (1970).(d) Cross-sectional view of normal oceanic crust underlying the BCP proposed byUchupi et al. (1971) andKlitgord et al. (1984).BCP, Bahamas Carbonate Platform; CB, Ciao Basin; ES, Exuma Sound; PRT, Puerto Rico Trench; TC, Turks and Caicos; TOT, Tongue of the Ocean.
Setting of the BCP and the Great Arc of the Caribbean 2.1.Plate Reconstructions of the Central Atlantic and Gulf of Mexico-Caribbean 2.1.1.Central Atlantic Rift and Passive Margin Phase (Triassic-Early Jurassic, 230-80 Ma) Figure 2.

Figure 2 .
Figure 2. Mesozoic-Cenozoic plate tectonic reconstructions of the Bahamas rifted-passive margins and its conjugates on the Guinea Plateau (GP) in west Africa and the Demerara Plateau (DP) in northeastern South America modified from Müller et al. (2019).(a) Earliest Jurassic reconstruction (200 Ma) of the syn-rift phase of the Central Atlantic Ocean with coeval formation of the Central Atlantic Magmatic Province, and a radial dike swarm shown by red lines centered on the BCP.The conjugate Guinea (GP) and Demerara (DP) volcanic plateaus of the BCP are outlined.(b) Zoom of earliest Jurassic reconstruction showing the restored locations of the three conjugates: Bahamas margin, GP, and the DP.(c) Late Jurassic (160 Ma) reconstruction of the opening of the southwestern Central Atlantic Ocean with the red star showing the interpreted location of the Bahamas hotspot at this time from Reuber et al. (2016) and the paired blue and green dashed lines showing the Jurassic to recent hotspot tracks for both limbs of the widening Central Atlantic Ocean.(d) Zoom of Late Jurassic reconstruction showing a more detailed view of the separation of the BCP from its conjugate Demerara and Guinea plateaus.(e) Early Cretaceous/Hauterivian (130 Ma) reconstruction of the creation of the Proto-Caribbean oceanic crust with lengthening of the track of the Bahamas hotspot.(f) Late Cretaceous/Turonian (90 Ma) reconstruction showing the initial collision of the Great Arc of the Caribbean (GAC) with the Chortis block in southern Mexico and with the Maracaibo block in northern South America.The yellow star indicates the proposed location of the Sierra Leone hotspot and plume head by Basile et al. (2020).Blue and pink dashed lines represent the hotspot tracks on both limbs of the Guinea and Demerara plateaus.(g) Early Paleocene (64 Ma) reconstruction of the initial collision of the Cuban segment between the western GAC and the BCP.(h) Middle Eocene reconstruction (50 Ma) showing the initial eastward translation of the Hispaniola segment of the Great Arc of the Caribbean along the left-lateral Oriente and EPGFZ fault zones.(i) Late Eocene (45 Ma) reconstruction showing the complete suturing of the Cuban segment of the GAC to the Bahamas.(j) Late Oligocene (25 Ma) reconstruction showing continued collision of the BCP with the GAC in Cuba and Hispaniola.(k) Late Pleistocene reconstruction showing the Caribbean Plate moving eastward with recent subduction of Atlantic Ocean crust beneath the Lesser Antilles arc.(l) Present-day tectonic setting with the dotted red line showing the hotspot track from Basile et al. (2020) between the Demerara and Guinea Plateaus and the yellow star showing the location of the Sierra Leone hotspot and its plume head.

Figure 3 .
Figure 3. (a) Bathymetric-topographic map of the Bahamas margin fromBecker et al. (2009) showing the location of wells and vintage seismic reflection data compiled for our study area indicated by the dashed, white line.(b) Regional well correlation along a 1,200-km transect crossing the northwestern Bahamas carbonate platform modified fromDale (2013).The oldest rocks penetrated by deep wells are Triassic volcaniclastic rocks in Great Isaac-1.Sedimentary sections within most of these wells consist of dolomitic limestone with interbedded anhydrite(Jacobs, 1977).Oil and gas shows are documented from all of the wells and are indicated on the well logs.Well abbreviations are: CS, Cay Sal-1; CC, Cayo Coco-2; LI, Long Island-1; DS, Doubloon Saxon-1; and GI, Great Isaac-1.

Figure 5 .
Figure 5. (a) Free-air gravity fromLiang et al. (2020) showing positive anomalies along the elongate and west-northwest-trending island arc crust of the GAC exposed on the islands of Cuba, Hispaniola, Puerto Rico, and the northern Lesser Antilles.More discontinuous, positive free-air gravity anomalies correlate with the numerous carbonate banks and islands of the Bahamas archipelago.(b) A prominent, negative Bouguer gravity marks the extinct suture zone between the Cuban segment of the GAC; the eastern extension of this suture zone in Hispaniola and Puerto Rico has been reactivated by present-day motion along the east-west-trending and oblique-slip North America-Caribbean plate boundary zone that also includes active faults of the Cayman Trough and Muertos Trough.The elongated area of the Bahamas carbonate platform and GAC separate the larger areas with positive anomalies marking Cretaceous oceanic crust of the Central Atlantic Ocean.In contrast, negative anomalies mark areas of continental crust in southeastern North America.(c) The total horizontal derivative of the Bouguer-gravity anomaly was used to define the Blake Spur, Jacksonville, and Bahamas fracture zones as linear boundaries marked by parallel high and low anomalies.(d) DNAG magnetic anomalies fromZietz (1982) show sparse anomalies in the southeastern Bahamas and broad wavelength positive anomalies throughout the northeastern Bahamas.The broad, magnetic anomalies indicate deeper magnetic sources likely related to continental crust.Interpretations for crustal boundaries are consistent with previous interpretations byDale (2013) andRomito and Mann (2021).

Figure 6 .
Figure 6.(a) Northeast-striking, dip-oriented 2D forward gravity model of transect A extending across the northwestern Bahamas margin from the Yucatan Basin to the Central Atlantic Ocean.Uplifted basement and deeply-buried faults within thinned continental crust are inferred to control elongate, northwest-trending basement highs observed in the northwestern BCP.The locations of gravity transects A-G are shown by the thick black lines.On all the gravity transects, the thin line represents the calculated gravity, and the thin dotted black line is the observed gravity.Thin vertical lines along the A-G profiles show refraction controls located within 55 km of the transect.The thick dashed black line on the A-G profiles represents the modeled flexural bulge along the southwestern margin of the BCP.(b) Northeast-striking, diporiented 2D forward gravity model of transect B that extends from the central Cayman Ridge to the Central Atlantic Ocean.21-km-thick continental crust with high elastic thickness and associated with Mesozoic salt in Cuba and the Exuma Sound support our interpretation for stretched continental crust beneath this area of the northwestern Bahamas.(c) Northeast-striking, dip-oriented 2D forward gravity model of transect C extending from the southern Cayman Ridge to the Atlantic Ocean.(d) Northeast-striking, dip-oriented 2D forward gravity modeling of transect D extending from the Cayman Trough, across Cuba, crossing a 90-km-wide basement low in the central Bahamas, and extending to the Central Atlantic Ocean in the northeast.(e) Northeast-striking, dip-oriented 2D forward gravity model of transect E extending from the central Colombian basin in the Caribbean Sea through the Windward Passage between Cuba and Hispaniola to the southeastern Bahamas and the Central Atlantic Ocean.15-km-thick oceanic crust with low elastic thickness (13.5 km) beneath the southeastern Bahamas supports the presence of volcanicallythickened oceanic crust as shown schematically in the schematic model for the Bahamas shown in Figure 1c.(f) Northeast-striking, dip-oriented 2D forward gravity model of transect F extending from the Beata Ridge in the central Caribbean Sea, across the island of Hispaniola, to the southeastern tip of the Bahamas platform, and to the Central Atlantic Ocean.(g) Northeast-striking, dip-oriented 2D forward gravity model of transect G extending from the central Venezuelan basin in the Caribbean Sea, across Puerto Rico and the Puerto Rico Trench, to the Central Atlantic Ocean.(h) Locations of transects A-G shown on a free-air gravity map with data compiled by Liang et al. (2020) with an overlay of major structural provinces.The location map is shown in greater detail in Figure 5a.CR, Cayman Ridge; CSB, Cay Sal Bank; BR, Blake Ridge; GBB, Great Bahamas Bank; OFZ, Oriente Fault Zone; TOT, Tongue of the Ocean; Bahamas; OBC, Old Bahamas Channel; BCP, Bahamas Carbonate Platform; ES, Exuma Sound; EPGFZ, Enriquillo-Plantain-Garden Fault Zone; HT, Hispaniola Trough; TC, Turks and Caicos; SFZ, Septentrional-Oriente Fault Zone; PR, Puerto Rico; PRT, Puerto Rico Trench; CT, Cayman Trough; CB, Colombian Basin; Te, Elastic thickness; Wb, Maximum flexural uplift.
Cuban Arc and BCP Transects D and E show the variations in crustal thickness from the Cayman Trough pull-apart basin, across the tip of southeastern Cuba and the Windward Passage, across the GAC-BCP suture zone described from marine seismic reflection lines by Oliviera da Sá et al. (2024), and to the Columbus basin and Great Inagua Island on the BCP.Transect E extends to the eastern Nicaraguan Rise and Colombian basin and continues 390 km further to the southwest than transect D.

4. 3 .
Southeastern Area of the Cuban Arc and BCP 4.3.1.Crustal Structure of the Beata Ridge in the Caribbean Sea

Figure 7 .
Figure 7. (a) Free-air gravity from Liang et al. (2020) with main structural provinces observed from the resulting gravity transects shown here and in Figure 6.The locations of transects H and I are noted by the thick black lines.(b) Northwest-striking, strike-oriented 2D forward gravity model of transect H extending along the entire length of the Bahamas carbonate platform (BCP) from Andros Island in the northwestern BCP to Puerto Rico in the southeast.The uneven, top basement surface in the northwest is interpreted as rifted continental crust and the smoother, top basement surface in the central Bahamas is inferred to be a volcanic province developed on normal oceanic crust, as shown schematically in Figure 1c.Along this 1300-km-long, strike-parallel transect, the modeled Moho tapers by an average of 3 km from northwest to southeast.(c) Northwest-striking, strike-oriented 2D forward gravity model of transect I of the GAC extending along the trend of the GAC from the Florida Straits in the northwest to the Muertos Trough in the southeast.Thickness variations of the crust along this regional cross-section likely reflect batholiths (thick) and intra-batholithic (thin) areas of the intraoceanic GAC along with areas of collision-controlled thickening and thinning.The thin line represents calculated gravity, and the dotted black line is observed gravity.Thin vertical lines on the transect profiles indicate the integration of refraction data points located 55 km or less from the transect.The thick dashed black line represents the modeled flexural bulge.GOM, Gulf of Mexico; WP, Windward Passage; CT, Cayman Trough; OFZ, Oriente Fault Zone.

Figure 8 .Figure 9 .
Figure 8.(a) Location of flexural models based on gravity data that are oriented perpendicular to the northwestward strike of the GAC-Bahamas collisional zone.All these flexural models support our interpretation of a flexural bulge shown by the dashed line with the magnitude of the height of the flexural bulge increasing from northwest to southeast.Elastic thickness (Te) for each crustal domain varies from a 19.7-km-thick elastic crust in the northwestern Bahamas to a 13.5-km-thick elastic crust in the central Bahamas, and to a 19.2-km-thick elastic crust in the southeastern Bahamas.In the southern Bahamas, the maximum flexural bulge indicated by the dashed line is deflected to a more east-west orientation by the Eocene to recent, eastward transport of the Hispaniola segment of the GAC on the Caribbean Plate.(b) Flexural uplift plotted against applied gravity and modeled depth to basement data for the more rigid and thicker continental crust observed along transect B. (c) Flexural uplift plotted against applied gravity and modeled depth to basement data to illustrate the weaker and thinner continental crust around the continent-ocean boundary in the area of transect D. (d) Flexural uplift plotted against applied gravity and modeled depth to basement data to illustrate the area of thickened, Atlantic ocean crust in the area of transect F. CS, Cay Sal-1; CC, Cayo Coco-2; LI, Long Island-1; DS, Doubloon Saxon-1; GI, Great Isaac-1.

Figure 10 .
Figure 10.(a) Free-air gravity from Liang et al. (2020) with main structural boundaries and provinces of the BCP and surrounding areas based on gravity models shown as black lines.For reference, the locations of salt diapirs of Triassic or Jurassic age in Exuma Sound and in central Cuba are shown by the white stars(Spector et al., 2016).The location of an outcrop within the Cuban thrust belt of Grenville-age granite (903 Ma) is shown by the white square in central Cuba(Renne et al., 1989).Total crustal thickness was derived by integrating the top basement and Moho topography from transects A-I shown in Figures6 and 7.The volcanically-thickened oceanic crust of the southeastern Bahamas is shown with thick black lines that correspond to their low-elastic thickness areas (Te).Radiogenic heat production values in the thinned continental crust of the northwestern Bahamas are shown at 1D model locations represented by the thick circles.The thick dashed line indicates the increasing eastward bulge caused by the eastward translation of the Hispaniola area as a result of the Eocene to recent eastward motion of the Caribbean Plate.(c) Oblique view of topographic and bathymetric data viewed to the northwest along the trend of the GAC-Bahamas collisional zone.Representative transects A, D, and F were selected from the transects shown on the map in Figure 5 to illustrate the full extent of the tectonic domains of the GAC, the BCP, and the suture along which they are welded.The main crustal provinces include: (1) full-thickness, Precambrian and Paleozoic continental crust of the North American Plate; (2) continent-ocean boundary between the thinned continental crust of North America and Jurassic oceanic crust of the Central Atlantic Ocean; (3) Jurassic-Cretaceous oceanic crust of the Central Atlantic Ocean; (4) area of thinned, continental basement of the Bahama carbonate platform; (5) area of hotspot-thickened oceanic crust of the Bahama carbonate platform; (6) inactive suture zone between the BCP and the Cuban segment of the GAC; (7) reactivated suture zone along the active Caribbean-North American plate boundary in Hispaniola and Puerto Rico; (8) Cretaceous-Paleogene island arc crust of the GAC; (9) Paleogene oceanic and thinned crust of the Caribbean back-arc basin; (10) inverted, Paleogene Caribbean back-arc basin; (11) Cretaceous oceanic crust and Caribbean large igneous province.BCP, Bahamas Carbonate Platform; TOT, Tongue of the Ocean; ES, Exuma Sound; CB, Colombian Basin; PRT, Puerto Rico Trench; PR, Puerto Rico; Te, elastic thickness.

Figure 11 .
Figure 11.Plate reconstructions showing the diachronous deformation related to the Paleocene-Miocene collision of the Bahamas margin and the GAC.(a) Diachronous, northwest-to-southeast collision determined by compilations of radiometric ages from Román et al. (2021), Hu et al. (2022) and Rojas-Agramonte et al.(2008, 2010).Locations of surficial, Mesozoic salt diapirs in Cuba and drilled salt diapirs in the Exuma Sound and Central Cuba are indicated by the white star(Spector et al., 2016).An isolated outcrop of granite of late Proterozoic (Grenville) age is noted by the white square within the fold-thrust belt of central Cuba(Renne et al., 1989).(b) Graph of zircon cooling ages from the GAC that decrease in age from Maastrichtian (68 Ma) in Cuba to Late Oligocene (25 Ma) in the northern Lesser Antilles based on compilation of ages from Hu et al. (2022), Rojas-Agramonte et al. (2010), and Román et al. (2021).(c) Late Oligocene (25 Ma) plate reconstruction showing crustal domains following Paleogene collision of the GAC and the Bahamas carbonate platform.(d) Present-day paleomagnetic vectors from Montheil et al. (2023) showing 45°of CCW rotation of the Northern Lesser Antilles block (NOLA) that is inferred to be a consequence of 500 km of crustal shortening induced by indentation of the GAC by the area of thickened oceanic crust of the southeastern Bahamas.CLIP, Caribbean Large Igneous Province; GAC, Great Arc of the Caribbean; GOM, Gulf of Mexico; PR, Puerto Rico; NOLA, Northern Lesser Antilles; SOLA, Southern Lesser Antilles.

Figure 12 .
Figure 12.(a) Sedimentary thickness map of the study area based on the results of 2D gravity modeling with thickly sedimented areas of the Bahamas carbonate platform shown in cool colors and thinly sedimented areas of the GAC and Atlantic Ocean shown in hot colors.Northeast-trending sedimentary depocenters in the thinned continental area of the northern Bahamas platform are interpreted as northeast-oriented, salt-filled rifts that are parallel to our proposed continent-ocean boundary (COB).Wells drilled in the South Florida basin(Klitgord et al., 1984), the Straits of Florida(Dallmeyer, 1984), and in the northernmost Bahamas at the Great Isaac-1 well(Jacobs, 1977) all penetrated volcanic rocks that range in age from the earliest Jurassic (199 Ma) to the late Jurassic (160 Ma).We propose this as the site of the Bahamas hotspot, which tracked southeast with the opening of the Central Atlantic Ocean.Abbreviations: CS, Cay Sal-1; DS, Doubloon Saxon-1; GI, Great Isaac-1.(b) 1D burial and thermal history modeling results for the Great Isaac-1 well (GI) in the northwestern Bahamas (cf., map in Figure4for locations).(c) 1D burial and thermal history modeling results for Cay Sal-1 well (CS).(d) 1D burial and thermal history modeling results for Doubloon Saxon-1 well (DS).Lithospheric parameters used for each well are shown.In general, crustal thinning and radiogenic heat production increase to the southeast in the direction of the COB in the heavy black line.Except for Great Isaac-1, all Cretaceous source rocks would remain immature for hydrocarbons on the structural highs on which the wells were drilled-but source rocks may be mature in the intervening sedimentary basins.
Figure 12.(a) Sedimentary thickness map of the study area based on the results of 2D gravity modeling with thickly sedimented areas of the Bahamas carbonate platform shown in cool colors and thinly sedimented areas of the GAC and Atlantic Ocean shown in hot colors.Northeast-trending sedimentary depocenters in the thinned continental area of the northern Bahamas platform are interpreted as northeast-oriented, salt-filled rifts that are parallel to our proposed continent-ocean boundary (COB).Wells drilled in the South Florida basin(Klitgord et al., 1984), the Straits of Florida(Dallmeyer, 1984), and in the northernmost Bahamas at the Great Isaac-1 well(Jacobs, 1977) all penetrated volcanic rocks that range in age from the earliest Jurassic (199 Ma) to the late Jurassic (160 Ma).We propose this as the site of the Bahamas hotspot, which tracked southeast with the opening of the Central Atlantic Ocean.Abbreviations: CS, Cay Sal-1; DS, Doubloon Saxon-1; GI, Great Isaac-1.(b) 1D burial and thermal history modeling results for the Great Isaac-1 well (GI) in the northwestern Bahamas (cf., map in Figure4for locations).(c) 1D burial and thermal history modeling results for Cay Sal-1 well (CS).(d) 1D burial and thermal history modeling results for Doubloon Saxon-1 well (DS).Lithospheric parameters used for each well are shown.In general, crustal thinning and radiogenic heat production increase to the southeast in the direction of the COB in the heavy black line.Except for Great Isaac-1, all Cretaceous source rocks would remain immature for hydrocarbons on the structural highs on which the wells were drilled-but source rocks may be mature in the intervening sedimentary basins.