Environmental implication of subaqueous lava flows from a continental Large Igneous Province: Examples from the Moroccan Central Atlantic Magmatic Province (CAMP)
Introduction
Earth history is punctuated with occasional emissions of large volumes of basaltic magma, termed to Large Igneous Provinces (LIP's), (Sheth Hetu, December 2007, Coffin and Eldholm, 1994, Ernst and Buchan, 2001, Bryan and Ernst, December 2007), They have induced drastic climate changes and mass extinctions. One of the largest LIP is the Central Atlantic Magmatic Province (CAMP), which was emplaced around 201 My ago, during the initial stages of Pangea supercontinent break-up that gave rise to the Central Atlantic opening (Olsen et al., 2004, Marzoli et al., 2004).
Although corresponding to a continental volcanic event, CAMP volcanism presents evidence for interaction of the eruptive activity with water (e.g., Manspeizer, 1980, Olsen et al., 2003). In southern Portugal this interaction is mostly the result of subterranean water leading to an abundance of phreato-magmatic pyroclastic deposits (Martins et al., 2008). These are absent in Morocco, but in the other hand there are frequent examples of subaqueous lava morphologies that include pillow lavas (Foye, 1924, Olsen et al., 2005, Greenberger et al., 2015) and subaquatic sheet flows indicating the presence of sufficiently deep surface water bodies into which the lavas flowed (Youbi et al., 2003). The present work aims at contributing to the physical and environmental characterization of the CAMP subaqueous basaltic successions of the Marrakech High-Atlas regions of Aït-Ourir (N31 32 59.2 & W7 40 2.26), Jbel Imzar (N31 35 46.9 & W7 25 49.3), and Oued Lhar-Herissane (N31 36 44.7 & W7 22 48.8). These areas exhibit some of the best exposed pillow-lavas and volcano-sedimentary successions in Morocco, which contribute to characterize the paleo-environmental conditions prevalent at this area of Pangea during the volcanic activity.
Section snippets
Geodynamic and geological setting
Intracontinental rifting, leading to Pangea break-up and Central Atlantic opening, initiated during latest Permian-earliest Triassic times and propagated northward along the trend of the Variscan orogen (Ruellan, 1985, Ruellan et al., 1985, Medina, 1995, Medina, 2000, El Arabi et al., 2006). Pangea rifting was accompanied by CAMP extrusion (Marzoli et al., 1999) a LIP mostly composed of low-titanium tholeitic basalts. CAMP magmatism is represented by the remains of intrusive rocks (crustal
The structure of subaqueous flows
The subaquatic lava flows in the High Atlas region present variable aspects. They may locally correspond to densely packed pillows, to pillows dispersed into more or less abundant hyaloclastite matrix, and more or less extended sheet flows presenting well-developed undulated and thin columnar jointing. Pillow lavas and hyaloclastite containing pillows may pass laterally into sheet flows. At the Middle Fm. of Aït-Ourir and Oued Lhar, the subaquatic sequence starts with densely packed pillows,
Pillow lavas morphometry
A morphometry of the pillow lavas was performed by measuring the horizontal (H) and vertical (V) diameters of individual pillows. Whenever possible the measures were obtained on sections as perpendicular as possible to the axis of the pillow. This task was extremely difficult in outcrops where the pillows were intensely weathered and observed in a 2D surface; at Oued Lhar, however, the outcrop allows a 3D observation of the subaquatic sequence. At all locations (Aït-Ourir, Jbel Imzar and Oued
Mineralogy of sedimentary beds and peperites
Sediments were sampled along the Jbel Imzar (Fig. 7) and Sidi Rahal (Fig. 8) sections and analysed by X-Ray diffraction at Instituto Andaluz de Ciencias de la Tierra (Granada, Spain).
The lithostratigraphic analysis of the volcanic succession at Jbel Imzar revealed 14 superimposed flows, organized into four formations and separated by sediments. Three sedimentary intervals were sampled: E1–red and black-shales beneath the lavas from the Lower Fm.; E2 –peperitic sediment (White et al., 2000,
Discussions and conclusions
The succession of lava flow is subdivided into the Lower, Middle, Upper and Recurrent Formations. The emplacement of basalts may induce an important thermal effect onto the adjacent sediments; therefore train an effect on the clay and mineral assemblages.
The pillow lavas and some silty and sandy sediment indicate subaquatic environment.
Some sediment between basalt flows have been affected by hydrothermal fluids circulation, resulting into interactions at the basalt-sediment interface. This is
Acknowledgments
Many thanks to:
-Dr. Michel Seranne, CNRS-GEOCSIENCES, University of Montpellier for his remarks and his suggestions.
-Prof. Anne de Vernal (Geotop-UQAM, Canada) for palynoflore analysis.
References (50)
A Sr-Nd isotope and REE study of late Triassic dolerites from the Pyrenees (France) and the Messejana dyke (Spain and Portugal)
Earth Planet. Sci. Lett.
(1985)- et al.
Thermal and hydrothermal effects of Triassic basalt casting-on Liassic clays of the Argana Basin (Morocco)
Comptes Rendus Geosci.
(2002) - et al.
Age of jurassic continental tholeiits of french Guyana, surinam and Guinea: implication for the initial opening of the central atlantic ocean
Earth Planet. Sci. Lett.
(1997) - et al.
Première caractérisation palynologique du Trias moyen dans le Haut-Atlas ; implications pour l’initiation du rifting téthysien au Maroc
Comptes Rendus Geosci.
(2006) Hydrothermal alteration and diagenesis of terrestrial lacustrine pillow basalts: coordination of hyperspectral imaging with laboratory measurements
Geochimica Cosmochimica Acta
(2015)- et al.
Geochemistry of the oldest Atlantic oceanic crast suggests mantle plume involvement in the early history of the Central Atlantic Ocean
Earth Planet. Sci. Lett.
(2001) - et al.
The Central Atlantic Magmatic Province at the Triassic–Jurassic boundary: paleomagnetic and 40Ar/39Ar evidence from Morocco for brief, episodic volcanism
Earth Planet. Sci. Lett.
(2004) - et al.
Rift-related magmatism of the central atlantic magmatic province in algarve, southern Portugal
Lithos
(2008) Non-plume magmatism and rifting during the opening of the central Atlantic Ocean
Tectonophysics
(2000)Development of continental lithospheric mantle as reflected in the chemistry of the Mesozoic Appalachian tholeiites, USA
Earth Planet. Sci. Lett.
(1990)
40Ar/39Ar dating and geochemistry of tholeiitic magmatism related to the early opening of the Central Atlantic rift
Earth Planet. Sci. Lett.
Peperite: a review of magma-sediment mingling
J. Volcanol. Geotherm. Res.
The Mesozoïc tholeiitic province of northwest Africa: a volcanotectonic record of the early opening of Central Atlantic
Origin and metamorphism of peperite and associated rocks in the Devonian Elwell Formation, northern Sierra Nevada, California
Geol. Soc. Am. Bull.
Revised definition of Large Igneous Province (LIP)
Earth Sci. Rev.
Geochimistry of the early jurassic messejana-plascencia dyke (Portugal-Spain); implication on the origin of the central atlantic magmatic province
J. Pertrol.
Large Igneous Provinces: crustal structure, dimensions, and external consequences
Rev. Geophys.
The Central Atlantic Magmatic Province (CAMP) in Brazil : petrology, geochemistry, 40Ar/39Ar ages, paleomagnetism and geodynamic implications
Le volcanisme permien et fini-triasique dans le Haut-Atlas de Marrakech, Maroc
Morphology, internal architecture, and emplacement mechanisms of lava flows from the Central Atlantic Magmatic Province (CAMP) of Argana basin (Morocco)
Large Igneous Provinces (LIPs), giant dyke swarms, and mantle plumes: significance for breakup events within Canada and adjacent regions from 2.5 Ga to present
Can. J. Earth Sci.
Large mafic magmatic events through time and links to mantle plume heads
Pillow structure in the Triassic basalts of Connecticut
Geol. Soc. Am. Bull.
New evidence for geologically-instantaneous emplacement of earliest Jurassic Central Atlantic magmatic province basalts on the North American margin
Geology
Mechanism of burial metamorphism of argillaceous sediments: 1. Mineralogical and chemical evidence
Geol. Soc. Am. Bull.
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