Full length articleTwo Types of mafic rocks in southern Tibet: A mark of tectonic setting change from Neo-Tethyan oceanic crust subduction to Indian continental crust subduction
Graphical abstract
Introduction
The subduction of continental crust in continental collisional orogens follows the subduction of oceanic crust to mantle depths, closure of the oceanic basin, and eventual continent–continent collision (e.g., Ernst, 2005, Castro et al., 2013, Gerya, 2014, Dash et al., 2015). These sequential processes are significant not only for high-pressure (HP) to ultrahigh-pressure (UHP) metamorphism of subducted crustal rocks (e.g., Chopin, 2003, Ernst and Liou, 2008, Zheng et al., 2012) but also for the recycling of crustal materials into the deep mantle (e.g., Zindler and Hart, 1986, Willbold and Stracke, 2010, Zheng, 2012, Zhao et al., 2013). In an orogen formed by continent–continent collision, the subduction of oceanic crust would have predated the subduction of continental crust, and because oceanic crust subjected to eclogite-facies metamorphism has a high density, it can pull the continental crust into the mantle where it experiences UHP metamorphism (Forsyth and Uyeda, 1975). Thus, in this scenario, both oceanic and continental crustal materials would be recycled into the mantle during continent–continent collision. It is assumed that oceanic crust undergoes metamorphic dehydration during subduction and that aqueous fluids derived from the subducted oceanic crust alter the peridotite of the overlying mantle wedge, thus generating the mantle source for oceanic arc basalts (e.g., Kelemen et al., 2003, Schmidt and Poli, 2003, Spandler and Pirard, 2013). In this process, the residual oceanic crust is subducted farther into the deep mantle to provide the mantle source for intraplate oceanic island basalts (OIBs), which are enriched in high-field-strength elements (e.g., Nb and Ta) and have depleted Sr–Nd isotopic values (Hofmann and White, 1982, Hofmann, 1997, Stracke et al., 2003, Chauvel et al., 2008). The subducted continental crust may become dehydrated and partially melted at depths of 80–130 km in a continental subduction zone (e.g., Zhang et al., 2008, Chen et al., 2013a, Chen et al., 2013b, Hermann et al., 2013). Thus, the fluids or melts derived from the subducted continental crust would also metasomatize the peridotite of the mantle wedge that overlies the continental slab (Zheng et al., 2012). An enriched mantle (ultramafic metasomatite), generated by reactions between mantle peridotite and the hydrous felsic melts derived from the partial melting of the deeply subducted continental crust, provides a likely source of the post-collisional potassic–ultrapotassic mafic rocks that are found in continent–continent collisional orogens, and these mafic rocks exhibit arc-like trace element patterns and enriched Sr–Nd isotope compositions (Prelević et al., 2008, Prelević et al., 2013, Guo et al., 2013a, Guo et al., 2013b, Guo et al., 2015, Zhao et al., 2013, Zhao et al., 2015). The existence of two types of crust–mantle interaction (i.e., oceanic crust–mantle and continental crust–mantle) during continent–continent collision means that the geochemical transition from OIB-like basalts to post-collisional potassic–ultrapotassic mafic rocks could provide a window into the processes involved during these two types of slab–mantle interaction.
The Tibetan Plateau is an ideal location to investigate processes associated with continent–continent collision (Allégre et al., 1984, Molnar et al., 1993). For example, southern Tibet records the subduction of Neo-Tethyan oceanic lithosphere, the subsequent collision of the Indian and Asian continents, and subduction of the India continental lithosphere (e.g., Chung et al., 2005). However, it is commonly difficult to identify the processes associated with the transition from the subduction of the Neo-Tethyan oceanic crust to the subduction of the Indian continent during the evolution of this orogen (Chung et al., 2005 and references therein). Recently, the Eocene (∼45 Ma) Langshan mafic rocks (gabbros) have been discovered in the Gyangze region of southern Tibet and have been shown to have clear OIB-like characteristics (Ji et al., 2016). Unlike these OIB-like magmatic rocks, which are of limited extent in southern Tibet, the Miocene (23–8 Ma) post-collisional potassic–ultrapotassic mafic rocks are widely distributed within the Lhasa Block of southern Tibet (Turner et al., 1996, Miller et al., 1999, Ding et al., 2003, Williams et al., 2004, Zhao et al., 2009).
In this study, we collated existing data on the Langshan mafic rocks (gabbros) (herein, Eocene mafic rocks) and the Miocene (23–8 Ma) Xuruco Lake–Dangre Yongcuo Lake (XDY) potassic–ultrapotassic mafic rocks (herein, Miocene mafic rocks) in southern Tibet to investigate (1) the mantle source of both group of rocks and (2) whether the transition from Eocene to Miocene mafic rocks records the tectonic evolution from subduction of Neo-Tethyan oceanic crust to subduction of Indian continental crust.
Section snippets
Geology of the study area
The Tibetan Plateau comprises the Songpan–Gangzi, Qiangtang, Lhasa, and Himalaya blocks from north to south. The Lhasa block is bounded by the Bangong–Nujiang suture zone (BNSZ) to the north and the Indus–Yarlung Zangbo suture zone (IYZSZ) to the south (Fig. 1a). The BNSZ formed from the Middle Jurassic to the Early Cretaceous (Yin and Harrison, 2000, Kapp et al., 2007, Zhu et al., 2011, Zhu et al., 2013, Zhu et al., 2016, Pan et al., 2012 Zhang et al., 2012, Fan et al., 2014) and the IYZSZ
Magma sources
The data used in this study for the Eocene mafic rocks were obtained from Ji et al. (2016), and the data for the Miocene mafic rocks were obtained from Liao et al., 2002, Ding et al., 2003, Ding et al., 2006, Gao et al. (2007), Zhao et al. (2009), Guo et al., 2013a, Guo et al., 2013b. To exclude crustal contamination and obvious fractional crystallization, we used only those samples with MgO > 6.5 wt%. Details regarding data selection are given in Supplementary text 1. The ages and geochemistry
Transition from sodic OIB-like magmas to potassic–ultrapotassic mafic rocks
Recent studies have ascribed the change from sodic OIB-like basalts (mafic dikes) to potassic mafic intrusive rocks in the Hong’an–Dabie orogens of east-central China to mantle sources with different types of recycled crustal material (oceanic crust versus continental crust) (Dai et al., 2012, Dai et al., 2015, Dai et al., 2017, Zhao et al., 2013, Zhao et al., 2015, Zheng et al., 2015, Zheng and Chen, 2016). These rocks are related to the closure of the Paleo-Tethys, which involved first the
Implications for the tectonic evolution from oceanic crust to continental crust subduction
It has previously been thought that the Late Triassic–Early Jurassic (210–174 Ma) magmatic belt in southern Tibet recorded the onset of the subduction of Neo-Tethyan oceanic crust (Zhang et al., 2007, Yang et al., 2008, Zhu et al., 2008, Zhu et al., 2011, Ji et al., 2009, Guo et al., 2013a, Kang et al., 2014 Song et al., 2014, Meng et al., 2015). However, the recent discovery of Middle–Late Triassic (237–212 Ma) volcanic rocks in the southern Lhasa subterrane has revealed that the northwards
Conclusions
The Eocene mafic rocks (gabbros) and Miocene Xuruco Lake–Dangre Yongcuo Lake potassic–ultrapotassic mafic rocks in southern Tibet exhibit significantly different geochemical features, which indicates that they originated from two types of mantle source. The Eocene mafic rocks exhibit OIB-like trace element patterns and depleted Sr–Nd radiogenic isotope compositions, consistent with a mantle source that was generated by the reaction of felsic melts derived from subducted Neo-Tethyan oceanic
Declaration of Competing Interest
The authors declared that they have no conflicts of interest to this work.
Acknowledgments
This research was supported by the National Key Research and Development Project of China (project 2016YFC0600305) and the Natural Science Foundation of China (41573024, 41602341, and 41873037). We thank the journal editor and two anonymous reviewers for their constructive and thoughtful comments.
References (138)
- et al.
Generation of new continental crust by sublithospheric silicic-magma relamination in arcs: a test of Taylor's andesite model
Gondwana Res.
(2013) - et al.
Synexhumation anatexis of ultrahigh-pressure metamorphic rocks: Petrological evidence from granitic gneiss in the Sulu orogen
Lithos
(2013) - et al.
Post-collisional ultrapotassic rocks and mantle xenoliths in the Sailipu volcanic field of Lhasa terrane, south Tibet: petrological and geochemical constraints on mantle source and geodynamic setting
Gondwana Res.
(2017) - et al.
Zircon U-Pb ages, geochemistry, and Sr-Nd-Pb-Hf isotopes of the Nuri intrusive rocks in the Gangdese area, southern Tibet: Constraints on timing, petrogenesis, and tectonic transformation
Lithos
(2015) Ultrahigh-pressure metamorphism: Tracing continental crust into the mantle
Earth Planet Sci Lett
(2003)- et al.
India's hidden inputs to Tibetan orogeny revealed by Hf isotopes of Transhimalayan zircons and host rocks
Earth Planet. Sci. Lett.
(2011) - et al.
Tibetan tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism
Earth Sci. Rev.
(2005) - et al.
The nature and timing of crustal thickening in Southern Tibet: geochemical and zircon Hf isotopic constraints from postcollisional adakites
Tectonophysics
(2009) - et al.
Mesozoic and Cenozoic volcanic rocks from central and southern Tibet: 39Ar–40Ar dating, petrological characteristics and geodynamical significance
Earth Planet. Sci. Lett.
(1986) - et al.
The nature of orogenic lithospheric mantle: geochemical constraints from postcollisional mafic-ultramafic rocks in the Dabie orogen
Chem. Geol.
(2012)
Tectonic development from oceanic subduction to continental collision: Geochemical evidence from postcollisional mafic rocks in the Hong’an-Dabie orogens
Gondwana Res.
Petrology, structural setting, timing, and geochemistry of Cretaceous volcanic rocks in eastern Mongolia: constraints on their tectonic origin
Gondwana Res.
The Andean-type Gangdese Mountains: paleoelevation record from the Paleocene-Eocene Linzhou Basin
Earth Planet. Sci. Lett.
The ultrapotassic rocks: characteristics, classification, and constraints for petrogenetic models
Earth Sci. Rev.
Precambrian geodynamics: concepts and models
Gondwana Res.
Petrogenesis of Early to Middle Jurassic granitoid rocks from the Gangdese belt, Southern Tibet: implications for early history of the Neo-Tethys
Lithos
The origin of Cenozoic basalts from Central Inner Mongolia, East China: the consequence of recent mantle metasomatism genetically associated with seismically observed paleo-Pacific slab in the mantle transition zone
Lithos
Mantle plumes from ancient oceanic crust
Earth Planet. Sci. Lett.
The timing of India-Asia collision onset – facts, theories, controversies
Earth Sci. Rev.
Os-Nd-Sr isotopes in Miocene ultrapotassic rocks of southern Tibet: partial melting of a pyroxenite-bearing lithospheric mantle?
Geochim. Cosmochim. Acta
Zircon U-Pb chronology and Hf isotopic constraints on the petrogenesis of Gangdese batholiths, southern Tibet
Chem. Geol.
Transition from oceanic to continental lithosphere subduction in southern Tibet: Evidence from the Late Cretaceous-Early Oligocene (∼ 91–30 Ma) intrusive rocks in the Chanang-Zedong area, southern Gangdese
Lithos
Geochronology and geochemistry of the Sangri group volcanic rocks, southern Lhasa terrane: implications for the early subduction history of the Neo-Tethys and Gangdese magmatic arc
Lithos
Melting experiments on homogeneous mixtures of peridotite and basalt: application to the genesis of ocean island basalts
Earth Planet. Sci. Lett.
Eocene Neotethyan slab breakoff in southern Tibet inferred from the Linzizong volcanic record
Tectonophysics
Cenozoic plate reconstruction of Southeast Asia
Tectonophysics
The onset of India-Asia continental collision: early, steep subduction required by the timing of UHP metamorphism in the western Himalaya
Earth Planet. Sci. Lett.
Postcollisional potassic and ultrapotassic rocks in southern Tibet: mantle and crustal origins in response to India-Asia collision and convergence
Geochim. Cosmochim. Acta
Identifying mantle carbonatite metasomatism through Os-Sr-Mg isotopes in Tibetan ultrapotassic rocks
Earth Planet. Sci. Lett.
Highly fractionated Late Eocene (∼35 Ma) leucogranites in the Xiaru Dome, Tethyan Himalaya, South Tibet
Lithos
Early Late Cretaceous (ca. 93 Ma) norites and hornblendites in the Milin area, eastern Gangdese: Lithosphere–asthenosphere interaction during slab roll-back and an insight into early Late Cretaceous (ca. 100–80 Ma) magmatic “flare-up” in southern Lhasa (Tibet)
Lithos
Late Cretaceous crustal growth in the Gangdese area, southern Tibet: petrological and Sr-Nd-Hf-O isotopic evidence from Zhengga diorite-gabbro
Chem. Geol.
Subduction of Indian continent beneath southern Tibet in the latest Eocene (∼35 Ma): insights from the Quguosha gabbros in southern Lhasa block
Gondwana Res.
A slab breakoff model for the Neogene thermal evolution of South Karakorum and South Tibet
Earth Planet. Sci. Lett.
Reaction between MORB-eclogite derived melts and fertile peridotite and generation of ocean island basalts
Earth Planet. Sci. Lett.
Mantle contributions to crustal thickening during continental collision: evidence from Cenozoic igneous rocks in southern Tibet
Lithos
Contribution of syncollisional felsic magmatism to continental crust growth: a case study of the Paleogene Linzizong volcanic succession in southern Tibet
Chem. Geol.
Tectonic evolution of the Qinghai-Tibet Plateau
J. Asian Earth Sci.
The chemical composition of subducting sediment and its consequences for the crust and mantle
Chem. Geol.
Mediterranean tertiary lamproites derived from multiple source components in postcollisional geodynamics
Geochim. Cosmochim. Acta
Recycling plus: a new recipe for the formation of Alpine-Himalayan orogenic mantle lithosphere
Earth Planet. Sci. Lett.
Cenozoic mantle composition evolution of southern Tibet indicated by Paleocene (∼ 64 Ma) pseudoleucite phonolitic rocks in central Lhasa Terrane
Lithos
The tectonic setting of ophiolites in the western Qinghai-Tibet Plateau, China
J. Asian Earth Sci.
Himalayan architecture constrained by isotopic tracers from clastic sediments
Earth Planet. Sci. Lett.
Slab–mantle interactions: 3 Petrogenesis of intraplate magmas and structure of the upper mantle
Chem. Geol.
Composition of the continental crust
Treat. Geochem.
Generation of mobile components during subduction of oceanic crust
Treat. Geochem.
Structure and evolution of the Himalaya-Tibet orogenic belt
Nature
Abrupt tectonics and rapid slab detachment with grain damage
PNAS
Melting relations of MORB-sediment melanges in underplated mantle wedge plumes: implications for the origin of Cordilleran-type batholiths
J. Petrol.
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