Syn-collisional magmatic record of Indian steep subduction by 50 Ma

2020 ◽  
Author(s):  
Yue Qi ◽  
Chris J. Hawkesworth ◽  
Qiang Wang ◽  
Derek A. Wyman ◽  
Zheng-Xiang Li ◽  
...  
Keyword(s):  
High Volume ◽  
Isotope Ratios ◽  
Eastern Himalaya ◽  
Continental Lithosphere ◽  
Southern Tibet ◽  
Geochemical Composition ◽  
Crustal Rocks ◽  
Continental Subduction ◽  
Magmatic Rocks ◽  
Formation And Evolution

Subduction of Indian continental lithosphere during the Asia-India collision played an important role in the formation and evolution of the Himalaya-Tibetan orogen. However, the geometry of early Indian continental subduction remains debated. Given that the Indian continent is characterized by enriched isotope ratios (87Sr/86Sr > 0.730, εNd(t) < −10), relative to those in subducted oceanic materials (87Sr/86Sr < 0.704, εNd(t) ≈ +8), changes in the composition of magmatic rocks with time, in particular their radiogenic isotope ratios, is used to constrain the timing and nature of continental subduction. This study reports the field relations, zircon U-Pb ages and geochemical composition of a syn-collisional batholith that crosscuts the central Indus-Yarlung Zangbu suture in the Saga area of southern Tibet. Zircon U/Pb ages for the batholith mainly range from 50 to 46 Ma. Samples from the Lopu Range batholith have enriched zircon Hf (εHf(t) = −0.4 to −8.6) and whole rock 87Sr/86Sri = 0.7094−0.7121 and εNd(t) = −7.3 to −9.8, suggesting that they were derived from a mixture of juvenile Gangdese and isotopically enriched Indian crustal materials. This result indicates that subduction of Indian crustal rocks occurred before 50 Ma in the central Himalaya. The geochemical composition and distribution of high volume ca. 51 Ma magmatism in the Gangdese belt, combined with thermal models of the subduction zone, suggests a steepening of the subducted Indian continental lithosphere occurred between the onset of India-Asia collision (59 Ma) and 46 Ma in the central-eastern Himalaya.

Late Oligocene–early Miocene transformation of postcollisional magmatism in Tibet

Geology ◽  
2019 ◽  
Vol 47 (8) ◽  
pp. 776-780 ◽  
Author(s):  
Zhengfu Guo ◽  
Marjorie Wilson
Keyword(s):  
Evolutionary Model ◽  
Climate Forcing ◽  
Early Miocene ◽  
The Tibetan Plateau ◽  
Carbonate Sediments ◽  
Continental Lithosphere ◽  
Continental Subduction ◽  
Magmatic Rocks ◽  
Modern Analogue ◽  
Comprehensive Compilation

Abstract Uplift of the Tibetan Plateau is thought to be one of the most important orogenic and climate forcing events of the Cenozoic Era, associated with geodynamic changes related to India-Asia collision and subsequent continental lithosphere subduction. However, the fate and scale of the subducted continental lithosphere segments remain highly controversial. Using a comprehensive compilation of the spatiotemporal distribution of postcollisional magmatic rocks across Tibet, together with new geochemical and Sr-Nd-Pb isotopic data and modeling simulations, we propose a holistic, two-stage evolutionary model to explain the link between genesis of the magmas and continental subduction. The magmatism prior to 25 Ma resulted from continuous upwelling of a carbonate-rich upper-mantle plume induced by northward underthrusting of Indian oceanic and continental lithosphere with its cover of Tethyan platform carbonate sediments, whereas magmatism after 25 Ma was related to opposing north-directed and south-directed continental subduction. Our model indicates a transformation in the distribution and nature of the magmatism in Tibet at ca. 25 Ma, which reflects a significant change in the Himalayan-Tibetan orogen and associated mantle dynamic processes in the early Miocene. Understanding this transformation could have important implications for the utility of the Himalayan-Tibetan system as a modern analogue for ancient orogens.

Importance of continental subductions for the growth of the Tibetan plateau

2013 ◽  
Vol 184 (3) ◽  
pp. 199-223 ◽  
Author(s):  
Stéphane Guillot ◽  
Anne Replumaz
Keyword(s):  
Tibetan Plateau ◽  
Rheological Behaviour ◽  
High Strength ◽  
The Tibetan Plateau ◽  
Continental Lithosphere ◽  
Southern Tibet ◽  
Continental Subduction ◽  
Northern Tibetan Plateau ◽  
Convergence System ◽  
Northern Portion

Abstract How and when the Tibetan plateau developed has long been a puzzling question with implications for the current understanding of the behaviour of the continental lithosphere in convergent zones. We present and discuss recent data acquired in geology and geophysics and through igneous and metamorphic petrology and palaeo-altitude estimates. It appears from this research that Tibet initially resulted from the accretion of the Gondwana continental blocks to the southern Asian margin during the Palaeozoic and Mesozoic eras. These successive accretions have potentially favoured the creation of local landforms, particularly in southern Tibet, but no evidence exists in favour of the existence of a proto-Tibetan plateau prior to the Cenozoic. Moreover, before the India-Asia collision, the Tibetan crust had to be sufficiently cold and rigid to transfer the horizontal forces from India to northern Tibet and localize the deformation along the major strike-slip faults. However, these successive accretions associated with subductions have metasomatized the Tibetan lithospheric mantle and largely explain the potassium- and sodium-rich Cenozoic magmatism. Another consequence of this contamination by fluids is the softening of the Tibetan lithosphere, which favoured intra-continental subductions. The timing and the geochemical signatures of the magmatism and the palaeo-altitudes suggest the early growth of the Tibetan plateau. By the Eocene, the southern plateau and the northern portion of Himalaya would be at an altitude of approximately 4000 meters, while the central and northern Tibetan plateau was at altitudes of approximately 2000 to 3000 meters at the Eocene-Oligocene transition. From all of these data, we propose a model of the formation of the Tibetan plateau coupled with the formation of Himalaya, which accounts for more than 2500 km of convergence accommodated by the deformation of the continental lithospheres. During the early Eocene (55-45 Ma), the continental subduction of the high-strength Indian continental lithosphere dominates, ending with the detachment of the Indian slab. Between 45 and 35 Ma, the continental collision is established, resulting in the thickening of the internal Himalayan region and southern Tibet and the initiation of intra-tibetan subductions. By 35 Ma, the southward subduction of the intra-tibetan Songpan-Ganze terrane ends in slab break-off and is relayed by the oblique subduction of the Tarim the Athyn Tagh propagated northeastward beneath the Qilina Shan. Southward, the dextral Red River fault accommodated the southeastward extrusion of the Indochina block. During the Miocene, specifically, between 25 and 15 Ma, the Indian slab undergoes a second break-off, while the central part of Tibet is extruded eastward. Northward, the continental subduction beneath the Qilian Shan continues. Discontinuous periods of magmatic activity associated with slab detachments play a fundamental role in the convergence process. These periods lead locally to a softening of the mid-crust by magma heat transfer and to the granulitisation of the lower crust, which becomes more resistant. We propose that due to these alternating periods of softening and hardening of the Tibetan crust, the rheological behaviour of the convergence system evolves in space and time, promoting homogeneous thickening periods alternating with periods of localised crustal or lithospheric deformations.

scholarly journals Petrogenesis and Geodynamic Implications of Miocene Felsic Magmatic Rocks in the Wuyu Basin, Southern Gangdese Belt, Qinghai-Tibet Plateau

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 655
Author(s):  
Hanzhi Chen ◽  
Mingcai Hou ◽  
Fuhao Xiong ◽  
Hongwei Tang ◽  
Gangqiang Shao
Keyword(s):  
Lower Crust ◽  
Volcanic Rocks ◽  
Tibet Plateau ◽  
Southern Tibet ◽  
Mixed Product ◽  
Good Opportunity ◽  
Magmatic Rocks ◽  
Adakitic Rocks ◽  
Felsic Volcanic ◽  
Qinghai Tibet Plateau

Miocene felsic magmatic rocks with high Sr/Y ratios are widely distributed throughout the Gangdese belt of southern Tibet. These provide a good opportunity to explore the magmatic process and deep dynamic mechanisms that occurred after collision between the Indo and the Asian plates. In this paper, felsic volcanic rocks from the Zongdangcun Formation in the Wuyu Basin in the central part of the southern Gangdese belt are used to disclose their origin. Zircon U-Pb geochronology analysis shows that the felsic magmatism occurred at ca. 10.3 ± 0.2 Ma, indicating that the Zongdangcun Formation formed during the Miocene. Most of these felsic magmatic rocks plot in the rhyolite area in the TAS diagram. The rhyolite specimens from the Zongdangcun Formation have the characteristics of high SiO2 (>64%), K2O, SiO2, and Sr contents, a low Y content and a high Sr/Y ratio, and the rocks are rich in LREE and depleted in HREE, showing geochemical affinity to adakitic rocks. The rocks have an enriched Sr-Nd isotopic composition (εNd(t) = −6.76 to −6.68, (87Sr/86Sr)i = 0.7082–0.7088), which is similar to the mixed product of the juvenile Lhasa lower continental crust and the ancient Indian crust. The Hf isotopes of zircon define a wide compositional range (εHf(t) = −4.19 to 6.72) with predominant enriched signatures. The Miocene-aged crustal thickness in southern Tibet, calculated on the basis of the Sr/Y and (La/Yb)N ratios was approximately 60–80 km, which is consistent with the thickening of the Qinghai-Tibet Plateau. The origin of Miocene felsic magmatic rocks with high Sr/Y ratios in the middle section of the Gangdese belt likely involved a partial melting of the thickened lower crust, essentially formed by the lower crust of the Lhasa block, with minor contribution from the ancient Indian crust. After comprehensively analyzing the post-collisional high Sr/Y magmatic rocks (33–8 Ma) collected from the southern margin of the Gangdese belt, we propose that the front edge tearing and segmented subduction of the Indian continental slab may be the major factor driving the east-west trending compositional changes of the Miocene adakitic rocks in southern Tibet.

Leucogranites in Lhozag, southern Tibet: Implications for the tectonic evolution of the eastern Himalaya

Lithos ◽  
2017 ◽  
Vol 294-295 ◽  
pp. 246-262 ◽  
Author(s):  
Chunmei Huang ◽  
Zhidan Zhao ◽  
Guangming Li ◽  
Di-Cheng Zhu ◽  
Dong Liu ◽  
...  
Keyword(s):  
Tectonic Evolution ◽  
Eastern Himalaya ◽  
Southern Tibet

scholarly journals Supplemental Material: Isotopic spatial-temporal evolution of magmatic rocks in the Gangdese belt: Implications for the origin of Miocene post-collisional giant porphyry deposits in southern Tibet

2021 ◽  
Author(s):  
Chen-Hao Luo ◽  
Rui Wang ◽  
et al.
Keyword(s):  
Spatial Distribution ◽  
Temporal Evolution ◽  
Magma Mixing ◽  
Mixing Models ◽  
Southern Tibet ◽  
Porphyry Deposits ◽  
Magmatic Rocks

Two supplemental pictures and five supplemental tables. The pictures exhibit the Nd-Hf isotopic spatial distribution of the Gangdese belt magmatic rocks, southern Tibet, by using the average isotopic values of per 0.5 longitude (Fig. S1) and two additional magma mixing models related to the Jurassic and Cretaceous Gangdese belt magmatic rocks, southern Tibet (Fig. S2). The talbes contain all the data used in this research and their references.

scholarly journals The role of Edge-Driven Convection in the generation of volcanism I: a 2D systematic study

2020 ◽  
Author(s):  
Antonio Manjón-Cabeza Córdoba ◽  
Maxim Ballmer
Keyword(s):  
Numerical Models ◽  
High Volume ◽  
Oceanic Lithosphere ◽  
Companion Paper ◽  
Small Scale ◽  
Continental Lithosphere ◽  
Transient Phenomenon ◽  
Mantle Viscosity ◽  
Wide Range

Abstract. The origin of intraplate volcanism is not explained by the plate tectonic theory, and several models have been put forward for explanation. One of these models involves Edge-Driven Convection (EDC), in which cold and thick continental lithosphere is juxtaposed to warm and thin oceanic lithosphere to trigger convective instability. To test whether EDC can produce long-lived high-volume magmatism, we run numerical models of EDC for a wide range of mantle properties and edge (i.e., the oceanic-continental transition) geometries. We find that the most important parameters that govern EDC are the rheological paramaters mantle viscosity η0 and activation energy Ea. However, even the maximum melting volumes found in our models are insufficient to account for island-building volcanism on old seafloor, such as at the Canary Islands and Cape Verde. Also, beneath old seafloor, localized EDC-related melting commonly transitions into widespread melting due to small-scale sublithospheric convection, inconsistent with the distribution of volcanism at these volcanic chains. In turn, EDC is a good candidate to sustain the formation of small seamounts on young seafloor, as it is a highly transient phenomenon that occurs in all our models soon after initiation. In a companion paper, we investigate the implications of interaction of EDC with mantle-plume activity.

Origin of syn-collisional granitoids in the Gangdese orogen: Reworking of the juvenile arc crust and the ancient continental crust

2021 ◽  
Author(s):  
Yu-Wei Tang ◽  
Long Chen ◽  
Zi-Fu Zhao ◽  
Yong-Fei Zheng
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Continental Collision ◽  
Late Eocene ◽  
Igneous Rocks ◽  
Early Eocene ◽  
Southern Tibet ◽  
Crustal Rocks ◽  
Mafic Magmas ◽  
T Values

Granitoids at convergent plate boundaries can be produced either by partial melting of crustal rocks (either continental or oceanic) or by fractional crystallization of mantle-derived mafic magmas. Whereas granitoid formation through partial melting of the continental crust results in reworking of the pre-existing continental crust, granitoid formation through either partial melting of the oceanic crust or fractional crystallization of the mafic magmas leads to growth of the continental crust. This category is primarily based on the radiogenic Nd isotope compositions of crustal rocks; positive εNd(t) values indicate juvenile crust whereas negative εNd(t) values indicate ancient crust. Positive εNd(t) values are common for syn-collisional granitoids in southern Tibet, which leads to the hypothesis that continental collision zones are important sites for the net growth of continental crust. This hypothesis is examined through an integrated study of in situ zircon U-Pb ages and Hf isotopes, whole-rock major trace elements, and Sr-Nd-Hf isotopes as well as mineral O isotopes for felsic igneous rocks of Eocene ages from the Gangdese orogen in southern Tibet. The results show that these rocks can be divided into two groups according to their emplacement ages and geochemical features. The first group is less granitic with lower SiO2 contents of 59.82−64.41 wt%, and it was emplaced at 50−48 Ma in the early Eocene. The second group is more granitic with higher SiO2 contents of 63.93−68.81 wt%, and it was emplaced at 42 Ma in the late Eocene. The early Eocene granitoids exhibit relatively depleted whole-rock Sr-Nd-Hf isotope compositions with low (87Sr/86Sr)i ratios of 0.7044−0.7048, positive εNd(t) values of 0.6−3.9, εHf(t) values of 6.5−10.5, zircon εHf(t) values of 1.6−12.1, and zircon δ18O values of 5.28−6.26‰. These isotopic characteristics are quite similar to those of Late Cretaceous mafic arc igneous rocks in the Gangdese orogen, which indicates their derivation from partial melting of the juvenile mafic arc crust. In comparison, the late Eocene granitoids have relatively lower MgO, Fe2O3, Al2O3, and heavy rare earth element (HREE) contents but higher K2O, Rb, Sr, Th, U, Pb contents, Sr/Y, and (La/Yb)N ratios. They also exhibit more enriched whole-rock Sr-Nd-Hf isotope compositions with high (87Sr/86Sr)i ratios of 0.7070−0.7085, negative εNd(t) values of −5.2 to −3.9 and neutral εHf(t) values of 0.9−2.3, and relatively lower zircon εHf(t) values of −2.8−8.0 and slightly higher zircon δ18O values of 6.25−6.68‰. An integrated interpretation of these geochemical features is that both the juvenile arc crust and the ancient continental crust partially melted to produce the late Eocene granitoids. In this regard, the compositional evolution of syn-collisional granitoids from the early to late Eocene indicates a temporal change of their magma sources from the complete juvenile arc crust to a mixture of the juvenile and ancient crust. In either case, the syn-collisional granitoids in the Gangdese orogen are the reworking products of the pre-existing continental crust. Therefore, they do not contribute to crustal growth in the continental collision zone.

Magnetotelluric imaging of a fossil oceanic plate in northwestern Xinjiang, China

Geology ◽  
2020 ◽  
Vol 48 (4) ◽  
pp. 385-389 ◽  
Author(s):  
Y.X. Xu ◽  
B. Yang ◽  
A.Q. Zhang ◽  
S.C. Wu ◽  
L. Zhu ◽  
...  
Keyword(s):  
Subcontinental Lithospheric Mantle ◽  
Oceanic Plate ◽  
Continental Lithosphere ◽  
Magnetotelluric Data ◽  
Long Period ◽  
Continental Plate ◽  
Formation And Evolution ◽  
Magnetotelluric Imaging ◽  
Plate Subduction ◽  
Continental Accretion

Abstract Because an oceanic plate colliding with a continental plate will usually be subducted and recycled into the deep mantle, a fossil oceanic plate after the closure of an ancient ocean has rarely been imaged in the subcontinental lithospheric mantle. This has led to a long-standing debate about the fate of subducted ocean plates. The problem can be addressed by imaging the lithosphere in a continental accretion zone with past ocean subduction. We present a study using long-period magnetotelluric data that reveals a large shallow-mantle conductor in a Phanerozoic accretion area in northwestern Xinjiang, China. This conductor extends >300 km laterally at depths from 120 to 220 km and resembles a segment of a fossil oceanic plate. The reduced resistivity is ascribed to the volatile-bearing metasomatic minerals, based on its relatively fertile nature and low temperature. Our results demonstrate that an oceanic plate can be trapped in continental lithosphere, underscoring the significance of oceanic plate subduction to continental accretion, and shedding new light on our understanding of continental formation and evolution.

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