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.

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.

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.

Miocene Olivine Leucitites in the Hoh Xil Basin, Northern Tibet: Implications for Intracontinental Lithosphere Melting and Surface Uplift of the Tibetan Plateau

2020 ◽  
Vol 61 (1) ◽  
Author(s):  
Yue Qi ◽  
Qiang Wang ◽  
Ying-Tang Zhu ◽  
Lian-Chang Shi ◽  
Ya-Nan Yang
Keyword(s):  
Tibetan Plateau ◽  
Lithospheric Mantle ◽  
The Tibetan Plateau ◽  
Nd Isotope ◽  
Northern Tibet ◽  
Surface Uplift ◽  
Enriched Mantle ◽  
Magmatic Rocks ◽  
Low Degree ◽  
Pliocene Magmatism

Abstract The generation of Miocene–Pliocene post-collisional magmatic rocks in northern Tibet was coeval with surface uplift, meaning that understanding the petrogenesis of these rocks should provide clues to the mechanism of uplift of the Tibetan Plateau. However, the nature of the source(s) of Miocene–Pliocene post-collisional rocks is unresolved, especially for potassic–ultrapotassic rocks. This study focuses on 16 Ma olivine leucitites in the Hoh Xil Basin of northern Tibet, which display the lowest SiO2 (43·4–48·8 wt%) contents of all Miocene–Pliocene magmatic rocks in northern Tibet and have high MgO (4·85–8·57 wt%) contents and high K2O/Na2O (>1) ratios. Whole-rock geochemical compositions suggest that the olivine leucitites did not undergo significant fractional crystallization or crustal assimilation. All samples are enriched in large ion lithophile elements relative to high field strength elements, and they exhibit uniform whole-rock Sr–Nd isotope [(87Sr/86Sr)i = 0·7071–0·7077 and εNd(t) = −3·1 to −3·9] and olivine O isotope (5·8–6·6 ‰, mean of 6·2 ± 0·2 ‰, n = 21) compositions. We propose that the olivine leucitites were derived by low-degree partial melting of phlogopite-lherzolite in garnet-facies lithospheric mantle. Given the tectonic evolution of the Hoh Xil Basin and adjacent areas, we suggest that southward subduction of Asian (Qaidam block) lithosphere after India–Asia collision transferred potassium and other incompatible elements into the lithospheric mantle, forming the K-enriched mantle source of the Miocene–Pliocene potassic–ultrapotassic rocks. Removal of lower lithospheric mantle subsequently induced voluminous Miocene–Pliocene magmatism and generated >1 km surface uplift in the Hoh Xil Basin.

Early Miocene continental subduction and rapid exhumation in the western Mediterranean

Geology ◽  
2006 ◽  
Vol 34 (11) ◽  
pp. 981 ◽  
Author(s):  
John P. Platt ◽  
Robert Anczkiewicz ◽  
Juan-Ignacio Soto ◽  
Simon P. Kelley ◽  
Matthew Thirlwall
Keyword(s):  
Western Mediterranean ◽  
Early Miocene ◽  
Continental Subduction

scholarly journals Neogene tectonics and climate forcing of carnivora dispersals between Asia and North America

2015 ◽  
Vol 7 (3) ◽  
pp. 2445-2479 ◽  
Author(s):  
H. Jiang ◽  
T. Deng ◽  
Y. Li ◽  
H. Xu
Keyword(s):  
North America ◽  
Tibetan Plateau ◽  
Climate Forcing ◽  
Driving Mechanism ◽  
The Tibetan Plateau ◽  
Abstract Exchange ◽  
Terrestrial Mammals ◽  
Global Cooling ◽  
Environmental Events ◽  
Tectonic Movements

Abstract. Exchange records of terrestrial mammals can be combined with available tectonic and climatic documents to evaluate major biological and environmental events. Previous studies identified four carnivoran dispersals between Eurasia and North America in the Neogene, namely, at ∼ 20, 13–11, 8–7, and ∼ 4 Ma. In order to evaluate driving mechanism of these biological events, we collected, compared and analyzed a large number of published records. The results indicate that the carnivoran dispersal from Eurasia to North America at ∼ 20 Ma was probably caused by intense tectonic movements in Asia. During 13–11 Ma, global cooling possibly drove the mammal exchanges between Eurasia and North America. By comparison, the carnivoran dispersal from Eurasia to North America at 8–7 Ma was probably caused by the combination of global cooling and tectonic movements of the Tibetan Plateau. Similar to during 13–11 Ma, the carnivoran exchanges between Eurasia and North America at ∼ 4 Ma were possibly driven by global cooling.

scholarly journals Taphonomy and palaeoecology of the White Hunter Local Fauna

2017 ◽  
Author(s):  
Troy Myers
Keyword(s):  
Dry Forest ◽  
Early Miocene ◽  
Mammalian Fauna ◽  
Local Fauna ◽  
Open Forest ◽  
Modern Analogue ◽  
Wide Range ◽  
Closed Forest ◽  
Body Sizes ◽  
World Heritage Area

The White Hunter (WH) Local Fauna (LF) is one of the oldest assemblages from the Riversleigh World Heritage Area, belonging to Faunal Zone A and tentatively dated at approximately 24 Ma. The mammalian fauna has many plesiomorphic taxa and a wide range of body sizes are represented, although it is depauperate in medium to large arboreal mammals and over-represented by small to medium-sized macropodoids, vombatomorphians and carnivores. The non-mammalian vertebrate fauna also covers a wide body size range. The palaeoenvironmental conditions at the time of deposition have been contentious, ranging from hypotheses of cold and dry woodland to warm, wet rainforest, and many climatic and vegetation combinations in between. The autecologies of various species provide only equivocal support for palaeoenvironmental conclusions. Taphonomic and palaeoecologic data were tested herein to further illuminate palaeoenvironmental understanding. Mammalian post-cranial elements were examined for degree of weathering, abrasion, fragmentation, taxonomic bias and susceptibility to transport. No obvious bias against small vertebrates was observed. The fauna does not appear to represent a mixed-assemblage. Animals most likely died within close proximity to the site of deposition, although the absence of scavenger/carnivore damage militates against predation as the main source of accumulation. Trampling of elements may have been significant. Results suggest that WH may have been a moderately large ephemeral water body, subject to periodic drying and fed by a slow-moving creek. The climate was cooler than the early Miocene, with a distinct wet and dry season. Surrounding vegetation may have been a type without modern analogue combining structural, but not floristic, equivalents of open dry forest and closed rainforest. There is no evidence for gradational wet open forest types, but this may represent a rapid move to closed forest. These results are reinforced by palaeocommunity analysis of Riversleigh LFs which unite WH LF with a suite of early Miocene Lfs as a similar palaeocommunity type, perhaps antecedent to them.

Closure of the Bangong–Nujiang Tethyan Ocean in the central Tibet: Results from the provenance of the Duoni Formation

2019 ◽  
Vol 89 (10) ◽  
pp. 1039-1054 ◽  
Author(s):  
Zhicai Zhu ◽  
Qingguo Zhai ◽  
Peiyuan Hu ◽  
Sunlin Chung ◽  
Yue Tang ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Late Cretaceous ◽  
Suture Zone ◽  
The Tibetan Plateau ◽  
Tectonic History ◽  
Magmatic Rocks ◽  
Two Samples ◽  
Delta Sequence ◽  
History Of ◽  
Central Tibet

ABSTRACT The closure of the Bangong–Nujiang Tethyan Ocean (BNTO) and consequent Lhasa–Qiangtang collision is vital to reasonably understanding the early tectonic history of the Tibetan Plateau before the India-Eurasia collision. The timing of the Lhasa–Qiangtang collision was mainly constrained by the ophiolite and magmatic rocks in previous studies, with only limited constraints from the sedimentary rocks within and adjacent to the Bangong–Nujiang suture zone. In the middle segment of the Bangong–Nujiang suture zone, the Duoni Formation, consisting of a fluvial delta sequence with minor andesite interlayers, was originally defined as the Late Cretaceous Jingzhushan Formation and interpreted as the products of the Lhasa–Qiangtang collision during the Late Cretaceous. Our new zircon U-Pb data from two samples of andesite interlayers demonstrate that it was deposited during the latest Early Cretaceous (ca. 113 Ma) rather than Late Cretaceous. Systemic studies on the sandstone detrital model, heavy-mineral assemblage, and clasts of conglomerate demonstrate a mixed source of both Lhasa and Qiangtang terranes and ophiolite complex. Clasts of conglomerate contain abundant angular peridotite, gabbro, basalt, chert, andesite, and granite, and minor quartzite and gneiss clasts also exist. Sandstones of the Duoni Formation are dominated by feldspathic–lithic graywacke (Qt25F14L61 and Qm13F14L73), indicative of a mixture of continental-arc and recycled-orogen source origin. Detrital minerals of chromite, clinopyroxene, epidote, and hornblende in sandstone also indicate an origin of ultramafic and mafic rocks, while garnets indicate a metamorphosed source. Paleocurrent data demonstrate bidirectional (southward and northward) source origins. Thus, we suggest that the deposition of the Duoni Formation took place in the processes of the Lhasa–Qiangtang collision during the latest Early Cretaceous (∼ 113 Ma), and the BNTO had been closed by this time.

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