Supplemental Material: Post-collisional crustal thickening and plateau uplift of southern Tibet: Insights from Cenozoic magmatism in the Wuyu area of the eastern Lhasa block

The nature and timing of post-collisional crustal thickening and its link to surface uplift in the eastern Lhasa block of the southern Tibetan plateau remain controversial. Here we report on Cenozoic magmatism in the Wuyu area of the eastern Lhasa block. The Eocene (ca. 46 Ma) trachyandesites and trachydacites show slight fractionation of rare earth elements (REE), slightly negative Eu and Sr anomalies, and relatively homogeneous Sr-Nd and zircon Hf isotopes (87Sr/86Sr(i) = 0.7050−0.7063, εNd(t) = −0.92 to −0.03, εHf(t) = +2.6 to +4.8). Previous studies have suggested Neo-Tethys oceanic slab break-off at 50−45 Ma; thus, the Wuyu Eocene magmatism could represent a magmatic response to this slab break-off and originate from relatively juvenile Lhasa crust. The Miocene (ca. 15−12 Ma) dacites and rhyolites have adakitic affinities, e.g., high Sr (average 588 ppm), Sr/Y (29−136), and La/Yb (30−76) values, low Y (4−12 ppm) and Yb (0.4−0.9 ppm) contents, and variable Sr-Nd and zircon Hf isotopes (87Sr/86Sr(i) = 0.7064−0.7142, εNd(t) = −11.7 to −3.7, εHf(t) = −3.2 to +4.5). Their more enriched Sr-Nd-Hf isotopes relative to the Eocene lavas indicate that they should be derived from mixed Lhasa lower crust comprising juvenile crust, ultrapotassic rocks, and probably Indian lower crust-derived rocks. This study has also revealed the transformation from Eocene juvenile and thin crust with a thickness of <40 km to Miocene mixed and thickened crust with a thickness of >50 km. Combined with published tectonic data, we suggest that both lithospheric shortening and magma underplating contributed to eastern Lhasa block post-collisional crustal thickening. Given the spatial-temporal distribution of eastern Lhasa block magmatism and regional geology, we invoke a post-collisional tectonic model of steep subduction of the Indian plate and subsequent westward-propagating plate break-off beneath the eastern Lhasa block, which caused the surface uplift.

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

Minerals ◽

10.3390/min11060655 ◽

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.

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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

10.1130/gsab.s.14356130.v4 ◽

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.

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Supplemental Material: Cambrian magmatic flare-up, central Tibet: Magma mixing in proto-Tethyan arc along north Gondwanan margin

10.1130/gsab.s.13652948.v1 ◽

2021 ◽

Author(s):

Pei-yuan Hu ◽

et al.

Keyword(s):

Tibetan Plateau ◽

Analytical Methods ◽

Magma Mixing ◽

Mixing Model ◽

Lhasa Terrane ◽

The North ◽

Magmatic Rocks ◽

Central Tibetan Plateau ◽

Central Tibet

Data, magma mixing model, and analytical methods of the Cambrian magmatic rocks from the North Lhasa terrane, central Tibetan Plateau.

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The Timing of Metamorphism, Magmatism, and Cooling in the Zanskar, Garhwal, and Nepal Himalaya

Journal of Nepal Geological Society ◽

10.3126/jngs.v11i0.32786 ◽

1995 ◽

Vol 11 ◽

Author(s):

M. P. Searle

Keyword(s):

Hanging Wall ◽

Crustal Thickening ◽

Indian Plate ◽

Eastern Himalaya ◽

Normal Faults ◽

The Tibetan Plateau ◽

Main Central Thrust ◽

Southern Tibet ◽

Peak Metamorphism ◽

Exhumation Rates

Following India-Asia collision, which is estimated at ca. 54-50 Ma in the Ladakh-southern Tibet area, crustal thickening and timing of peak metamorphism may have been diachronous both along the Himalaya (pre-40 Ma north Pakistan; pre-31 Ma Zanskar; pre-20 Ma east Kashmir, west Garhwal; 11-4 Ma Nanga Parbat) and cross the strike of the High Himalaya, propagating S (in Zanskar SW) with time. Thrusting along the base of the High Himalayan slab (Main Central Thrust active 21-19 Ma) was synchronous with N-S (in Zanskar NE-SW) extension along the top of the slab (South Tibet Detachment Zone). Kyanite and sillimanite gneisses in the footwall formed at pressure of 8-10 kbars and depths of burial of 28-35 km, 30- 21 Ma ago, whereas anchimetamorphic sediments along the hanging wall have never been buried below ca. 5-6 km. Peak temperatures may have reached 750 on the prograde part of the P-T path. Thermobarometers can be used to constrain depths of burial assuming a continental geothermal gradient of 28-30 °C/km and a lithostatic gradient of around 3.5-3.7 km/kbar (or 0.285 kbars/km). Timing of peak metamorphism cannot yet be constrained accurately. However, we can infer cooling histories derived from thermochronometers using radiogenic isotopic systems, and thereby exhumation rates. This paper reviews all the reliable geochronological data and infers cooling histories for the Himalayan zone in Zanskar, Garhwal, and Nepal. Exhumation rates have been far greater in the High Himalayan Zone (1.4-2.1 mm/year) and southern Karakoram (1.2-1.6 mm/year) than along the zone of collision (Indus suture) or along the north Indian plate margin. The High Himalayan leucogranites span 26-14 Ma in the central Himalaya, and anatexis occurred at 21-19 Ma in Zanskar, approximately 30 Ma after the collision. The cooling histories show that significant crustal thickening, widespread metamorphism, erosion and exhumation (and therefore, possibly significant topographic elevation) occurred during the early Miocene along the central and eastern Himalaya, before the strengthening of the Indian monsoon at ca. 8 Ma, before the major change in climate and vegetation, and before the onset of E-W extension on the Tibetan plateau. Exhumation, therefore, was primarily controlled by active thrusts and normal faults, not by external factors such as climate change.

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Supplemental Material: Magmatic record of continuous Neo-Tethyan subduction after initial India-Asia collision in the central part of southern Tibet

10.1130/gsab.s.13195283.v2 ◽

2020 ◽

Author(s):

Feng Huang ◽

et al.

Keyword(s):

Analytical Methods ◽

Southern Tibet ◽

Data Tables

Analytical methods, data (Tables S1–S4), and modeling results (Tables S5–S6).

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

10.1130/gsab.s.12746846 ◽

2020 ◽

Author(s):

Yue Qi ◽

QIANG WANG ◽

et al.

Keyword(s):

Cross Section ◽

Analytical Methods ◽

Southern Tibet ◽

Analytical Results ◽

Geological Cross Section

Analytical methods, field geological cross-section, and analytical results for the Lopu Range batholith from southern Tibet.

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Crustal thickening and endogenic oxidation of magmatic sulfur

Science Advances ◽

10.1126/sciadv.aba6342 ◽

2020 ◽

Vol 6 (31) ◽

pp. eaba6342

Author(s):

Ming Tang ◽

Cin-Ty A. Lee ◽

Wei-Qiang Ji ◽

Rui Wang ◽

Gelu Costin

Keyword(s):

Oxidation State ◽

Sulfur Oxidation ◽

Ore Deposits ◽

Crustal Thickening ◽

Sulfate Content ◽

Southern Tibet ◽

Ore Deposit ◽

First Order ◽

Outstanding Problem ◽

Relationship Of

Porphyry ore deposits, Earth’s most important resources of copper, molybdenum, and rhenium, are strongly associated with felsic magmas showing signs of high-pressure differentiation and are usually found in places with thickened crust (>45 kilometers). This pattern is well-known, but unexplained, and remains an outstanding problem in our understanding of porphyry ore deposit formation. We approach this problem by investigating the oxidation state of magmatic sulfur, which controls the behavior of ore-forming metals during magma differentiation and magmatic-hydrothermal transition. We use sulfur in apatite to reconstruct the sulfur oxidation state in the Gangdese batholith, southern Tibet. We find that magma sulfate content increased abruptly after India-Eurasia collision. Apatite sulfur content and the calculated magma S6+/ΣS ratio correlate with whole-rock dysprosium/ytterbium ratio, suggesting that residual garnet, favored in thickened crust, exerts a first-order control on sulfur oxidation in magmatic orogens. Our findings link sulfur oxidation to internal petrogenic processes and imply an intrinsic relationship of magma oxidation with synmagmatic crustal thickening.

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Early Cenozoic partial melting of meta-sedimentary rocks of the eastern Gangdese arc, southern Tibet, and its contribution to syn-collisional magmatism

Geological Society of America Bulletin ◽

10.1130/b35763.1 ◽

2021 ◽

Author(s):

Yuan-Yuan Jiang ◽

Ze-Ming Zhang ◽

Richard M. Palin ◽

Hui-Xia Ding ◽

Xuan-Xue Mo

Keyword(s):

Partial Melting ◽

Lower Crust ◽

Sedimentary Rocks ◽

Late Carboniferous ◽

Southern Tibet ◽

Magmatic Arc ◽

Magmatic Rocks ◽

Deep Crust ◽

Juvenile Crust ◽

Early Cenozoic

Continental magmatic arcs are characterized by the accretion of voluminous mantle-derived magmatic rocks and the growth of juvenile crust. However, significant volumes of meta-sedimentary rocks occur in the middle and lower arc crust, and the contributions of these rocks to the evolution of arc crust remain unclear. In this paper, we conduct a systematic study of petrology, geochronology, and geochemistry of migmatitic paragneisses from the eastern Gangdese magmatic arc, southern Tibet. The results show that the paragneisses were derived from late Carboniferous greywacke, and underwent an early Cenozoic (69−41 Ma) upper amphibolite-facies metamorphism and partial melting at pressure-temperature conditions of ∼11 kbar and ∼740 °C, and generated granitic melts with enriched Hf isotopic compositions (anatectic zircon εHf(t) = −10.57 to +0.78). Combined with the existing results, we conclude that the widely distributed meta-sedimentary rocks in the eastern Gangdese arc deep crust have the same protolith ages of late Carboniferous, and record northwestward-decreasing metamorphic conditions. We consider that the deeply buried sedimentary rocks resulted in the compositional change of juvenile lower crust from mafic to felsic and the formation of syn-collisional S-type granitoids. The mixing of melts derived from mantle, juvenile lower crust, and ancient crustal materials resulted in the isotopic enrichment of the syn-collisional arc-type magmatic rocks of the Gangdese arc. We suggest that crustal shortening and underthrusting, and the accretion of mantle-derived magma during the Indo-Asian collision transported the supracrustal rocks to the deep crust of the Gangdese arc.

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