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

2020 ◽  
Author(s):  
Lu-Lu Hao ◽  
Qiang Wang ◽  
Andrew C. Kerr ◽  
Jin-Hui Yang ◽  
Lin Ma ◽  
...  
Keyword(s):  
Lower Crust ◽  
Temporal Distribution ◽  
Crustal Thickening ◽  
Indian Plate ◽  
Hf Isotopes ◽  
Southern Tibet ◽  
Tectonic Model ◽  
Surface Uplift ◽  
Thin Crust ◽  
Cenozoic Magmatism

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.

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

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.

scholarly journals Cenozoic uplift of the Central Andes in northern Chile and Bolivia—reconciling paleoaltimetry with the geological evolution

2016 ◽  
Vol 53 (11) ◽  
pp. 1227-1245 ◽  
Author(s):  
Simon Lamb
Keyword(s):  
Lower Crust ◽  
Central Andes ◽  
Crustal Thickening ◽  
Direct Result ◽  
Western Margin ◽  
Crustal Shortening ◽  
Eastern Cordillera ◽  
Surface Uplift ◽  
Geological Evolution ◽  
History Of

The Cenozoic geological evolution of the Central Andes, along two transects between ∼17.5°S and 21°S, is compared with paleo-topography, determined from published paleo-altimetry studies. Surface and rock uplift are quantified using simple 2-D models of crustal shortening and thickening, together with estimates of sedimentation, erosion, and magmatic addition. Prior to ∼25 Ma, during a phase of amagmatic flat-slab subduction, thick-skinned crustal shortening and thickening (nominal age of initiation ∼40 Ma) was focused in the Eastern and Western Cordilleras, separated by a broad basin up to 300 km wide and close to sea level, which today comprises the high Altiplano. Surface topography at this time in the Altiplano and the western margin of the Eastern Cordillera appears to be ∼1 km lower than anticipated from crustal thickening, which may be due to the pull-down effect of the subducted slab, coupled to the overlying lithosphere by a cold mantle wedge. Oligocene steepening of the subducted slab is indicated by the initiation of the volcanic arc at ∼27–25 Ma, and widespread mafic volcanism in the Altiplano between 25 and 20 Ma. This may have resulted in detachment of mantle lithosphere and possibly dense lower crust, triggering 1–1.5 km of rapid uplift (over ≪5 Myrs) of the Altiplano and western margin of the Eastern Cordillera and establishing the present day lithospheric structure beneath the high Andes. Since ∼25 Ma, surface uplift has been the direct result of crustal shortening and thickening, locally modified by the effects of erosion, sedimentation, and magmatic addition from the mantle. The rate of crustal shortening and thickening varies with location and time, with two episodes of rapid shortening in the Altiplano, lasting <5 Myrs, that are superimposed on a long-term history of ductile shortening in the lower crust, driven by underthrusting of the Brazilian Shield on the eastern margin.

scholarly journals 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

2020 ◽  
Author(s):  
Lu-Lu Hao ◽  
Qiang Wang ◽  
et al.
Keyword(s):  
Analytical Methods ◽  
Crustal Thickening ◽  
Southern Tibet ◽  
Magmatic Rocks ◽  
Plateau Uplift ◽  
Cenozoic Magmatism

The analytical methods and results for the Wuyu Cenozoic magmatic rocks from the eastern Lhasa block of southern Tibet.

scholarly journals 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

2020 ◽  
Author(s):  
Lu-Lu Hao ◽  
Qiang Wang ◽  
et al.
Keyword(s):  
Analytical Methods ◽  
Crustal Thickening ◽  
Southern Tibet ◽  
Magmatic Rocks ◽  
Plateau Uplift ◽  
Cenozoic Magmatism

The analytical methods and results for the Wuyu Cenozoic magmatic rocks from the eastern Lhasa block of southern Tibet.

Crustal thickening prior to 38Ma in southern Tibet: Evidence from lower crust-derived adakitic magmatism in the Gangdese Batholith

2012 ◽  
Vol 21 (1) ◽  
pp. 88-99 ◽  
Author(s):  
Qi Guan ◽  
Di-Cheng Zhu ◽  
Zhi-Dan Zhao ◽  
Guo-Chen Dong ◽  
Liang-Liang Zhang ◽  
...  
Keyword(s):  
Lower Crust ◽  
Crustal Thickening ◽  
Southern Tibet

Late Cretaceous magmatism in the NW Lhasa Terrane, southern Tibet: Implications for crustal thickening and initial surface uplift

2019 ◽  
Vol 132 (1-2) ◽  
pp. 334-352 ◽  
Author(s):  
Ming Lei ◽  
Jian-Lin Chen ◽  
Ji-Feng Xu ◽  
Yun-Chuan Zeng ◽  
Qiu-Wei Xiong
Keyword(s):  
Late Cretaceous ◽  
Oceanic Lithosphere ◽  
Crustal Thickening ◽  
Geochemical Data ◽  
Initial Surface ◽  
Southern Tibet ◽  
Late Mesozoic ◽  
Lhasa Terrane ◽  
Surface Uplift ◽  
Cretaceous Magmatism

Abstract Crustal thickening and uplift of southern Tibet have been widely associated with India-Asia continental collision during the Cenozoic. However, recent studies indicated that the crust of the northwestern (NW) Lhasa Terrane was thickened during the late Mesozoic. Here we report geochronological and geochemical data for the Gaerqiong diorite porphyries (GPs) and Xiongma plutons (XPs) in the NW Lhasa terrane, southern Tibet. Zircon U-Pb dating suggests that these intrusive rocks were generated at ca. 85 and ca. 88 Ma, respectively. The GPs are characterized by high MgO, Cr, and Ni contents, and they have adakitic affinities. These geochemical features, combined with their depleted εNd(t) (+1.7 to +2.0), 87Sr/86Sr(i) (0.705103–0.705259), and zircon εHf(t) (+5.2 to +10.2) isotopic compositions, indicate that the GPs were produced by partial melting of the delaminated juvenile continental crust. In contrast, the XPs are composed of host granites and mafic microgranular enclaves (MMEs). The MMEs have low SiO2 and high MgO contents, and low εHf(t) (–14.0 to –5.8) values, indicating that their parental magmas were derived from an enriched mantle. The host granites have high SiO2 and low MgO contents, and variable εNd(t) (–7.4 to –6.3) and zircon εHf(t) (–11 to –4.1) values. These observations, combined with the presence of MMEs in the Xiongma granites, suggest that the host granites were the result of mixing of crust- and mantle-derived magmas. Detailed study of these two plutons, combined with the previous researches, suggests that Late Cretaceous (ca. 90 Ma) magmatism in the NW Lhasa Terrane occurred in a post-collisional extensional setting related to delamination of the regionally thickened lithosphere after collision of the Lhasa-Qiangtang Terranes. We propose that the crust of the NW Lhasa Terrane reached a maximum thickness (average of &gt;50 km) before the Late Cretaceous (ca. 90 Ma). This crustal thickening was caused by underplating of mafic magmas during slab roll-back and break-off of the southward-subducting Bangong-Nujiang oceanic lithosphere and subsequent tectonic thrusting during Qiangtang-Lhasa Terrane collision, respectively. Given that crustal thickening generally results in elevated terrain, the regional uplift (driven by isostasy due to crustal thickening) probably commenced before the Late Cretaceous (ca. 90 Ma).

scholarly journals A Downgoing Indian Lithosphere Control on Along-Strike Variability of Porphyry Mineralization in the Gangdese Belt of Southern Tibet

2020 ◽  
Vol 116 (1) ◽  
pp. 29-46 ◽  
Author(s):  
Xiang Sun ◽  
Yongjun Lu ◽  
Qiang Li ◽  
Ruyue Li
Keyword(s):  
Porphyry Copper ◽  
Tectonic Setting ◽  
Igneous Rocks ◽  
Crustal Thickening ◽  
Hf Isotopes ◽  
Porphyry Copper Deposits ◽  
Bulk Rock ◽  
Southern Tibet ◽  
Copper Deposits ◽  
Isotope Data

Abstract The E-trending Gangdese porphyry copper belt in southern Tibet is a classic example of porphyry mineralization in a continental collision zone. New zircon U-Pb geochronological, zircon Hf-O, and bulk-rock Sr-Nd isotope data for the Miocene mineralizing intrusions from the Qulong, Zhunuo, Jiru, Chongjiang, and Lakange porphyry copper deposits and Eocene igneous rocks from the western Gangdese belt, together with literature data, show that both Paleocene-Eocene igneous rocks and Miocene granitoids exhibit coupled along-arc isotopic variations, characterized by bulk-rock ɛNd(t) and zircon ɛHf(t) values increasing from ~84° to ~92°E and then decreasing toward ~95°E. These are interpreted to reflect increasing contributions of subducted Indian continental materials from ~92° to ~84°E and from ~92° to ~95°E, respectively. The Miocene mineralizing intrusions were derived from subduction-modified Tibetan lower crust represented isotopically by the Paleocene-Eocene intrusions, with contributions from Indian plate-released fluids and mafic melts derived from mantle metasomatized by subducted Indian continental materials. Involvement of isotopically ancient Indian continental materials increased from east (Qulong) to west (Zhunuo), which is interpreted to reflect an increasingly shallower angle of the downgoing Indian slab from east to west, consistent with geophysical imaging. Exploration of Gangdese Miocene porphyry copper deposits should focus on the Paleocene-Eocene arc where the subarc mantle was mainly enriched by fluids from the subducted Neo-Tethyan oceanic slab. Neodymium-Hf isotope data for mineralizing igneous rocks from porphyry copper deposits globally show no obvious correlations with Cu endowment. Although Nd-Hf isotopes are useful for imaging lithospheric architecture through time, caution must be taken when using Nd-Hf isotopes to evaluate the potential endowment of porphyry copper deposits, because other factors such as tectonic setting, crustal thickening, magma differentiation, fluid exsolution, and ore-forming processes all play roles in determining Cu endowments and grades.

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.

Sign in / Sign up

Export Citation Format

Share Document