Post-collisional ore-bearing adakitic porphyries from Gangdese porphyry copper belt, southern Tibet: Melting of thickened juvenile arc lower crust

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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Himalayan and Trans Himalayan granitic rocks in and adjacent to Nepal and their mineral potential

Journal of Nepal Geological Society ◽

10.3126/jngs.v1i1.32668 ◽

1981 ◽

Vol 1 (1) ◽

Author(s):

A. H. G. Mitchell

Keyword(s):

Root Zone ◽

Porphyry Copper ◽

Tectonic Setting ◽

Granitic Rocks ◽

Main Central Thrust ◽

Southern Tibet ◽

Late Mesozoic ◽

The North ◽

Augen Gneiss ◽

Host Rocks

Granitic rocks occupying eight distinct tectonic settings can be recognized in the Himalayas and Transhimalayas. In the Lower Himalayas geographical belt a few plutons of two-mica granite intrude the lowest unit of the Nawakot Complex or Midland Group. More extensive are sheet- like lies of augen gneiss intrusive within a possibly thrust bounded succession carbonates and graphitic schists beneath the Main Central Thrust to the north. The most abundant granites in the Lower Himalayas are the two- mica cordierite- bearing granite within klippen; minor tin and tungsten mineralization is associated with these plutons, which are of late Cambrian age. Within the Higher Himalayas above the Main Central Thrust, the ‘Central Crystallines’ or Central Gneisses include pegmatites and pegmatitic granites intrusive into gneisses of probable early Proterozoic age; these have same potential for ruby, sapphire, aquamarine and possibly spodumene. Further north within the Higher Himalayan succession a southern belt of anatectic two- mica granites and leucogranites of mid-Tertiary age is favorable for tin, tungsten and uranium mineralization; a northern belt of granites or gneisses is of uncertain age and origin. North of the Indus Suture in the Transhimalayas extensive batholiths of hornblende granodiorite representing the root zone of a late Mesozoic to early Eocene volcanic arc are associated with porphyry copper deposits. Further north in southern Tibet the tectonic, setting for reported granitic bodies of Tertiary age is uncertain; their location suggests that they could be favorable host rocks for tin, uranium and porphyry molybdenum mineralization.

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Lithium isotopic evidence for subduction of the Indian lower crust beneath southern Tibet

Gondwana Research ◽

10.1016/j.gr.2019.07.016 ◽

2020 ◽

Vol 77 ◽

pp. 168-183 ◽

Cited By ~ 4

Author(s):

Shihong Tian ◽

Zengqian Hou ◽

Xuanxue Mo ◽

Yuheng Tian ◽

Yue Zhao ◽

...

Keyword(s):

Lower Crust ◽

Southern Tibet ◽

Isotopic Evidence

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Formation and composition of the Late Cretaceous Gangdese arc lower crust in southern Tibet

Contributions to Mineralogy and Petrology ◽

10.1007/s00410-020-01696-y ◽

2020 ◽

Vol 175 (6) ◽

Cited By ~ 1

Author(s):

Liang Guo ◽

Oliver Jagoutz ◽

William J. Shinevar ◽

Hong-Fei Zhang

Keyword(s):

Late Cretaceous ◽

Lower Crust ◽

Southern Tibet

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Early Jurassic adakitic rocks in the southern Lhasa sub-terrane, southern Tibet: petrogenesis and geodynamic implications

Geological Magazine ◽

10.1017/s0016756817000577 ◽

2017 ◽

Vol 155 (1) ◽

pp. 132-148 ◽

Cited By ~ 11

Author(s):

XINFANG SHUI ◽

ZHENYU HE ◽

REINER KLEMD ◽

ZEMING ZHANG ◽

TIANYU LU ◽

...

Keyword(s):

Partial Melting ◽

Lower Crust ◽

Inductively Coupled Plasma ◽

Early Jurassic ◽

Oceanic Plate ◽

Southern Tibet ◽

Inductively Coupled ◽

Adakitic Rocks ◽

Plasma Mass Spectrometry ◽

Geochemical Studies

AbstractCretaceous–Miocene adakitic rocks in the southern Lhasa sub-terrane have been intensively investigated, while possible Early Jurassic adakitic rocks in this area have been largely neglected. Petrological and geochemical studies revealed adakitic affinities of an Early Jurassic quartz diorite intrusion with mafic enclaves and three tonalite bodies from the Jiacha area in the southern Lhasa sub-terrane. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating suggests crystallization ages of 199–179 Ma for these rocks. Both quartz diorites and tonalites have typical adakitic geochemical characteristics such as high Al2O3 (15.14–18.22 wt.%) and Sr (363–530 ppm) contents, low Y (4.46–15.9 ppm) and Yb (0.51–1.74 ppm) contents and high Sr/Y ratios of 27–106. The adakitic quartz diorites are further characterized by high MgO (2.63–3.46 wt.%), Mg# (48–54) and εHf(t) (6.6–13.4) values, which were probably produced by partial melting of a subducted oceanic slab with a mantle contribution. The adakitic tonalites have very low abundances of compatible elements and relatively low εHf(t) values (3.5–10.3), and are interpreted to have formed by partial melting of Neoproterozoic mafic lower crust. Upwelling asthenosphere, triggered by rollback of the subducting Bangong–Nujiang (Meso-Tethys) oceanic plate, provided the necessary heat for slab and lower crust melting, resulting in the geochemical diversity of the coexisting felsic intrusive rocks. Contrary to other models, this study further demonstrates that the Bangong–Nujiang oceanic plate was subducted southward beneath the Lhasa terrane during the Early Jurassic.

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Adakites from continental collision zones: Melting of thickened lower crust beneath southern Tibet

Geology ◽

10.1130/g19796.1 ◽

2003 ◽

Vol 31 (11) ◽

pp. 1021 ◽

Cited By ~ 662

Author(s):

Sun-Lin Chung ◽

Dunyi Liu ◽

Jianqing Ji ◽

Mei-Fei Chu ◽

Hao-Yang Lee ◽

...

Keyword(s):

Lower Crust ◽

Continental Collision ◽

Southern Tibet

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Subduction of the Indian lower crust beneath southern Tibet revealed by the post-collisional potassic and ultrapotassic rocks in SW Tibet

Gondwana Research ◽

10.1016/j.gr.2015.09.005 ◽

2017 ◽

Vol 41 ◽

pp. 29-50 ◽

Cited By ~ 30

Author(s):

Shi-Hong Tian ◽

Zhu-Sen Yang ◽

Zeng-Qian Hou ◽

Xuan-Xue Mo ◽

Wen-Jie Hu ◽

...

Keyword(s):

Lower Crust ◽

Southern Tibet

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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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