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

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.

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

2021 ◽  
Author(s):  
Yuan-Yuan Jiang ◽  
et al.
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Sedimentary Rocks ◽  
Hf Isotope ◽  
Chemical Compositions ◽  
Trace Element Data ◽  
Southern Tibet ◽  
Magmatic Arc ◽  
Isotope Data ◽  
Early Cenozoic

The chemical compositions of minerals from the paragneisses (Tables S1–S3), the zircon and monazite age and trace element data of the paragneisses and leucosome (Tables S4–S5), and the zircon Lu-Hf isotope data of the paragneisses and leucosome (Table S6) from the eastern Gangdese magmatic arc.

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

2021 ◽  
Author(s):  
Yuan-Yuan Jiang ◽  
et al.
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Sedimentary Rocks ◽  
Hf Isotope ◽  
Chemical Compositions ◽  
Trace Element Data ◽  
Southern Tibet ◽  
Magmatic Arc ◽  
Isotope Data ◽  
Early Cenozoic

The chemical compositions of minerals from the paragneisses (Tables S1–S3), the zircon and monazite age and trace element data of the paragneisses and leucosome (Tables S4–S5), and the zircon Lu-Hf isotope data of the paragneisses and leucosome (Table S6) from the eastern Gangdese magmatic arc.

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.

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

2017 ◽  
Vol 155 (1) ◽  
pp. 132-148 ◽  
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.

The Kamusite A2-type granites in the Karamaili tectonic belt, Xinjiang (NW China): tracing staged postcollisional delamination in the eastern Junggar

2020 ◽  
pp. 1-26
Author(s):  
Bowen Zhang ◽  
Chuan Chen ◽  
Xiaoping Gong ◽  
Yaxiaer Yalikun ◽  
Kadeliya Kaheman
Keyword(s):  
Partial Melting ◽  
Large Scale ◽  
Late Carboniferous ◽  
Zircon Geochronology ◽  
High Field Strength ◽  
Original Source ◽  
Type Granite ◽  
Juvenile Crust ◽  
Tectonic Belt ◽  
Extensional Setting

Abstract The Kamusite pluton is located in the eastern Junggar area, the westernmost segment of the Karamaili structural belt, and is predominantly composed of medium granite and microgranite with an exposure area of 30 km2. The U–Pb zircon geochronology of the Kamusite granites indicates that they crystallized in the late Carboniferous period (328–321 Ma). These granites exhibit high contents of SiO2 (76.09–77.85 wt %) and K2O + Na2O (8.01–9.06 wt %), but low MgO (0.01–0.14 wt %), CaO (0.07–0.32 wt %) and TiO2 (0.01–0.13 wt %) contents, showing alkalic–calcic, weakly peraluminous and ferroan features. They are depleted in Ba, Sr, Ti and P and enriched in Rb and some high-field-strength elements (Hf, Nd, Ta and Y); their rare earth element patterns are slightly right-leaning with strongly negative Eu anomalies, high 10 000 * Ga/Al (3.4–5.36, >2.6) and especially high Y/Nb ratios (1.61–10.33, >1.2), showing the geochemical characteristics of A2-type granite. These granites were produced by partial melting in a high-temperature, low-pressure, reduced and anhydrous environment and experienced extensive fractional crystallization, which concomitantly resulted in tin mineralization. Combining the high positive zircon ϵHf(t) values of +10.9 to +15.76 with young Hf (TDM2) model ages (638–330 Ma), it can be suggested that underplating-related mantle-derived materials were the original source of the Kamusite A2-type granites; namely, these granites formed by the partial melting of juvenile crust. The record of large-scale magmatism indicates that the whole tectonic belt was in a postcollisional extensional setting induced by staged delamination from west to east during the late Carboniferous to early Permian periods.

Tectonic and magmatic evolution of the Aqishan-Yamansu belt: A Paleozoic arc-related basin in the Eastern Tianshan (NW China)

2020 ◽  
Author(s):  
Shuanliang Zhang ◽  
Huayong Chen ◽  
Pete Hollings ◽  
Liandang Zhao ◽  
Lin Gong
Keyword(s):  
Partial Melting ◽  
Oceanic Crust ◽  
Lower Crust ◽  
Early Carboniferous ◽  
Late Carboniferous ◽  
Igneous Rocks ◽  
Calc Alkaline ◽  
Eastern Tianshan ◽  
Depleted Mantle ◽  
T Values

The Aqishan-Yamansu belt in the Chinese Eastern Tianshan represents a Paleozoic arc-related basin generally accompanied by accretionary magmatism and Fe-Cu mineralization. To characterize the tectonic evolution of such an arc-related basin and related magmatism and metallogenesis, we present a systematic study of the geochronology, whole-rock geochemistry, and Sr-Nd isotopes of igneous rocks from the belt. New zircon U-Pb ages, in combination with published data, reveal three phases of igneous activity in the Aqishan-Yamansu belt: early Carboniferous felsic igneous rocks (ca. 350−330 Ma), late Carboniferous intermediate to felsic igneous rocks (ca. 320−305 Ma), and Permian quartz diorite and diorite porphyry dikes (ca. 280−265 Ma). The early Carboniferous felsic rocks are enriched in large ion lithophile elements (LILEs) and depleted in Nb, Ta, and Ti, showing arc-related magma affinities. Their positive εNd(t) values (3.3−5.9) and corresponding depleted mantle model ages (TDM) of 0.83−0.61 Ga, as well as high MgO contents, Mg# values, and Nb/Ta ratios, suggest that they were derived from lower crust with involvement of mantle-derived magmas. The late Carboniferous intermediate igneous rocks show calc-alkaline affinities, exhibiting LILE enrichment and high field strength element (HFSE) depletion, with negative Nb and Ta anomalies. They have high MgO contents and Mg# values with positive εNd(t) values (3.9−7.9), and high Ba/La and Th/Yb ratios, implying a depleted mantle source metasomatized by slab-derived fluids and sediment or sediment-derived melts. The late Carboniferous felsic igneous rocks are metaluminous to peraluminous with characteristics of medium-K calc-alkaline I-type granites. Given the positive εNd(t) values (6.3−6.6) and TDM ages (0.56−0.53 Ga), we suggest the late Carboniferous felsic igneous rocks were produced by partial melting of a juvenile lower crust. The Permian dikes show characteristics of adakite rocks. They have relatively high MgO contents and Mg# values, and positive εNd(t) values (7.2−8.5), which suggest an origin from partial melting of a residual basaltic oceanic crust. We propose that the Aqishan-Yamansu belt was an extensional arc−related basin from ca. 350 to 330 Ma; this was followed by a relatively stable carbonate formation stage at ca. 330−320 Ma, when the Kangguer oceanic slab subducted beneath the Central Tianshan block. As the subduction continued, the Aqishan-Yamansu basin closed due to slab breakoff and rebound during ca. 320−305 Ma, which resulted in basin inversion and the emplacement of granitoids with contemporary Fe-Cu mineralization. During the Permian, the Aqishan-Yamansu belt was in postcollision extension stage, with Permian adakitic dikes formed by partial melting of a residual oceanic crust.

scholarly journals Generation of Tonalitic and Dioritic Magmas by Coupled Partial Melting of Gabbroic and Metasedimentary Rocks within the Deep Crust of the Famatinian Magmatic Arc, Argentina

2009 ◽  
Vol 50 (5) ◽  
pp. 841-873 ◽  
Author(s):  
Juan E. Otamendi ◽  
Mihai N. Ducea ◽  
Alina M. Tibaldi ◽  
George W. Bergantz ◽  
Jesús D. de la Rosa ◽  
...  
Keyword(s):  
Partial Melting ◽  
Magmatic Arc ◽  
Metasedimentary Rocks ◽  
Deep Crust

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 ◽  
Roberto F. Weinberg ◽  
Zengqian Hou
Keyword(s):  
Lithospheric Mantle ◽  
Lower Crust ◽  
Isotopic Ratios ◽  
Crustal Growth ◽  
Deposit Formation ◽  
Southern Tibet ◽  
Porphyry Deposit ◽  
Arc Magmas ◽  
Magmatic Rocks ◽  
Three Stages

Crustal growth is commonly associated with porphyry deposit formation whether in continental arcs or collisional orogens. The Miocene high-K calc-alkaline granitoids in the Gangdese belt in southern Tibet, associated with porphyry copper deposits, are derived from the juvenile lower crust with input from lithospheric mantle trachytic magmas, and are characterized by adakitic affinity with high-Sr/Y and La/Yb ratios as well as high Mg# and more evolved isotopic ratios. Researchers have argued, lower crust with metal fertilization was mainly formed by previous subduction-related modification. The issue is that the arc is composed of three stages of magmatism including Jurassic, Cretaceous, and Paleocene−Eocene, with peaks of activity at 200 Ma, 90 Ma, and ca. 50 Ma, respectively. All three stages of arc growth are essentially similar in terms of their whole-rock geochemistry and Sr-Nd-Hf isotopic compositions, making it difficult to distinguish Miocene magma sources. This study is based on ∼430 bulk-rock Sr-Nd isotope data and ∼270 zircon Lu-Hf isotope data and >800 whole-rock geochemistry analyses in a 900-km-long section of the Gangdese belt. We found large scale variations along the length of the arc where the Nd-Hf isotopic ratios of the Jurassic, Cretaceous, and Paleocene−Eocene arc rocks change differently from east to west. A significant feature is that the spatial distribution of Nd-Hf isotopic values of the Paleocene−Eocene arc magmas and the Miocene granitoids, including metallogenic ones, are “bell-shaped” from east to west, with a peak of εNd(t) and εHf(t) at ∼91°E. In contrast, the Jurassic and Cretaceous arc magmas have different isotopic distribution patterns as a function of longitude. The isotopic spatial similarity of the Paleocene−Eocene and Miocene suites suggests that the lower crust source of the metallogenic Miocene magmas is composed dominantly of the Paleocene−Eocene arc rocks. This is further supported by abundant inherited zircons dominated by Paleocene−Eocene ages in the Miocene rocks. Another important discovery from the large data set is that the Miocene magmatic rocks have higher Mg# and more evolved Sr-Nd-Hf isotopic compositions than all preceding magmatic arcs. These characteristics indicate that the involvement of another different source was required to form the Miocene magmatic rocks. Hybridization of the isotopically unevolved primary magmas with isotopically evolved, lithospheric mantle-derived trachytic magmas is consistent with the geochemical, xenolith, and seismic evidence and is essential for the Miocene crustal growth and porphyry deposit formation. We recognize that the crustal growth in the collisional orogen is a two-step process, the first is the subduction stage dominated by typical magmatic arc processes leading to lower crust fertilization, the second is the collisional stage dominated by partial melting of a subduction-modified lower crust and mixing with a lithospheric mantle-derived melt at the source depth.

Slab break-off origin of 105 Ma A-type porphyritic granites in the Asa area of Tibet

2020 ◽  
Vol 157 (8) ◽  
pp. 1281-1298
Author(s):  
Hang Li ◽  
Ming Wang ◽  
Xiao-Wen Zeng ◽  
An-Bo Luo ◽  
Yun-Peng Yu ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Early Cretaceous ◽  
Lower Crust ◽  
Isotopic Analysis ◽  
Geochemical Analysis ◽  
Geodynamic Evolution ◽  
Southern Tibet ◽  
Magmatic Rocks ◽  
Oceanic Sediment ◽  
Slab Window

AbstractThe study of the petrogenesis of some magmatic rocks with special geochemical attributes provides effective information for us to explore the deep geodynamic background of their formation. A series of granitic porphyry dykes have been found in the mélange zone of the Asa region in southern Tibet, whose genesis may be closely related to the evolution of the Meso-Tethyan Ocean. Regional geodynamic evolution is investigated by whole-rock geochemical analysis, zircon U–Pb dating and Lu–Hf isotopic analysis of two porphyritic granites. The Asa porphyritic granites have high SiO2 (74.29–78.65 wt %) and alkalis (Na2O + K2O = 6.51–9.35 wt %) contents, and low Al2O3 (11.60–14.51 wt %), CaO (0.04–0.19 wt MgO (0.01–0.10 wt %) contents. They are enriched in Zr, Nb, Ce, Y and Hf and depleted in Ti, Ba, Sr and P, consistent with A-type granites. The samples are relatively rich in LREEs, with LREE/HREE ratios of 1.73–3.04. They display negative Eu anomalies (Eu/Eu* = 0.24–0.28) and obvious Ce anomalies in some samples. Zircon U–Pb analyses show that the porphyritic granites formed in late Early Cretaceous time, 107.4 to 105.5 Ma. Zircon εHf(t) values are in the range of 6.9 to 12.0. These data indicate that the porphyritic granites were sourced from interaction between mantle-derived and juvenile lower crust-derived melts, with the addition of oceanic sediment-derived melts. This occurred when the subducting Bangong–Nujiang oceanic crust split to create a slab window. Rising asthenosphere triggered re-melting of lower crust basalts, resulting in the formation of the late Early Cretaceous A-type granites around Asa.

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