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.

scholarly journals Permian felsic volcanic rocks in the Pannonian Basin (Hungary): new petrographic, geochemical, and geochronological results

2019 ◽  
Vol 109 (1) ◽  
pp. 101-125 ◽  
Author(s):  
Máté Szemerédi ◽  
Réka Lukács ◽  
Andrea Varga ◽  
István Dunkl ◽  
Sándor Józsa ◽  
...  
Keyword(s):  
Pannonian Basin ◽  
Volcanic Rocks ◽  
Western Carpathians ◽  
Geochemical Data ◽  
Significant Similarity ◽  
Magmatic Rocks ◽  
Close Relationship ◽  
Felsic Volcanic ◽  
Felsic Volcanic Rocks ◽  
Extensional Setting

AbstractTwo distinct Permian volcanic epochs were revealed in the Pannonian Basin (eastern Central Europe) by U–Pb zircon geochronology: an older one (~ 281 Ma, Cisuralian) in the ALCAPA Mega-unit (Central Transdanubia, Hungary) and a younger volcanic episode (~ 267–260 Ma, Guadalupian) in the Tisza Mega-unit (Southern Transdanubia and the eastern Pannonian Basin, Hungary). The former is represented by dacitic subvolcanic rocks (dykes) and lavas, while the latter is dominantly by crystal-rich rhyolitic–rhyodacitic/dacitic ignimbrites and subordinate rhyodacitic/dacitic lavas. Whole-rock (major and trace element) geochemical data and zircon U–Pb ages suggest close relationship between the samples of Central Transdanubia and volcanic rocks of the Northern Veporic Unit (Western Carpathians, Slovakia), both being part of the ALCAPA Mega-unit. Such correlation was also revealed between the Permian felsic volcanic rocks of the Apuseni Mts (Romania) and the observed samples of Southern Transdanubia and the eastern Pannonian Basin that are parts of the Tisza Mega-unit. The older volcanic rocks (~ 281–265 Ma) could be linked to post-orogenic tectonic movements, however, the youngest samples (~ 260 Ma, eastern Pannonian Basin, Tisza Mega-unit) could be formed in the extensional setting succeeding the post-collisional environment. On the whole, the observed Permian magmatic rocks show significant similarity with those of the Western Carpathians.

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.

Chapter 4 Paleoproterozoic (2.0–1.8 Ga) syn-orogenic sedimentation, magmatism and mineralization in the Bothnia–Skellefteå lithotectonic unit, Svecokarelian orogen

2020 ◽  
Vol 50 (1) ◽  
pp. 83-130 ◽  
Author(s):  
Pietari Skyttä ◽  
Pär Weihed ◽  
Karin Högdahl ◽  
Stefan Bergman ◽  
Michael B. Stephens
Keyword(s):  
Volcanic Rocks ◽  
Shear Zones ◽  
Low Grade ◽  
Lower Grade ◽  
Magmatic Arc ◽  
The North ◽  
Magmatic Rocks ◽  
Structural Style ◽  
Volcanogenic Massive Sulphide ◽  
Felsic Volcanic

AbstractThe Bothnia–Skellefteå lithotectonic unit is dominated by turbiditic wacke and argillite (Bothnian basin), deposited at 1.96 (or older)–1.86 Ga, metamorphosed generally under high-grade conditions and intruded by successive plutonic suites at 1.95–1.93, 1.90–1.88, 1.87–1.85 and 1.81–1.76 Ga. In the northern part, low-grade and low-strain, 1.90–1.86 Ga predominantly magmatic rocks (the Skellefte–Arvidsjaur magmatic province) are enclosed by the basinal components. Subduction-related processes in intra-arc basin and magmatic arc settings, respectively, are inferred. Changes in the metamorphic grade and the relative timing of deformation and structural style across the magmatic province are linked to major shear zones trending roughly north–south and, close to the southern margin, WNW–ESE. Zones trending WNW–ESE and ENE–WSW dominate southwards. Slip along the north–south zones in an extensional setting initiated synchronously with magmatic activity at 1.90–1.88 Ga. Tectonic inversion steered by accretion to a craton to the east, involving crustal shortening, ductile strain and crustal melting, occurred at 1.88–1.85 Ga. Deformation along shear zones under lower-grade conditions continued at c. 1.8 Ga. Felsic volcanic rocks (1.90–1.88 Ga) host exhalative and replacement-type volcanogenic massive sulphide deposits (the metallogenic Skellefte district). Other deposits include orogenic Au, particularly along the ‘gold line’ SW of this district, porphyry Cu–Au–Mo, and magmatic Ni–Cu along the ‘nickel line’ SE of the ‘gold line’.

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.

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.

History of subduction erosion and accretion recorded in the Yarlung Suture Zone, southern Tibet

2019 ◽  
Vol 483 (1) ◽  
pp. 517-554 ◽  
Author(s):  
Kathryn Metcalf ◽  
Paul Kapp
Keyword(s):  
Volcanic Rocks ◽  
Suture Zone ◽  
Geological Mapping ◽  
Published Data ◽  
Southern Tibet ◽  
Slab Rollback ◽  
History Of ◽  
Subduction Erosion ◽  
Felsic Volcanic ◽  
Almost All

AbstractThe history of pre-Cretaceous subduction accretion and erosion along the Yarlung Suture Zone remains poorly constrained. We present new geological mapping along c. 200 km of the suture zone, 4881 detrital zircon U–Pb ages, and sandstone petrography for the subduction complex and Tethyan Himalayan strata. We provide the first documentation of the c. 158 Ma marine Xiazha Formation, which contains volcanic clasts of intermediate to felsic volcanic rocks and ooids with both calcareous and volcanic cores. Based on our new data and synthesis of published data, we present a model in which the Zedong arc represents the southwards migration of the Gangdese arc onto a forearc ophiolite that was generated proximal to the southern Asian margin during Neotethyan slab rollback at 160–150 Ma. This contrasts with previous suggestions that the Zedong arc, Yarlung ophiolites and subduction complex rocks developed above an intra-oceanic subduction zone thousands of kilometres south of Asia. Although Gangdese arc magmatism began in the Middle Triassic, the only forearc units preserved are 160 Ma until collision between the Xigaze forearc basin and Tethyan Himalaya at c. 59 Ma. This suggests that almost all pre-Cretaceous forearc assemblages have been removed by subduction erosion at the trench.

scholarly journals Geochemistry and Petrography of the Sediments From the Marginal Areas of Qinghai Lake, Northern Tibet Plateau, China: Implications for Weathering and Provenance

2021 ◽  
Vol 9 ◽  
Author(s):  
Huifei Tao ◽  
Lewei Hao ◽  
Shutong Li ◽  
Tao Wu ◽  
Zhen Qin ◽  
...  
Keyword(s):  
Chemical Weathering ◽  
Volcanic Rocks ◽  
Source Rocks ◽  
Coarse Grained ◽  
Tibet Plateau ◽  
Qinghai Lake ◽  
Chemical Compositions ◽  
Geochemical Composition ◽  
Clastic Rocks ◽  
Felsic Volcanic

The provenance study of the sediments from Qinghai Lake is of great significance for the understanding of geological and climatic evolution processes of the Tibet Plateau on the one hand and for evaluating the controlling factors of the sediment components on the other hand. The samples were collected from five rivers, foreshore, beach, beach bar, and aeolian sand dune in the Qinghai Lake. The bulk geochemical composition, petrography, and mineralogy features of the samples are analyzed. The results show that: 1) Qinghai Lake sediments experienced low-intensity chemical weathering from the source areas to the deposition sites and were affected by some recycled detrital materials and 2) the source rocks for the sediments include felsic rocks (granite, granodiorite, and felsic volcanic rocks), carbonate, metamorphic rocks (marble and meta-volcanic rocks), and clastic rocks with the felsic source rocks to have the most important impact on the chemical compositions of the sediments. The geochemical indicator of Al2O3/TiO2 reflects that the provenance of fine-grained sediments from the center of Qinghai Lake is more mafic than the coarse-grained sediments from the margin of the Qinghai Lake, suggesting that the hydraulic sorting of grain size probably plays an important role in the geochemical compositions of the sediments. The mafic elements were probably preferentially enriched in muds.

scholarly journals Generation of late Mesozoic felsic volcanic rocks in the Hailar Basin, northeastern China in response to overprinting of multiple tectonic regimes

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Zheng Ji ◽  
Qi-An Meng ◽  
Chuan-Biao Wan ◽  
De-Feng Zhu ◽  
Wen-Chun Ge ◽  
...  
Keyword(s):  
Partial Melting ◽  
Early Cretaceous ◽  
Lower Crust ◽  
Late Jurassic ◽  
Volcanic Rocks ◽  
Late Mesozoic ◽  
Hailar Basin ◽  
Felsic Volcanic ◽  
Felsic Volcanic Rocks ◽  
Zircon Saturation

Abstract We performed zircon U–Pb age dating and geochemical analyses of late Mesozoic felsic volcanic rocks in the Hailar Basin, NE China, with the aim of eclucidating their emplacement ages, origin and geodynamic significance. The volcanic rocks consist of dacites, rhyolites and rhyolitic tuffs. Laser ablation–inductively coupled plasma–mass spectrometry zircon U–Pb dating results suggest that the rocks were erupted during the Late Jurassic–Early Cretaceous (161–117 Ma). They belong to the high-K calc-alkaline series and can be divided into two groups. Group I rocks are metaluminous to weakly peraluminous, contain low concentrations of heavy rare earth elements (HREEs) and high field strength elements (HFSEs), and have low zircon saturation temperatures (average 786 °C), all of which indicate an I-type affinity. In contrast, Group II rocks have higher HREE and HFSE concentrations and zircon saturation temperatures (average 918 °C), suggesting an A-type affinity. All the felsic volcanic rocks have positive εHf(t) values of 1.43–12.32 with two-stage model ages of 1110–401 Ma. Our data indicate that the I-type felsic volcanic rocks formed from magmas generated by partial melting of a dominantly juvenile mica-bearing K-rich basaltic lower crust, whereas the A-type felsic volcanic rocks originated from the partial melting of a dry mafic–intermediate middle–lower crust that was dehydrated but not melt depleted. Based on the present results and previous research, we propose that the Late Jurassic I- and A-type felsic volcanic rocks in the Hailar Basin were formed in a post-collisional environment related to break-off of the subducted oceanic slab of the Mongol–Okhotsk Ocean and the subsequent gravitational collapse of the orogenically-thickened crust after closure of the ocean. In contrast, the Early Cretaceous I- and A-type felsic volcanic rocks were erupted in an extensional setting related to rollback of the subducted Paleo-Pacific Plate.

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