Early Neoproterozoic magmatism in the Central Qilian block, NW China: Geochronological and petrogenetic constraints for Rodinia assembly

2020 ◽  
Vol 132 (11-12) ◽  
pp. 2415-2431 ◽  
Author(s):  
Yilong Li ◽  
Wenjiao Xiao ◽  
Zhuoyang Li ◽  
Ke Wang ◽  
Jianping Zheng ◽  
...  
Keyword(s):  
Partial Melting ◽  
South China ◽  
Tibet Plateau ◽  
Main Role ◽  
Precambrian Basement ◽  
Continental Arc ◽  
Wide Range ◽  
Back Arc ◽  
T Values ◽  
Early Neoproterozoic

Abstract The supercontinent Rodinia existed as a coherent large landmass from 900 to 750 Ma and is now dispersed over all current major continents. Controversy has long surrounded the reconstructions of the East Asian blocks in Rodinia, especially the South China craton and nearby microcontinents. The Central Qilian block is a Precambrian microcontinent in the early Paleozoic Qilian orogenic belt, which is located in the northeastern part of the Qinghai-Xizang (Tibet) Plateau and marks the junction of the North China, South China and Tarim cratons. The formation and tectonic affinity of the Precambrian basement in the Central Qilian block is unclear, which affects our understanding of the assembly of Rodinia. The Huangyuan Group and the Maxianshan Group crop out in the eastern part of the block and represent the lower part of the basement. In this paper, we present a systematic study of the petrology, whole-rock geochemistry, and geochronology of amphibolites and orthogneisses from the Huangyuan and Maxianshan Groups. The protolith of the amphibolites was tholeiitic and calc-alkaline gabbro or gabbroic diorite formed in a continental arc environment, with laser ablation–inductively coupled plasma mass spectrometry (LA-ICPMS) zircon U-Pb ages of 967–957 Ma, a wide range of εHf(t) values of –3.74 to +5.06 and TDM1 model ages peaking at 1470 Ma and 1607 Ma. Minor inherited zircon grains with older ages of 1207–1515 Ma were collected from the amphibolites. The primitive magma was derived from partial melting of a spinel-facies fertile (lherzolite) lithospheric mantle that was modified by fluids and melts from a subducted slab. Fractionation of olivine, Fe-Ti oxides and plagioclase played a dominant role in the magma differentiation for gabbroic rocks in the Huangyuan Group, while fractionation of olivine and clinopyroxene controlled differentiation to form Maxianshan Group gabbros. The protolith of orthogneisses includes weakly peraluminous I-type and A2-type granites with consistent LA-ICPMS zircon U-Pb ages of 963–936 Ma, a wide range of εHf(t) values of –3.86 to +6.15 and TDM2 model age peaks at 2001 Ma and 1772 Ma. A few inherited zircon grains yield ages of 1033–2558 Ma. The peraluminous I-type granites resulted from a low-pressure partial melting process and the peraluminous A-type granites were derived from a charnockite source heated by large-scale magmatic underplating. Fractionation of plagioclase, biotite, and K-feldspar from the magma played the main role during the generation of the granitoids. The intrusion of these granites is related to a back-arc extension. It is inferred that the lower part of Precambrian basement of the Central Qilian block is composed mainly of early Neoproterozoic rock assemblages formed in a trench-arc-basin system during the assembly of the Rodinia supercontinent, with probable existence of late Paleoproterozoic to Mesoproterozoic continental nuclei. Combining our results with existing data, we identify a sequence of initial intra-oceanic subduction (ca. 1121–967 Ma) in front of a continental nucleus, continuous subduction of oceanic crust beneath the continental mass with formation of a mature continental arc and a back-arc basin (ca. 967–896 Ma) and continental rifting (<ca. 882 Ma) during the formation of the Central Qilian block. As a mature continental arc after ca. 967 Ma, the Central Qilian block was located at the margin of Rodinia and faced the Neoproterozoic Mirovoi Ocean. The breakup of the supercontinent left the Central Qilian block as a late Neoproterozoic isolated arc terrane.

Subduction-related magmatic imprint of most Philippine ophiolites: implications on the early geodynamic evolution of the Philippine archipelago

2004 ◽  
Vol 175 (5) ◽  
pp. 443-460 ◽  
Author(s):  
Rodolfo A. Tamayo* ◽  
René C. Maury* ◽  
Graciano P. Yumul ◽  
Mireille Polvé ◽  
Joseph Cotten ◽  
...  
Keyword(s):  
Partial Melting ◽  
Subduction Zone ◽  
Volcanic Rocks ◽  
The Philippines ◽  
Island Arc ◽  
Island Arcs ◽  
Geodynamic Evolution ◽  
Wide Range ◽  
Opening And Closing ◽  
Back Arc

Abstract The basement complexes of the Philippine archipelago include at least 20 ophiolites and ophiolitic complexes. These complexes are characterised by volcanic sequences displaying geochemical compositions similar to those observed in MORB, transitional MORB-island arc tholeiites and arc volcanic rocks originating from modern Pacific-type oceans, back-arc basins and island arcs. Ocean island basalt-like rocks are rarely encountered in the volcanic sequences. The gabbros from the ophiolites contain clinopyroxenes and plagioclases showing a wide range of XMg and An values, respectively. Some of these gabbros exhibit mineral chemistries suggesting their derivation from basaltic liquids formed from mantle sources that underwent either high degrees of partial melting or several partial melting episodes. Moreover, some of the gabbros display a crystallization sequence where orthopyroxene and clinopyroxene appeared before plagioclase. The major element compositions of coexisting orthopyroxenes and olivines from the mantle peridotites are consistent with low to high degrees of partial melting. Accessory spinels in these peridotites display a wide range of XCr values as well with some of them above the empirical upper limit of 0.6 often observed in most modern mid-oceanic ridge (MOR) mantle rocks. Co-existing olivines and spinels from the peridotites also exhibit compositions suggesting that they lastly equilibrated under oxidizing mantle conditions. The juxtaposition of volcanic rocks showing affinities with modern MOR and island arc environments suggests that most of the volcanic sequences in Philippine ophiolites formed in subduction-related geodynamic settings. Similarly, their associated gabbros and peridotites display mineralogical characteristics and mineral chemistries consistent with their derivation from modern supra-subduction zone-like environments. Alternatively, these rocks could have, in part, evolved in a supra-subduction zone even though they originated from a MOR-like setting. A simplified scenario regarding the early geodynamic evolution of the Philippines is proposed on the basis of the geochemical signatures of the ophiolites, their ages of formation and the ages and origins of the oceanic basins actually bounding the archipelago, including basins presumed to be now totally consumed. This scenario envisages the early development of the archipelago to be largely dominated by the opening and closing of oceanic basins. Fragments of these basins provided the substratum on top of which the Cretaceous to Recent volcanic arcs of the Philippines were emplaced.

Neoproterozoic Amdo and Jiayuqiao microblocks in the Tibetan Plateau: Implications for Rodinia reconstruction

2020 ◽  
Author(s):  
Yiming Liu ◽  
Yuhua Wang ◽  
Sanzhong Li ◽  
M. Santosh ◽  
Runhua Guo ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
South China ◽  
Tectonic Setting ◽  
Parental Magma ◽  
Tibet Plateau ◽  
Geochemical Data ◽  
The Tibetan Plateau ◽  
South China Craton ◽  
Neoproterozoic Magmatism ◽  
T Values

The Tibetan Plateau is composed of several microblocks, the tectonic affinity and paleogeographic correlations of which remain enigmatic. We investigated the Amdo and Jiayuqiao microblocks in central Tibet Plateau with a view to understand their tectonic setting and paleogeographic position within the Neoproterozoic supercontinent Rodinia. We present zircon U-Pb and Lu-Hf isotope, and whole-rock geochemical data on Neoproterozoic granitic gneisses from these microblocks. Zircon grains from the Jiayuqiao granitic gneiss yielded an age of 857 ± 9 Ma with variable εHf(t) values (−8.9 to 4.0). The Amdo granitic gneisses yielded ages of 893 ± 5 Ma, 807 ± 5 Ma, and 767 ± 11 Ma, with εHf(t) values in the range of −4.9 to 3.5. Geochemically, the granitoids belong to high-K calc-alkaline series, with the protolith derived from partial melting of ancient crustal components. The ascending parental magma of the Amdo granitoids experienced significant mantle contamination as compared to the less contaminated magmas that generated the Jiayuqiao intrusions. In contrast to the Lhasa, Himalaya, South China, and Tarim blocks, we suggest that the Amdo and Jiayuqiao microblocks probably formed a unified block during the Neoproterozoic and were located adjacent to the southwestern part of South China craton. The Neoproterozoic magmatism was probably associated with the subduction of the peripheral ocean under the South China craton and the delamination of lithospheric mantle beneath the Jiangnan orogen.

scholarly journals Final-Stage Magmatic Record of Paleo-Asian Oceanic Subduction? Insights from Late Permian to Early Triassic Intrusive Rocks in the Yanbian Area, Easternmost Central Asian Orogenic Belt

Minerals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 799
Author(s):  
Chao Zhang ◽  
Franz Neubauer ◽  
Zheng-Hong Liu ◽  
Fang-Hua Cui ◽  
Qing-Bin Guan
Keyword(s):  
Partial Melting ◽  
Granitic Rocks ◽  
Early Triassic ◽  
Crustal Material ◽  
Late Permian ◽  
The North ◽  
Wide Range ◽  
Intrusive Rocks ◽  
Subduction Setting ◽  
T Values

This paper reports new zircon LA–ICP–MS U–Pb and Hf isotope data, and whole-rock major and trace element data for Late Permian to Early Triassic intrusive rocks in the Yanbian area, NE China. These data provide new insights into the timing of the final subduction of the Paleo-Asian Ocean beneath the North China Craton. The zircon U–Pb age data indicate that a suite of Late Permian to Early Triassic intrusive rocks related to subduction is present within the Yanbian area. The Late Permian intrusive rocks consist of diorites while the Early Triassic granites and hornblende gabbros constitute a geochemically bimodal igneous rock association. Furthermore, the Early Triassic granites show the geochemical characteristics of shoshonitic rocks. All the rocks are characterized by enrichment in LILEs and LREEs, and depletion in HREEs and HFSEs, suggesting they formed in a subduction setting. Zircons from the Early Triassic gabbros have εHf(t) values and TDM2 ages of +7.6 to +10.7 and 735–1022 Ma, respectively, suggesting that they formed from a primary magma generated by the partial melting of lithospheric mantle material that had been previously modified by subduction-related fluids. The Late Permian diorites have εHf(t) values and TDM2 ages of +0.5 to +9.5 and 853 to 1669 Ma, respectively, while they have high contents of Al2O3, Fe2O3, and low contents of SiO2, Cr, and Ni, indicating Late Permian diorites should derive from the mantle and are influenced by some crustal material. Early Triassic granitic rocks have a wide range of εHf(t) values and TDM2 ages of −4.8 to +9.4 and 852 to 2136 Ma, respectively. Their zircons imply that the Early Triassic granites could be mainly derived from partial melting of the crust, with minor contribution of the crustal material of an ancient crust. The Early Triassic bimodal intrusive rocks in Yanbian area, combined with the regional geologic information; therefore, record a final post-subduction extensional environment due to the break-off of the previously subducted slab.

Early Devonian (415–400 Ma) A-type granitoids and diabases in the Wuyishan, eastern Cathaysia: A signal of crustal extension coeval with the separation of South China from Gondwana

2020 ◽  
Vol 132 (11-12) ◽  
pp. 2295-2317 ◽  
Author(s):  
Yujia Xin ◽  
Jianhua Li ◽  
Lothar Ratschbacher ◽  
Guochun Zhao ◽  
Yueqiao Zhang ◽  
...  
Keyword(s):  
Partial Melting ◽  
South China ◽  
Crustal Extension ◽  
Eastern Asia ◽  
The South ◽  
Early Devonian ◽  
Enriched Mantle ◽  
Key Issues ◽  
Tethys Ocean ◽  
T Values

Abstract The evolution of the South China continental crust and its linkage to the assembly and rifting of eastern Gondwana are key issues in the understanding of the early Paleozoic evolution of eastern Asia. We report U-Pb zircon ages and geochemical and Lu-Hf isotopic data for the South Fufang and Yingshang granitoids and the Mayuan diabases from the Wuyishan of eastern South China. The zircons yielded U-Pb ages of ca. 414–404 and ca. 409–401 Ma for the granitoids and diabases, respectively. Petrographic and geochemical features indicate that the granitoids are peraluminous A-type granites, expressed by high Ga/Al ratios and high Zr, Nb, Ce, Y, and rare earth element contents. They show negative zircon εHf(t) values (–15.4 to –5.8), consistent with the derivation from a crustal source. The granitoids likely originated from partial melting of dry granulite residues in the lower crust. The diabases show depletion in Ti, and negative correlations between FeOt and Mg#, and SiO2 and TiO2/FeOt, reflecting clinopyroxene, olivine, and Fe-Ti oxide fractionation. Their negative zircon εHf(t) values (–4.5 to –0.4) indicate an ancient enriched-mantle origin. The diabases likely originated from partial melting of a sub-continental lithospheric mantle. We interpret these A-type granitoids and diabases as post-orogenic, formed during extensional collapse of thickened crust. Their generation indicates that South China experienced crustal extension during the Early Devonian. The extension occurred coevally with global rifting that led to the separation of the continental blocks of eastern Asia from eastern Gondwana, which was associated with the Early Devonian opening of the paleo–Tethys Ocean.

Early Neoproterozoic (∼850Ma) back-arc basin in the Central Jiangnan Orogen (Eastern South China): Geochronological and petrogenetic constraints from meta-basalts

2013 ◽  
Vol 231 ◽  
pp. 325-342 ◽  
Author(s):  
Yuzhi Zhang ◽  
Yuejun Wang ◽  
Hongyan Geng ◽  
Yanhua Zhang ◽  
Weiming Fan ◽  
...  
Keyword(s):  
South China ◽  
Back Arc ◽  
Early Neoproterozoic

scholarly journals Petrogenesis of Dacites in a Triassic Volcanic Arc in the South China Sea: Constraints From Whole Rock and Mineral Geochemistry

2022 ◽  
Vol 9 ◽  
Author(s):  
Wu Wei ◽  
Chuan-Zhou Liu ◽  
Ross N. Mitchell ◽  
Wen Yan
Keyword(s):  
Rare Earth ◽  
South China Sea ◽  
Rare Earth Elements ◽  
Partial Melting ◽  
South China ◽  
Volcanic Rocks ◽  
The South China Sea ◽  
South China Block ◽  
The South ◽  
T Values

Triassic volcanic rocks, including basalts and dacites, were drilled from Meiji Atoll in the South China Sea (SCS), which represents a rifted slice from the active continental margin along the Cathaysia Block. In this study, we present apatite and whole rock geochemistry of Meiji dacites to decipher their petrogenesis. Apatite geochronology yielded U-Pb ages of 204–221 Ma, which are identical to zircon U-Pb ages within uncertainty and thus corroborate the formation of the Meiji volcanic rocks during the Late Triassic. Whole rock major elements suggest that Meiji dacites mainly belong to the high-K calc-alkaline series. They display enriched patterns in light rare earth elements (LREE) and flat patterns in heavy rare earth elements (HREE). They show enrichment in large-ion lithophile elements (LILE) and negative anomalies in Eu, Sr, P, Nb, Ta, and Ti. The dacites have initial 87Sr/86Sr ratios of 0.7094–0.7113, εNd(t) values of -5.9–-5.4 and εHf(t) values of -2.9–-1.7, whereas the apatite has relatively higher initial 87Sr/86Sr ratios (0.71289–0.71968) and similar εNd(t) (-8.13–-4.56) values. The dacites have homogeneous Pb isotopes, with initial 206Pb/204Pb of 18.73–18.87, 207Pb/204Pb of 15.75–15.80, and 208Pb/204Pb of 38.97–39.17. Modeling results suggest that Meiji dacites can be generated by <40% partial melting of amphibolites containing ∼10% garnet. Therefore, we propose that the Meiji dacites were produced by partial melting of the lower continental crust beneath the South China block, triggered by the underplating of mafic magmas as a response to Paleo-Pacific (Panthalassa) subduction during the Triassic. Meiji Atoll, together with other microblocks in the SCS, were rifted from the South China block and drifted southward due to continental extension and the opening of the SCS.

Late Paleozoic- Early Mesozoic tectonics of Hainan Island: Key to understanding Paleotethyan geology

2020 ◽  
Author(s):  
Huiying He ◽  
Peter Cawood ◽  
Yuejun Wang
Keyword(s):  
South China ◽  
Tectonic Evolution ◽  
Hainan Island ◽  
Igneous Rocks ◽  
Late Paleozoic ◽  
Calc Alkaline ◽  
Early Mesozoic ◽  
History Of ◽  
Back Arc ◽  
T Values

<p>In Southeast Asia, establishing the origin and associated tectonic setting of Late Paleozoic-Early Mesozoic igneous rocks is complicated by structural overprinting and the complex tectonic evolution of the Paleotethyan regime. Hainan Island, located at the south-eastern margin of the Paleotethys, and lacking significant tectonic overprints is a key to understand amalgamation history of the Indochina and South China blocks and to constraining the tectonic evolution of Paleotethys ocean in southeast Asia.</p><p>The Late Paleozoic-Early Mesozoic record of igneous rocks on Hainan Island includes the following. 1) ca. 350 Ma island arc andesites and ca. 330 Ma metabasites, the latter with both MORB- and arc-like geochemical affinities, positive ε<sub>Nd</sub>(t) values of +5.86 – +9.85 and rare inherited zircons with a zircon age of 1400 Ma inferred to be derived from a MORB source with the input of a slab-derived component. Together with the ~350 Ma island arc andesites, the Carboniferous tectonic environment is supposed to be a continental back-arc basin setting. 2) Late Permian gneiss granitoids (272-252 Ma) characterized by a gneissic foliation and calc-alkaline I-type geochemical affinities with negative Nb-Ta and Ti anomalies, related to metasomatized mantle wedge modified by the sediment-derived component in a continental arc setting. 3) ca. 257 Ma arc-like andesites, which further validate a subduction-related setting. 4) Peraluminious Early-Middle Triassic massive granitoids (251–243 Ma) with slightly high A/CNK ratios, δ<sup>18</sup>O values (up to 11.75 ‰) and Sr/Y ratios, inferred to have formed in a compressive regime from a mixed source of greywacke and metabasite. 5) Middle-Late Triassic (242–225 Ma) high-K calc-alkaline granitoids with high zircon temperatures (842–867°C) and geochemical signatures of A-type granites. They show slightly low whole-rock ε<sub>Nd</sub>(t) and zircon ε<sub>Hf</sub>(t) values, suggestive of the derivation from a metabasite–greywacke source in an extensional setting. 6) ca. 240 Ma gabbro-dolerites showing enrichment in LILEs, depletion in HFSEs, negative ε<sub>Nd</sub> (t)-ε<sub>Hf</sub> (t) values (−8.45 to −1.05 and −5.9 to −2.7, respectively) and crustal-like δ<sup>18</sup>O values (7.26–8.70‰), it is implied that the Hainan Island entered into post-collisional environment in response to the asthenosphere upwelling shortly after the closure of back-arc basin.</p><p>Thus, Hainan Island provides a record of Carboniferous back-arc basin opening, followed by an extended Permian–Triassic history of subduction-related consumption leading to orogenic assembly and extensional collapse between the South China and Indochina blocks. Such a tempo-spatial pattern is consistent with that along the Song Ma–Ailaoshan suture zone rather than the magmatic history of eastern South China and indicates that the Paleotethys extended west to at least Hainan Island in the Late Paleozoic-Early Mesozoic.</p>

Petrogenesis of the Early Palaeozoic granitoids from the Yunkai massif, South China block: implications for a tectonic transition from compression to extension during the Caledonian orogenic event

2017 ◽  
Vol 155 (8) ◽  
pp. 1776-1792 ◽  
Author(s):  
XIAO-FEI QIU ◽  
XIAO-MING ZHAO ◽  
HONG-MEI YANG ◽  
SHAN-SONG LU ◽  
TUO JIANG ◽  
...  
Keyword(s):  
Partial Melting ◽  
South China ◽  
Alkaline Rock ◽  
South China Block ◽  
Rock Series ◽  
Calc Alkaline ◽  
Tectonic Regime ◽  
Type Granite ◽  
Early Palaeozoic ◽  
T Values

AbstractA comprehensive geochronological and geochemical study was carried out on the gneissic monzogranites, porphyritic granodiorites and charnockites in the Gaozhou complex of the Yunkai massif in the southern part of the South China block to better understand the Early Palaeozoic tectonic regime of the South China block. Laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) U–Pb dating of zircons indicates an age of 453.2 ± 5.1 Ma to the formation of the gneissic monzogranites, whereas the porphyritic granodiorites and charnockites were generated at 437.0 ± 1.5 Ma and 435.2 ± 2.2 Ma, respectively. The gneissic monzogranites show geochemical features consistent with the high-K, calc-alkaline rock series and are strongly peraluminous. They have SiO2contents ranging from 67.75 to 69.65 wt. % and relatively low CaO contents (1.66–1.94 wt. %). Their REE patterns are fractionated with enriched LREEs and negative Eu anomalies. The samples also show enrichment in LILEs (e.g. Rb and K) and Pb, and depletion in Sr, Ba and HFSEs (e.g. Nb, Ta, Ti and P). They haveεNd(t) values of −8.2 to −7.7. Conversely, the porphyritic granodiorites and charnockites are characterized as medium-K, calc-alkaline rock series and weakly to strongly peraluminous. They exhibit pronounced depletions in HFSEs and positive Pb anomalies. Compared to the earlier gneissic monzogranites, these rocks have relatively lower SiO2(65.50–69.36 wt. %), but higher CaO contents (3.34–4.05 wt. %), and have slightly lowerεNd(t) values (−9.1 to −8.4). Petrography and geochemical compositions of the gneissic monzogranites indicate that they are S-type granite and likely formed by partial melting of Neoproterozoic to Early Palaeozoic immature metagreywackes; whereas The porphyritic granodiorites and charnockites are A-type granite and likely derived from low degrees of partial melting of the dry, granulitic residue depleted by prior extraction of granitic melt. The new data for the Caledonian granitoids in the Yunkai massif suggest that they were formed in a post-collisional tectonic setting. They represent the earliest post-collisional alkaline magmatism reported so far in the Yunkai massif, and thus indicate a tectonic regime switch, from compression to extension, as early as the Late Ordovician to Early Silurian (~450–435 Ma).

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