Origin of the Alxa Block, western China: New evidence from zircon U–Pb geochronology and Hf isotopes of the Longshoushan Complex

Gong, Jing‐Xu; Zhang, Jianxin; Wang, Zongqi; Yu, Shengyao; Li, Huaikun; Li, Yunshuai

doi:10.1016/j.gr.2015.06.014

Cited by 86 publications

(64 citation statements)

References 103 publications

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“…Zircons with ages ranging from 775 to 520 Ma are consistent with the timing of the opening and spreading of the Qilian Ocean, which (Gong et al, 2015;Xiao et al, 2015). (b) A compilation of detrital zircon ages of basement rocks in the Qilian region (Gehrels et al, 2003;Li et al, 2007;Tung et al, 2007).…”

Section: Provenance Of the Detrital Zirconssupporting

confidence: 58%

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Detrital zircon record of rivers' sediments in the North Qilian Orogenic Belt: Implications of the tectonic evolution of the northeastern Tibetan Plateau

Kang

Chen

et al. 2018

Geological Journal

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The North Qilian Orogenic Belt (NQOB) is an important element of the northern edge of the Tibetan Plateau, and several rivers run along it. Zircon U–Pb dating, trace elements, and Hf isotopic data derived from the sediments carried by the rivers have been used to deduce the crustal evolution of the NQOB. U–Pb ages obtained from detrital zircons found in the sediments of the Zamu, Zhuanglan, and Beida rivers can be divided into five major age groups, that is, 2,600–1,500, 1,500–1,100, 1,100–650, 550–400, and 360–150 Ma, and the corresponding peaks occur at ~2,450, ~1,750, ~950, ~450, and ~250 Ma. Archean components, which may be derived from the ancient continental nucleus in the region, are rare in the river sediments. The zircon grains with ages of 360–150 Ma are most likely related to crustal thickening and decompression melting in a post‐collisional tectonic setting. The age distribution patterns indicate that the sediments carried by the Zamu, Zhuanglang, and Beida rivers are derived from the NQOB. Furthermore, the Hf isotopic compositions of Meso‐ and Neoarchean, Mesoproterozoic, Grenvillian, Pan‐African, Caledonian, and Hercynian zircon age groups exhibit a wide range of εHf (t) values, suggesting diverse sources. The existence of strongly negative εHf (t) values among the Grenvillian and Paleoproterozoic zircons indicates that the source magma included reworked Palaeoarchean crustal materials. New results indicate that continental rifting and the opening of the Qilian Ocean occurred at 775–520 Ma; the subduction and closure of the Qilian Ocean occurred at 520–440 Ma; arc–continent collision and continental subduction occurred at 440–420 Ma; and orogen collapse and extension occurred at 400–360 Ma. Our study indicates that the formation of the NQOB was mainly related to the evolutionary history of the Proto‐Tethys Ocean.

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Section: Provenance Of the Detrital Zirconssupporting

confidence: 58%

“…Relative probability density diagrams of U–Pb ages. (a) A compilation of basement ages for the Alxa Block (Gong et al, ; Xiao et al, ). (b) A compilation of detrital zircon ages of basement rocks in the Qilian region (Gehrels et al, ; Li et al, ; Tung et al, ).…”

Section: Discussionmentioning

confidence: 99%

Detrital zircon record of rivers' sediments in the North Qilian Orogenic Belt: Implications of the tectonic evolution of the northeastern Tibetan Plateau

Kang

Chen

et al. 2018

Geological Journal

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“…Plots of zircon ε Hf ( t ) versus 206 Pb/ 238 U age for the samples in this study. The ε Hf ( t ) values for early Permian plutons from the Nuru–Langshan Tectonic Zone are cited from Dan, Li, Wang, Tang, et al (); Liu et al (); and Zhang et al (); the ε Hf ( t ) values for Precambrian basement rocks are cited from Gong et al (); Zhang et al (); and Dan, Li, Wang, Wang, and Liu () [Colour figure can be viewed at wileyonlinelibrary.com]…”

Section: Resultsmentioning

confidence: 99%

LateCarboniferous–earlyPermian arc magmatism in the south‐westernAlxaTectonicBelt (NW China):Constraints on the latePalaeozoic subduction history of thePalaeo‐AsianOcean

et al. 2018

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The tectonic setting of the Alxa Tectonic Belt (ATB) during the late Palaeozoic is highly controversial. The nature and tectonic origin of the late Palaeozoic magmatism in the ATB are key to resolving the current controversy. This paper provides field, petrographic, geochemical, and zircon U‐Pb‐Hf isotopic data for the late Palaeozoic granitoids and volcanic rocks from the south‐western ATB. The granitoids display a wide range of SiO2 contents from diorite, granodiorite, to granites, with widely distributed hydrous minerals such as hornblende and biotite. They are calc‐alkaline to high‐potassium calc‐alkaline, metaluminous with an enrichment of light rare earth elements and large‐ion lithophile elements (LILE), and a depletion of high‐field‐strength elements (HFSE). The presence of mafic‐intermediate enclaves in the plutons suggests the role of crust–mantle interaction in generating the granitoids. The volcanic rocks show “block‐in‐matrix” structures in the field. They are dacite‐porphyry and rhyolite and show calc‐alkaline characteristics with an enrichment of LILE and a depletion of HFSE. Laser ablation inductively coupled plasma mass spectrometry zircon U‐Pb dating shows that the granitoids and enclaves crystallized during ~317–287 Ma and the dacite porphyry formed at ~295 Ma. Hf‐in‐zircon isotopic compositions reveal predominately positive εHf (t) values and Neoproterozoic TDMC ages for the magmatic rocks, indicating mixing between mantle‐derived magma and Precambrian basement during their genesis. The diagnostic field, geochemical data, and isotopic data imply these rocks were generated in a subduction‐related active continental margin setting. The presence of A2‐type granite indicates an extensional environment resulted from slab rollback in a retreating accretionary context can best interpret the large‐scale late Carboniferous–early Permian magmatism in the ATB. Our new data, combined with published data, imply that a large active continental margin existed in the Beishan, Alxa, and the northern margin of the North China Craton, due to the south‐dipping subduction of the Palaeo‐Asian Ocean (PAO) in the late Palaeozoic. Therefore, our data suggest that the PAO did not close until after the early Permian.

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“…The ages of magmatic activities are from the Paleoproterozoic to Neopaleozoic and are concentrated in the Paleoproterozoic and the Paleozoic [19,20,26,27,[33][34][35][36]. The remarkable Jinchuan ore-bearing mafic to ultrabasic rocks formed at 800~850 Ma [37][38][39].…”

Section: Geological Settingmentioning

confidence: 99%

Paleoproterozoic Multiple Tectonothermal Events in the Longshoushan Area, Western North China Craton and Their Geological Implication: Evidence from Geochemistry, Zircon U–Pb Geochronology and Hf Isotopes

et al. 2018

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Abstract:The Alxa block is located in the southwestern margin of the North China Craton. The Paleoproterozoic tectonic evolution, crustal growth and tectonic affinity of the block remain unknown or controversial. The Longshoushan (LS) area is one of the few areas that outcrop Paleoproterozoic to crystalline basement rocks in the Alxa Block. In this study, we preset whole-rock geochemistry, zircon U-Pb geochronology and Lu-Hf isotope data from metagabbro, metadiorite, quartz syenite, granitic leucosome and pegmatoid leucosome in the LS area. These rocks all are enriched in LREE and LILE, and depleted in HREE and HFSE. Eight new LA-ICP-MS zircon U-Pb ages yielded three magmatic ages of 2044 Ma, 2029 Ma and 1940 Ma, and three metamorphic ages of 1891 Ma, 1848 Ma and 1812 Ma. Lu-Hf analyses reveal that the magmatic zircons and anatectic/metamorphic zircons from all the rock types are characterized by positive εHf(t) (−0.16 to 10.89) and variable εHf(t) (−11.21 to 6.24), respectively. Based on the previous studies and our new data, we conclude that the LS area experienced three magmatic events (2.5-2.45 Ga, 2.1-2.0 Ga and~1.95-1.91 Ga) and three regional metamorphism/anataxis events (~1.93-1.89 Ga, 1.86-1.84 Ga and~1.81 Ga) in Paleoproterozoic. The age-Hf isotope data establishes two main crustal growth events at~2.9-2.5 Ga and~2.2-2.0 Ga in the LS area. These data indicate that the LS area experienced intraplate extensional setting in the middle Paleoproterozoic, and continental subduction, collision and exhumation in the late Paleoproterozoic. Combining the geochronological framework and tectonic evolution, we suggest that the Alxa Block is part of the Khondalite Belt.

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Origin of the Alxa Block, western China: New evidence from zircon U–Pb geochronology and Hf isotopes of the Longshoushan Complex

Cited by 86 publications

References 103 publications

Detrital zircon record of rivers' sediments in the North Qilian Orogenic Belt: Implications of the tectonic evolution of the northeastern Tibetan Plateau

Detrital zircon record of rivers' sediments in the North Qilian Orogenic Belt: Implications of the tectonic evolution of the northeastern Tibetan Plateau

LateCarboniferous–earlyPermian arc magmatism in the south‐westernAlxaTectonicBelt (NW China):Constraints on the latePalaeozoic subduction history of thePalaeo‐AsianOcean

Paleoproterozoic Multiple Tectonothermal Events in the Longshoushan Area, Western North China Craton and Their Geological Implication: Evidence from Geochemistry, Zircon U–Pb Geochronology and Hf Isotopes

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