Duobagou Permian–Triassic granites from the Dunhuang orogenic belt, NW China: implications for the tectonic evolution of the southernmost Central Asian Orogenic Belt

2020 ◽  
pp. 1-17
Author(s):  
Zhendong Wang ◽  
Yuanyuan Zhang ◽  
Xiangjiang Yu ◽  
Zhaojie Guo
Keyword(s):  
Partial Melting ◽  
Tectonic Evolution ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Crustal Growth ◽  
Central Asian ◽  
Granitic Intrusions ◽  
Mantle Component ◽  
Type Granite ◽  
T Values

Abstract The Duobagou Permian–Triassic granites of the Dunhuang orogenic belt are of great importance in understanding the tectonic evolution of the southernmost Central Asian Orogenic Belt. LA-ICP-MS U–Pb zircon ages indicate that Permian–Triassic granitic intrusions from the Duobagou area formed at 276–274 Ma and 246 ± 1 Ma. These granites have high SiO2, Na2O and K2O, but low Al2O3, CaO and MgO contents and belong mainly to the high-K calc-alkaline I-type granite series. Based on whole-rock geochemistry and Sr–Nd and zircon Hf isotopes, the Duobagou Permian–Triassic granites were dominantly derived from the partial melting of lower continental crust formed during late Palaeoproterozoic to Mesoproterozoic times in a post-collisional extensional setting. Permian granites with zircon ϵHf(t) values of −5.4 to +3.1 and Hf model ages of TDM2 = 1.14–1.70 Ga indicate the involvement of a mantle component in their petrogenesis. Triassic granites with higher zircon ϵHf(t) values (+0.5 to +3.8) and TDM2 = 1.08–1.31 Ga suggest more juvenile sources caused by a greater contribution of mantle-derived melts, indicating a significant crustal growth. Regional extension from lithospheric delamination and heating from asthenospheric upwelling were proposed to have triggered the partial melting of lower crust, resulting in the generation of the Permian–Triassic magmatism. This may have been the mechanism for the significant crustal growth during Permian and Triassic times in the southernmost Central Asian Orogenic Belt.

Granitoids of the Central Asian Orogenic Belt and continental growth in the Phanerozoic

2000 ◽  
Vol 91 (1-2) ◽  
pp. 181-193 ◽  
Author(s):  
Bor-ming Jahn ◽  
Fuyuan Wu ◽  
Bin Chen
Keyword(s):  
Central Asia ◽  
Basaltic Magma ◽  
Orogenic Belt ◽  
Source Rocks ◽  
Central Asian Orogenic Belt ◽  
Central Asian ◽  
Wide Range ◽  
Mantle Component ◽  
T Values ◽  
Lower Crustal

The Central Asian Orogenic Belt (CAOB), also known as the Altaid Tectonic Collage, is characterised by a vast distribution of Paleozoic and Mesozoic granitic intrusions. The granitoids have a wide range of compositions and roughly show a temporal evolution from calcalkaline to alkaline to peralkaline series. The emplacement times for most granitic plutons fall between 500 Ma and 100 Ma, but only a small proportion of plutons have been precisely dated. The Nd-Sr isotopic compositions of these granitoids suggest their juvenile characteristics, hence implying a massive addition of new continental crust in the Phanerozoic. In this paper we document the available isotopic data to support this conclusion.Most Phanerozoic granitoids of Central Asia are characterised by low initial Sr isotopic ratios, positive εNd(T) values and young Sm—Nd model ages (TDM) of 300-1200 Ma. This is in strong contrast with the coeval granitoids emplaced in the European Caledonides and Hercynides. The isotope data indicate their ‘juvenile’ character and suggest their derivation from source rocks or magmas separated shortly before from the upper mantle. Granitoids with negative εNd(T) values also exist, but they occur in the environs of Precambrian microcontinental blocks and their isotope compositions may reflect contamination by the older crust in the magma generation processes.The evolution of the CAOB is probably related to accretion of young arc complexes and old terranes (microcontinents). However, the emplacement of large volumes of post-tectonic granites requires another mechanism, probably through a series of processes including underplating of massive basaltic magma, intercalation of basaltic magma with lower crustal granulites, partial melting of the mixed lithologic assemblages leading to generation of granitic liquids, followed by extensive fractional crystallisation. The proportions of the juvenile or mantle component for most granitoids of Central Asia are estimated to vary from 70% to 100%.

scholarly journals Crustal growth and reworking: A case study from the Erguna Massif, eastern Central Asian Orogenic Belt

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Chenyang Sun ◽  
Wenliang Xu ◽  
Peter A. Cawood ◽  
Jie Tang ◽  
Shuo Zhao ◽  
...  
Keyword(s):  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Crustal Growth ◽  
Central Asian ◽  
Mesozoic Granitoids ◽  
Tectonic Settings ◽  
Crustal Heterogeneity ◽  
Erguna Massif ◽  
T Values

AbstractDespite being the largest accretionary orogen on Earth, the record of crustal growth and reworking of individual microcontinental massifs within the Central Asian Orogenic Belt (CAOB) remain poorly constrained. Here, we focus on zircon records from granitoids in the Erguna Massif to discuss its crustal evolution through time. Proterozoic–Mesozoic granitoids are widespread in the Erguna Massif, and spatiotemporal variations in their zircon εHf(t) values and TDM2(Hf) ages reveal the crustal heterogeneity of the massif. Crustal growth curve demonstrates that the initial crust formed in the Mesoarchean, and shows a step-like pattern with three growth periods: 2.9–2.7, 2.1–1.9, and 1.7–0.5 Ga. This suggests that microcontinental massifs in the eastern CAOB have Precambrian basement, contradicting the hypothesis of significant crustal growth during the Phanerozoic. Phases of growth are constrained by multiple tectonic settings related to supercontinent development. Calculated reworked crustal proportions and the reworking curve indicate four reworking periods at 1.86–1.78 Ga, 860–720 Ma, 500–440 Ma, and 300–120 Ma, which limited the growth rate. These periods of reworking account for the crustal heterogeneity of the Erguna Massif.

NEOPROTEROZOIC TECTONIC EVOLUTION OF THE OPHIOLITIC BAYANKHONGOR SUTURE ZONE, CENTRAL ASIAN OROGENIC BELT (CENTRAL MONGOLIA)

2019 ◽  
Author(s):  
James R. Worthington ◽  
◽  
Claire E. Bucholz ◽  
Uyanga Bold ◽  
Francis A. Macdonald ◽  
...  
Keyword(s):  
Tectonic Evolution ◽  
Suture Zone ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Central Mongolia ◽  
Central Asian

Quantifying the growth of continental crust through crustal thickness and zircon Hf-O isotopic signatures: A case study from the southern Central Asian Orogenic Belt

2021 ◽  
Author(s):  
Yujian Wang ◽  
Dicheng Zhu ◽  
Chengfa Lin ◽  
Fangyang Hu ◽  
Jingao Liu
Keyword(s):  
Continental Crust ◽  
Crustal Thickness ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Crustal Thickening ◽  
Crustal Growth ◽  
Isotopic Signatures ◽  
Central Asian ◽  
Southern Central ◽  
Juvenile Crust

Accretionary orogens function as major sites for the generation of continental crust, but the growth model of continental crust remains poorly constrained. The Central Asian Orogenic Belt, as one of the most important Phanerozoic accretionary orogens on Earth, has been the focus of debates regarding the proportion of juvenile crust present. Using published geochemical and zircon Hf-O isotopic data sets for three belts in the Eastern Tianshan terrane of the southern Central Asian Orogenic Belt, we first explore the variations in crustal thickness and isotopic composition in response to tectono-magmatic activity over time. Steady progression to radiogenic zircon Hf isotopic signatures associated with syn-collisional crustal thickening indicates enhanced input of mantle-derived material, which greatly contributes to the growth of the continental crust. Using the surface areas and relative increases in crustal thickness as the proxies for magma volumes, in conjunction with the calculated mantle fraction of the mixing flux, we then are able to determine that a volume of ∼14−22% of juvenile crust formed in the southern Central Asian Orogenic Belt during the Phanerozoic. This study highlights the validity of using crustal thickness and zircon isotopic signatures of magmatic rocks to quantify the volume of juvenile crust in complex accretionary orogens. With reference to the crustal growth pattern in other accretionary orogens and the Nd-Hf isotopic record at the global scale, our work reconciles the rapid crustal growth in the accretionary orogens with its episodic generation pattern in the formation of global continental crust.

Genesis of the Wuxing Pt–Pd-rich Cu–Ni sulfide deposit in the eastern Central Asian Orogenic Belt: evidences from geochronology, elemental geochemistry, and Sr–Nd–Hf isotopic data

2019 ◽  
Vol 56 (4) ◽  
pp. 380-398 ◽  
Author(s):  
Jing-gui Sun ◽  
Yun-peng He ◽  
Ji-long Han ◽  
Zhong-yu Wang
Keyword(s):  
Crustal Contamination ◽  
Early Period ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Geochemical Data ◽  
Sulfide Deposit ◽  
Late Period ◽  
Enriched Mantle ◽  
Central Asian ◽  
T Values

The Wuxing Pt–Pd-rich Cu–Ni sulfide deposit in Heilongjiang Province, Northeast China, is located to the northeast of the Dunhua–Mishan fracture of the eastern Central Asian Orogenic Belt. The mafic–ultramafic complex consist of early-period hornblende–olivine pyroxenite, diopsidite, and hornblende pyroxenite and late-period gabbro and diabase units. An early-period hornblende pyroxenite yielded a zircon U–Pb age of 208.2 ± 2.6 Ma and a late-period diabase yielded a U–Pb age of 205.6 ± 1.1 Ma, with zircon εHf(t) values of +1.24 to +8.13. The early- and late-period lithofacies are relatively enriched in LILE (Rb, Ba, and Sr) and LREE, and variably depleted in HFSE (Nb, Ta). The whole-rock and single-mineral analyses of the early-period lithofacies yield (87Sr/86Sr)i ratios of 0.7055–0.7083 and εNd(t) ratios of −7.98–+3.10. These geochemical data suggest that the parental magmas of the Wuxing complex are high-Mg subalkaline basaltic in nature and were derived from an enriched mantle source. The magmas chamber formed after the injection of magma into the crust along with crustal contamination, producing early crystalline minerals and ore-bearing magmas. The rupturing of the magma chamber released evolved magmas, which then ascended and generated Pt–Pd-bearing lithofacies and Cu–Ni sulfide orebodies by fractional crystallization, accumulation, and liquation. During the late period, the residual magma invaded the early lithofacies and Cu–Ni orebodies. The fluids exsolved from the gabbroic magmas concentrated the mineralized metal elements and enhanced the precipitation of Pt–Pd-bearing veinlet-disseminated orebodies and Pt–Pd–Cu–Ni orebodies.

Geochemical signature of Paleozoic accretionary complexes of the Central Asian Orogenic Belt in South Mongolia: Constraints on arc environments and crustal growth

2006 ◽  
Vol 227 (3-4) ◽  
pp. 236-257 ◽  
Author(s):  
Christoph Helo ◽  
Ernst Hegner ◽  
Alfred Kröner ◽  
Gombosuren Badarch ◽  
Onongin Tomurtogoo ◽  
...  
Keyword(s):  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Crustal Growth ◽  
Geochemical Signature ◽  
Central Asian
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