Possible early Neoproterozoic magmatism associated with slab window in the Pingshui segment of the Jiangshan-Shaoxing suture zone: Evidence from zircon LA-ICP-MS U-Pb geochronology and geochemistry |
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| Authors: | ZhiHong Chen KunYi Guo YongGuan Dong Rong Chen LongMing Li YiHong Liang ChunHai Li XiMing Yu Ling Zhao GuangFu Xing |
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| Institution: | (1) Nanjing Institute of Geology and Mineral Resources, Nanjing, 210016, China;(2) Department of Earth Sciences, The University of Hong Kong, Hong Kong, China;(3) College of Earth Sciences, Jilin University, Changchun, 130026, China;(4) Zhejiang Pingtong Gorporation, Shaoxing, 310520, China |
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| Abstract: | We report here geochemical data, U-Pb zircon ages, and Hf isotopes for the high-Mg diorites (HMDs), Nb-enriched basaltic porphyrys
(NEBPs) and plagiogranites (PLAGs) in the Pingshui segment of the Jiangshan-Shaoxing suture zone. The HMDs are characterized
by high Mg# (>60), high Na and LREE contents, depletion of HREE and HFSE, and pronounced positive εNd(t) values of 7.0 to 7.7, similar to some adakitic high-Mg andesites. The NEBPs are relatively Na-rich (Na2O/K2O>6) and display high abundances of P2O5 (∼1.00%), TiO2 (∼3.08%) and HFSE (e.g., Nb=9.53–10.27 ppm). Their Nd isotopic compositions (εNd(t)=6.8–8.0) are comparable to those of the HMDs. The PLAGs are metaluminous (A/CNK=0.84–0.89) and sodic (Na2O/K2O>10). Their depletion in HFSE (e.g., Nb, Ta) is consistent with “SSZ-type” plagiogranite. Zircon LA-ICP-MS U-Pb dating yields
an age of 932±7 Ma for the HMD, 916±6 Ma for the NEBP, and 902±5 Ma for the PLAG, respectively, indicating that they were
products of early Neoproterozoic magmatism. The PLAGs exhibit relatively high zircon Hf isotopes and positive εHf(t) values of 11.0 to 16.2, consistent with their Nd isotopic data (εNd(t)=7.5–8.4). Such features are similar to those of oceanic plagiogranites in ophiolites and distinct from those of crust-derived
granites. The PLAGs were most likely derived from partial melting of subducted oceanic crust in an active continental margin.
Considering these results in the context of the regional geology, we suggest that a slab window in the subducting oceanic
crust between the Yangtze Block and Cathaysia Block was possibly the principal cause for the unique arc magmatism in the area.
The upwelling asthenosphere below the slab window may have provided significant thermodynamic conditions.
Supported by China Geological Survey (Grant No. 1212010610611) and the Ministry of Land and Resources (Grant No. 200811015) |
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| Keywords: | zircon LA-ICP-MS U-Pb dating geochemistry slab window early Neoproterozoic Pingshui of Shaoxing Jiangshan-Shanxing suture zone |
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