Geochronology and petrogenesis of Middle Permian S-type granitoid in southeastern Guangxi Province, South China: Implications for closure of the eastern Paleo-Tethys
Geochronology and petrogenesis of Middle Permian S-type granitoid in southeastern Guangxi Province, South China: Implications for closure of the eastern Paleo-Tethys
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DOI：
10.1016/j.tecto.2016.05.048
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发表时间：
2016-07
期刊：
影响因子：
2.9
通讯作者：
Yanjun Li;Jun-hao Wei;M. Santosh;Jun Tan;L. Fu;Shaoqing Zhao
中科院分区：
文献类型：
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作者：
Yanjun Li;Jun-hao Wei;M. Santosh;Jun Tan;L. Fu;Shaoqing Zhao
邦溪-陈兴缝合带是研究古特提斯洋东部闭合历史的重要区域。在广西东南部广泛分布的S型花岗岩基中，邻近这条缝合线的是那里花岗闪长岩。本文报道了该地区新发现的中二叠世S型花岗岩的锆石U-Pb年龄、常量和微量元素地球化学及Sr-Nd-Hf同位素地球化学。LA-ICP-MS锆石U-Pb年代学结果表明，纳里花岗闪长岩的侵位年龄为265 ± 2 ~ 262 ± 2 Ma。内相和外相的特征在于可变的SiO2（66.91-71.39重量%），高Al 2 O 3（12.99- 14.04wt.%），K2 O + Na 2 O（4.78-5.98重量%），A/CNK值为1.11-1.50，与典型S型花岗岩相似。岩石富集Rb、Th、U和轻稀土元素，具弱Eu负异常，亏损Nb、Ta、Ti，具典型的弧形亲合力。它们具有相对较高的（87 Sr/86 Sr）比值（0.7228至0.7331），较低的εNd（t）值（− 13.6至− 11.9）和较低的锆石εHf（t）值（− 21.9至− 8.8）。高的全岩Nd同位素模式年龄（2.00- 2.02Ga）和锆石Hf同位素模式年龄（1.59- 2.20Ga）表明，它们可能是由古老的下地壳部分熔融形成的，地幔源区的贡献较小。花岗闪长岩具有大陆弧的亲缘性，可能形成于俯冲环境。结合已有的金沙江哀牢山-宋马缝合带和邦溪-陈兴缝合带二叠纪-三叠纪弧-碰撞岩浆活动资料，提出东古特提斯俯冲可能始于中二叠世，是由中南地块向北俯冲到华南地块之下并在中三叠世闭合触发的。
The Bangxi-Chenxing suture zone is an important region to address the history of closure of the eastern Paleo-Tethys ocean. Among the widespread S-type granite batholiths in the SE Guangxi Province adjacent to this suture is the Nali granodiorite. Here we report zircon U–Pb ages, major and trace element geochemistry, and Sr–Nd–Hf isotope geochemistry of a newly found Middle Permian S-type granite in this region. LA-ICP-MS zircon U–Pb geochronology yields emplacement ages of 265 ± 2 to 262 ± 2 Ma for the Nali granodiorite. Both the inner and outer phases are characterized by variable SiO2(66.91–71.39 wt.%), high Al2O3(12.99–14.04 wt.%), K2O + Na2O (4.78–5.98 wt.%), and A/CNK values (1.11–1.50), resembling those of typical S-type granites. The rocks are enriched in Rb, Th, U and light rare earth elements with weak negative Eu anomalies, and show depletion in Nb, Ta, Ti, with typical arc-like affinity. They have relatively high (87Sr/86Sr)iratios of 0.7228 to 0.7331, low εNd(t) values of − 13.6 to − 11.9, and low zircon εHf(t) values (− 21.9 to − 8.8). High whole-rock Nd isotopic model ages (2.00–2.02 Ga) and zircon Hf isotopic model ages (1.59–2.20 Ga), indicate that they might have been generated by partial melting of ancient lower crust with minor contribution from mantle sources. The granodiorite shows continental arc affinity and likely formed within a subduction setting. By combining previously extant data for Permo-Triassic arc-/collision-related magmatism in the Jinshajiang-Ailaoshan-Song Ma and Bangxi-Chenxing suture zones, we propose that the subduction of the eastern Paleo-Tethys might have started during Middle Permian triggered by the northward subduction of the Indochina Block (ICB) beneath the South China Block (SCB) and closure during Middle Triassic.