基于斜锆石年代学和全岩地球化学研究阿尔金造山带红柳沟地区基性岩成因

Petrogenesis Research of Basic Rock in the Hongliugou Area of the Altun Orogen Based on Baddeleyite Chronology and Whole-Rock Geochemical Analyses

  • 摘要: 诸多证据表明阿尔金地块有可能参与了Rodinia超大陆的裂解过程,然而,该地区此前并未见有关板内性质基性-超基性岩体的报道。阿尔金造山带红柳沟地区出露一套基性-超基性岩体,本文采用LA-ICP-MS、XRF、ICP-MS和MC-ICP-MS等技术手段对其中的基性岩组分进行了斜锆石U-Pb定年研究、全岩主量元素、微量元素(包括稀土元素)及Sr-Nd同位素研究。结果表明:基性岩的侵位年龄为748±87Ma,岩石化学属性属于拉班玄武岩。Zr/Sm比值为26~33,Zr/Y比值为3.2~5.5,显示出板内玄武岩的元素特征。La、Ba、Nb、Zr、Th等元素特征显示岩浆源区可能遭受过俯冲流体的改造。全岩主量、微量元素及Sr、Nd同位素测试结果显示该基性岩浆源于软流圈地幔低程度(<5%)的部分熔融,源区贫石榴石(<1%)。这些地球化学特征指示阿尔金地区的基性-超基性岩体形成于大陆裂谷环境。与前人在华南和塔里木地区发现的与Rodimia超大陆裂解相关的基性岩相比,本次报道的红柳沟基性岩形成时代相近,岩石地球化学属性类似,很可能是Rodinia超大陆裂解的产物。

     

    Abstract: Previous studies suggest that the Alton Block may have participated in the breakup of the Rodinia supercontinent, however, there have been no prior reports of intraplate basic-ultrabasic rock bodies in the region. A suite of basic-ultrabasic rock bodies has been exposed in the Hongliugou area of the Alton Orogen. An integrated analytical approach utilizing LA-ICP-MS, XRF, ICP-MS, and MC-ICP-MS was employed to systematically investigate the mafic components, including baddeleyite U-Pb geochronology, whole-rock major and trace elements (including rare earth elements), and Sr-Nd isotopic compositions. The results indicate a crystallization age of 748±87Ma for the basic rocks, with geochemical characteristics consistent with the tholeiitic basalt. The Zr/Sm ratio ranges from 26 to 33, and the Zr/Y ratio from 3.2 to 5.5, reflecting the elemental characteristics typical of intraplate basalt. The presence of La, Ba, Nb, Zr, and Th suggests that the magma source region may have experienced alteration by subduction-related fluids. Whole-rock major and trace element analyses, along with Sr and Nd isotopic data, indicate that the basic magma originated from low-degree (<5%) partial melting of the aesthenosphere mantle, with a source region characterized by low garnet content (<1%). These geochemical features imply that the basic-ultrabasic rock bodies discovered in the Alton region formed in a continental rift environment. The Hongliugou mafic rocks exhibit robust temporal and geochemical parallels with Neoproterozoic mafic magmatism documented in the South China and Tarim blocks, both of which have been genetically linked to the Rodinia supercontinent breakup. The temporal congruence (~750Ma) and diagnostic intraplate basalt affinities (tholeiitic series with subduction-modified mantle signatures) observed in these rocks strongly support their classification as petrogenetic products of Rodinia’s rifting episodes.

     

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