Geochronology and geochemistry of late Carboniferous–Middle Jurassic magmatism in the Helong area, NE China: Implications for the tectonic transition from the Paleo‐Asian oceanic to circum‐Pacific regime
Geochronology and geochemistry of late Carboniferous–Middle Jurassic magmatism in the Helong area, NE China: Implications for the tectonic transition from the Paleo‐Asian oceanic to circum‐Pacific regime
复制标题
DOI：
10.1002/gj.3611
复制
发表时间：
2020-03
影响因子：
1.8
通讯作者：
Jie Tang;Ao‐Peng Li;Wenliang Xu
中科院分区：
文献类型：
--
作者：
Jie Tang;Ao‐Peng Li;Wenliang Xu
本文对贺龙地区晚石炭世—中侏罗世侵入岩进行了新的锆石U-Pb年龄和全岩主微量元素测定。这些资料限制了古亚洲洋相向环太平洋构造过渡的时间。U-Pb锆石定年表明，合龙地区晚石炭世—中侏罗世岩浆事件可划分为晚石炭世、中二叠世、早中三叠世、晚三叠世、早侏罗世和早中侏罗世。晚石炭世花岗闪长岩和中二叠世二长花岗岩属于钙碱性系列，与ⅰ型花岗岩类具有亲缘关系，表明它们形成于北陆构造中心下古亚洲洋板块向南俯冲的典型安第斯型大陆弧环境。和龙地区中三叠统花岗闪长岩和二长花岗岩与阿达质岩具有亲缘关系，母岩浆来源于下大陆地壳增厚的部分熔融作用。晚三叠世ⅰ型二长花岗岩与同时期超镁铁质-基性岩构成双峰型火成岩组合，与同时期a型花岗岩和流纹岩构成伸展环境。结合240 ~ 225 Ma沉积的缺失，研究区经历了与古亚洲洋最终闭合有关的早-中三叠世挤压到晚三叠世伸展的转变。中侏罗统早-早辉长岩、闪长岩、花岗闪长岩和二长花岗岩均为钙碱性，富集低稀土和低硫元素，而富集三稀土和低硫元素。结合中国东北地区早侏罗世火成岩钾含量从大陆边缘到陆内区域的空间变化，以及早侏罗世增生杂岩的存在，我们认为和龙地区早-早中侏罗世岩浆活动形成于与古太平洋板块俯冲到欧亚大陆之下有关的活跃大陆边缘环境。我们认为，古亚洲洋相构造向环太平洋构造的转变发生在晚三叠世—早侏罗世。
In this study, we present new U–Pb zircon ages and whole‐rock major and trace element data for the late Carboniferous–Middle Jurassic intrusive rocks in the Helong area, NE China. These data constrain the timing of tectonic transition from the Paleo‐Asian oceanic regime to the circum‐Pacific regime. U–Pb zircon dating indicates that the late Carboniferous–Middle Jurassic magmatic events in the Helong area can be subdivided into late Carboniferous, middle Permian, Early–Middle Triassic, Late Triassic, Early Jurassic, and early Middle Jurassic. The late Carboniferous granodiorites and middle Permian monzogranites belong to the calc‐alkaline series and have an affinity to I‐type granitoids, suggesting that they formed in a typical Andean‐type continental arc setting due to the southward subduction of the Paleo‐Asian oceanic plate beneath the NCC. The Middle Triassic granodiorites and monzogranites in the Helong area exhibit an affinity to adakitic rocks with their parental magma derived by the partial melting of thickened lower continental crust. The Late Triassic I‐type monzogranites and coeval ultramafic–mafic rocks constitute a bimodal igneous rock association, together with coeval A‐type granites and rhyolites, signifying an extensional environment. Combined with the absence of 240‐ to 225‐Ma sedimentation, the study area experienced a change from Early–Middle Triassic compression to Late Triassic extension related to the final closure of the Paleo‐Asian Ocean. The Early–early Middle Jurassic gabbros, diorites, granodiorites, and monzogranites are calc‐alkaline in nature and enriched in LREE and LILE but depleted in HREE and HFSE. Combined with the spatial variations in K contents of Early Jurassic igneous rocks in NE China from the continental margin to intracontinental region, and the presence of an Early Jurassic accretionary complex, we suggest that Early–early Middle Jurassic magmatism in the Helong area formed in an active continental margin setting related to the subduction of the Paleo‐Pacific Plate beneath Eurasia. We conclude that the tectonic transition from the Paleo‐Asian oceanic regime to the circum‐Pacific regime occurred in the Late Triassic–Early Jurassic.