滇东南里呼地区中—晚二叠世洋中脊玄武岩的发现及其对区域构造环境的指示OA

There has been a significant controversy for a long time regarding the paleogeographical environ-ment of the Carboniferous-Permian period in the southeastern Yunnan region.One viewpoint holds that it be-longs to the platform facies,while another contends that it is of the basin facies.This controversy has severely re-stricted the in-depth understanding of the tectonic evolution of the Youjiang Basin.Through a 1∶50 000 regional geological survey,a set of pillow basic volcanic rocks from the Middle-Late Permian period was discovered in the Lihu area,Funing County,southeastern Yunnan.Its main lithologies include dense massive basalt,spherulitic(pi-critic)basalt interbedded with basaltic volcanic breccia.The chondrite-normalized rare earth element distribution curves of these volcanic rocks are flat,similar to the characteristics of the E-MORB.On the primitive mantle-nor-malized trace element spider diagrams,the rocks show relatively enriched elements such as K,Rb,Ba,and Th,while elements like Ti and P are relatively depleted.In the tectonic setting diagrams,the projection points of these rocks fall into the ocean ridge and ocean floor area,as well as the oceanic ridge tholeiite area respectively,gener-ally exhibiting the characteristics of high-potassium tholeiite of the ocean ridge.Based on this,it is believed that this set of volcanic rocks from the Middle-Late Permian period is the product of the rapid expansion of the You-jiang Ocean Basin.Combining with previous research results,it is speculated that the southeastern Yunnan region should have been a multi-island ocean basin environment composed of stable shallow-water sediments,oceanic is-lands,deep-water areas,and the open ocean basin during the Late Paleozoic era.This discovery provides impor-tant reference materials for the tectonic evolution of the Youjiang Ocean Basin.