朝鲜半岛咸北地区晚二叠世基性火山岩的地球化学特征:岩石成因与地质意义

Late Permian mafic volcanic rocks in the Hambuk massif,Korean Peninsula: Geochemistry,origin and tectonic implications

晚古生代火山作用既是探究朝鲜半岛北部大地构造归属的基本要素,又是认识东北亚大陆两大构造域转折之际地球动力学过程的关键窗口。针对咸北地区会宁基性火山岩开展的离子探针锆石U-Pb年代学和地球化学研究表明,其喷发时代为晚二叠世(257±3Ma);主要岩石类型包括玄武安山岩和安山岩,其Si O2含量介于51.9%~55.3%,Mg#变化于40~58,属于钙碱性系列;岩石富集大离子亲石元素、亏损高场强元素(如Nb,Ta,Ti),并具有高正的锆石εH f(t)(+10^+16)值。元素-同位素地球化学示踪指示该基性火山岩的岩浆源区为俯冲沉积物熔体交代而形成的不均一岩石圈地幔,其部分熔融则可能归因于俯冲后的板内伸展背景。会宁基性火山岩不仅为判定咸北地块属于中亚造山带在朝鲜半岛的东延部分提供了岩石学证据,而且与中国相邻地块上的同期岩浆事件一道,构成见证古亚洲洋东段沿西拉木伦-长春-延边一线断裂带最终闭合的空间标记。

Constraining the Late-Paleozoic volcanism in the northern North Korea is critical not only for facilitating the tectonic division in the Korean Peninsula,but also for probing geodynamic process at the transitional stage of tectonic regimes in NE Asia.This geochronological and geochemical study documents the Late Permian mafic volcanic rocks from the Hambuk massif of North Korea.SIMS zircon U-Pb dating yields an eruption age at 257 ± 3 Ma.These rocks exhibit moderate enrichment in large ion lithophile elements and light REE,slightly negative Eu anomalies,and clear depletion in high field strength elements（ e.g.,Nb,Ta,Ti）.They show a range of zircon εH f（ t） values from ＋ 10 to ＋ 16.These geochemical features suggest that their generation most likely involves a precursory metasomatism stage of mantle peridotites by melts from subduction-related sediments and an immediate partial melting stage.With a depleted mantle parentage and possible tectonic link to post-orogenic extensional regime,these rocks could present a spatial hallmark not only for monitoring the extension of the eastern Central Asian Orogenic belt（ CAOB） into the Korean Peninsula,but also for tracing the final location of the cryptic suturing zone of the Paleo-Asian Ocean.