扬子地块西缘古-中元古代基性岩浆活动及其构造意义

Researchers have certified the important role that the Yangtze Block plays in the reconstruction of the Rodinia supercontinent, but it is still uncertain whether or not this Block was a component of the Paleo-Mesoproterozoic Columbia supercontinent. .The Paleo-Mesoproterozoic mafic magmatism are widespread on the ancient continents and provide an important means of tracking major periods of continental rifting and supercontinent fragmentation. Therefore, these mafic rocks can not only provide constraints on the compositions of the upper mantle, but also give crucial data on the timing and the lithospheric evolution processes of the Paleo-Mesoproterozoic ancient continents..The late Paleo- to Mesoproterozoic volcanic, intrusive, and sedimentary rocks along the western margin of the Yangtze Block are targets for understanding the early history of the Yangtze Block and the relationship of the Yangtze Block and the Columbia supercontinent. Moreover, a number of mafic volcanic rocks and dykes (or intrusions) have been certified in the Hekou Group in Huili area, and Huili Group in the Huili area, and Kunyang Group in the Dongchuan area, SW China. However, the ages and geochemical characteristics of these mafic rocks have yet been documented, and the petrogenesis of the rocks is not well understood. .In this study, we present systematic in petrology and mineralogy; Cameca, SHRIMP, and LA-ICP-MS U-Pb zircon U-Pb ages, and Cameca, SHRIMP baddeleyite U-Pb ages; major and trace elements, and Nd-O-Hf isotopic geochemistry for the these ma?c volcanic rocks and dykes (or intrusions) in the western margin of the Yangtze Block. The aims are to (1) to determine the precise crystallization age, (2) to discuss the origin and nature of the parental magma, and petrogenesis for these rocks, (3) the genetic relationship between these ma?c dykes (intrusions) and coeval meta-volcanic rocks, and (4) shed new lights on the regional late Paleo-Mesoproterozoic magmatic-tectonic evolution, and the relationship of the Yangtze Block and the Columbia supercontinent.

扬子地块在重建 Rodinia 超大陆中发挥了重要的作用，但目前关于其与Columbia超大陆之间关系的研究仍然很少。古-中元古代的基性岩浆活动对于研究该时期地球演化及Columbia超大陆的重建具有重要意义。前人和申请人最近在扬子西缘研究证实存在该时期基性火山岩和岩脉 (体)，但已有的研究仍然较为薄弱。本研究拟选取会理河口和通安地区、东川拖布卡地区的变质基性火山岩和基性岩脉 (体) 为研究对象，以锆石Cameca、SHRIMP 和LA-ICP-MS U-Pb及斜锆石Cameca和TIMS U-Pb定年方法准确厘定它们的形成时代，通过不同时代和类型火山岩和岩脉的元素和Nd-O-Hf多元同位素特征，揭示基性岩浆活动的地幔源区、岩浆的性质及演化特征，探讨岩脉 (体) 与同时代变质火山岩的成因联系，进而更加深入地阐明该区在该时期岩石圈演化过程及其与Columbia超大陆的联系。

本项目通过对昆阳群迤纳厂组中层状凝灰岩和火山角砾岩所含锆石进行LA–ICP–MS U–Pb定年来限定迤纳厂组的最大沉积年龄。近200粒碎屑锆石的207Pb/206Pb年龄大致可以分为四组：1.75–1.88Ga，1.90–2.00Ga，2.02–2.20Ga和2.30–2.40Ga，且最老年龄在3.0Ga左右，而最年轻年龄在1750 Ma左右。这一定年结果反映了迤纳厂组的沉积上限大约为1.75 Ga，并且在康滇地区可能还有更老的基底存在。通过SIMS 锆石U–Pb同位素分析，会理群天宝山群中酸性火山岩的形成年龄为1025 ± 13 Ma和1021 ± 6.4 Ma。因此，昆阳群和会理群的形成时代在 ~1.7–~1.0 Ga之间。以上研究表明，大红山群、河口群、下昆阳群 (也称东川群) 和下会理群是出露于不同地区但形成时代上相同的地层。.通过SIMS 锆石U–Pb同位素定年结果表明，河口岩体为约1.7 Ga镁铁质岩浆活动形成的。通过其锆石和斜锆石SIMS U–Pb定年，结果表明赋存Fe–Ti–V氧化物矿床竹箐基性岩体群的形成年龄为约1.5 Ga。此外，会理群天宝山群中镁铁质岩脉的SIMS 锆石U–Pb年龄为1023 ± 6.7 Ma。目前的工作表明，河口群、昆阳群和会理群中的侵入体主要包括约1.7 Ga辉长岩、辉绿岩和花岗岩、约1.5 Ga辉长岩和辉绿岩, ~1.1–1.0 Ga辉长岩和花岗岩。.河口镁铁质侵入体被认为是形成于一个非造山的拉张环境。因此，约1.7 Ga被认为是扬子地块西缘广泛分布的非造山岩浆活动的开始。我们认为约1.7–1.5 Ga镁铁质岩浆活动最可能与Columbia超大陆裂解有关的非造山岩浆活动的产物。而四川会理约1.0 Ga 天宝山组火山岩和辉绿岩的形成被认为四堡造山带之前扬子地块和华夏地块初次碰到造成的碰撞裂谷环境下形成的。