扬子陆块西缘中元古代菜子园蛇绿混杂岩的厘定及其地质意义

发布时间：2018-05-10 04:41

本文选题：菜子园蛇绿混杂岩 + 中元古代　；参考：《地质通报》2017年11期

【摘要】：对扬子陆块西缘会理关河—通安地区菜子园蛇绿混杂岩进行了厘定。菜子园蛇绿混杂岩主要以强烈剪切变形的基质和洋板构造岩块混杂堆积为特征。基质主要有变质粉砂岩、板岩、硅质板岩、片岩、千枚岩等。洋板构造岩块由蛇纹岩、辉长岩、玄武岩、硅质岩、大理岩等组成,部分地区玄武岩保留枕状构造,各岩块之间为构造接触关系。菜子园蛇绿混杂岩中桃树湾辉长岩和玄武岩具有轻稀土元素亏损、类似N-MORB(正常洋中脊玄武岩)的稀土元素配分模式,相对于N-MORB富集大离子亲石元素,亏损Nb、Ta高场强元素,极低的Nb/U(9.74)、Nb/Th(3.02)和V/Ti(0.1)平均值,具典型MORB-like玄武岩(前弧玄武岩-FAB)地球化学特征,认为可能形成于洋内弧环境。桃树湾辉长岩LA-ICP-MS锆石U-Pb同位素定年表明,辉长岩的年龄为1375±7Ma(MSWD=1.2,n=21),可能代表菜子园-通安洋洋壳初始俯冲的时间。菜子园蛇绿混杂岩的厘定,对重新认识通安群(通安组)的属性,研究扬子陆块西缘古—中元古代地层系统、地质演化、岩浆作用、构造定位,重新划分扬子陆块基底大地构造单元,以及探索全球Columbia超大陆裂解到Rodinia超大陆汇聚的演化过程等都具有重要意义。
[Abstract]:The ophiolitic melange of Caiziyuan in the western margin of Yangtze block, Huiguanhe-Tongan area, is determined. Caiziyuan ophiolite melange is mainly characterized by strong shearing deformation matrix and oceanic plate tectonic block migmatism. The matrix mainly has metamorphic siltstone, slate, siliceous slate, schist, phyllite and so on. The oceanic plate tectonic block is composed of ophiolite, gabbro, basalt, siliceous rock, marble and so on. The Taoshuwan gabbro and basalt in the Caiziyuan ophiolitic melange are characterized by light REE depletion, similar to N-MORBB (normal oceanic ridge basalt) REE distribution model, enriched in large ion lithophile elements relative to N-MORB, and depleted in NB Ta high field strength elements. The very low average values of NB / U ~ (9.74) and V / Ti ~ (0.1) have typical geochemical characteristics of MORB-like basalts (forearc basalts), suggesting that the internal arc environment may be formed in Yu Yang. The LA-ICP-MS zircon U-Pb isotopic dating of the gabbro in Taoshuwan shows that the age of the gabbro is 1375 卤7 Ma MSWD1. 2 ~ (2) N ~ (2 +) ~ (21), which may represent the time of initial subduction of the Caiziyuan-Tongan oceanic crust. The determination of the Aiziyuan ophiolitic melange is of great importance to the recognition of the attributes of the Tong'an Group (Tongan formation) and the study of the Paleo-Mesoproterozoic stratigraphic system, geological evolution, magmatism and tectonic location of the western margin of the Yangtze block. It is of great significance to reclassify the basement tectonic units of the Yangtze block and to explore the evolution of the global Columbia supercontinent splitting to the Rodinia supercontinent convergence.
【作者单位】：中国地质调查局成都地质矿产研究所;
【基金】：国家自然科学基金项目《扬子西缘新元古代澄江组火山-沉积序列及其对盆地性质的约束》(批准号:41502114) 中国地质调查局项目《乌蒙山区地质矿产综合调查》(编号:DD20160019);《龙门山-滇中成矿带通安和宁蒗地区地质矿产调查》(编号:DD20160017)
【分类号】：P534.3;P588

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