摘要:
巴西卡拉加斯(Carajás)地区发育古老的太古宙变质基底,是世界上矿床类型最丰富、资源聚集程度最高的成矿区之一。在太古宙花岗岩-绿岩为主体的结晶基底中,含有大量紫苏花岗岩、奥长花岗岩-英云闪长岩-花岗闪长岩(trondhjemite-tonalite-granodiorite,TTG)岩套和未完全解体的变质深成岩,目前对其认识仍存在较大分歧。岩浆岩的正确划分和精细研究是深入认识南美克拉通演化的重要手段,在调查卡拉加斯地区基底中变质侵入岩的基础上,结合前人资料将其进一步划分为中太古代的紫苏花岗岩、层状基性—超基性岩和TTG岩套,新太古代的基性—超基性杂岩、TTG岩套、同构造花岗岩、后构造花岗岩等,以及古元古代的碱性花岗岩。结合岩石学、地球化学和年代学方法综合分析了卡拉加斯地区的花岗质深成岩,锆石U-Pb测年获得的花岗岩207Pb/206Pb表面年龄集中在2 899~2 831 Ma、2 742~2 622 Ma和1 919 Ma 3个时期,认为南美克拉通在经历了古太古代陆核形成、中太古代古大陆增生后,在太古宙末期和古元古代发生了二阶段的克拉通化过程,在中元古代—新元古代克拉通开始被破坏。通过对比南美克拉通与华北克拉通的早期演化过程,推测南美克拉通的构造演化早期受地幔柱控制,晚期转变为以板块构造为主导的大陆增生机制。研究有助于深入认识和对比矿集区成矿过程及其成矿效应。
Abstract:
The Archean metamorphic basement is developed in Carajás area of Brazil, which is one of the most abundant mineral deposits and the highest degree of resource accumulation deposits in the world. A large amount of charnockite, (trondhjemite-tonalite-granodiorite,TTG) rock series and metamorphic plutons that haven't completely disintegrated exsit in the crystalline basement of Archean granite-greenstone, with large perception diffe-rence. The correct division and fine study of igneous rocks are important means to further understand the evolution of South American Craton. Based on the investigation of metamorphic basement intrusive rocks, and combined with previous data, the authors decomposed it into the charnockite of Paleoarchean, the mafic-ultramafic rocks and the TTG gneiss suite of Mesoarchean, and the mafic-ultramafic rocks, the TTG gneiss suite, the syntectonic granite and the post-tectonic granite of Neoarchean, and the alkaline granite of Paleoproterozoic. The granitic plutons in Carajás area were comprehensively analyzed with geological, geochemical and geochronological methods. The 207Pb/206Pb surface ages of granite by Zircon U-Pb method is concentrated in three periods: 2 899~2 831 Ma, 2 742~2 622 Ma and 1 919 Ma. After the formation of continental nucleus in Paleoarchean and continental hyperplasia in Mesoarchean, South America craton experienced two stage cratonic consolidation process in Late Archaean and Paleoproterozoic, and it began to destroyed in Mesoproterozoic and Neoproterozoic. Comparing the similarities and differences between North China Craton and South America Craton, the authors presumed that the mechanism of tectonic evolution was controlled by mantle plume tectonics in the early continental tectonics, and transformed into tectonics accretion mechanism dominated by plate motion. This research is beneficial to deepening knowledge and comparison of metallogenic process and its effects in ore concentrate area.
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