摘要
通过研究1980—1998年获取的西秦岭组(群)级岩石地层单元和花岗岩类的地球化学数据,如地层中稳定元素的比值和含量的接近程度指示的物源关系、A型花岗岩的微量元素证据、构造环境判别图解等,结合前人的地球物理数据解释成果,论述了新元古代以来西秦岭造山过程;进一步阐明了造山过程与成矿作用之间的关系。利用组级岩石地层单元的相对均一性,引入I型花岗岩判别方法——SiO2-P关系判别法,在印证前人成果的基础上获得新认识。认为新元古代以来,西秦岭的地壳演化可以划分为以下4个过程:中元古代末期至震旦纪早期华北和扬子板块的汇聚—分离—汇聚过程,震旦纪晚期—奥陶纪的伸展过程,志留纪—侏罗纪的自东至西的汇聚过程,泥盆纪—中新生代自东至西乃至西秦岭全区的板内伸展过程。华北地块和扬子地块在中元古代、新元古代和震旦纪的某个时期曾相互接近,震旦纪后逐渐相互远离并形成多岛洋盆。志留纪前后,依次发生过洋内俯冲、弧陆碰撞和洋陆俯冲。南北板块的碰撞始于泥盆纪,结束于侏罗纪,但富铝矿物含量高的与碰撞有关的S-型花岗岩形成于三叠纪。两板块的碰撞自东部的勉略一带逐渐向西迁移至迭部一带,震旦系至三叠系依次增生至华北板块,随后与消减、拆沉的扬子板块有关的板内伸展及相应花岗岩类的入侵自东部的党川地区向西迁移,直至全区整体处于伸展状态。不管早古生代的弧陆碰撞机制是什么,迭部—略阳断裂至少在志留纪以来在西秦岭的地壳演化中起着主要作用。沉积成矿的峰期是志留纪和泥盆纪,对应于洋盆开裂至洋盆关闭的转换期;热液成矿的峰期是三叠纪和侏罗纪,与印支—燕山期岩浆活动期一致,对应于碰撞向板内伸展的转换期。
Based on geochemical data of stratigraphic units of different levels and granitoid intrusives acquired in West Qinling from the 1980s to 1990s,such as concentrations and ratios of immobile elements and trace element indicators of A-type granites in combination with previous interpretation of geophysical data,the authors investigated the orogenic process of West Qinling since Neoproterozoic,and probed into the relationship between the orogenic process and the metallic mineralization.In comparison with previous studies,the formation-level stratigraphic unit was reasonably adopted on account of its relative homogeneity,the SiO2-P relation was introduced to differentiate I-type granites from other types,and the results have validated previous knowledge with the obtaining of some new understanding.The authors consider that the evolution of West Qinling since Neoproterozoic may be divided into four processes,i.e.,the convergence-split-convergence process from late Mesoproterozoic to early Sinian,the extensional process from late Sinian to Ordovician,the westward contraction process from Silurian to Jurassic,and the westward intraplate extension process,which even extended to the whole West Qinling region from Devonian to Mesozoic-Cenozoic. The north China block and the Yangtze block was close to each other in certain periods of Mesoproterozoic,Neoproterozoic and Sinian;after Sinian,they were gradually away from each other and developed a multi-island sea basin between them.There were intra-oceanic subduction,arc continent collision and ocean continent subduction before or in Silurian.The collision of the North China craton and the Yangtze craton might have started in Devonian and ended in Jurassic,whereas the S-type granites which were enriched in aluminum-rich minerals and related to syn-collision were formed in Triassic.The collision of the two plates migrated westward from Lueyang to Diebu,so that the Sinian to Triassic strata accreted successively to the North China craton.Subsequent intraplate extension and granitoid intrusion related to subduction and delamination of Yangtze plate also migrated westward from eastern Dangchuan till the development of the extension in whole West Qinling region in Meso-Cenozoic.No matter what the mechanism of arc continent collision was in early Paleozoic,the Diebu-Lueyang fault must have played a leading role in the evolution of West Qinling since at least Silurian. The peaks of sedimentary mineralization were Silurian and Devonian,corresponding to the transitional period from ocean splitting to ocean closing.The peaks of hydrothermal mineralization were Triassic and Jurassic during which the Indosinian-Yanshanian magmatism prevailed,corresponding to the transitional period from collision to intracontinental extension.
出处
《中国地质》
CAS
CSCD
北大核心
2011年第3期637-656,共20页
Geology in China
基金
“固体介质中多元素地球化学场的线性与非线性竞争规律及其应用”项目(GPMR200904)资助
关键词
新元古代以来
造山过程
地球化学证据
成矿背景
西秦岭
甘肃
since Neoproterozoic
orogenic process
geochemical evidence
metallogenic background
West Qinling
Gansu