摘要
湖南塔山、阳明山岩体位于扬子地块和华夏地块的结合部位,主要由不同粒度的斑状二长花岗岩构成,其中塔山岩体的粗中粒、中细粒、中粒斑状二长花岗岩的锆石La-ICP-MS定年结果分别为221.3±0.9Ma、221.5±1.9Ma、213.4±1.1Ma,阳明山中细粒斑状二长花岗岩的年龄为213.7±1.0Ma,均属印支晚期花岗岩。花岗岩富SiO_2(70.43%~74.06%)、Al_2O_3(13.25%~15.37%)、高A/CNK(1.03~1.24)、高分异指数DI(85.25~93.0)、富集Rb、Th、U、Ta,亏损Ba、Sr、Nb、Ti,具明显的负Eu异常(δEu=0.15~0.45),为高分异的过铝花岗岩。高(^(86)Sr/^(87)Sr)_i(0.72993~0.77391)、低ε_(Nd)(t)(-9.9^-12.11)、Nd的t_(DM2)(1801~1978Ma)较大等特征,表明塔山、阳明山花岗岩为壳源S型花岗岩。结合其形成年龄和区域构造背景,认为塔山、阳明山岩体是在印支运动晚期挤压作用向伸展作用转换形成的局部伸展-减薄的机制下,由加厚地壳中的中元古代变质砂屑岩、变质泥岩部分熔融形成,并经历了分离结晶作用。年龄为3523Ma的继承锆石核显示本区可能存在古太古代的古老基底。
The Yangmingshan-Tashan batholith, located at the junction of the Yangtze and Cathysia blocks, is mainly composed of monzonitic granites with different granularity and phenocryst content. In this article, a research combined of LA-MC-ICP-MS zircon U-Pb chronology, geochemistry and Sr-Nd isotopes on several samples of different lithologies of granitoid is reported to constraint its petrogenesis and tectonic setting. The result shows three granitic samples of different granularity from the Tashan bathoilth yield ages from 213.4 - 221.5 Ma, while one sample from Yangmingshan batholith yields a age of 213.7 - 1.0Ma, both of them belong to late Indosinian. Geochemically these samples are relatively enriched in SiO2 （70.43%- 74. 06%） and Al2O3 （A/CNK = 1.03 - 1.24） that can be easily identified as peraluminous series. Further discrimination indicates metagraywackes are the dominate source materials to the Tashan batholith, and metapelites to the Yangmingshan batholith. High Rb, Th, U, Ta abundances and strong depletion of Ba, Sr, Nb, Ti, Eu, elements indicates they experience high fractionation process. High （86Sr/87Sr）i ratios （0. 72993-0. 77391） and low eNa（t） values （-9.9- -12.11） with toM2 （Nd） of 1801- 1978Ma reveal that their sources have involved in the crustal cycle for a long time. Intergrated with Indosinian tectonic involvement of South China, partial melting of thickened middle crust under local extension-thinning mechanism may be the key factor controlling the granitic intrusionism of the Tashan- Yangmingshan region. 3523 Ma inherited core of one zircon show that ancient Archaeozoic basement did exist in this region.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2016年第2期284-303,共20页
Acta Geologica Sinica
基金
中国地质调查项目(12120114020701)
地质矿产调查评价项目(1212011120804)资助的成果
