摘要
白马山复式岩体位于湘西雪峰山弧形构造隆起带与湘中白马山-龙山-紫云山EW向构造带的交汇处,由水车、龙潭、小沙江和龙藏湾超单元花岗岩组成。锆石LA-ICP-MS U-Pb同位素定年显示,水车、龙潭、小沙江、龙藏湾超单元花岗岩的侵位年龄分别为424.9±2.2Ma、228.2±1.3Ma、225.3±1.1Ma和215.0±1.2Ma。水车超单元形成于加里东期,其余3个超单元花岗岩均形成于印支晚期,首次系统搭建了白马山复式岩体的年代学格架。印支期龙潭和小沙江超单元花岗岩具有低硅、低碱、准铝质-弱过铝质的特点,显示较强的Rb、Th、U、Pb正异常和Nb、Sr、P、Ti负异常,具有较弱的负Eu异常(δEu为0.55~1.07);富集Sr同位素[(~(87)Sr/~(86)Sr)i=0.719027~0.721297]、亏损Nd同位素[ε_(Nd)(t)=-10.5~-9.4]和锆石Hf同位素[ε_(Hf)(t)=-7.7~-4.1],具有古老的Nd同位素(1.76~1.85Ga)和Hf同位素(1.42~1.83Ga)二阶段模式年龄。相反,龙藏湾超单元花岗岩具有高硅、高碱、强过铝质的特点,显示较强的Rb、Th、U、Ta、Pb正异常和Ba、Nb、Sr、Ti负异常,显示强的负Eu异常(δEu=0.28~0.51)和高(~(87)Sr/~(86)Sr)i值(0.741441~0.748761),具有负的ε_(Nd)(t)值(-11.3~-10.7)和ε_(Hf)(t)值(-11.5~-3.5),Nd同位素(1.87~1.91Ga)和Hf同位素(1.47~1.97Ga)二阶段模式年龄更老。结合元素和同位素地球化学特征,可推断出龙潭和小沙江超单元花岗岩是华南古老地壳基底中基性变质火成岩混有变质沉积岩发生部分熔融形成的I型或者I-S过渡性质的花岗质岩石,而龙藏湾超单元花岗岩则由华南成熟度更高的古老地壳基底富粘土变沉积岩发生部分熔融形成的S型花岗岩。白马山复式岩体中印支期超单元花岗岩很可能是华南板块受印支板块碰撞挤压后地壳发生伸展减薄,由加厚的地壳发生部分熔融形成的。这些印支期花岗岩与其周缘的金、钨矿床在时、空上具有密切联系,可能具有良好的成矿潜力;湘中地区印支期花岗岩的成岩、成矿作用在强度和广度上可能远高于过去的传统认识。
The Baimashan granitic complex,located in the intersection of the NE-trending Xuefengshan arc uplift and the EWtrending Baimashan-Longshan-Ziyunshan structural belt,consists of Shuiche,Longtan,Xiaoshanjiang,and Longcangwan granite units.Zircon LA-ICP-MS U-Pb dating reveals that the Shuiche,Longtan,Xiaoshanjiang and Longcang units were emplaced at 424.9±2.2 Ma,228.2±1.3 Ma,225.3±1.1 Ma and 215.0±1.2 Ma,respectively.Granites from the Longtan and Xiaoshajiang units are metaluminous to weakly peraluminous with low Si and alkali contents.They are strongly enriched in Rb,Th,U and Pb,but depleted in Nb,Sr,P and Ti.They are characterized by relatively high REE concentrations with weakly Eu negative anomalies(δEu=0.55~1.07).All samples from Longtang and Xiaoshajiang units exhibit high(87 Sr/86 Sr)ivalues(0.741441~0.748761),and negativeεNd(t)(-10.5~-9.4)andεHf(t)(-11.5~-3.5)values with Proterozoic two-stage Nd(1.76~1.85 Ga)and Hf(1.42~1.83 Ga)model ages.In contrast,granite samples collected from the Longzangwan unit are strongly enriched in Rb,Th,U,Ta and Pb,but depleted in Ba,Nb,Sr,and Ti,with strongly Eu negative anomalies(δEu=0.28~0.51).The samples usually have relatively high(87Sr/86Sr)ivalues(0.741441~0.748761),negativeεNd(t)(-11.3~-10.7),andεHf(t)(-11.5~-3.5)values,with older Nd and Hf model ages of 1.87~1.91 Ga and 1.47~1.97 Ga,respectively.In combination with Sr-Nd-Hf isotopic and bulk-rock geochemical data,it can be concluded that the parental magmas of granites from the Longtan and Xiaoshajiang units were likely to be derived from the partial melting of the ancient intermediate-mafic meta-igneous rock and meta-sedimentary rock of the upper continental crust in South China.Granites of the Longcangwan unit were likely to be formed by reworking of meta-sedimentary materials and display S-type affinity.The Indosinian granites in the Baimashan granitic complex were probably emplaced under the extensional background after continental collision between the South China block and the Indo-China block.The Au-W deposits around the Baimashan complex are temporally and spatially related with the Indosinian granites,and therefore the Indosinian granites are potentially favourable for Au-W mineralization.The Indosinian granitic activities and related Au-W-(Sb)mineralization in central Hunan may be more prevalent and more intensive than conventionally considered during the past several decades.
作者
王川
彭建堂
徐接标
阳杰华
胡阿香
陈宪佳
WANG Chuan;PENG JianTang;XU JieBiao;YANG JieHua;HU A'Xiang;CHEN Xianjia(MOE Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring,School of Geoscience and Info-Physics,Central South Uniersity,Changsha 410083,China;State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550002,China;College of Civil Engineering,Hunan City University,Yiyang 413000,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2021年第3期805-829,共25页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41972090、41473043)资助。
关键词
白马山复式岩体
印支期花岗岩
岩石成因
成矿效应
湘中地区
华南
Baimashan granitic complex
Indosinian granite
Petrogenesis
Metallogenic effect
Centeral Hunan
South China
