豫西崤山韩沟岩体锆石U-Pb定年、地球化学特征及地质意义

Zircon U-Pb dating and geochemical features of Hangou granitic body in Xiaoshan Mountain, western Henan Province, and its geologic implications

韩沟二长花岗斑岩岩体位于崤山北部,其成因研究不仅可对崤山北部构造演化提供重要约束,而且可为区域找矿提供新思路。对韩沟岩体中黑云母二长花岗斑岩进行了LA-ICP-MS锆石U-Pb定年,20个测点的206Pb/238U年龄为142~147 Ma,加权平均年龄为(145.1±0.7)Ma。韩沟岩体具有高硅、富碱高钾、贫镁低钙的特征,属于富钾钙碱性花岗岩类(KCG)。韩沟岩体的稀土配分模式具有右倾、轻稀土富集及重稀土亏损的特征,(La/Yb)N范围为10.41~11.51,显示弱正Eu异常。韩沟岩体样品富集大离子亲石元素,亏损高场强元素Nb、Ta,在微量元素蛛网图上显示明显的Nb、Ta及Ti负异常。韩沟岩体具有高Sr、低Y和低Yb的特征,属于埃达克岩,Na_2O和K_2O含量表明其为C型埃达克岩。韩沟岩体是加厚大陆下地壳的部分熔融形成的,部分熔融源区的残余相矿物包括石榴石和金红石,且无(富钙)斜长石残留。崤山北部至少经历了~145 Ma和~130 Ma两次规模不等的岩石圈拆沉作用,韩沟岩体为~145Ma规模较小岩石圈拆沉作用的产物。韩沟岩体的形成时代与~145 Ma区域成岩成矿期相接近,在岩石圈拆沉作用这一灾变过程中,必然导致深部流体的大规模活动及其快速释放,表明韩沟岩体周缘及深部应具有较大的Au成矿潜力,其周缘11个Au矿床(点)就是最好的找矿证明。

Hangou monzonitic granite porphyry body lies in northern Xiaoshan Mountain,western Henan Province.Petrogenetic significant for estimating mineralization potential.The zircon U-Pb dating method of LA-ICP-MS was used to confirm the age of biotite monzonitic granite porphyry sample named LLHG01from Hangou rock body.The results of20zircon spots are consistent with207Pb/235U-206Pb/238U trend line,with206Pb/238U ages being from142Ma to147Ma,and weighted average age being(145.1±0.7)Ma.Hangou rock body is characterized by higher SiO2and alkali,enrichment of K2O,and lower MgO and CaO.Compositional spots of Hangou rock body fall into high-K calc-alkaline series in the SiO2-K2O diagram,and it belongs to K-rich calc-alkaline granite(KCG).In chondrite-normalized REE patterns,Hangou rock body samples have shown the characteristics of LREEenrichment and HREE depletion with trivial Eu positive anomaly,whose(La/Yb)N ratios are from10.41to11.51.Samples from Hangou rock body are enriched in large ion lithophile elements and depleted in high field-strength elements,which has formed troughs of Nb,Ta and Ti in spider diagram.Samples of Hangou rock body have higher Sr and lower Y and Yb,suggesting that Hangou rock body is adakite.According to the content of Na2O and K2O,Hangou rock body is C-type adakite.Hangou rock body originated from partial melting of the thickened lower crust,and its residual phases of partial melting source included garnet and rutile,with no plagioclase.North Xiaoshan Mountain area underwent the process of lithosphere delamination of different scales in^145Ma and^130Ma,and Hangou rock body is a product of smaller scale lithosphere delamination that occurred at^145Ma.The formation age of Hangou rock body falls into the time interval of^145Ma stage of acid magmatism and endogenetic mineralization in western Henan Province.In the disaster process of lithosphere delamination in Hangou area,huge deep fluids were driven and discharged rapidly,suggesting that Hangou rock body and its concealed part have large mineralization potential.There are11Au deposits and Au mineralization spots around Hangou rock body,which constitute the best exploration evidence.