甘肃北山造山带南缘石板泉一带花岗岩地球化学特征及构造意义

GEOCHEMICAL GHARACTERISTICS OF GRANITE IN SHIBANQUAN AREA OF BEISHAN OROGENIC BELT AND ITS TECTONIC SIGNIFICANCE

甘肃北山石板泉岩体锆石U-Pb年龄为211～200 Ma;211～214 Ma;215～216 Ma,侵入时代为晚三叠世诺利阶（Norian）,岩石具高硅低铝、富钾贫钠、非常低Sr（37.1×10-6～94.7×10-6）高Yb（2.19×10-6～4.1×10-6）的南岭型花岗岩特征,A/CNK=0.89～0.96之间,σ=1.82～2.54。明显富集Rb、Th、K等大离子不相容元素（LILE）,亏损Ti、Sr、P、Nb、Ta等高场强元素（HFSE）,稀土元素分布曲线呈明显的＂燕式＂型,其形成可能来源于下地壳部分熔融,源区深度较浅、水含量、压力和氧逸度均很低,处于还原状态下的伸展构造背景。研究其区域构造—岩浆演化,对认识北山地区构造演化和指导区域矿产预测评价均具有重要的理论和实际意义。

The granite of U-Pb age has 211 ~200Ma, 211 ~214Ma, 215 ~216Ma in Shibanquan area,intrusive age of Late Triassic Norian（three Norian）, their characteristics has high silicon low aluminum, sodium potassium rich lean, very low Sr Sr（37.1×10-6~94.7×10-6）high Yb（2.19×10-6~4.1×10-6）, A / CNK mediated in between 0.89~0.96, σ is between 1.82~2.54. The geochemical characteristics of trace elements in the rocks show that significantly enriched in Rb, Th, K ions are incompatible elements（LILE）, obviously depletion of Ti, Sr, P,Nb, Ta and other elements（HFSE）, rare earth element distribution curve shows obvious ＂swan＂, its formation may be derived from partial melting of the lower crust, low water content,low pressure and low oxygen fugacity, the extension of reduction conditions tectonic background. Study on the regional tectonic, magmatic evolution, to understanding of the tectonic evolution and guide regional mineral prediction and assessment of the Beishan area has important theoretical and practical significance.