浙西晚中生代富碱高钾花岗岩类的岩石地球化学特征及构造意义

浙西晚中生代侵入岩分布广泛,在江山、龙游和遂昌三县(市)接壤地带厘定出一套富碱高钾花岗岩类。初步研究表明,以往被认为是I型的该套花岗质岩石应属铝质A型花岗质岩石,在空间上明显受江山—绍兴断裂带及其柘岱口—溪口断裂带的控制,呈北东向带状展布。该岩类由石英正长岩、石英正长斑岩、正长岩、石英二长岩、二长岩、二长花岗岩、花岗岩和花岗斑岩组成,以富碱高钾为显著特点,莱特碱度率 (A.R)为2.14~5.76,过碱指数(AKI值)为0.58~0.96 (平均0.83),偏铝到过铝质 (A/NKC＝0.93~1.30,平均1.05),富含稀土元素 (∑REE＝226.65×10^-6~429.18×10^-6)和较高的Zr＋Nb＋Ce＋Y元素组合值(282×10^-6~826×10^-6,平均482×10^-6),而亏损Ba、Ta、Nb、P、Ti等, 在Na₂O-K₂O>成因类型判别图解中全部落入A型花岗岩区,反映其具A型花岗质岩石的成分特征。洪公岩体与沐尘岩体的Nd同位素模式年龄为1.2~1.6Ga,反映其主要起源于地壳物质的部分熔融。区域背景、构造被动定位特点和地球化学综合分析表明,该套富碱高钾花岗岩类形成于后碰撞构造环境,是早白垩世早期该区重要的构造—岩浆热事件的产物。

Petrogeochemistry of Late Mesozoic alkali-rich potassium-high granitoid in western Zhejiang and its tectonic significance

The western part of Zhejiang features a wide distribution of late Mesozoic intrusive rock,where a set of alkali-rich potassium-high granitoid is recognized in the contiguous area among Jiangshan,Longyou and Suichang.Preliminary studies show that the formerly defined I-type granitoid is instead aluminum base A-type granitic rock,and that it is stretched in band-shaped north-east direction under obvious controls of Jiangshan-Shaoxing fault zone and Zhedaikou-Xikou fault zone in space.This type of rock is comp...