黑龙江沙河子地区中侏罗世岩体地质地球化学特征及成因探讨

黑龙江沙河子地区岩浆活动强烈,主要岩体为似斑状黑云英云闪长岩、正长花岗岩、碱长花岗岩,通过对岩体进行锆石年龄分析测试和岩石地球化学的分析研究,结果表明似斑状黑云英云闪长岩、正长花岗岩、碱长花岗岩形成时代为中侏罗世。中侏罗世正长花岗岩—碱长花岗岩是同源岩浆经历了平衡部分熔融—结晶分异作用形成。中侏罗世岩体随SiO_2含量的增加,岩石从似斑状黑云英云闪长岩—正长花岗岩—碱长花岗岩,岩石由钙碱性演化为碱性,DI值进一步升高,SI值进一步降低,显示岩浆结晶分异程度愈来愈高,演化更彻底的特点。似斑状黑云英云闪长岩具有I-S型花岗岩特征,属于壳幔混合成因。中侏罗世正长花岗岩—碱长花岗岩,属于高钾钙碱性花岗岩类,具有A型花岗岩的特征,其形成与后造山—造山后构造环境相关。

Geochemical characteristics and genesis of middle Jurassic rock body in Shahezi area, Heilongjiang

Magmatic activity is intense in the Shahezi area of Heilongjiang Province. The main rock bodies are porphyritic biotite tonalite, adamellite and alkali feldspar granite. Through zircon age analysis and petrogeochemical analysis of the rock bodies, the results show that the porphyritic biotite tonalite, adamellite and alkali feldspar granite were formed in the Middle Jurassic. Middle Jurassic adamellite-alkali adamellite is a homologous magma formed by equilibrium partial melting-crystallization differentiation. With the increase of SIO₂ content, the rocks in the Middle Jurassic changed from porphyritic biotite tonalite-adamellite-alkali feldspar granite. The rocks changed from calc-alkaline to alkaline, the DI value further increased, and the Si value further decreased, indicating the characteristics of higher and higher crystallization differentiation degree and more thorough evolution of magma. The porphyritic biotite tonalite has the characteristics of I-S granite and belongs to the crust-mantle mixed origin. The Middle Jurassic adamellite-alkali adamellite belongs to high-potassium calc-alkali granite and has the characteristics of type A granite. Its formation is related to post-orogeny-post-orogenic tectonic environment.