黑龙江宝山一带海西晚期强过铝花岗岩地质地球化学及岩石成因

黑龙江宝山地区在构造上位于兴蒙造山带东部的松嫩地块和佳木斯地块之间的伊春-延寿花岗岩带北段,区内分布大面积的古生代-中生代花岗岩.其中海西晚期花岗岩,岩性主要为碱长花岗岩、二长花岗岩和花岗闪长岩等,锆石U-Pb法 LA-ICP MS测年结果为252.6±3 Ma.其主量元素表现出富Si、略富Al、富碱质和低Mg、低Ca的特点;微量元素表现出富集Rb、Nd、K、Pb、U和亏损Nb、Ta、P、Ti等高场强元素的特点,并且Sr、Ba呈明显的负异常;稀土元素具有明显的轻稀土元素富集、重稀土元素相对亏损的特征,轻重稀土元素分馏程度较高.岩石总体上属于高钾钙碱性花岗岩,是岩浆经历了高度结晶分异作用的产物.矿物化学和岩石地球化学特征表明其特征类似于S型花岗岩,源岩物质来自于地壳.

Geology-geochemistry and petrogenesis of Late Hercynian granites in Baoshan ar ea, Heilongjiang Province

The Baoshan area in Heilongjiang Province is tectonically located in the north of the Yichun-Yanshou fold belt lying between the Songliao Block and the Jiamusi Block in the east of the Xingmeng oregenic belt. Large volumes of Paleozoic-Mesozoic granitic rocks are distributed in this area. This paper deals emphatically on the Late Hercynian granitoids composed of alkali-feldspar granite, monzogranite and granodiorite. LA-ICP MS (laser inductively coupled plasma mass spectrometry) zircon U-Pb dating yielded an age of 252.6± 3 Ma. Major element analyses show high SiO_2 and alkali content, slightly high Al_2O_3 content and low MgO and CaO content. Trace element studies demonstrate the enrichment of Rb, Nd, K, Pb, U and depletion of HFSE (high field strength elements) such as Nb, Ta, P, Ti. The samples are enriched in LREE (light rare earth elements) and depleted in HREE (heavy rare earth elements), suggesting a high degree of fractionation. The granites generally belong to the high-K calc-alkaline series and might be produced by the magma that experienced a high degree of crystallization differentiation. Mineral chemistry and petrological geochemistry show that the granites are quite similar to S-type granite, with the material source derived from the crust.