大兴安岭中段五岔沟地区蛤蟆沟林场A型花岗岩年代学、岩石地球化学及构造背景研究

对大兴安岭中部五岔沟镇蛤蟆沟林场花岗岩体研究结果表明，蛤蟆沟林场花岗岩体主要岩性组合为碱长花岗岩、黑云母正长花岗岩、黑云母二长花岗岩和花岗斑岩，其LA-ICP-MS锆石U-Pb测年结果为136.97±0.99Ma、135.85±0.78Ma、126.04±0.48Ma和135.87±0.49Ma，表明其形成时代为早白垩世。岩石主量元素具有富硅、富钾的特征，A/CNK值介于0.997~1.05之间，稀土元素相对富集轻稀土元素、亏损重稀土元素，并具有较为明显的Eu负异常，微量元素相对富集大离子亲石元素和高场强元素，贫Ba、Sr、Ti、P，这些特征表明蛤蟆沟林场花岗岩为铝质A型花岗岩，是中下地壳岩石部分熔融的产物，形成于大陆裂谷或板内构造环境（A1型花岗岩），代表了伸展的大地构造背景，可能是受到古太平洋俯冲和蒙古鄂霍次克洋闭合的双重影响。

Geochronology, petro-geochemistry and tectonic setting of Hamagou forest farm A-type granites in Wuchagou area, central Great Xinggan Range

This paper studys Hamagou forest farm granites in Wuchagou town, central Great Xinggan Range. The granites consist of alkali feldspar granite, biotite syenogranite, biotite adamellite and granite porphyry in lithology. The LA-ICP-MS zircon U-Pb determination yield concordant ages of 136.97±0.99Ma, 135.85±0.78Ma, 126.04±0.48Ma and 135.87±0.49Ma, indicating intrusive time of the granites is the early Cretaceous. The chemical analyses show that the granites have high SiO2, K2O contents, A/CNK ratios ranging from 0.997 to 1.05. The REE patterns are characterized by enrichment of LREEs relative to HREEs and distinct negative Eu anomalies in chondrite-normalized REE diagram. The trace elements relatively enrich large ion lithophile elements (LILE), high field strength elements (HFSE) and poor Ba, Sr, Ti, P. These features suggest that the Hamagou forest farm granites belong to aluminous A-type granite which derived from partial melting of middle or lower crustal rocks with a typical character of A1-type granite (rift valley or within plate) representing an extensional tectonic setting, which may be due to the double impact by the subduction of paleo-Pacific plate and the closure of Mongol-Okhotsk Ocean.