黑龙江东部桦南地区早白垩世花岗闪长斑岩的成因及其地质意义

Petrogenesis of Early Cretaceous granodiorite-porphyry from Huanan area in eastern Heilongjiang and its geological implication

为确定黑龙江省东部桦南地区早白垩世花岗闪长斑岩的岩石成因及其构造背景,对花岗闪长斑岩样品进行了锆石U-Pb年代学与地球化学测试分析。LA-ICP-MS锆石U-Pb同位素分析结果显示,桦南地区花岗闪长斑岩形成于(123±1)Ma的早白垩世。岩石具有较高的SiO_2(66.06%~68.75%)和全碱(6.40%~7.23%)含量,较低的MgO(1.19%~1.50%)含量,并且富集大离子亲石元素(Rb、Ba、Th、U、K)和轻稀土元素,亏损Nb、Ta、Ti及P元素,显示其具有I型花岗岩属性。花岗闪长斑岩的正ε_(Hf)(t)值(+6.30^+11.51)及其二阶段模式年龄(778~445Ma)指示其原始岩浆来源于新生地壳物质的部分熔融。结合年代学、地球化学特征与区域地质调查结果,认为桦南地区早白垩世花岗闪长斑岩的形成与太平洋板块的俯冲作用有直接联系。

To determine the petrogenesis and tectonic setting of the Early Cretaceous granodiorite-porphyry from Huanan area in eastern Heilongjiang, zircon U-Pb dating and geochemical analyses on the granodiorite-porphyry samples are carried out. The results of LA-ICP-MS zircon U-Pb dating indicate that the granodiorite-porphyry in Huanan area formed during the Early Cretaceous with the age of (123 ± 1) Ma. These rocks show characteristics of I-type granites based on their contents of high Si02 (66. 06% ?68. 75% ) and Na20 + K20 (6. 40% ?7. 23% ) , with low MgO (1. 19% ?1. 50% ) , enrichment in large ion lithophile elements ( e. g . ,Rb, Ba, Th,U , K) and light rare earth elements, and depletion in Nb, Ta, Ti and P. The positive s m (t) values ( +6. 30 ^+ 11.51) of the granodiorite-porphyry and their corresponding Hf two-stage model ages (778 ?445 Ma) indicate that the parental magma was derived from partial melting of juvenile crustal material. According to the geochronological data, geochemical features and regional geological surveying, the authors propose that the formation of the Early Cretaceous granodiorite-porphyry in Huanan area was related to the subduction of Paleo-Pacific Plate.