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为了揭示闽西南龙岩地区大洋、莒舟花岗岩体的成因、侵位时代及其与成矿的关系,在岩石学、地球化学研究基础上,利用LA-MC-ICPMS锆石U-Pb、Lu-Hf同位素测试方法对上述岩体进行年龄测定及铪同位素示踪。岩石学特征表明大洋、莒舟岩体具有多期次侵入特征,岩性主要为花岗岩、似斑状花岗岩以及花岗闪长岩。大洋岩体花岗闪长岩的年龄为(136.2±0.9)Ma,细粒花岗岩的年龄为(125.0±1.7)Ma,似斑状花岗岩的年龄为(132.0±0.2)Ma,莒舟似斑状花岗岩的年龄为(132.4±0.8)Ma。岩石地球化学成分上具有富硅、富铝、低钛、高钾钙碱性特征,富集大离子亲石元素(K、Rb、Cs、Pb等),亏损高场强元素(Nb、Ta、Zr、Ce、Ti等),微量元素表现出后造山伸展背景的特征。稀土含量较低,总稀土含量分别为92.76×10–6~176.26×10–6和116.63×10–6~213.95×10–6,具有显著的负铕异常(δEu=0.01~0.54)和稀土分布模式差异性特征。总体上具有较高的Na2O+K2O值、Ga/Al值及Rb含量,低Zr含量,具有高分异Ⅰ型花岗岩成因特征。两个代表性样品锆石εHf(t)值分别为–16.47~–5.95和–11.05~–3.35,对应的二阶段模式年龄分别为1567~2221 Ma和1400~1889 Ma,来源于古元古—中元古代地壳物质重熔。在以上研究基础上,讨论了两个岩体的成因及其所代表的构造环境,进而探讨了大洋、莒舟花岗岩与成矿的关系。
In order to reveal the genesis and emplacement age of the oceanic and Qiongzhou granite bodies and the relationship with mineralization in the Longyan area, western Fujian Province, based on the petrology and geochemistry, the zircon U-Pb and Lu- Hf isotope test method for the age of the rock mass determination and hafnium isotope trace. Petrological characteristics indicate that the oceanic and Qiongzhou plutons have multi-stage intrusive characteristics, and the lithologies are mainly granite-like granulite and granodiorite. The age of granodiorite in Dayang pluton is (136.2 ± 0.9) Ma, the age of fine granite is (125.0 ± 1.7) Ma, the age of plagioclase granite is (132.0 ± 0.2) Ma, The age was (132.4 ± 0.8) Ma. The geochemical composition of rocks is rich in silicon, aluminum, titanium, high potassium and calcium alkaline, enrichment of large ion lithophile elements (K, Rb, Cs, Pb, etc.), loss of high field strength elements (Nb, Ta, Zr, Ce, Ti, etc.). Trace elements show the characteristics of post-orogenic extension. The content of rare earth is low and the content of total rare earths is 92.76 × 10-6 ~ 176.26 × 10-6 and 116.63 × 10-6 ~ 213.95 × 10-6, respectively. There are significant negative Eu anomaly (δEu = 0.01 ~ 0.54) and REE Pattern difference characteristics. In general, it has high Na2O + K2O, Ga / Al and Rb contents and low Zr contents, and is characterized by the genesis of high-differentiation type I granites. The εHf (t) values of zircons from two representative samples are -16.47 ~ -5.95 and -11.05 ~ -3.35 respectively, and the corresponding two-stage models are 1567-2221 Ma and 1400-1889 Ma, respectively, derived from the Paleoproterozoic- Middle Proterozoic crust material remelting. Based on the above studies, the genesis of the two rock mass and the tectonic environment it represents are discussed. Then the relationship between the oceanic and Qiaozhou granites and mineralization is discussed.