北苏鲁变辉长岩锆石U-Pb年龄和Lu-Hf同位素组成及其对源区的指示

发布时间：2018-03-17 03:07

本文选题：岩浆锆石　切入点：变辉长岩　出处：《大地构造与成矿学》2017年02期 　论文类型：期刊论文

【摘要】：在北苏鲁经历超高压变质的花岗片麻岩中零星分布着一些变质表壳岩包体或者残片,通常称之为荆山群。北苏鲁荆山群的年代学特征以及构造亲缘性仍不清楚。本文报道了威海市郊和海阳所附近的荆山群露头,有脉状变质辉长岩侵入到荆山群岩系中。对上述两处变质辉长岩中锆石的阴极发光照片、稀土元素配分模式和Th/U比值的综合分析表明,它们均为岩浆锆石,部分岩浆锆石具有弱发光效应和岩浆韵律环带的核部、以及被改造的强发光效应的边部,但未见新生的变质锆石。未被改造的岩浆锆石微区的LA-ICP-MS U-Pb定年结果表明,威海市郊变辉长岩(S4-2)的~(207)Pb/~(206)Pb年龄值变化范围是1831~1966 Ma,加权平均年龄为1870±34 Ma(MSWD=0.6);海阳所变辉长岩(H3)中绝大部分锆石的~(207)Pb/~(206)Pb年龄值变化范围是1769~1887 Ma,加权平均年龄为1839±37 Ma(MSWD=0.5),两件样品共同记录了一致的ca.1.85 Ga岩浆事件。另外,海阳所变辉长岩中3颗捕获的岩浆锆石分别测得ca.2.9 Ga、ca.2.3 Ga和ca.2.1 Ga等三组~(207)Pb/~(206)Pb年龄。两件样品ca.1.85 Ga岩浆锆石具有相似的Hf同位素组成,其ε_(Hf)(t)=-6.1~-10.7,t_(DM2)=2.74~2.98 Ga,捕获ca.2.1 Ga和ca.2.9 Ga锆石的ε_(Hf)(t)值和t_(DM2)年龄分别是-1.9和2.7 Ga、-4.8和3.5 Ga。锆石U-Pb年龄、Lu-Hf同位素特征表明,北苏鲁两处变辉长岩记录的岩浆事件与胶北前寒武纪陆壳的多期演化历史一致,变辉长岩及其围岩荆山群可能是源自胶北的外来地质体。
[Abstract]:In the granitic gneiss which experienced ultrahigh pressure metamorphism in North Sulu, there are some metamorphic crust inclusions or fragments scattered in the granitic gneiss. It is commonly called Jingshan Group. The geochronological characteristics and structural phylogeny of Jingshan Group in North Sulu are still unclear. The outcrop of Jingshan Group in Weihai suburb and near Haiyang is reported in this paper. The dike metamorphic gabbro intruded into the Jingshan formation. The cathodoluminescence photographs of zircon from the two metamorphic gabbro rocks mentioned above, the REE distribution model and the Th/U ratio, show that they are magmatic zircon. Some magmatic zircon have weak luminescence effect and the nucleus of magmatic rhythmic ring belt, and the edge of the modified strong luminescence effect, but no new metamorphic zircon is found. The LA-ICP-MS U-Pb dating results of unmodified magmatic zircon microregion indicate that, The variation range of Pb age value is 1831 / 1966 Ma.The weighted average age is 1870 卤34 MaMSWD0. 6; the zircon of most zircon in Haiyang gabbro (H3) varies in the range of 1769 ~ 1887 Ma, weighted average age is 1 839 卤37 MaMMSWD ~ (0. 5), the range of zircon is 207PbP / P ~ (206) Pb age range is 1769 ~ 1887 Ma, weighted average age is 1 839 卤37 Ma-MSWD ~ (0. 5), two samples of zircon from Haiyang metamorphic gabbro (H3) vary in the range of 1769 ~ 1887 Ma, weighted average age is 1839 卤37 Ma-MSWDU ~ (0.5). The consistent ca.1.85 Ga magma events were recorded together. Three captured magmatic zircons from the altered gabbro in Haiyang, Haiyang, have been measured for three sets of zircons, such as ca.2.9 Gaanca.2.3 Ga and ca.2.1 Ga, respectively. The two samples of ca.1.85 Ga magmatic zircon have similar HF isotopic compositions. Its 蔚 -hfhftttig (-6.1) -10.7t ~ (-10. 7) T ~ (2 +) ~ + ~ (2) ~ (-) ~ (2.74) ~ (2.98) Ga.The 蔚 ~ (+) ~ (-1) of ca.2.1 Ga and ca.2.9 Ga zircon are -1.9 and 2.7 Ga-4.8 ~ (-4.8) and 3.5GaZr ~ (-4.8), respectively. The Lu-Hf isotopic characteristics of zircon U-Pb age indicate that the zircon U-Pb age is Lu-Hf isotopic characteristics of the zircon. The magmatic events recorded in the two metamorphic gabbro rocks in North Sulu are consistent with the multi-stage evolution history of the Precambrian continental crust in Jiaobei. The metamorphic gabbro and its surrounding rock Jingshan group may be from the exotic geological bodies in Jiaobei.
【作者单位】：青岛海洋地质研究所国土资源部海洋油气资源与环境地质重点实验室;中国地质大学(武汉)地球科学学院;中国海洋大学海洋地球科学学院;
【基金】：国家自然科学基金面上项目(41172189) 国土资源部中国地质大调查项目(GZH200800501、1212011220113)联合资助
【分类号】：P595;;P597

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