胡正祥,陈超,毛新武,杨青雄,邓乾忠,孔令耀,杨成

• 1:湖北省地质调查院

摘要(Abstract)：

在《湖北省区域地质志》修编过程中,将原花山群北部沿着土门—小阜—园潭一带分布的一套火山岩夹少量碎屑岩组合解体出来,新定义为土门岩组,代表青白口纪扬子北缘的一套岛弧火山—碎屑岩建造,标准剖面在李家塆—土门公路边。土门岩组以基性玄武岩为主,中性安山岩和酸性英安岩、流纹岩次之,局部夹有少量的火山碎屑岩和粉砂岩,受后期构造活动影响产生一定程度的变形和轻微的变质作用。土门岩组火山岩SiO_2的含量为50.47%~81.57%,由基性、中性、酸性三个端元组成,大部分表现为钙碱性系列的特点,少量表现为拉斑玄武岩系列特点,轻稀土元素(LREE)富集,具有"右倾"的稀土配分模式以及一定程度的负Eu异常,富集大离子亲石元素(LILE)RB、Ba、K、Pb,亏损高场强元素(HFSE)Nb、Ta、Ti等,这些特征与典型的岛弧火山岩基本相符。分别对土门和园潭酸性火山岩进行LA-ICP-MS锆石U-Pb测年,获得土门英安岩成岩年龄为841 Ma,园潭酸性火山岩的成岩年龄为(827.9±5.9)Ma(MSWD=0.57),二者同属青白口纪,都代表土门岩组火山岩的形成时间。土门岩组岛弧火山岩可能是扬子北缘晋宁期洋陆俯冲消减的产物,结合已经获得的三里岗岛弧中酸性侵入岩858~876 Ma和基性辉长岩871 Ma年代学资料,说明扬子北缘大洪山地区至少在876~828 Ma发生了一定规模的洋—陆俯冲消减作用。

关键词(KeyWords)： 岩石地层;化学地层;锆石U-Pb测年;地球化学;岛弧火山—碎屑岩;土门岩组;青白口纪;扬子北缘

Abstract:

Keywords:

基金项目(Foundation): 湖北省地质局科技项目(KJ2015-1);; 中国地质调查局项目(12120113012800、DD20160030-06)资助

作者(Author): 胡正祥,陈超,毛新武,杨青雄,邓乾忠,孔令耀,杨成

DOI: 10.19839/j.cnki.dcxzz.2017.03.009

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