摘要
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。
During the revision of new regional geology of Hubei Province, we first defined Tureen Forma- tion-complex as a suite of volcanic rocks with a small amount of clastic rock, which were previously regar- ded as part of the Huashan Group. The Tureen Formation-complex is distributed in the Tumen-Xiaobu- Yuantan area and represents late Qingbaikouan island arc volcanic-sedimentary rocks in the northern mar- gin of Yangtze block. The type section is located along the Lijiawan-Tumen road in Tureen County. The Tureen Formation-complex mainly consists of basic basalt, with some intermediate andesite and felsic da- cite, rhyolite, and minor amount of pyroclastic rock and siltstone. Affected by the tectonic activities, the Tumen Formation-complex is moderately deformed and slightly metamorphosed. SiO2 composition of the volcanic rocks in the Tumen Formation-complex ranges from 50.47% to 81.57%, consisting of mafic, in- termediate, and felsic end members. Most volcanic rocks show features of calc-alkalic sequence and a few of them show features of tholeiite sequence. Rare earth elements in these volcanic rocks are LREE-en- riched, with a right-inclined pattern, some degree of negative Eu anomalies, enrichment in large ion litho- phile elements （such as Rb, Ba, K, and Pb）, and depletion in high field-strength element （such as Nb, Ta, and Ti）. These geochemical features are characteristic of island arc volcanic rocks. LA-ICP-MS zircon U-Pb ages of felsic volcanic rocks of the Tumen Formation-complex at Tumen and Yuantan are 841 Ma and 827.9±5.9 Ma （MSWD=0. 57） respectively, suggesting that the Tumen Formation-complex is Qingbaik- ouan in age. These island arc volcanic rocks may have been the products of oceanic-continental collision in the northern margin of the Yangtze block during the Jinning Orogeny. Together with 858-876 Ma island arc intermediate-felsic intrusive rocks and 871 Ma mafic gabbros at Sanligang, volcanic rocks in the Tumen Formation-complex indicate that oceanic-continental collision occurred in the Dahongshan region, northern margin of Yangtze block, around 876-828 Ma.
作者
胡正祥
陈超
毛新武
杨青雄
邓乾忠
孔令耀
杨成
HU Zheng-xiang CHEN Chao MAO Xin-wu YANG Qing-xiong DENG Qian-zhong KONG Ling-yao YANG Cheng(Hubei Geological Survey, Wuhan 43003)
出处
《地层学杂志》
CSCD
北大核心
2017年第3期304-317,共14页
Journal of Stratigraphy
基金
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
关键词
岩石地层
化学地层
锆石U—Ph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
lithostratigraphy, chemostratigraphy, zircon U-Pb dating, geochemistry,island arc volcanic- clastic rocks, Tumen Formation-complex, Qingbaikou Period, Yangtze Block
