滇西昌宁更戛乡下泥盆统向阳寺组硅质岩地球化学特征及构造环境探讨  

Geochemical characteristics and tectonic environment discussion of chert from the Lower Devonian Xiangyangsi Formation in Gengga, Changning, Western Yunnan

作　　者：胡元邦 侯中健[1] 邓江红[1] 李峥[1] 林寿海 杨蜜蜜[1] 

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]四川省地矿局区域地质调查队,四川成都610213

出　　处：《中国地质》2016年第2期650-661,共12页Geology in China

基　　金：四川省教育厅项目(80303-KZY006);中国地质调查局地质调查工作项目(12120113048700);成都理工大学国土资源部构造成矿成藏重点实验室及成都理工大学矿物学;岩石学;矿床学国家重点(培育)学科联合资助~~

摘　　要：滇西昌宁更戛乡下泥盆统向阳寺组位于冈瓦纳大陆与泛华夏大陆间昌宁—孟连结合带北段西侧。文章首次发现向阳寺组中存在硅质岩,并对其硅质岩的地球化学特征等进行了深入研究。硅质岩中发育海百合茎、放射虫及硅藻。地球化学分析表明,向阳寺组硅质岩Si O2质量分数为85.43%-93.50%,Al/（Al＋Fe＋Mn）平均值为0.77,处于生物成因范畴;硅质岩稀土元素分析结果为其REE总量平均值为53.208×10-6,稀土元素北美页岩标准化配分曲线相对平坦,δCe平均值为1.02,δEu平均值为1.01,LaN/CeN平均值为0.99,LaN/YbN平均值为0.84,表明硅质岩形成于近大陆边缘的深海沉积环境。随着早泥盆世昌宁—孟连洋的快速扩张,保山地块边缘区域性同沉积断裂发育,造成了更戛乡向阳寺组大面积的硅质岩沉积。结合硅质岩地球化学特征的分析与古生物研究,认为更戛乡向阳寺组硅质岩属冈瓦纳大陆保山地块边缘亲昌宁—孟连古特提斯洋的深海沉积的产物。The Lower Devonian Xiangyangsi Formation is located in the west of Changning-Menglian suture belt at the junction ofthe Gondwanaland and the Pan- Cathaysian continent in Gengga, Changning, western Yunnan. The chert was discovered in the Xiangyangsi Formation for the first time, and the geochemistry of the chert was studied. Crinoidal stems with radiolarians and diatoms are distributed in chert. An analysis of the data of major elements shows that the values of Si O2 are relatively high, being in the range of 85.43%- 93.50%, the average ratio of Al/（Al ＋ Fe ＋ Mn） obtained in chert is 0.77, suggesting that the chert of the Xiangyangsi Formation is characteristic of biogenesis activity, along with some chemical activity. An analysis of the data of REE shows that the values of REE are 53.208×10-6, δCe has a value of 1.02, and δEu has a value of 1.01. The average ratio of LaN/YbN and LaN/YbNis 0.99 and 0.84, suggesting the continental margin and deep-sea environment. With the rapid expansion of ChangningMenglian Ocean, a wide chert deposition took place due to the regional synsedimentary fault on the continental margin of Baoshan massif from Early Devonian. In combination with the characteristics of chert geochemical and the paleontological research, the authors hold that the Xiangyangsi Formation in Gengga is characterized by deep- sea deposition on the continental margin of Baoshan massif of Gondwanaland close to Changning-Menglian Paleo-Tethys Ocean.

关 键 词：古特提斯 昌宁—孟连带 下泥盆统向阳寺组 硅质岩 地球化学 构造环境 

分 类 号：P588.244[天文地球—岩石学]