摘要
四川宣汉地区二叠系茅口组和吴家坪组的硅岩,主要以结核状、条带状和团块状产出。根据硅岩的岩石学及地球化学特征,对其成因进行了系统研究。野外观察硅岩形态多样,与围岩呈缝合线状接触,在剖面上受一定层位控制,团块状硅岩中含石灰岩斑块等。显微镜下观察,硅岩中见方解石残余结构及白云石菱形假晶等。野外观察和显微镜下观察表明这些硅岩应为交代作用形成。常量元素分析表明硅岩以SiO2为主(69.61%～99.21%),其他化学成分含量较低(0.01%～16.07%),Fe/Ti、(Fe+Mn)/Ti及Al/(Al+Fe+Mn)值反映了硅岩的形成与热水活动有关,样品点在Al-Fe-Mn三角图中的投影位于富铁端;微量元素Co/Ni、V、Ti/V、Th/U和Rb/Sr值都较低,样品点在(Cu+Co+Ni)-Fe-Mn三角图中的投影也位于富铁端;硅岩中稀土元素总量低(低于10×10-6),Ce明显负异常,Eu弱负异常,LREE/HREE值低,Eu/Eu*值相对较高。上述特征表明研究区硅岩在形成过程中有热水物质参与沉积,在成岩过程中通过SiO2交代作用形成。
Nodular, striped and lump-shaped siliceous rocks of the Permian are primarily distributed in the Maokou and Wujiaping Formations in Xuanhan region, Sichuan Province. The origins of the sili- ceous rocks have been researched systematically based on their lithological and geochemical characteris- tics. Field observations about the siliceous rocks suggest that the shape of siliceous rocks is diversified, and they contact with surrounding rocks in line shape. They are controlled by certain position in the sec- tion, and the lump-shaped siliceous rocks contain limestone nodules. Thin section analyses suggest the relic texture of calcite and dolomite rhombus pseudomorphic crystal could be found in the siliceous rocks. Field observations and thin section analyses suggest the origin of siliceous rocks is metasomatosis. The ma- jor element analysis indicates SiO2 is the main chemical composition （69.61%--99.21%）, others are extremely lower （0.01%--16.07% ）, some major element ratios of Fe/Ti, （Fe＋Mn）/Ti, A1/（ Al＋Fe＋ Mn） reflect the formation of siliceous rocks is associated with the hydrotherm activities, and the samples are projected in the unit where Fe being rich in the A1-Fe-Mn diagram; Stone trace element ratios including Co/Ni, V, Ti/V, Th/U, Rb/Sr are relatively lower, and the samples are projected in the unit where Fe being rich in the （Cu＋Co＋Ni） -Fe-Mn diagram too; The ZREE （〈10×10^-6） is lower, Ce is remarka- ble negative anomalies, Eu is negative anomalies slightly, LREE/HREE is lower and the Eu/Eu＊ is rela- tively high. All these features above suggest that there may be hydrotherm participating in during the sedi- mentary proeess, and siliceous rocks are formed by metasomasis during the diagenetic process.
出处
《古地理学报》
CAS
CSCD
北大核心
2009年第6期670-680,共11页
Journal of Palaeogeography：Chinese Edition
基金
中国石油化工股份有限公司海相油气勘探前瞻性项目"南方二叠系定量岩相古地理研究与油气预测"的部分成果
关键词
硅岩
地球化学特征
成因机制
二叠系
四川宣汉
siliceous rocks, geochemical character, mechanism of origin, Permian, Xuanhan region of Sichuan Province
