苏皖坡缕石粘土中蛋白石特征及其成因意义  

CHARACTERISTICS AND SIGNIFICANCE OF OPALS IN PALYGORSKITE CLAY AT THE BOUNDARY BETWEEN JIANGSU AND ANHUI PROVINCES

作　　者：陈天虎[1] 徐晓春[1] Huifang Xu 岳书仓[1] 

机构地区：[1]合肥工业大学资源与环境工程学院,安徽合肥230009 [2]新墨西哥大学地球与行星科学系

出　　处：《矿物学报》2005年第1期81-88,共8页Acta Mineralogica Sinica

基　　金：国家自然科学基金项目(批准号:40072017;40331001)

摘　　要：TEM和XRD研究表明,在苏皖坡缕石粘土矿床的蛋白石坡缕石层中存在opal A和opal CT两种结构的蛋白石。蛋白石坡缕石层主要含坡缕石、opal A、opal CT,以及少量白云石和其它矿物,由富opal A层和富opal CT层互层组成,交互层的厚度在几个厘米左右。蛋白石坡缕石层中的矿物基本是自生矿物,从蒸发湖水中化学沉淀形成。矿物组成特征研究表明,蛋白石坡缕石层的矿物组分(Si、Mg、Al)来源于盆地周围玄武岩淋滤的浅层地下水。根据Opal A和Opal CT溶解度图解和坡缕石、白云石形成物理化学条件图解,当湖水具有高浓度溶解SiO2和Mg2+时,有利于opal A和坡缕石形成,当湖水具有低浓度溶解SiO2时,有利于opal CT结晶。因此,沉淀SiO2的结构状态取决于地下水补给的湖水溶解SiO2浓度。富opal A和富opal CT交互层的形成是古气候、古水文周期性变化的指示。富opal CT层指示高地下水补给流入量,低蒸发量,湖水低盐度和溶解组分,代表湿润气候时期;而富opal A层代表低地下水补给流入量,高蒸发量,高溶解组分浓度,代表干旱气候时期。TEM and XRD results showed that opals in the palygorskite opal layers of palygorskite clay deposits at the boundary between Anhui and Jiangsu Provinces are divided into opal-A and opal-CT. The palygorskite-opal layers consist of palygorskite, opal-A, opal-CT, a small amount of dolomite and other minerals. These layers show oscillation of opal-A-rich layer (OARLs) and opal-CT-rich layers (OCTRLs). The thickness of the layers may vary in a range of several centimeters. All these minerals are authigenic minerals that crystallized from solutions of evaporating lake. It is proposed that the components for the minerals (Si, Mg, Al) were supplied by shallow groundwater that is from surrounding basalt. OCTRLs indicate the periods of humid climate with a high input of groundwater and low evaporation that is low in soluble components. However, OARLs indicate the periods of dry climate with a low input of groundwater and high evaporation that contains high soluble components. The lake water with the high concentrations of soluble silica and other components favors the formation of opal-A and palygorskite. However, the lake water with the low concentrations of soluble silica and other components favors the crystallization of opal-CT with a small amount of palygorskite. So the formation of silica polymorphism is controlled by the concentrations of soluble silica in lake water that is derived mainly from groundwater. The oscillation of opal-A and opal-CT layers may be used as an indicator of odical changes of paleoclimate and paleohydrology.

关 键 词：粘土 蛋白石 成因分析 地质背景 矿物学特征 

分 类 号：P619.231[天文地球—矿床学]