板峪口组大理岩中的变质流体

The Metamorphic Fluid in Marble of Banyukou Formation

山西五台山区板峪口组大理岩的总体矿物组合为透闪石、金云母、白云石、方解石、微斜长石和石英,岩石变质时受缓冲作用控制。口泉主沟内绿帘石脉体中流体的X_(CO_2)为0.08,而围岩白云岩中X_(CO_2)大于0.4,同一地点脉体和围岩中变质溶液具有不同的X_(CO_2)说明溶液成分受缓冲作用控制。绿帘石脉体内溶液成分保持X_(CO_2)=0.8不变则说明溶液成分受渗滤作用控制。围岩内矿物组合为金云母、透闪石、方解石和白云石也说明溶液成分受渗滤作用控制。总的说来,本地区的变质溶液成分是缓冲作用加渗滤作用的综合结果。 本区变质时所通过的流体数量一般不超过岩石体积的1/4。当岩石内有单矿物脉体时,脉体内所通过的流体数量较高。绿帘石脉内所通过的流体大致相当于岩石体积(99％)。

The metamorphism of marble of Banyukou Formation in Wutaishan region, Shanxi province, is controlled by buffering process according to its total mineral assemblage of tremolite, phlogopite, dolomite, calcite, microclineane, quartz. The Xco_2 of fluid in epidote vein in the Kouquan valley is 0.08; while in its surrounding dolostone, larger than 0.4. The difference in Xco_2 in the vein and its surrounding rock also provides evidence that the fluid composition is controlled by buffering. The fluid composition in epidote vein remains unchanged, it shows that fluid composition is controlled by infiltration. The mineral assemblage in country rock is phlogopite, tremolite, calcite, and dolomite, which furthermore indicates that fluid composition is controlled by infilatration. To sum up, the metamorphic fluid composition in this region is controlled by combined buffering and infiltration.The infiltrated fluid is usually less than 1/4 rock volume. Where is monomineral vein, there is more abundant infiltrated fluid, which in epidote vein is as high as whole rock volume(99％).