Mineralogy and geochemistry at DSDP Leg 64 Holes

At DSDP Site 477, late Quaternary diatomaceous muds and delta-derived silty-sand turbidites at 2000 meters water depth have been extensively and progressively altered by a deep-seated heat source beneath a sill. Bulk petrologic and microprobe analyses have identified a crudely zoned paragenesis within 260 meters sub-bottom which ranges from unaltered to slightly altered oozes (0-50 m), anhydrite-dolomite claystones (105-125 m), illite-chlorite-pyrite claystones (125-140 m), chlorite-pyrite-calcite-carbonaceous claystones with traces of K-feldspar, albite, epidote (140-190 m), and chlorite-epidote-quartz-albite-pyrrhotite-sphene sandstone (190-260 m). Several petrologic features suggest rapid processes of ocean floor metamorphism: (1) friable and porous textures, (2) abundant relict grains with overgrowths, (3) idiomorphic habits on epidotes, feldspars, and quartz, and (4) a steep gradient in levels of alteration. Many aspects of this hydrothermal assemblage are similar to hydrothermally metamorphosed sandstones of the Cerro Prieto, Mexico, geothermal area.

在深海钻探计划（Deep Sea Drilling Project, DSDP）477站位，水深2000米处的晚第四纪硅藻质软泥及三角洲成因粉砂质砂浊积岩，已被岩床下方的深部热源广泛且持续地蚀变。全岩岩石学与微探针分析结果显示，海底以下260米范围内存在粗略分带的矿物共生组合：0~50米为未蚀变至轻微蚀变的软泥，105~125米为硬石膏-白云石粘土岩，125~140米为伊利石-绿泥石-黄铁矿粘土岩，140~190米为含微量钾长石、钠长石、绿帘石的绿泥石-黄铁矿-方解石-碳质粘土岩，190~260米为绿泥石-绿帘石-石英-钠长石-磁黄铁矿-榍石砂岩。多项岩石学特征指示该区域存在快速海底变质作用：(1) 疏松多孔的结构；(2) 大量发育增生边的残余颗粒；(3) 绿帘石、长石与石英呈自形晶习性；(4) 蚀变程度具有陡梯度变化。该热液矿物组合的诸多特征与墨西哥塞罗普列托（Cerro Prieto）地热区的热液变质砂岩极为相似。