塞浦路斯特罗多斯型洋壳最上部500米剖面(CY—1钻孔)中的不透明矿物、磁性及其蚀变作用的研究

Cyprus Drillhole CY-1:Oxide Petrography,Magnetic Properties and Alteration in a Section the Uppermost Half Kilometer of Troodos Type Oceanic Crust

引言近十年来为了鉴别大洋盆地中线性磁异常模式的起源,对洋壳磁化强度的研究显示了极大的兴趣。目前了解洋壳(尤其在深部)可以通过几种方法,如在推测为构造断崖的附近进行海底拖曳打捞、通过大洋基底钻探或通过考察蛇绿岩剖面等。拖曳打捞和钻探均可从原地洋壳的各个层位获得样品,但是在钻探大洋基底时,大多数钻孔的穿透小于100米,一些深孔也小于600米。

Stusdy of the oxide minerals and measurement of the megnetic properties of about 100 samples distributed over a 475m continuous drillcore section from the uppermost part of extrusive sequence of the Troodos,Cyprus,ophiolite close to 3503’N,3310’E in the vicinity of Malounda yields the following major results:-Low temperature alteration is intense to a depth of 260 m,below which it is relatively much subdued.-Saturation magnetization,natural remanence intensity and initial susceptibility all increase continuously with depth throughout the section.-Curie temperature decreases with depth to 260 m,below which a change in the style in the thermal decay of magnetization behaviour takes place.-Pillowed and massive flows differ in their magnetic properties.The rdsults are consistent with the downwards decrease in low temperature alteration previously noted from the distribution of secondary minerals.The downwards variations in magnetic properties closely follow in both sense and magnitude of the trends observed in DSDP Hole 417A.This supports the inter-pratation of the upper,reddened facies of the Troodos extrusive sequence as being due to prolonged drawdown of cold sea water,and suggests that the magnetization of at least the upper part of the Troodos ophiolite is a reliable guide to ocean crust magnetization.