青岛榴辉岩相蛇绿混杂岩的岩石学证据及退变质P-T轨迹

ECLOGITE-FACIES OPHIOLITE MELANGE IN QINGDAO:ITS PETROLOGICAL EVIDENCE AND P-T PATH

青岛榴辉岩相蛇绿混杂岩发育在胶南隆起北缘地缝合线附近,构造侵位于胶南群云母斜长片麻岩中。它主要由斜方辉橄岩、玄武质和玄武安山质火山岩及少量杂砂岩和硅质岩组成。它与一般仰冲蛇绿岩的主要区别是:玄武质和玄武安山质岩石普遍遭受了榴辉岩相变质作用并发生强烈的糜棱岩化和退变质作用。强烈的退变质作用使大部分榴辉岩变为含石榴石石英斜长角闪岩,但仍保留有少量榴辉岩透镜体。它们可能是俯冲陆壳前缘岛弧地壳或岛弧型蛇绿岩残片的推覆体。它的退变质P-T轨迹表明,在其上升过程中热传导速率较高,这可能与该岩石强烈糜棱岩化和含水有关。

Eclogite-facies ophiolite melange in Qindao area was emplaced into mica-plagioclase gneiss of the Jiaonan Group, which is near the suture between the North China and Yangtze blocks. It is composed mainly of harzburgite, basaltic and basalt-andesitic lavas, and a small amount of graywacke and silicalite. The eclogite-facies ophiolite melange differs ftom genera 1 ophiolites in K-enrichment, strong ductile shear deformation or mylonitization, and eclogite-facies metamorphism of basaltic and basalt-andersitic volcanic rocks. Most of the eclogites have been retrograded into garnet-bearing amphibolite, and a few have been subjected to strong retrogressive metamorphism and occur as blobs or lenses in the garnet-bearing amphibolite. These suggest that the eclogite-facies ophiolite melange is a fragment of subducted oceanic crust uplifted by thrust. Its P-T path suggests that its thermal transmission was faster, which may be related with abundant water in these rocks.