苏鲁地体超高压矿物的三维空间分布

采用激光拉曼技术,配备电子探针和阴极发光测试,确认苏鲁地体大多数花岗质片麻岩,所有类型片麻岩、斜长角闪岩、蓝晶石英岩和大理岩的锆石中均隐藏以柯石英为代表的超高压包体矿物组合。其中花岗质片麻岩典型超高压包体矿物为柯石英±多硅白云母;副片麻岩为柯石英+石榴子石+绿辉石、柯石英±石榴子石+硬玉+多硅白云母+磷灰石、柯石英+多硅白云母±磷灰石;斜长角闪岩为柯石英+石榴子石+绿辉石±金红石;蓝晶石英岩为柯石英+蓝晶石+金红石+磷灰石、柯石英+蓝晶石+多硅白云母+金红石;大理岩为柯石英+透辉石、柯石英+橄榄石。表明苏鲁地体由榴辉岩及其围岩所组成的巨量陆壳物质曾普遍发生深俯冲,并经历了超高压变质作用。锆石的矿物包体分布特征及相应的阴极发光图像研究表明,在同一样品中,锆石的成因特征存在明显差异。有的锆石显示继承性(碎屑)锆石的核(core)、超高压变质的幔(mantle)和退变质的边(rim);有的锆石则具有超高压的核、幔和退变质的边;而有的锆石却记录了深俯冲的核、超高压的幔和退变质的边。标志着苏鲁超高压变质带各类岩石副矿物锆石均具有十分复杂的结晶生长演化历史。因此,在充分研究锆石中矿物包体性质、分布特征以及相应阴极发光图像的基础上,采用SHRIMP离子探针技术,在锆石晶体的不同

Three-Dimensional Distribution of Ultrahigh-Pressure Minerals in Sulu Terrane

Coesite-bearing ultrahigh-pressure mineral inclusions were identified in zircons from most granitic gneisses, all paragneisses, amphibolites, kyanite quartzites and marbles in the Sulu terrane. The UHP mineral inclusion assemblages are characterized by coesite? phengite in zircons from granitic gneisses, coesite + garnet + om-phacite, coesite? garnet+ jadeite +phengite + apatite and coesite+ phengite?apatite in zircons from paragneisses, coesite + garnet+ omphacite?rutile in zircons from amphibolites, coesite + kyanite + rutile + apatite and coesite + kyanite + phengite + rutile in zircons from kyanite quartzites, and coesite + diopside and coesite + olivine in zircons from marbles. These evidences suggest that voluminous continental materials, consisting mainly of protoliths of eclogite and country rocks were commonly subjected to deep subduction and ultrahigh-pressure metamorphism, and then rapidly returned to the earth's surface. In general, the distribution of mineral inclusions in zircons and cathodoluminescence images of zircons from the same zircon sample displays distinct zonings from core to rim. Some zircon grains can be genetically correlated with inherited (detrital) core (C), UHP metamorphic mantle (M) and retrogressive rim (R), some with UHP metamorphic core and mantle, and retrogressive rim, and still some with subduction core, UHP metamorphic mantle and retrogressive rim. These data indicate that the complex growth-evolution histories were preserved in zircons from all metamorphic rocks in the Sulu terrane. Cathodoluminescence images reveal irregular zoning patterns and various thicknesses of cores, mantles and rims. The abundance of inclusions complicates the conventional U-Pb age dating; therefore, the SHRIMP microspot U-Pb analyses are essential for protolith, ultrahigh-pressure and retrogressive age dating.