ABSTRACT

The Badajoz-Córdoba Unit (BCU, SW Iberian Massif) is a Variscan high-P unit mainly constituted by metapelites, metagreywackes, orthogneisses, Grt-amphibolites, and retrogressed eclogites (high-P metamorphism at c. 377 Ma). Discovery of rare metapelites with well-preserved high-P mineral assemblages, including large garnets up to 1 cm in diameter with abundant inclusions, chloritoid (up to X_Mg = 0.32), kyanite, staurolite, chlorite, phengite (up to Si = 3.16 apfu), paragonite, margarite, and rutile, allows detailed determination of the tectonothermal evolution of the unit. Pseudosection modelling of representative samples indicates that this mineral assemblage formed in blueschist facies (near eclogite facies transition) at P conditions higher than 20 kbar at c. 525°C and that it underwent a subsequent severe exhumation and moderate heating. The lithological composition of the BCU, the age of high-P metamorphism and the characteristics of the high-P mineral assemblages are similar to those found in other high-P and low to intermediate-T units of the Variscan Orogen. All these units form part of a single blueschist-eclogite facies metamorphic belt formed during Late Devonian subduction of the external margin of Gondwana.

摘要

Badajoz-Córdoba Unit (BCU, SW Iberian Massif) 是一个 Variscan 高压单元，主要由变泥质岩、变灰岩、正方麻岩、Grt 角闪岩和后退榴辉岩（约 377 Ma 的高压变质作用）构成。发现具有保存完好的高 P 矿物组合的稀有变泥质岩，包括直径达 1 厘米的大石榴石，具有丰富的包裹体、绿泥石（高达 X _Mg = 0.32)、蓝晶石、十字石、绿泥石、菱沸石（最高 Si = 3.16 apfu）、云母、玛格丽特和金红石，可以详细确定单元的构造热演化。代表性样品的伪剖面模型表明，这种矿物组合在蓝片岩相（近榴辉岩相转变）中形成，P 条件高于 20 kbar，c。525°C，并随后经历了严重的挖掘和适度的加热。BCU的岩性组成、高P变质作用时代和高P矿物组合特征与Variscan造山带其他高P和中低T单元相似。所有这些单元构成了在冈瓦纳外缘晚泥盆世俯冲期间形成的单个蓝片岩-榴辉岩相变质带的一部分。