Nueva interpretación petrológica y tectónica de las anfibolitas pobres en calcio del antiforme de Arinteiro (NO del Macizo Ibérico). I: Descripción de las anfibolitas pobres en calcio y rocas asociadas

Abstract

Ca-poor amphibolites are characterized by unusual mineral assemblages, and they can be related to different tectonic settings. In this work we describe the amphibolites that outcrop in the Arinteiro massif. In this massif, a great variety of litologies occurs among which amphibolites, garnet-bearing fine-grained amphibolites, Ca-poor amphibolites and calc-silicate rocks are the most abundant. In the first part of the paper we describe the different associations found both in the Ca-poor amphibolites and in the calc-silicate rocks ofthe Arinteiro massif. The mineral chemistry ofthe Ca-poor amphibolites shows a progressive impoverishment in calcium of the different associations. Previous works assigned the origin of this massif to hidrothermal alteration of an ophiolite. However, its structural position over the ophiolitic units, the probable linkage to shear zones and the calcium impoverishment, all point to a different origin for this massif, probably related to fluid circulation in shear zones, as it is proposed in the second part of this paper