Stratigraphy, petrography and tectonics of the manganese-bearing Buritirama Formation, Northern Carajás Domain, Amazon Craton

Abstract The Buritirama Formation (BF) occurs at the extreme north of the Carajás Province, close to the contact with the Bacajá domain, in the southeastern portion of the Amazon Craton (Brazil). The BF consists of a 40 km long, ca. 3 km wide NW-SE trending structure arranged in four imbricated thrusts that individualize three main stratigraphic units. The lower unit is composed of orthoquartzite followed by carbonate-silicate rocks. The intermediate unit hosts a supergene manganese ore deposit formed by weathering of kutnohorite-rich marble. Quartzite/mica-quartz schist followed by carbonate-silicate rocks make up the upper unit. The local basement is constituted by orthogneiss-migmatite (Xingu Complex) and the Buritirama metagranite. Mineral chemistry data and metamorphic textures record high consumption of carbonate and quartz to produce clinopyroxenes. The structural assemblage of the BF records mass transport from NE to SW and the following deformational phases: D1 (compressional ductile), D2 (compressional brittle) and D3 (extensional brittle). The BF is interpreted as part of a platformal depositional system positioned at the border of the Carajás domain, which was probably inverted, deformed and metamorphosed during the Transamazonian event (ca. 2.1 Ga), in a deformation belt related to the amalgamation between the Carajás and Bacajá domains.

**摘要** 布蒂里马组（Buritirama Formation, BF）出露于巴西亚马逊克拉通（Amazon Craton）东南部的卡拉加斯省（Carajás Province）最北端，紧邻巴卡哈地块（Bacajá domain）接触带。该组地层发育长约40 km、宽约3 km的北西-南东向构造带，由4条叠瓦逆冲断层划分为3个主要地层单元：下部单元以正石英岩（orthoquartzite）为主体，后续层位为碳酸盐-硅酸盐岩；中部单元赋存由富锰方解石（kutnohorite）大理岩经风化作用形成的表生锰矿床；上部单元由云母石英片岩（mica-quartz schist）及后续的碳酸盐-硅酸盐岩构成。区域基底由正片麻岩-混合岩（Xingu Complex，欣古杂岩）与布蒂里马变花岗岩（Buritirama metagranite）组成。矿物化学数据与变质组构记录了碳酸盐与石英大规模消耗以形成单斜辉石（clinopyroxenes）的过程。BF的构造组合记录了北东向南西的物质运移，以及先后3期变形作用：D1（压缩韧性变形）、D2（压缩脆性变形）与D3（伸展脆性变形）。研究认为BF属于卡拉加斯地块边界处的台地沉积体系的一部分，该体系可能在约2.1 Ga的亚马孙造山事件（Transamazonian event）中发生构造反转、变形与变质作用，其形成于与卡拉加斯地块与巴卡哈地块拼合相关的变形带内。