Leucocratic syenogranites the Macururé Domain, Sergipano Orogenic System, Northeastern Brazil: Glória Sul Stock

ABSTRACT: The Glória Sul Stock (SGS) (41 km2) is a round-shaped pluton, which intrudes the metasediments of the central area of the Macururé Domain, in the Sergipano Orogenic System (SOS). The stock encompasses a number of leucocratic syenogranites, including biotite syenogranite, muscovite-biotite bearing syenogranite and muscovite syenogranite. Mafic microgranular enclaves with syenitic composition are abundant in the biotite syenogranites but very rare in the muscovite-biotite bearing syenogranites. The syenogranites are predominantly metaluminous although the more evolved rocks show a peraluminous character. They can be classified as I-type and high-K calc-alkaline rocks. The syenitic enclaves are metaluminous and show shoshonitic geochemical characteristics. Geochemical modeling suggests that petrological diversity may be explained by considering mixing between peraluminous magma with ca. 73% SiO2 and a mafic shoshonitic magma with ca. 56% SiO2. Trace elements contents (Ba = 1,179 - 319 ppm; Rb = 351 - 55.3 ppm; Y = 16.7 - 1.6 ppm) are higher in the enclaves than in the granites. REE contents range from 38.58 - 299.21 ppm; LaN/YbN = 12.57 - 137.22 and Eu/Eu* = 0.72 - 1.94. The present data indicates that granitogenesis in the Macururé Domain (DM) is complex as well as that the widespread leucocratic syenogranites are post-tectonic, having been generated through interaction between peraluminous rhyolitic magmas and mantellic shoshonitic magmas.

摘要：格洛里亚苏尔岩株（SGS）面积为41 km²，属圆形深成岩体，侵入于塞尔吉帕诺造山带（Sergipano Orogenic System, SOS）马库鲁雷构造域中部的变沉积岩中。该岩株发育多种浅色正长花岗岩类岩石，包括黑云母正长花岗岩、含白云母-黑云母正长花岗岩以及白云母正长花岗岩。以正长岩成分为主的镁铁质微粒包体在黑云母正长花岗岩中较为富集，但在含白云母-黑云母正长花岗岩中极为罕见。该类正长花岗岩整体为准铝质，而演化程度更高的岩石则表现出过铝质特征，可归类为I型高钾钙碱性岩石。正长岩质包体为准铝质，具备钾玄岩系地球化学特征。地球化学模拟结果表明，其岩石学多样性可通过SiO₂含量约73%的过铝质岩浆与SiO₂含量约56%的镁铁质钾玄岩质岩浆的混合作用得到合理解释。包体的微量元素含量（Ba=1179~319 ppm；Rb=351~55.3 ppm；Y=16.7~1.6 ppm）高于花岗岩类岩石。稀土元素（Rare Earth Elements, REE）含量介于38.58~299.21 ppm之间，标准化镧/镱比值（LaN/YbN）为12.57~137.22，铕异常值（Eu/Eu*）为0.72~1.94。本次研究数据显示，马库鲁雷构造域（DM）的花岗岩成因作用较为复杂，且广泛分布的浅色正长花岗岩类岩石为后构造期产物，其形成源于过铝质流纹质岩浆与幔源钾玄岩质岩浆的相互作用。