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Reconstruction of the effusive and explosive deposits of the Aruri and Salustiano formations in the Tapajós Domain, Southern Amazonian Craton, from field relationship, petrography and geochemistry
Journal of South American Earth Sciences ( IF 1.7 ) Pub Date : 2021-04-01 , DOI: 10.1016/j.jsames.2020.103095
André Massanobu Ueno Kunifoshita , Felipe Holanda dos Santos , João Gabriel Motta

Abstract Proterozoic Silicic Large Igneous Provinces (SLIP) are part of the geological inventory since they record the planet's thermal evolution. The Amazonian Craton hosted the poorly understood Uatuma SLIP, which formed ca. 1.88 Ga years ago. The so-called Uatuma magmatism represents the volcanic products of SLIP. This magmatism also refers to specific stratigraphic units, such as the Uatuma, Iriri, and Iricoume groups. The Aruri and Salustiano formations within the Iriri Group represent an important SLIP stratigraphy segment transitioning from effusive to explosive volcanism. However, this interval is still undisclosed and lacks a thorough comparison of the Iriri Group stratigraphy. From field observations, detailed petrographic description, new geochemistry data on the Aruri and Salustiano formations, and a compilation of geochemistry data on the Uatuma SLIP, we present the litho-stratigraphy for the two formations and a comparison to the other levels of the SLIP stratigraphy. Our data show a predominance of effusive over explosive volcanism and a set of intermediate rocks that intrude the sequence. The Aruri Formation contains six lithofacies organized as interbedded facies representing coherent rhyolitic lava flows and volcaniclastic rocks (tuffs), which are intruded by massive dacite dykes. The Salustiano Formation contains three lithofacies that comprehend coherent rhyolite flows and ignimbrites. Whole-rock geochemistry data indicate that the felsic facies rocks represent rhyolites to alkali-rhyolites (>70% SiO2) of the high-K calc-alkaline to shoshonite series with metaluminous to a peraluminous character. The rocks are considered as formed in transitional settings from a mature arc to an extensional regime. The comparison to the remainder of the Iriri Group corroborates an interpretation of their origin as subaerial volcanism with coeval effusive and explosive phases in a caldera-type volcanic system and epiclastic rocks deposited in a distal position concerning the volcanic center. The whole-rock geochemistry is similar to the other levels of the Uatuma SLIP and confirms the large extent of the ca. 1.88 Ga years ago in the Amazonian Craton.

中文翻译:

从田间关系、岩石学和地球化学重建亚马孙克拉通南部 Tapajós 域中 Aruri 和 Salustiano 地层的喷流和爆炸性沉积物

摘要 元古界硅质大型火成岩省 (SLIP) 是地质清单的一部分,因为它们记录了地球的热演化。亚马逊克拉通承载着人们知之甚少的 Uatuma SLIP,它形成于约 1.88 年前。所谓的 Uatuma 岩浆活动代表了 SLIP 的火山产物。这种岩浆作用还涉及特定的地层单元,例如 Uatuma、Iriri 和 Iricoume 群。Iriri 群内的 Aruri 和 Salustiano 地层代表了一个重要的 SLIP 地层段,从喷发性火山活动过渡到爆发性火山活动。然而,这个区间仍未公开,缺乏对 Iriri Group 地层的彻底比较。从实地观察、详细的岩相描述、关于 Aruri 和 Salustiano 地层的新地球化学数据,以及 Uatuma SLIP 地球化学数据的汇编,我们展示了两个地层的岩性地层,并与 SLIP 地层的其他层级进行了比较。我们的数据显示,爆发性火山活动和一组侵入序列的中间岩石占主导地位。Aruri 组包含六个岩相,组织为互层相,代表连贯的流纹质熔岩流和火山碎屑岩(凝灰岩),它们被大量英安岩脉侵入。Salustiano 组包含三个包含连贯流纹岩流和熔凝岩的岩相。全岩地球化学数据表明,长英质相岩石代表高钾钙碱性至钾长石系列的流纹岩至碱性流纹岩(>70% SiO2),具有金属铝质至过铝质特征。岩石被认为是在从成熟弧到伸展状态的过渡环境中形成的。与 Iriri 群其余部分的比较证实了对它们起源的解释,即它们的起源是在火山口型火山系统中具有同时期喷发和爆炸相的地下火山作用,以及沉积在火山中心远端位置的外碎屑岩。全岩地球化学与 Uatuma SLIP 的其他水平相似,并证实了大约 10 年的大范围。1.88 Ga 年前在亚马逊克拉通。与 Iriri 群其余部分的比较证实了对它们起源的解释,即它们的起源是在火山口型火山系统中具有同时期喷发和爆炸相的地下火山作用,以及沉积在火山中心远端位置的外碎屑岩。全岩地球化学与 Uatuma SLIP 的其他水平相似,并证实了大约 10 年的大范围。1.88 Ga 年前在亚马逊克拉通。与 Iriri 群其余部分的比较证实了对它们起源的解释,即它们的起源是在火山口型火山系统中具有同时期喷发和爆炸相的地下火山作用,以及沉积在火山中心远端位置的外碎屑岩。全岩地球化学与 Uatuma SLIP 的其他水平相似,并证实了大约 10 年的大范围。1.88 Ga 年前在亚马逊克拉通。
更新日期:2021-04-01
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