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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Characterization of the volcanic and hypabissal rocks of the Paleoproterozoic Iricoume Group in the Pitinga region and Balbina Lake area, Amazonian Craton, Brazil: Petrographic distinguishing features and emplacement conditions
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Characterization of the volcanic and hypabissal rocks of the Paleoproterozoic Iricoume Group in the Pitinga region and Balbina Lake area, Amazonian Craton, Brazil: Petrographic distinguishing features and emplacement conditions

机译：巴西亚马孙克拉通市Pitinga地区和Balbina湖地区古元古代Iricoume群的火山岩和下斜岩的特征：岩相学特征和进位条件

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The Iricoume Group (1.897 to 1.875 Ma) is a widespread volcanic sequence in the Amazonian Craton, South American Platform. In the Pitinga region, it consists of acidic to intermediate ignimbrites with cogenetic surge and ash-fall deposits associated to hypabissal and effusive acidic rocks. In the Balbina Lake area it consists of acidic to intermediate effusive rocks, crystal-rich ignimbrites and pumice-rich ignimbrites. Detailed petrographic studies of phenocrysts and crystal fragments provided characterization and distinctive features of pyroclastic, effusive and hypabissal rocks. The phenocrysts of hypabissal rocks were affected by high temperature resorption and flow-related physical fragmentation, the effusive rocks can have a considerable content of crystal fragments due to intense dissolution and fragmentation of the phenocrysts and the pyroclastic rocks crystal fragments are generated mainly by decompression mechanic fragmentation. Dissolution and resorption of quartz and feldspar crystals may have acted at pressure conditions between 500 MPa and 100 MPa, in response to rapid decompression in the magma ascent. The viscosity values of 7,5-10 log η (Pa s) for anhydrous conditions decrease exponentially with estimated water addition. The amount of phenocrysts and their intratelluric character in the volcanic units of Iricoume Group can be related to a magma chamber with high content of crystals. We suggest that even with the addition of water in the magma, the viscosities had a drastic increase with progressive crystal growth due to the viscosity dependence on the solid fraction and the deposits were generated by the extrusion of viscous lava and pyroclastic flows.
机译：Iricoume集团（1.897至1.875 Ma）是南美平台亚马逊克拉通的一个广泛的火山岩层。在皮廷加地区，它由酸性到中度的火成岩组成，伴有潮热和灰岩沉积，与成岩质和喷发性酸性岩石有关。在巴尔比纳湖地区，它由酸性至中性喷出性岩石，富含晶体的火成岩和富含浮石的火成岩组成。详细的岩石学研究表明，火山碎屑岩，喷发岩和斜方岩具有特征和独特的特征。高温吸收和与流动相关的物理碎裂作用影响了下斜岩的隐晶石，由于隐晶石的强烈溶解和碎裂，使喷出的岩石中含有大量的晶体碎片，而火山碎屑岩的晶体碎片主要是由减压机制产生的。碎片化。响应岩浆上升的快速减压，石英和长石晶体的溶解和吸收可能在500 MPa至100 MPa的压力条件下起作用。在无水条件下，粘度值7,5-10 logη（Pa s）随估计的加水量呈指数下降。 Iricoume Group火山单元中的隐晶的数量及其星内特性可能与具有高晶体含量的岩浆室有关。我们认为，即使在岩浆中加水，由于粘度对固体成分的依赖性，粘度也随着晶体的逐步生长而急剧增加，并且沉积物是由粘性熔岩和火山碎屑流的挤压而产生的。

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