...
  • 主题
高级搜索  >
历史搜索 清空历史
首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >Structures and lithofacies of inferred silicic conduits in the Parana-Etendeka LIP, southernmost Brazil
【24h】

Structures and lithofacies of inferred silicic conduits in the Parana-Etendeka LIP, southernmost Brazil

机译：巴西最南端的Parana-Etendeka LIP中推断的硅质导管的结构和岩相

获取原文
获取原文并翻译 | 示例
           
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

Extensive silicic units in the Parana-Etendeka LIP have been long interpreted as pyroclastic density currents (rheomorphic ignimbrites) derived from the Messum Complex in Namibia. In recent literature, however, they have been characterized as effusive lava flows and domes. In this paper we describe structures and lithofacies related to postulated silicic lava feeder conduits at Mato Perso, Sao Marcos and Jaquirana-Cambara do Sul areas in southern Brazil. Inferred conduits are at least 15-25 m in width and the lithofacies include variably vesicular monomictic welded and non-welded breccias in the margins to poorly vesicular, banded, spherulitic and microfractured vitrophyres in the central parts. Flat-lying coherent vitrophyres and massive obsidian are considered to be the subaerial equivalents of the conduits. Large-scale, regional tectonic structures in southern Brazil include the NE-SW aligned Porto Alegre Suture, Leao and Acotea faults besides the Antas Lineament, a curved tectonic feature accompanying the bed of Antas river. South of the Antas Lineament smaller-scale, NW-SE lineaments limit the exposure areas of the inferred conduits. NE-SW and subordinate NW-SE structures within this smaller-scale lineaments are represented by the main postulated conduit outcrops and are parallel to the dominant sub-vertical banding in the widespread banded vitrophyre lithofacies. Upper lava flows display flat-lying foliation, pipe-like and spherical vesicles and have better developed microliter. Petrographic characteristics of the silicic vitrophyres indicate that crystal-poor magmas underwent distinct cooling paths for each inferred conduit area. The vitrophyre chemical composition is defined by the evolution of trachydacitic/dacitic vitrophyres with 2-65 wt% SiO2 to rhyodacite and rhyolite with 66-68 wt% SiO2. The more evolved rocks are assigned to the latest intrusive grey vitrophyre outcropping in the center of the conduits. Degassing pathways formed during fragmentation and fracturing episodes within the conduits may have helped to inhibit the explosivity of the eruptions. Based on the documented lithofacies architecture, we attribute the source of the silicic lava flows in the studied localities to tectonic-controlled, local conduits, rather than pyroclastic density currents from distant vent areas. (C) 2017 Elsevier B.V. All rights reserved.
机译：长期以来，Parana-Etendeka LIP中广泛的硅质单元被解释为源自纳米比亚的Messum Complex的火山碎屑密度流（变质的火成岩）。但是，在最近的文献中，它们被描述为喷出的熔岩流和穹顶。在本文中，我们描述了巴西南部Mato Perso，Sao Marcos和Jaquirana-Cambara do Sul地区与假定的硅质熔岩给水管道有关的结构和岩相。推断出的导管的宽度至少为15-25 m，岩相的边缘包括可变的单泡的微焊接的和非焊接的角砾岩，中部的泡囊，带状，球状和微破裂的玻璃体较弱。平坦的连贯的玻璃体和块状黑曜石被认为是导管的空中等效物。巴西南部的大型区域构造构造包括NE-SW对准的Porto Alegre缝合线，Leao和Acotea断层，以及Antas Lineament（伴随Antas河床的弯曲构造特征）。在Antas Lineament较小规模的南部，NW-SE lineaments限制了推断导管的暴露区域。该较小规模的构造中的NE-SW和下级NW-SE结构以假定的主要导管露头为代表，并且与宽带状玻璃体岩相中的主要亚垂直带平行。上层熔岩流显示出平坦的叶状，管状和球形囊泡，微升也更好。硅质玻璃质的岩石学特征表明，对于每个推断的导管区域，晶体贫乏的岩浆都经历了不同的冷却路径。该玻璃体化学组成是由具有2-65 wt％SiO2的菱锰矿/ datictic萎缩物演变为具有66-68 wt％SiO2的流纹岩和流纹岩形成的。演化程度更高的岩石被分配到导管中心的最新侵入性灰色玻璃体露头。在管道内的破碎和破裂事件中形成的脱气路径可能有助于抑制喷发的爆炸性。基于已记录的岩相体系，我们将研究区域内硅质熔岩流的来源归因于构造控制的局部管道，而不是来自远处喷口区的火山碎屑密度流。 （C）2017 Elsevier B.V.保留所有权利。

著录项

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号