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首页> 外文期刊>GSA Bulletin >The Chulitna terrane of south-central Alaska: A rifted volcanic arc caught between the Wrangellia composite terrane and the Mesozoic margin of North America
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The Chulitna terrane of south-central Alaska: A rifted volcanic arc caught between the Wrangellia composite terrane and the Mesozoic margin of North America

机译：阿拉斯加中南部的丘利特纳（Chulitna）地貌：裂谷火山弧夹在兰格利亚（Wrangellia）复合地层和北美中生代边缘之间

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摘要

The Chulitna terrane is an enigmatic, fault-bounded package of mid-Paleozoic to early Mesozoic sedimentary rocks and volcanics that are exotic to North America and show no clear affinity with any of the other allochthonous terranes in southern Alaska. Geologic mapping and geochemical analyses of Triassic strata from the Chulitna terrane indicate Triassic rifting of a Devonian volcanic arc and development of an asymmetric basin that was later deformed in the Cretaceous within the broadly defined suture between the Wrangellia composite terrane and the Mesozoic margin of North America. The structure of the region consists of an overturned synclinorium that verges southeast, Triassic strata in the core of the syncline, and basement rocks exposed in the hanging walls of a series of out-of-syncline thrusts on the southeastern, upright limb. The basement of the complex consists of serpentinite, vesicular flows of basaltic andesite with minor pillow lavas, and volcanic debris with blocks of andesite and minor Devonian red chert. From southeast to northwest, there are systematic changes in the facies associated with Triassic strata that overlie this basement. To the southeast, the basement is unconformably overlain by bedded sedimentary breccias that consist of subangular clasts of basement lithologies, including red chert, serpentinite, and andesite. Further to the northwest, in the hanging wall of a more rearward thrust, the red-bed strata consist of conglomerate intermixed with siltstone and cross-bedded sandstone. In the northwest on the overturned limb of the syncline, the red beds are composed of siltstone and sandstone interfingered with limestone. There is an overall increase in the thickness of the red-bed unit from southeast to northwest. On the northwestern limb of the syncline, the red beds overlie a 1500-m-thick basalt sequence with columnar jointed flows and pillow basalts interbedded with limestone. Geochemical analyses of clinopyroxene phenocrysts in the basalts show similarities with island-arc basalts, suggesting that volcanism was related to early rifting of an oceanic arc. A marine sandstone unit overlies the entire red-bed package along a flooding surface and thins to the southeast. These results are consistent with Triassic deposition within a rifted volcanic arc, an upland erosion surface to the southeast, and increasing thickness of the Triassic section toward a basin-bounding fault in the northwest. This basin was initially ~18 km wide prior to accretion along the Mesozoic margin of North America, which resulted in southeast-vergent folding and 30% shortening.
机译：Chulitna地层是古生界中期至中生代早期沉积岩和火山 的一个神秘的，断层边界包裹，对北美来说是奇特的，并且没有明显的亲和力 与阿拉斯加南部的任何其他异源地层。 丘利特纳地层三叠纪地层的地质制图和地球化学分析表明，泥盆纪的三叠纪裂谷火山弧和不规则盆地的发展，该不对称盆地在宽范围定义的 缝合线中在白垩纪中变形，在兰格利亚复合地层和中生界 < / sup>北美利润率。该区域的结构由向东南倾斜的倾斜斜斜同步层，向斜心线中的三叠纪 地层和基底中暴露于 的基底岩石组成。东南直立的肢体上一系列不同步的推力 的悬挂壁。复杂的 的基底包括蛇纹石，玄武质安山岩 的囊泡流动和少量枕状熔岩，以及 块安山岩和较小泥盆纪的火山碎屑红石。从东南到西北， 覆盖该基底的与三叠纪 地层相关的相系发生了系统的变化。在东南部，基底 不一致地被层状沉积角砾岩覆盖，该沉积的角砾岩由基底岩性的亚角碎屑组成，包括 红石，蛇纹岩和安山岩。在西北部， 在向后推力更大的悬挂壁中，由砾岩组成的红层地层 由粉砂岩和交叉层状的 砂岩。在西北向斜向倾斜的四肢上， 红层由粉砂岩和砂岩和指状的 与石灰岩组成。从东南到西北，红层单元的厚度 总体增加。在向斜线的西北部​​ 上，红色层床覆盖着厚度为1500 m的玄武岩 序列，柱状节理流和枕形玄武岩交错插入 和石灰石。玄武岩中斜辉石斑晶 的地球化学分析显示出与岛弧玄武岩的相似之处，这表明 火山作用与大洋弧的早期裂开有关。 一个海洋砂岩单元覆盖整个红层包裹 以及洪水表面，并向东南变薄。这些结果 与裂谷火山 弧中的三叠纪沉积，东南部的高地侵蚀表面以及三叠纪剖面向西北部盆地边界断层 。该盆地最初沿北美中生代缘增生前约18 km宽，这导致东南向折叠并缩短了30％。 上>

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  • 来源
    《GSA Bulletin》 |2009年第8期|979-991|共13页
  • 作者

    Tony Gilman; Maureen Feineman; Donald Fisher;

  • 作者单位

    Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA;

    Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA;

    Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA;

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