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Southern continuation of the Coast shear zone and Paleocene strain partitioning in British Columbia-southeast Alaska

机译：不列颠哥伦比亚省东南部阿拉斯加海岸剪切带的南部延续和古新世应变分区

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摘要

This paper documents the newly recognized southern continuation of the early Tertiary Coast shear zone, extending its known length by 350 km to more than 1200 km. Three sites along the shear zone in British Columbia, Douglas Channel, Bella Coola, and Machmell River, have similar histories during the period ca. 65–55 Ma. The shear zone is 2–11 km thick and is defined by well-developed mylonite zones that strike northwest and dip steeply northeast. Motion on the shear zone was predominantly reverse, with the northeast side up. Synkinematic plutons are common in the shear zone. Lower plate rocks, high-grade gneiss derived from an ancient continental margin assemblage, show little evidence of the extensive deformation and plutonism in the shear zone. North of Bella Coola, high- grade gneiss forms the upper plate, but to the south weakly metamorphosed rocks of Stikinia compose the upper plate. Geochronologic data show that the shear zone was active between ca. 60 and 55 Ma at Douglas Channel, ca. 62 and 56 Ma at Bella Coola, and after 66 and before 56 Ma near the Machmell River. These features match those of the Coast shear zone in southeast Alaska and adjacent British Columbia. Together the shear zones formed a continental-scale reverse ductile fault in Paleocene time. Plate reconstructions show an oblique component to the dominantly dextral transcurrent Paleocene margin. Partitioning of this motion across the continental margin produced a regional system of strike-slip faults and contraction on the Coast shear zone.
机译：本文记录了新认识到的第三纪早期剪切带的南部延续，将已知长度延长了350 km至1200 km以上。在不列颠哥伦比亚省的 剪切带，道格拉斯海峡，贝拉·库拉， 和Machmell河沿岸的三个地点，在 ca时期具有相似的历史。 65–55马。剪切带厚2–11 km， 由发达的麦粒岩带定义，该带撞击西北 并向东北倾斜。剪切带上的运动主要是 反向，东北侧朝上。动力学上的冲动 在剪切带中很常见。下部板块岩石，是来自古代大陆边缘组合的高品位 片麻岩， 几乎没有证据表明剪切带中广泛的变形和岩体作用 。在贝拉库拉（Bella Coola）北部，上片由高级片麻岩 形成，而在南部则由薄弱变质的 岩石构成上板。年代学 数据表明，剪​​切带在大约两个月之间处于活动状态。道格拉斯海峡，大约60和 55 Ma Bella Coola， 在62 Ma和56 Ma之间，在Machmell河附近，在66 Ma之后和56 Ma之前。这些 功能与 东南阿拉斯加和邻近的不列颠哥伦比亚省的Coast剪切带相匹配。在古新世 时间内，剪切带 共同形成了大陆性逆韧性断裂。板块重建显示了 主要是右旋跨流新世边缘的倾斜分量。跨大陆边缘对该运动进行分区 在海岸剪切 带上形成了走滑断层和收缩的区域 系统。 / sup>

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  • 来源
    《GSA Bulletin》 |2001年第8期|961-975|共15页
  • 作者

    Margaret E. Rusmore; George Gehrels; G.J. Woodsworth;

  • 作者单位

    Department of Geology, Occidental College, Los Angeles, California 90041, USA;

    Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA;

    Geological Survey of Canada, 101-605 Robson Street, Vancouver, British Columbia V6B 5J3, Canada;

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