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首页> 外文期刊>Geosphere >Evolution of the early Mesozoic Cordilleran arc: The detrital zircon record of back-arc basin deposits, Triassic Buckskin Formation, western Arizona and southeastern California, USA
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Evolution of the early Mesozoic Cordilleran arc: The detrital zircon record of back-arc basin deposits, Triassic Buckskin Formation, western Arizona and southeastern California, USA

机译：早期中生代科尔氏乳房的演变弧：后弧盆地沉积物，三叠纪荞麦面，西亚利桑那州和美国东南部的替代锆石记录

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摘要

A shift in the depositional systems and tectonic regime along the western margin of Laurentia marked the end of the Paleozoic Era. The record of this transition and the inception and tectonic development of the Permo-Triassic Cordilleran magmatic arc is preserved in plutonic rocks in southwestern North America, in successions in the distal back-arc region on the Colorado Plateau, and in the more proximal back-arc region in the rocks of the Buckskin Formation of southeastern California and west-central Arizona (southwestern North America). The Buckskin Formation is correlated to the Lower–Middle Triassic Moenkopi and Upper Triassic Chinle Formations of the Colorado Plateau based on stratigraphic facies and position and new detrital zircon data. Calcareous, fine- to medium-grained and locally gypsiferous quartzites (quartz siltstone) of the lower and quartzite members of the Buckskin Formation were deposited in a marginal-marine environment between ca. 250 and 245 Ma, based on detrital zircon U-Pb data analysis, matching a detrital-zircon maximum depositional age of 250 Ma from the Holbrook Member of the Moenkopi Formation. An unconformity that separates the quartzite and phyllite members is inferred to be the Tr-3 unconformity that is documented across the Colorado Plateau, and marks a transition in depositional environments. Rocks of the phyllite and upper members were deposited in wholly continental depositional environments beginning at ca. 220 Ma. Lenticular bodies of pebble to cobble (meta) conglomerate and medium- to coarse-grained phyllite (subfeldspathic or quartz wacke) in the phyllite member indicate deposition in fluvial systems, whereas the fine- to medium-grained beds of quartzite (quartz arenite) in the upper member indicate deposition in fluvial and shallow-lacustrine environments. The lower and phyllite members show very strong age and Th/U overlap with grains derived from Cordilleran arc plutons. A normalized-distribution plot of Triassic ages across southwestern North America shows peak magmatism at ca. 260–250 Ma and 230–210 Ma, with relatively less activity at ca. 240 Ma, when a land bridge between the arc and the continent was established. Ages and facies of the Buckskin Formation provide insight into the tectono-magmatic evolution of early Mesozoic southwestern North America. During deposition of the lower and quartzite members, the Cordilleran arc was offshore and likely dominantly marine. Sedimentation patterns were most strongly influenced by the Sonoma orogeny in northern Nevada and Utah (USA). The Tr-3 unconformity corresponds to both a lull in magmatism and the “shoaling” of the arc. The phyllite and upper members were deposited in a sedimentary system that was still influenced by a strong contribution of detritus from headwaters far to the southeast, but more locally by a developing arc that had a far stronger effect on sedimentation than the initial phases of magmatism during deposition of the basal members.
机译：沿着劳伦西亚西部边缘的沉积系统和构造制度的转变标志着古生代时代的末端。这种过渡的记录和烫发型Cordilleran岩浆弧的初始和构造开发在北美西南部的浮标岩石中保存在科罗拉多州高原的远端后弧区域，并且在更近的背部 - 在加利福尼亚州东南部和亚利桑那州西部（北美西南部）的Buckskin形成的岩石地区。基于地层相机和地位和新的替代锆石数据，荞麦面形成与科罗拉多平原的下层三叠腹部和上三叠系Chinle形成相关。在CA之间的边缘海洋环境中沉积了碎屑的钙质，细微粒细菌和局部石膏石英岩（石英硅铁晶）（石英硅铁晶）。 250和245 mA，基于脱条子U-PB数据分析，与霍尔布鲁克地区形成的甲状腺炎最大沉积年龄为250 mA的甲状腺炎最大沉积年龄。将石英岩和阈值构件分开的无关，被推断为在科罗拉多州的高原上记录的TR-3非整合性，并标记沉积环境中的过渡。从加利福尼亚州开始的全部大陆沉积环境中沉积了Phyllite和上部成员的岩石。 220 mA。卵石卵石的扁卵体（meta）卵石和中粗粒细胞的植物体积粒子（Meta-to粗粒）在植物体系中的沉积沉积，而石英石（石英芳香素）的细微粒度床沉积上部构件表示在河流和浅湖环境中的沉积。下部和丸钛矿成员显示出非常强大的年龄，含有衍生自Cordillan弧型芦苇的谷物的重叠。北美西南部三叠纪年龄的标准化分布图显示了加利福尼亚州的峰岩岩。 260-250 mA和230-210 mA，在CA相对较少。 240 mA，当弧和大陆之间的陆桥建立时。 Buckskin形成的年龄和相面积深入了解北美早期中生代西区的Tectono-Magmatic演变。在较低和石英岩成员的沉积期间，Cordilleran弧度是近海，可能是占主导地位的海洋。沉淀模式受到内华达州北部和犹他州（美国）的索诺玛organy的影响。 TR-3不整合对应于岩浆中的平静和弧的“浅层”。 Phyllite和上部成员沉积在沉积体系中，沉积体系仍然受到碎屑的强烈贡献，这些碎屑从远向东南部的碎屑队的巨大贡献，而是通过开发弧线的局部局部对沉淀物的影响远远超过岩浆的初始阶段沉积基底构件。

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