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首页> 外文期刊>Progress in Earth and Planetary Science >Structural context and variation of ocean plate stratigraphy, Franciscan Complex, California: insight into mélange origins and subduction-accretion processes
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Structural context and variation of ocean plate stratigraphy, Franciscan Complex, California: insight into mélange origins and subduction-accretion processes

机译：加利福尼亚方济各会综合体的海洋板层地层的结构背景和变化：对混杂岩成因和俯冲-增生过程的认识

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The transfer (accretion) of materials from a subducting oceanic plate to a subduction-accretionary complex has produced rock assemblages recording the history of the subducted oceanic plate from formation to arrival at the trench. These rock assemblages, comprising oceanic igneous rocks progressively overlain by pelagic sedimentary rocks (chert and/or limestone) and trench-fill clastic sedimentary rocks (mostly sandstone, shale/mudstone), have been called ocean plate stratigraphy (OPS). During accretion of OPS, megathrust slip is accommodated by imbricate faults and penetrative strain, shortening the unit and leading to tectonic repetition of the OPS sequence, whereas OPS accreted at different times are separated by non-accretionary megathrust horizons. The Franciscan subduction complex of California accreted episodically over a period of over 150 million years and incorporated OPS units with a variety of characteristics separated by non-accretionary megathrust horizons. Most Franciscan OPS comprises MORB (mid-ocean-ridge basalt) progressively overlain by chert and trench-fill clastic sedimentary rocks that are composed of variable proportions of turbidites and siliciclastic and serpentinite-matrix olistostromes (sedimentary mélanges). Volumetrically, the trench-fill component predominates in most Franciscan OPS, but some units have a significant component of igneous and pelagic rocks. Ocean island basalt (OIB) overlain by limestone is less common than MORB-chert assemblages, as are abyssal serpentinized peridotite slabs. The earliest accreted OPS comprises metabasite of supra-subduction zone affinity imbricated with smaller amounts of metaultramafic rocks and metachert, but lacking a clastic component. Most deformation of Franciscan OPS is localized along discrete faults rather than being distributed in the form of penetrative strain. This deformation locally results in block-in-matrix tectonic mélanges, in contrast to the sedimentary mélanges making up part of the clastic OPS component. Such tectonic mélanges may include blocks and matrix derived from the olistostromes. Franciscan subduction and OPS accretion initiated in island arc crust at about 165–170?Ma, after which MORB and OIB were subducted and accreted following a long (tens of mega-ampere) gap with little or no accretion. Following subduction initiation, a ridge crest approached the trench but probably went dormant prior to its subduction (120–125?Ma), after which the subducted oceanic crust became progressively older until about 95?Ma. From 95?Ma, the age of subducted oceanic crust decreased progressively until arrival of the Pacific-Farallon spreading center led to termination of subduction and conversion to a transform plate boundary.
机译：物质从俯冲洋洋板转移到（俯冲-增生复合体）产生了岩石组合，记录了俯冲洋洋板从地层到到达海沟的历史。这些岩石组合包括海洋火成岩，逐渐被上层沉积岩（（石和/或石灰岩）和沟槽填充碎屑沉积岩（主要是砂岩，页岩/泥岩）覆盖，被称为海床地层学（OPS）。在OPS增生过程中，巨大的冲断滑移被岩性断裂和穿透应变所适应，从而缩短了单元并导致了OPS序列的构造重复，而在不同时间增生的OPS被非增生的超冲断层分开了。加利福尼亚的方济各会俯冲情结在1.5亿年的时间里逐渐增加，并合并了具有各种特征的OPS单元，这些特征被非增生性大推力层分开。大部分方济各会的OPS包括MORB（大洋中部玄武岩），逐渐被石和沟槽填充碎屑沉积岩覆盖，这些沉积岩由不同比例的浊积岩和硅质碎屑和蛇纹岩基质低聚岩（沉积混杂岩）组成。从体积上讲，在大多数方济各会的OPS中，沟槽填充组分占主导地位，但某些单元中火成岩和中上层岩石中有很大一部分。覆有石灰石的大洋玄武岩（OIB）较MORB cher石组合少见，深渊蛇纹石化橄榄岩板也是如此。最早增生的OPS包含超俯冲带亲和性的异位位点，与少量的金属亚铁岩石相和后cher相交汇，但缺乏碎屑成分。 Franciscan OPS的大部分变形都分布在离散断层上，而不是以渗透应变的形式分布。与构成碎屑OPS组成部分的沉积混杂岩相比，这种变形在局部形成了块状构造混杂岩。这样的构造混杂体可包括源自橄榄岩的块和基质。在岛弧地壳中约165-170？Ma开始方济各会俯冲和OPS增生，此后，经过长距离（数十兆安培）的间隙，MORB和OIB被减低并增生，几乎没有增生。俯冲开始后，海脊到达海沟，但在俯冲之前可能处于休眠状态（120-125？Ma），此后俯冲的洋壳逐渐变老，直至约95？Ma。从95Ma开始，俯冲洋壳的年龄逐渐减小，直到太平洋-Farallon扩散中心到达导致俯冲终止并转变为转换板块边界。

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