Calcite twinning fabrics along the Middle America trench, Costa Rica and the Motagua sinistral fault, Honduras and Jamaica: Tectonic implications for the Caribbean plate
Calcite twinning fabrics along the Middle America trench, Costa Rica and the Motagua sinistral fault, Honduras and Jamaica: Tectonic implications for the Caribbean plate
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DOI：
10.1016/j.jsames.2020.102816
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发表时间：
2020-12
影响因子：
1.8
通讯作者：
J. Craddock;K. Neilson;C. M. Petersen;R. Porter;D. Malone
中科院分区：
文献类型：
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作者：
J. Craddock;K. Neilson;C. M. Petersen;R. Porter;D. Malone
加勒比板块的白垩纪洋壳作为一个以横断层（N 和 S）和俯冲边缘（W [东板片倾角] 和 E [西板片倾角]）为界的压痕板块，有着漫长而复杂的构造历史，没有应变数据。中新世弧前沉积物和增生蛇绿岩沿哥斯达黎加太平洋中部海岸暴露，保留了多种褶皱和断层样式。这些碎屑沉积物是随着中美洲海沟的演化而沉积在弧前的，含有方解石胶结物，并被方解石脉横切。对蓬塔多米尼加和尼科亚半岛蛇绿岩这两个方解石组中的机械孪晶的分析（8 个样本，n = 267 个孪晶）保留了一致的亚水平缩短应变，其方向平行于当前海沟轴，大多数与增生相关的褶皱轴也是如此。方解石孪生应变的差异应力大小平均值为 -450 条，几乎没有证据表明存在孪生应变叠印（低 NEV）。沿中美洲海沟的仰冲部分涉及与海沟平行的水平缩短的一个组成部分。莫塔瓜断层起源于中美洲海沟，向东延伸至加勒比板块的北边界，作为左旋边缘。罗阿坦群岛是沿莫塔瓜断层南侧由南倾岩石组成的一系列岛屿。最近变形的碎屑沉积物覆盖在片麻岩、片岩（40Ar-39Ar 黑云母年龄为 14Ma）、无牙形石的大理石和推测白垩纪年龄的蛇绿岩碎片上。这些大理石的孪生研究（n = 6 个样本，n = 425 个双胞胎）保留了 N-S，水平缩短应变，垂直于左旋板块边界。方解石孪晶应变平均值 -36 MPa 的差异应力大小。仅在组合样品（n = 189 粒）中存在应变叠印（高 NEV；n = 47），记录了 132°、5° 处的水平缩短应变。牙买加还沿着东莫塔瓜断层（开曼海槽）进行孪生应变研究，对始新世石灰岩和较年轻的方解石脉（n = 4 个样本；n = 136 个孪生）保留了垂直于左旋板块边界的水平缩短应变。将孪生应变结果与加勒比板块周围的区域 GPS、震源机制和 SKS 各向异性结果进行了比较，特别是沿着哥斯达黎加西缘的中美洲海沟，对俯冲提供了一些新见解动态。
The Cretaceous oceanic crust of the Caribbean plate has a long and complex tectonic history as an indentor plate bounded by transcurrent faults (N and S) and subduction margins (W [east slab dip] and E [west slab dip]) with no strain data. Miocene forearc sediments and accreted ophiolites are exposed along the central Pacific coast of Costa Rica and preserve a variety of folding and faulting styles. These clastic sediments, deposited in the forearc as the Middle America trench evolved, contain calcite cements and are cross cut by calcite veins. Analysis of the mechanical twins in these two calcite groups (8 samples, n = 267 twins) at Punta Dominical and the Nicoya Peninsula ophiolite preserve a consistent sub-horizontal shortening strain that is oriented parallel to the current trench axis, as are most of the accretion-related fold axes. Differential stress magnitudes for the calcite twinning strain average −450 bars, and there is little evidence of a twinning strain overprint (low NEVs). Obduction along the Middle America trench involves, in part, a component of trench-parallel horizontal shortening.The Motagua fault originates in the Middle America trench and strikes east as the northern boundary of the Caribbean plate as a sinistral margin. The Roatan Islands are a series of islands composed of south-dipping rocks along the southern side of the Motagua fault. Recent, deformed clastic sediments are drapped over gneisses, schists (40Ar-39Ar biotite age of 14 Ma), conodont-free marbles and ophiolitic fragments of presumed Cretaceous age. Twinning studies (n = 6 samples, n = 425 twins) of these marbles preserve a N–S, horizontal shortening strain, normal to the sinistral plate boundary. Differential stress magnitudes for the calcite twinning strain average −36 MPa. Only in a combined sample (n = 189 grains) is a strain overprint (high NEVs; n = 47) present, which records horizontal shortening strain at 132°, 5°. Jamaica is also along the eastern Motagua fault (Cayman trough) and twinning strain studies in Eocene limestones and younger calcite veins (n = 4 samples; n = 136 twins) preserve a horizontal shortening strain normal to the sinistral plate boundary.Twinning strain results are compared to regional GPS, focal mechanism and SKS anisotropy results around the Caribbean plate, especially along the Middle America trench on the western margin of Costa Rica with some new insights into subduction dynamics.