The effect of carbonate cementation of underthrust sediments on deformation styles during underplating
The effect of carbonate cementation of underthrust sediments on deformation styles during underplating
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逆冲沉积物碳酸盐胶结作用对底侵变形样式的影响
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发表时间：
1990
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通讯作者：
J. Sample
中科院分区：
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作者：
J. Sample
在收敛边缘变形过程中排出的流体导致各种成岩反应，包括碳酸盐胶结作用，这些反应改变了变形沉积物的流变学。在现代辐合边缘的浅层沉积物中，碳酸盐胶结物的体积很小，但在阿拉斯加一个古老的增生杂岩中，砂岩中含有大量的碳酸盐胶结物，这些胶结物形成于底板发生之前。碳酸盐岩除脉状方解石外，主要为早期方解石替代骨架颗粒或充填孔隙，其次为铁白云石，主要为充填孔隙的胶结物。在典型样品中，含量范围为2 - 16%，平均约为9%。Kodiak砂岩中碳酸盐岩充填的平均孔隙度与现代辐合边缘正常压实砂岩中4-5 km深度的孔隙度相对应。地层温度很难精确确定，但可能在100°C到200°C之间。大部分胶结作用发生在与底板有关的逆冲断层、褶皱和板岩解理形成之前。胶结岩化作用通过(1)填满孔隙空间，提高峰值强度，(2)增强黏聚力，改变了砂岩的流变特性，使圆锥状流动不再是一种可行的变形机制。显著变形前的岩化作用使科迪亚克组的下覆形成相对连贯的双相。
Fluids expelled during deformation at convergent margins lead to a variety of diagenetic reactions, including carbonate cementation, which alter the rheology of the deforming sediment. The volume of carbonate cement in shallow sediments at modern convergent margins is small, but sandstones in an ancient accretionary complex in Alaska contain significant amounts of carbonate cement that formed before underplating occurred. Other than vein calcite, carbonates are early calcite replacing framework grains or filling pore spaces, followed by ankerite that occurs mainly as pore-filling cement. Amounts range from 2–16 weight percent in typical samples, averaging about 9 weight percent. Mean porosity filled by carbonate in Kodiak sandstones corresponds to porosities expected at depths of 4–5 km in normal compacting sands underthrust at modem convergent margins. The temperatures of formation are difficult to determine precisely, but were probably between 100°C and 200°C. The bulk of cementation occurred before the formation of thrust faults, folds, and slaty cleavage related to underplating. Lithification by cementation changed the rheology of sandstones by (1) filling pore space and increasing peak strength, and (2) increasing cohesion so that paniculate flow was no longer a viable deformation mechanism. Lithification before significant deformation contributed to underplating of the Kodiak Formation as relatively coherent duplexes.