Isotopic geochemistry of burial-metamorphosed volcanogenic sediments, Great Valley sequence, northern California
Isotopic geochemistry of burial-metamorphosed volcanogenic sediments, Great Valley sequence, northern California
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北加州大山谷序列埋藏变质火山沉积物的同位素地球化学
DOI：
10.1016/0016-7037(83)90308-3
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发表时间：
1983
影响因子：
5
通讯作者：
L. Land
中科院分区：
文献类型：
--
作者：
R. Suchecki;L. Land
加州北部大谷层序8500m厚剖面的同位素和矿物学数据表明，在侏罗纪-白垩纪弧外盆地中，随着埋藏温度的升高，蒙皂石转化为粘土矿物，导致自生矿物的δ18O值发生变化。泥岩中粘土矿物组合的特征是，随着地层深度的增加，粘土矿物按比例增加，蒙脱石/粘土矿物混层的δ18O值呈亏损，地层位置从+21.9%下降到+15.5%。SMOW。基于粘土-矿物成岩过程中平衡分馏的自生相氧同位素数据模拟表明，泥岩中方解石和砂岩中方解石胶结物的δ18O值在最大埋藏期间沿约25℃/km的温度梯度沉淀至约6-7 km。蒙脱石/10ä粘土矿物混层的δD值在−69%至−44%之间。SMOW。根据氧同位素数据计算的温度，氢和氧同位素数据表明，蒙皂石经历了晚期脱水，可能缓冲了地层水的组成，从海水到δ18O≈+8%的同位素组成。Smow和δD≈−25%。SMOW。泥岩和砂岩方解石的δ~(13)C值表明，自生方解石的结晶作用与有机成岩作用有关，在此过程中，随着埋藏温度的升高，溶解的HCOT-3在~(13)C中不断富集。在层序底部和紧邻蛇绿岩基岩之上，数百米的地层被更多的氧气(δ18O≅+4~+5%)蚀变。热液来自蛇绿岩，可能处于最大埋藏深度。
Isotopic and mineralogic data from an 8500-m thick section of the Great Valley sequence, northern California, indicate that changes in the δ18O values of authigenic minerals resulted from the conversion of smectite to a 10 Å clay-mineral as temperature increased with burial in the Jurassic- Cretaceous outer-arc basin. The clay-mineral assemblage in mudstone is characterized by a proportional increase of the 10 Å clay-mineral with increasing stratigraphic depth, and by a depletion in the δ18O value of the mixed-layer smectite/10 Å clay-mineral with descending stratigraphic position from +21.9 to + 15.5%. SMOW. Modeling of the oxygen isotopic data from authigenic phases, based on equilibrium fractionation during clay-mineral diagenesis, indicates that δ18O values of calcite in mudstones and of calcite cements in sandstone precipitated along a temperature gradient of about 25°C/km during maximum burial to about 6–7 km. δD values of the mixed-layer smectite/10 Å clay-mineral range between −69 to −44%. SMOW. Using temperatures calculated from the oxygen isotopic data, the deuterium and oxygen isotopic data indicate that the smectite underwent late-stage dehydration and probably buffered the composition of formation waters from sea water values to isotopic compositions of δ18O ≈ +8%. SMOW and δD ≈ −25%. SMOW. The δ13C values of calcite from mudstone and sandstone imply that crystallization of authigenic calcite was linked to organic diagenesis during which dissolved HCOt-3was continuously enriched in13C as temperature increased with burial. At the base of the sequence and immediately overlying the ophiolitic basement rocks, several hundred meters of strata were altered by more oxygen-depleted (δ18O ≅ +4 to +5%.) hydrothermal fluids emanating from the ophiolitic rocks, probably at maximum burial depth.