Sandstone dikes in dolerite sills: Evidence for high-pressure gradients and sediment mobilization during solidification of magmatic sheet intrusions in sedimentary basins
Sandstone dikes in dolerite sills: Evidence for high-pressure gradients and sediment mobilization during solidification of magmatic sheet intrusions in sedimentary basins
复制标题
辉绿岩基岩中的砂岩脉：沉积盆地岩浆片侵入凝固过程中高压梯度和沉积物流动的证据
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
S. Planke
中科院分区：
文献类型：
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作者：
H. Svensen;I. Aarnes;Y. Podladchikov;E. Jettestuen;Camilla H. Harstad;S. Planke
在南非卡鲁盆地，沉积岩脉在花岗岩基岩侵入体中很常见。这些岩脉是近垂直的，宽达2米，有时还含有丰富的沉积岩和花斑岩碎片。基质由接触变质砂岩组成。没有岩石学证据表明沉积岩脉内发生了熔融。加热过程中的最高温度仅限于斜长石和黑云母稳定场，或高于∼350°C。对砂岩岩脉进行的热模拟表明，经过几百年的岩床冷却，岩脉的温度可达到350~450℃。计算的冷却门槛及其接触晕的压力历史表明，大量的流体压力异常在短时间尺度上(1-15年)发展，并保持了100多年。计算的基床(-7~-22 Mpa)和光环(4-22 Mpa)内的压力异常是显著的，这可能解释了底板破裂和泥沙从光环向底板的迁移。我们认为，沉积岩脉代表了流体压力梯度较高的具有底板侵入的沉积盆地的共同特征。因此，沉积岩脉意味着孔隙流体可以在短时间尺度上从金柱中逸出，代表了微裂缝形成期间的流体损失和猛烈喷口形成期间的流体损失之间的中间状态。
Sediment dikes are common within dolerite sill intrusions in the Karoo Basin in South Africa. The dikes are subvertical and as much as 2 m wide, sometimes with abundant fragments of sedimentary rocks and dolerite. The matrix consists of contact-metamorphic sandstone. There is no petrographic evidence for melting within the sediment dikes. The maximum temperature during heating is restricted to the plagioclase and biotite stability field, or above ∼350 °C. Thermal modeling of a sandstone dike in a dolerite sill shows that a temperature of 350–450 °C is reached in the dike after a few hundred years of sill cooling. The calculated pressure history of a cooling sill and its contact aureole shows that substantial fluid pressure anomalies develop on a short time scale (1–15 yr) and are maintained for more than 100 yr. Calculated pressure anomalies in the sill (-7 to -22 MPa) and the aureole (4–22 MPa) are significant and may explain sill fracturing and sediment mobilization from the aureole into the sill. We conclude that sediment dikes represent common features of sedimentary basins with sill intrusions in which fluid pressure gradients have been high. Sediment dikes thus signify that pore fluids may escape from the aureoles on a short time scale, representing an intermediate situation between fluid loss during formation of microfractures and fluid loss during violent vent formation.