Glassy pseudotachylyte veins from the Fuyun fault zone, northwest China
Glassy pseudotachylyte veins from the Fuyun fault zone, northwest China
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DOI：
10.1016/0191-8141(94)90019-1
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发表时间：
1994
影响因子：
3.1
通讯作者：
A. Lin
中科院分区：
文献类型：
--
作者：
A. Lin
玻璃状假速晶岩产于中国西北部富蕴断裂带的花岗糜棱岩中。粉末 X 射线衍射数据表明，富蕴假速石的细粒基质从几乎结晶到完全玻璃（少量到 90 wt% 玻璃）不等。粉末X射线衍射图还表明，玻璃型假速石脉中的碎屑主要由石英颗粒组成。富蕴拟速晶石中也常见具有淬火或快速冷却结构、囊泡和杏仁核、流动结构和圆形碎片的微晶石。这些拟速晶石的平均整体化学成分与母岩相似。但玻璃基质的 SiO2 成分较低，比母岩低 5-15 wt%。假速水剂含有 2–3 wt% 的水 (H2O)。使用将水的溶解度与压力联系起来的实验数据，估计了对应于大约1.5公里深度的假速水石地层的大约400巴的岩石静压。由于纯 SiO2 玻璃的存在，可以估算出 1450°C 的最低温度。 X 射线衍射和化学数据表明，富蕴拟速晶岩是在浅层地震断层过程中通过在水饱和条件下选择性熔融而形成的，而不是通过完全熔融或沿断层表面的主岩破碎而形成。
Glassy pseudotachylytes occur in granitic mylonites from the Fuyun fault zone, northwest China. Powder X-ray diffraction data indicate that the fine-grained matrices of the Fuyun pseudotachylytes vary from almost crystalline to complete glass (a few to 90 wt% glass). Powder X-ray diffraction patterns also indicate that clasts in the glass type pseudotachylyte veins mostly consist of quartz grains. Microlites displaying quenched or rapid-cooling textures, vesicles and amygdules, flow structures, and rounded fragments are also common in the Fuyun pseudotachylytes.The average bulk chemical compositions of these pseudotachylytes are similar to those of the host rocks. But the glass matrix has a low SiO2component which is 5–15 wt% lower than that of the host rocks. The pseudotachylytes contain 2–3 wt% water (H2O). Using experimental data which relate the solubility of water to pressure, approximately 400 bars lithostatic pressure corresponding to approximately 1.5 km depth, of pseudotachylyte formation is estimated. A minimum temperature estimate of 1450°C can be estimated due to the presence of the pure SiO2glass.The X-ray diffraction and chemical data indicate that the Fuyun pseudotachylytes formed during seismic faulting at shallow depths by selective melting under water-saturated conditions rather than by total melting or by crushing of the host rocks along fault surfaces.