Peak Metamorphic Conditions of Garnet Amphibolites Beneath the Semail Ophiolite: Implications for an Inverted Pressure Gradient
Peak Metamorphic Conditions of Garnet Amphibolites Beneath the Semail Ophiolite: Implications for an Inverted Pressure Gradient
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包浆蛇绿岩下石榴石角闪岩的峰值变质条件：对倒压力梯度的影响
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发表时间：
1998
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通讯作者：
E. Gnos
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作者：
E. Gnos
蛇绿岩下的石榴石角闪岩形成压力为1.1±0.2 GPa.同一变质岩底中的绿片岩相岩石的压力估计为0.45-0.55 GPa.因此，除了蛇绿岩变质岩系中众所周知的逆温梯度外，在2000米以上还存在0.3~2.0兆帕/米的逆变变质压力梯度。在一个70米厚的序列中，每隔10米系统采集一次样品，其中包含石榴石+斜长石+角闪石(±透辉石±钛铁矿±金红石)组合，通过对样品的温度估计，可以使用不同的温度计确定平均倒变质温度梯度为1至4°C/m。石榴石角闪岩中的压力是根据厘米大小的蓝晶石的存在，通过将观察到的组合与相关公布的实验结果进行比较，并通过非均相平衡计算来估计的。不同的估计结果导致峰值P-T条件为800±100°C和1.1±0.2 GPa.那个.。
Garnet amphibolites beneath the Semail Ophiolite formed at 1.1 ± 0.2 GPa and greenschist-facies rocks in the same metamorphic sole yielded pressure estimates of 0.45 to 0.55 GPa. Thus, in addition to the well-known inverted thermal gradient in subophiolitic metamorphic sequences, an inverted metamorphic pressure gradient of 0.3 to 2.0 MPa/m over <2000 m also exists. Temperature estimates for samples systematically collected every 10 m across a 70 m thick sequence that contains the assemblage garnet + plagioclase + amphibole (± diopside ± ilmenite ± titanite ± rutile) allowed the determination of an average inverted metamorphic temperature gradient of 1 to 4°C/m, using different thermometers. Pressures in garnet amphibolites were estimated from the presence of cm-sized kyanite, by comparison of the observed assemblage with relevant published experimental results, and by using heterogeneous equilibrium calculations. The different estimations result in peak P-T conditions of 800 ± 100°C and 1.1 ± 0.2 GPa. Th...