Testing a Pseudotachylyte Geothermometer

0003482 O 'Hara一种简单的新地质温度计，用于测量熔融岩石（所谓的假玄武玻璃），可以估计熔融过程中周围岩石的温度，目前正在一个含化石的陆内假玄武玻璃断层带（科罗拉多的霍姆斯特克剪切带）和挪威西部的超深假玄武玻璃上进行测试。 温度（因此深度）估计沿着断层带的摩擦熔化给出了三维图片的破裂几何形状。 摩擦熔融似乎是地壳中古代地震活动的少数指标之一，摩擦熔融的深度被认为与地震体制相对应。 认识到一些pseudotachylytes叠印的韧性组构，以及超深pseudotachylytes的发现，表明摩擦熔融不仅限于脆性上地壳。 摩擦熔融的深度分布信息对地壳的流变行为及其地震活动的可能性具有重要的制约作用，断层作用下的摩擦熔融可以看作是一个绝热热泵，断层在围岩温度下工作。 这些功中的一部分被转化为热量，从而在更高的温度下产生熔体。 转换过程的效率仅取决于热源之间的温差。 如果可以对效率进行估计，并且假设其中一个热源的温度，则可以计算另一个热源的温度。 它示出在这里，摩擦熔体体积的比例，机械磨损体积在自然pseudotachylytes是一个代理的比例，在断层的热能与机械能，并且这个比例是独立的断层面积，位移，应力和矿物学。从四个不同的假玄武玻璃岩地点获得的初步数据（没有被韧性组构覆盖）得出合理的环境温度估计值为132- 484 oC，对应于上地壳和中地壳。 地质温度计得出挪威西部榴辉岩相假玄武玻璃的围岩温度为627- 827 oC，与670 oC的独立估计值一致。 地质温度计似乎适用于整个地壳。

0003482O'HaraA simple new geothermometer for frictionally melted rocks (so called pseudotachylytes) that allows estimate of ambient country rock temperature during melting is being tested on a fossil intracontinental pseudotachylyte-bearing fault zone the (Homestake shear zone, Colorado) and ultradeep pseudotachylytes from western Norway. Temperature (and hence depth) estimates on frictional melting along fault zones give a three dimensional picture of the rupture geometry. Frictional melting appears to be one of the few indicators of ancient seismic activity in the crust and the depth of frictional melting is thought to correspond to the seismic regime. The recognition that some pseudotachylytes are overprinted by ductile fabrics, together with the discovery of ultra-deep pseudotachylytes, suggests that frictional melting is not confined solely to the brittle upper crust. Information on the depth distribution of frictional melting places important constraints on the rheological behavior of the crust and its potential to behave seismically.Frictional melting during faulting can be regarded as an adiabatic heat pump in which the fault does work at the ambient country rock temperature. Some of this work is converted to heat producing a melt at a higher temperature. The efficiency of the conversion process depends solely on temperature difference between the heat reservoirs. If an estimate of efficiency can be made and the temperature of one of the heat reservoirs is assumed, the temperature of the other reservoir can be calculated. It is shown here that the ratio of frictional melt volume to mechanical wear volume in natural pseudotachylytes is a proxy for the ratio of thermal to mechanical energy during faulting, and that this ratio is independent of fault area, displacement, stress and mineralogy. Thermodynamic arguments indicate it depends solely on temperature.Preliminary data from four different pseudotachylyte localities, which are not overprinted by ductile fabrics, yield reasonable ambient temperature estimates of 132-484oC, corresponding to the upper and middle crust. The geothermometer yields a country rock temperature of 627- 827oC for eclogite-facies pseudotachylytes from western Norway, consistent with an independent estimate of 670oC. The geothermometer appears to be applicable throughout the entire crust.