Density of UHP Metamorphic Rocks from CCSD Main Hole

摘要

For learning the densities of UHP metamorphic rocks and the differences between logging and core test density, this study displayed the density profiles obtained by well logging and core test at the 5 000 m deep CCSD-MH (Chinese Continental Scientific Drilling Main Hole), compared log density with core's. The upper section (100-700 and 1 600-2 000 m) of CCSD-MH, which consists of mainly eclogite and amphibolite, displays high densities (2.8-3.6 g/cm3). The lower section (2 000-5 000 m), which consists of mainly orthogneiss and paragneiss, displays low densities (2.6-2.7 g/cm3). The retrogression lowered the density of eclogite. Thus the density profile of CCSD-MH was mainly governed by lithologies. The variation of log density was coherent with that of core test on the whole, and the log density was a little lower than core's. The density log is severely affected by the cavings and breakouts of borehole, so it is necessary to correct the density log properly.