Probing Magnetically the Paleotemperature in a Gouge: The Example from the Chinshui Shales from the Chelungpu Fault
Wednesday, 16 December 2015
Poster Hall (Moscone South)
The frictional heating is considered as a large component of earthquake energy releasing. However, probing the paleotemperature in fault gouge is still a challenge. The magnetic minerals could be neoformed/altered by thermal process within fault zone. In this study, we aim to estimate the paleotemperature by using low-temperature magnetic analyses (10K-300K) of wall rock (Chinshui Shale) and fault gouge zone from Taiwan Chelungpu-fault Drilling Project (TCDP). A piece of hanging wall rock sample from FZB1194 (fault zone within Hole-B at depth of 1,194 m) was grinded to powder and was stepwise heated within argon atmosphere from 90 to 550 ºC for one hour. The starting material is characterized by a very high content of nanoparticles. During laboratory heating, we observed the gradual destruction of the content of nanoparticles in the range 120°C up to 350°C, and the disappearance of Verwey transition at temperature higher than 350°C. The FZB1194 and FZB1243 were sampled from upper to lower parts including deformed sediments, black material disks, and black gouge zones. The magnetic analysis results show trends that we attribute to paleotemperature reached within the gouge. The deformed sediments seem unheated with respect to Chinshui Shales. In contrast, the proxy of paleotemperature of black material disk and gouge indicate >350°C and <250°C respectively. Tracking paleotemperature along a profile permits to identify several seismic events in the same gouge zone.