Using Raman Spectroscopy of Carbonaceous Materials to track exhumation of an active orogenic belt: An example from Eastern Taiwan

Abstract

The burial and exhumation history of an orogen can provide insights into the thermal history of rocks in the mountain belt. Asynchronous collision will exhume materials to the surface at different times and expose different metamorphic grades along the orogenic axis. By tracking the thermal signals of eroded materials, it is possible to compare spatial patterns of exhumation along the mountain belt. Previous studies such as bulk mineralogy of sandstones, crystallinity of clay minerals, and fission track thermochronology all suggest that the Pliocene to Pleistocene meta-sedimentary deposits within the preserved basins of the Coastal Range reflect the unroofing history of the Central Range in Eastern Taiwan. In this study, modern sediments from six drainages of the east Central Range (Liwu, Mugua, Laku- Laku, Luye, Jinlun, and Hsuhai Rivers) and three basin sections of meta-sedimentary deposits from the Coastal Range (Shuilien, Chimei, and Madagida sections) were sampled to reconstruct the thermal signals of each drainage along the modern orogenic axis and reconstruct temporal variations of thermal signals in preserved Plio-Pleistocene sedimentary rocks.The temperature index (T.I.) of modern sediments determined by Raman spectroscopy of carbonaceous materials are medium to high (0.4–0.8). In conjunction with bio- and magneto-stratigraphy, our data suggest that the northern Shuilien area has been receiving detritus of medium metamorphic grade from the exhumed orogeny in the north from 3.4 Ma and higher grade since 2 Ma; meanwhile, the southern Madagida section has been mostly taking in juvenile detritus from the south part of the orogen until 1 Ma. The central Chimei section has started collecting mature detritus since 1.24 Ma. The data suggest that the Plio-Pleistocene basins contain a good record of orogen evolution.