Using Raman Spectroscopy of Carbonaceous Material to Explore the Metamorphic Temperature and its Tectonic Implications in the Southern Hsuehshan Range, Taiwan Orogen

The mechanisms of regional metamorphism in convergent orogens are still debated, with two perspectives on timing—either linked to convergence processes or pre-convergence rifting. The Hsuehshan Range in Taiwan experienced rifting from the Eocene to the Miocene, followed by a convergence since the late Miocene. In this study, we discuss the metamorphic mechanism of the Hsuehshan Range by combining Raman spectroscopy of carbonaceous material (RSCM) for the peak metamorphic temperatures and zircon fission track for the cooling ages, to constrain the burial temperature before the convergence.

In central Hsuehshan Range, RSCM temperatures peaked at 480°C, decreasing northward and southward. In the central-northern region, RSCM temperatures correlated positively with stratigraphic ages. However, in the southern region, east of the Tili Fault, temperatures increased eastward without matching stratigraphic ages.

In some areas, RSCM temperatures (260-300°C) indicate total reset during the late Cenozoic orogeny, while zircon fission-track ages show partial reset. Higher RSCM temperatures (>400°C) lack significant new biotite growth.

We propose that during the rifting stage, strata experienced peak metamorphism, followed by cooling before the late Cenozoic orogeny, thus explaining inconsistencies between RSCM temperatures and zircon fission track ages. The deposit thickness variations in the rifting basin that are contributed to the RSCM temperatures, show no apparent stratigraphic correlation.