Presenter: Hou-Ping Ho
Date: 2017/03/09
Abstract
The use of pyrrhotite as an index mineral to delineate metamorphic isograds has long been proposed. The minerals of iron sulfide will change faces with the increase of metamorphism, for example, pyrite become to pyrrhotite. In order to understand magnetic characteristics of low-grade metamorphic rocks in the Hsuehshan Range and the Central Range of Taiwan, rock magnetic measurements of the hysteresis loop, X-ray diffractions and scanning electron microscope were carried out on samples collected from the Eocene to Miocene strata along the Northern and Southern Cross-Island Highway. The stratigraphic position of the first appearance of pyrrhotite in both the Northern and Southern Cross-Island Highways is very consistent with the anchizone/epizone boundary defined by illite crystallinity. This is helpful for stratigraphic correlation between the formations in the Hsuehshan and the Central Ranges. In addition, the authors tested the possibility that pyrrhotite could have a detrital origin by conducting a source-to- sink study and found pyrrhotite in metamorphic rocks of the Taiwan Central Range. They suggest that detrital pyrrhotite is a potentially important remanence carrier in sedimentary basins that receive input from exhumed regional metamorphic belts in orogenic zones around the world. Finally, they reported that pyrrhotite is more common than magnetite in Taiwan’s orogen, which has been exhumed episodically during the Plio-Pleistocene. In conclusion, apart from its utility as a tracer for source-to- sink transport of sediments, pyrrhotite can also be used to reconstruct the exhumation and denudation history of Taiwan’s orogen and similar orogens with high denudation rates.
Reference
Horng, C. S., & Roberts, A. P. (2006). Authigenic or detrital origin of pyrrhotite in sediments?: Resolving a paleomagnetic conundrum. Earth and Planetary Science Letters, 241(3), 750-762.
洪崇勝、陳國航、林俊宏(2011)臺灣北部橫貫公路低度變質岩之岩石磁學 兼論雪山山脈與中央山脈之地層對比。經濟部中央地質調查所特刊第二十 五號，第 167-179 頁。
Horng, C. S., Huh, C. A., Chen, K. H., Lin, C. H., Shea, K. S., & Hsiung, K. H. (2012). Pyrrhotite as a tracer for denudation of the Taiwan orogen. Geochemistry, Geophysics, Geosystems, 13(8).