Provenance of detrital tourmalines from Proterozoic metasedimentary rocks in the Picuris Mountains, New Mexico, using Laser-Induced Breakdown Spectroscopy

Tourmaline is a useful mineral for determining provenance of sediments. Here, detrital tourmaline has been used to evaluate provenance for the Rinconada and Piedra Lumbre formations in the Copper Hill Anticline, Picuris Mountains, New Mexico, USA to assess the existence of the Mesoproterozoic Picuris Orogeny. This orogeny has been proposed by other authors based on the presence of 1600-1475 Ma detrital zircons in the Piedra Lumbre Formation of the Hondo Group and Yavapai age (1780-1700 Ma) detrital zircons in units underlying the Piedra Lumbre Formation, including the Rinconada Formation. Optically distinct detrital cores of tourmaline grains from the Rinconada and Piedra Lumbre formations were analyzed using Laser-Induced Breakdown Spectroscopy (LIBS) to establish likely lithologic sources. A total of 209 LIBS spectra of detrital grains were collected from the Rinconada Formation, 50 of which were tourmaline. Based on multivariate analysis of these 50 tourmalines, 24 are most likely from pelitic metamorphic rocks, four from calcareous metamorphic rocks, eight from Li-poor pegmatites and silicic igneous rocks, and 14 from hydrothermal rocks. In contrast, none of the 3274 LIBS spectra collected from the Piedra Lumbre Formation were from tourmaline. Source regions for the Rinconada and Piedra Lumbre formations are interpreted to be different due to the presence of tourmaline in the Rinconada Formation and its absence in the Piedra Lumbre Formation. Based on detrital tourmaline data, evidence for a change in provenance supports the proposed Picuris Orogeny.