New Mexico Geological Society Annual Spring Meeting — Abstracts

Assembly of southwestern Laurentia during the Paleoproterozoic Yavapai and Mazatzal orogenies is well-documented. An additional tectonic event, the Mesoproterozoic Picuris Orogeny, has been proposed (Daniel et al., 2013, GSA Bulletin, 125:1423-1441) based on 1600-1475 Ma detrital zircons in the Piedra Lumbre Formation of the Hondo Group, Picuris Mountains, northern New Mexico. These ages are consistent with source rock derivation from Australia and Antarctica. Units underlying the Piedra Lumbre Fm., including the Rinconada Formation, contain detrital zircons with a unimodal age of ca. 1710 Ma (Daniel et al., 2013), most likely sourced from local rocks of Yavapai age. This study evaluates the change in provenance by analyzing detrital tourmalines from the Rinconada and Piedra Lumbre Fms in the Copper Hill Anticline, Picuris Mountains. Tourmaline is an ideal mineral for sediment provenance studies because it forms in a wide pressure-temperature-composition range, incorporates a fingerprint of its host rock chemistry, has very slow diffusion rates, and is resistant to abrasion. By focusing on distinct detrital cores in tourmaline grains, reflecting the original lithologic association in which tourmaline formed, a change in source region can be evaluated. Laser-Induced Breakdown Spectroscopy (LIBS) spectra are rich in information, including the concentrations of all elements, isotopic ratios, and information on the structure of the analyzed material, thus helping to identify source lithology and changes in provenance. LIBS spectra are modeled using Partial Least Squares Regression (PLSR) in a matching algorithm developed to identify the lithology in which the tourmaline crystallized. In this study, 209 spectra were collected from the Rinconada Fm. and 50 of those spectra were tourmaline. Of the 50 tourmaline spectra from the Rinconada Fm., 24 crystallized in pelitic metamorphic rocks, 4 crystallized in calcareous metamorphic rocks, 8 crystallized in Li-poor pegmatites and silicic igneous rocks, and 14 crystallized in hydrothermal and miscellaneous rocks. In contrast, none of the 3274 spectra collected from the Piedra Lumbre Fm. were tourmaline. Source regions for the Rinconada and Piedra Lumbre Fms are interpreted to be different due to the presence of tourmaline in the Rinconada Fm. and the lack of tourmaline in the Piedra Lubmre Fm.