METHOD DEVELOPMENT OF LASER-INDUCED BREAKDOWN SPECTROSCOPY AS A PROVENANCE TOOL FOR MODERN SEDIMENTS

Growing in its scope of geological applications, Laser-Induced Breakdown Spectroscopy (LIBS) is a rapid, cost-efficient, and user-friendly analytical technique that acquires information on the relative abundance of elements in a substance. This project seeks to develop a method in which LIBS is applied to provenance analysis of sediments in a modern drainage basin. By analyzing heavy detrital grains and grains from whole-rock samples exposed in the basin, detrital grains can be correlated to their host rock. While the exposed bedrock lithologies in the area have common heavy accessory minerals, LIBS spectra should capture the variations in elemental composition inherited from their environment of crystallization and be able to discriminate between bedrock lithologies. The basin, about 1.5 km² in size, is located in the Baylor Peak region of the Organ Mountains in southern New Mexico. Sediment samples are taken just above major confluences of the drainage basin and all exposed rock units are collected. Heavy minerals are separated from all samples and analyzed using LIBS. A decision tree that consists of a series of multivariate Partial Least Squares Regression (PLSR) models is used to classify the thousands of spectra by mineral species. Additional models, one for each mineral, are calibrated using exposed bedrock samples to classify each grain by its host rock. Mineral grains from sediment samples should only correlate to lithological units that are upstream in the particular drainage pathway from which the sample is taken. Preliminary data are presented from sediment samples located at the highest and lowest elevations in the drainage basin. At the highest elevation, heavy minerals from the sediment should only correlate to the rhyolite porphyry of Baylor Mountain. The lowest sample location should include mineral grains that correlate to a number of exposed lithologies. The success of this project could mean that LIBS is a viable tool to supplement or replace traditional analytical techniques which can be costly and time-consuming.