PROVENANCE ANALYSIS OF SEDIMENTS RELATED TO THE CAMBRIAN ROSS OROGEN, ANTARCTICA: LASER-INDUCED BREAKDOWN SPECTROSCOPY ANALYSIS OF DETRITAL TOURMALINE

Tourmaline (tur) is a complex borosilicate mineral with the ability to incorporate a large number of chemical elements that reflect its host, which makes it ideal for provenance studies. It is sufficiently durable to persist through erosional, depositional and metamorphic episodes, while retaining the chemical signature of its lithological source. The most common source lithologies for tourmaline comprise six major groups and are modeled in this work based on elemental fingerprints within ca. 250 samples with known host-rocks by applying the multivariate techniques of principal component analysis (PCA) and partial least squares regression (PLSR) to Laser-Induced Breakdown Spectroscopy (LIBS) spectra. These categories include: lithium-cesium-tantalum-rich pegmatites (LCT), niobium-yttrium-fluorine-rich pegmatites (NYF), metacarbonate rocks, pelitic metamorphic rocks, silicic igneous rocks, and hydrothermal deposits. LIBS spectra of detrital tur grains from Neoproterozoic passive-margin sandstones and Cambrian-Ordovician syn- and late-tectonic Ross Orogen sandstones from East Antarctica were sorted into the six major source-lithology categories using PLSR and cluster analysis was used to define compositional groups within each category. Passive-margin sediments contain tur from NYF, hydrothermal, and silicic igneous sources. Some of these populations persist from the passive margin stage through the syn- and late-tectonic stages of the Ross Orogen; new populations of NYF, hydrothermal and silicic igneous tur as well as tur from LCT, metapelitic, and metacarbonate sources also occur in the syn- and late-tectonic sediments. Consistent with detrital zircon geochronology, it is possible that the populations of syn- and late-tectonic detrital tur shared by the passive-margin sediments were either recycled from deformed passive-margin sedimentary rocks or derived from similar sources during tectonic exhumation. New tur sources were produced by igneous, metamorphic, and hydrothermal processes during the Ross Orogen. This study demonstrates that provenance studies based on the chemical analysis of detrital tur with LIBS and multivariate analysis is viable and can discriminate changing source patterns.