NEW U-Pb DETRITAL ZIRCON GEOCHRONOLOGY OF QUARTZITES FROM THE ALBION-RAFT RIVER-GROUSE CREEK METAMORPHIC CORE COMPLEX OF SOUTHERN IDAHO: IMPLICATIONS FOR NEOPROTEROZOIC TO CAMBRIAN CORRELATIONS

Previous workers constructed a regional tectonostratigraphic framework for Neoproterozoic to Cambrian rocks across western North America, providing insights into provenance trends during rifting. While these rocks show strong similarities along much of the ancient rift margin, more outboard strata have since been deformed and metamorphosed, leading to uncertainty about their regional correlatives and stratigraphic positions. Within the Albion Mountains in the Albion-Raft River-Grouse Creek (ARG) metamorphic core complex of southern Idaho and northern Utah, workers have debated the age of a thick, predominantly quartzitic, fault-bounded package of metasedimentary rocks in the hanging wall of the Basin-Elba fault. These rocks were variably interpreted by prior workers as Ordovician to Paleoproterozoic in age, raising questions about their stratigraphic correlation to rocks exposed in the footwall of the Basin-Elba fault and correlative rocks in the Raft River Mountains ~50 km to the south. We collected six new samples from rocks in the hanging wall of the Basin-Elba fault and analyzed them using LA-ICP-MS. Detrital zircon age distributions exhibit an up-section loss of Stenian (1.0–1.2) grain ages followed by a prominent 1.5–1.7 Ga age peak at the top, similar to other known Neoproterozoic to Cambrian units throughout the northern Rocky Mountains.

We then used multidimensional scaling (MDS) techniques to evaluate a possible correlation among U-Pb detrital zircon age distributions from these rocks, the McCoy Creek Group of Nevada, the Brigham Group of Idaho and Utah, and the Raft-River sequence of northern Utah. Quantitative comparison using MDS shows that Neoproterozoic strata of the McCoy Creek Group and Brigham Group are most similar to the lower units in the Basin-Elba thrust hanging wall, whereas the stratigraphically highest units are most similar to other well-known Cambrian units. We interpret that deposition of protoliths of these rocks spanned the Neoproterozoic to Cambrian transition. Although our tentative correlations better place rocks from the hanging wall of the Basin-Elba fault into the established tectonostratigraphic framework, the apparent absence of these rocks in the Raft River Sequence is anomalous.