CHARACTERIZING HEMATITE IN CLASTIC SANDSTONE INJECTITES OF THE COLORADO FRONT RANGE USING PALEOMAGNETISM AND ROCK MAGNETISM

Sandstone injectites within the Pikes Peak Granite of the Colorado Front Range have been a point of interest since first observation in 1894. They are massive, mature sandstones that range from being centimeters in width to tens of meters and have no internal depositional stratigraphy. They trend N-S along the Ute Pass Fault Zone, but lack a nearby source rock. Previous studies on the dikes have shown probable timing of emplacement, but not a clear emplacement mechanism. Geochronological dating has constrained timing of dike emplacement to the Proterozoic and there are three primary hypotheses for method of emplacement: (1) glaciation deposition during a Snowball Earth event, (2) liquefaction and remobilization of sandstone, and (3) shallow sea deposition. This study focuses on characterizing magnetic minerals through rock magnetic and paleomagnetic analyses and microscopy to understand possible emplacement mechanisms of the dikes and use paleomagnetic dating to confirm age constraints on the dikes. Anisotropy of Magnetic Susceptibility (AMS) analysis was run on 117 core specimens from twenty five sub-sites, with preliminary findings indicating oblate fabrics in 11 sites, triaxial in 10, isotropic in two and prolate in two. These results indicating a strong tendency towards oblate magnetic fabrics are similar to observations made throughout other clastic dike studies. Although a good portion of the samples display AMS, there is another portion that preserve remanent magnetizations. Previous study has shown three characteristic remanent magnetizations were observed in clastic dikes with a characteristic remanent magnetization overlapping other Precambrian pole positions, (virtual geomagnetic pole = -13.9°N, 153.5°E°, dp=18.9, dm=33.5), and two additional component remanent magnetizations interpreted as chemical remanent magnetizations (CRMs) acquired during the late Paleozoic and end Mesozoic. All CRMs are interpreted to reside in hematite based on unblocking temperatures above 580 °C after stepwise thermal and AF demagnetization. Additional Scanning Electron Microscope (SEM) and reflected light microscopy will be conducted as well to confirm presence of hematite as the primary magnetic carrier and to discern the presence of magnetic fabric alignment as indicated by preliminary AMS analysis.