PALEOMAGNETIC AND PETROGRAPHIC INVESTIGATION OF CLASTIC DIKES IN THE PIKES PEAK GRANITE, FRONT RANGE, COLORADO

Clastic dikes of unknown age and origin occur within the Pikes Peak Granite along nearly 75km of Colorado’s Front Range. These dikes are spatially associated with north and northwesterly trending thrust faults along the eastern margins of the range. The study area focuses on clastic dikes which are parallel to the predominately northern trending Ute Pass Fault near Woodland Park, Colorado, as well as dikes which trend northwesterly and are parallel to the Pine Gulch Fault near Pine, Colorado. Paleomagnetic sampling and subsequent demagnetization of these dikes indicates the presence of a complex multicomponent magnetization with at least four components. An easterly and moderately steep component residing in hematite was resolved from several dikes and corresponds to a late Precambrian to early Cambrian pole position when compared to the apparent polar wander path of North America. This early magnetization may have been acquired soon after emplacement of the dikes and is therefore interpreted as a primary magnetization. An east-southeasterly and shallow magnetization, also residing in hematite, yields a pole of early Paleozoic age. Another southeasterly and moderately shallow magnetization yields a direction that is late Paleozoic. The fourth component is northwesterly and steep down and is Mesozoic or Cenozoic in age. These results are similar to a previous paleomagnetic study (Kost, MS thesis, Univ. Colorado) in 1984 of different dikes which found poorly defined early and late Paleozoic, as well as Mesozoic-Cenozoic components. Petrographic analysis of the dikes is ongoing to determine the origin of the sands, which some authors have suggested is Cambrian age Sawatch sandstone. The dikes are mostly composed of quartz, with smaller percentages of feldspars and abundant authigenic hematite, which gives many of the dikes their red coloration. The dikes are predominately quartz cemented, with varying degrees of induration. The compositional variations between the dikes when coupled with the complex magnetization history suggests that the dikes have been subjected to several events that have led to one or more remagnetizations since their emplacement.