KINEMATIC ANALYSIS OF SEVIER OROGENY AND BASIN AND RANGE FAULTS OF THE ALLENS RANCH 7.5' QUADRANGLE, WEST-CENTRAL UTAH

The Allens Ranch quadrangle lies at the northern end of the East Tintic Mountains west of Utah Lake near the eastern margin of the Great Basin of central Utah. Geologic mapping of the quadrangle is focused on improving the understanding of the structural geology of the region, Paleozoic stratigraphy, and volcanic stratigraphy. The study is focused specifically on the kinematic and structural history of faulting and deformation within the quadrangle. Previous unpublished mapping of the quadrangle by Proctor (1985) identified the location of most of the faults within the quadrangle, but his detailed map is missing the faults’ sense-of-shear indicators and kinematic data. The NE trending faults are being examined to determine if their origin is related to fold and thrust faulting of the Mesozoic Sevier Orogeny or Late Neogene Basin and Range extension. This information will be useful for any future mineral exploration or reclamation of existing mines. The larger and richer replacement ore bodies in the East Tintic Mining District occur where the thrusts are cut by the NE-trending mineralized fissures and tear faults (Morris and Lovering, 1979). The structural history of the NE trending faults of the quadrangle was reconstructed from strike, dip and slip kinematic data (fault slickenline orientations, minor shear zones, fold axis orientations, fault orientations, etc.) and plotted using a stereograph to determine stress directions. Results from NE trending faults on Gardison Ridge show evidence for right lateral strike slip motion and give a σ₁ at about 280º, indicating Sevier related movement which also produced the large N-trending east-verging folds. The Tintic Davis Canyon fault, however, shows evidence for a combination of normal and strike-slip movement. Consequently we interpret this NNE-trending fault to be Basin and Range related but, perhaps with some strike-slip motion possibly related to Sevier age deformation. Over steepened volcaniclastic alluvial fans of Eocene-Oligocene age also show evidence that the eastern portion of the East Tintic Mountains experienced Basin and Range tilting of about 8º to the east.