| Popis: |
Dynamic analyses of quartz deformation lamellae and microfractures in lower Paleozoic quartzites from the White River Uplift record a northwest direction of compression which can be related to joint and fault orientations and in situ stress determinations. Crystallographic orientations of deformation lamellae resemble those formed in the subbasal I, relatively nonselective domain. Microfractures in quartz grains form orthogonal sets of generally north-northeast– and west-northwest–trending fracutres which are approximately normal to bedding. The strongest set of microfractures in most samples lies in the σ – σ 2 plane deduced from deformation lamellae analyses, suggesting that the microfractures are extensional features. Maxima of microfractures correspond to maxima of joints measured at adjacent locations. The strikes of prominent west-northwest sets of microfractures and joints are subparellel to the dominant northwest strike of faults on the uplift. In situ stress measurements conducted in the Piceance Basin and Rangely, Colorado, areas indicate principal stress orientations similar to those determined from quartz deformation lamellae, microfractures, and joints which are pre-uplift to early uplift, late Laramide fabric elements. |
