Structural evolution of the northeastern Santa Catalina Mountains, Arizona: A glimpse of the pre-extension history of the Catalina complex.

摘要

The Catalina complex, like the other Cordilleran metamorphic core complexes, experienced an episode of profound middle Tertiary extension that resulted in low-angle mylonite zones and detachment faults. However, the northern and eastern parts of the complex escaped significant middle Tertiary deformation and preserved a record of the complicated Mesozoic and early Cenozoic tectonic history that preceded middle Tertiary extension. A detailed examination of the northeastern Santa Catalina Mountains and a reconnaissance study of the rest of the Catalina complex reveal evidence for Cretaceous-earliest Tertiary (Laramide) thrusting and an enigmatic episode of early Tertiary (Eocene?) magmatic intrusion, metamorphism and ductile deformation. Laramide thrusting is represented by the Edgar and Youtcy thrusts. The Edgar thrust, a southwest(?)-vergent bedding-subparallel fault that repeats 300-500 m of section, is intruded by the 64 Ma Leatherwood Quartz Diorite. The northeast(?)-vergent Youtcy thrust repeats at least 1300 m of section and is intruded by the Eocene(?) Wilderness Granite. The early Tertiary orogenic event is represented in the northeastern Santa Catalina Mountains by the Eocene(?) Wilderness Granite, its metamorphic aureole, widespread low-grade metamorphism, bedding-subparallel foliations, east-trending lineations, and several bedding-subparallel stretching(?) faults that omit strata. Numerous kinematic indicators show that the ductile deformation involved top-to-the-east shear. Cross-cutting relationships between the foliation, the faults and the Wilderness Granite and coincident gradients in strain magnitude, metamorphic grade, rock ductility, and fault offset demonstrate that intrusion, metamorphism, ductile flow and faulting were all contemporaneous and that the heat source for the metamorphism and ductile flow was the Wilderness Granite. Evidence for the early Tertiary event extends into the rest of the Catalina complex but lineation trends and shear directions vary considerably from region to region. Furthermore, abundant steep east-striking foliations within the Wilderness Granite batholith appear to have formed during this event. The tectonic significance of the early Tertiary orogenic episode is unclear. Three hypotheses may explain the wide variety of early Tertiary structures: forceful diapiric intrusion of the Wilderness Granite, late-stage Laramide thrusting imposed on a tilted section, or early-stage crustal extension.