Petrology of late Cretaceous and Cenozoic grantic rocks, East Humboldt Range, northeastern Nevada
Batum, Melissa Ann
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Cordilleran metamorphic core complexes form a discontinuous belt along the eastem North Amerícan CordiIIera from southem Canada to northwestem Mexico (Coney, 1980). Previous studies suggested that the age and tectonic significance of Cordilleran metamorptiic core complexes were related to Mesozoic regional compression (Thorman, 1977; Davis et al., 1980; DeWitt, 1980; Brown and Read, 1983; Coney and Harms, 1984). Cordilleran core complexes were thought to be uplifted deep crustal zones that formed behind Mesozoic thrust belts (Coney and Harms, 1984). Other studies, however, suggested that core complex development is mainly Tertiary in age and extensional in orígin (Coney, 1980; Críttenden. 1980; Howard, 1980; Snoke, 1980; Coney and Harms, 1984; McGrew, 1992). The latter of these two mechanisms, Tertiary continental extension, best explains the age and type of structures associated with the development of the Ruby-East Humboldt metamorphic core complex in northeastem Nevada (Snoke, 1980; McGrew, 1992). Along with the formation of metamorpluc core complexes, the relationship between Tertiary magmatism and the development of continental ríft zones is currently the subject of debate (Metcalf and Smith, 1995). The cause-and-effect relationships between magmatism and extension, as well as the timing and mode of magma generation duríng extension, are still unresolved (Metcalf and Smith, 1995). Resolution of some of the problems regarding the linkage between magmatism and extension involves several important issues including (1) the nature of magmatism and its relationship to extension in both a spatial and temporal sense, (2) the petrogenesis of magmas produced before, duríng, and after extension, (3) the significance of pluton emplacement, and (4) geophysical constraints on the formation of continental ríft zones (MetcalfandSmith, 1995).