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- Characteristics and implications of ca. 1.4 Ga deformation across a Proterozoic mid-crustal section, Wet Mountains, Colorado, USA
Characteristics and implications of ca. 1.4 Ga deformation across a Proterozoic mid-crustal section, Wet Mountains, Colorado, USA
Auteur :
V. Jones III
James,
S. Siddoway
Christine,
N. Connelly
James
Date de publication : 21/09/2010
Type : Article
Thème : Lithosphère
Couverture :
Etats-Unis d'Amérique
URL Article :
http://www.geo.umass.edu/structure/Jones%20et%20al-Lithosphere-2010-WetMtns.pdfURL Source :
http://www.geo.umass.edu 
Télécharger le document :
(1,86 MB) characteristics_implications_deformation_proterozoic_mid-crustal_wet-mountains_colorado.pdfRésumé/Sommaire :
In the Wet Mountains, Colorado, Proterozoic rocks exposed along an oblique north-south tilted section preserve evidence of regional deformation and high temperature metamorphism in the middle and lower crust at ca. 1435–1365 Ma. Deformation of gneisses in the northern Wet Mountains is partitioned within discrete zones of subvertical foliation and northeast-trending folds, a product of northwest-southeast contraction or constriction associated with transcurrent deformation. Gneisses in the north are generally not migmatitic, and granitic intrusions form discrete bodies with distinct contacts. Shear zone foliation is cut by a late syntectonic dike with a U-Pb zircon age of 1430+5/–3 Ma, constraining the age of shear zone deformation in the upper crust. In the central to southern Wet Mountains, gneisses exhibit migmatitic foliation that dips moderately northeast, with dip- to oblique-slip mineral lineation throughout. Granite forms pervasive sills and interconnected sheets with gradational or indistinct contacts. Gneissic granite that yields a U-Pb zircon age of 1435 ± 4 Ma was emplaced into amphibolite gneiss containing 1436 ± 2 Ma metamorphic zircon. Younger, foliated granite sills were emplaced at 1390 ± 10 Ma. Our new results indicate contemporaneous deformation and metamorphism throughout the middle and lower crust at ca. 1.4 Ga. We interpret the zone of migmatitic crust pervaded by granite to represent a weak, low-viscosity, fl owing lower crust that controlled the pattern of distributed deformation in the comparatively strong, brittle crust above. Thus, the Wet Mountains may be viewed as a deeply exhumed analog for the mid-crustal, low-viscosity layers that are inferred to exist in modern intracontinental orogenic settings and continental rift provinces.
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