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Metamorphic Core Complexes

References:Okaya and Thompson, 1986, GSA Special Paper 208Dokka, 1986, GSA Special Paper 208Rehrig, 1986, GSA Special Paper 208Wernicke, 1992, G3 Ch. 12

Wernicke, 1992 Wernicke, 1992

Wernicke, 1992

Smith, 1978, fig. 6-1

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Thinned Crust ModelAssume:A 42 km thick crust as in the Colorado PlateauDensity contrast of 0.4 g/cc3

If extended and thinned to 50% (28 km) it would sink 1.7 km

Okaya and Thompson, 1986

Intrusion Model� Basin and Range stands ~ 1 km asl

� Low density mass must have intruded

� Mantle derived products are the likely solution

Metamorphic Core

Complexes

� Mid-crustal metamorphic rocks in fault contact with stratified cover

� Washington to Idaho

Rocky MountainCore Complexes

Sierra Wasatch Region

� Major zone of metamorphic core complexes

Mojave-Sonoran Region

� Another zone of metamorphic core complexes

Detachment Faulting� Mylonitic rocks suggest high heat flow and

intrusion� Flat crustal anisotropy� Fluid-induced strain softening � Hydrothermal chlorite breccias above mylonite

Wernicke, 1981

Generation of Detachments

� Many mechanisms can produce them

� Common features of Detachments

� Crustal extension

� Shallow dipping sole plate

� Ductile mylonitic zone beneath detachment

� Chloritic breccia above detachment

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Metamorphic Core Complex Uplift

� Isostatic response to upper-plate denudation

� Lower plate attenuation

� Magmatic upwelling

Rehrig, 1986

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Harcuvar ComplexHarcuvar Complex

Rehrig, 1986