Petrology of the Chilliwack batholith, North Cascades, Washington: generation of calc-alkaline granitoids by melting of mafic lower crust with variable water fugacity

Article Abstract:

Petrologic analysis of calc-alkaline (CA) granitoid rocks from the Chilliwack batholith in North Cascades, WA, revealed the role played by fractional crystallization and crustal anatexis in the generation of the granitoids. It was suggested, however, that petrologic differences between the intermediate and leucocratic plutons of the batholith resulted mainly from differential melting reactions in the CA magma. Origin for the granitoid magma was surmised to be an amphibolitic lower crust with rare earth elements and strontium-niodynium isotopic characterictics similar to the exposed gabbros.

Washington, Composition, Granite, Washington (State), Alkalic igneous rocks

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The age and origin of a thick mafic-ultramafic keel from beneath the Sierra Nevada batholith

Article Abstract:

The Sierra Nevada mountain range in California exposes a large Mesozoic composite Cordilleran batholith. Several Miocene mafic-intermediate volcanic centers in this batholith contain xenoliths of lower crustal and upper mantle origin. Determination of the Sm-Nd and Rb-Sr ages, the 143Nd/144Nd and the 87Sr/86Sr isochron intercepts of nine samples from a suite of lower crustal and upper mantle xenoliths indicated a direct connection to the Sierra Nevada batholith outcrops and the xenoliths. There is physical evidence of an approximately 100 km thick basolith section.

Geology, Stratigraphic, Mesozoic Era, Stratigraphy, Sierra Nevada (United States), Rocks, Igneous, Xenoliths

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Geochemistry of mafic dykes in the Antarctic Peninsula continental-margin batholith: a record of arc evolution

Article Abstract:

Detailed east-west and north-south sampling of mafic dikes in the Antarctic Peninsula continental-margin batholith were conducted to determine temporal and spatial variations in mantle sources of mafic magma supplying this arc. Results showed that the dikes are compositionally diverse and can be divided into five groups: calc-alkaline, shoshonite, high large ion lithophile elements tholeiite, tholeiite and ocean island basalt-like. The dikes provide data about magma sources during the Mesozoic-Cenozoic subduction history.

Geochemistry, Antarctic Peninsula, Dikes (Geology)

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