Evidence for the generation of juvenile granitic crust during continental extension, Mineral Mountains Batholith, Utah

Field, chemical and isotopic data are consistent with the batholith being derived through differentiation of material recently separated from the lithospheric mantle, with little involvement of pre-Oligocene crust. The batholith ranges in composition and texture from diabase and gabbro to high-silica rhyolite and granite and is distinctly calcalkaline in nature. Field evidence for anatexis of intermediate-composition Oligocene crust and magma mixing suggest that fractional melting and mixing were important processes during the evolution of the batholith. Major oxide and rare earth element data for the batholith are consistent with chemical evolution of the magma system being controlled by fractionation of hornblende, plagioclase and sphene during partial melting, and mixing between gabbro and granite. Isotopic data indicate a lithospheric mantle source for mafic rocks in the study area and, on the basis of field data and their similarity in isotopic compositions, granitic rocks are interpreted to be derived indirectly from the same source during Basin and Range extension