Mineralogy, petrology, geochemistry and crystal size distribution of Tertiary plutons of the central Wasatch Mountains, Utah.

摘要

Eleven Tertiary (28-41 Ma) intrusives crop out in the Wasatch Intrusive Belt in the central Wasatch mountains, Utah. They include, from west to east, three phaneritic stocks, the Little Cottonwood (LCS), the Alta (AS) and the Clayton Peak (CPS), five porphyritic stocks (collectively the Park City Porphyries), the Park Premier porphyry (PPS), and Indian Hollow Plug (IHP).;Quantitative modelling, coupled with the features described above, suggests that a genetic link between all of the intrusives is permissible. Thus, with the exception of CPS, these intrusives may represent a single magma source which intruded successively later and deeper to the west. CPS is likely related to the other plutons as the deviations from the chemical trends may represent a greater degree of crustal contamination.;Mafic enclaves and schlieren are enriched in mafic minerals and occur along the outer margins of LCS and AS. The mineral assemblages, as well as mineral chemistries, of enclaves and schlieren are identical to those of their respective host plutons. They are more mafic due to the higher modal abundance of mafic minerals. Chemistry and textures suggest that the enclaves and schlieren are comagmatic, possibly cumulate in origin. Crystal size distribution (CSD) analyses of Fe-Ti oxides and biotite reveal that magmatic processes such as crystal settling and convection, possibly accompanied with fines destruction, were occurring in LCS and AS. Data for the remainder of the stocks implies that continuous nucleation and growth occurred throughout the solidus interval. For these stocks, the data suggest that the growth rates were lower and thus, residence times higher for CPS than for the porphyritic stocks.;These intrusives are calc-alkaline, generally metaluminous I-type granitoids. Harker variation diagrams generally exhibit linear trends. However, CPS is depleted in Al