Metasomatic transformations of carbonate rocks observable in quarries of Riverside, California, United States
The results of skarn-forming processes at contacts of the multiphase Southern California Batholith with carbonate rocks accessible to study in quarries in Riverside, California, involve prograde metasomatic transformations of marmorized dolomites and calcareous rocks in contact with granitic melts and contaminated magmas. The processes of contact assimilation are proved to have been controlled by the emplacement of granitic melts overheated relative to subliquidus melts (with the overheated melts prone to approach the composition of granodiorite, syenite, and gabbro) into skarnified marbles. The degree of magma overheating was evaluated based on G.F. Smith’s data on linear melting temperature variations for anhydrous intrusive rocks with various SiO2 concentrations ( 1100°C for contaminated rocks, ΔT 350°). This corresponds to the thermal regime of the development of mineralogically contrasting hypabyssal skarn aureoles: magnesian at contacts with granite magmas and calcic at contacts with melts of high basicity. The peripheral parts of the aureoles ubiquitously contain preserved zones of forsterite calciphyres and periclase marbles, whereas skarns at mafic intrusions consist of high-temperature silicates of decreasing Mg contents: monticellite, merwinite, melilite, and spurrite. Prograde and retrograde mineralforming processes in the metasomatic rocks and their facies affiliation are analyzed, and the chemical composition of the minerals are examined. The Riverside skarn aureoles are compared with other compositionally contrasting skarn aureoles that developed in contacts with granite magmas and melts of increasing basisity.