Trace element and calculated temperature variation in quartz and titanite in the 36 Ma Harrison Pass population, Ruby Mountains NE Nevada
Deans, Jeremy R. L.
MetadataShow full item record
The 36 Ma Harrison Pass pluton is composed of four units defined by previous studies: the Toyn Creek hornblende biotite granodiorite interpreted as a hybrid, the Corral Creek biotite monzogranite interpreted as the felsic end member of mixing for the Toyn Creek unit, sheets of leucocratic two‐mica monzogranite and the Green Mountain Creek two‐mica monzogranite. Field and petrogenetic evidence for mixing of intermediate magmas and fractionation has been presented. Quartz and titanite provide a record of these processes through trace element encorporation during growth. Using LA‐ICP‐MS, trace elements in quartz and titanite were measured. The TitaniQ thermometer for Ti in quartz and the Zr in titanite thermobarometer were used to estimate temperatures of crystallization. Quartz from the Toyn Creek unit are reversely zoned in calculated temperature, but trace element variation in quartz is insignificant suggesting mixing of thermally distinct, but compositionally similar magmas. Titanite calculated temperature and REE variation is reversely zoned suggesting mixing of thermally and compositionally distinct magmas. Quartz from the Corral Creek and Green Mountain Creek units are normally zoned in calculated temperature and trace elements suggesting the magma was cooling during growth. Trace elements in quartz from the Toyn Creek and Corral Creek units do not overlap, suggesting the Corral Creek unit may not be the felsic end member of mixing for the Toyn Creek unit. Trace elements in quartz from a porphyritic roof dike overlap with quartz compositions from the Corral Creek unit, but the dike is interpreted to originate from the Toyn Creek unit based on bulk‐rock geochemistry and mineral assemblage, suggesting quartz grains from the felsic end member were incorporated by mixing into the hybrid Toyn Creek magma. Trace elements in a phenocryst of quartz from a mafic magmatic enclave overlap with quartz compositions from the Toyn Creek unit suggesting the quartz phenocryst in the enclave oringinated in the Toyn Creek magma. This study shows chemical variation in individual crystals, which is easily overlooked at the whole rock scale, can be used to interpret and constrain magma processes. The calculated temperature and REE variations in titanite suggest magma mixing occurred in the Toyn Creek unit. The calculated temperature and trace element variation in quartz suggests the Toyn Creek unit was assembled in batches. Temperature and trece element zoning in quartz from the Corral Creek and Green Mountain Creek units are consistent with fractional crystallization.