Supplemental road log 1, from Lordsburg to Redrock to Ash Creek in the northern Burro Mountains, New Mexico
— Virginia T. McLemore, O. Tapani Ramo, and Paula J. Kosunen

The Redrock area in the northern Burro Mountains in southwestern New Mexico is a complex Proterozoic terrain consisting of metamorphic rocks (Bullard Peak and Ash Creek Series) intruded by a variety of granitic rocks. The purpose of this trip is to acquaint visitors with the complexity of the Proterozoic granitic rocks. Stops I and 2 are on the Redrock Wildlife Refuge; permission must be obtained from the New Mexico Game and Fish Department to enter refuge. At Stop l, we will examine the relationships between anorthosite xenoliths, metamorphic xenoliths, and miarolitic biotite granite [Redrock granite (informal name)]. Approximately 50 small anorthosite xenoliths are scattered in a northeast-trending zone throughout the miarolitic biotite granite phase of the Redrock granite. No other Proterozoic anorthosite occurrences have been reported from New Mexico and they are, in general, quite rare throughout the United States.

At Stop 2, we will have lunch and examine an intrusive contact between the Redrock granite (hornblende-granite phase) and Jack Creek rapakivi granite (informal name). Rapakivi is Finnish for rotten or crumbly rock and describes the tendency of the rapakivi granite found throughout the eastern portion of the game refuge to weather easily. The rapakivi texture refers to the mantling of K-feldspar phenocrysts by plagioclase. Most rapakivi granites are middle-early Proterozoic, although rapakivi textures have been described from some Phanerozoic and Archean granites. The petrogenesis of rapakivi granites is controversial and questions remain as to the source of the rapakivi magma, the genetic relationships between the granite and penecontemporaneous mafic rocks, the origin of the rapakivii texture, and the tectonic setting of these rocks.

At Stop 3 we will examine possible coeval enclaves and synplutonic dikes of lamprophyre (minette) found associated with the Jack Creek rapakivi granite. The relationship and petrogenesis of spatial and temporal association between the rapakivi granite and minette remains unknown. Spatial and temporal association of rapakivi granite and lamprophyre is rare in the world.