Mantle Metasomatism and Alkaline Magmatism

Slickrock Mountain intrusive complex, Big Bend National Park, Texas
-
Published:January 01, 1987
Slickrock Mountain consists of two major sills intruded into Upper Cretaceous calcareous sandstone. The sills are an older Eocene quartz syenite approximately 200 m thick and a younger Oligocene alkali olivine gabbro approximately 100 m thick. Smaller mafic dikes and sills are abundant in the area. The quartz syenite contains fayalitic olivine and zoned alkali feldspar with plagioclase cores set in an intergranular ground-mass of anorthoclase, sanidine, quartz, clinopyroxene, magnetite, and apatite. The smaller mafic intrusions commonly contain kaersutite megacrysts and an assemblage of crustal xenoliths that includes coarse-grained gabbro and partially fused feldspathic arenite. Major and trace element data do not support the derivation of the felsic compositions from the mafic ones by simple crystal fractionation at low pressure. The presence of kaersutite megacrysts and partially fused crustal xenoliths in nearby sills and dikes suggests that derivation of the Slickrock quartz syenite from some combination of fractionation and crustal assimilation at elevated pH2O is possible. However, trace element concentrations indicate that the syenitic and gabbroic rocks are petrogenetically unrelated.
- Aguja Formation
- Big Bend National Park
- Brewster County Texas
- Cenozoic
- clastic rocks
- Cretaceous
- diorites
- Eocene
- gabbros
- genesis
- geochemistry
- Gulfian
- igneous rocks
- intrusions
- megacrysts
- Mesozoic
- mineral composition
- Oligocene
- olivine gabbro
- Paleogene
- petrography
- petrology
- plutonic rocks
- sandstone
- sedimentary rocks
- sills
- syenites
- Tertiary
- Texas
- trace elements
- United States
- Upper Cretaceous
- Slickrock Mountain Complex