Journal of Petrology | Volume 44 | Number 4 | Pages 713-732 | 2003
© Oxford University Press 2003
Petrogenesis of Mesozoic, Peraluminous Granites in the Lamoille Canyon Area, Ruby Mountains, Nevada, USA
1 DEPARTMENT OF GEOSCIENCES, TEXAS TECH UNIVERSITY, LUBBOCK, TX 79409-1053, USA
2 DEPARTMENT OF GEOLOGY AND GEOPHYSICS, UNIVERSITY OF WYOMING, LARAMIE, WY 82071-3006, USA
3 US GEOLOGICAL SURVEY, MS 975, 345 MIDDLEFIELD ROAD, MENLO PARK, CA 94025, USA
E-mail: Cal.Barnes{at}ttu.edu.
Two groups of closely associated, peraluminous, two-mica granitic gneiss were identified in the area. The older, sparsely distributed unit is equigranular (EG) with initial 
Nd 
- 8·8 and initial 87Sr/86Sr 0·7098. Its age is uncertain. The younger unit is Late Cretaceous (80 Ma), pegmatitic, and sillimanite-bearing (KPG), with Nd from -15·8 to -17·3 and initial 87Sr/86Sr from 0·7157 to 0·7198. The concentrations of Fe, Mg, Na, Ca, Sr, V, Zr, Zn and Hf are higher, and K, Rb and Th are lower in the EG. Major- and trace-element models indicate that the KPG was derived by muscovite dehydration melting (<35 km depth) of Neoproterozoic metapelitic rocks that are widespread in the eastern Great Basin. The models are broadly consistent with anatexis of crust tectonically thickened during the Sevier orogeny; no mantle mass or heat contribution was necessary. As such, this unit represents one crustal end-member of regional Late Cretaceous peraluminous granites. The EG was produced by biotite dehydration melting at greater depths, with garnet stable in the residue. The source of the EG was probably Paleoproterozoic metagraywacke. Because EG magmatism probably pre-dated Late Cretaceous crustal thickening, it required heat input from the mantle or from mantle-derived magma.
KEY WORDS: leucogranite; Late Cretaceous; crustal melting; Sevier orogeny; peraluminous
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