Lackey Reports on Batholith Beginnings

In the April issue of Geosphere, Jade Star Lackey and colleagues report on the origin and evolution of the Fine Gold Intrusive Suite, a ~2000 square kilometer group of trondhjemites, tonalities, and granodiorites in the western Sierra Nevada batholith, CA. The study is the first comprehensive geochronology and isotopic study (using the mineral zircon) of the Fine Gold suite, and sheds considerable new light on the nascent stages of magmatism in the Sierran magmatic arc. In addition, the study presents the first published hafnium isotope analyses in the Sierra, which together with oxygen isotopes, show a marked transition in magma sources from ones that recycle accreted terranes, to those that assimilated North American continental crust. Pomona student authors on the project include Cameron Windham (PO’11) and Ryan Frazer (PO’09), and the study was done in collaboration with researchers at CSU-Northridge (Cecil), U. of Arizona (Gehrels), and U. of Oregon (Bindeman).