Granitic rocks are commonly used as a means to study chemical evolution of continental crust. In particular, their isotopic compositions reflect the relative contributions of mantle and crustal sources in their genesis. In Laurentia, a distinctive belt of Mesoproterozoic A-type or “anorogenic” granites of ∼1.4 Ga age was emplaced within composite, heterogeneous Proterozoic crust. Zircons are an...

The Indian Peak volcanic field is representative of the more than 50,000 km3 of ashflow tuff and tens of calderas in the Great Basin that formed during the Oligocene-early Miocene "ignimbrite flareup" in southwestern North America. The field formed about 32 to 27 Ma in the southeastern Great Basin and consists of the centrally positioned I n d i Peak caldera complex and a surrounding blanket of...

The hydrous species geospeedometer is based on the homogeneous interconversion reaction between molecular H2O species and OH species in silicate melts and glasses. Here we report new data for the calibration of the geospeedometer in rhyolitic glass, extending the coverage of quench rate to 94 K/s and of H2Ot to 7.7 wt.% by using a piston-cylinder apparatus at low pressures (200–500 MPa) to prev...

pillow lavas are locally conspicuous. A unit consisting of dark, thinly bedded sandstone and siltstone, lccally ranging to several hundred feet thick, is lowermost in the exposed section. The middle division consists of about 3,500 feet of mixed andesi.:e and basalt volcaniclastic rocks ~ lahar, tuff breccia, volcanic sandstone, and conglomeratic beds which rest on relatively thin, fossiliferou...

Data from the U.S. Geological Survey’s National Water Information System (NWIS) database reveal the existence of a number of thermally anomalous areas on the eastern Snake River Plain (ESRP) aquifer, most of them near its margins, and NWIS temperature and chemistry data provided conclusive evidence that thermal waters originating in the hot rhyolitic rocks underlying the ESRP basalts inject hea...