Thermal behavior of various solid feldspars are different, namely those of bivalent cations show no change in the distribution of Al and Si atoms, whereas feldspars of univalent cations become more disordered with raising temperature. In the latter case Al atoms migrate from the sites they occupe at low temperatures and interchange positions with the Si atoms. At high temperatures (but stil...

We examine a database containing the results of Ar/Ar step-heating experiments performed on 194 basement K-feldspars to recover thermal history information. Qualitative examination of Ar/Ar systematics reveals that about half of the K-feldspars examined are sufficiently well behaved to be suitable for thermal history analysis. Correlation algorithms are developed to quantitatively assess the de...

At Long Valley (LV) model Sr isotope phenocryst ages and absolute U–Pb zircon ages from precaldera Glass Mountain (GM) and caldera-related Bishop Tuff (BT) rhyolites show that these crystals track >1 Myr of evolution of a voluminous rhyolite magmatic system. In detail, strong disparities between the different age populations complicate ideas for a unified model for rhyolite generation, differen...

We examine a database containing the results of Ar/Ar step-heating experiments performed on 194 basement K-feldspars to recover thermal history information. Qualitative examination of Ar/Ar systematics reveals that about half of the K-feldspars examined are sufficiently well-behaved to be suitable for thermal history analysis. Correlation algorithms are developed to quantitatively assess the de...

It is often assumed that physical and chemical processes determine the geochemical budgets of base cations on the earth's surface. Little or no consideration has been given to microbial processes despite the abundance of micro-organisms in surface and sub-surface environments (e.g. 106-109 bacteria cells/cm 3 in soils) combined with their ability to excrete a wide range of organic acids and che...