Dorn, R.I., ]990. Quaternary alkalini ty f luctuations recorded in rock varnish microlaminat ions on western U.S.A. volcanics. Palaeogeogr., Palaeoclimatol. , Palaeoecol., 76:291 310. Rock varnish contains an a l te rnat ing micron-scale layering of manganese-r ich and manganese-poor microchemical laminations. Holocene varnishes have lower Mn:Fe ratios when exposed to alkaline environments and ...

The target of this research is recognition the alteration zones utilizing concentration-area fractal methodology according to reflection main minerals each zone that enhanced by Spectral Feature Fitting (SFF) method due Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) satellite images in Saryazd porphyry system, central Iran. alterations mineralization developed Eocene vo...

a r t i c l e i n f o Keywords: silica-undersaturated volcanism 238 U-230 Th-226 Ra-210 Pb series disequilibria magma transport and residence time carbonate metasomatism volcanic hazard assessment The silica-undersaturated Nyiragongo volcanics, located in the East African Rift, have globally unique chemical compositions and unusually low viscosities, only higher than carbonatite lavas, for terr...

We present a comprehensive geochemical data set for the most recent volcanics from the Mariana Islands, which provides new constraints on the timing and nature of fluxes from the subducting slab. The lavas display many features typical of island arc volcanics, with all samples showing large negative niobium anomalies and enrichments in alkaline earth elements and lead (e.g., high Ba/La and Pb/C...

INTRODUCTION The Barketille subterrane is part of the peri-cratonic Kootenay termne, deposited along the western edge of ancestral North America. The Kooteoay temme, and possible correlative rocks of northern British Columbia and Yukon, contain numc~ous volcanogenic massive solphide deposits, concentrated largely in EoCambrian to Early Cambrian and Middle Devonian to Early Mississippian times. ...