A generally finely crystalline or glassy igneous rock resulting from volcanic action at or near the earth's surface, either ejected explosively or extruded as lava. The term includes near-surface intrusions that form a part of the volcanic structure.
Nd and Pb isotopic analyses from stratigraphic sampling from Somma-Vesuvius volcanic complex, Italy, during the last 3550 years point to contributions from heterogeneous lithosphere, continental crust, and magma mixing.
Mineralogical data on samples from the surface and from drill cores, with geological observations help to understand the hydrology and effects of geology on acid-rock drainage in a mineralized alpine watershed.
This map, compiled from geologic mapping conducted (1985-1992) by the U.S. Geological Survey as part of the Alaska Mineral Resource Assessment Program, builds upon previous USGS work unraveling the magmatic history of the Alaska-Aleutian Range batholith.
A geologic map constructed primarily from reconnaissance studies from the 1950s to 1990s. The rocks of the map area range from Proterozoic age metamorphic rocks of the Kanektok metamorphic complex to Quaternary age mafic volcanic rocks of Nunivak Island.