During the Neogene and Quaternary, potassic and ultrapotassic magmas erupted in association with shoshonitic and calc-alkalic magmas across much of the Italian peninsula. On the basis of the temporal and spatial distribution of this volcanism, and its mineralogical and compositional characteristics, three different magmatic provinces have been defined. The northwesternmost province, the Tuscan Magmatic Province, is domi nated by leucite-free ultrapotassic rocks (lamproite), shoshonite, and minor calc-alkalic rocks. The Roman Magmatic Province is dominated by leucite-bearing rocks with variable degrees of silica saturation, from undersaturated (leucitites and plagio-leucitites) to strongly undersaturated (kamafugites), but minor amounts of shoshonitic to high-potassium calc-alkalic rocks are still present. The Lucanian Magmatic Province, located at the southeasternmost edge of the volcanic belt, is dominated by foiditic (haüynites and leucitites) and kamafugitic (melilitites) members, all strongly under-saturated in silica. In spite of these petrologic differences, the Neogene Italian potassic and ultrapotassic rocks display similar trace-element patterns. Depletion in high field strength elements with respect to large ion lithophile elements is a common feature. Sr, Nd, and Pb isotopic compositions of mafic high-MgO rocks range widely, relating mainly to geographic location of eruption and to enrichment in alkalies. The Os isotopic composition of these samples, however, does not clearly correlate with eruption location, but is dependent on the amount of “continental crust component” added to the magmas. Some of the studied samples are compatible with crustal contamination en route to the surface. In most cases, however, there are several lines of evidence suggesting the possibility that crustal components were added directly to the mantle source prior to partial melting. Large amounts (many tens of weight percent) of “crustal component” must be added to the peridotitic mantle in order to obtain the 187 Os/ 188 Os of the lamproites in Tuscany. These large amounts of crustal components have been recycled into the mantle in the form of either melts or fluids. The recycling can be reconciled with a veined mantle in which the crustal component is concentrated. Partial melting of veins would then produce the high-silica and high-magnesium lamproitic magmas from Tuscany. Dilution of the crustal components by increasing partial melting of surrounding mantle peridotite, or alternatively, a reduction of metasomatic veins, could then produce shoshonitic and high-K calc-alkalic mafic magmas. Southeastward geochemical and isotopic variations are reconciled with decreasing direct contributions from crustal components introduced into the mantle by sub-duction, but an increasing role of subducted fluids from dehydration of CO 2 -rich sediments. The coupled isotopic and chemical characteristics of Italian magmas cannot be reconciled with an ocean-island basalt (OIB)–like primary magma composition due to the substantial overprinting by crustal- and or subduction-related components.

The Western North American Volcanic and Intrusive Rock Database (NAVDAT— http://navdat.geo.ku.edu and http://navdat.geongrid.org ) is a relational database that serves as a repository for chemical and age data for igneous rocks in this region and allows, for the first time, the voluminous, high-quality, igneous rock data generated over the past thirty years to be integrated into time-space-composition models of western North American igneous activity. As in other continental regions, the analysis of geochemical, geochronological, and geospatial data from igneous rocks has played a critical role in the understanding of the tectonic evolution of western North America. However, the seminal, regional-scale studies of the tectonic evolution of this region remain primarily those undertaken in the 1970s, prior to the explosion in the number of high-quality chemical and isotopic studies of North American igneous rocks that occurred during subsequent decades. There has been little concerted effort to integrate these new data into regional tectonic models of western North America, due in large part to the lack of a unified, high-quality database for igneous rocks in this region. As a result, the potential that these data have for providing new fundamental insights into the tectonic evolution of the continent remains largely untapped. The NAVDAT effort is designed to remedy this situation. At its core, NAVDAT is a Web-accessible petrologic database with a schema compatible with existing petrologic databases (GEOROC, PetDB), but with an emphasis on a structure that will easily allow these data to be queried and manipulated as functions of age, composition, and geographic position. The NAVDAT user interface includes a number of advanced query options including both graphical and map-plotting analysis tools as well as close linking between data and reference information for the source of the data. NAVDAT allows investigations of continent-scale patterns in magmatism and provides the means to address how local variations in the age, composition, and location of igneous rocks fit into a regional context. The latter ability will produce more thorough and rigorous assessments of the relationships between volcanism and lithospheric deformation, including continental mantle delamination, the controls of subducted slab orientation on space-time-composition patterns of magmatism, and the role of mantle plumes in continental evolution. NAVDAT also will provide basic information on volcanic hazards and geothermal resources in western North America. The overall goal is for NAVDAT to become a rich data tool, an important part of the national geoinformatics effort, and a functioning component of an overall national geoscience cyberinfrastructure.

Field, petrographic, geochemical, and limited chronologic information allow for construction of a composite stratigraphic section for the approximately 1-km-thick exposure of basaltic lavas in the Pueblo Mountains region of the Oregon Plateau. Comparison of the Pueblo basalts with those of Steens Mountain and the Columbia Plateau suggests that these flood-basalts were derived from a common mid-Miocene magmatic event, possibly marking the initiation of back-arc spreading along the western margin of the Wyoming craton. Geochemical and Sr-isotopic variations within the Pueblo basalts and, more specifically, vertical variations within the Pueblo composite section, define two distinct groups of basalt and three phases of evolution. Within-group variations are modeled by low-pressure fractional crystallization, whereas the between-group variations are attributed primarily to different degrees of interaction between crustal materials and ascending Pueblo primary magmas during the three distinct phases of volcanism.