Basaltic andesite

About: Basaltic andesite is a research topic. Over the lifetime, 1199 publications have been published within this topic receiving 54278 citations.

A Guide to the Chemical Classification of the Common Volcanic Rocks

Abstract: A system is presented whereby volcanic rocks may be classified chemically as follows:I. Subalkaline Rocks:A. Tholeiitic basalt series:Tholeiitic picrite-basalt; tholeiite; tholeiitic andesite.B. Calc-alkali series:High-alumina basalt; andesite; dacite; rhyolite.II. Alkaline Rocks:A. Alkali olivine basalt series:(1) Alkalic picrite–basalt; ankaramite; alkali basalt; hawaiite; mugearite; benmorite; trachyte.(2) Alkalic picrite–basalt; ankaramite; alkali basalt; trachybasalt; tristanite; trachyte.B. Nephelinic, leucitic, and analcitic rocks.III. Peralkaline Rocks:pantellerite, commendite, etc.

Geochemistry of eocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey

Abstract: Analytical data for Sr, Rb, Cs, Ba, Pb, rare earth elements, Y, Th, U, Zr, Hf, Sn, Nb, Mo, Ni, Co, V, Cr, Sc, Cu and major elements are reported for eocene volcanic rocks cropping out in the Kastamonu area, Pontic chain of Northern Turkey. SiO2% versus K2O% relationship shows that the analyzed samples belong to two major groups: the basaltic andesitic and the andesitic ones. High-K basaltic andesites and low-K andesites occur too. Although emplaced on continental type basement (the North Anatolian Crystalline Swell), the Pontic eocene volcanics show elemental abundances closely comparable with typical island arc calc-alkaline suites, e.g. low SiO2% range, low to moderate K2O% and large cations (Cs, Rb, Sr, Ba, Pb) contents and REE patterns with fractionated light and almost flat heavy REE patterns. ΣREE and highly charged cations (Th, U, Hf, Sn, Zr) are slightly higher than typical calc-alkaline values. Ferromagnesian elements show variable values. Within the basaltic andesite group the increase of K%, large cations, ΣREE, La/Yb ratio and high valency cations and the decrease of ferromagnesian element abundances with increasing SiO2% content indicate that the rock types making up this group developed by crystalliquid fractionation of olivine and clinopyroxene from a basic parent magma. Trace element concentration suggest that the andesite group was not derived by crystal-liquid fractionation processes from the basaltic andesites, but could represent a distinct group of rocks derived from a different parent magma.

Orogenic Andesites and Plate Tectonics

Abstract: 1 What is "Typical Calcalkaline Andesite"?.- 1.1 Introduction.- 1.2 Definition of Orogenic Andesite.- 1.3 Magma Series Containing Orogenic Andesites.- 1.4 Overview.- 2 The Plate Tectonic Connection.- 2.1 Spatial Distribution of Active Orogenic Andesite Volcanoes.- 2.2 Initiation of Subduction.- 2.3 Cessation of Subduction.- 2.4 Collisions.- 2.5 Reversal of Subduction Polarity.- 2.6 Forearc and Transform Fault Volcanism.- 2.7 Anomalously Wide Volcanic Arcs.- 2.8 Andesites Clearly Not at Convergent Plate Boundaries.- 2.9 Conclusions.- 3 Geophysical Setting of Volcanism at Convergent Plate Boundaries.- 3.1 Topography, Gravity, Heat Flow, and Conductivity.- 3.2 Crustal Thickness, Structure, and Age.- 3.3 Upper Mantle Beneath the Forearc, Volcanic Arc, and Backarc Regions.- 3.4 Dipping Seismic Zones (Benioff-Wadati Zones) and Underthrust Lithosphere.- 3.5 Partial Melting and Magma Ascent Beneath Volcanic Arcs.- 3.6 Magma Chambers Beneath Orogenic Andesite Volcanoes.- 3.7 Conclusions.- 4 Andesite Magmas, Ejecta, Eruptions, and Volcanoes.- 4.1 Characteristics of Andesite Magma.- 4.1.1 Temperature.- 4.1.2 Density.- 4.1.3 Rheology.- 4.1.4 Miscellaneous Properties and Applications.- 4.2 Andesite Rock, Eruption, and Edifice Types.- 4.3 Variations in Magma Composition During and etween Historic Andesite Eruptions.- 4.4 Variations in Rock Composition During Evolution of Stratovolcanoes.- 4.5 Conclusions About Andesite Magma Reservoirs.- 4.6 Stress Fields and Volcano Spacings Within Volcanic Arcs.- 4.7 Relationships Between the Timing of Arc Volcanism and Plate Movements.- 4.8 Magma Eruption Rates at Convergent Plate Boundaries.- 4.9 Relative Proportions of Andesite.- 5 Bulk Chemical Composition of Orogenic Andesites.- 5.1 Rock Analyses: Significance, Averages, and Representative Samples and Suites.- 5.2 Major Elements.- 5.2.1 Silica Contents and Harker Variation Diagrams.- 5.2.2 Alkalies.- 5.2.3 Iron and Magnesium.- 5.2.4 Titanium.- 5.2.5 Aluminum and Calcium.- 5.2.6 Phosphorous.- 5.2.7 CIPW Normative Mineralogy.- 5.3 Volatiles.- 5.3.1 Water.- 5.3.2 Carbon Dioxide.- 5.3.3 Sulfur.- 5.3.4 Halogens.- 5.3.5 Oxygen.- 5.4 Trace Elements.- 5.4.1 The K-Group: Rb, Cs, Ba, and Sr.- 5.4.2 REE Group: Rare Earth Elements Plus Y.- 5.4.3 The Th Group: Th,U, and Pb.- 5.4.4 The Ti Group: Zr, Hf, Nb, and Ta.- 5.4.5 The Compatible Group: Ni, Co, Cr, V, and Sc.- 5.4.6 The Chalcophile Group: Cu, Zn, and Mo.- 5.4.7 Trace Element Systematics.- 5.5 Isotopes.- 5.5.1 Strontium.- 5.5.2 Lead.- 5.5.3 Neodymium.- 5.5.4 Inert Gases.- 5.5.5 U-Disequilibrium.- 5.5.6 Oxygen.- 5.5.7 Synthesis of Isotope Data.- 5.6 Comparison with Andesites Not at Convergent Plate Boundaries.- 5.7 Geochemical Distinctiveness of Volcanism at Convergent Plate Boundaries.- 5.8 Conclusions: Chemical Diversity of Orogenic Andesites.- 6 Mineralogy and Mineral Stabilities.- 6.1 Plagioclase.- 6.2 Pyroxenes.- 6.3 Amphibole.- 6.4 Olivine.- 6.5 Oxides.- 6.6 Garnet.- 6.7 Other Minerals.- 6.8 Inclusions in Orogenic Andesites.- 6.9 Mineral Stabilities in Andesite Magma.- 6.10 Trace Element Equilibria Between Minerals and Melt.- 6.11 Conclusions.- 7 Spatial and Temporal Variations in the Composition of Orogenic Andesites.- 7.1 Variations in Magma Composition Across Volcanic Arcs.- 7.2 Variations in Magma Composition Along Volcanic Arcs.- 7.3 Effects of Plate Convergence Rate on Magma Composition.- 7.4 Relationships Between Compositions of Orogenic Andesites and Adjacent Oceanic Crust.- 7.5 Changes in the Composition of Orogenic Andesites During Earth History.- 8 The Role of Subducted Ocean Crust in the Genesis of Orogenic Andesites.- 8.1 Characteristics of Subducted Ocean Crust Beneath Volcanic Arcs.- 8.2 Circumstantial Evidence of Slab Recycling in Arc Volcanism.- 8.3 Are Orogenic Andesites Primary Melts of Subducted Ocean Floor Basalt? No.- 8.4 The Sediment Solution.- 8.5 IRS Fluids and Maxwell's Demons.- 8.6 Conclusions.- 9 The Role of the Mantle Wedge.- 9.1 Characteristics of the Mantle Wedge.- 9.2 Circumstantial Evidence that Arc Magmas Originate Within the Mantle Wedge.- 9.3 Are Orogenic Andesites Primary Melts of Only the Mantle Wedge? Rarely.- 9.4 Fluid Mixing, Metasomatism, and Demonology in the Mantle Wedge.- 10 The Role of the Crust.- 10.1 Circumstantial Evidence for Crustal Involvement in Orogenic Andesites.- 10.2 Crustal Anatexis.- 10.3 Crustal Assimilation.- 11 The Role of Basalt Differentiation.- 11.1 General Arguments for and Against Differentiation.- 11.2 Roles of Plagioclase, Pyroxenes, and Olivine.- 11.3 Role of Magnetite and the Plagioclase-Orthopyroxene/Olivine-Augite-Magnetite (POAM) Model.- 11.4 Role of Amphibole.- 11.5 Role of Garnet.- 11.6 Role of Accessory Minerals: Apatite, Chromite, Sulfides, Biotite.- 11.7 Role of Magma Mixing.- 11.8 Role of Other Differentiation Mechanisms.- 11.9 Differentiation Processes Leading to Andesites in Anorogenic Environments.- 12 Conclusions.- 12.1 Andesite Genesis by POAM-Fractionation: the Most Frequent Mechanism.- 12.2 Some Outstanding Problems Requiring Clarification.- 12.3 Origin of Tholeiitic Versus Calcalkaline Andesites.- 12.4 Origin of Across-Arc Geochemical Variations.- 12.5 Epilog.- References.

Experimental investigations of the role of H2O in calc-alkaline differentiation and subduction zone magmatism

Abstract: Phase relations of natural aphyric high-alumina basalts and their intrusive equivalents were determined through rock-melting experiments at 2 kb, H2O-saturated with fO2 buffered at NNO. Experimental liquids are low-MgO high-alumina basalt or basaltic andesite, and most are saturated with olivine, calcic plagioclase, and either high-calcium pyroxene or hornblende (±magnetite). Cr-spinel or magnetite appear near the liquidus of wet high-alumina basalts because H2O lowers the appearance temperature of crystalline silicates but has a lesser effect on spinel. As a consequence, experimental liquids follow calcalkaline differentiation trends. Hornblende stability is sensitive to the Na2O content of the bulk composition as well as to H2O content, with the result that hornblende can form as a near liquidus mineral in wet sodic basalts, but does not appear until liquids reach andesitic compositions in moderate Na2O basalts. Therefore, the absence of hornblende in basalts with low-to-moderate Na2O contents is not evidence that those basalts are nearly dry. Very calcic plagioclase (>An90) forms from basaltic melts with high H2O contents but cannot form from dry melts with normal are Na2O and CaO abundances. The presence of anorthite-rich plagioclase in high-alumina basalts indicates high magmatic H2O contents. In sum, moderate pressure H2O-saturated phase relations show that magmatic H2O leads to the early crystallization of spinel, produces calcic plagioclase, and reduces the total proportion of plagioclase in the crystallizing assemblage, thereby promoting the development of the calc-alkaline differentiation trend.