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The Proterozoic terrane of the Black Hills, South Dakota, includes the composite Harney Peak leucogranite and associated pegmatites that were emplaced into metamorphosed pelites and graywackes. Available dates indicate that granite generation post-dated regional metamorphism and deformation that have been attributed to collision of the Wyoming and Superior cratons at ~1760 Ma. Previous radiogenic...
Incorporating upper mantle differentiation through decompression melting in a numerical mantle convection model, we demonstrate that a compositionally distinct root consisting of depleted peridotite can grow and remain stable during a long period of secular cooling. Our modeling results show that in a hot convecting mantle partial melting will produce a compositional layering in a relatively short...
The Oetmoed Granite-Migmatite Complex (OGMC), Central Damara Orogen, Namibia, consists of grt- and crd-bearing S-type granites and hbl- and titanite-bearing A-type granites that intruded into crd-sil-Kfs-bearing metasedimentary rocks, stromatic migmatites and nebulites. Stromatic migmatites formed by limited in situ partial melting of metapelites under H 2 O-saturated conditions at ~700 ...
Pelitic and semi-pelitic granulites from Namaqualand, South Africa underwent dehydration melting and developed leucosome domains in which large garnets are intimately associated with coarse-grained quartz in lobate embayments and inclusions. Local retrograde replacement of leucosome anhydrous phases by coarse biotite and/or sillimanite is not uncommon, but is far from universally developed. Also developed...
The Thor-Odin dome region of the Shuswap metamorphic core complex, British Columbia, contains migmatitic rocks exhumed from the deep mid-crust of the Cordilleran orogen. Extensive partial melting occurred during decompression of the structurally deepest rocks, and this decompression path is particularly well recorded by mafic boudins of silica-undersaturated, aluminous rocks. These mafic boudins contain...
During the Pliocene, simultaneously with the opening of the Tyrrhenian Sea, mafic magmas were erupted in NE Sardinia (Orosei-Dorgali area). These range from mildly alkaline with sodic affinity (about 80% of exposure) to tholeiitic (about 20%). The tholeiitic rocks (basaltic andesite) are slightly more evolved than the alkaline ones and show geochemical features (e.g., Mg#<63; Ni<150 ppm and...
Spectacular shallow-level migmatization of ferrogabbroic rocks occurs in a metamorphic contact aureole of a gabbroic pluton of the Tierra Mala massif (TM) on Fuerteventura (Canary Islands). In order to improve our knowledge of the low pressure melting behavior of gabbroic rocks and to constrain the conditions of migmatization of the TM gabbros, we performed partial melting experiments on a natural...
Melt inclusions in clinopyroxenes from lherzolitic xenoliths from the deep lithospheric mantle beneath the Slave Craton (Lac de Gras area, Canada) reveal multiple origins for carbonatitic melts. One type of inclusions consists of a series of silicate–carbonate–silicate concentric layers, interpreted to have unmixed under disequilibrium conditions during rapid ascent to the surface. Bulk major- and...
Tonalite–trondhjemite–granodiorite (TTG) magmatism provides a window into the composition of the Earth's earliest crust, and on rates of heat transfer during the Archaean. However, the tectonic setting in which these magmas form, and the physical mechanisms by which TTG melt segregates from its partially molten source rock, are poorly understood. Here we present some simple models aimed at predicting...
Three xenoliths erupted as ejecta during recent violent explosion of Stromboli volcano (Aeolian Islands) were investigated in this paper. They consist of high-temperature mineral association (cordierite, hercynite spinels, sillimanite, ±plagioclase, ±mullite, ±corundum) and abundant glass (10–70 vol.%), and may be classified as buchites. The peraluminous composition of the xenoliths, their trace element...
The petrogenesis of the Hercynian magmatic rocks of the Albera Massif (eastern Pyrenees) is investigated in this work, in order to establish spatial and temporal relationships between deformation episodes, high temperature–low pressure metamorphism and igneous activity, by using fieldwork together with petrological and geochemical methods.Hercynian magmatic rocks comprise (i) calc-alkaline granitoids...
Calculations of fractional crystallization (FC) and assimilation fractional crystallization (AFC) at 11 kb for a variety of primitive magmatic compositions and a mafic assimilant demonstrate that none of them has a bulk composition suitable to be parental to massif anorthosites. Mafic compositions thought to be parental to massif anorthosites have Mg′ values of 0.6 to 0.4 and form coherent arrays...
We report petrologic and geochemical features of anhydrous granulites from the eastern Sierras Pampeanas, Argentina. Aluminous Grt–Crd-bearing granulite is the most abundant rock type in the study region, and hosts intermediate Opx–Grt bearing granulites as interlayered lenses. Both granulite types crystallized under similar P–T conditions of T=850–900 °C and P c. 7.5 kbar. The formation of Grt–Crd...
The Korosten complex is a Paleoproterozoic gabbro–anorthosite–rapakivi granite intrusion which was emplaced over a protracted time interval — 1800–1737 Ma. The complex occupies an area of about 12000 km 2 in the north-western region of the Ukrainian shield. About 18% of this area is occupied by various mafic rocks (gabbro, leucogabbro, anorthosite) that comprise five rock suites: early anorthositic...
The 62–52 Ma Ladybird granite (LBG) suite is a peraluminous, leucocratic, S-type, quartz monzonitic to granitic suite which occurs as batholiths, stocks, dikes, sills, and pegmatite veins predominantly in the high-grade rocks of the Shuswap complex, in southeastern British Columbia. The emplacement of the LBG was synchronous with the production of abundant migmatites within Thor–Odin dome of the Monashee...
Garnet is an uncommon accessory mineral in igneous rocks but is petrologically significant. The Peñón Rosado granite (469±4 Ma) at Cerro Asperecito is an S-type granite that contains an unusual amount of magmatic garnet. Combined petrology, chemistry/mineralogy and whole-rock geochemistry indicates that the magma was produced by partial melting of the surrounding metasedimentary rocks and subsequent...
The Emeishan continental flood basalt (ECFB) sequence in Dongchuan, SW China comprises a basal tephrite unit overlain by an upper tholeiitic basalt unit. The upper basalts have high TiO 2 contents (3.2–5.2 wt.%), relatively high rare-earth element (REE) concentrations (40 to 60 ppm La, 12.5 to 16.5 ppm Sm, and 3 to 4 ppm Yb), moderate Zr/Nb and Nb/La ratios (9.3–10.2 and 0.6–0.9, respectively)...
The mantle section of the Tethyan-type Othris Ophiolite, Greece, records tectono-magmatic processes characteristic of both mid-ocean ridges and supra-subduction zones. The Othris Ophiolite is a remnant of the Jurassic Neotethys Ocean, which existed between Eurasia and Gondwanaland. Othris peridotites range from fertile plagioclase lherzolites to depleted harzburgites. Abundances of Al 2 O...
Low pressure partial melting of basanitic and ankaramitic dykes gave rise to unusual, zebra-like migmatites, in the contact aureole of a layered pyroxenite–gabbro intrusion, in the root zone of an ocean island (Basal Complex, Fuerteventura, Canary Islands). These migmatites are characterised by a dense network of closely spaced, millimetre-wide leucocratic segregations. Their mineralogy consists of...
A number of models of continental collision already exist, but the role of foregoing oceanic plate subduction or variable coupling between plates still remains to be explored. In addition, heat generation by radioactive decay may be quite variable. For example, our geochemical data from low-to-high grade metamorphic rocks of the Lesser and Higher Himalayan sequences reveal measured heat production...
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