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We have studied the influence of Ca-Tschermaks (Calcium Tschermaks or CaTs) content of clinopyroxene on the partitioning of trace elements between this phase and silicate melt at fixed temperature and pressure. Ion probe analyses of experiments carried out in the system Na 2 O-CaO-MgO-Al 2 O 3 -SiO 2 , at 0.1 MPa and 1218 o C, produced crystal-melt partition...
A previously published scheme for the high temperature disposal of nuclear waste in deep boreholes requires that granite host rock partially melted by the heat from the waste can be completely recrystallized on the time scale of the cooling of the waste. Experimental studies of dynamic recrystallization of a typical S-type crustal granite were therefore undertaken under the pressure (=0.15 GPa) and...
A high temperature, deep borehole disposal scheme for nuclear waste is outlined. This requires that granite host rock can be partially melted by the heat from the waste then completely recrystallized, both on the time scale of the cooling of the waste. Experimental studies of non-equilibrium partial melting of a typical S-type crustal granite were carried out under the conditions likely to arise during...
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...
The peak metamorphic conditions of subducted continental crust in the Dora-Maira massif (Western Alps) have been revised by combining experimental results in the KCMASH system with petrologic information from whiteschists. Textural observations in whiteschists suggest that the peak metamorphic assemblage garnet+phengite+kyanite+coesite+/-talc originates from the reaction kyanite+talc garnet+coesite+liquid...
A model metasomatized lherzolite composition contains phlogopite and pargasite, together with olivine, orthopyroxene, clinopyroxene and spinel or garnet as subsolidus phases to 3 GPa. Previous works established that at >=1.5 GPa, phlogopite is stable above the dehydration solidus, determined by the melting behaviour of pargasite and coexisting phases. At 2.8 GPa, melts with residual phlogopite+garnet...
The position of the transition from spinel peridotite to garnet peridotite in a simplified chemical composition has been determined experimentally at high pressures and high temperatures. The univariant reaction MgCr 2 O 4 +2Mg 2 Si 2 O 6 =Mg 3 Cr 2 Si 3 O 12 +Mg 2 SiO 4 , has a negative slope in P-T space...
Two-layer experiments where a hydrous mafic glass is attached to a powdered tonalite have been performed at conditions of 850 to 1000 °C and 6 to 10 kbar. The aim of these experiments is to simulate the effects of fluids released from a crystallizing hydrous magma emplaced within a tonalitic continental crust. This process has been inferred from field observations and geochemical relationships in...
Although many explanations have been proposed for the internal zonation of granitic pegmatites, the most widely accepted model is attributed to R.H. Jahns. Jahns and Burnham [Jahns, R.H., Burnham, C.W., 1969. Experimental studies of pegmatite genesis: I. A model for the derivation and crystallization of granitic pegmatites. Econ. Geol. 64, 843–864] said that pegmatites owe their distinctive textural...
High-pressure (HP) and ultra-high pressure (UHP) terranes are excellent natural laboratories to study subduction-zone processes. In this paper we give a brief theoretical background and we review experimental data and observations in natural rocks that constrain the nature and composition of the fluid phase present in HP and UHP rocks. We argue that a fluid buffered by a solid residue is compositionally...
The Alban Hills ultrapotassic volcanic district is one of the main districts emplaced during Quaternary time along the Tyrrhenian margin of Italy. Alban Hills lava flows and scoria clasts are made up essentially of clinopyroxenes and leucites and their chemical composition is mostly K-foiditic. Differentiated products (MgO<3 wt.%) are characterised by low SiO 2 concentration (<50 wt...
This paper examines phase equilibria and mass balance constraints on Fe enrichment in tholeiitic liquids in plutonic environments. The peak of Fe enrichment is thought to roughly coincide with magma saturation in Fe–Ti oxides; and olivine starts to react with the liquid at about the same time. This crucial stage of crystallization is examined in detail using a compilation of chemical analyses of 64...
The compositions of kimberlite magma and associated melts during eruption and hypabyssal intrusion are elusive due to contamination by xenolithic material and strong alteration, notably by serpentinisation. Textures and mineralogical attributes of kimberlite dykes and sills indicate that some groundmass minerals, including igneous calcite, are replaced in the process of serpentinisation. Large volume...
Partial melting experiments at 40, 50 and 60 kbar pressure on three peridotite compositions with 0.5–0.63 wt.% H 2 O and 2.0–3.2 wt.% CO 2 added indicate melting temperatures only marginally above continental geotherms. Most experiments were performed on a composition with 1.5 wt.% K 2 O added, which causes a further decrease of about 40 °C in melting temperature. Melts progress...
The Miocene-aged Yungay and Fortaleza ignimbrites (YFI), 9° S, Cordillera Blanca, Peru, share geochemical affinities typical of Phanerozoic adakite-like rocks and Archaean tonalite–trondhjemite–granodiorite (TTG) suites. In this contribution, we will investigate the melt source region(s) of the adakitic ignimbrites and their relationship to the dynamic tectonic regime in Peru at the time of eruption...
Few previous studies on orogenic plagioclase peridotites, and recent low-P subsolidus experiments on lherzolites (Borghini et al., 2010; J.Petrology 51, 229–254) have revealed that the composition of plagioclase is a marker of varying P conditions in mantle peridotites. Here we confirm this inference, by comparing microstructural–chemical features observed in natural plagioclase-facies recrystallized...
Assimilation of foreign material into a granitic magma body entails mixing between two end-member components: the initially solid assimilant, and the original magma, whose composition is mostly represented by a granitic liquid. In this study, we assess the interactions between a haplogranite liquid made to the composition of the minimum at 200MPa H 2 O (Ab 38.23 Or 28.72 Qtz...
The Late Devonian (374Ma) Cerberean Cauldron forms the northern part of the Marysville Igneous Complex, in Central Victoria, Australia, filled with around 900km 3 of intra-caldera ignimbrites. The basal volcanic formation is the rhyolitic high-Al Rubicon Ignimbrite, overlain by a larger volume of crystal-rich rhyolitic low-Al Rubicon Ignimbrite, which grades upward into the voluminous, rhyodacitic...
Based on previous and new results on partial melting experiments of pyroxenites at high pressure, we attempt to identify the major element signature of pyroxenite partial melts and to evaluate to what extent this signature can be transmitted to the basalts erupted at oceanic islands and mid-ocean ridges. Although peridotite is the dominant source lithology in the Earth's upper mantle, the ubiquity...
The presence of plagioclase+spinel lherzolites among ocean floor samples and in some ophiolite complexes invites speculation on their origin and relationships to processes of magmatism and lithosphere refertilisation beneath mid-ocean ridges. In an experimental approach to their petrogenesis, we have determined the compositions of liquids and co-existing minerals in the six phase assemblage [liquid+olivine+orthopyroxene+clinopyroxene+plagioclase+spinel]...
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