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Contributions to Mineralogy and Petrology
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Continental crust buried during collisional orogeny typically records pressures of 3 GPa or lower; however, pressures much higher than this are recorded locally, which would suggest burial to mantle depths. Deep continental subduction is not observed in active orogens and should be hindered by the positive buoyancy of sialic crust relative to the mantle. Non-lithostatic pressure caused by mechanical contrasts between rock types provides an alternative explanation for extreme pressures recorded i...
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Temperatures of crystallization for all or portions of three thin granitic pegmatite dikes in southern California are derived from feldspar solvus thermometry, with supporting data from the K/Cs ratio of K-feldspar, the extent of Al/Si order in K-feldspar, and the texture of granophyre found along the margins of dikes. Although K-feldspars become perthitic and increasingly ordered toward the centers of dikes, their ratio of K/Cs falls from margin to core along trajectories that reflect fractiona...
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A trace element may substitute into a mineral by more than one substitution mechanism, complicating the thermodynamic description of its partition coefficients. In order to understand this phenomenon better, the mineral/melt partition coefficients for all 14 rare earth elements (REE) plus Y and Sc were measured experimentally for coexisting forsterite and protoenstatite in the system CaO–MgO–SiO2 ± Al2O3 ± TiO2 at 1406 °C and atmospheric pressure. For both phases, the results show these large tr...
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The occurrence of high-aluminum orthopyroxene megacrysts (HAOMs) in several massif-type Proterozoic anorthosite complexes has been used as evidence of their polybaric crystallization. Here, we report such petrographic and geochemical (XRF and EMPA) evidence from HAOMs discovered in the 1.64 Ga Ahvenisto rapakivi granite—massif-type anorthosite complex in southeastern Finland. Two different types of HAOMs were recognized: type 1 HAOMs are individual, euhedral-to-subhedral crystals, and up to 15 c...
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This study presents a new petrological–geochemical data set for the Monte Capio and Alpe Cevia mafic–ultramafic sequences, which are exposed in the deepest levels of the Ivrea–Verbano Zone. These sequences are composed of a peridotite core, with dunite in the center, mantled by minor orthopyroxene-dominated pyroxenites and subordinate hornblende gabbronorites. Amphibole is ubiquitous in the peridotites and the pyroxenites (≤ 15 vol % and 10–40 vol %, respectively), and the peridotite–pyroxenite ...
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We present a combined garnet Lu–Hf and Sm–Nd, zircon and monazite U–Pb, hornblende Ar–Ar, and zircon U–Th/He geochronology study on a garnet-bearing amphibolite from the Cathaysia Block in Southern China. Pseudosection modeling and garnet–clinopyroxene thermometry indicate that the amphibolite attained peak metamorphic conditions of approximately 0.9 GPa and 780 °C. The Lu–Hf garnet date of 402.7 ± 1.0 Ma and Sm–Nd date of 331.6 ± 3.6 Ma define a ~ 70 Myr difference for the same garnet fractions...
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Silicon is one of the major elements in the solute of subduction zone fluids. The source information of Si in the fluids is useful for constraining the material exchange between the oceanic crust and mantle. Myanmar jadeitites result from crystallization of subduction zone fluids at high pressures, which can be used as a proxy for the chemical composition of the fluids. This paper reports high-precision Si isotope data of jadeitites, and associated amphibole-rich blackwall, serpentinites, and mi...
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Measurements of U–Th–Pb, Lu–Hf and oxygen isotopes as well as selected trace and rare earth elements were carried out on zircon grains from high-grade metasedimentary rocks from the Albany–Fraser Orogen in southwest Australia. Oxygen isotopes from detrital zircon domains yield δ18O (VSMOW) values ranging from 5.8 to 8.0‰ and exhibit coupled Hf- and O-isotope compositions. In contrast, metamorphic zircon domains show considerably less variability in O-isotope compositions with a median δ18O of 5....
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Piton de la Fournaise started a new eruptive cycle in June 2014 after 41 months of quiescence. The small eruptions in June, February 2015, May, and July produced evolved basalts, whereas magmas of the large August–November eruption became increasingly mafic. Compositional zoning of olivine crystals was analysed to model diffusion times representing residence times between magma mixing and eruption. These correlate to the geophysical and geochemical records. Olivine crystals of various core compo...
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Experiments were performed from 950 to 1250 °C and 1.5–2.4 GPa to determine the effect of pressure (P) on the temperature (T)-dependent partitioning of Al between olivine and spinel, using mixtures of natural spinel, olivine, clino- and ortho-pyroxene. When compared to 100 kPa experiments, the results show that there is no discernible effect of pressure on the Al-in-olivine thermometer at PT conditions relevant to the spinel peridotite facies. In our experiments with high-Cr spinel, we see no ch...
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Geology
Basalt
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Olivine