Journal of GEOsciences Table of Contents for the Journal of GEOsciences. List of articles from the latest print issue.http://www.jgeosci.orgen-US Journal of GEOsciences <![CDATA[ Petrogenetic evolution of a Late Jurassic calc-alkaline plutonic complex, Klamath Mountains Province, U.S.A.: quantification by major- and trace-element modelling ]]> Medaris GLJr, Svojtka M, Ackerman L, Cotkin SJ; Vol. 64, issue 2, pages 81 - 103
This investigation illustrates the use of major and trace elements to evaluate the petrogenetic evolution of the Late Jurassic Russian Peak Plutonic Complex in the Klamath Mountains Province, northern California, U.S.A. The two principal plutons in the complex consist of quartz diorite and granodiorite, both of which were most likely derived by partial melting of amphibolitic oceanic crustal sources and ultimately emplaced at a shallow level of ˜10 km (Ptotal ˜ 3 kbar). The major-element compositional variations in quartz diorite are consistent with crystallization of plagioclase (45 %) and amphibole (69 %) and resorption of clinopyroxene (-14 %). Major-element variations in granodiorite could have resulted from crystallization of plagioclase (60 %), amphibole (26 %), and biotite (14 %). Trace elements in whole-rocks and amphibole record different degrees of fractional crystallization, whole-rocks reflecting differentiation on a plutonic scale, and amphibole crystals reflecting differentiation on the scale of an individual sample. Quartz diorite experienced 10% fractional crystallization for the suite as a whole and 45% for individual samples; in contrast, granodiorite experienced 40% crystallization for the suite and 80% for individual samples. For both quartz diorite and granodiorite, comparisons of whole-rock REE patterns with those for melts calculated to be in equilibrium with amphibole demonstrate that the whole-rock REE compositions represent a combination of crystals and melts from evolving magmas, rather than melts alone. ]]> Original paper
<![CDATA[ Petrogenesis of Miocene subvolcanic rocks in the Western Outer Carpathians (southeastern Moravia, Czech Republic) ]]> Buriánek D, Kropáč K; Vol. 64, issue 2, pages 105 - 125
Neogene subvolcanic rocks in southeastern Moravia form numerous dykes and laccoliths, ranging from clinopyroxene-amphibole and amphibole trachybasalt, through trachyandesite, to biotite-amphibole trachydacite. Leucocratic and melanocratic cumulate gabbro and basalt enclaves up to 70 cm in diameter are rarely present, respectively, within the trachydacite and trachyandesite.
The parental magmas rose along tensional fissures spatially related to the Nezdenice Fault but probably never reached the surface. The range of major (e.g., SiO2 44-62 wt. %, mg# 20-65) and trace-element compositions can be explained through magma mixing and mingling and subsequent fractional crystallization.
Mineral chemistry shows limited compositional variation of mafic minerals. Diopside phenocrysts indicate narrow ranges of XMg 0.65-0.84 and usually display normal zoning with small Mg-rich cores and Fe-rich rims. Phlogopites from the trachydacite and gabbro enclaves show a mutually similar composition (XFe 0.36-0.43 and IVAl 2.44-2.59). Amphiboles from individual samples of basalt, trachybasalt and trachyandesite are likewise chemically relatively homogeneous (XMg 0.51-0.86, Si 5.78-6.55). Chemical compositions of amphibole phenocrysts from the trachybasalts and trachyandesites indicate multi-stage crystallization at depth of 32 to 21 km for this magmatic system. Systematic changes in Si, Ti, VIAl, XMg contents in amphiboles from trachydacites and gabbro enclaves can be explained by fractional crystallization in a shallower magma reservoir (˜20-10 km). ]]> Original paper
<![CDATA[ TETGAR_C: a novel three-dimensional (3D) provenance plot and calculation tool for detrital garnets ]]> Knierzinger W, Wagreich M, Kiraly F, Lee EY, Ntaflos T; Vol. 64, issue 2, pages 127 - 148
This paper presents a new interactive MATLAB-based visualization and calculation tool (TETGAR_C) for assessing the provenance of detrital garnets in a four-component (tetrahedral) plot system (almandine-pyrope-grossular-spessartine). Based on a freely-accessible database and additional electron-microprobe data, the chemistry of more than 2,600 garnet samples was evaluated and used to create various subfields in the tetrahedron that correspond to calc-silicate rocks, felsic igneous rocks (granites and pegmatites) as well as metasedimentary and metaigneous rocks of various metamorphic grades. These subfields act as reference structures facilitating assignments of garnet chemistries to source lithologies. An integrated function calculates whether a point is located in a subfield or not. Moreover, TETGAR_C determines the distance to the closest subfield’s mean value. Compared with conventional ternary garnet discrimination diagrams, this provenance tool enables a more accurate assessment of potential source rocks by reducing the overlap of specific subfields and offering quantitative testing of garnet compositions. In particular, a much clearer distinction between garnets from greenschist-facies rocks, amphibolite-facies rocks, blueschist-facies rocks and felsic igneous rocks is achieved. Moreover, TETGAR_C enables a distinction between garnet grains with metaigneous and metasedimentary provenance. In general, metaigneous garnet tends to have higher grossular content than metasedimentary garnet formed under similar P-T conditions. ]]> Original paper
<![CDATA[ Complementing knowledge about rare sulphates lonecreekite, NH4Fe3+(SO4)2·12 H2O and sabieite, NH4Fe3+(SO4)2: chemical composition, XRD and RAMAN spectroscopy (Libušín near Kladno, the Czech Republic) ]]> Žáček V, Škoda R, Laufek F, Košek F, Jehlička J; Vol. 64, issue 2, pages 149 - 159
Lonecreekite and sabieite, hydrous and anhydrous ferric ammonium sulphates, were identified among the products of a long-lasting subsurface fire in the waste heap of the Schoeller coal mine in Libušín near Kladno, Central Bohemia, Czech Republic. No monomineralic fractions could be extracted as the minerals occur in a fine-grained aggregate with minor ferroan boussingaultite, tschermigite, and traces of efremovite. Powder X-ray diffraction, electron-microprobe analysis and Raman spectroscopy were used to identify the mineral phases in the mixture.
The empirical formula of lonecreekite is [(NH4)0.98K0.02]∑1.00 (Fe0.70Al0.24Mg0.02)∑0.96 (SO4) 2.05·12 H2O, and the calculated unit-cell (Pa ) parameter a = 12.2442(2) Å, with a cell volume of V = 1835.68(9) Å3.
The composition of sabieite corresponds to the formula [(NH4)0.98K0.02]∑1.00 (Fe0.70Al0.24Mg0.02)∑0.96 (SO4) 2.05, and the calculated unit-cell parameters (P321) are a = 4.826(1) Å, c = 8.283(2) Å, V = 167.10(8) Å3, assuming that only the 1T polytype is present. Raman spectroscopy was conducted on both minerals, giving strong Raman bands at 1037 cm-1 1), 1272 cm-1 3), 462 cm-1 2), 643 cm-1 4), 313 (M-O vibration) for sabieite; and at 991 cm-1 1), 1132 and 1104 cm-1 3), 461 and 443 cm-1 2), and 616 cm-1 4) for lonecreekite (where ν1 and ν3 are stretching modes of the (SO4)-group and ν2 and ν4 are bending modes). The sabieite most probably formed by in situ decomposition of the siderite-bearing sedimentary rock at ˜115-350 °C. The lonecreekite originated through hydration of the sabieite when the sample was stored at ambient temperature. Empirical formulae of associated ferroan boussingaultite and tschermigite are also given, respectively, as (NH4)2 (Mg0.62Fe0.36Mn0.06)∑1.04 (SO4)1.97·6 H2O and [(NH4)0.98K0.02]∑1.00 (Al0.97Fe0.06)∑1.03 (SO4)2.97·12 H2O. ]]> Original paper