Table of Contents for the Journal of GEOsciences. List of articles from the latest print issue.http://www.jgeosci.orgen-US http://www.jgeosci.org/jgeosci_cover.jpghttp://www.jgeosci.org Janoušek V; Vol. 57, issue 1, page: 1
]]> http://www.jgeosci.org/rss.php?ID=jgeosci.114 Editorial http://www.jgeosci.org/rss.php?ID=jgeosci.114 Majka J, Be’eri-Shlevin Y, Gee DG, Ladenberger A, Claesson S, Konečný P, Klonowska I; Vol. 57, issue 1, pages 3 - 23
Monazite from granulite-facies rocks of the Åreskutan Nappe in the Scandinavian Caledonides (Seve Nappe Complex, Sweden) was dated using in-situ U-Th-total Pb chemical geochronology (CHIME). Multi-spot analyses of a non-sheared migmatite neosome yielded an age of 439 ± 3 Ma, whereas a sheared migmatite gave 433 ± 3 Ma (2σ). Although the obtained dates are rather similar, a continuous array of single dates from c. 400 Ma to c. 500 Ma suggests possibly a more complex monazite age pattern in the studied rocks. The grouping and recalculation of the obtained results in respect to Y-Th-U systematics and microtextural context allowed distinguishing several different populations of monazite grains/growth zones.
In the migmatite neosome, low-Th and low-Y domains dated at 455 ± 11 Ma are considered to have grown under high-grade sub-solidus conditions, most likely during a progressive burial metamorphic event. The monazites with higher Th and lower Y yielded an age of 439 ± 4 Ma marking the subsequent partial melting event caused by decompression. The youngest (423 ± 13 Ma) Y-enriched monazite reveals features of fluid-assisted growth and is interpreted to date the emplacement of the Åreskutan onto the Lower Seve Nappe.
In the sheared migmatite, the high-Th and low-U (high Th/U) monazite with variable Y contents yielded an age of 438 ± 4 Ma, which is interpreted to date the partial melting event. Relatively U-rich rims on some of the monazite grains again reveal features of fluid-assisted growth, and thus their age of 424 ± 6 Ma is interpreted as timing the nappes emplacement. These results call, however, for further more precise, isotopic (preferably ion microprobe) dating of monazite in the studied rocks. ]]> http://www.jgeosci.org/rss.php?ID=jgeosci.112 Original Paper http://www.jgeosci.org/rss.php?ID=jgeosci.112 Llorens T, Moro MC; Vol. 57, issue 1, pages 25 - 43
Sn-Nb-Ta-Ti oxides occur as accessory minerals in the granitic facies of the External Unit in the Jálama Batholith (Salamanca, Spain) and in the related LCT pegmatite dikes of the rare-element class. Moreover, abundant cassiterite and columbite-group minerals crystallized in the Cruz del Rayo peribatholithic pegmatite dikes, cutting the pre-Ordovician low-grade metasedimentary rocks of the surrounding Schist-Graywacke Complex.
Cassiterite, rutile, ilmenite and tantalite-(Fe) occur disseminated in the border facies of the External Unit, especially throughout the tourmaline-bearing leucogranite and the apical aplites. Additionally, cassiterite, rutile and Ta-rich rutile developed locally in the intragranitic pegmatite dikes.
Two types of peribatholithic pegmatites can be distinguished at Cruz del Rayo: (i) granite-like pegmatites, with columbite-(Fe) I and II and cassiterite, in which the influence of metasomatic fluids led to formation of the late albite unit and crystallization of tantalite-(Fe), and (ii), greisen-like bodies, which contain high amounts of columbite-(Fe), columbite-(Mn), tantalite-(Mn) I and II as well as cassiterite.
The primary oxide assemblage in both types of the peribatholithic pegmatite dikes would have crystallized as a result of magmatic differentiation of the residual melts coming from the Jálama granitic cupola. However, crystallization of the secondary assemblage, richer in Fe and Ta, is interpreted mainly as a consequence of interaction with external fluids coming from the metamorphic host rocks, more or less mixed with meteoric fluids, although partial dissolution and re-precipitation could also have played an important role, as well. ]]> http://www.jgeosci.org/rss.php?ID=jgeosci.113 Original Paper http://www.jgeosci.org/rss.php?ID=jgeosci.113 Vlček V, Skála R, Goliáš V, Drahokoupil J, Čížek J, Strnad L, Ederová J; Vol. 57, issue 1, pages 45 - 52
Samples of naturally irradiated fluorite have been analyzed by means of X-ray powder diffraction analysis (XRPD), differential scanning calorimetry (DSC) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The diffraction patterns of all irradiated samples show peak broadening caused by micro-strain, which was evaluated by Williamson-Hall method, and an increase in the unit cell parameter. The DSC analysis showed an exothermic peak at 273 °C corresponding to enthalpy change about 16 kJ.mol^-1. This value is an order of magnitude higher than calculated change due to unit cell volume increase that is only 2 kJ.mol^-1. The LA-ICP-MS did not show any significant substitutions, which might account for observed unit-cell parameter increase. The results have shown that high radiation doses lead to formation of defect clusters. ]]> http://www.jgeosci.org/rss.php?ID=jgeosci.110 Original Paper http://www.jgeosci.org/rss.php?ID=jgeosci.110 Kharbish S; Vol. 57, issue 1, pages 53 - 62
Oriented single-crystals of trippkeite (CuAs₂O₄) and an isostructural mineral schafarzikite (FeSb₂O₄) were investigated by polarized Raman spectroscopy. The internal vibrations, i.e. the stretching and bending modes, of trippkeite occur between 250 and 850 cm^-1, and those of schafarzikite between 200 and 750 cm^-1. The higher mass and the longer bond distances of the SbO₃ groups readily explain the lower wavenumbers of the latter. Comparing the spectra of minerals containing XO₃ pyramids with those of the minerals from the present study, approximate similarities in the spectral features are evident. A clear distinction between Raman spectra of separated and interconnected (As,Sb)O₃ groups is not observed. ]]> http://www.jgeosci.org/rss.php?ID=jgeosci.111 Original Paper http://www.jgeosci.org/rss.php?ID=jgeosci.111