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Introduction This study was undertaken to quantify an early estimate about the low temperature of the fayalite-saturated cotectic in the system Fa-An-Ab. The original estimate of this thermal effect was developed by the senior author in ~1988 from published studies of the systems Fa-An and Fa-Ab. Because the fayalite-saturated composition also occurs in some syenites, we considered that rock type and its genesis to be a logical target for comparison. The fayalite component of olivine in crystallizing melts can have a profound effect on the fractionation of

American Mineralogist, Volume 98, pages 1074–1077, 2013 0003-004X/13/0506–1074$05.00/DOI: http://dx.doi.org/10.2138/am.2013.4410 1074 Letter High-pressure aragonite phenocrysts in carbonatite and carbonated syenite xenoliths within an alkali basalt VratisLaV Hurai,1,* Monika HuraioVá,2 rastisLaV MiLoVský,3 JarMiLa LuptákoVá,3 and Patrik konečný4 1Geological Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 840 05 Bratislava, Slovakia 2Department of Mineralogy and Petrology, Comenius University, Mlynská dolina, 842 15 Bratislava, Slovakia 3

References Andersen, T., Erambert, M., Larsen, A.O., & Selbekk, R.S. (2010). Petrology of nepheline syenite pegmatites in the Oslo Rift, Norway: Zirconium silicate mineral assemblages as indicators of alkalinity and volatile fugacity in mildly agpaitic magma. Journal of Petrology, 51(11), 2303-2325. DOI: 10.1093/petrology/egq058 Bellezza, M., Merlino, S., & Perchiazzi, N. (2009a). Mosandrite: Structural and crystal-chemical relationships with rinkite. The Canadian Mineralogist, 47, 897-908. DOI: 10.3749/canmin.47.4.897 Bellezza, M., Merlino, S., Perchiazzi, N

American Mineralogist, Volume 98, pages 426–438, 2013 0003-004X/13/0203–426$05.00/DOI: http://dx.doi.org/10.2138/am.2013.4068 426 Geochemistry of pyrochlore minerals from the Motzfeldt Center, South Greenland: The mineralogy of a syenite-hosted Ta, Nb deposit Jamie a. mccreath,1,* adrian a. Finch,1,† donald a. herd,1 and ashlyn armour-Brown2 1Center for Earth Resources St Andrews (CERSA) and Department of Earth Sciences, University of St Andrews, Irvine Building, St Andrews, Fife, KY16 9AL, U.K. 2Angus & Ross plc, Kirkbymoorside, York, U.K. aBstract

; Tanis et al. 2015 ) that rutile is increasingly more soluble in halogen-bearing (e.g., F, Cl) aqueous fluids evolved during prograde metamorphism in subduction environments. Slab-derived fluids are not pure water, but instead contain significant amounts of dissolved alkalis (Na, K), halogens (F, Cl), and aluminosilicates (Si, Al) ( Manning 2004 ). This study investigates rutile hosted by a scapolite-rich syenite pegmatite ( Owen and Greenough 1999 ) preserved as a megablock in a large-scale fault breccia that outcrops in cliffs and foreshore at Clarke Head, Nova

American Mineralogist, Volume 87, pages 1377–1383, 2002 0003-004X/02/0010–1377$05.00 1377 INTRODUCTION The model that the coarsening of cryptoperthite to microperthite is promoted by the presence of water as a cata- lyst was developed from studies of alkali feldspars in the Klokken syenite, southwest Greenland (Parsons 1968; Par- sons and Brown 1984; Smith and Brown 1988; etc.). The model of these authors involves subsolidus reactions to form microtextures expected in ternary and alkali feldspars accom- panying cooling of syenitic intrusions from magmatic to

CaMgSiO4 (Ricker and Osborn 1954). It has been argued that the inability of Fe- Mg olivine to incorporate appreciable amounts of Ca, even in Ca-saturated systems, is presumably due to the large ionic size of Ca compared to Fe, Mg, or Mn (Brown 1980). Hence, crys- tal-chemical reasons may be responsible at least in part for high distribution coefficients of Ca between Ca-rich phases and oli- * E-mail: markl@uni-tuebingen.de The influence of T, aSiO2, and fO2 on exsolution textures in Fe-Mg olivine: An example from augite syenites of the Ilimaussaq Intrusion, South

“Silicified” pyrochlore from nepheline syenite (mariupolite) of the Mariupol Massif, SE Ukraine: A new insight into the role of silicon in the pyrochlore structure Magdalena duMańska-słowik1,*, adaM Pieczka1, gioacchino TeMPesTa2, zbigniew olejniczak3 and wiesław heflik1 1Department of Mineralogy, Petrography, and Geochemistry, Faculty of Geology, Geophysics and Environmental Protection, AGH–University of Science and Technology, 30 Mickiewicza Avenue, Kraków 30-059, Poland 2Dipartimento Geomineralogico, Università degli Studi di Bari, Via Orabona, 4, I-70125

Abstract

This paper presents new data derived from field sampling and from a thorough description of lamprophyres located in southeastern Altai and northwestern Mongolia in terms of their mineralogy, textures, and chemical composition. The swarms of alkaline mafic dikes in the area coexist with granosyenite-monzodiorite and gabbro-dolerite intrusions and spatially coincide with an ore district of Sb-Hg, Ag-Sb, Ni-Co-As, Cu-Mo-W, and CaF2 hydrothermal mineralization. All lamprophyres belong to the Early Mesozoic Chuya complex formed in an intracontinental enviroment. Their distribution and orientation is controlled by two large fault zones. The Chuya dikes were investigated at two localities, namely, Yustyd and South-Chuya. The Yustyd lamprophyres intrude Middle-Upper Devonian black shale of the Yustyd depression. At South Chuya, lamprophyres, together with the Tarkhata granosyenite-monzodiorite complex, are hosted by Cambrian and Ordovician metamorphic rocks of the South-Chuya Range. Ar-Ar (phlogopite) and U-Pb (SHRIMP, zircon) ages of the lamprophyre dikes indicate long and continuous period of the formation of the Chuya complex (250-235 Ma). Major- and trace-element compositions of the lamprophyres from both localities and of the syenite indicate their origin from the same magma source. The textures and structures of the lamprophyre and plutonic rocks, their mineral assemblages and the chemistry of the rock-forming minerals provide clues to the evolution of the parental alkaline mafic magma and fluid regime.

, their provenance is a hint that Acadian-Neoacadian terranes may hold similarly deeply subducted rocks to those known from contiguous Caledonian terranes in Greenland and Europe, which contain HPGs as well as the second-largest UHP terrane (by geographic extent) ( Gilotti and Elvevold 2002 ; Gilotti and Krogh Ravna 2002 ; Hacker et al. 2010 ; Gilotti 2013 ; Klonowska et al. 2017 ). Some Acadian rocks have already been suggested as being indicative of deep subduction (e.g., Peterman et al. 2016 ). Implications for syenites and aluminous xenoliths Our model of the