Mechanism of Mineral Reactions Inferred from Textures of Impure Dolomitic Marbles from East Greenland

Abstract

Mineral assemblages and chemical compositions of minerals found in impure dolomitic marbles embedded in gneisses and migmatites of the E. Greenland Caledonian fold belt (Scoresby Sund) suggest that the marbles were metamorphosed near 630 °C at 5 kb pressure. The analysis of complex textural and mineralogical relations among minerals such as dolomite, calcite, forsterite, pargasite, chlorite, spinel, diopside and phlogopite led to the conclusion that the major mineralogical features of the rocks were probably caused by sodium metasomatism at constant temperature and pressure. The effect of the inferred sodium metasomatism may be summarized by three schematic reactions all involving modal changes of excess dolomite, calcite, forsterite, chlorite and spinel: (a) nucleation and growth of pargasite, (b) resorption of phlogopite, and (c) growth of pargasite from phlogopite.

The nature and distribution of fluids during amphibolite facies metamorphism, Naxos (Greece)

“…Similarly, the occurrence of texturally late pargasite and dravitic (Mg-rich) tourmaline in sapphirine-bearing assemblages suggests that the infiltrating fluid was sodium and boron-bearing. The aluminous composition of Mg-chlorite and pargasite (Table 1) in both sapphirinepresent and -absent assemblages indicates that they grew at temperatures in excess of 600°C (Rice, 1977;Bucher-Nurimen, 1982;Matsueda et al, 1983). Fluid infiltration responsible for Mg-chlorite + pargasite growth may therefore have been synchronous with, or have post-dated, the M2B peak.…”

Clintonite-bearing assemblages in chondrodite marbles from the contact aureole of the Třebíčský Pluton, Moldanubian Zone, Bohemian Massif

“…%), high chondrodite/clintonite ratios and isotopic composition of calcite support introduction of H 2 O, Si and very likely also F into the system, whereas Na and K were removed. Based on detailed study of reaction textures, similar dealkalization reactions producing chlorite and/or spinel instead of clintonite, and forsterite instead of chondrodite were described for amphibole and phlogopite (Kretz 1980, Bucher-Nurminen 1982, Novák 1989). However, they were not tested experimentally and the breakdown of pargasite and phlogopite is still unclear; perhaps a high acidity of fluids may have operated (cf.…”

“…However, they were not tested experimentally and the breakdown of pargasite and phlogopite is still unclear; perhaps a high acidity of fluids may have operated (cf. Bucher-Nurminen 1982).…”

“…It occurs chiefly in contact metamorphosed dolomite marbles, calcic and magnesian skarns (e.g. Burnham 1959, Shabynin 1973, Bucher-Nurminen 1976, Rice 1979, Bucher Frey 1994, Sugaki et al 2000, Woodford et al 2001 and rarely in rodingites (Rice 1983, Dubiñska 1997, Dubiñska et al 2004. Ackermand et al (1986) described for the first time clintonite from regional metamorphic rock with the assemblage Cal+Ol+Cpx+Spl+Sph+Chl.…”

“…Only a low number of chemical analyses of clintonite have been published up to now and the data concerning concentrations of F and valence of Fe are rather exceptional (Rice 1979, MacKinney et al 1988, Alietti et al 1997, Grew et al 1999. Based on the mineral assemblages and textural relations, mineral reactions producing clintonite involve calcite, spinel, forsterite and diopside (Rice 1979), less commonly also phlogopite, pargasite, chlorite and monticellite (Bucher-Nurminen 1976, Ulmer 1983. Novák Houzar (1996) published the first comprehensive description of clintonite closely associated with chondrodite from marbles at Tasov (Fig.…”