Ankerite

About: Ankerite is a research topic. Over the lifetime, 859 publications have been published within this topic receiving 23960 citations.

Metamorphic petrology of the Negaunee Iron Formation, Marquette District, northern Michigan; mineralogy, metamorphic reactions, and phase equilibria

Abstract: Progressive regional metamorphism of the Negaunee Iron Formation in the Marquette district from chlorite to sillimanite grade has resulted in the development of three metamorphic zones and two subzones. The diagnostic zone assemblages are, in order of increasing grade: 1, siderite + quartz + or - ankerite + or - minnesotaite + or - stilpnomelane + or - magnetite; 2, grunerite + or - quartz + or - ankerite + or - magnetite and grunerite + or - siderite + or - ankerite + or - magnetite; 3a, grunerite + or - garnet + or - quartz + or - magnetite and grunerite + or - Ca amphibole + or - quartz + or - calcite + or - magnetite; 3b, grunerite + or - olivine + or - clinopyroxene + or - quartz + or - calcite + or - magnetite and grunerite + or - Ca amphibole + or - olivine + or - magnetite. The grunerite, garnet, and Ca amphibole, and olivine and clinopyroxene isograds define the boundaries between the respective zones and subzones. Temperature estimates are approximately 300 degrees C for zone 1 and approximately 600 degrees C for subzone 3b. Pressure is estimated at between 200 to 300 MPa. Microprobe analyses of coexisting minerals indicate general attainment of exchange equilibrium and a strong localized influence of bulk composition on mineral chemistry.Theoretical analysis of phase relations on isobaric T-X (sub CO 2 ) diagrams leads to the following conclusions:1. Throughout zone 1, minnesotaitc-bearing assemblages are diagnostic of low X (sub CO 2 ) values, stilpnomelane-bearing assemblages represent low to medium values, and chlorite-bearing assemblages represent medium to high X (sub CO 2 ) values. Juxtaposition of these three assemblages at one locality indicates that fluid phase compositional gradients most likely existed.2. Throughout zone 3, actinolite-, hornblende-, and garnet-bearing assemblages reflect similar low to high X (sub CO 2 ) values. The continued juxtaposition of these various assemblages suggests the continued presence of fluid-phase compositional gradients into the highest grade metamorphic zones.3. Metamorphic reactions caused substantial, localized CO 2 enrichment in the coexisting fluid phase. A diversity of T-X (sub CO 2 ) paths was followed, typically differing on the scale of individual mesobands.

The carbonatites and fenites of Chipman Lake, Ontario

Abstract: Simple and composite dikes of dolomitic and ankeritic carbonatite, up to one meter thick, cut and fenitize Archean country rocks around Chipman Lake, Ontario. The carbonate compositions define a complete series from dolomite to ankerite, and coexist with calcite. Cathodoluminescence studies indicate an early dolomitic phase brecciated by later ankeritic carbonate. DropJike inclusions of burbankite within the dolomite are taken as evidence for an early Na-rich fluid or immiscible liquid. Compositional data are given for burbankite and other phases in the carbonatite, including synchysite, parisite, bastnasite, norsethite, barytocalcite (alstonite?), strontianite, apatite, strontian apatite, monazite and F-rich phlogopite. The fenites comprise Na- and K-rich feldspars, magnesio-arfvedsonite and aegirine, with phlogopite particularly concentrated along carbonatite contacts. The evolution of the carbonatite liquid from magnesian to more iron-rich compositions paralleled a decrease in the Na:K ratio, which was responsible for early fenitization of a predominantly sodic character changing later to potassium fenitization.