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Monograph available for loan

Pegmatites (2008)

London, David ; Mineralogical Association of Canada

Ottawa : Mineralogical Association of Canada

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Call number: 11/M 08.0291

In: The Canadian mineralogist

Type of Medium: Monograph available for loan

Pages: xx, 347 S. + 1 CD-ROM

ISBN: 9780921294474

Series Statement: The Canadian mineralogist : Special publication 10

Classification:

Mineralogy

Location: Reading room

Branch Library: GFZ Library

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Experimental reactions of amphibolite with boron-bearing aqueous fluids at 200 MPa: implications for tourmaline stability and partial melting in mafic rocks (1989)

Morgan, George B. ; London, David

Springer

Contributions to mineralogy and petrology 102 (1989), S. 281-297

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Reactions between hornblende-plagioclase amphibolite and acidic and alkaline B-bearing aqueous fluids have been investigated by experiments at 475°–600° C and 200 MPa. At 600° C, hornblende+calcic plagioclase react to form tourmaline+danburite+clinopyroxene+quartz in acidic fluids containing ≥0.5–1.0 wt% B2O3.Tourmaline is precipitated directly from acidic fluids, and the reaction is driven by neutralization of fluids by Na±Ca derived from the breakdown of reactant solids. The concentration of B2O3 in fluids needed to stabilize tourmaline increases as pH increases (above approximately 6.0), and tourmaline is unstable in alkaline fluids (pH 〉 approximately 6.5–7.0) regardless of B concentration. In addition to acid-base relations, tourmaline stability is favored by comparatively higher activity coefficients for Al species in acidic fluids. The concentrations of Al and Si in fluid increase with alkalinity, with the eventual production of felsic borosilicate melts through partial melting of the plagioclase component of the amphibolite. In seeded experiments, tourmaline also contributes components to melt. Partial melting is evident in the range 500°–525° C at 200 MPa in experiments with ≥8wt% B2O3 in fluid as Na2B4O7. The experimental results are applied primarily to metasomatic reactions between mafic rocks and borate fluids derived from granitic magmas, but tourmaline stability and partial melting in mafic regional metamorphic systems are also discussed briefly.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00373721

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3

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Sheet silicates of the Lawler Peak granite, Arizona: chemistry, structural variations, and exsolution (1990)

Ferrow, Embaie A. ; London, David ; Goodman, Kathleen S. ; [et al.]

Springer

Contributions to mineralogy and petrology 105 (1990), S. 491-501

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Coarse-grained muscovite, biotite, and chlorite from the Lawler Peak granite, Yavapai County, Arizona, have been studied with electron microprobe analysis, powder X-ray diffraction, transmission electron microscopy (TEM), electron diffraction, and analytical TEM methods. All three sheet silicates exhibit multiple polytypes and an abundance of stacking faults and dislocations. Chlorite formed by subsolidus replacement of biotite. Muscovite also may have formed by replacement of biotite and other minerals, but there is no clear microstructural evidence to support either a primary or secondary origin for the coarse-grained muscovite. X-ray and electron diffraction reveal that the muscovite consists of two separate phases, which give rise to splitting of diffraction maxima. TEM experiments suggest that the two components resulted from exsolution, which produced two symmetry-related sets of irrationally oriented lamellae with a wavelength averaging about 10 nm. Exsolution occurred in both 1M and 2M1 muscovite. Although the lamellae are too small to analyze directly, the muscovite bulk composition and structural data are consistent with the separation of celadonitic and muscovite components.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00302490

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Vapor-undersaturated experiments with Macusani glass+H2O at 200 MPa, and the internal differentiation of granitic pegmatites (1989)

London, David ; Morgan, George B. ; Hervig, Richard L.

Springer

Contributions to mineralogy and petrology 102 (1989), S. 1-17

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Vapor-undersaturated fractional crystallization experiments with Macusani glass (macusanite), a peraluminous rhyolite obsidian, at 200 MPa yield mineralogical fabrics and zonation, and melt fractionation trends that closely resemble those found in zoned granitic pegmatites and other granitoids of comparable composition (typically peraluminous, Li-Be-Ta-rich deposits). The zonation from the edge of charges inward is characterized by: (1) fine-grained sodic feldspar-quartz border zones; (2) a fringe of very coarse-grained graphic quartz-feldspar intergrowths that flair radially toward melt and terminate with nearly monophase K-feldspar; (3) cores of very coarse-grained, nearly monominerallic quartz or virgilite (LiAlSi5O12)±mica; and (4) late-stage, fine-grained albite+mica intergrowths that are deposited from alkaline, Na-rich interstitial melt at vapor saturation. Similar experimental products have been observed in compositionally simpler, less evolved systems. Liquid lines of descent from initially H2O-undersaturated runs are marked by a decrease in SiO2, and increases in Na/K, B, P, F, H2O, and a variety of trace lithophile cations. These trends are believed to be governed by three factors: (1) disequilibrium growth of feldspars (±quartz) via metastable supersaturation; (2) fractionation of melt toward SiO2-depleted, Na-rich compositions due to increases in B, P, and F; and (3) changes in nucleation and growth rates, mostly as a function of the H2O content of melt (X w m ). In contrast, experiments that are cooled below the liquidus from the field of melt+aqueous vapor (London et al. 1988) fail to replicate pegmatitic characteristics in most respects. On the basis of these and other experiments, we suggest that the formation of pegmatite fabrics stems primarily from fractional crystallization in volatile-rich melts, and that enrichments in normally trace lithophile elements result from melt differentiation trends toward increasingly alkaline, silica-depleted compositions. Although vapor saturation at near-solidus and subsolidus conditions may promote extensive recrystallization, an aqueous vapor phase does not appear to be necessary for the generation of most of the salient characteristics of pegmatites.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01160186

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Behavior and effects of phosphorus in the system Na2O−K2O−Al2O3−SiO2−P2O5−H2O at 200 MPa(H2O) (1993)

London, David ; Morgan, George B. ; Babb, Harold A. ; [et al.]

Springer

Contributions to mineralogy and petrology 113 (1993), S. 450-465

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract The addition of phosphorus to H2O-saturated and initially subaluminous haplogranitic (Qz−Ab−Or) compositions at 200 MPa(H2O) promotes expansion of the liquidus field of quartz, a marked decrease of the solidus temperature, increased solubility limits of H2O in melt at low phosphorus concentrations, and fractionation of melt out of the haplogranite plane (projected along an Or28 isopleth) toward a peralkaline, silica-poor but quartz-saturated minimum composition. The partition coefficient for P2O5 between aqueous vapor and melt with an ASI (aluminum saturation index, mol Al/[mol Na+K])=1 is negligible (0.06), and consequently so are the effects of phosphorus on other melt-vapor relations involving major components. Phosphorus becomes more soluble in vapor, however, as the concentration of a NaPO3 component increases via the fractionation of melt by crystallization of quartz and feldspar. The experimental results here corroborate existing concepts regarding the interaction of phosphorus with alkali aluminosilicate melt: phosphorus has an affinity for alkalis and Al, but not Si. Phosphorus is incorporated into alkali feldspars by the exchange component AlPSi-2. For subaluminous compositions (ASI=1), the distribution coefficient of phosphorus between alkali feldspar and melt, D[P]Af/m, is 0.3. This value increases to D[P]Af/m=1.0 at a melt ASI value of 1.3. The increase in D[P]Af/m with ASI is expected from the fact that excess Al promotes the AlPSi-2 exchange. With this experimental data, the P2O5 content of feldspars and whole rocks can reveal important facets of crystallization and phosphorus geochemistry in subaluminous to peraluminous granitic systems.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00698315

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6

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Boron in granitic magmas: stability of tourmaline in equilibrium with biotite and cordierite (1997)

Wolf, Michael B. ; London, David

Springer

Contributions to mineralogy and petrology 130 (1997), S. 12-30

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Experiments at 750 °C, 200 MPa(H2O), a (H2O)=1, and fO2∼Ni-NiO established that the equilibrium among tourmaline, biotite, cordierite, and melt (± spinel, aluminosilicate, or corundum) occurs with ∼2 wt% B2O3 in strongly peraluminous melt with an aluminosity, measured by the parameter ASI, of 〉1.2. The experiments demonstrate the relationship of tourmaline stability to the activity product of the tourmaline components boron and aluminum, which are inversely related to one another. Tourmaline is unstable in metaluminous to mildly peraluminous melts (ASI 〈1.2) at 750 °C regardless of their boron content. For a given aluminosity, addition of components such as F requires a greater boron content of melt at this equilibrium. The stability of tourmaline increases with decreasing temperatures below 750 °C. At the inception of melting, tourmaline breaks down incongruently to assemblages containing crystalline AFM silicates (biotite, cordierite, garnet, sillimanite), aluminates (spinel, corundum), and B-enriched but Fe-Mg-poor melt. Granitic melts are likely to be undersaturated in tourmaline from the start of their crystallization, and their initial boron contents will be limited by the abundance of tourmaline in their source rocks. Quartzofeldspathic (gneissic, metapelitic) rocks that reached conditions of the granulite facies and still contain (prograde) tourmaline are rare, and probably have never yielded a partial melt. Most leucogranitic magmas will initially crystallize biotite, cordierite, or garnet, but not tourmaline. With crystallization, the Fe-Mg content of melt decreases, and the B2O3 content increases until the tourmaline-biotite and/or tourmaline-cordierite (or garnet) equilibria are attained. The B2O3 content of melt is buffered as long as these equilibria continue to operate, but low initial Fe-Mg contents of the magmas limit the quantity of boron that can be consumed by these reactions to 〈1 wt% B2O3. Normally, leucogranitic magmas contain insufficient Fe and Mg to conserve all boron as tourmaline and thus lose a large fraction of magmatic boron to wallrocks. Leucogranites and pegmatites with tourmaline as an early and only AFM silicate mineral probably contained 〉2 wt% B2O3 in their bulk magmas.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004100050346

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Melt-vapor solubilities and elemental partitioning in peraluminous granite-pegmatite systems: experimental results with Macusani glass at 200 MPa (1988)

London, David ; Hervig, Richard L. ; Morgan, George B.

Springer

Contributions to mineralogy and petrology 99 (1988), S. 360-373

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Vapor-saturated experiments at 200 MPa with peraluminous, lithophile-element-rich rhyolite obsidian from Macusani, Peru, reveal high miscibility of H2O and silicate melt components. The H2O content of melt at saturation (11.5+-0.5 wt.%) is almost twice that predicted by existing melt speciation models. The corresponding solubility of melt components in vapor decreases from 15 wt.% dissolved solids (750°–775° C) to 9 wt.% at 600° C. With regard to major and most minor components, macusanite melt dissolves congruently in vapor. Among the elements studied (B, P, F, Li, Rb, Cs, Be, Sr, Ba, Nb, Zr, Hf, Y, Pb, Th, U, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm), only boron has a vapor/melt partition coefficient (D[B]) consistently ≥1 at superliquidus temperatures (〉645° C). Phosphorus and fluorine behave similarly, with D[P] and D[F]〈0.5. Little or no significant vapor/melt fractionation is evident among most periodic groups (alkalis, alkaline earths, Zr/Hf, or the REE). The temperature dependence of vapor/melt partition coefficients is generally greatest for cations with charge ≥ +3 (except Nb and U); most vapor/melt partition coefficients for trace elements increase with decreasing temperature to the liquidus. Crystallization proceeds by condensation of crystalline phases from vapor; most coexisting melts are aphyric. Changes in the major element content of melt are dominated by the mineral assemblage crystallized from vapor, which includes subequal proportions of white mica, quartz, albite, and orthoclase. The volumetric proportion of (mica + or-thoclase)/albite increases slightly with decreasing T, creating a sodic, alkaline vapor. Vapor deposition of topaz (T≤500° C), which consumes F from melt, returns K/Na ratios of melt to near unity with the vapor-deposition of albite. The abundances of most trace elements in residual melt change little with the crystallization of major phases, but in some cases are strongly controlled by the deposition of accessory phases including apatite (T≤550° C), which depletes the melt in P and REE. Below the liquidus, boron increasingly favors the vapor over melt with decreasing temperatures.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00375368

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Crystallization of the Little Three layered pegmatite-aplite dike, Ramona District, California (1999)

Morgan VI, George B. ; London, David

Springer

Contributions to mineralogy and petrology 136 (1999), S. 310-330

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Subhorizontally layered pegmatite-aplite bodies are characterized by fine-grained, sodic to granitic aplite that is usually juxtaposed abruptly above by much coarser-grained, commonly graphic potassic pegmatite. Although well studied, there currently is little concensus as to how such dikes form. The Little Three dike near Ramona, California, is representative of such zoned bodies in this and other regions, and contains discontinuous miarolitic pockets near the base of the graphic pegmatite zone. Tourmaline, garnet, biotite, and muscovite show no changes in major- or minor-element compositions indicative of progressive magmatic fractionation until the immediate vicinity of the main miarolitic zone, where they record abrupt and extreme enrichments in Li, F, and Mn. There is no correlation of chemical changes in the dike with the appearance of small miarolitic vugs well below the main miarolitic zone, nor is there any indication that the aplite, graphic pegmatite, or miarolitic pockets represent separate magma injections. The chemistries of tourmaline, garnet, and micas, however, preclude conventional models of Rayleigh fractionation or traditional zone refining. Textural features and modeled cooling histories indicate that the dike cooled quickly and might have solidified partially or totally to glass before crystallization commenced. Geothermometry based on the compositions of coexisting plagioclase and homogeneous, nonperthitic K-feldspar indicates inward crystallization of the dike, from ∼400–435 °C at the margins to ∼350–390 °C within 20–30 cm of the pocket horizon, then a sharp decrease to 240–275 °C in the pockets where K-feldspar is perthitic. We interpret the feldspar geothermometry (except perhaps in the miarolitic cavities) to reflect the temperatures at crystallization fronts that advanced into the pegmatite, first from the foot wall and eventually joined by a similar front downward from the hanging wall. Crystallization down from the hanging wall may have commenced after ∼70–80% of the foot wall aplite had crystallized. The very abrupt increases of Li, Mn, and F in tourmaline and garnet near the miarolitic zone appear to be explained best by the process of constitutional zone refining, in which a fluxed crystallization front sweeps an incompatible element-enriched boundary layer through a solid or semi-solid. After these two highly fluxed boundary layers merged near the main miarolitic zone, compositional evolution could have proceeded by crystal-melt fractionation.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004100050541

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