TY  - JOUR
A1  - Förster, Hans-Jürgen
A1  - Rhede, Dieter
T1  - The Be-Ta-rich granite of Seiffen (eastern Erzgebirge, Germany)
BT  - accessory-mineral chemistry, composition, and age of a late-Variscan Li-F granite of A-type affinity
JF  - Neues Jahrbuch für Mineralogie : Abhandlungen
N2  - The mildly peraluminous granite of Seiffen, in the eastern Erzgebirge of Germany, is exposed by drillcores and associated with an abandoned Sri mine. The granite is of Stefanian age, with overlapping Th-U-total Pb monazite (302 +/- 4 Ma) and K-Ar siderophyllite ages (301 +/- 5 Ma). It is among the youngest granites in the Erzgebirge, emplaced in an extensional setting. The medium-grained, equigranular granite classifies as high-F, low-P Li-mica granite of A-type affinity. It is spatially associated with a high-Si rhyolitic microgranite, documenting the shallow intrusion level of this igneous association. Zircon, monazite-(Ce), and xenotime-(Y) constitute important radioactive accessory minerals in the granite, hosting the major proportions (> 80-90%) of the bulk-rock budgets of the REE, Y, and Th. A significant percentage of U (40-50%) may reside within unidentified phases or precipitated along grain boundaries. The most uncommon accessory phase is late-magmatic ytterbian xenotime-(Y) containing up to 11.2 wt% Yb2O3, in addition to 7.3 wt% Er2O3 and 7.9 wt% Dy2O3. The Seiffen granite (epsilon(Nd(300)) = -4.6) is geochemically evolved and rich in Sri (23-63 ppm) and W (11-14 ppm). It contains elevated to high concentrations of incompatible lithophile elements such as F, Li, Ga, Rb, Y, Nb, Cs, REE, Th, and U, thus having much in common chemically with subvolcanic ongonites. The most prominent compositional feature is the strong enrichment (in ppm) in Be (51-55) and Ta (23-28). The granite exhibits flat chondrite-normalized REE patterns (La-N/Lu-N = 1.35-1.48) and a moderate negative Eu anomaly (Eu/Eu* = 0.12-0.13). Indications for alteration-induced, postmagmatic disturbances of initial elemental abundances are weak and mainly relate to the ore-forming elements Sri and U.
KW  - Li-F granite
KW  - Th-U-Pb monazite age
KW  - beryllium
KW  - tantalum
KW  - ytterbian xenotime-(Y)
KW  - ongonite
KW  - post-collisional setting
Y1  - 2006
U6  - https://doi.org/10.1127/0077-7757/2006/0055
SN  - 0077-7757
VL  - 182
IS  - 3
SP  - 307
EP  - 321
PB  - Schweizerbart
CY  - Stuttgart
ER  - 
TY  - JOUR
A1  - Thomas, Rainer
A1  - Webster, J. D.
A1  - Rhede, Dieter
A1  - Seifert, W.
A1  - Rickers, Karen
A1  - Förster, Hans-Jürgen
A1  - Heinrich, Wilhelm
A1  - Davidson, P.
T1  - The transition from peraluminous to peralkaline granitic melts: Evidence from melt inclusions and accessory minerals
JF  - Lithos : an international journal of mineralogy, petrology, and geochemistry
N2  - Fractional crystallization of peraluminous F- and H(2)O-rich granite magmas progressively enriches the remaining melt with volatiles. We show that, at saturation, the melt may separate into two immiscible conjugate melt fractions, one of the fractions shows increasing peraluminosity and the other increasing peralkalinity. These melt fractions also fractionate the incompatible elements to significantly different degrees. Coexisting melt fractions have differing chemical and physical properties and, due to their high density and viscosity contrasts, they will tend to separate readily from each other. Once separated, each melt fraction evolves independently in response to changing T/P/X conditions and further immiscibility events may occur, each generating its own conjugate pair of melt fractions. The strongly peralkaline melt fractions in particular are very reactive and commonly react until equilibrium is attained. Consequently, the peralkaline melt fraction is commonly preserved only in the isolated melt and mineral inclusions. We demonstrate that the differences between melt fractions that can be seen most clearly in differing melt inclusion compositions are also visible in the composition of the resulting ore-forming and accessory minerals, and are visible on scales from a few micrometers to hundreds of meters.
KW  - granite melts
KW  - magma evolution
KW  - melt inclusions
KW  - melt-melt immiscibility
KW  - peraluminosity
KW  - peralkalinity
KW  - accessory minerals
Y1  - 2006
U6  - https://doi.org/10.1016/j.lithos.2006.03.013
SN  - 0024-4937
VL  - 91
IS  - 1-4
SP  - 137
EP  - 149
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Harlov, Daniel E.
A1  - Johansson, L.
A1  - Van Den Kerkhof, A.
A1  - Förster, Hans-Jürgen
T1  - The role of advective fluid flow and diffusion during localized, solid-state dehydration : Sondrum Stenhuggeriet, Halmstad, SW Sweden
N2  - A localized dehydration zone, Sondrum stone quarry, Halmstad, SW Sweden, consists of a central, 1 m wide granitic pegmatoid dyke, on either side of which extends a 2.5-3 m wide dehydration zone (650-700 degrees C; 800 MPa; orthopyroxene-clinopyroxene-biotite-amphibole-garnet) overprinting a local migmatized granitic gneiss (amphibole-biotite- garnet). Whole-rock chemistry indicates that dehydration of the granitic gneiss was predominantly isochemical. Exceptions include [Y + heavy rare earth elements (HREE)], Ba, Sr, and F, which are markedly depleted throughout the dehydration zone. Systematic trends in the silicate and fluorapatite mineral chemistry across the dehydration zone include depletion in Fe, (Y + HREE), Na, K, F, and Cl, and enrichment in Mg, Mn, Ca, and Ti. Fluid inclusion chemistry is similar in all three zones and indicates the presence of a fluid containing CO2, NaCl, and H2O components. Water activities in the dehydration zone average 0.36, or XH2O = 0.25. All lines of evidence suggest that the formation of the dehydration zone was due to advective transport of a CO2-rich fluid with a minor NaCl brine component originating from a tectonic fracture. Fluid infiltration resulted in the localized partial breakdown of biotite and amphiboles to pyroxenes releasing Ti and Ca, which were partitioned into the remaining biotite and amphibole, as well as uniform depletion in (Y + HREE), Ba, Sr, Cl, and F. At some later stage, H2O-rich fluids (H2O activity > 0.8) gave rise to localized partial melting and the probable injection of a granitic melt into the tectonic fracture, which resulted in the biotite and amphibole recording a diffusion profile for F across the dehydration zone into the granitic gneiss as well as a diffusion profile in Fe, Mn, and Mg for all Fe-Mg silicate minerals within 100 cm of the pegmatoid dyke
Y1  - 2006
SN  - 0022-3530
ER  - 
TY  - JOUR
A1  - Breiter, Karel
A1  - Förster, Hans-Jürgen
A1  - Skoda, Radek
T1  - Extreme P-, Bi-, Nb-, Sc-, U- and F-rich zircon from fractionated perphosphorous granites: the peraluminous Podlesi granite system, Czech Republic
N2  - The strongly peraluminous and P-rich, protolithionite and zinnwaldite leucogranites from Podlesi, western Krusne Hory Mts., Czech Republic, contain accessory zircon with extraordinary enrichment of several elements, which constitute trace elements in common zircon. Elements showing a not yet reported anomalous enrichment include P (up to 20.2 wt.% P2O5; equivalent to 0.60 apfu, formula calculated on the basis of 4 oxygen atoms), Bi (up to 9.0 wt.% Bi2O3; 0.086 apfu), Nb (up to 6.7 wt.% Nb2O5, 0.12 apfu), Sc (up to 3.45 wt.% Sc2O3; 0.10 apfu), U (up to 14.8 wt.% UO2; 0.12 apfu) and F (up to 3.81 wt.% F; 0.42 apfu). Strong enrichment of P preferentially involved the berlinite-type substitution (2 Si4+ double left right arrow P5+ + Al3+) implying that significant Al may enter the Si position in zircon. Incorporation of other exotic elements is primarily governed by the xenotime (Si4++Zr4+ double left right arrow P5++Y3+), pretulite (Sc3++P5+ double left right arrow Zr4++Si4+), brabantite-type (Ca2++(U, Th)(4+)+2P(5+) double left right arrow 2Zr(4+)+2Si(4+)), and ximengite-type (Bi3++P5+double left right arrow Zr4++Si4+) substitution reactions. One part of the anomalous zircons formed late-magmatically, from a strongly peraluminous, P-F-U-rich hydrous residual melt that gave rise to the zinnwaldite granite. Interaction with aggressive residual fluids and metamictization have further aided in element enrichment or depletion, particularly in altered parts of zircon contained in the protolithionite granite. Most of the zircon from F-rich greisens have a composition close to endmember ZrSiO4 and are chemically distinct from zircon in its granite parent. This discrepancy implies that at Podlesi, granitic zircon became unstable and completely dissolved during greisenization. Part of the mobilized elements was reprecipitated in newly grown, hydrothermal zircon.
Y1  - 2006
UR  - http://www.sciencedirect.com/science/journal/00244937
U6  - https://doi.org/10.1016/j.lithos.2005.08.011
SN  - 0024-4937
ER  - 
TY  - JOUR
A1  - Förster, Hans-Jürgen
T1  - Composition and origin of intermediate solid solutions in the system thorite-xenotime-zircon-coffinite
N2  - A comprehensive survey of the accessory-mineral assemblages in Variscan granites of the German Erzgebirge and Pan-African granites from Jordan revealed the occurrence of intermediate solid solutions of the tetragonal thorite- xenotime-zircon-coffinite mineral group with partially novel compositions. These solid solutions preferentially formed in evolved and metasomatically altered, P-poor leucogranites of either I- or A-type affinity. Thorite from the Erzgebirge contained up to 18-8 Wt-% Y2O3, 16.1 wt.% ZrO2, and 23.3 Wt-% UO2. Xenotime and zircon have incorporated Th in abundances up to 36.3 wt.% and 41.8 wt.% ThO2, respectively. Extended compositional gradation with only minor gaps is confined to hydrated members of this mineral group, and is observed to exist between thorite and xenotime, thorite and coffinite, and Y-HREE-bearing thorite and zircon. Complex, hydrous solid solutions containing elevated abundances of three or more of the endmembers are subordinate. Previously reported intermediate solid solutions between anhydrous zircon and xenotime, and anhydrous zircon and thorite, are not observed and are in conflict with experimental work demonstrating very limited miscibility between anhydrous species of endmember composition. The majority of hydrous intermediate solid solutions in the Th-Y-Zr-U system are likely thermodynamically unstable. Instead, they are probably metastable responses to unusual physico-chemical conditions involving various parameters and conditions, the relative importance of which is incompletely known. Leaching and dissolution of preexisting accessory phases during interaction with F-bearing hydrous fluids enriched in Th, Y(HREE), Zr, and/or U, and common deposition of the various elements at disequilibrium (supersaturation) seems to play a key role, but other processes may be of similar importance. Experimental work involving hydrous conditions and complex systems composed of more than two endmembers are needed to shed light into the stability relations of the chemically uncommon compositions treated in this study.
Y1  - 2006
UR  - http://www.sciencedirect.com/science/journal/00244937
U6  - https://doi.org/10.1016/j.lithos.2005.08.003
SN  - 0024-4937
ER  - 
TY  - JOUR
A1  - Harlov, Daniel E.
A1  - Tropper, Peter
A1  - Seifert, Wolfgang
A1  - Nijland, Timo
A1  - Förster, Hans-Jürgen
T1  - Formation of Al-rich titanite (CaTiSiO4O-CaAlSiO4OH) reaction rims on ilmenite in metamorphic rocks as a function of fH(2)O and fO(2)
N2  - Reaction rims of titanite on ilmenite are described in samples from four terranes of amphibolite-facies metapelites and amphibolites namely the Tamil Nadu area, southern India; the Val Strona, area of the Ivrea-Verbano Zone, northern Italy, the Bamble Sector, southern Norway, and the northwestern Austroalpine Otztal Complex. The titanite rims, and hence the stability of titanite (CaTiSiO4O) and Al-OH titanite, i.e. vuaganatite (hypothetical end-member CaAlSiO4OH), are discussed in the light of fH(2)O- and fO(2)-buffered equilibria involving clinopyroxene, amphibole, biotite, ilmenite, magnetite, and quartz in the systems CaO-FeO/Fe2O3-TiO2-SiO2-H2O-O-2 (CFTSH) and CaO-FeO/Fe2O3-Al2O3- SiO2-H2O-O-2 (CFASH) present in each of the examples. Textural evidence suggests that titanite reaction rims on ilmenite in rocks from Tamil Nadu, Val Strona, and the Bamble Sector originated most likely due to hydration reactions such as clinopyroxene + ilmenite +quartz+ H2O = amphibole +titanite and oxidation reactions such as amphibole + ilmenite + O-2 = titanite + magnetite + quartz + H2O during amphibolite-facies metamorphism, or, as in the case of the Otztal Complex, during a subsequent greenschist-facies overprint. Overstepping of these reactions requires fH(2)O and fO(2) to be high for titanite formation, which is also in accordance with equilibria involving Al-OH titanite. This study shows that, in addition to P, T, bulk-rock composition and composition of the coexisting fluid, fO(2) and fH(2)O also play an important role in the formation of Al-bearing titanite during amphibolite- and greenschist-facies metamorphism.
Y1  - 2006
UR  - http://www.sciencedirect.com/science/journal/00244937
U6  - https://doi.org/10.1016/j.lithos.2005.08.005
SN  - 0024-4937
ER  -