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  -