@article{FuchsFoersterBrauneetal.2018, author = {Fuchs, Sven and F{\"o}rster, Hans-J{\"u}rgen and Braune, K. and F{\"o}rster, A.}, title = {Calculation of Thermal Conductivity of Low-Porous, Isotropic Plutonic Rocks of the Crust at Ambient Conditions From Modal Mineralogy and Porosity}, series = {Journal of geophysical research : Solid earth}, volume = {123}, journal = {Journal of geophysical research : Solid earth}, number = {10}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9313}, doi = {10.1029/2018JB016287}, pages = {8602 -- 8614}, year = {2018}, abstract = {Thermal conductivity (lambda) is an essential physical property of minerals and rocks and fundamental in constraining the thermal field of the lithosphere. In case that adequate samples to measure lambda are not available, it could be indirectly inferred from calculation. One of the most widely applied indirect methods for rocks involve modal mineralogy and porosity as parameters that are incorporated into mathematical mean or mixing models. Robust inferences from these approaches for crystalline rocks were impeded by a small number of studied samples or restriction to certain rock types. We employ this method and examine its applicability to low-porosity plutonic rocks by calculating bulk thermal conductivity lambda(b) for 45 samples covering the entire range from gabbro/diorite to granite. We show that the use of the harmonic-mean model for both rock matrix and porosity provided a good match between lambda(b.meas) and lambda(b.calc) of <10\% deviation (2 sigma), with relative and absolute errors amounting to 1.49.7\% and 4.44.9\%, respectively. The results of our study constitute a big step forward to a robust conclusion on the overall applicability of the harmonic-mean model for inferring lambda(b) of isotropic, low-porosity, mafic to silicic plutonic and metamorphic rocks with an acceptable magnitude of error. Drill cuttings and enclaves form particularly interesting objects for application of this method, as they are poorly suited for direct measurement. Well-derived lambda values for those rocks would permit to calculate heat flow and to model more profoundly the thermal state of the deeper lithosphere.}, language = {en} } @article{FoersterRhede2006, author = {F{\"o}rster, Hans-J{\"u}rgen and Rhede, Dieter}, title = {The Be-Ta-rich granite of Seiffen (eastern Erzgebirge, Germany)}, series = {Neues Jahrbuch f{\"u}r Mineralogie : Abhandlungen}, volume = {182}, journal = {Neues Jahrbuch f{\"u}r Mineralogie : Abhandlungen}, number = {3}, publisher = {Schweizerbart}, address = {Stuttgart}, issn = {0077-7757}, doi = {10.1127/0077-7757/2006/0055}, pages = {307 -- 321}, year = {2006}, abstract = {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.}, language = {en} } @article{ThomasWebsterRhedeetal.2006, author = {Thomas, Rainer and Webster, J. D. and Rhede, Dieter and Seifert, W. and Rickers, Karen and F{\"o}rster, Hans-J{\"u}rgen and Heinrich, Wilhelm and Davidson, P.}, title = {The transition from peraluminous to peralkaline granitic melts: Evidence from melt inclusions and accessory minerals}, series = {Lithos : an international journal of mineralogy, petrology, and geochemistry}, volume = {91}, journal = {Lithos : an international journal of mineralogy, petrology, and geochemistry}, number = {1-4}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0024-4937}, doi = {10.1016/j.lithos.2006.03.013}, pages = {137 -- 149}, year = {2006}, abstract = {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.}, language = {en} } @article{FoersterFoersterOberhaenslietal.2010, author = {F{\"o}rster, Hans-J{\"u}rgen and F{\"o}rster, Andrea and Oberh{\"a}nsli, Roland and Stromeyer, Dietrich}, title = {Lithospheric composition and thermal structure of the Arabian Shield in Jordan}, issn = {0040-1951}, doi = {10.1016/j.tecto.2008.11.014}, year = {2010}, abstract = {In this paper, a unique set of samples from the uppermost crust down to the lithospheric mantle of Jordan is analyzed for composition and petrophysical properties (density. thermal conductivity, radiogenic heat production) These data, covering a vertical section of almost 65 km. are used in conjunction with surface heat flow to generate a detailed and comprehensive lithospheric thermal model that reflects the conditions of the Arabian Shield (AS) prior to the post- Oligocene onset of lithosphere thinning and Voluminous basaltic volcanism. The pre-Miocene model geotherms, based on conductive surface heat flows of 55 and 60 mW m(-2). (a) meet the range of lithosphere-asthenosphere boundary depths of 110-160 km known from seismology, (b) conform to results of thermomechanical models on the on.-in of the Dead Sea basin that started in Miocene time. and (c) are consistent with typical xenolith-derived geotherms for terranes of similar age and lithospheric thickness. Moho temperatures (at depths between 35 and 40 km) of the AS in pre-Miocene times were most likely in the order of 530-650 degrees C, with mantle heat flows averaging between 24 and 29 mW m(-2) Results contradict former views of the late Proterozoic/early Cambrian-stabilized AS being an anomalously cold terrane A "cold" thermal structure inferred from previously measured low surface heat flows (generally <= 45 mW m(-2)) is inconsistent with the thickness, composition, and petrophysical properties of the stable lithosphere of the shield.}, language = {en} } @article{WeberAbuAyyashAbueladasetal.2009, author = {Weber, Michael H. and Abu-Ayyash, Khalil and Abueladas, Abdel-Rahman and Agnon, Amotz and Alasonati-Taš{\´a}rov{\´a}, Zuzana and Al-Zubi, Hashim and Babeyko, Andrey and Bartov, Yuval and Bauer, Klaus and Becken, Michael and Bedrosian, Paul A. and Ben-Avraham, Zvi and Bock, G{\"u}nter and Bohnhoff, Marco and Bribach, Jens and Dulski, Peter and Ebbing, Joerg and El-Kelani, Radwan J. and Foerster, Andrea and F{\"o}rster, Hans-J{\"u}rgen and Frieslander, Uri and Garfunkel, Zvi and G{\"o}tze, Hans-J{\"u}rgen and Haak, Volker and Haberland, Christian and Hassouneh, Mohammed and Helwig, Stefan L. and Hofstetter, Alfons and Hoffmann-Rothe, Arne and Jaeckel, Karl-Heinz and Janssen, Christoph and Jaser, Darweesh and Kesten, Dagmar and Khatib, Mohammed Ghiath and Kind, Rainer and Koch, Olaf and Koulakov, Ivan and Laske, Maria Gabi and Maercklin, Nils}, title = {Anatomy of the Dead Sea transform from lithospheric to microscopic scale}, issn = {8755-1209}, doi = {10.1029/2008rg000264}, year = {2009}, abstract = {Fault zones are the locations where motion of tectonic plates, often associated with earthquakes, is accommodated. Despite a rapid increase in the understanding of faults in the last decades, our knowledge of their geometry, petrophysical properties, and controlling processes remains incomplete. The central questions addressed here in our study of the Dead Sea Transform (DST) in the Middle East are as follows: (1) What are the structure and kinematics of a large fault zone? (2) What controls its structure and kinematics? (3) How does the DST compare to other plate boundary fault zones? The DST has accommodated a total of 105 km of left-lateral transform motion between the African and Arabian plates since early Miocene (similar to 20 Ma). The DST segment between the Dead Sea and the Red Sea, called the Arava/Araba Fault (AF), is studied here using a multidisciplinary and multiscale approach from the mu m to the plate tectonic scale. We observe that under the DST a narrow, subvertical zone cuts through crust and lithosphere. First, from west to east the crustal thickness increases smoothly from 26 to 39 km, and a subhorizontal lower crustal reflector is detected east of the AF. Second, several faults exist in the upper crust in a 40 km wide zone centered on the AF, but none have kilometer-size zones of decreased seismic velocities or zones of high electrical conductivities in the upper crust expected for large damage zones. Third, the AF is the main branch of the DST system, even though it has accommodated only a part (up to 60 km) of the overall 105 km of sinistral plate motion. Fourth, the AF acts as a barrier to fluids to a depth of 4 km, and the lithology changes abruptly across it. Fifth, in the top few hundred meters of the AF a locally transpressional regime is observed in a 100-300 m wide zone of deformed and displaced material, bordered by subparallel faults forming a positive flower structure. Other segments of the AF have a transtensional character with small pull-aparts along them. The damage zones of the individual faults are only 5-20 m wide at this depth range. Sixth, two areas on the AF show mesoscale to microscale faulting and veining in limestone sequences with faulting depths between 2 and 5 km. Seventh, fluids in the AF are carried downward into the fault zone. Only a minor fraction of fluids is derived from ascending hydrothermal fluids. However, we found that on the kilometer scale the AF does not act as an important fluid conduit. Most of these findings are corroborated using thermomechanical modeling where shear deformation in the upper crust is localized in one or two major faults; at larger depth, shear deformation occurs in a 20-40 km wide zone with a mechanically weak decoupling zone extending subvertically through the entire lithosphere.}, language = {en} } @article{SeifertRhedeFoersteretal.2009, author = {Seifert, Wolfgang and Rhede, Dieter and F{\"o}rster, Hans-J{\"u}rgen and Thomas, Rainer}, title = {Accessory minerals as fingerprints for the thermal history and geochronology of the Caledonian Rumburk granite}, issn = {0077-7757}, doi = {10.1127/0077-7757/2009/0147}, year = {2009}, abstract = {Accessory minerals of the Caledonian Rumburk granite are investigated to gain insight into its magmatic and post-magmatic evolution history. Recent geothermometers calibrated for trace elements in rutile (Zr), zircon (Ti), and quartz (Ti) were used to determine mineral-formation temperatures, which are compared with T data obtained from melt and fluid-inclusion Studies on quartz. Improved electron-microprobe analytical conditions allowed distinguishing several generations of rutile. Submicron-sized rutile needles included in quartz crystallized at around 739 +/- 13 degrees C and, thus, are evidently magmatic. Simultaneous crystallization of the high-T rutile and quartz is the favoured concept compared with an exsolution model for the needles. Th-U-total Pb dating of xenotime-(Y) by electron microprobe yielded a bimodal age distribution of 494 +/- 8 Ma (2 sigma; n = 44) and 311 +/- 8 Ma (2 sigma; n = 48), which is missing in monazite-(Ce). The older age correlates with the early Ordovician granite emplacement age Suggested by earlier isotopic Studies. The younger Carboniferous age also may be geologically reasonable, because the granite experienced a minor tectonothermal overprint during the Variscan orogenesis. However, whether this event has caused the resetting of the isotopic system in the xenotime is uncertain. This also holds for the age of the partial breakdown of monazite and xenotime into reaction coronas composed of fluorapatite, allanite-(Ce), epidote +/- clinozoisite. This alteration assemblage was likely produced already during autometasomatic reworking of the solidifying magma in Ordovician time, but it cannot be excluded that it relates to a Carboniferous fluid imprint connected with late-Variscan processes.}, language = {en} } @article{KeutschFoersterStanleyetal.2009, author = {Keutsch, Frank N. and F{\"o}rster, Hans-J{\"u}rgen and Stanley, Chris J. and Rhede, Dieter}, title = {The discreditation of hastite, the orthorhombic dimorph of CoSe2, and observations on trogtalite, cubic CoSe2, from the type locality}, issn = {0008-4476}, doi = {10.3749/canmin.47.4.969}, year = {2009}, abstract = {"Hastite", the orthorhombic dimorph of CoSe2, formerly considered as a valid mineral species occurring in the Trogtal quarries, Harz Mountains, Germany, is discredited as being identical with ferroselite, orthorhombic FeSe2. The discreditation has been unanimously approved by the IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) (IMA No. 07-E). We also provide observations on the composition, homogeneity, and origin of trogtalite (cubic CoSe2) from its type locality.}, language = {en} } @article{FoersterRomerGottesmannetal.2009, author = {F{\"o}rster, Hans-J{\"u}rgen and Romer, Rolf L. and Gottesmann, B{\"a}rbel and Tischendorf, Gerhard and Rhede, Dieter}, title = {Are the granites of the Aue-Schwarzenberg Zone (Erzgebirge, Germany) a major source for metalliferous ore deposits? : a geochemical, Sr-Nd-Pb isotopic, and geochronological study}, issn = {0077-7757}, doi = {10.1127/0077-7757/2009/0138}, year = {2009}, abstract = {The Aue-Schwarzenberg Granite Zone (ASGZ), in the western Erzgebirge of Germany, is composed of small, late- Variscan F-poor biotite and two-mica granites. The biotite granites (Aue granite suite, Beierfeld, Bernsbach) are weakly to mildly peraluminous (A/CNK = 1.07-1.14; 70-76 wt\% SiO2), display similar Sr-87/Sr-86 initial ratios (0.7065-0.7077; t = 325 Ma), and exhibit a narrow range in epsilon Nd-325 (-2.6 to -3.5). They are closely affiliated compositionally with the biotite granites in the distant, more voluminous Nejdek massif (Czech Republic). The two-mica granites (Schwarzenberg granite suite, Lauter) are Si-rich (74-77 wt\% SiO2) and mildly to strongly peraluminous (A/CNK = 1.17- 1.26). The granites from Schwarzenberg Lire distinctly higher in their Sr(i)ratios (0.709-0.713; t = 325 Ma) and possess lower values of epsilon Nd-325 (-4.9 to -5.2) relative to the biotite granites. The Lauter granites have a Nd-isotopic composition between -3.6 and -4.0 (t = 325 Ma). Mean Th-U-total Pb uraninite ages (Ma +/- 2 sigma) obtained for the granites from the Aue Suite (324.3 +/- 3. 1), Beierfeld (323.7 +/- 3.1), Bernsbach (320.7 +/- 2.9), Schwarzenberg (323.3 +/- 2.4), and the Kirchberg granite al Burkersdorf (322.7 +/- 3.5) indicate that magmatism in the ASGZ commenced in the Namurian and took place early within the major episode of granite formation in the Erzgebirge-Vogtland zone (327-318 Ma). Geochemical and mineralogical patterns of variably altered samples imply that the ASGZ granites are unlikely to have significantly contributed to the formation of spatially associated metalliferous ore deposits (Sn, W, Mo, Ph, Zn, Bi, Co, Ni), except for uranium. In particular the Aue granite suite should have served as major Source for U accumulated in the economically important post-granitic deposits of Schneeberg and Schlema-Alberoda.}, language = {en} } @article{WebsterThomasFoersteretal.2004, author = {Webster, J. D. and Thomas, R. and F{\"o}rster, Hans-J{\"u}rgen and Seltmann, R. and Tappen, C.}, title = {Geochemical evolution of halogen-enriched granite magmas and mineralizing fluids of the Zinnwald tin-tungsten mining district, Erzgebirge, Germany}, issn = {0026-4598}, year = {2004}, abstract = {We remelted and analyzed crystallized silicate melt inclusions in quartz from a porphyritic albitezinnwaldite microgranite dike to determine the composition of highly evolved, shallowly intruded, Li- and F-rich granitic magma and to investigate the role of crystal fractionation and aqueous fluid exsolution in causing the extreme extent of magma differentiation. This dike is intimately associated with tin- and tungsten-mineralized granites of Zinnwald, Erzgebirge, Germany. Prior research on Zinnwald granite geochemistry was limited by the effects of strong and pervasive greisenization and alkali-feldspar metasomatism of the rocks. These melt inclusions, however, provide important new constraints on magmatic and mineralizing processes in Zinnwald magmas. The mildly peraluminous granitic melt inclusions are strongly depleted in CAFEMIC constituents (e.g., CaO, FeO, MgO, TiO2), highly enriched in lithophile trace elements, and highly but variably enriched in F and Cl. The melt inclusions contain up to several thousand ppm Cl and nearly 3 wt\% F, on average; several inclusions contain more than 5 wt\% F. The melt inclusions are geochemically similar to the corresponding whole-rock sample, except that the former contain much more F and less CaO, FeO, Zr, Nb, Sr, and Ba. The Sr and Ba abundances are very low implying the melt inclusions represent magma that was more evolved than that represented by the bulk rock. Relationships involving melt constituents reflect increasing lithophile-element and halogen abundances in residual melt with progressive magma differentiation. Modeling demonstrates that differentiation was dominated by crystal fractionation involving quartz and feldspar and significant quantities of topaz and F-rich zinnwaldite. The computed abundances of the latter phases greatly exceed their abundances in the rocks, suggesting that the residual melt was separated physically from phenocrysts during magma movement and evolution. Interactions of aqueous fluids with silicate melt were also critical to magma evolution. To better understand the role of halogen-charged, aqueous fluids in magmatic differentiation and in subsequent mineralization and metasomatism of the Zinnwald granites, Cl-partitioning experiments were conducted with a F-enriched silicate melt and aqueous fluids at 2,000 bar (200 MPa). The results of the experimentally determined partition coefficients for Cl and F, the compositions of fluid inclusions in quartz and other phenocrysts, and associated geochemical modeling point to an important role of magmatic-hydrothermal fluids in influencing magma geochemistry and evolution. The exsolution of halogen-charged fluids from the Li- and F- enriched Zinnwald granitic magma modified the Cl, alkali, and F contents of the residual melt, and may have also sequestered Li, Sri, and W from the melt. Many of these fluids contained strongly elevated F concentrations that were equivalent to or greater than their Cl abundances. The exsolution of F-, Cl-, Li-, +/- W- and Sn-bearing hydrothermal fluids from Zinnwald granite magmas was important in effecting the greisenizing and alkali-feldspathizing metasomatism of the granites and the concomitant mineralization}, language = {en} } @article{TischendorfRiederFoersteretal.2004, author = {Tischendorf, Gerhard and Rieder, M. and F{\"o}rster, Hans-J{\"u}rgen and Gottesmann, B{\"a}rbel and Guidotti, C. V.}, title = {A new graphical presentation and subdivision of potassium micas}, issn = {0026-461X}, year = {2004}, abstract = {A system based on variation of the octahedrally coordinated cations is proposed for graphical presentation and subdivision of tri- and dioctahedral K micas, which makes use of elemental differences (in a.p.f.u.): (Mg - Li) [= mgli] and (Fe-tot + Mn + Ti - Al-VI) [= feal]. All common true tri- and dioctahedral K micas are shown in a single polygon outlined by seven main compositional points forming its vertices. Sequentially clockwise, starting from Mg-3 (phlogopite), these points are: Mg2.5Al0.5, Al(2.167)square(0.833), Al1.75Li1.25, Li2Al (polylithionite), Fe22+Li, and Fe-3(2+) (annite). Trilithionite (Li1.5Al1.5), Li1.5Fe2+Al0.5, Fe22+Mg, and Mg2Fe2+ are also located on the perimeter of the polygon. IMA-siderophyllite (Fe22+Al) and muscovite (Al(2)square) plot inside. The classification conforms with the IMA-approved mica nomenclature and differentiates among the following mica species according to their position in a diagram consisting of nigh and feal axes plotted orthogonally; trioctahedral: phlogopite, biotite, siderophyllite, annite, zinnwaldite, lepidolite and tainiolite: dioctahedral: muscovite, phengite and celadonite. Potassium micas with [Si] <2.5 a.p.f.u. including IMA-siderophyllite, KFe22+AlAl2Si2O10(OH)(2), and IMA-eastonite, KMg2AlAl2Si2O10(OH)(2) seem not to form in nature. The proposed subdivision has several advantages. All common true, trioctahedral and dioctahedral K micas, whether Li-bearing or Li-free, are shown within one diagram, which is easy to use and gives every mica composition an unambiguously defined name. Mica analyses with Fe2+, Fe3+, Fe2+ + Fe3+, or Fe-tot can be considered, which is particularly Valuable for microprobe analyses. It facilitates easy reconstruction of evolutionary pathways of mica compositions during crystallization, a feature having key importance in petrologically oriented research. Equally important, the subdivision has great potential for understanding many of the crystal-chemistry features of the K micas. In turn this may allow one to recognize and discriminate the extent to which crystal chemistry or bulk composition controls the occurrence of some seemingly possible or hypothetical K mica}, language = {en} }