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1 Institut für Angewandte Geowissenschaften, Technische Universität Darmstadt, Schnittspahnstr. 9, D-64287 Darmstadt, Germany
1,2 Mineralogisches Institut, Universität Erlangen, Schlossgarten 5, D-91054 Erlangen, Germany
3 Mineralogisches Institut der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
e-mail: wmueller{at}geo.tu-darmstadt.de
A metamorphosed ultramafic rock, penetrated by the KTB pilot hole at a depth of 1382.36 m, contains the assemblage Ca-amphibole — anthophyllite — chlorite — talc, formed at about 630°C/10 kbar under conditions of the high-P amphibolite facies. EMP analyses of the Ca-amphibole yielded magnesiohastingsite (to pargasite) compositions with (Al+Fe3++Cr+Ti)[6] of 1.0-1.2 p.f.u. and (Fe2++Mn)/(Mg+Fe2++Mn) ratios of 0.10-0.16, while coexisting anthophyllite has (Al+Fe3++Cr+Ti)[6] 
0.16 and (Fe2++Mn)/(Mg+Fe2++Mn) ratios of 0.21-0.29. Chlorite is clinochlore with Al[4]/(Al[4]+Si) of 0.27-0.30 and Fe2+/(Fe2++Mg) of 0.12-0.14.
TEM investigations revealed, for the first time, a complex lamellar intergrowth in the sequence talc 
anthophyllite anthophyllite/cummingtonite intercalations anthophyllite Ca-amphibole. This lamellar intergrowth is about 15 µm in width, but individual cummingtonite lamellae intercalated with dominant anthophyllite are only 1 µn wide. All the amphiboles share the directions b* and a*; anthophyllite and the monoclinic amphiboles are intergrown along (100); anthophyllite and talc are intergrown with (100)Ath//(001)Tlc. In other areas anthophyllite and chlorite are intergrown with a* Ath//c*Chl and b*Ath//b*Chl and Ca-amphibole exsolves lamellae of cummingtonite //(100). With one possible exception, cummingtonite has the space group C2/m. Anthophyllite displays chain multiplicity faults //(010), anthophyllite and cummingtonite chain arrangement faults //(100). Microstructures suggest that anthophyllite was formed at the expense of cummingtonite that is interpreted as a high-T precursor phase testifying to a possible earlier, granulite-facies metamorphic stage. During the retrograde P-T path, on cooling presumably below 500-550°C, anthophyllite exsolves platelets or lamellae of gedrite with {hk0} composition planes. Orientations close to {230} and {110} have been recorded, so far not described in the literature. Alteration products of biotite are composed of clinochlore and a sheet silicate intermediate in composition between chlorite and biotite, i.e., with partly high K contents, but with chlorite metric.
Key-words: amphibole-chlorite-talc intergrowths, anthophyllite, gedrite exsolutions, cummingtonite, Ca-amphibole, orientation relationships, chain multiplicity faults, chain arrangement faults, TEM..
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