Talc-chlorite-amphibole felses of the KTB pilot hole, Oberpfalz, Bavaria: Protolith characteristics and phase relationships

Matthes, Siegfried; Okrusch, Martin; Schüssler, Ulrich; Richter, P.; Gehlen, Kurt v.; Röhr, Ch.

doi:10.1007/bf01163125

Cited by 13 publications

(19 citation statements)

References 16 publications

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“…Bulk rock analyses (Matthes et al 1995) indicate an ultrabasic to basic (SiO 42-46 wt.%) Mg-rich chemistry typical of mela-olivine gabbro-norites. The CIPW norm displays normative olivine, hypersthene, diopside and plagioclase.…”

Section: Petrographymentioning

confidence: 99%

“…Based on mineralogy and textures, different petrographic types of ultramafic rocks have been distinguished by Matthes et al (1995). A feature common to all types is that various amphiboles, chlorite and talc make up more than 70 vol.% of the rock.…”

Section: Petrographymentioning

confidence: 99%

“…Additional phases, such as antigorite, clinopyroxene, plagioclase, calcite and biotite, do not occur in all samples. The main type of ultramafics (type A after Matthes et al 1995), found in a 5-m-thick layer, is composed of a finegrained matrix of calcic amphibole, orthoamphibole, chlorite and talc ( '90 vol.%). In addition, porphyroclasts of diopsidic clinopyroxene and of brown pargasitic hornblende are present (Fig.…”

Section: Petrographymentioning

confidence: 99%

“…from the Spessart (Matthes and Kra¨mer 1955;Matthes and Schubert 1967;Nasir 1990), the Odenwald (Schubert 1969;Knauer et al 1974) and the Erbendorf-Vohenstrauss zone (Voll 1960;Schu¨ssler 1990). A new finding of ultramafic rocks with this particular assemblage was recently reported from the pilot hole of the German Deep Drilling Program (KTB) by Matthes et al (1995). The drill site is located within the Erbendorf-Vohenstrauss zone (Franke et al 1995, and references therein) at the eastern margin of the Bohemian massif.…”

Section: Introductionmentioning

confidence: 99%

“…The ultramafic talc-chlorite-orthoamphibole-calcic amphibole felses and schists from KTB form intercalations within metagabbro-amphibolite sequences. From the close spatial relation with metagabbros, the ultramafic rocks were interpreted as cumulates metamorphosed under amphibolite-facies conditions (Matthes et al 1995). Appropriate P-T data for the ultramafic rocks are not yet available.…”

Section: Introductionmentioning

confidence: 99%

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Phase relations of calcic amphibole–orthoamphibole–chlorite- talc assemblages, with applications to ultramafic rocks from the KTB pilot hole, Bavaria

Schmädicke¹,

Okrusch²

1997

Geol Rundsch

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Lenses of ultramafic rocks intercalated within a metagabbro-amphibolite sequence were encountered in the KTB pilot hole. A pervasive metamorphic overprint formed the dominating assemblage calcic amphibole-orthoamphibole-chlorite-talc. In this study the phase relations of ultramafic rocks are investigated in order to (a) constrain the stability field of this assemblage in general, and (b) define the equilibrium pressure-temperature (P-T) conditions of this assemblage in the ultramafic rocks from the KTB borehole. For that purpose, phase equilibria were calculated in the model systems. Thereby, the continuous compositional change of solid solutions with pressure and temperature was modeled, including the Tschermak's substitution and the MgFe \ exchange. Based on these results, petrogenetic grids were constructed, revealing that calcic amphibole-orthoamphibole-chlorite-talc assemblages cover a stability field of (650-770°C/1P 14 kbar (CMASH) and (550-650°C/1P14 kbar (CMFASH), respectively. This explains the widespread occurrence of the considered assemblage. Based on the bulk rock composition of the KTB samples, a special P-T diagram was constructed, limiting the stability field of the calcic amphibole-orthoamphibole-chlorite-talc assemblage. At 580°C the stability field extends from 6 to 14 kbar pressure, and shrinks to 10-11 kbar at 630°C. Conventional estimates using the mineral compositions of the KTB samples yield a temperature around 630°C, at which the calculated stability field of calcic amphibole-orthoamphibole-chlorite-talc extends from 10 to 11 kbar.

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Section: Petrographymentioning

confidence: 99%

Section: Petrographymentioning

confidence: 99%

Section: Petrographymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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