P. Richter’s research while affiliated with University of Wuerzburg and other places

Comprehensive geochemical investigations of metabasites yielded constraints for a correlation of, or discrimination between the different tectonic units within the northeast Bavarian crystalline basement. The Münchberg nappe pile consists of at least five large tectonic units which exhibit differences in lithology, in part also in metamorphic grade and in metamorphic history. The metabasites in each of these nappes show their own, significant geochemical characteristics. The lowermost tectonic unit, the Bavarian lithofacies, includes the anchimetamorphic Ordovician Randschieferserie which contains alkaline basalts. In their geochemistry, they are similar to the metabasites of the Fichtelgebirge crystalline complex in the autochthonous Saxo-thu-ringian. The next higher tectonic unit of the Munchberg nappe pile, the Prasinit-Phyllit-Serie contains metabasites which can be derived from subalkaline basalts with a clear calc-alkaline tendency. There is a striking geochemical resemblance to the metabasites of the Erbendorf Greenschist Zone (EGZ) underscoring the similar lithology of both allochthonous units which appear to be in a similar tectonic position. The Randamphibolit-Serie higher up in the Munchberg nappe pile consists of metabasites with tholeiitic characteristics and a pronounced differentiation trend. The next higher tectonic unit, the Liegendserie of the Munchberg gneiss complex s. str., contains metagabbros to metagabbronorites with a high-Al basaltic composition. The amphibolites and banded hornblende gneisses of the overlying Hangendserie are of sub- alkaline basaltic character with calc-alkaline affinity. The Zone Erbendorf-Vohenstrauss (ZEV) is currently regarded as an allochthonous unit equivalent to the higher crystalline nappes of the Munchberg pile. However, the geochemical character of the metabasites do not encourage such a correlation. Neither the schistose and striped amphibolites nor the flaseramphibolites of the ZEV with their N-MORB and E-MORB character respectively, find convincing counterparts in the crystalline nappes of the Munchberg pile. However, an interestingly close resemblance exists between the schistose and striped amphibolites in the ZEV, on the one hand, and in the autochthonous Zone Tirschenreuth-Mahring (ZTM) and the adjacent Moldanubian sensu strictu, on the other. Owing to the absence of age criteria, our results cannot be used, so far, to reconstruct the paleogeographical position of the individual tectonic units, based on the geochemical characteristics of their respective metabasites.

The Spessart Crystalline Complex, north-west Bavaria contains two orthogneiss units of granitic to granodioritic composition, known as the Rotgneiss and Haibach gneiss, respectively, which are structurally conformable with associated metasediments. The igneous origin of the Rotgneiss is apparent from field and textural evidence, whereas strong deformation and recrystallization in the Haibach gneiss has obscured most primary textures. New geochemical data as well as zircon morphology prove the Haibach gneiss to be derived from a granitoid precursor, which was chemically similar to the Rotgneiss protolith, thus suggesting a genetic link between those two rock units. Both gneiss types have chemical compositions typical of anatectic two-mica leucogranites. They show characteristics of both I- and S-type granites. Rb-Sr whole rock data on the Haibach gneiss provide an isochron age of 40714 Ma (IR = 0.70770.0007; MSWD 2.2), which is slightly younger than the published date for the Rotgneiss (43915 Ma; IR=0.70480.0026; MSWD 4.9). Single zircon dating of six idiomorphic grains, using the evaporation method, yielded a mean 207Pb/206Pb age of 41018 Ma for the Haibach gneiss and 41818 Ma for the Rotgneiss. Both zircon ages are within analytical error of the Rb-Sr isochron dates and are interpreted to reflect the time of protolith emplacement in Silurian times. Three xenocrystic zircon grains from the Rotgneiss yielded 207Pb/206Pb ages of 227812, 249013 and 273410 Ma, respectively, suggesting that late Archaean to early Proterozoic crust was involved in the generation of the granite from which the Rotgneiss is derived. Although it is assumed that the granitic protoliths of the two gneisses were formed through anatexis of older continental crust, the relatively low 87Sr/86Sr initial ratios of both gneisses may also indicate the admixture of a mantle component. The Rotgneiss and the Haibach gneiss thus document granitic magmatism at an active continental margin during late Silurian times.

The metagabbro-amphibolite sequences in the KTB pilot hole contain intercalations of talc-chlorite-amphibole felses (or ''hosbachites''), which show transitional contacts to the adjacent metagabbros. The hosbachites are characterized by relics of a primary igneous texture and still contain igneous minerals like clinopyroxene, biotite and pseudomorphs after olivine, while brown Ca-amphibole was presumably formed in a late-magmatic stage. The geological, textural, mineralogical and geochemical evidence indicates that the hosbachites were derived from ultramafic cumulates, differentiated from a basaltic magma, either in the inner parts of dolerite sills or in small gabbro intrusions. A pervasive metamorphic overprint under medium-pressure, amphibolite-facies conditions which was accompanied by penetrative deformation led to assemblages with green Ca-amphibole +/- anthophyllite +/- cummingtonite +/- tremolite/actinolite + clinochlore + talc + olivine + ilmenite +/- Cr-bearing spinel + sulfides. Phase relationships are consistent with a prograde P-T path leading to the formation of anthophyllite from olivine + talc at peak metamorphic temperatures of 640-700-degrees-C, at assumed pressures of 8-10 kbar, similar to those derived from mineral assemblages in the adjacent metabasites and metasediments. High-pressure relics locally present in coronitic metagabbros and retrograded eclogites of the KTB pilot hole were not recognized in the hosbachites. A retrograde overprint under greenschist-facies conditions led to the total replacement of igneous or metamorphic olivine by aggregates of antigorite + magnetite, chloritization of biotite and the formation of late tremolite/actinolite.

Matchless is one of several metamorphosed massive copper-zinc sulfide deposits associated with the Matchless amphibolite belt in the upper Proterozoic Damara orogen (SWA/Namibia). In the footwall of the ore shoots are pyrite-bearing quartz-muscovite-(chlorite) schists with interlayered bands of massive pyrite-quartz rock and a distinctive biotite-rich marker schist. In the hanging wall of the ore shoots the wall rock consists of chloritic schists containing variable proportions of quartz, ankerite, and calcic amphibole, bands of magnetite quartzite, calc-silicate rock, and amphibolite. This rock association is regarded as representing a premetamorphic stratigraphic sequence. The initial deposit was formed in a subsiding trough in which active turbidite sedimentation formed the precursor rocks of the Kuiseb schists. Sedimentation was interrupted by submarine volcanic activity which produced the basaltic protolith of the Matchless amphibolite. Metal sulfides were precipitated from convecting hydrothermal fluids generated by the reaction of seawater with subsea-floor basalts and clastic sediments.

Major-, trace- and rare-earth element chemistry studies of metabasite intercalations within different tectonic units of the East Bavarian crystalline basement leads to the following geochemical classification: The flaser amphibolites of the Erbendorf-Vohenstrauss Zone (ZEV) exhibit an enriched, E-MORB- or intraplate-like tholeiitic character, whereas the schistose and striped amphibolites of the ZEV and of the Tirschenreuth-Mahring Zone show N-MORB compositions. The metagabbros of the ZEV are transitional between these two types. The metabasites of the Erbendorf Greenschist Zone are similar to modern island-arc basalts (tholeiitic to calc-alkaline). The Fichtelgebirge crystalline complex contains amphibolites of enriched tholeiitic to alkaline i.e., intraplate character.In most of the investigated metabasites, a post-basaltic/post-gabbroic mobilization of the trace elements cannot be recognized. An exception is Ba which is generally enriched. This may be due to pre-metamorphic hydrothermal alteration processes and/or to a synmetamorphic chemical exchange with adjacent metasediments. The contact-metamorphic overprint of some flaser amphibolites from the ZEV by the intrusion of the Variscan Falkenberg granite led to enrichment in Li, Rb, K and W, a simultaneous depletion in Ca, Sr, Cr and Ni, and a decrease in the K/Rb ratio. Nb, Ce, P, Zr, Ti and V scatter in a much wider range than in the unaffected flaser amphibolites, although with no clear tendency for enrichment or depletion. A mobilization of P and the LREE's in some schistose and striped amphibolites of the ZEV and in the contact-metamorphosed flaser amphibolites is presumably a result of post-granitic hydrothermal alteration which is indicated by enrichment of As as a pathfinder element.