Gravity anomalies in the KTB area and their structural interpretation with special regard to the granites of the northern Oberpfalz (Germany)

Abstract

By fieldwork within the frame of the KTB project a new set of 1800 gravity data has become available. Prominent Bouguer anomalies are produced by the ZEV (high with !6 mGal), the Grafenwo¨hr block (low with !24 mGal) and the granites (low with !46 mGal). The vertical gradient map gives information about the near-surface structure. In addition, spectral analysis and upward continuation of the field data give information about depth extension of the granites and other units. The density structure of the crust is outlined by 3D interactive forward modeling. Regional anomalies are caused by the Erbendorf body and the dipping Moho. Local and dominating anomalies have different sources: (a) the foreland sediments with an underlying deep structure (possibly of ZEV material); (b) the ZEV metamorphic units (gneisses and metabasites); and (c) the granites. The ZEV units are controled by the steeply inclined SE1 reflector as a tectonic element. The Falkenberg granite provides two thirds of the total granitic volume and its depth reaches 6.5 km, whereas other granites reach depths of 2-3 km. The nature of the crustal material below the granites and of the Erbendorf body remains unknown.

The Use of Wave-field Directivity for Velocity Estimation: Moving Source Profiling (MSP) Experiments at KTB

“…To choose an appropriate initial model all available information has been used including surface geology, a vertical geological profile in the pilot hole (RÖ HR et al, 1990), results of the 3-D seismic campaign ISO89 (HLUCHY et al, 1992), core sample studies of the Falkenberg granite (WÖ HRL, 1981), velocity model 1001 near the KTB site (WIEDERHOLD, 1992), results of gravity modeling (CASTEN et al, 1997). In a tectonically overprinted region such as the KTB environment, anisotropy is also an important effect.…”

The Fe-Mn phosphate aplite ‘Silbergrube’ near Waidhaus, Germany: epithermal phosphate mineralization in the Hagendorf-Pleystein pegmatite province

“…The Hagendorf pegmatite fades out into an aplitic root zone underneath the main pegmatite body and aplitic bodies form the earliest felsic mobilizates in the Hagendorf-Pleystein pegmatite province (Dill et al, 2007b). This aplitic body marks the transition of lenses and dykes of synkinematic primitive tourmaline-and garnetbearing aplitic bodies, previously mapped and denominated as metaaplites or orthogneisses by Forster (1965), into post-kinematic fractionated granites whose root zones are deduced so far only from gravity maps (Casten et al, 1997). The youngest and most fractionated felsic igneous rock type is the Kreuzstein albite-zinnwalditetopaz granite which is abundant in Sn, Ta and Nb.…”