TSK 11 Göttingen 2006 Riller et al.
 Identification of upper-
 crustal discontinuities us-
 ing dip curvature analysis
 of isostatic residual gravity:
 examples from the central
 Andes Poster
 Ulrich Riller1 Hans-Joachim Götze2
 Sabine Schmidt2 Robert Trumbull3
 Fernado Hongn4 Ivan Petrinovic4
 Structural analysts are often faced with
 the problem of identifying prominent
 structural discontinuities covered by
 post-tectonic sedimentary or volcanic
 rocks. Gravity fields are often used to
 delineate the trace of buried disconti-
 nuities but are frequently found to be
 too crude to localize discontinuities ad-
 equately. Here, we introduce the im-
 portance of dip curvature of the iso-
 static residual gravity for identifying
 upper-crustal discontinuities. The rela-
 tionship between Bouguer gravity, iso-
 static residual gravity and its dip curva-
 ture, first-order structural elements and
 distribution of Neogene volcanic rocks
 was examined in the central Andean
 plateau, more specifically, the southern
 Altiplano and the Puna. In the southern
 Altiplano, strong positive Bouguer grav-
 ity corresponds to areas affected by late-
 Cenozoic faulting and large-scale fold-
 ing of upper crust. Dip curvature anal-
 ysis of isostatic residual gravity shows
 that elongate zones of maximum cur-
 vature correspond remarkably well with
 the structural grain defined by first-
 order folds and faults. Similarly, iso-
 static residual gravity in the Puna is
 1 Museum für Naturkunde der Humboldt-U-
 niversität zu Berlin, Invalidenstrasse 43,
 10115 Berlin, Germany 2 Universität Kiel,
 Germany 3 GeoForschungsZentrum Pots-
 dam, Germany 4 CONICED and Universidad
 Nacional de Salta, Argentina
 largely controlled by prominent, upper-
 crustal structures but also by the dis-
 tribution of Miocene and younger vol-
 canic rocks. The Central Andean Grav-
 ity High, in particular, is confined by
 Neogene volcanic rocks and is mostly
 associated with areas of low topog-
 raphy, i.e., fault-bounded, internally-
 drained basins. Dip curvature analy-
 sis of the isostatic residual gravity field
 shows that elongate zones of maximal
 curvature correlate with the strike of
 prominent Neogene faults. Our study
 suggests that such analysis constitutes
 an important tool for imaging upper-
 crustal structures, even those which are
 not readily apparent at surface. For ex-
 ample, upper-crustal faults in the Salar
 de Atacama area, the presence of which
 is suggested by the dip curvature of
 residual gravity, offers a plausible ex-
 planation as to the pronounced angular
 departure of the volcanic belt from its
 overall meridional trend and its narrow-
 ing south of the salar. In contrast to
 previous interpretations, our study sug-
 gests that gravity anomalies of the Cen-
 tral Andes arise chiefly from late Ceno-
 zoic volcanism and tectonism. Further-
 more, dip curvature analyses of gravity
 fields bear a great potential for eluci-
 dating first-order structural elements of
 deformed upper-crustal terranes such as
 the modern Andes.
 1