Open AccessGravimetric determination of an intrusive complex under the Island of Faial (Azores): some methodological improvements
Author(s) -
Camacho Antonio G.,
Nunes J. Carlos,
Ortiz Esther,
França Zilda,
Vieira Ricardo
Publication year - 2007
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2007.03539.x
Subject(s) - geology , gravity anomaly , tectonics , bouguer anomaly , inversion (geology) , seismology , terrain , volcano , geophysics , lineament , isostasy , volcanism , density contrast , geomorphology , geodesy , paleontology , lithosphere , ecology , physics , astronomy , oil field , biology
SUMMARY We present some improvements of a gravity inversion method to determine the geometry of the anomalous bodies for priori density contrasts. The 3‐D method is based on an exploratory process applied, not for the global model, but for the steps of a growth approach. The (positive and/or negative) anomalous structure is described by successive aggregation of cells, while its corresponding gravity field remains nearly proportional to the observed one. Moreover, a simple (e.g. linear) regional trend can be simultaneously adjusted. The corresponding program is applied to new gravity data on the volcanic island of Faial (Azores archipelago). The inversion approach shows a subsurface anomalous structure for the island, the main feature being an elongated high‐density body. The body is interpreted as a compact sheeted dyke swarm, emplaced along Faial‐Pico Fracture Zone, a leaky transform structure that forms the current boundary between Eurasian and African plates in the Azores area. The new results in this paper are (1) a Bouguer gravity anomaly map, (2) several improvements in the inversion process (robust process, optimal balance fitness/model magnitude), (3) a new gravimetric method for estimating the mean terrain density, (4) a 3‐D model for subsurface mass anomalies in Faial and (5) some interpretative conclusions about a main intrusive complex detected under the island as a wall‐like structure extending from a depth of 0.5 to 6 km b.s.l., with a N100°E trend and corresponding to an early fissural volcanic episode controlled by the regional tectonics.