Acquisition and modelling of gravimetric data over the Matacães salt diapir (Torres Vedras, Lusitanian Basin, Portugal)

Abstract

The objective of the present work is to analyze the sub-surface geometry of the Matacães (Torres Vedras, Portugal) salt diapir, taking into consideration the geodynamic context that led to its formation.
With this objective, a campaign took place in the surrounding area of the Matacães salt diapir in order to gather gravimetric data, as well as the acquisition of global positioning (GPS) and altimetry data, with a total of 233 measurement points with special  relevance to the flanks of the diapir.
After the correction and processing of the gathered data, different anomaly maps were constructed (Bouguer, Regional and Residual Anomaly), which enabled the identification and delimitation with more precision of the Matacães salt diapir, and also the recognition of the depocenters in Bombarral, Turcifal and Arruda sub-basins.
A NW-SE profile was drawn over the Bouguer anomaly map, in order to cross perpendicularly the main structures that exist in the area under study (Structural Lineament Torres Vedras – Montejunto)  in order to intercept the Matacães salt diapir (outcropping).
The gravimetric modeling of the selected profile enabled the construction of two hypothetical models  of the sub-surface geometry of the Matacães salt diapir. The most appropriate model, whichexplains the geometry of the Matacães Diapir, is the one that takes into account the different tectonic periods (distensive-compressive) that were registered in the Lusitanian Basin, with special relevance to the Miocene compressive period. In this context, the Matacães Diapir has intermediary characteristics between a namakier and a “salt tongue”.