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Ó Springer 2005

A magnetic anomaly study offshore the Canary Archipelago M. Catala´n, J. Martı´ n Davila & ZEE Working Group* Real Instituto y Observatorio de la Armada, San Fernando 11000, Ca´diz, Spain Key words: Canary Islands, geomagnetism, marine magnetic anomalies, underplating

Abstract A scalar magnetic anomaly map of the regions offshore the Canary Archipelago is presented here. This map is based on measurements taken inside the Exclusive Economic Zone Project framework. This paper contains a description of the data set, whose accuracy and internal consistency are analysed. The magnetic anomalies are described and the main structural trends are highlighted. This analysis has served to detect two possible fractures with a NW–SE component: one separates Fuerteventura from Gran Canaria Island, and the other apparently runs through Fuerteventura. The latter finding agrees with a 1.7 km depth offset, between its northern and southern halves, detected by the algorithm based on the Euler Deconvolution. A similar approach has been performed, estimating the depth to the top of the most significant anomalies. This result shows that the most noteworthy magnetic anomaly source of the archipelago, which lies between Tenerife and Gran Canaria Island, seems to be located at an average depth of 4 km below sealevel. A spectral analysis was performed to estimate the depth extent of the deepest anomalies. It argues the presence of sub-crustal magnetic sources (underplating) in the archipelago. A standard Euler Deconvolution analysis was executed to analyse the spatial distribution of these mantle-like sources. Our results seem to support the existence of magmatic underplating under Gran Canaria, Tenerife, and Fuerteventura, and suggest this possibility for La Palma.

Introduction

Magnetic geological setting

This paper focuses on the processing and inversion of magnetic anomaly data from the Canary Archipelago, inside the Exclusive Economic Zone framework. We have produced a scalar magnetic anomaly map, and, by applying some operators (e.g., analytical signal and Euler Deconvolution), we have highlighted structural features and trends around this area, and inferred the depth and location of the causative bodies. These results improve the resolution and expand on earlier work in the area. Additionally, the magnetic data can now be correlated with other data with the same level of accuracy and resolution.

The Canary Archipelago is located on the border of the northwestern Africa passive continental margin. Its geographical location indicates that the oceanic crust on which these islands were built is Early Jurassic in age (150–170 Ma). To improve our understanding of this zone we have compiled magnetic data from the Geophysical Data System (GEODAS) (Metzger and Campagnoli, 2003) and merged them into a single 0.2°
0.2° grid covering the following geographical frame: 35°N–25°N and 5°W–25°W (Figure 1). Figure 1 shows a magnetic anomaly pattern which is clearly unbalanced and is dominated by a spectacular feature, M0–M4 anomalies, p