Emilio Herrero Bervera: Miocene Tejeda Caldera Complex, Gran Canaria Island, Spain
Channel: Institute for Rock Magnetism
Date: 2021-06-02

12th Institute for Rock Magnetism Conference

Lightning Talk

Title: On the Rock Magnetic Properties and Petrofabric (AMS) Analyses of Trachytic, Phonolitic, Basaltic Dikes and Conesheets Emplaced on the Miocene Tejeda Caldera Complex, on Gran Canaria Island, Spain

Authors: Emilio Herrero Bervera (1) & Manuel Calvo Rathert (2)

Institutions:
(1) SOEST-Hawaii Institute of Geophysics and Planetology, University of Hawai'i, 1680 East West Road, POST 715 and 716, Honolulu, HI
(2) Universidad de Burgos. Departamento de Física. Escuela Politécnica Superior. Avenida de Cantabria s/n
09006 Burgos, Spain

Abstract:
The Miocene Tejeda Complex on Gran Canaria (Canary Islands) is characterized by more than 500 trachytic and phonolitic conesheets, dikes, hypabyssal syenite stocks and subordinate radial dikes from a 20-km diameter intrusive complex in the volcaniclastic fill of the Miocene Tejeda caldera (20 x 35 km) on Gran Canaria, Canary Islands. The dikes intruded concentrically around a central axis or radial symmetry and dip uniformly an average of~41 degrees toward the center.
We have conducted a pilot study of magnetic properties as well as Anisotropy of Magnetic Susceptibility (AMS) on a variety of dikes (trachytic and phonolitic and basaltic in composition) to investigate the possibility of obtaining petrofabrics results that would allow us to test the origin of the formation of the Tejeda conesheets that most likely resulted from deformation processes due to resurgent doming initiated by recurrent replenishment of a flat laccolith-like magma chamber. The current ideas indicate that the formation of the cone-shaped fractures were originated by a magma supply exceeding the volume that could be compensated for by up-doming of the overlying caldera fill.

Thus far, our AMS results indicate that all the ten intrusives studied despite their different lithologies are susceptible of carrying a measurable magnetic signal. Low-field magnetic susceptibility vs temperature (k-T 28-700°C) experiments have identified mainly one primary magnetic mineral phase namely stoichiometric magnetite, Curie temperature of 585oC, SIRM, hysteresis loops and back-field were performed and yielded a series of secondary magnetic mineral present as well and corroborated by FORC’s results. The petrofabric in the intrusive bodies results show coherent flow azimuths regardless of their time of emplacement. Three main types of magnetic fabrics, (i.e. A to C) were found. Fabric type A (plane Kmax-Kint parallel to the dike plane) represents magma flow direction within the intrusives and is the dominant fabric (~60% of all the intrusives) studied thus far.The Kmax axis inclinations show that about 70% of the intrusives were fed by inclined vertical magma fluxes (inclinations greater than 30°), and the rest of them (~30%) by horizontal to sub-horizontal magma fluxes. Vertical magma flow means inclined magma injection inside fractures, and become more probable as the source is therefore located very close to the origin of the caldera.