P. Schmoldt, PhD - MTNet - DIAS

11.2. PICASSO Phase I investigation
composition of the Tajo Basin subsurface, in particular regarding conducting phase
constituents, are required before instructive assumption can be made about the connectivity
of those phases. It should be noted that the PICASSO Phase I investigation
and the seismic tomography model revealed an extension of the Iberian Massif beneath
large parts of the southern Tajo Basin, further to the east than suggested by
surface geology maps. In surface geology maps the Iberian Massif is only mapped
to the west of the Tajo Basin, due to the fact that in the basin relevant outcrops are
covered by sediments.
• An electrically conductive – seismically slow anomaly in the middle and lower crust
beneath the Campo de Montiel region (southern Tajo Basin). The anomaly is situated
in the region associated with the Iberian Massif, and remnants of asthenospherederived
melt intruded during Pliocene times are inferred as the origin of the anomaly.
The intrusion is associated with the second sequence of volcanic activity in the Calatrava
Volcanic Province (CVP), located to the west of the PICASSO Phase I profile.
The proposed source region for the asthenospheric melt is situated to the east of
the PICASSO Phase I profile, with the assumed connection path between source region
and volcanic province intersecting the PICASSO Phase I profile in the Campo
de Montiel region. Due to a lack of a significant high surface heat flow expression
in the southern Tajo Basin region, contribution of a hydrous phase was concluded,
which lowers the solidus, increases electric conductivity, and lowers seismic velocity
in the region. Dehydration processes of the slab subducting beneath Alboran
Domain and Betic Cordillera were identified as the potential source for the hydrous
phase in the Tajo Basin crust, based on reduced electric resistivities and seismic velocities
of the mantle in-between the region associated with the slab and the crustal
anomaly. However, large-scale fluid circulation as discussed in Jones [1992, and
references therein] cannot be excluded as the source of the conducting phase.
• An extensive region of significantly reduced electric resistivity in the lithosphericmantle
beneath the central Tajo Basin area, coinciding with low seismic velocities.
Low resistivity – low velocity features at mantle depths are indicative of significant
melt or fluid phases or increased temperatures, and it is concluded that this anomaly
is an expression of a HIMU-like 7 reservoir, the source of volcanic events throughout
central and western Europe as well as in northern Morocco. A contribution of fluids
originating from dehydration of the subducting slab beneath Alboran Domain and
Betic Cordillera is possible. More detailed constraints on the deep-seated features
in the Tajo Basin mantle are, however, impeded by the low signal-to-noise ratio of
long-period impedance estimates in the PICASSO Phase I dataset.
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