Publication Date:
2021-12-15
Description:
The small Plio-Quaternary volcanic centre of Cabezo Negro de Tallante in SE Spain includes a thick deposit of
polymictic pyroclastic tuff-breccia, whose fragments are agglutinated by a carbonate-rich component. This feature is also observed in other monogenetic volcanic centres cropping out in the Tallante-Cartagena volcanic district. The carbonate fraction has been recently interpreted in literature as representing a mantle component,
therefore pointing to the existence of a diffuse carbonatitic activity in the area.
Based on detailed sedimentological (presence of pisoids and root remnants), petrographic (presence of plagioclase and absence of euhedral silicate minerals in the calcite plagues), mineral chemistry (Ba-Sr-poor calcite composition), whole-rock chemistry (overall low incompatible element content in the pure carbonate fraction and a
monotonous trace element negative correlation with CaO) as well as isotopic constraints (perfect correlations between Sr-Nd-Pb isotopic ratios with CaO in the basaltic and carbonate fraction, as well as heavy δ18O and light
δ13C isotopic composition of the carbonate fraction), we propose a secondary origin for the carbonate component,
excluding any contribution of mantle carbonatite melts. The presence of carbonates infiltrating the abundant
mantle and crustal xenolith fragments found in the pyroclastic breccia is not related to the presence of
carbonatitic melts at mantle to lower crustal depths, but to in-situ fragmentation of the Strombolian tuffbreccia deposit, followed by secondary carbonate infiltration. The pyroclastic breccia was indeed affected by an
alternation of carbonate precipitation and dissolution in a vadose zone, where the activity of bacteria, fungi,
roots and meteoric water led to the formation of a calcrete (caliche)-type deposits.
Basaltic rocks (hawaiites and basanites) occur in the area as scoria and lava fragments in the pyroclastic breccia as
well as small lava flows. They have been modelled with a low-degree partial melting of an amphibole-bearing
peridotitic mantle close to the lithosphere-asthenosphere boundary. The origin of the mildly alkaline sodic basaltic activity in SE Spain post-dates the abundant and long-lasting subduction-related volcanic phase in the Betic
Chain. Its origin is explained without requiring the presence of any thermal anomaly, but simply as consequence
of the difference of lithospheric depths and edge-driven-type small-scale convection
Description:
Published
Description:
106140
Description:
5V. Processi eruttivi e post-eruttivi
Description:
JCR Journal
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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