RT Journal Article
T1 Magma flow, exsolution processes and rock metasomatism in theGreat Messejana–Plasencia dyke (Iberian Peninsula)
A1 Silva, Pedro F.
A1 Henry, Bernard
A1 Marques, Fernando Ornelas
A1 Font, Eric
A1 Mateus, António
A1 Vegas Martínez, Ramón
A1 Miranda, Jorge Miguel
A1 Palomino, Ricardo
A1 Palencia Ortas, Alicia
AB Magma flow in dykes is still not well understood; some reported magnetic fabrics are contradictoryand the potential effects of exsolution and metasomatism processes on the magneticproperties are issues open to debate. Therefore, a long dyke made of segments with differentthickness, which record distinct degrees of metasomatism, the Messejana–Plasencia dyke(MPD), was studied. Oriented dolerite samples were collected along several cross-sectionsand characterized by means of microscopy and magnetic analyses. The results obtained showthat the effects of metasomatism on rock mineralogy are important, and that the metasomaticprocesses can greatly influence anisotropy degree and mean susceptibility only when rocksare strongly affected by metasomatism. Petrography, scanning electron microscopy (SEM)and bulk magnetic analyses show a high-temperature oxidation-exsolution event, experiencedby the very early Ti-spinels, during the early stages of magma cooling, which was mostlyobserved in central domains of the thick dyke segments. Exsolution reduced the grain sizeof the magnetic carrier (multidomain to single domain transformation), thus producing compositefabrics involving inverse fabrics. These are likely responsible for a significant numberof the ‘abnormal’ fabrics, which make the interpretation of magma flow much more complex.By choosing to use only the ‘normal’ fabric for magma flow determination, we havereduced by 50 per cent the number of relevant sites. In these sites, the imbrication angle of themagnetic foliation relative to dyke wall strongly suggests flow with end-members indicatingvertical-dominated flow (seven sites) and horizontal-dominated flow (three sites).
PB Blackwell Publishing Ltd
SN 0956-540X
YR 2008
FD 2008
LK https://hdl.handle.net/20.500.14352/50148
UL https://hdl.handle.net/20.500.14352/50148
LA eng
NO The definitive version is available at www.blackwell-synergy.com
DS Docta Complutense
RD 9 abr 2025