Ferropicrite from the Lalibela area in the Ethiopian large igneous province
Abstract
Ferropicrite and picritic ferrobasalt lava flows near Lalibela in the Oligocene (~ 30 Ma) Ethiopian large igneous provence (LIP) are associated with ultratitaniferous transitional basalt and picrites of the second high-Ti (HT2) series. The dominant phenocryst in the studied samples is Mg-rich olivine (up to Mg# 88.4) with high CaO contents (to 0.42 wt. %) and kink band structure is absent, indicating that olivines are crystalized from a melt. Spinel inclusions and microphenocrysts are characterized by extremely high Cr# (79-84), moderate Mg# (18-51), moderate Fe3+# (11-26) and contains 3.6-14.8 wt. % TiO2. The clinopyroxene phenocrysts are Mg#=73-88, TiO2=0.84-2.9 wt. %, and Al2O3= 1.2-4.1 wt. % in the cores. The REE contents of clinopyroxenes display enrichment in LREE (LaN/YbN=1.2-1.9) and MREE (EuN/YbN=3.3-4.3) relative to HREE. Relative depletion of HFSE (e.g. Nb and Zr) is also observed. In general, these trace element characteristics of clinopyroxene are similar with those of high-Ti 2 basalts. The estimated MgO content of liquid is about 23.5 wt. % and mantle potential temperature may have been as high as ~ 1638 OC. This temperature (Tp) is higher (by some 100 OC) than those estimated for the African-Arabian traps (~ 1520 OC). The studied samples exhibit very low Al2O3/TiO2 (1.8-2.2) and high Zr/Y (8.2-10.2) ratios. These may indicate the important role for garnet during melting and that the lavas were formed by small degree of partial melting which apparently contradicts to the high Cr# of spinel. In view of low Cr/Al ratio of the bulk rock, the high Cr# of spinel suggests very high temperature of the magma (and the plume). The origin of these ferropicrite and picritic ferrobasalt rocks could be attributed to high pressure partial melting of pyroxenite that possibly incorporate recycled oceanic crust components. Keywords: Ferropicrite, large igneous province, Oligocene, pyroxinite, Lalibela
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMED51B0611D
- Keywords:
-
- 1000 GEOCHEMISTRY