Cr-Zr-armalcolite-bearing lamproites of Cancarix, SE Spain

Abstract

Lamproites with high MgO, high SiO2 affinity are abundant only in SE Spain where the Cancarix outcrop (in the province of Albacete) occurs. The rocks of Cancarix are peralkaline, saturated to oversaturated in silica, very high in K20, Th and LREE. The mineralogy and petrography show some variations which depend on the conditions of emplacement and rate of cooling of the magma. The following phases may be present: olivine, phlogopite, K-amphibole, clinopyroxene, sanidine, orthopyroxene, apatite, and, in minor amounts, Cr-spinel, minerals of the pseudobrookite group, ilmenite, roedderite, dalyite, carbonate, analcime (probably pseudomorphous on leucite), a silica phase, rutile, pyrochlore (?), britholite (?) and glass. The lamproites of Cancarix contain Cr-Zrarmalcolite, which is typical of lunar basalts and which has been found also in kimberlites. The composition of early magmatic spinel and the occurrence of Cr-Zr-armalcolite indicate low oxygen fugacity for the primitive magma and related mantle source, in agreement with recent experimental data on lamproitic systems. The redox conditions changed during crystallisation, leading to increase of the Fe3+/Fe ~+ ratio in the system. During the later stages of crystallisation, the residual melts/fluids were depleted in alumina and enriched in several components, e.g. Na, Zr, Fe, REE, C1, etc. stabilising Na-Fe-clinopyroxene, dalyte, arfvedsonitic rims around K-richterite and other alumina-free phases which, on a chemical basis, have been identified as britholite and pyrochlore. Rough comparison with experimental systems and the geochemistry of the rocks suggests that the magma was generated at shallow depth (<<20 kbar) in the lithospheric mantle, which, after early depletion, underwent strong enrichment in many 'incompatible' elements.

Geochemical and Pb–Sr–Nd isotopic composition of the ultrapotassic volcanic rocks from the extension-related Çamardı-Ulukışla basin, Niğde Province, Central Anatolia, Turkey

“…They resemble the profiles of other subduction-related potassic lavas (e.g. Contini et al, 1993;O'Brienetal., 1995;Dostal et al, 1998). Traceelement patterns for the Ulukışla ultrapotassic volcanic rocks also show small depletions in Zr and Hf (Fig.…”

Magmatic evolution of the Gaussberg lamproite (Antarctica): volatile content and glass composition

“…For instance, similar chemical and mineralogical evolution is reported in Contini et al (1993) for the lamproite of Cancarix (SE Spain), where phlogopite, instead of leucite, follows olivine in the sequence of crystallization.…”

Britholite, monazite, REE carbonates, and calcite: Products of hydrothermal alteration of allanite and apatite in A-type granite from Stupné, Western Carpathians, Slovakia

“…BGM are locally enriched in actinide elements, particularly in Th and less in U which are the regular source of their metamictization. Thorium content in britholite-(Ce), fluorbritholite-(Ce), and fluorcalciobritholite compositions with Ce N Y can reach~3 to 23 wt.% ThO 2 or 0.06 to 0.68 apfu (Contini et al, 1993;Della Ventura et al, 1999;Melluso et al, 2010;Oberti et al, 2001;Orlandi et al, 1989;Pekov et al, 2007). In contrast, BGM compositions with Y N Ce contain notably lesser Th (up to~2 wt.% ThO 2 ; Griffin et al, 1979;Payette and Martin, 1986;Pekov et al, 2011;Smith et al, 2002).…”