Petrogenetic significance of ocellar camptonite dykes in the Ditrău Alkaline Massif, Romania

Abstract

Camptonite dykes intrude the rift-related Mesozoic igneous body of the Ditrău Alkaline Massif, Eastern Carpathians, Romania. We present and discuss mineral chemical data, major and trace elements, and the Nd isotopic compositions of the dykes in order to define their nature and origin. The dykes are classified as the clinopyroxene-bearing (camptonite-I) and clinopyroxene-free (camptonite-II) varieties. Camptonite-I consists of aluminian-ferroan diopside phenocrysts accompanied by kaersutite, subordinate Ti-rich annite, albite to oligoclase and abundant calcite-albite ocelli. Camptonite-II comprises K-rich hastingsite to magnesiohastingsite, Ti-rich annite, albite to andesine, abundant accessory titanite and apatite, and silicate ocelli filled mainly with plagioclase (An 4-34 ). A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT

Origin of mafic and ultramafic cumulates from the Ditrău Alkaline Massif, Romania

“…8D). These values are similar to those of the Ditrău lamprophyres (La/Yb = 15-38; Batki et al, 2014).…”

“…3). Intercumulus amphibole has higher Mg# and SiO 2 contents and lower K 2 O, FeO t , Ba (<300 ppm), Sr (<350 ppm) and Zr (<115 ppm) contents than cumulus amphibole crystals (see Table II (Batki et al, 2014). Some cumulus amphibole crystal rims are richer in FeO t and poorer in TiO 2 and Mg# than their cores indicating crystallisation towards a slightly more evolved magma or under different conditions (Fig.…”

“…% and 2.9 wt.%, respectively, like those of the Ditrău camptonites (Batki et al, 2014). They have variable Cr concentrations (440-5300 ppm), and contain 75-120 ppm Sr and 50-200 ppm Zr (see Table IV …”

“…Morogan et al (2000) were the first to propose that the parental melt of Ditrău Alkaline Massif were derived from OIB-like basanitic magmas. Batki et al (2014) proposed that parental melts of the…”

“…Generalised descriptions of these ultramafic bodies have been extensively reported over the past 150-years (e.g. Bagdasarian, 1972;Batki et al, 2014;Codarcea et al, 1957;Dallmeyer et al, 1997;Fall et al, 2007;Herbich, 1859;Ianovici, 1933Ianovici, , 1938Jakab, 1998;Kräutner and Bindea, 1998;Mauritz, 1912;Mauritz et al, 1925;Morogan et al, 2000;Pál-Molnár, 1992, 1994, 2000, 2010bPál-Molnár and Árva-Sós, 1995;Streckeisen, 1952Streckeisen, , 1954Streckeisen, , 1960Streckeisen and Hunziker, 1974), but none of these studies have considered their mineral scale petrology, petrogenesis and P-T conditions of cumulate formation in detail. New petrography, whole-rock and mineral chemistry data are presented in this paper and are used to assess the crystallisation history, the depth of formation of the ultramafic cumulates and their petrogenesis.…”