The origins of contrasting zoning patterns in hyalophane from olivine leucitites, Northeast China

Abstract

Olivine (ol) leucitite lavas from Northeast China contain hyalophanes with contrasting Ba-zoning patterns. The hyalophanes occur: (1) in a magmatic inclusion (DZ2n), consisting of barian-titanian phlogopite + hyalophane + leucite + sodalite, and (2) as a mantle surrounding a sanidine megacryst (DZ19). Hyalophanes contain 4.6-20.2 mol.% celsian (Cn). The DZ2n hyalophane is normally zoned with respect to Ba (decreasing Ba toward rim), whereas the hyalophane mantle of megacryst DZ19 is reversely zoned. DZ2n probably crystallised from an extensively evolved (>80 wt.% crystallisation) potassic melt derived from a primitive magma chemically similar to the host, at relatively low temperatures and pressures (e.g. T-720 ~ P-2 kbar). Competition with barian-titanian phlogopite for Ba, and limited Ba supply from the residual melt are the main cause for the normal Ba zonation. Sanidine megacryst DZ19 originated as a high P-T product (e.g. T >950 ~ P > 15 kbar) of an evolved leucite (lc) basanite/trachybasalt genetically related to ol-leucitites. Subsequently, it was incorporated into the host ol-leucititic magma at which point it was partially resorbed and then mantled by hyalophane. An increase in KBa affliq values with decreasing temperature and pressure and cocrystallisation of the hyalophane mantle with Ba-free phases may have caused the unusual reverse zonation.

Zr- AND Ba-RICH MINERALS FROM THE PONTE NOVA ALKALINE MAFIC-ULTRAMAFIC MASSIF, SOUTHEASTERN BRAZIL: INDICATION OF AN ENRICHED MANTLE SOURCE

“…In the southern satellite area, Ba-rich feldspar is easily found as an interstitial phase, oikocrysts enclosing submillimetric chadacrysts of plagioclase, and even as a mantle surrounding other feldspar grains (Fig. 7A), as in other magmatic occurrences (Flohr & Ross 1990, Zhang et al 1993a. In general, Ba-rich alkali feldspar crystals of the southern satellite area tend to be normally zoned, with decreasing levels of Ba toward the rim.…”

“…Barium-rich alkali feldspar, in igneous rocks, is generally found in basanites, phonolites, minettes, and carbonatites (Zhang et al 1993a, Deer et al 2001, Chakhmouradian & Mitchell 2002. However, it has also been found in other igneous associations, e.g., granite suites (Essene et al 2005), and even in cumulates in gabbroic lunar meteorites (Fagan et al 2008).…”

Origin of early Cambrian black-shale-hosted barite deposits in South China: Mineralogical and geochemical studies

“…6E and F) for the first time in such deposits. Hyalophane is an isomorphous mixture of potassium and barium feldspars, and is widely found in various rock types, including igneous rocks (Zhang et al, 1993), dykes (Beran et al, 1992;Qu et al, 2012) and metamorphic rocks (Essene et al, 2005). Irrespective of the rock type, the presence of this mineral is generally associated with barium-rich hydrothermal fluids and is thus generally regarded as evidence of hydrothermal activity (Kříbek et al, 1996;Hou et al, 2001).…”

Origin and geological significance of the 1.81 Ga hyalophane-rich pegmatite veins from the high-pressure granulite terrain in the Central Zone of North China Craton

“…In addition, the characteristics of these hyalophanes are consistent with global typical hyalophanes in the Or-Ab-Cn ( Figure 5 Sample 08YK01: the pure hyalophane pegmatite vein; sample 08YK03: the hyalophane-rich pegmatite vein, (hyalophane + clinopyroxene + titanite + epidote). Other data are from the global typical hyalophanes [32][33][34][35][36]). …”

“…Hyalophane is found in alkaline rocks, granites and pegmatites. For example, hyalophanes occurred in inclusions and overgrown around sanidine megacryst were found in olivine leucitite lavas from Northeast China [34]. In addition, occurrences of hyalophanes have been reported from ultrapotassic volcanic rocks, potassic intrusive rocks, and some alkaline silicic lavas.…”