Corona structure from arc mafic-ultramafic cumulates: The role and chemical characteristics of late-magmatic hydrous liquids

Abstract

The Genina Gharbia mafic -ultramafic complex consisting of peridotite, pyroxenite, and gabbronorite represents a remnant of a hydrous magma chamber that was crystallized at the mantle -crust boundary. The hydrous nature of the magma is expressed in the high modal (up to 60%) of amphibole in cumulates and is reflected in variable textural and chemical features of the complex. One of the important manifestations of the hydrous nature is the development of a corona structure between olivine and plagioclase. The corona texture and mineralogy varied according to the activity of the interstitial liquid, temperature, and P H 2 O . The corona in peridotite is limited to thin (<100 microns) orthopyroxene and/or amphibole shells. Thick orthopyroxene -(orthopyroxene -spinel symplectites) -clinopyroxene -amphibole coronas are common in norite. Extensive analysis of different minerals of various textures by electron microprobe and laser ablation inductively coupled plasma mass spectrometry (LA -ICP -MS) revealed distinct chemical difference between the interstitial and cumulus phases of the corona. The corona pyroxenes and amphibole are depleted in V, Ti, Zr, and Nb and enriched in LREE, reflecting the LI-LE -rich and HFSE -depleted nature of the evolved hydrous liquid. The textural and chemical features of the corona are consistent with the formation of corona minerals at the late -magmatic stage. The orthopyroxene corona in peridotite crystallized directly from the evolved melt, while the amphibole corona developed at the expense of plagioclase. Variable corona minerals in norite are the result of direct crystallization from progressively evolved magma during cooling and continuous increase in P H 2 O .

Constraints on the origin of gabbroic rocks from the Moldanubian-Moravian units boundary (Bohemian Massif, Czech Republic and Austria)

“…Mafic to ultramafic complexes with coronitic textures of ca. 570-550 Ma and very similar geochemical and Sm-Nd isotopic characteristics were reported by Cottin et al (1998) from the Panafrican Belt in Hoggar and the Panafrican Eastern Desert terrane in Egypt (Helmy et al 2008). Both regions are possible candidates for areas from which the Armorican and Brunovistulian crustal fragments could be derived.…”

“…de Haas 2002), but olivine-plagioclase coronas were described from low-pressure (up to 1 kbar) domains (Turner & Stuewe 1992). They may be formed either by late magmatic processes during reaction of cumulus phases with hydrous interstitial liquids, or in the solid state due to the activities of fluid-assisted metamorphic processes (Claeson 1998;de Haas et al 2002;Ikeda et al 2007;Helmy et al 2008).…”

What underlies the Philippine island arc? Clues from the Calaton Hill, Tablas island, Romblon (Central Philippines)

“…In most cases, the corona consists of an inner shell of orthopyroxene around olivine, rimmed by clinopyroxene and/or amphibole + spinel symplectite. Disequilibrium between olivine and plagioclase assisted by late stage magmatic fluids (Claeson, 1998;De Haas et al, 2002;Helmy et al, 2008) or through metamorphic processes (Gardner and Robins, 1974;Mongkoltip and Ashworth, 1983;Trolliard et al, 1988;Cruciani et al, 2008). In the first model, coronitic amphiboles are thought to have grown early at the magmatic stage and continued cooling aided by the progressive concentration of hydrous liquid.…”

“…The pervasive amphibole occurrence in the different lithologies from Calaton Hill reflects the derivation of the protoliths from the place where hydrous magmas or aqueous fluids where available. Arc mafic magmas are commonly hydrous and undergo partial fractional crystallization and accumulation at different crustal levels (DeBari and Coleman, 1989;Meurer and Claeson, 2002;Greene et al, 2006;Helmy et al, 2008).…”

Silicate‐oxide mineral chemistry of mafic–ultramafic rocks as an indicator of the roots of an island arc: The Chilas Complex, Kohistan (Pakistan)

“…g) may have resulted from subsolidus re‐equilibration during cooling from magmatic temperatures, but there are other possibilities, such as medium‐/low‐pressure metamorphism, the likely action of late magmatic hydrous fluids (Helmy et al . ), or static recrystallization during increasing load pressure in a thickening arc crust (Ishiwatari ). Jan and Karim () and Yoshino et al .…”