In:
Mineralogical Magazine, Mineralogical Society, Vol. 79, No. 3 ( 2015-06), p. 545-581
Abstract:
Gem minerals at Lava Plains, northeast Queensland, offer further insights into mantle-crustal gemformation under young basalt fields. Combined mineralogy, U-Pb age determination, oxygen isotope and petrological data on megacrysts and meta-aluminosilicate xenoliths establish a geochemical evolution in sapphire, zircon formation between 5 to 2 Ma. Sapphire megacrysts with magmatic signatures (Fe/Mg ∼100–1000, Ga/Mg 3–18) grew with ∼3 Ma micro-zircons of both mantle (δ 18 O 4.5–5.6%) and crustal (δ 18 O 9.5–10.1‰) affinities. Zircon megacrysts (3±1 Ma) show mantle and crustal characteristics, but most grew at crustal temperatures (600–800°C). Xenolith studies suggest hydrous silicate melts and fluids initiated from amphibolized mantle infiltrated into kyanite+sapphire granulitic crust (800°C, 0.7 GPa). This metasomatized the sapphire (Fe/Mg ∼50–120, Ga/Mg ∼3–11), left relict metastable sillimanite-corundum-quartz and produced minerals enriched in high field strength, large ion lithophile and rare earth elements. The gem suite suggests a syenitic parentage before its basaltic transport. Geographical trace-element typing of the sapphire megacrysts against other eastern Australian sapphires suggests a phonolitic involvement.
Type of Medium:
Online Resource
ISSN:
0026-461X
,
1471-8022
DOI:
10.1180/minmag.2015.079.3.04
Language:
English
Publisher:
Mineralogical Society
Publication Date:
2015
detail.hit.zdb_id:
2034522-7
SSG:
13
Permalink