Olivine ‘leucitites’, their xenolith and megacryst suites, Hoskings Peaks, north Queensland

B.J, Barron; A.D.C, Robertson; Sutherland, F L

doi:10.1080/08120099608728251

Cited by 9 publications

(5 citation statements)

References 31 publications

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“…Assuming that the anorthoclasite suite materials come from near-Moho depths and that the ascent rate of the basanitic magmas was metres per second, they would still have been entrained in their host magmas at temperatures of >1100ºC for several hours to several days, limiting their chances of survival as polycrystalline and polyphase xenoliths. Barron et al (1996) concluded that coarse xenocrysts of zircon, green sodic clinopyroxene, anorthoclase and corundum from Queensland were probably disaggregated relics of strongly differentiated vein assemblages from the mantle. Similar deductions were made with respect to the Scottish anorthoclasite suite (Aspen et al, 1990).…”

Section: Discussionmentioning

confidence: 98%

“…Salic dykes and veins in the deep lithosphere Barron et al (1996) concluded that coarse xenocrysts of zircon, green sodic clinopyroxene, anorthoclase and corundum from Queensland were probably disaggregated relics of strongly differentiated vein assemblages from the mantle. Similar deductions were made with respect to the Scottish anorthoclasite suite (Aspen et al, 1990).…”

Section: Discussionmentioning

confidence: 99%

“…However, the majority of the feldspar megacrysts are not considered to be phenocrystal but to be corroded xenocrysts resulting from disaggregation of coarse-grained rocks, such as are represented by the ultrasalic xenoliths (cf. Irving, 1974;Upton et al, 1983;Barron et al, 1996). The observation that the binary to ternary feldspars show no visible exsolution lamellae implies that they grew and were entrained and transported while still above their solvus temperatures.…”

Section: Descriptionmentioning

confidence: 99%

“…Guo et al (1996a,b) proposed that at least two components were required, (1) granite/syenite pegmatite and (2) carbonatite. Crystallization in evolved mantle veins, originating from dynamic zone-refining, was suggested by Barron et al (1996) whereas Aspen et al (1990) considered the possibility that the peraluminous character may have resulted from loss of alkalis in a fugitive carbonatite phase from carbonate-rich salic magma. Whereas the actual involvement of carbonatite magmas in these parageneses is unproven, there is widespread evidence that carbonate was a significant component at least within the peraluminous magmas from which corundum crystallized.…”

Section: Corundum-bearing Magmatic Assemblagesmentioning

confidence: 99%

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Megacrysts and salic xenoliths in Scottish alkali basalts: derivatives of deep crustal intrusions and small-melt fractions from the upper mantle

Upton¹,

Finch²,

Słaby³

2009

Mineral. mag.

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ABSTR ACTCa-poor and typically Na-rich feldspar megacrysts are common associates of spinel lherzolitic and pyroxenitic xenoliths in Scottish alkalic basalts. Associated megacrysts and composite megacrysts and salic xenoliths include apatite, magnetite, zircon, biotite, Fe-rich pyroxene(s) and corundum. The salic xenoliths and related megacrysts are referred to collectively as the 'anorthoclasite suite': the majority of the samples are inferred to derive from the disaggregation of coarse-grained, typically Na-rich, syenitic protoliths at depth. Rare occurrences of euhedral anorthoclase megacrysts, together with zircon dating, imply that the suite crystallized at, or very shortly before, their entrainment by the basaltic host magmas. Some evidence suggests that the anorthoclasite suite protoliths lie within ultramafic (pyroxenitic) domains in the deep crust. The latter are inferred to be pegmatites, crystallized from carbonated trachytic magmas with widely variable Ca, Na, K, Ba and trace-element contents, and to have ranged from metaluminous to peraluminous. Crystal zonation and resorption textures within the salic xenoliths imply that the crystallization of the parent magmas was complex. Confirmation of this comes from cathodoluminescence studies of the feldspars showing that early ('primary') anorthoclases and potassian albites exhibit partial replacement by a more potassic feldspar. A third generation of potassic feldspar (enriched in an assortment of trace elements and deduced to have crystallized from a carbonated high-K melt) forms transecting zoned veins in which carbonate fills the axial zone.Whereas most of the anorthoclasite suite materials are inferred to have grown from metaluminous magmas, the occurrence of magmatic corundum in salic xenoliths indicates crystallization from magmas that were peraluminous. The corundum-bearing samples also contain Nb-rich oxide minerals and their associated feldspars have the highest rare-earth element (REE) contents. Accordingly, the peraluminous trachyte magmas are deduced to have been specifically enriched in high field-strength trace elements. It is proposed that formation of the anorthoclasite suite protoliths is a phenomenon closely related to that of salic glass 'pockets', well known from spinel lherzolite xenoliths around the world. Not only are there compositional affinities, but both sets of phenomena appear to have closely pre-empted the ascent of alkali basalt (host) magmas. We propose that the two sets of phenomena are linked and that the anorthoclasite suite derived from coarse-grained sheets, generated by the aggregation of salic melt fractions rising from the shallow mantle and heralding the onset of basaltic magmatism.

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Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Descriptionmentioning

confidence: 99%

Section: Corundum-bearing Magmatic Assemblagesmentioning

confidence: 99%

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Megacrysts and salic xenoliths in Scottish alkali basalts: derivatives of deep crustal intrusions and small-melt fractions from the upper mantle

Upton¹,

Finch²,

Słaby³

2009

Mineral. mag.

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show abstract

“…Partition coefficients for the calculation of clinopyroxene parental magma from Hart and Dunn (1993). and trace elements (Aspen et al, 1990;Liu et al, 1992;Hegner et al, 1995;Barron et al, 1996;Lee et al, 1996;Witt-Eickschen and Kramm, 1998;Rankenburg et al, 2005). Calculated parental melts for the BMG group, slightly differ from Vitim picrite-basalts, in having lower Pb content and (La/Yb) n ratios (Fig.…”

Section: Relation With Erupted Basaltic Magmasmentioning

confidence: 98%