Low-Pressure Phase Relationships in the System Na2O--CaO--FeO--MgO--Al2O3--SiO2 at 1100 C, with Implications for the Differentiation of Basaltic Magmas

Shi, Ping Ping

doi:10.1093/petrology/34.4.743

Cited by 33 publications

(17 citation statements)

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“…Experiments by Toplis et al (1994), carried out under constant pressure (1-atm) and temperature (1072°C), show that the stability field of pigeonite is enhanced by increasing the liquid P 2 O 5 content. Furthermore, for relatively constant liquid P 2 O 5 contents (0-1.5 wt.%), pigeonite saturation will occur in the most SiO 2 -and alkali-rich and MgO-poor melts, in good agreement with the experimental results of Grove and Juster (1989) and Shi (1993).…”

Section: Stability Of Pigeonitesupporting

confidence: 82%

Dual origin of Fe–Ti–P gabbros by immiscibility and fractional crystallization of evolved tholeiitic basalts in the Sept Iles layered intrusion

Namur

Charlier

Holness

2012

Lithos

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We present a detailed study of two ca. 200 m-thick apatite-bearing ferrogabbro horizons of the Sept Iles layered intrusion (Canada). These rocks are the most evolved cumulates of the megacyclic units (MCU) I and II, and mark the transition between basaltic and silicic magmatism. They are made up of plagioclase (An 55-34 ), olivine (Fo 66-21 ), clinopyroxene (Mg#75-55), ilmenite, magnetite, apatite, ± pigeonite and are a significant source of Fe-Ti-P ore. Ferrogabbros have relatively uniform bulk-rock compositions in MCU I but are bimodal in MCU II. The liquid lines of descent for major elements in equilibrium with cumulates of MCU I and II have been calculated using a forward model formalism. Both trends evolve towards SiO 2 -enrichment and FeO t -depletion after saturation in Fe-Ti oxides. However, because of magma mixing in MCU II, they do not follow the same path. Evolved liquids from MCU II are shown to enter the experimentally-determined two liquid stability field, while MCU I liquids do not. Immiscibility in MCU II and its absence in MCU I are supported by the presence of contrasted reactive symplectites in cumulate rocks. Apatite-bearing ferrogabbros in MCU II have crystallized from distinct immiscible Fe-rich and Si-rich silicate melts which have physically segregated in the slow-cooling magma chamber. Two different types of cumulate rocks are thus produced: leucocratic and melanocratic gabbros. This is consistent with the presence of Si-rich and Fe-rich melt inclusions in apatite. In contrast, homogeneous ferrogabbros from MCU I were produced by simple fractional crystallization of a homogeneous liquid. Our data suggest that immiscibility could also explain the large geochemical variability of ferrogabbros in the Upper Zone of the Bushveld Complex (South Africa).

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Section: Stability Of Pigeonitesupporting

confidence: 82%

Dual origin of Fe–Ti–P gabbros by immiscibility and fractional crystallization of evolved tholeiitic basalts in the Sept Iles layered intrusion

Namur

Charlier

Holness

2012

Lithos

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“…The FPIR consists of very fine-grained low-Ca pyroxene overgrown by augite, silica-rich mesostasis, and Fe, Ni-metal nodules. of Kohn and Schofield (1994) Blundy et al (1995) from experiments in the CaO-MgO-Al 2 O 3 -SiO 2 -Na 2 O system, and 0.046 ± 0.011 obtained by Shi (1993) in the CaOMgO-Al 2 O 3 -SiO 2 -FeO-Na 2 O system. Based on these observations, we infer that the determined values for element partitioning between augite and melt of the SIR are largely controlled by the melt compositions, and that the augites crystallized from a highly polymerized melt enriched in moderately volatile elements such as Cr, Mn, and Na.…”

Section: Element Partitioning Between Augite and Glassy Mesostasis Inmentioning

confidence: 89%

Silica‐rich igneous rims around magnesian chondrules in CR carbonaceous chondrites: Evidence for condensation origin from fractionated nebular gas

Krot

Libourel

Goodrich

et al. 2004

Meteorit & Planetary Scien

128

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Silica-rich igneous rims around magnesian chondrules in CR carbonaceous chondrites: Evidence for condensation origin from fractionated nebular gasAlexander N. KROT Abstract-The outer portions of many type I chondrules (Fa and Fs <5 mol%) in CR chondrites (except Renazzo and Al Rais) consist of silica-rich igneous rims (SIRs). The host chondrules are often layered and have a porphyritic core surrounded by a coarse-grained igneous rim rich in low-Ca pyroxene. The SIRs are sulfide-free and consist of igneously-zoned low-Ca and high-Ca pyroxenes, glassy mesostasis, Fe, Ni-metal nodules, and a nearly pure SiO 2 phase. The high-Ca pyroxenes in these rims are enriched in Cr (up to 3.5 wt% Cr 2 O 3 ) and Mn (up to 4.4 wt% MnO) and depleted in Al and Ti relative to those in the host chondrules, and contain detectable Na (up to 0.2 wt% Na 2 O). Mesostases show systematic compositional variations: Si, Na, K, and Mn contents increase, whereas Ca, Mg, Al, and Cr contents decrease from chondrule core, through pyroxene-rich igneous rim (PIR), and to SIR; FeO content remains nearly constant. Glass melt inclusions in olivine phenocrysts in the chondrule cores have high Ca and Al, and low Si, with Na, K, and Mn contents that are below electron microprobe detection limits. Fe, Ni-metal grains in SIRs are depleted in Ni and Co relative to those in the host chondrules. The presence of sulfide-free, SIRs around sulfide-free type I chondrules in CR chondrites may indicate that these chondrules formed at high (>800 K) ambient nebular temperatures and escaped remelting at lower ambient temperatures. We suggest that these rims formed either by gas-solid condensation of silica-normative materials onto chondrule surfaces and subsequent incomplete melting, or by direct SiO (gas) condensation into chondrule melts. In either case, the condensation occurred from a fractionated, nebular gas enriched in Si, Na, K, Mn, and Cr relative to Mg. The fractionation of these lithophile elements could be due to isolation (in the chondrules) of the higher temperature condensates from reaction with the nebular gas or to evaporation-recondensation of these elements during chondrule formation. These mechanisms and the observed increase in pyroxene/olivine ratio toward the peripheries of most type I chondrules in CR, CV, and ordinary chondrites may explain the origin of olivine-rich and pyroxene-rich chondrules in general.

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“…The compositions of such multiply saturated liquids vary broadly, as demonstrated in Fig. 19 by a series of liquids along the 11008C isotherm equilibrated with olivine, low-and high-Ca pyroxenes, and plagioclase (Shi, 1993). Skaergaard experimental liquids (three points labelled 'SK' in Fig.…”

Section: R E Ac T I O N Ow I N G To R E L At I V E M Ov E M E N T O Fmentioning

confidence: 95%

“…Other curves, lines and points, with the exception of the cotectic, lie on the quartz-normative side off the projection plane [see Veksler (2009) for a detailed description of the projection method]. Open diamond, CMAS invariant liquid (Longhi, 1987); filled diamond, Fe-rich, silica-saturated liquid (Nielsen et al, 1988); open circles, liquids along the 11008C isotherm (Shi, 1993); filled circles, Skaergaard liquid compositions (Thy et al, 2006). The position of the fo þ di þ en þ plag þ liquid univariant curve (labelled as fo þ di þ en þ plag) of the CMASN system is according to Soulard et al (1992).…”

Section: R E Ac T I O N Ow I N G To R E L At I V E M Ov E M E N T O Fmentioning

confidence: 99%

Silicate Liquid Immiscibility within the Crystal Mush: Late-stage Magmatic Microstructures in the Skaergaard Intrusion, East Greenland

Holness

Stripp

Humphreys

et al. 2010

Journal of Petrology

136

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Low-Pressure Phase Relationships in the System Na2O--CaO--FeO--MgO--Al2O3--SiO2 at 1100 C, with Implications for the Differentiation of Basaltic Magmas

Cited by 33 publications

References 0 publications

Dual origin of Fe–Ti–P gabbros by immiscibility and fractional crystallization of evolved tholeiitic basalts in the Sept Iles layered intrusion

Dual origin of Fe–Ti–P gabbros by immiscibility and fractional crystallization of evolved tholeiitic basalts in the Sept Iles layered intrusion

Silica‐rich igneous rims around magnesian chondrules in CR carbonaceous chondrites: Evidence for condensation origin from fractionated nebular gas

Silicate Liquid Immiscibility within the Crystal Mush: Late-stage Magmatic Microstructures in the Skaergaard Intrusion, East Greenland

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