Spinel in CV chondrules: Investigating precursor legacy and chondrule thermal histories. (1st April 2022)

• Record Type: Journal Article
• Authors: Schnuriger, Nicolas; Cartier, Camille; Villeneuve, Johan; Batanova, Valentina; Regnault, Maxence; Marrocchi, Yves
• Is Part Of: Meteoritics & planetary science. Volume 57:Number 5(2022)
• Page Start: 1018
• Page End: 1037
• Publication Date: 2022-04-01
• Subjects: Meteorites -- Periodicals; Planetology -- Periodicals; 523.4
• DOI: 10.1111/maps.13802
• Languages: English
• ISSNs: 1086-9379

Abstract

Abstract: In carbonaceous chondrites, Mg‐spinel (MgAl2 O4 ) grains are ubiquitous in refractory inclusions but rarely reported in chondrules, where they may correspond to minerals either (i) inherited from chondrule precursors or (ii) crystallized from chondrule melts. Here, we report high‐current quantitative electron microprobe measurements and secondary ion mass spectrometry oxygen isotopic analyses of Mg‐spinel‐bearing chondrules in the CV3 carbonaceous chondrites Northwest Africa 10235 and Allende. Compared to spinels in refractory inclusions, chondrule spinels are characterized by higher Cr contents and 16 O‐poorer oxygen isotopic signatures (∆ 17 O ≡ δ 17 O−0.52 × δ 18 O, from −2 to −6‰). Because the similar Δ 17 O values of chondrule olivine and spinel crystals imply their comagmatic origin, we applied a geothermometer based on the Al‐Cr distribution between these minerals to determine their crystallization temperatures. The calculated temperatures range from 1200 to 1640 °C (mean = 1470 °C), most being lower than the estimated liquidus temperature of porphyritic chondrules (~1600 °C). Our results suggest that chondrules experienced relatively slow cooling rates (slower than a few hundreds of °C h −1 ), which is in good agreement with models of chondrule formation invoking nonlinear or two‐stage cooling rates.