3:00 PM - 3:15 PM
[PPS08-06] Crystallization temperature of chondrule minerals inferred from Al-in-olivine thermometry
Keywords:Al-in-olivine thermometry, protosolar disk, chondrule
Chondrules in primitive meteorites are key objects to reveal the early evolution of the solar protoplanetary disk environments. Although formation mechanisms of chondrules are currently debated, nebular shock-wave heating seems currently one of the most favored candidates [1]. In this model, a chondrule precursor is experiencing supersonic drag by a post-shock gas that is instantly compressed by a shock wave, then frictional forces are heating the precursor. This model predicts that a peak temperature of the heating chondrule precursor depends on gas density of the chondrule-forming region and relative velocity between post-shock gas and dust [e.g., 2]. Therefore, these chondrule formation conditions could be constrained by determining the heating temperature of the chondrule precursor.
In this study we constrain lower limit of the heating temperature of chondrule precursor using Al-in-olivine thermometry, a geo-thermometer used for determining the co-precipitation temperature of olivine and spinel [3, 4]. To discuss temporal and spatial dependence of the heating temperature of the chondrule precursor, we selected 12 chondrules that have been studied for Al-Mg formation age (~1.8 to 3.0 million years after CAI formation) and oxygen isotope ratios (−2.8‰ < Δ17O < 0.4‰, where Δ17O = δ17O − 0.52 × δ18O) [5-9]. They are from pristine meteorites MET 00452 (L/LL3.05, N=2), NWA 8276 (L3.00, N =2), Acfer 094 (Ungrouped C3.00, N = 5), DOM 08006 (CO3.01, N = 3). Elemental compositions of spinel were measured with the JEOL JXA-8200 EPMA at the National Institute of Polar Research and those of olivine were measured with the CAMECA SX-Five FE-EPMA at the University of Wisconsin-Madison. Analysis of Al in olivine was performed at high beam current (200nA) and involved aggregating Al counts from three spectrometer to improve detection limits (0.0011 wt% Al2O3). Reported uncertainties for the calculated temperatures are either 2SE of the calculated temperatures for each olivine-spinel pair in a given chondrule or ±25 ℃ that is an uncertainty of empirical calibration for Al-in-olivine thermometry [3, 4], whichever is larger.
The Fo contents (= [Mg]/[Mg+Fe] in molar %) of chondrule olivine grains range from 48 to 83 and thus all chondrules studied are classified as type II chondrules. Al2O3 contents of olivine grains and Cr# (= [Cr]/[Cr+Al] in molar ratio) of spinel grains range from 0.018 to 0.155 wt% and 0.4 to 0.7, respectively. The calculated co-precipitation temperatures of olivine and spinel range from 1273 ± 25 to 1424 ± 25 ℃ for ordinary chondrite chondrules and from 1218 ± 129 to 1349 ± 87 ℃ for carbonaceous chondrite chondrules.
Schnuriger et al. [10] investigated crystallization temperature of type I chondrules in CV3 chondrites using the Al-in-olivine thermometry. Although the calculated temperatures ranging from 1200 to 1640 ℃ [10] are more variable than those determined from the present study, the lower limit of the temperature (1200 ℃,[10]) is broadly consistent with our estimate for ordinary chondrite chondrules (1273 ± 25 ℃). Thus, the present results as well as [11] indicate that heating mechanisms that could heat the chondrule precursor with temperatures above 1200 ℃ are required for chondrule formation in the inner and outer Solar System during the period of 1.8-3.0 million years after CAI formation. We will discuss the temporal and spatial gas density distribution that is required for heating the chondrule precursors above 1200 ℃ during the conference.
References: [1] Desch et al (2012) MAPS 47, 1139-1156. [2] Iida et al (2002) Icarus 153, 430-450. [3] Wan et al (2008) Am. Min. 93, 1142-1147. [4] Coogan et al (2014) Chem. Geol. 368, 1-10. [5] Ushikubo et al (2013) GCA 109, 280-295. [6] Hertwig et al (2019) GCA 253, 111-126. [7] Siron et al (2021) GCA 293, 103-126. [8] Siron et al (2022) GCA 324, 312-345. [9] Zhang et al (2022) Chem. Geol. 608, 121016. [10] Schnuriger et al (2022) MAPS 57, 1018-1037.
In this study we constrain lower limit of the heating temperature of chondrule precursor using Al-in-olivine thermometry, a geo-thermometer used for determining the co-precipitation temperature of olivine and spinel [3, 4]. To discuss temporal and spatial dependence of the heating temperature of the chondrule precursor, we selected 12 chondrules that have been studied for Al-Mg formation age (~1.8 to 3.0 million years after CAI formation) and oxygen isotope ratios (−2.8‰ < Δ17O < 0.4‰, where Δ17O = δ17O − 0.52 × δ18O) [5-9]. They are from pristine meteorites MET 00452 (L/LL3.05, N=2), NWA 8276 (L3.00, N =2), Acfer 094 (Ungrouped C3.00, N = 5), DOM 08006 (CO3.01, N = 3). Elemental compositions of spinel were measured with the JEOL JXA-8200 EPMA at the National Institute of Polar Research and those of olivine were measured with the CAMECA SX-Five FE-EPMA at the University of Wisconsin-Madison. Analysis of Al in olivine was performed at high beam current (200nA) and involved aggregating Al counts from three spectrometer to improve detection limits (0.0011 wt% Al2O3). Reported uncertainties for the calculated temperatures are either 2SE of the calculated temperatures for each olivine-spinel pair in a given chondrule or ±25 ℃ that is an uncertainty of empirical calibration for Al-in-olivine thermometry [3, 4], whichever is larger.
The Fo contents (= [Mg]/[Mg+Fe] in molar %) of chondrule olivine grains range from 48 to 83 and thus all chondrules studied are classified as type II chondrules. Al2O3 contents of olivine grains and Cr# (= [Cr]/[Cr+Al] in molar ratio) of spinel grains range from 0.018 to 0.155 wt% and 0.4 to 0.7, respectively. The calculated co-precipitation temperatures of olivine and spinel range from 1273 ± 25 to 1424 ± 25 ℃ for ordinary chondrite chondrules and from 1218 ± 129 to 1349 ± 87 ℃ for carbonaceous chondrite chondrules.
Schnuriger et al. [10] investigated crystallization temperature of type I chondrules in CV3 chondrites using the Al-in-olivine thermometry. Although the calculated temperatures ranging from 1200 to 1640 ℃ [10] are more variable than those determined from the present study, the lower limit of the temperature (1200 ℃,[10]) is broadly consistent with our estimate for ordinary chondrite chondrules (1273 ± 25 ℃). Thus, the present results as well as [11] indicate that heating mechanisms that could heat the chondrule precursor with temperatures above 1200 ℃ are required for chondrule formation in the inner and outer Solar System during the period of 1.8-3.0 million years after CAI formation. We will discuss the temporal and spatial gas density distribution that is required for heating the chondrule precursors above 1200 ℃ during the conference.
References: [1] Desch et al (2012) MAPS 47, 1139-1156. [2] Iida et al (2002) Icarus 153, 430-450. [3] Wan et al (2008) Am. Min. 93, 1142-1147. [4] Coogan et al (2014) Chem. Geol. 368, 1-10. [5] Ushikubo et al (2013) GCA 109, 280-295. [6] Hertwig et al (2019) GCA 253, 111-126. [7] Siron et al (2021) GCA 293, 103-126. [8] Siron et al (2022) GCA 324, 312-345. [9] Zhang et al (2022) Chem. Geol. 608, 121016. [10] Schnuriger et al (2022) MAPS 57, 1018-1037.