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Positive correlation between shock stage and petrologic type in ordinary chondrites: Implications for the internal structures and thermal histories of ordinary‐chondrite parent asteroids

Year: 2024
Type: article
Abstract: H, L, and LL chondrites all exhibit positive correlations between mean shock stage and petrologic type. At a given shock energy, hot samples exhibit more intense shock features than cold samples. After the ordinary‐chondrite (OC) parent asteroids were collisionally disrupted, jumbled, and gravitationally reassembled, the correlations between mean shock stage and petrologic type may have resulted from stochastic collisions into material of different temperatures that were randomly distributed in the near‐surface regions of the rubble‐pile asteroids. Late‐stage processes including shock events and post‐shock annealing affected the preexisting correlations to only minor degrees. This model, combined with literature data, permits the following scenario: Each principal OC asteroid initially had an onion‐shell structure with deeply buried type 6 materials cooling slowly, yielding young closure ages in Pb‐phosphate data. The OC bodies were disrupted at ~60 Ma, locking in the Pb‐phosphate record of the onion‐shell structure. The H‐chondrite parent body was collisionally disrupted somewhat later than the L or LL bodies and was thus somewhat cooler at the time of disruption. In the OC asteroidal rubble piles, materials of different petrologic types cooled at similar rates through ~500°C, precluding a correlation between petrologic type and metallographic cooling rate. Shortly after rubble‐pile formation, materials of higher petrologic types remained hotter than materials of lower petrologic types. The hotter materials recorded more intense shock features from the common meteoroid flux, leading to positive correlations in each OC asteroid between petrologic type and mean shock stage. The cooler H‐chondrite materials manifested a lower range in mean shock stage.
DOI: 10.1111/maps.14284
Language: English
Open Access status: hybrid
Estimated APC paid: $3,240
Award: WE PROPOSE TO CONDUCT A SERIES OF INVESTIGATIONS OF THE MINERALOGIC COMPONENTS OF CHONDRITIC METEORITES THAT ARE THOUGHT TO HAVE FORMED ON PLANETESIMALS WITH THE GOAL OF DEVELOPING IMPROVED CHRONOLOGICAL CONSTRAINTS ON THEIR FORMATION AND ON THE OVERALL AQUEOUS EVOLUTION ON ASTEROIDS. OUR ANALYSES ARE DIRECTED TOWARD DEVELOPING A BETTER UNDERSTAND OF THE SEQUENCE AND TIMING OF MAJOR EVENTSIN PLANETARY ACCRETION AND DIFFERENTIATION WHICH IS DIRECTLY RELEVANT TO THE GOALS OF THE EMERGING WORLDS SOLICITATION TO UNDERSTAND THE FORMATION AND EARLY EVOLUTION OF THE SOLAR SYSTEM AND THE STRATEGIC QUESTION OF LEARNING HOW DID THE SUNS FAMILY OF PLANETS SATELLITES AND MINOR BODIES FORM AND EVOLVE?WE WILL UTILIZE CHRONOLOGICAL TOOLS THAT WE AND OTHERS HAVE PREVIOUSLY DEVELOPED IN A COORDINATED APPROACH UTILIZING PETROGRAPHY CHEMISTRY AND IN SITU ISOTOPIC ANALYSES. TIMESCALES OF EARLY GEOLOGIC ACTIVITY ON ASTEROIDAL PARENT BODIES OF METEORITES WILL BE ADDRESSED BY COUPLED ANALYSES OF THE MN-CR O-ISOTOPE AND C-ISOTOPE SYSTEMS IN CARBONATES AND OTHER SECONDARY MINERALS OF CARBONACEOUS CHONDRITES. PREVIOUS DATA SHOW THAT DIFFERENT CARBONATE MINERALOGIES IN CI CHONDRITES HAVE DISTINCT OXYGEN AND CARBON ISOTOPIC COMPOSITIONS SUGGESTING AN EVOLUTION OF FLUID COMPOSITIONS ON THE CI PARENT BODY. WE HAVE DEVELOPED A METHOD TO IMPROVE THE ACCURACY OF MN-CR DATING OF CARBONATES AND WE PROPOSE TO USE THE NEWEST GENERATION ION MICROPROBE AT UCLA TO DELINEATE THE FULL RANGE AND TIMING OF FLUID EVOLUTION ON THE PARENT ASTEROIDS OF CI AND OTHER SELECT CARBONACEOUS CHONDRITES. WE ALSO PROPOSE TO FOLLOW UP INTRIGUING HINTS OF 60FE ACTIVITY IN EARLY-FORMED CARBONATES VIA SIMS ANALYSES AND RESONANT IONIZATION MASS SPECTROMETRY (RIMS) ANALYSES WITH OUR COLLABORATOR ANDY DAVIS AT THE UNIVERSITY OF CHICAGO. AL-MG AND FE-NI SYSTEMATICS WILL BE MEASURED IN SELECT CHONDRULES FROM UNEQUILIBRATED CHONDRITES BY BOTH SIMS AND RIMS TO BETTER UNDERSTAND THE ABUNDANCE AND DISTRIBUTION OF 60FE IN THE EARLY SOLAR SYSTEM.A PLANETARY MAJOR EQUIPMENT REQUEST IS MADE FOR PURCHASE OF A MULTI-SAMPLE INTRODUCTION SYSTEM FOR OUR NEW CAMECA IMS 1290 ION MICROPROBE. THE IMS 1290 IS THE PRIMARY INSTRUMENT FOR THE RESEARCH PROPOSED HERE AND IT SERVES OTHER FUNDED AND PROPOSED NASA PROJECTS AS WELL PROJECTS BROUGHT TO THE NSF NATIONAL ION MICROPROBE FACILITY. THE INSTRUMENT WAS PURCHASED WITH SUBSTANTIAL ($4M) SUPPORT FROM THE NSF MAJOR RESEARCH INSTRUMENTATION PROGRAM NEVERTHELESS WE COULD ONLY AFFORD TO OUTFIT WITH THE MOST BASIC SINGLE-SAMPLE INTRODUCTION SYSTEM. THE NEW SYSTEM WILL ALLOW THE STORAGE OF UP TO SIX SAMPLES IN THE VACUUM ANTECHAMBER ADJACENTTO THE ANALYSIS CHAMBER. THIS WILL ENABLE IMPROVEMENTS IN BACKGROUND LEVELS OF VOLATILE ELEMENTS AND WILL THEREFORE LEAD TO HIGHER RELIABILITY AND HIGHER EFFICIENCY OF ANALYSES INCLUDING THE OXYGEN AND CARBON ISOTOPE MEASUREMENTS PROPOSED HERE.
OpenAlex ID: W4404146667
FWCI: 1.335
Cites: 85
Cited by: 7
Related to: 10