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Modeling enstatite chondrites: Reduced rocks with a pinch of oxidized material (affected by varying H 2 O (g)) derived from planetesimals shocked during the epoch of giant–planet migration

Year: 2025
Type: article
Abstract: The O‐, N‐, Mo‐, Ru‐, Os‐, Cr‐, Ti‐, Ni‐, Fe‐, Nd‐, Ca‐, Zn‐, Sr‐, and Mg‐isotopic compositions of enstatite chondrites are essentially identical to those of the Earth and Moon. These correspondences suggest enstatite chondrites formed at ≈1 AU as the only known chondrite groups that accreted in the vicinity of a major planet. Bulk Earth has a higher Mg/Si weight ratio (1.09) than enstatite chondrites (0.63–0.76) and aubrites (0.84). Earth could have accreted from a mixture of these materials along with forsterite (Mg/Si = 1.73) and niningerite [(Mg,Fe)S] from the lower mantles of aubritic parent asteroids whose crusts and upper mantles were stripped off by hit‐and‐run collisions. The highly reducing conditions in which enstatite chondrites formed resulted from the dehydration of the inner regions of the nebula caused by outward diffusion of water vapor; this lowered the H 2 O/H 2 ratio of the gas. The minor fraction of oxidized material in enstatite chondrites formed earlier—when the H 2 O/H 2 ratio was briefly enhanced by inward‐migrating ice particles. Enstatite chondrites are the most shocked chondrite groups, exhibiting a large variety of shock features—for example, deformed silicate lattices; petrofabrics; brecciation; shock veins; metal globules; coesite; impact‐melt textures; impact‐produced phases (keilite, sinoite, graphite and F‐rich minerals); and fractionated bulk REE patterns. The Ar‐Ar, Rb‐Sr and I‐Xe ages of enstatite chondrites indicate many of these rocks were shocked early in Solar System history, 4520–4563 Ma ago. This interval stretches back to the period of giant‐planet migration, when the 1 AU region became dynamically excited.
DOI: 10.1111/maps.70080
Language: English
Open Access status: hybrid
Estimated APC paid: $3,300
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: W4416981996
FWCI: 0.91
Cites: 162
Cited by: 2
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