Correlated silicon and titanium isotopic compositions of presolar SiC grains from the Murchison CM2 chondrite Frank Gyngard ⇑ , Sachiko Amari, Ernst Zinner 1 , Kuljeet Kaur Marhas 2 Laboratory for Space Sciences and the Department of Physics, Washington University, One Brookings Drive, St. Louis, MO 63130, USA Received 10 October 2016; accepted in revised form 16 September 2017; available online 23 September 2017 Abstract We report correlated Si, and Ti isotopic compositions and elemental concentrations of 238 presolar SiC grains from the Murchison CM2 meteorite. Combined with measurements of the C and N isotopic compositions of these 238 grains, 220 were determined to be of type mainstream, 10 type AB, 4 type Y and 4 type Z. SiC grains of diameter J 2.5 mm, to ensure enough material to attempt Ti measurements, were randomly chosen without any other prejudice. The Ti isotopic compositions of the majority of the grains are characterized by enrichments in 46 Ti, 47 Ti, 49 Ti, and 50 Ti relative to 48 Ti, and show linear isotopic correlations indicative of galactic chemical evolution and neutron capture of the grains parent stars. The variability in the observed Ti signal as a function of depth in most of the grains indicates the presence of distinct subgrains, likely TiC that have been previously observed in TEM studies. Vandium-51 concentrations correlate with those of Ti, indicating V substitutes for Ti in the TiC matrix in many of the grains. No isotopic anomalies in 52 Cr/ 53 Cr ratios were observed, and Cr concentra- tions did not correlate with those of either Ti or V. Ó 2017 Elsevier Ltd. All rights reserved. Keywords: Presolar grains; Galactic chemical evolution; Nucleosynthesis; Silicon carbide; NanoSIMS; Asymptotic branch stars 1. INTRODUCTION Meteorites, or colloquially ‘‘rocks from space”, are a multi-variate agglomeration of minerals and dust sourced from a variety of astrophysical bodies. While some space rocks are certainly cometary, lunar, or Martian in origin, the vast majority originate from the asteroid belt – the deb- ris of asteroidal collisions that by happenstance made its way to Earth and survived atmospheric melting. The iso- topic composition of the most primitive components of these rocks, specifically Ca-Al-rich inclusions (e.g., Jacobsen et al., 2008), is the foundation upon which the age of the Solar System is determined. Additionally, the ele- mental compositions of carbonaceous chondritic meteorites form the basis of the primordial, undifferentiated composi- tion of the proto-solar nebula; essentially, a snapshot of the Solar System at its formation. For a full, detailed discus- sion, see McSween and Huss (2010). Within these very primitive meteorites, there is a glue (‘‘matrix”) that holds the rock together. Very simply, this is a fine-grained dust which can contain large isotopic anomalies when compared with any known compositions anywhere in the Solar System. These grains are typically C-rich (e.g., SiC, graphite, or nanodiamonds) or O-rich (e.g., alumina, spinel, hibonite, or silicates) and are termed presolar or stardust (Nittler and Ciesla, 2016). These preso- lar grains are literally time capsules from long-extinguished stars; their elemental and isotopic compositions represent the unaltered fingerprints of the nucleosynthesis of the building blocks of the Solar System and ourselves. Among these astrophysical time capsules, SiC is the best-studied of all presolar grains: thousands of individual https://doi.org/10.1016/j.gca.2017.09.031 0016-7037/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: fgyngard@gmail.com (F. Gyngard). 1 Deceased on July 30, 2015. 2 Present address: Planetary and Geoscience Division, Physical Research Laboratory, Ahmedabad, Gujarat 380009, India. www.elsevier.com/locate/gca Available online at www.sciencedirect.com ScienceDirect Geochimica et Cosmochimica Acta 221 (2018) 145–161