Abundance, major element composition and size of components and matrix in CV, CO and Acfer 094 chondrites

Chondrules: Ubiquitous Chondritic Solids Tracking the Evolution of the Solar Protoplanetary Disk

“…However, given the low abundance of W in chondritic components such as chondrules, it is not possible to date individual objects thereby necessitating the pooling of a significant amount of chondrules to obtain sufficient mounts of W. Using this approach, Budde et al (2016) recently attempted to provide a chronology of the Allende CV chondrite chondrule formation based on the 182 Hf-182 W system. In particular, these authors inferred that the 3 Myr duration of chondrule formation documented by Connelly et al (2012) is inconsistent with presumed chemical and isotopic complementary between chondrules and matrix that supports models of local and brief chondrule formation (Hezel and Palme 2010;Palme et al 2015;Ebel et al 2016). They hypothesised that the Pb-Pb ages reflect late stage parent body alteration without providing any specific mechanism to explain isochrons as old as CAIs.…”

“…Several heat sources have been proposed for the thermal processing of chondrule precursors, including shock waves (Boss and Graham 1993;Connolly and Love 1998;Hood 1998;Connolly et al 2006), current sheets (Joung et al 2004), x-winds (Shu et al 1997), magnetised disk wind (Salmeron and Ireland 2012), and colliding planetesimals (Asphaug et al 2011;Sanders and Scott 2012). A longstanding paradigm used to constrain chondrule-formation models is the so-called chemical complementarity that apparently exists between chondrules and matrix in individual chondrite groups (Hezel and Palme 2010;Palme et al 2015;Ebel et al 2016). In this model, it is proposed that chondrules and matrix are genetically related and formed in highly localised regions of the protoplanetary disk.…”

“…A number of studies have investigated the apparent chemical relationship between chondrules and matrix in individual chondrite groups (Hezel and Palme 2010;Palme et al 2015;Ebel et al 2016). These studies have concluded that the average compositions of chondrules and matrix are typically different for a number of elements in an individual chondrite whereas the bulk composition, which reflects a mixtures of chondrules and matrix, has approximately a solar elemental abundance.…”

Mixing and Transport of Dust in the Early Solar Nebula as Inferred from Titanium Isotope Variations among Chondrules

“…The origin of these once-molten silicate spherules remains debated, but the currently favored hypothesis states that chondrules formed by the melting of dust aggregates in the solar nebula, induced by shock waves or current sheets (e.g., Desch et al 2005;McNally et al 2013;Morris et al 2012). Alternative models, such as those in which chondrules are the result of protoplanetary impacts (e.g., Sanders & Scott 2012), are problematic because they cannot satisfy the chemical (Bland et al 2005;Ebel et al 2016;Hezel & Palme 2008;Palme et al 2015) and isotopic (Budde et al 2016a;Budde et al 2016b) complementarity observed between chondrules and matrix. This complementarity implies that within a given chondrite, chondrules and matrix derive from a common reservoir of dust, and that after their formation neither appreciable chondrules nor matrix were lost.…”

Tungsten isotopic constraints on the age and origin of chondrules

“…However, the origin of chondrules remains poorly understood, and a wide range of possible formation mechanisms has been proposed: (i) chondrules may have formed through collisions between protoplanetary bodies (4-6); (ii) chondrules may have formed near the Sun and were then transported outward by protostellar jets (7); and (iii) chondrules may have formed through more localized melting events of nebular dust caused by shock waves (8,9) or current sheets (10). Although many recent models argue for an impact origin of chondrules (4)(5)(6), the observation that chondrules and matrix from carbonaceous chondrites are chemically complementary lends strong support to an origin of both components from a single reservoir of nebular dust (11)(12)(13). However, the significance of this chemical chondrule-matrix complementarity and whether it can distinguish between a nebular or impact origin of chondrules is debated (6).…”