Metallic nodules are common in metamorphosed ordinary chondrites. The origin of metal nodules has been debated because the mechanism of the formation of metal nodules is not known. Several proposed scenarios, e.g., the metal nodules and veins could be shock melted products of chondritic metal grains (Widom et al., 1986, Rubin 1999), and/or could be formed by shock-induced vaporization of bulk chondrite material consisting of small metal grains, silicates, and troilite (Widom et al., 1986), or formed by sub-solidus growth (Kong et al., 1998). Nebular origins proposed for nodules were not very compelling because such nodules are not found in unequilibrated ordinary chondrites. In this study, we tested these hypotheses of origin and formation of metal nodules and veins in L chondrites by collection of a comprehensive set of siderophile element analyses, which include many refractory (e.g., W, Re, Os, Ir, Pt, Ru, Rh, Mo) and volatile (Au, As, Sb, Cu, Ga, Ge, Sn) elements by laser ablation ICP-MS. The siderophile element patterns of metal grains measured as spots and tracks show large enrichments and depletions in the more compatible siderophile elements (Re, Os, Ir); a limited range of W and Mo abundances; Pd abundances that plot both above and below bulk L chondrite metal; high Au-As abundances; and systematic depletions of Cu, Sb and Sn. Therefore, the results of this study indicate that the origin of observed compositional variations of siderophile elements from metallic nodules in samples is partial melts of L chondritic composition that have undergone some fractional crystallization. Models involving sub-solidus growth or troilite volatilization/recondensation fail to meet the constraints imposed by the siderophile element patterns of the nodule metal. Sub-solidus cooling resulted in kamacite-taenite fractionation which disturbed magmatic relationships between Co and Ni and Au and As, but retained those of Re and Ir with Os. A grain retaining a diffusive profile provided constraints on temperature (T=1573±100 K) and timescale ~1 year, for the melting processes that implies a well-insulated post-shock environment for cooling of the nodules. A comparison of the bulk nodule composition with calculated bulk metallic fractions of H, L and LL chondrites indicates that the nodules are more reduced than the composition of L chondrite metallic fractions and are similar to the metallic fractions of H chondrites. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of
Science. / Summer Semester, 2012. / July 2, 2012. / Compositions and origin, L-Chondrites, Metal nodules, Ordinary chondrites / Includes bibliographical references. / Munir Humayun, Professor Directing Thesis; Vincent Salters, Committee Member; Leroy Odom, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_183519 |
| Contributors | Pekeroğlu-Temurtaş, Elif (authoraut), Humayun, Munir (professor directing thesis), Salters, Vincent (committee member), Odom, Leroy (committee member), Department of Earth, Ocean and Atmospheric Sciences (degree granting department), Florida State University (degree granting institution) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource, computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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