Mesozoic diabase (dolerite) dikes and sills occur throughout the circum-Atlantic margin. This study investigates those dikes occurring in North Carolina (USA). Approximately half of the study area is typified by north-trending quartz-normative tholeiitic dikes. The remaining areas, or "domains" are dominated by northwest-trending olivine diabase. The olivine diabase is resolved into four distinct varieties based on petrography, trace elements and abundances of silica, iron, alumina, and calcium. / High FeO olivine (HFO) diabase has greater than 10.59 percent FeO* and consists of at least three subgroups that arose from a common HFO parental melt. One subgroup (FeHFO diabase) has FeO* abundances of more than 12 percent, is a likely parent for alkaline olivine diabase, and resulted from extraction of orthopyroxene, clinopyroxene, (and plagioclase?). / Most HFO analyses do not exceed 12 percent FeO* and may be resolved into two distinct petrogenetic groups--one is dominantly primary, the other is dominantly sub-primary. Though ternary extraction (olivine, clinopyroxene, spinel) cannot be ruled out, primary HFO, most likely represents olivine extraction and orthopyroxene assimilation (i.e. incongruent melting). Sub-primary HFO diabase represents clinopyroxene, olivine and spinel extraction. Crustal fractionation of sub-primary HFO yielded the (north-trending) high FeO* quartz diabase (HFQ). The fourth olivine diabase group is uniformly low in FeO* (less than 10.15 weight percent) and exhibits continuous variation from primary tholeiitic to sub-primary calc-alkaline (high-alumina) compositions. This low FeO olivine (LFO) diabase resulted from slightly smaller amounts of mantle melting than HFO magma (17.5 vs. 20 percent, respectively). / The apparent discrepancy between mantle settings of fractionation and the absence of high pressure phases (e.g. orthopyroxene) in the phenocryst assemblage is due to the premise of isobaric fractionation. The mechanism of fractionation proposed for all olivine diabase (except the FeHFO group) is incremental polybaric fractionation (IPF). This variation of polybaric fractionation incorporates the compressibility of basaltic magmas and relates the original idea (developed on a premise of ascending diapirs within ductilely deformable aesthenosphere) to transport and fractionation of magmas through lithospheric regimes of brittle deformation. / Source: Dissertation Abstracts International, Volume: 49-06, Section: B, page: 2095. / Major Professor: Paul C. Ragland. / Thesis (Ph.D.)--The Florida State University, 1988.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_76326 |
| Contributors | Whittington, David., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 258 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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