Mesozoic diabase dikes of Virginia, part of the Eastern North America dike swarm, display a wide variety of mineralogical and chemical characteristics, representative of most mineralogical and chemical groups described from other portions of the swarm. The large sample population is used for this study (nearly 200 samples total) has revealed that the previously described diabase groups (excepting HTQ) actually belong to part of a continuum of compositions generated predominantly by a low-pressure fractionation sequence. / Petrographically, the diabases can be classified into three groups, which also display some geochemical distinctions. The OSB group is characterized by abundant olivine as a phenocryst and/or groundmass component and the presence of a Cr-Al spinel as inclusions in olivine or as part of the groundmass assemblage. Chemically this group is the most primitive. The GRB-group samples have the most evolved chemistries and are recognized by the presence of interstitial granophyre and a phenocryst assemblage of plagioclase + clinopyroxene +/- olivine. The chemically intermediate SGA group lacks granophyre and spinel and is dominated by plagioclase and olivine phenocrysts. / Major- and compatible trace-element geochemical trends show that typical SGA-group samples can be derived by crystallization of approximately 17-20% olivine with minor spinel from a magma similar in composition to primitive OSB-group samples. Additional crystallization of 60-70% olivine + plagioclase + clinopyroxene (15:60:24) can yield the most evolved GRB-group compositions. / OSB-group samples with compositions that are primitive with respect to major- and compatible trace-element chemistries display a wide and continuous range of incompatible trace-element (ITE) contents and ratios. While some of this variation may be the result of varying degrees of partial melting of the source region, the range of observed ITE ratios requires a source region that is heterogeneous with respect to these elements. / Source: Dissertation Abstracts International, Volume: 48-03, Section: B, page: 0682. / Thesis (Ph.D.)--The Florida State University, 1987.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_76087 |
| Contributors | CUMMINS, LAURA ELAINE., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 500 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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