Other
Scientific paper
Sep 1970
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1970comp...29..195w&link_type=abstract
Contributions to Mineralogy and Petrology, Volume 29, Issue 3, pp.195-214
Other
22
Scientific paper
Major and trace element analyses of over one hundred Mesozoic dolerite dikes from eastern North America have established three main chemical types: 1) olivine-normative; 2) high-TiO2 quartz-normative; and 3) low-TiO2 quartz-normative; and a less common high-Fe2 O3 * (Σ Fe as Fe2O3) quartz-normative type. Quartz-normative dikes predominate from Nova Scotia to Maryland whereas olivine-normative dikes predominate in North and South Carolina. In Virginia and Georgia these types occur in approximately equal abundance. The high-Fe2O3 * quartz-normative type may be a result of local differentiation. The other quartz-normative types are chemically distinct from each other and probably evolved from different parental magmas. The olivine-normative type may be representative of these parental magmas, and either the parental magmas overlap in composition or only one magma is represented by analyzed olivine-normative dikes. Simple crystal fractionation models coupled with constraints on liquidus phases imposed by recent experimental studies reveal that 1) all three quartz-normative types can be derived from the olivine-normative type by the removal of slightly different cumulate assemblages, but not by contamination with any common crustal composition, and 2) the two-main quartz-normative types are related to each other by neither crystal fractionation nor contamination processes. According to the models, any of the quartz-normative types can be derived from the olivine-normative type by 60 70% accumulation, with the cumulate consisting primarily of ˜50% plagioclase, 25 30% olivine, and ˜15% clinopyroxene. The concept of vertical inhomogeniety with respect to incompatible elements in the upper mantle source areas is invoked as a possible explanation for the chemically distinct parental magmas. The spatial distribution of the chemical types and the gross outcrop pattern of the dike swarm clearly indicate that the tectonic environment of the northern Appalachian region differed from that of the southern part during the early Mesozoic.
Ragland Paul C.
Weigand Peter W.
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