DIABASE DIKES, EASTERN ARBUCKLE MOUNTAINS, OKLAHOMA: TWO MAGMATIC SUITES AND REGIONAL IMPLICATIONS

Numerous northwest-striking diabase dikes cut massive 1350-1400 Ma granitic rocks in the eastern Arbuckle Mountains. Most of the dikes were apparently emplaced during Early Cambrian rifting that resulted in the formation of the Southern Oklahoma aulacogen. Whole rock K-Ar results suggest some of these dikes are older and may be near the age of the host granitic rocks. However, there is no petrographic difference in the dikes, and the K-Ar isotopic system is plagued by excess radiogenic argon.

Detailed trace element and Nd and Sr isotope geochemistry reveal that there are two distinct suites of diabase dikes. Compared to the apparently older dike set, the younger dikes are characterized by lower Mg number, by greater abundances of incompatible elements such as K, Ti, P, Y, Zr, Nb, Ta, Th, and by light and medium rare earths. The younger dikes also have higher initial Sr and lower initial Nd isotopic ratios.

Diabasic dikes are common throughout the widespread granite-rhyolite terranes in the Proterozoic basement of central United States. These dikes record extensional events and probably play a major role as seismic reflectors that help define the thickness and extent of the separate terranes. The early northwest-striking diabase dikes in the eastern Arbuckle Mountains may record an extensional event that led to the formation and preservation of the enigmatic 10 km-thick layered Precambrian reflections in southwest Oklahoma and adjacent Texas. A direct relationship is now obscured by Cambrian and later rifting that separates them.