Cambrian Magmatism Along the Southern Laurentian Margin: New Petrologic Constraints from Well Cuttings in the Southern Oklahoma Aulacogen (USA)

Abstract:

Magmatism in the Southern Oklahoma aulacogen (SOA) is associated with >250,000 km³ of early Cambrian aged mafic-silicic intrusives and effusive products possibly related to the opening of the Iapetus Ocean. In the vicinity of the Arbuckle Mts., thick mafic to intermediate lava packages interbedded with rhyolite lavas and sedimentary strata are exposed in the subsurface and penetrated by oil and gas exploration wells. We have sampled cuttings from six wells exposed along the strike of the SOA with the aim of petrographically, geochemically, and isotopically characterizing the rocks to better understand their tectonomagmatic affinity. Cuttings were observed under a binocular microscope to ensure textural homogeneity; XRF bulk chemistry from these samples show that they are relatively unaltered based on analytical totals and alteration indices. The samples plot as basalts to andesites (e.g., 47-64 wt. % SiO₂) and are primarily tholeiitic. On discrimination diagrams, these samples fall in “intraplate” fields, consistent with continental basalt volcanism, including flood basalt eruptions. These lavas show Zr/Nb values ranging from 6.8 to 11.1, K/Nb values ranging from 300-600, and Ba/Nb values ranging from 10-20, which are similar to EM1 OIB. The samples also show trace element patterns consistent with OIB-like mantle sources when normalized to primitive mantle, and similar geochemical traits to the Roosevelt Gabbros that crop out along strike of the SOA in the Wichita Mts.. Sr, Nd, and Pb isotope analysis is ongoing. Chemostratigraphic variations show the possibility of several lava packages. The geochemical analyses of the SOA lava flows provide insight into how these magmas formed as well as what tectonic regime (e.g., lower-mantle derived plume, upper-mantle extension, or “leaky” transform fault) produced the volcanism that affected the southern margin of Laurentia during the formation of the SOA; we favor the involvement of a deep mantle plume.