WHY DOES KANSAS HAVE KIMBERLITES – A REVIEW

Igneous rocks are relatively rare in Kansas, but Cretaceous-age kimberlites and lamproites are present in the eastern part of the state. Their existence in the mid-continent of North America is controversial, given that they erupted through basement rocks consisting predominantly of juvenile and continental margin volcanic arcs that were accreted to the SE margin of North America during the Proterozoic (1.8-1.6 Ga), i.e. far from the thick (i.e. >200 km) Archean craton typically associated with the mantle conditions that give rise to volatile and trace element-enriched melt formation. Petrological models [1] for the origin of Kansas kimberlites propose small degree partial melts of carbonate-bearing garnet lherzolite or harzburgite but with no explanation for how the conditions for melt generation are met. Others propose a role for a mantle plume / hotspot [2] or large-scale extension inboard of the continental margin [3]. In an attempt to explain the increase in kimberlite emplacement across North America during the Cretaceous, Currie and Beaumont [4] hypothesized the existence of a lithosphere-scale structure called the “kimberlite corridor”—which extends from northern Canada to the Gulf of Mexico and includes the Kansas kimberlites; they relate this feature to flat-slab subduction of the Farallon Plate. In contrast, [5] recognized that most Cretaceous kimberlites occur adjacent to strongly attenuated lithosphere at the edge of the North American craton, and attribute kimberlite genesis to edge-driven decompression melting of an OIB-type deep-mantle source. The Kansas kimberlites occur within this transition zone, but they are also ~65 km west of, and sub-parallel to, the axis of the late Precambrian Midcontinent Rift System. A deep lithospheric connection with the MCR has never been explored. This presentation will review the current petrological, geochemical and geophysical data in light of these various models for kimberlite petrogenesis, with a focus on the kimberlites of Riley and Marshal Counties in northeast Kansas.

[1] Cullers et al., 2012, http://www.kgs.ku.edu/Publications/OFR/2012/OFR12_17/index.html; [2] Chu et al., 2013, Nature Geosci, v. 6, p. 963; [3] Duke et al., 2014, EPSL, v. 403, p. 1014; [4] Currie and Beaumont, 2011, EPSL, v. 303, p. 59; [5] Kjarsgaard et al., 2017, G3, v. 18.