Cambrian (?) Mill Creek diabase dike swarm, eastern Arbuckles: A Glimpse of Cambrian rifting in the Southern Oklahoma Aulacogen Edward G. Lidiak1, Rodger E. Denison2, and Robert J. Stern3 1Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15260. [email protected]. Corresponding author. 215141 Kingstree Drive, Dallas, Texas 75248. [email protected]. 3Department of Geosciences, The University of Texas at Dallas, Box 830688, Richardson, Texas 75083-0688. rjstern@ utdallas.edu. ABSTRACT INTRODUCTION A swarm of Cambrian (?) diabase dikes intrude The Southern Oklahoma Aulacogen (SOA) is a well- the 1390-1365 Ma granitoids of the eastern Arbuck- known transverse structure that trends west-northwest in le Mountains of Oklahoma. The dikes strike predom- the southern North American craton. Exposures within the inantly N60°W parallel to the rifted margin of the SOA reveal faults that record extension and which may Southern Oklahoma Aulacogen and are interpreted as be interpreted as related to its formation. Mesoproterozo- being related to Cambrian opening of that structure. ic basement underlies much of the region and ~1390 Ma The dikes, referred to here as the Mill Creek diabas- gneiss and granodiorite and ~1365 Ma granite are exposed es, are olivine-normative to quartz-normative tholeiitic in the eastern Arbuckle Mountains (Figures 1, 2). Diabase basalts. Their tholeiitic character is further indicated dikes are widespread throughout the core of the eastern Ar- T by high Fe2O3 (total Fe), moderate to high TiO2, low buckles. These dikes are referred to here as the Mill Creek P O , and low Nb/Y ratio. Mg numbers (Mg#) of 52-36 2 5 diabase dike swarm for excellent exposures in Mill Creek are indicative of derivative basaltic liquids which are Quarry (Figures 2, 3), which is here designated as the type consistent with the fine-grained, equigranular mineral locality. In the quarry, a swarm of steeply dipping diabase assemblage of plagioclase + augite + Fe-Ti oxides ± oliv- dikes (from <1 m to several meters wide) intrudes the Troy ine of most diabases. Granite. The dikes strike predominantly west-northwest The timing and tectonic setting of the diabas- and may have been intruded along fractures co-genet- es suggest that they were intruded in association ic with faulting and Cambrian deformation. We interpret with the Early Cambrian break-up of the southern these dikes as being emplaced during formation of the SOA Laurentian supercontinent. These dikes testify to the probable existence and subsequent break-up and part of the Southern Oklahoma Aulacogen Large Ig- of a large igneous province (LIP) in this region and neous Province (SOA–LIP) (Lidiak et al., 2005; Hanson demonstrate that Cambrian LIPs were composi- et al., 2011, 2013). In addition, a number of diabase dikes tionally similar to better-known break-up LIPs of may have been emplaced earlier, apparently about the time Mesozoic and younger age. This occurrence is the that the Mesoproterozoic granitoids formed. These dikes, only evidence that we can find for the presence of along with a suite of silicic west-northwest-trending mi- a break-up LIP in southern Laurentia, but we ar- crogranite porphyry dikes, record a Mesoproterozoic struc- gue that compositional similarities with other, bet- tural trend that influenced Paleozoic structure. Dikes from ter preserved LIPs warrant the conclusion that the the two diabase suites cannot be easily distinguished pe- Cambrian break-up LIP of the southern mid-conti- trographically but have distinct geochemical signatures as nent was similarly extensive. discussed below. The Mill Creek diabase dike swarm occurs along the present northern margin of the SOA (Figure 1). Similar Cambrian diabase dikes crop out about 200 km to the west 105 Lidiak et al. tion with diabase; these two observations suggest that there A Anadarko was little contamination by the surrounding country rocks. Basin Wichita Southern Mtns These dikes must have fed a volcanic field but there are no Oklahoma Aulacogen Arbuckle known basalt flows associated with the Mill Creek diabase 35° Mtns 5 5 dike swarm. Southern Granite-Rhyolite Ouachita Mtns Province Basement (~ 1.4 Ga) 5 � edge of Gulf REGIONAL SETTING Coastal Plain ont ic Fr Approxeimctoante T t ille 1.1 Ga) l e Grenv B The late Neoproterozoic-Cambrian continental mar- d l 5 o gin in the southern and eastern North American craton F Grenville-Age Basement (~ a Ouachita Llano t Uplift i 5 formed in a passive-margin tectonic setting in which car- Tectonic Front h c a ° u 30 5 O bonate-shelf facies and rifted-margin basins developed 5 during the initial opening of the Iapetus Ocean (Rankin, 1976; Rankin et al., 1989; Thomas, 1989, 1993; Viele and 105° Thomas, 1989; Harry and Londono, 2004). This extension- 100° 95° al episode was accompanied in the Appalachians (Rankin, B 102°W 100°W 1976) and in the SOA (Gilbert, 1983) by extensive mag- 37°N OKLAHOMA • Southern EXPLANATION Arbuckle Oklahoma Mountains matism. In the Appalachians there were two main episodes • • Aulacogen 0 200 Ouachita Ouachita Foldbelt of magmatism at 615 to 564 Ma and at about 550 to 540 km Foldbelt Ma (Cawood et al., 2001; Puffer, 2002). In east-central Carlton Rhyolite Group Mexico a mafic dike swarm records a separation date of • • Eastern Arbuckle 546 Ma (Keppie et al., 2006). Mafic igneous activity in the • • Province • • • • • • Wichitas is approximately 10 to 20 Ma younger but is well • Eastern Arbuckle Province Outcrops constrained at 534 to 528 Ma (Lambert et al., 1988; Hogan • • High Angle Fault et al., 1995, 1996; Hames et al., 1998). These dates record the initial stages of rifting along the southern margins of Ouachita Front • the Laurentian craton. The rifting associated with the SOA Well to Basement 0 10 is best exposed in southern Oklahoma (Figure 1), but this km rifting episode affected regions far to the west-northwest Figure 1: A) Generalized tectonic map of Texas and across the Texas Panhandle and into Colorado (Hansen and adjacent regions of Oklahoma and New Mexico. Base Peterman, 1968; Olson et al., 1977). Detailed mapping in map and Phanerozoic structures adapted from Viele the Precambrian basement of the eastern Arbuckles (Den- and Thomas (1989) with additions from Ham et al. ison, 1973) documents the abundance of N60°W-striking (1964). Precambrian boundaries and provinces adapt- diabase dikes. A rose diagram (Denison, 1982, 1995) and ed from (Ewing (1990, 1991) and Van Schmus et al. later measurements show the trend of 365 diabase dikes as (1993). B) Main tectonic elements of southeastern measured in the field (Figure 4). This trend parallels the Oklahoma adapted from Ham et al. (1964). late Paleozoic structural direction of about N60°W, and we Fig. 1 speculate that Ediacaran-Cambrian “SOA” rift structures may have controlled the development of Late Paleozoic in the Wichita Mountains (Gilbert, 1982, 1983; Price et al., “Ouachita” structures. 1996) and are present in the subsurface within the confines of the SOA (Ham et al., 1964; Puckett, 2011; Puckett et AGES OF INTRUSION al., 2011). In the eastern Arbuckles, Phanerozoic sedimen- tary rocks lie unconformably on the basement, testifying Table 1 lists available K-Ar whole rock dates for east- to a significant amount of erosion after dike emplacement. ern Arbuckle diabase dikes (Denison, unpublished Mobil The dike rocks are fine grained, suggesting that the present data). Three of the ten dates are in the expected ~500 Ma level of exposure corresponds to an emplacement depth of age range, and two others are ~1300 Ma. The other five only a km or so beneath the Cambrian surface. Dike con- samples give dates of 748, 795, 1098, 1532, and 2074 Ma; tacts are sharp and rare xenoliths of granite show no reac- these dates do not correspond to ages of rocks in the Ar- 106 Oklahoma Geological Survey Guidebook 38 Cambrian(?) Mill Creek diabase dike swarm, eastern Arbuckles buckles and may be too old, due to inher- 96°52"30" 96°15' 00" 34°30'00" + Mill Creek Quarry 34°30'00" + ited 40Ar, or too young, due to 40Ar loss. A R 5 E Phanerozoic Sediments R 9 E concerted effort to extract and date zircons Mill Creek Wapanucka T 02 and/or baddeleyite from these dikes, as 170* * 2 44 40 39 48 S well as efforts to obtain reliable Ar/ Ar 49 • 46 50 *31 *205 •202 Reagan 19 204 203 • 147 * 07 ages, is critically needed in order (1) to *34 13 17 * •14 04 •Troy 146• 18 *•09 •* * *05 206 •01•207 *20 * determine exactly when the inferred Cam- 26 • * •22 T brian (Mill Creek) dikes were emplaced 28 42 29* 37 3 •11 12 •38 40 • *36 * S in the SOA and (2) to test the idea that 03 •10 • • 06 *• 192 * •32 Coleman some of these Arbuckle diabase dikes are 201 ••208 significantly older than Cambrian. Ravia Tishomingo Milburn 96°52"30" 96°15' 00" A Cambrian age of the Mill Creek 34°07'30" + 34°07'30" + diabases is suggested by the fact that di- Burch Granodiorite (1390±7 Ma) Tishomingo Granite (1363±8 Ma) abase dikes in both the Arbuckle and Blue River Gneiss Wichita areas cut the voluminous felsic Troy Granite (1368±3 Ma) (1389±10 Ma) 0 5 10 volcanics of the Cambrian Carlton Rhyo- • Mill Creek Diabase Localities lite Group (Ham et al., 1964; Gilbert and * Low-Th Diabase Localities KM Hughes, 1986; Hogan et al., 1998). These dikes represent the culmination of Cam- Figure 2: Geologic map of Precambrian rocks of the eastern FArbuckleig. 2 Mountains, Oklahoma (Denison, 1973), showing location of Mill Creek brian igneous activity in the SOA. In ad- Quarry and location of eastern Arbuckle diabase samples studied in this dition, at least another episode of diabase report.