| dc.description.abstract | The Magnet Cove Igneous Complex (MCIC) in Arkansas consists of multiple ring dikes of silica undersaturated rocks including various syenites, ijolites, phonolites, trachytes, and carbonatite (Erickson and Blade, 1963). The emplacement of the rocks is hypothesized to be from outside-in, with the outermost syenite ring emplaced first, and the carbonatite last (Erickson and Blade, 1963). There is an abundance of titanium- and zirconium-rich minerals including perovskite, titanite, and schorlomite, kimzeyite garnet. This study used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) after petrography characterization to date emplacement of the MCIC and test if these Ti minerals are suitable as U-Pb reference materials. Results will contribute to the discussion on the cause of Cretaceous magmatism in the midcontinent US. One perovskite grain was analyzed with 34 spots of 35μ size. Of the garnets, multiple grains were analyzed and the number was dependent on rock type, surface area of the grain, and inclusion-rich material. Upwards of 40 spots were used on each rock type and were all 85μm. 85μm size was based on U and Pb concentrations. The age of perovskite was initially calculated to be 85.7 ± 5.5 Ma, which is slightly younger than previous estimates of the MCIC. However, when the common Pb ratio was anchored at 0.82 ± 0.04, it is closer to other calculated ages at 100.5 ± 1.7 Ma. Garnet ages were calculated from four different rock types: fine-grained ijolite (FGI), garnet-pseudoleucite syenite (GPS), garnet ijolite (GI), and garnet-biotite ijolite (GBI). Each rock achieved a slightly different age; however, the age range sits within the bounds between 98.1 Ma and102.8 Ma, which is consistent with the estimates for the magmatism in the Arkansas Alkaline Province (AAP). FGI: 98.5 ± 0.6 Ma, GPS: 101.4 ± 0.5 or 101.1 ± 0.5 with an anchored common Pb at 0.8 ± 0.08, GI: 98.1 ± 0.6 Ma, GBI: 102.8 ± 0.6 Ma. U-Pb dating of schorlomite by LA-ICP-MS is ongoing and will test their use as potential reference materials in future studies. | en_US |
