New Mexico Geological Society Annual Spring Meeting — Abstracts

Metasedimentary rocks in the northern Burro Mountains have an uncertain age, depositional setting, and tectonic significance.  Amato et al. (2008) dated two samples within a phyllite unit located in the eastern region of the Redrock area, and reported maximum depositional ages (MDA) of 1753 Ma (n=73), and 1673 Ma (n=44). U/Pb detrital zircon dates and field mapping from this study have identified five distinctive metasedimentary units within the Redrock area, and the zircon ages indicate that some of these units were deposited >400 m.y. later during the Grenville Orogeny. A biotite-albite-actinolite schist in the western part of the field area has a MDA of 1233 ± 11 Ma (n=38), and a metacarbonate unit, also located in the western region, has a MDA of 1230 ± 11 Ma (n=28). A more metamorphosed phase of the phyllite adjacent to these units has been dated at 1643 ± 26 Ma (n=28) and is part of the Mazatzal province sedimentary protolith section. The schist and metacarbonate units are intruded on the west by 1.23–1.22 Ga granite and anorthosite (Rämö et al., 2003; this study). These ages and field relationships are consistent with deposition of sediments in a back arc basin during Grenville extension, and bimodal magmatism ~5-10 m.y. later which resulted in the intrusion of the granite suite. These field relationships indicate that there is an unconformity between Mazatzal-age (1.7-1.6 Ga) and Grenville-age (1.2 Ga) sedimentary rocks in the western region of the Redrock area. In addition, at least two generations of normal faults post-date the deposition of these sediments, creating complex structural relationships. Results from this study suggest a previously unrecognized Grenville basin in the Burro Mountains.

References:

1. Amato, J.M., Boullion, A.O., Serna, A.M., Sanders, A.E., Farmer, G.L., Gehrels, G.E.,and Wooden, J.L., 2008, Evolution of the Mazatzal province and the timing of the Mazatzal Orogeny: Insights from the U-Pb geochronology and geochemistry of igneous and metasedimentary rocks in southern New Mexico: Geological Society of America Bulletin, v. 120, p. 328–346.
2. McLemore, V.T., Dunbar, N., Kosunen, P.J., Rämö, O.T., Heizler, M., and Haapala, I., 2002, Geology and geochemistry of the Redrock granite and anorthosite xenoliths(Proterozoic) in the northern Burro Mountains, Grant County, New Mexico, USA: Bulletin of the Geological Society of Finland, v. 74, p. 7–52.
3. Rämö, O. T., McLemore, V. T., Hamilton, M. A., Kosunen, P. J., Heizler, M., and Haapala, I., 2003, Intermittent 1630-1220 Ma magmatism in central Mazatzal Province; new geochronologic piercing points and some tectonic implications: Geology, v. 31, p. 335-338.