New Mexico Geological Society Annual Spring Meeting — Abstracts

The Mazatzal province is thought to be a juvenile arc terrane that accreted onto southern Laurentia during the ~1.65 Ga Mazatzal orogeny. Thermal overprinting and local deformation during the emplacement of anorogenic granites at ~1.46 Ga has made it difficult to date Proterozoic fabrics and assign the deformation to either of these events. Detrital and igneous zircon U-Pb ages were obtained by LA-MC-ICPMS from four localities in southern New Mexico within the Mazatzal province. These localities include the Kingston District, Mud Springs, Caballo Mountains, and San Andres Mountains. These dates will be used to constrain the timing of deformation and the relationship of these rocks to the Mazatzal island arc system.

Detrital zircons were collected from quartzite, phyllite, a muscovite-biotite-quartz schist, a quartz-rich amphibolite, and conglomerate. Samples range from undeformed to highly deformed. Zircons from each sample form a single peak between 1.68–1.64 Ga. A slightly deformed quartzite from the Caballo Mountains yields the youngest maximum depositional age (MDA) of 1643±10 Ma (all uncertainties at 2s), while undeformed to slightly deformed quartzites in the San Andres yielded MDAs of 1652±6 Ma (Amato et al., 2008), 1675±16 Ma, and 1680±32 Ma. Two phyllites were dated from the San Andres and yielded MDA’s of 1657±10 Ma and 1666±10 Ma. A quartz-rich amphibolite, with a possible sedimentary origin, from Mud Springs Mountain yielded a MDA of 1655±14 Ma. A conglomerate from the Kingston District has very little muscovite which suggests slight metamorphism; however, it appears to be undeformed. This samples yielded a MDA of 1661±42 Ma.

Zircons from granites, orthogneisses, and a gneissic granite were dated. A highly deformed gneissic granite from the Caballo Mountains yielded the oldest crystallization age of 1681±24 Ma. Several granites are either undeformed to only slightly deformed. These include San Andres granites at 1626±21 Ma (Serna, 2006), 1643±22 Ma, and 1679±46 Ma, and an undeformed granite from the Cookes Range at 1646±40Ma. An undeformed granite from the Kingston Mining District yielded a crystallization age of 1659±24 Ma. Orthogneisses from the San Andres yielded crystallization ages of 1647±14 Ma (Amato et al., 2008) and 1650±8 Ma. The youngest deformed igneous rock is an orthogneiss from the Florida Mountains that yields a crystallization age of 1623±14 Ma (Amato and Mack, 2012).

Some degree of deformation is found in all of the localities except the Kingston District where the undeformed conglomerate and undeformed granite were located. The other localities have ~1.4 Ga granites nearby which could have caused deformation in those areas, whereas the Kingston District rocks appear to have escaped significant deformation. If this is the case then much of the deformation in southern New Mexico could be linked to the ~1.4 Ga magmatic event and not the Matatzal orogeny.

References:

1. Amato and Becker, 2012, NMGS Guidebook 63, p. 227-233
2. Amato and Mack, 2012, GSA Bulletin, v. 124, p. 1826-1840
3. Amato et al., 2008, GSA Bulletin, v. 120, p. 328-346
4. Serna, A.M., 2006, NMSU M.S. Thesis, 89 p