New Mexico Geological Society Annual Spring Meeting — Abstracts

A stratigraphy characterized by a wide range of metasedimentary and metavolcanic lithologies is present in the Ladron Mountains. Although significantly deformed, a distinct depositional sequence from oldest to youngest can be identified as follows: feldspathic quartzite, quartzite, metaconglomerate, biotite-muscovite phyllite/schist, metarhyolite, and amphibolite/chlorite schist. The stratigraphic relationships indicate significant facies variations both vertically and laterally. Preliminary interpretations include the presence of an uplifted source to the north, as suggested by the metaconglomerate grading laterally southward into increasingly finer-grained quartzites and pelitic units. Phyllite/schist grading vertically eastward into metarhyolite and amphibolite clearly reflects the onset of volcanism.

Detailed niapping (1:12,000) and petrographic analysis have tentatively documented three episodes of folding as well as later faulting. The oldest discernible deformational fabric. S1, is the major foliation found in the area. It is generally parallel to compositional layering (S0), trends NNE, and dips ESE. Folds with S1 as an axial plane (F1) are small, isoclinal, and uncommon. The presence of fish-hook folds and the parallelism with bedding suggests that S1 is partially transposed. This foliation is in turn folded on a mappable scale with a NE-trending, axial planar crenulation cleavage S2. F2 folds are open to tight with wavelengths up to 250 m and plunge to the SSE. Broad warping with an easterly plunge may represent F3 folds although the identification of an S3 fabric is uncertain.

The Ladron Mountain lithologies are probably correlative with those in the Manzano Mountains dated at about 1.7 Ga. Folding and faulting occurred before the intrusion of the 1.4 Ga Ladron granite. The deformational history is very similar to that found in the Precambrian rocks of northern New Mexico.