EXOTIC MESOPROTEROZOIC (1.5-1.6 GA) DETRITAL ZIRCON FROM THE METAMORPHOSED PIEDRE LUMBRE FORMATION IN THE PICURIS MOUNTAINS, NEW MEXICO, USA: PROVENANCE AND TECTONIC IMPLICATIONS
Samples of Vadito Group quartzite were collected 2 km to the south and 20 km to the east of the Marquenas Formation type locality. Ninety-five concordant ages from each quartzite sample yield identical age probability distributions characterized by a narrow, unimodal population (1.78-1.69 Ga) with peak modes at 1.71 Ga, consistent with derivation from local source terranes. Seventy grains from quartzite in the uppermost Piedre Lumbre Formation show a broad age distribution, with 12 age peaks between 2.42-1.46 Ga and a maximum peak at 1.63 Ga. Mesoproterozoic ages define peaks at 1.49, 1.53, and 1.59 Ga. Mesoproterozoic ages ca. 1.5-1.6 Ga are uncommon in North America and suggest derivation from exotic source terranes proximal to western Laurentia at 1.5 Ga. The type locality Cerro de las Marquenas Formation quartzite yields 98 concordant ages with 4 grains at 1.47 Ga, a broad Paleoproterozoic population with a 1.69 Ga peak, and minor Archean peaks. This detrital age spectrum confirms ca. 1.48-1.46 Ga detrital zircons previously reported for the Marquenas Formation.
Results require a Mesoproterozoic depositional age for the uppermost Piedre Lumbre Formation (1.49 Ga) and Marquenas Formation (1.45 Ga). The transition from unimodal to multimodal age distributions from the Vadito Group to the Marquenas and Piedre Lumbre Formations may reflect the influx of material from a non-Laurentian provenance such as Australia and/or Antarctica and a significant change in depositional and tectonic setting.
Regional metamorphism and deformation in the Picuris is post 1.45 Ga and not consistent with tectonic models of regional metamorphism and deformation related to the Mazatzal Orogeny or with an extended mid-crustal residence time (ca 1.65 to 1.45) followed by a reheating event.