Tectonomagmatic implications of metamorphosed tuffs for Mesoproterozoic basin evolution and intraplate orogenesis in the Picuris Mountains, New Mexico, USA

Recent Mesoproterozoic tectonic models for Laurentia integrate widespread records of pre- to synorogenic sedimentation, plutonism, and metamorphism. Some associated deformation within the southwestern United States has been reinterpreted as an expression of the Mesoproterozoic Picuris orogeny rather than an expression of the Paleoproterozoic Mazatzal orogeny; when combined with models for the progressive Laurentian assembly, this implies that the Picuris orogeny may have included an intraplate component inboard of the active 1.5−1.4 Ga convergent margin. Here, we evaluate aspects of this proposed tectonic regime using new zircon U-Pb, trace-element, and whole-rock compositional data from rarely exposed Mesoproterozoic metamorphosed tuffs in the Picuris Mountains of northern New Mexico. Whole-rock compositions and mineralogy indicate the metatuffs settled in the deep marine Trampas group basin and underwent low-temperature diagenetic alteration prior to metamorphism. Zircon crystallization ages indicate that volcanic activity contributed tuffs to the Trampas basin from ca. 1491 Ma to 1472 Ma. Zircon trace-element compositions differentiate between metatuffs with two unique geochemical signatures: one sourced from a magmatic arc, and one with an enriched mantle, possibly plume-influenced, source. Most, if not all, metatuffs are interpreted to be the products of distal arc volcanism, most likely related to subduction (a feature of the broader Picuris event) to the paleogeographic south of the Trampas basin between ca. 1.5 Ga and 1.45 Ga. Deep marine sediments of the Trampas group basin are inferred to have been deposited disconformably on ∼180−200-m.y.-older continental shelf sediments of the Hondo Group, suggesting basin subsidence facilitated by reactivation of older basin-bounding structures and, possibly, extension during the Mesoproterozoic preceding the main convergent phase of Picuris orogenesis. Thus, the record of the Picuris metatuffs is consistent with the recently proposed Laurentian Mesoproterozoic tectonic framework of transpression and/or along-strike migration of convergence, suggesting a role for pre-existing structures in focusing far-field stresses and intraplate orogenesis.