Jemez Lineament

Jemez Lineament
Name	Jemez Lineament
Location	New Mexico, Arizona, Colorado
Type	Structural lineament
Age	Neogene, Quaternary
Geology	Basaltic and rhyolitic volcanism, tectonic faulting

Jemez Lineament The Jemez Lineament is a northeast-trending zone of magmatic centers, volcanic fields, and structural weaknesses across the southwestern United States, primarily in New Mexico and Arizona. It connects a chain of volcanic fields, calderas, and igneous provinces and is implicated in regional tectonics related to the Rio Grande rift, Basin and Range Province, and the western margin of the North American Plate. The feature has been studied in the contexts of Plate tectonics, mantle dynamics, and continental magmatism by researchers at institutions such as the U.S. Geological Survey, New Mexico Institute of Mining and Technology, and University of New Mexico.

Geology and Tectonic Setting

The lineament lies at the intersection of Proterozoic cratonic elements and Phanerozoic tectonic provinces including the Colorado Plateau, the Rio Grande rift, and the Basin and Range Province. It overlies Precambrian basement terranes like the Yavapai Province and Mazatzal Province and crosscuts Paleozoic and Mesozoic strata such as the Permian Basin margins and Triassic sedimentary rocks. Regional stress fields associated with the Neogene extension of the Rio Grande rift and the broader western North America transtensional regime have reactivated preexisting faults and lithospheric heterogeneities, influencing the distribution of Cenozoic volcanism along the zone.

Geographic Extent and Major Features

The lineament extends roughly from eastern Arizona across northern New Mexico toward south-central Colorado, linking volcanic centers including the San Carlos Volcanic Field, Zuni-Bandera volcanic field, Mount Taylor volcanic field, the Jemez Mountains, the Raton-Clayton volcanic field, and the Acoma-Zuni Uplift region. Prominent features along the trend include calderas such as the Valles Caldera, stratovolcano remnants like Mount Taylor, and volcanic plateaus associated with basalt and rhyolite eruptions. Human settlements and cultural sites near the lineament include Los Alamos, Santa Fe, and ancestral Puebloan locations like Chaco Canyon and Pecos Pueblo, which intersect archaeological research on volcanic impacts.

Volcanism and Petrology

Volcanic products along the zone range from alkali basalts and tholeiitic basalts to high-silica rhyolites and dacites. Petrologic studies document mantle-derived magmas that experienced crustal assimilation and fractional crystallization beneath calderas such as Valles Caldera and extrusive centers like the Raton-Clayton volcanic field. Geochemical signatures include trace-element and isotopic affinities with enriched mantle sources, with involvement of lithospheric mantle and lower crustal components analogous to signatures observed in the Jemez line-adjacent volcanic provinces and in other continental rift settings like the East African Rift and the Iceland plume-influenced systems.

Structural Interpretation and Origins

Interpretations of the lineament invoke reactivation of Proterozoic sutures and shear zones, lithospheric thinning related to rifting, and mantle upwelling conduits that localize magmatism. Some models propose structural control by Precambrian transcurrent faults comparable to those recognized in the Transcontinental Proterozoic provinces, while alternative models emphasize passive mantle melt focusing beneath lithospheric steps akin to mechanisms proposed for the Rio Grande rift and the Sierra Madre Occidental. Debates continue regarding the relative roles of lithospheric versus asthenospheric processes and whether the lineament represents a linear plume-affected corridor or an expression of distributed intraplate extension.

Geophysical Evidence and Studies

Geophysical investigations have employed seismic tomography, gravity anomaly mapping, aeromagnetic surveys, and magnetotelluric sounding to image crustal and mantle structures beneath the zone. Seismic studies reveal low-velocity anomalies in the upper mantle beneath parts of the trend, comparable to observations beneath the Valles Caldera and Raton-Clayton areas, while gravity anomalies correlate with mafic intrusions and crustal thinning. Collaborative work by the U.S. Geological Survey, New Mexico Tech, and university research groups has integrated geochronology, geochemistry, and geophysics to constrain magma sources and plumbing systems, drawing methodological parallels with studies at Yellowstone Caldera and the Cascades Volcanic Arc.

Chronology and Evolution

Volcanic activity along the zone spans Neogene to Quaternary time, with ages ranging from Miocene basaltic volcanism to Pleistocene rhyolitic eruptions. Key chronometric constraints come from radiometric dating methods such as ^40Ar/^39Ar and U-Pb zircon geochronology applied to units at Mount Taylor and the Valles Caldera. Temporal patterns show episodic activity with migration and localization of centers, reflecting evolving stress regimes associated with the initiation and propagation of the Rio Grande rift and regional mantle dynamics through the Cenozoic.

Economic and Environmental Significance

The lineament influences regional geothermal gradients, hosting geothermal resources and hydrothermal alteration zones explored for energy potential near the Valles Caldera and other hot-spot areas. Mineralization associated with magmatic-hydrothermal systems includes epithermal and porphyry-style alteration analogous to deposits at other western U.S. igneous provinces, affecting mining interests near Grants, New Mexico and Raton, New Mexico. The volcanic history impacts regional water resources, soil development, and hazards assessments relevant to emergency planning for communities such as Los Alamos National Laboratory and cultural preservation at Pecos National Historical Park.

Category:Geology of New Mexico Category:Volcanism of the United States