Life in the USA is not normal. It feels pointless and trivial to be talking about small looks at the fascinating natural world when the country is being dismantled. But these posts will continue, as a statement of resistance. I hope you continue to enjoy and learn from them. Stand Up For Science!
Geologists sometimes use the word “lineament” to describe a suite of linear alignments whose nature is complex or uncertain. Maybe a fault zone, maybe a contact between rock types or tectonic terranes, maybe a string of volcanoes, an alignment of rivers or geophysical features, or some combination of those and other causes.
Generally, in geology a lineament should not usually be thought of as a line, but rather a zone, whose boundaries and position differ depending on who is using what as the basis for the lineament zone. Sometimes this suggests that we don’t really know what is going on – and sometimes that’s true; we probably know something is there and has a causal relationship to the features we see, but we may not be certain about the heritage of everything. That’s OK – it gives us things to explore!
The Jemez Lineament extends from southeastern Arizona northeastward toward the northeastern corner of New Mexico. On the surface it is marked by a linear set of quite recent (mostly less than 9 million years) volcanic piles and individual volcanic vents. In the subsurface it approximately marks the contact between two ancient terranes, the Yavapai (about 1,800 million years old) and the Mazatal (1,700 to 1,650 million years old). The Jemez Lineament is related to the contact zone between those two provinces and is the remnant of their collision about 1,650 to 1,600 million years ago, shown on the map at the top.
Both the Yavapai and Mazatal terranes were island arc complexes that collided with the core of North America, something like today’s Japan-Ryukyu-Taiwan arc colliding with East Asia. Yavapai accreted (was added) first, about 1,710 to 1,680 million years ago, and Mazatal came along about 20 to 80 million years later. The collisional contact (an old subduction zone) between them is a major weak zone that may reach as deep as the base of the crust. The Jemez Lineament today is interpreted as a hydrous subduction scar, and it has affected the tectonics and geologic history of this region for more than 1,500,000,000 years.
The second map highlights the relationship between the Jemez zone and the string of volcanic piles across northern New Mexico.
The northeast-southwest trending Jemez zone may have been jiggled and reactivated when the north-south Rio Grande Rift began to split New Mexico (and points north, into Colorado) in two about 25 million years ago. In the map above, you can also see a bit of offset on the north-south rift where it crosses the Jemez zone. That probably should not be thought of as a fault offset, but rather as an accommodation of variable mechanical behavior. By about 9 million years ago, magmas were able to exploit the Jemez weak zone and reach the surface in a 600-km-long belt.
Basaltic rocks at Petroglyph National Monument, near Albuquerque, are only about 156,000 to 200,000 years old (Thompson and others, 2020, Geologic map of Petroglyph National Monument and vicinity: USGS Scientific Invest. Map 3447) and are probably most closely related to faulting in the Rio Grande Rift. But they are also near the broad Jemez zone and could have been localized there by interacting weaknesses between the Rift and the Jemez zone.
The far northeastern limit of the Jemez volcanic piles is where Capulin Volcano sits. It’s a little cinder cone that erupted about 60,000 years ago, just yesterday geologically, but with a heritage likely going back to the Yavapai-Mazatal collision 1,625,000,000 years ago.
Whether the volcanic action along the Jemez lineament is continuing or dying out is unknown, and there is no systematic progression in age along the lineament toward the northeast even though Capulin is among the youngest eruptions along it. But if activity continues, we could see a volcano in Kansas in a few hundred thousand years or so. Yes, Kansas is just 175 km from the Capulin Volcano.
My photo of Capulin is from 1976. The original discovery of Folsom points and other archaeological features was at a location about 13 kilometers from Capulin Volcano. “Capulin” comes from the Spanish name for the chokecherries that grow on the slopes and rim of the cinder cone.
The name “Yavapai” is from a series of rocks named for Native American people of Arizona, whose name means “people of the sun.” Mazatal is from the Mazatal Mountains, possibly deriving ultimately from Nahuatl for “place of the deer.”
Thank you, very interesting. Did not know there was a string of volcanoes there. In the Pacific Northwest there's OWL--Olympic Wallowa Lineament. Various studies, but possibly less explanation than Jemez. There is even the view that it's nonexistent. However, Walla Walla County Emergency Management and DOE (Hanford) take it seriously enough because of earthquake possibility, based on records of a very strong earthquake in 1872 just east of the Cascades near Wenatchee.
Exceptionally well done, Richard!