title: Tijeras Greenstone
text: # Tijeras Greenstone
  
  The Tijeras Greenstone is a geologic formation in central New Mexico. It has a radiometric age of 1660 million years (Ma), corresponding to the Statherian period.
  
  ## History of investigation
  
  The unit was first defined by V.C. Kelley and S.A. Northrop in 1975. The formation was included in the Manzano Group by Mark Holland and coinvestigators in 2020.
  
  ## Geology
  
  The formation is exposed along a belt 1 mile (1.6 km) and 5.5 miles (8.9 km) long in Tijeras Canyon east of Albuquerque, New Mexico. It is a sequence of metavolcanic and metasedimentary beds, typically dark green in color, with its texture varying from unfoliated to strongly schistose. The dominant rock type is metabasalt of tholeiitic composition. The more foliated beds are chlorite or hornblende schist, but much of the formation is igneous rocks that have experienced only mild metamorphism. Metasedimentary rocks vary from quartzite through mica schist to marble, with one sequence of quartzite beds exceeding 610 meters (2,000 ft) in thickness. Metamorphic conditions reached 550±50°C and 2±1 kb pressure, corresponding to a low-pressure amphibolite facies.
  
  ## Footnotes
  
  * 1 2 3 4 Kelley, V.C.; Northrop, S.A. (1975). "Geology of the Sandia Mountains and vicinity, New Mexico". New Mexico Bureau of Mines and Mineral Resources Memoir. 29. Retrieved 18 March 2022.
  * ↑ Grambling, Tyler A.; Karlstrom, Karl E.; Holland, Mark E.; Grambling, Nadine L. (2016). "Proterozoic magmatism and regional contact metamorphism in the Sandia-Manzano Mountains, New Mexico, USA" (PDF). New Mexico Geological Society Field Conference Series. 67: 169–175. Retrieved 27 May 2020.
  * ↑ Holland, Mark E.; Grambling, Tyler A.; Karlstrom, Karl E.; Jones, James V.; Nagotko, Kimberly N.; Daniel, Christopher G. (September 2020). "Geochronologic and Hf-isotope framework of Proterozoic rocks from central New Mexico, USA: Formation of the Mazatzal crustal province in an extended continental margin arc". Precambrian Research. 347: 105820. doi:10.1016/j.precamres.2020.105820.
  * 1 2 Connolly, James R. (1992). "Structure and metamorphism in the Precambrian Cibola Gneiss and Tijeras Greenstone, Bernalillo County, New Mexico" (PDF). New Mexico Geological Society Field Conference Series. 33: 197–202. Retrieved 18 March 2022.
  