Overprinting (geology)

Overprinting is a geological process that superimposes a set of characteristics on rock that partially obscure earlier characteristics. Examples include metamorphic overprinting (superimposed metamorphism^[1]), in which new structure,^[2] texture, or mineral composition is imposed on existing rock.^[3][4] For example, the Tauern window of Alps contains beds that were originally metamorphosed to eclogite but have since been overprinted to the blueschist and then the greenschist facies.^[5] Likewise, deformation associated with the Mazatzal orogeny in Arizona and New Mexico, US, was subsequently overprinted by deformation associated with the Picuris orogeny.^[6]

In this orthogneiss from the Czech Republic the original igneous rock texture has been overprinted by foliation associated with metamorphism.

Geochemical signatures can also be overprinted when the geochemistry of a geological body is changed by eliminating or modifying the earlier geochemical signature.^[7][8]

References

1. Yardley, Bruce W. D. (1989). An Introduction to Metamorphic Petrology. Longman Earth Science Series. Harlow, Essex, England: Longman Scientific & Technical. p. 246. ISBN 0-582-30096-7.
2. Jackson, Julia A., ed. (1997). "metamorphic overprint". Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute. ISBN 0922152349.
3. Yardley 1989, pp. 211, 214.
4. Zhao, Lei; Zhai, Ming-Guo; Nutman, Allen P.; Oh, Chang-Whan; Bennett, Vickie C.; Zhang, Yanbin (July 2020). "Archean basement components and metamorphic overprints of the Rangnim Massif in the northern part of the Korean Peninsula and tectonic implications for the Sino-Korean Craton". Precambrian Research. 344: 105735. doi:10.1016/j.precamres.2020.105735. S2CID 218819425.
5. Yardley 1989, p. 211.
6. Mako, Calvin A.; Williams, Michael L.; Karlstrom, Karl E.; Doe, Michael F.; Powicki, David; Holland, Mark E.; Gehrels, George; Pecha, Mark (December 2015). "Polyphase Proterozoic deformation in the Four Peaks area, central Arizona, and relevance for the Mazatzal orogeny". Geosphere. 11 (6): 1975–1995. doi:10.1130/GES01196.1.
7. Jackson 1997, "overprint [geochron]".
8. Brewer, Timothy S.; Menuge, Julian F. (March 1998). "Metamorphic overprinting of SmNd isotopic systems in volcanic rocks: the Telemark supergroup, southern Norway". Chemical Geology. 145 (1–2): 1–16. doi:10.1016/S0009-2541(97)00114-9.