Inherited zircons in post-75 Ma igneous rocks of the western San Juan Mountains: Evidence for long-term involvement of Proterozoic lithosphere in magma production
— David A. Gonzales, [ed.]
Abstract:
Abstract—Inherited zircons in 75–4 Ma mafic to felsic igneous rocks in the western San Juan Mountains offer a glimpse into the provenance and genesis of magmas. Inherited zircon populations together with trace element and isotopic signatures lend evidence for long-term involvement of Proterozoic lithosphere with arc signatures regardless of composition, age, or tectonomagmatic regime. Inherited zircons in the 32–30 Ma San Juan Formation and Cenozoic breccia dikes-pipes compose 8% to 95% of total zircon populations and show the greatest age range (2700–63 Ma). These rocks contain high proportions of 1800–1390 Ma zircons attributed to the melting of Proterozoic basement rocks along with contamination by detrital zircons from Paleozoic to Cenozoic sedimentary rocks. Most plutonic rocks emplaced during the intervals 75–60 Ma and 32–26 Ma contain 9% to 100% inherited 1800–1390 Ma zircons, with minor Archean and post–1300 Ma contributions. This is evidence that partial melting of 1800–1390 Ma crust was a major contributor in magma production. In contrast, most 23–5 Ma felsic rocks produced during incipient rifting and injection of mantle melts into the middle-upper crust contain only 0–10% inherited zircons, possibly due to a melt source devoid of inherited populations or changing melt conditions. The data reveal the legacy of accreted Proterozoic lithosphere in the production of igneous rocks in the region over the past ~80 million years. This is an important consideration in reconstructing the magmatic history and provenance of magmas under shifting tectonic regimes.
Full-text (2.62 MB PDF)
Recommended Citation:
- Gonzales, David A., 2024, Inherited zircons in post-75 Ma igneous rocks of the western San Juan Mountains: Evidence for long-term involvement of Proterozoic lithosphere in magma production, in: New Mexico Geological Society, Guidebook, 74th Field Conference, Karlstrom, Karl E.;Koning, Daniel J.;Lucas, Spencer G.;Iverson, Nels A.;Crumpler, Larry S.;Aubele, Jayne C.;Blake, Johanna M.;Goff, Fraser;Kelley, Shari A., New Mexico Geological Society, Guidebook, 74th Field Conference, pp. 127-140. https://doi.org/10.56577/FFC-74.127