ABSTRACT

Mexico is an attractive place for provenance studies focused on reconstructing the tectonic evolution of North America. This is because Mexico hosts a well-preserved clastic record associated with some of the major Mesozoic and Cenozoic tectonic processes that shaped the face of this continent. However, the available information on Mexican pre-Mesozoic source terranes is presently insufficient for provenance analysis. With the aim of drawing the guidelines for provenance determination, we present here detrital modes, geochemical data, and zircon U-Pb ages for detritus derived from pre-Jurassic basement complexes of Mexico. Our data show that the various basement complexes produce distinctive detrital modes and supply diagnostic and compositionally different detrital heavy minerals that represent powerful provenance tracers. The Oaxacan Complex, Ayú Complex, and East Mexico Arc are the main sources of quartzo-feldspathic and feldspatho-quartzose detritus. Quartz with rutile needles, mesoperthitic K-feldspar, orthopyroxene, augitic to diopsidic clinopyroxene, and Mg- to Ca-rich almandine (Alm71–52Grs7–3Prp43–23Sps3–1Alm74–56Grs21–19Prp23–2Sps5–2) are common minerals in detritus from the Oaxacan Complex. The Ayú Complex supplies detritus marked by the occurrence of sagenitic biotite and white mica, as well as Mn-rich almandine (Alm69–66Grs4–3Prp18–11Sps19–10). Detritus from the East Mexico Arc contains any of these mineral phases ubiquitous in the Oaxacan and Ayú complexes. The Acatlán Complex is the main source of detritus dominated by metamorphic lithic grains and quartz, with minor amounts of feldspar. Lithic grains are rank 2–4 metabasitic, metapelitic, and metapsammitic–metafelsitic fragments. Diagnostic mineral phases are schorl–dravitic tourmaline, Na-amphibole, and helycitic garnet varying from a Ca- to Mn-rich almandine (Alm74–55Grs34–15Prp16–3Sps12–1-Alm70–46Grs20–15Prp3–1Sps32–12). Zircon U-Pb geochronology proves to have some virtues but also major limitations because: 1) the zircon U-Pb age signature of many different sources in Mexico is similar and 2) zircon documents a limited number of sources because of variations in zircon fertility.

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