Contrasting styles of Pre-Cenozoic and mid-Tertiary crustal evolution in northern Mexico: Evidence from deep crustal xenoliths from La Olivina

Journal Article · Tue Nov 10 04:00:00 EST 1992 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/92JB01493· OSTI ID:83357

Cameron, K L; Robinson, J V; Kuentz, D C; Collerson, K D ^[1]; Niemeyer, S ^[2]; Harmon, R S ^[3]; Bohlen, S R ^[4]

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1. Univ. of California, Santa Cruz, CA (United States)
2. Lawrence Livermore National Lab., CA (United States)
3. NERC Isotope Geosciences Lab., Keyworth (United Kingdom)
4. Geological Survey, Menlo Park, CA (United States)

The principal deep crustal rock types found at the La Olivina xenolith locality in southeastern Chihuahua, Mexico, are mafic granulites, paragneisses, and intermediate- to silicic-composition orthogneisses. These granulite facies xenoliths are interpreted in terms of two age groups, pre-Cenozoic and mid-Tertiary, based on previous ion probe dating of zircons from the xenoliths and on isotopic comparisons of the xenoliths to rocks of known age. The mafic granulites have Pb, Nd, and Sr isotopic compositions identical to those of Oligocene volcanic rocks from the La Olivina region. Compositionally, they are olivine-normative gabbroic cumulates, and they precipitated from two or more mid-Tertiary basalt to dacite or rhyolite assimilation/fractional crystallization series. Mineral assemblages in the xenoliths record pressures of {le} 7.2 kbar or depths of < 25 km. If these are the maximum pressures the rocks experienced and if the crust was > 35 km thick in Oligocene time as inferred from regional tectonic considerations, then the mafic granulites cannot be samples of basaltic magmas underplated near the crust-mantle boundary. The cumulate protoliths for the mafic granulites probably formed in magma chambers well above the Moho. The mafic granulites are plausibly ignimbrite fields of Mexico. Pre-Cenozoic and mid-Tertiary crustal evolution followed very different paths in northern Mexico. For example, Nd isotopic evidence for crustal recycling is much more evident in rocks associated with the Paleozoic convergence than in rocks produced during mid-Tertiary magmatism. Furthermore, mafic rocks are very rare in the pre-Cenozoic xenolith suite, but they dominate the mid-Tertiary one. The rarity of pre-Cenozoic mafic xenoliths suggests that Proterozoic and Paleozoic lower crust may have delaminated in response to crustal overthickening associated with the Ouachita collision event. 97 refs., 14 figs., 5 tabs.

• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 83357
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: B12 Vol. 97; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
AGE ESTIMATION
CENOZOIC ERA
EARTH CRUST
MEXICO
PLATE TECTONICS
ROCKS
TERTIARY PERIOD