Geochemistry of Lithic and Single-Crystal Inclusions in Basalt and a Characterization of the Upper Mantle-Lower Crust in the Engle Basin, Rio Grande Rift, New Mexico.

  1. Robert E. Riecker
  1. Richard G. Warren1,
  2. Albert M. Kudo2 and
  3. Klaus Keil2

Published Online: 21 MAR 2013

DOI: 10.1029/SP014p0393

Rio Grande Rift: Tectonics and Magmatism

Rio Grande Rift: Tectonics and Magmatism

How to Cite

Warren, R. G., Kudo, A. M. and Keil, K. (1979) Geochemistry of Lithic and Single-Crystal Inclusions in Basalt and a Characterization of the Upper Mantle-Lower Crust in the Engle Basin, Rio Grande Rift, New Mexico., in Rio Grande Rift: Tectonics and Magmatism (ed R. E. Riecker), American Geophysical Union, Washington, D. C.. doi: 10.1029/SP014p0393

Author Information

  1. 1

    Geochemical Applications (G-5) Group, Los Alamos Scientific Laboratory, Los Alamos, New Mexico 87545

  2. 2

    Department of Geology, University of New Mexico, Albuquerque, New Mexico 87131

Publication History

  1. Published Online: 21 MAR 2013
  2. Published Print: 1 JAN 1979

ISBN Information

Print ISBN: 9780875902142

Online ISBN: 9781118664988

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Keywords:

  • Basaltic volcanism;
  • Host basalts;
  • Lithic and single-crystal inclusions;
  • Petrography;
  • Upper mantle and lower crust

Summary

A suite of lithic and single-crystal inclusions occur within nepheline-normative, alkali-rich basanites in the eastern Engle basin of the southern Rio Grande rift. The inclusion suite includes lherzolites, pyroxenites, two-pyroxene granulites, and megacrysts of clinopyroxene, olivine, anorthoclase, and spinel. No inclusions are cognate to their basalt hosts; rather they form a petrographic sequence derived from depth. A plot of equilibrium temperatures of these inclusions from coexisting pyroxene compositions versus estimated limits of pressure stability for the observed phase assemblages was fitted to published steady-state conductive heat flow curves for the southern Rio Grande rift to yield a best-fit geotherm of 30°C/km and a heat flow of 2.3 HFU. We speculate the following positions of each inclusion type at depth: granulite 29 to 31 km, pyroxenite 32 to 36 km, megacrysts of olivine, clinopyroxene and pleonaste 32 to 36 km, and lherzolite 36 to >42 km depth. The position of the anorthoclase megacrysts is unknown but thought to be <29 km depth. The Mohorovicic discontinuity corresponds to a marked density increase from granulites to pyroxenites. The presence of similar inclusions beneath the rift, and within a rift-associated graben of the Mogollon volcanic field suggests that a similar petrologic sequence of pyroxenite, megacrysts, and granulite may be a characteristic subcrustal feature of the Rio Grande rift and possibly of the Mogollon volcanic field. Due to the high heat flow, lower pressure phases will be most important in fractionation of the basalts generated within the southern Rio Grande rift.