Academic Commons

Articles

The character of the Moho and lower crust within Archean cratons and the tectonic implications

Abbott, Dallas Helen; Mooney, Walter D.; Van Tongeren, Jill A.

Undisturbed mid Archean crust (stabilized by 3.0–2.9 Ga) has several characteristics that distinguish it from post Archean crust. Undisturbed mid-Archean crust has a low proportion of internal seismic boundaries (as evidenced by converted phases in seismic receiver functions), lacks high seismic velocities in the lower crust and has a sharp, flat Moho. Most of the seismic data on mid-Archean crust comes from the undisturbed portions of the Kaapvaal and Zimbabwe (Tokwe segment) cratons. Around 67–74% of younger Archean crust (stabilized by 2.8–2.5 Ga) has a sharp, flat Moho. Much of the crust with a sharp, flat Moho also lacks strong internal seismic boundaries, but there is not a one to one correspondence. In cases where its age is known, basaltic lower crust in Archean terranes is often but not always the result of post Archean underplating. Undisturbed mid-Archean cratons are also characterized by lower crustal thicknesses (Archean median range = 32–39 km vs. post-Archean average = 41 km) and lower crustal seismic velocities. These observations are shown to be distinct from those observed in any modern-day tectonic environment. The data presented here are most consistent with a model in which Archean crust undergoes delamination of dense lithologies at the garnet-in isograd resulting in a flat, sharp Moho reflector and a thinner and more felsic-intermediate crust. We discuss the implications of this model for several outstanding paradoxes of Archean geology.

Files

  • thumnail for Abbott_etal_August31_2013_revised_c.docx Abbott_etal_August31_2013_revised_c.docx application/x-msword 9.97 MB Download File

Also Published In

More About This Work

Academic Units
Lamont-Doherty Earth Observatory
Publisher
Elsevier
Published Here
September 28, 2015
Academic Commons provides global access to research and scholarship produced at Columbia University, Barnard College, Teachers College, Union Theological Seminary and Jewish Theological Seminary. Academic Commons is managed by the Columbia University Libraries.