کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6434107 | 1636778 | 2013 | 16 صفحه PDF | دانلود رایگان |
- The Moho characteristics of cratons are related to their stabilization age.
- Nearly 100% of undisturbed crust stabilized by 2.9-3.0Â Ga has a sharp, flat Moho.
- Around 67-74% of crust stabilized by 2.8-2.5Â Ga has a sharp, flat Moho.
- Crust with a sharp, flat Moho often lacks strong internal seismic boundaries.
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.
Journal: Tectonophysics - Volume 609, 8 December 2013, Pages 690-705