Abstract

By taking advantage of the recent availability of a broadband seismic data set from Networks NR and BX covering the entire country of Botswana, we conduct a systematic receiver function investigation of the topography of the 410 and 660 km discontinuities beneath the incipient Okavango rift zone (ORZ) in northern Botswana and its adjacent Archean-Proterozoic tectonic provinces in southern Africa. Similar to a previous mantle transition zone (MTZ) discontinuity study using data from a 1-D profile traversing the ORZ, a normal MTZ thickness is observed in most parts of the study area. This is inconsistent with the existence of widespread positive thermal anomalies in the MTZ and further implies that active thermal upwelling from the lower mantle plays an insignificant role in the initiation of continental rifting. The results also suggest that cold temperature presumably associated with thick cratonic keels has indiscernible influence on the thermal structure of the MTZ. The expanded data set reveals several isolated areas of slight (~10 km or smaller) MTZ thinning. The largest of such areas has a NE-SW elongated shape and is mostly caused by relative deepening of the 410 km discontinuity rather than shallowing of the 660 km discontinuity. These characteristics are different from those expected for a typical mantle plume. We speculate that the thinner-than-normal MTZ may be induced by minor thermal upwelling associated with late Mesozoic-early Cenozoic lithospheric delamination, a recently proposed mechanism that might be responsible for the high elevation of southern Africa.

Department(s)

Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Botswana; incipient rifting; mantle transition zone; Okavango rift; receiver function

Time Period

Precambrian

International Standard Serial Number (ISSN)

2169-9313; 2169-9356

Document Type

Article - Journal

Document Version

Final Version

File Type

text

Language(s)

English

Rights

© 2020 American Geophysical Union, All rights reserved.

Publication Date

01 Sep 2020

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