科研之友
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摘要
The postcollisional tectonic development of northeast Mozambique and subsequent cooling from high-temperature metamorphism is delineated with an extensive new set of U-Pb titanite, Ar-40/Ar-39 hornblende, and Ar-40/Ar-39 mica analyses. The complex data suggest a polyphase metamorphic history from the late Neoproterozoic to the Ordovician within the East African-Antarctic Orogen (EAAO), with marked differences between the major constituent blocks. In all the data sets, samples from the basement south of the Lurio Belt show generally younger ages than those from the north, resulting from a late metamorphic event and slow cooling between ca. 520 and 440 Ma. The ages north and south of the Lurio Belt are consistently offset by ca. 30-70 Ma, a difference that is maintained and even appears to increase during cooling from very high temperatures to ca. 350 degrees C. Based on the first-order assumption that all the ages are cooling ages, cooling rates in the south are estimated at ca. 7 degrees-8 degrees C/Ma, while those north of the Lurio Belt are faster at ca. 16 degrees C/Ma. The data are consistent with previous geochronological, petrographic, and field data and suggest a late high-temperature/low-pressure metamorphic event that affected only the basement rocks south of the Lurio Belt and portions of the latter. This late metamorphism and subsequent delayed, slower cooling agree well with a model of elevated heat flow following lithosphere delamination in the southern part of the orogen, which also explains the observed widespread granitoid magmatism, migmatization, and renewed deformation in the southern basement.
- 出版日期2012-9
