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| Titel |
Differential decay of the East-African Antarctic Orogen : an integrated examination of Northeastern Mozambique |
| VerfasserIn |
K. Ueda, J. Jacobs, B. Emmel, R. J. Thomas, R. Matola |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028015
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| Zusammenfassung |
| In Northeastern Mozambique, the late Proterozoic - early Paleozoic East African-Antarctic
Orogen can be subdivided into two major blocks that exhibit some relevant differences. The
line of divide is represented by the Lurio Belt, a kinematically poorly constrained
shear zone that also marks the conceptual northern limit of frequent late-tectonic
granitoid intrusions. Moreover, far-travelled granulite-facies nappes cover a much
larger area north of this belt (Viola et. al, 2008), giving rise to the assumption of
different exhumation and present exposure levels. U/Pb data from previous surveys
(e.g., Norconsult consortium, 2007) show coeval high-grade metamorphism in the
whole region between c. 610 - 550 Ma, while the block south of the Lurio Belt also
shows continuing metamorphism until c. 490 Ma that can be related to extension.
Geothermobarometry for samples from within the Lurio Belt (Engvik et. al, 2007) indicates
rapid exhumation after high-pressure granulite facies metamorphism and is consistant
with the assumption of long tectonic activity. A possible model for the outlined
pattern is the delamination of the orogenic root only in the southern part, followed by
rapid mechanical thinning as well as by isostatic accommodation along the Lurio
Belt.
A valuable marker was identified in the metasedimentary Mecuburi group that overlies the
southern basement. U/Pb analysis of detrital zircons have yielded a maximum deposition age
of c. 600 Ma, while metamorphism is recorded until c. 505 Ma. Investigations of
the relationship between metasediments and older basement show that the basal
contact is a fairly preserved depositional contact, allowing to suppose a conjoint
post-depositional evolution. It is notable that the timing of deposition shortly follows the
onset of the main, widespread high-grade metamorphism. Relatively high but variable
degrees of migmatisation in the Mecuburi Group require a phase of burial from
surface to deep levels after 600 Ma, followed by rapid exhumation latest at c. 505
Ma. Broad structural coherence between the Mecuburi group and the underlying
Mesoproterozoic basement of the Nampula Complex shows that the fabric of the
latter mainly records late Proterozoic to early Paleozoic deformation, potentially
obliterating any older imprints. The coherence rather suggests that Mesoproterozoic
units were not completely autochtonous, but significantly involved in continental
collision during Gondwana assembly. Equivalent patterns of spaced, ductile and
melt-bearing shear-zones from both the Mecuburi Group and the Nampula Complex
furthermore suggest that extension in the southern block occurred temporally close to
migmatisation, which in turn might have been promoted by heat flux increase at lower
crustal levels as a result of delamination. Differential cooling of the northern and
southern block is well evident in low-grade thermochronology. Apatite fission-track
ages are consistently younger south of the Lurio Belt than they are to the north.
However, this might rather reflect reactivation coeval with the late Jurassic - Early
Cretaceous opening of the Mozambique basin along the similarly oriented passive
margin than a continuation of accommodation movement following early Paleozoic
delamination.
Engvik, A., Tveten, E., Bingen, B, Viola, G, Erambert, M., Feito, P., De Azavedo, S., 2007. P-T-t evolution and
textural evidence for decompression of Pan-African high-pressure granulites, Lurio Belt, north-eastern
Mozambique. J.metamorphic Geol 25, 935-952.
Norconsult consortium, 2007. Mineral resources management capacity building project, Republic of Mozambique;
component 2: Geological infrastructure development project, Geological Mapping Lot 1; Sheet explanation:
32 sheets; scale 1:250’000, 778 pp. + annexes. Credit No. NDF335, Report No. B6.f., National Directorate
of Geology, Republic of Mozambique.
Viola, G., Henderson, I.H.C., Bingen, B., Thomas, R.J., Smethurst, M.A., de Azavedo, S., in press. Growth and
collapse of a deeply eroded orogen : Insights from structural, geophysical, and geochronological constraints
on the Pan-African evolution of NE Mozambique. Tectonics 27, TC5009, doi:10.1029/2008TC002284. |
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