Growth and collapse of a deeply eroded orogen : insights from structural, geophysical, and geochronological constraints on the Pan-African evolution of NE Mozambique
This paper presents results of a large multidiciplinary
geological mapping project in NE Mozambique, with a
focus on the structural evolution of this part of the East
African Orogen (EAO). It integrates field structural
studies with geophysical interpretations and presents
new geochronological data. The tectonic architecture
of NE Mozambique can be subdivided into five
megatectonic units on the basis of lithology, structure
and geochronology: unit 1, Paleoproterozoic Ponta
Messuli Complex in the extreme NW corner of NE
Mozambique, which represents the local NW foreland
to the EAO; unit 2, a collage of Mesoproterozoic
metamorphic complexes, which forms the basement to
unit 3, a stack of Neoproterozoic, NW directed
imbricate thrust nappes named here the ‘‘Cabo
Delgado Nappe Complex’’ (CDNC); unit 4, restricted
Neoproterozoic metasedimentary basins; and unit 5,
two exotic Neoproterozoic granulite me´ lange
complexes. The units were assembled during a long
and complex history of NWdirected shortening, which
commenced with nappe stacking and emplacement of
the CDNC over the Mesoproterozoic basement
terranes toward the NW foreland. It is proposed that
the CDNC and the Eastern Granulites farther north in
Tanzania are remnants of Neoproterozoic volcanic arcs
and microcontinents formed ‘‘outboard’’ of the
Mesoproterozoic continent after 596 ± 11 Ma. Field
and potential field geophysical data show that the
nappes were folded by regional-scale NE–SW
trending folds that formed in response to a later stage
of the same shortening episode and this episode gave
rise to the Lurio Belt, a prominent structural feature of
northern Mozambique and a key element (often as
suture zone) in many Gondwana reconstructions. The
Lurio Belt is here interpreted as a structure generated
during folding of the CDNC during later stages of the
progressive shortening event. It is, however, a
repeatedly reactivated shear zone, probably at the
site of an older (Mesoproterozoic?) discontinuity, with
an intense pure shear deformation history. It is cored
by strongly attenuated lenses of a granulitic tectonic
me´lange, the Ocua Complex (megatectonic unit 5) and
is intruded by Late Pan-African granitoids of the
Malema Suite. The compressional phase of the orogen
was postdated by NW–SE directed extension. New
U-Pb zircon and monazite dates show that extension
was initiated at circa 540 Ma in the eastern Lurio
Belt. It is argued that extension was the result of a
major episode of orogenic collapse of the EAO,
initiated by gravitational instabilities resulting from
crustal thickening during the shortening phase
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