Publication Date:
2021-03-29
Description:
The Precambrian basement of southern
Madagascar was reworked at high-grade
metamorphic conditions during the East
African Orogen (EAO of Stern, 1994)
that formed during assembly of Gondwana
in late Neoproterozoic/early Paleozoic
times. At the end of the EAO,
Madagascar is generally thought to be
sandwiched between southern India and
eastern Africa. Constraints on its paleoposition
are often inferred from similarities
in structural features on now
dispersed continental fragments, in particular
high-strain zones. Major zones
with (sub)vertical foliation planes can
be traced over hundreds of kilometres
in southern Madagascar and
have been interpreted as major vertical
ductile shear zones (e.g. Windley et
al. 1994; Martelat, 1998). The NW–SE
trending Ranotsara Zone (dashed rectangle
in Fig. 1) is regarded as an intracrustal
mega strike-slip shear zone with
a sinistral sense of shear that formed at
the end of the Proterozoic (e.g. Nicollet,
1990; de Wit et al., 2001). A
large number of studies have used the
Ranotsara Zone to propose Gondwana
reconstructions. The Ranotsara Zone
has been correlated with various ductile
shear zones in southern India, e.g.
with the Bhavani Shear Zone or the Moyar
Shear Zone (Katz & Premoli, 1979), the Palghat-Cauvery Shear Zone (de
Wit et al., 1995), the Karur-Kamban-
Painavum-Trichur Shear Zone (de Wit
et al., 2001; Ghosh et al. 2004) or with
the Achankovil Shear Zone (Windley et
al., 1994; Martelat, 1998).
Within Madagascar, the Ranotsara
Zone has been correlated along strike
with the more N–S trending Bongolava
Zone in central-western Madagascar
(Hottin 1976), and the Bongolava-
Ranotsara Zone has been further traced
into the Surma Shear Zone (Windley et
al. 1994) and its along-strike continuation,
the Aswa Shear Zone in eastern
Africa (Müller 2000). Chetty (2003)
suggested that the Ranotsara Zone is not only a mega shear zone, but also
a terrane boundary separating a region
with Archean crust to the north from
a region with Neoproterozoic crust to
the south. Our remote sensing and field
studies of southern Madagascar indicate
that the Ranotsara Zone is neither a
major terrane boundary nor an intracrustal
mega strike-slip shear zone and
therefore can not be used as a ‘piercing
point’ in Gondwana reconstructions...
Description:
conference
Keywords:
551
;
VAE 700
;
VAE 500
;
VAE 850
;
VEQ 300
;
VKB 294
;
Bau der Erdkruste großer Regionen der Erde {Geologie}
;
Geotektonische Entwicklung der Erdkruste {Geologie}
;
Festländische Lineamente {Geologie}
;
Madagaskar {Geologie}
;
Metamorphe Komplexe, Afrika {Petrologie}
;
Madagaskar 〈Süd〉
;
Präkambrium
;
Kristallin
;
Scherzone
;
Korrelation
;
Gondwana
Language:
German
Type:
anthologyArticle
,
publishedVersion
Format:
application/pdf
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