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Sumba
island covers an area of 11,150
square km which is now populated by about 350,000 people.
Generally the climate similar to other part of Indonesia where a
dry season (May to November), and a rainy season (December to
April).
The island of Sumba is well known of its
sandlewood,
horses, impressive megalithic tombs, typical hand woven textile
("ikat"), and still untouched beautiful beaches. There
are two entering point in to Sumba island from anywhere in the
Lesser Waingapu & Waikabubak (Tambolaka). These are the people
could enter Sumba for either by flight or boat.
Sumba
Island has a unique position with respect to the
Sunda-Banda arc as it represents an isolated
sliver of probable continental crust to the south
of active volcanic islands (Sumbawa, Flores )
within the forearc basin (Fig.1). It is situated
to the north of passage from the Java Trench (subduction
front) to the Timor Through (collision front). It
does not show still the effects of strong
compression in contrast to islands of the outer
arc system (Savu, Roti, Timor), while the magmatic
units make up a substantial part of the Late
Cretaceous to Paleogene stratigraphy.
Bathymetrically,
Sumba stands out as a ridge that separates the
Savu forearc basin (> 3000 m depth) in the east
and the Lombok forearc basin (> 4000 m depth)
in the west. Seismic refraction studies show
(Barber et al., 1981) that it is made up of 24 km
thick continental crust (Chamalaun et al., 1981).
Based on the results of tectonic studies helped by
paleomagnetism and geochemistry, several workers
considered Sumba as a microcontinent or a
continental fragment (Hamilton, 1979 ; Chamalaun
and Sunata, 1982 ; Wensink, 1994, 1997 ; Vroon et
al., 1996 ; Soeria-Atmadja et al., 1998 ).
Three
main geodynamic models for Sumba have been reviewed by
Chamalaun et al. (1982) and Wensink (1994) as follows : (i)
Sumba was originally a part of the Australian Continent
which was detached afterwards when the Wharton basin was
formed, drifted northwards and subsequently trapped behind
the eastern Java Trench (Audley-Charles, 1975 ; Otofuji et
al., 1981), (ii) Sumba was once part of Sundaland which was
drifted southwards during the opening of the Flores Basin
(Hamilton,1979, Von der Borch et al., 1983 ; Rangin et al.,
1990) and (iii) Sumba was either a microcontinent or part of
a larger continent within the Tethys, which later was
fragmented (Chamalaun and Sunata, 1982).
Three
distinct calc-alkaline magmatic episodes have been recorded
during Cretaceous - Paleogene, all of them characterized by
nearly similar rock assemblages (i.e pyroclastic rocks,
basaltic - andesitic lava flows and granodioritic
intrusions). They are respectively (i) the Santonian -
Campanian episode (86-77 Ma) represented by volcanic and
plutonic rock exposures in the Masu Complex from Eastern
Sumba, (ii) the Maastrichtian-Thanetian episode (71-56 Ma)
represented by the volcanic and plutonic units of Sendikari
Bay, Tengairi Bay and the Tanadaro Complex in Central Sumba
and finally (iii) the Lutetian - Rupelian episode (42-31 Ma)
of which the products are exposed at Lamboya and Jawila in
western part of Sumba. No evidence of Neogene magmatic
activity has been recorded so far.
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