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Flores island is
one of the Lesser Sunda islands located in the
eastern part of Sumbawa and Komodo National
Park with an approximately area of 14,300km2.
This island is the largest island on the east
nusa tenggara region.
Flores island is one of the island on East
Nusa Tenggara province. It stretches between
the east longitudes of 118° and 125°, and
between the latitudes of 8° and 8,58° south
and extends over a length of 360kms, NW of
Australia. It thus belongs to the
South-eastern islands of the Indonesian
archipelago (Nusa Tenggara province) with,
in particular, the islands of Timor and
Sumba.
Flores becomes one of the biggest island on
the territory of East Nusa Tenggara or NTT
which comprises 566 islands, including many
smaller islands which are not in-habitated
and unnamed. The three main islands are
Flores, Sumba and Timor from which comes the
term 'Flobamor', which has been familiar as
one of the names of NTT.
From a geodynamical point of view, this
island, flanked to the North by the Flores
basin and to the South by the Savu basin, is
volcanically active with at least 13 live
volcanoes. It also corresponds to an area of
intense seismic activity (12th December 1992
earthquake, magnitude 7.5).
Stratigraphic and magmatic (geochronology,
geochemistry) analysis shows that Flores is
a "young" island, emerging probably in the
upper Oligocene, surely by mid-Miocene.
In detail we distinguish :
»» A probably Oligocene cycle - middle to
upper Miocene, characterised by :
»»- An E-W volcanic axis (Kiro Formation)
where 17 sampled lavas yield radiometric
ages between 16 Ma and 8.4 Ma (end
Burdigalian to mid Tortonian) and one lava
between 27.7 Ma and 25.7 Ma (terminal
Oligocene)
»»- Heterochronous lateral sedimentary and
volcano sedimentary deposits, with
excessively reworked microfaunas. We
distinguish nonetheless, from base to top,
the turbiditic tufacious mid-Miocene
Nangapanda Formation, the neritic to reef
limestone middle to upper Miocene Bari
Formation, the chalky tufacious (with
pumices) upper Miocene Laka Formation
»»- An essentially volcanic terminal
Miocene to Plio-Quaternary cycle where 13
samples including 2 granodiorites have
been dated radiometrically at 6.7 Ma to
1.2 Ma.
Geochemical analysis of the volcanic rocks
from the two cycles previously described
(major elements, trace elements, ...) shows
we are dealing with insular arc orogenic
magmatism linked to a subduction. Flores is,
with regards to this aspect, at the oriental
end of the Sonde complex with, from West to
East, the islands of Sumatra, Java, Bali,
Lombok and Sumbawa.
From a regional and chronological point of
view, volcanic activity starts on Flores
when that of Sumba, having begun in the
upper Cretaceous, ceases. Thus, during the
Oligocene, Sumba island leaves its active
arc position for the external forearc basin,
while Flores takes over the volcanic
activity.
During the Plio-Quaternary, the Australian
continental plate, coming from the South,
collides to the East with the Eurasian
plate, at the Timor. Nonetheless, premises
of collision are felt to the West, near the
area of study, although still in the
subduction system, with the net surrection
of Sumba and the development of a relatively
modest meridian compression facing Flores,
marked by a network of active conjugate
faults and, North of the island, the North
verging "Flores sea" thrust, absorbing a
part of generated shortening |
