Ninth Regional Congress on Geology, Mineral and
Energy Resources of Southeast Asia- GEOSEA'98
17 - 19 August 1998 • Shangri-La Hotel, Kuala Lumpur,
Malaysia
Regional Tectonics Paper 18
The Triassic system of Thailand:
implication on geotectonic evolution of Southeast Asia
CHONGPAN CHONGLAKMANI
School of Geotechnology, Suranaree University of Technology
Nakhon Ratchasima,Thailand
Plate tectonic reconstructions of
Southeast Asia is quite complicated
as the areas are composed of several
terranes
accreted
by
complex
processes of subduction, collision and
transform faulting. The previous
proposed models are varied and
inconsistent because of disagreement
on suture identification, correlation of
various suture belts, and closure time
of remnant oceans. Parts of the
confusion are also from its complex
geology and misinterpretation of the
marine Triassic sediments. Detailed
studv of the Triassic stratigmphy
including its related volcanism,
magmatism
and
structural
development
is
critical
for
understanding
the
geotectonic
evolution and imposing constraint on
the proposed models.
Four main Triassic sedimentary
facies can be distinguished, viz. the
continental facies, the continental
platform facies, the marine intra-arc
facies. and the deep marine and
oceanic facies. The continental facies
characterized by alluvial fan, fluvial
and lacustrine subfacies (Huai Hin Lat
and
Kuchinarai
Formations)
represents the sediments of retroarc
foreland basins covering the areas of
northeastern Thailand (amalgamated
Indosinia and Sukhothai terranes). It
consists of sporadic fauna and flora in
the lacustrine sediments and as such
no
detailed
biostratigraphic
subdivision can be made. The
continental platform facies consists of
shallow marine shelf clastics and
carbonates. It is distributed in the
"Shan-Thai' (Lower Mae Moei and Si
Sawat Groups) and the Inthanon
(Phrao Limestone, Klaeng Limestone)
terranes. The marine intra-arc facies
(Lampang and Phrae Groups; Nam
Pat and Pong Nam Ron Formations) is
distributed
extensively
within
volcanoplutonic setting on the western
part
of
amalgamated
Sukhothai-Indosinia
terranes.
It
consists of shallow- water siliciclastic
and carbonate subfacies, the deeper
water turbidite subfacies. and its
associated rhyolitic and andesitic
volcanic subfacies. The intra-arc
marine facies contains prolific fauna.
Twelve
faunal
assemblages
of
bivalves and ammonoids can be
distinguished. They range in age from
Late Griesbachian to
Eariv
Norian.
These
faunal
assemblages form the basis for both
intrabasin
and
interbasin
correlation- in this region and adjacent
territories.
The deep marine and oceanic
facies consist of radiolarian chert.
pelagic limestone, turbidite and
basalts. They are distributed in two
zones. One extends from northcentral
to eastern and southern Thailand
forming isolated remnants of pelagic
overthrust
sheets
(Laem Ngob
Formation, Fang Chert) on the shallow
marine carbonates and siliciclastics of
the Inthanon terranes. The other
extends from northwestern, western
and southern Thailand (Mae Sariang
Group) representing linear belt lying
between "Shan-Thai" and Inthanon
terranes. Remnants of overthrust
sheets of oceanic sediments on the
platform carbonates and siliciclastics
of the "Shan-Thai" terrane are also
common' Thus two distinct Triassic
sutures can be distinguished in these
areas.
One
is
Chi
anarai-Chathaburi-Narathiwat
belt
which extends southward into the
Bentong-Raub belt of Malaysia. The
northward extension is into the
Changning-Menglion belt of Yunnan.
This main suture represents the wide
oceanic regime ransinz in ate form
Devonian to Late Triassic. The other
is Mae Sariang- Kanchanaburi belt
and it extends southward to western
Malaysia. This belt is complicated by
several younger linear fractures e.g.
Mae Ping, Three Pagodas. Ranong.
Khlong Marui etc.
The distribution of the Permian and
Triassic sequences and its
sedimentological development
indicate that Thailand and adjacent
territories is a complex orogenic
collage. The famous and well-known
Nan-Uttaradit-Sra Kaeo ophiolite belt
previously considered as representing
a Late Triassic suture is evidently a
Late Permian one. The major terrane
48
accretions are in the Late Triassic by
the processes of subduction to the
east. The juxtaposition of Triassic
deep marine and oceanic sediments
and shallow water platform sediments
on tile "Shan-Thai" and the Inthanon
terranes is the result of westward
overthrusting following the final
continental collision alone the two
defined suture zones.
The International Symposium and Field Workshop
GEODYNAMIC AND TECTONIC EVOLUTION OFYichang, People
CUINAAND RUATED GONDWANA CRUSTALFtAGINIENTS
10th- 20th,1999
-
October
Geodynamic Evolution of Loei
Area- Northeastern Thailand
Chongpan Chongla.kmani' and
Dietrich Helmcke'-
'School of Geotechnology, Institute of Engineering, Suranaree
University of Technology: III University Avenue, Muarrg District,
Nakhon Ratchasima 30000, Thailand
Institute of Geology and Dynamic of Lithosphere, University of
Gottingen, Goldshmidtstr.
3-37077, Gottingen, Germany
Based on the discovery of detrital chromian spinet in
sandstones
of
the
Permian
Nam
Duk
Formation
Chutakositkanon et al. (1997, 1999) suggest a new suture and
terrane boundary in north-central Thailand which they named
"Loei Suture" and which they trace from north of Loei through
Phetchabun to the region of Saraburi (Chutakositkanon et al.
1999, Fig.5).
We fully recognize the importance of the discovery of the chromian
spinet detritus in sandstones of the Nam Duk Formation since it confirms
the interpretation that the siliciclastic part of the Nam Duk Formation is
related to an evolving mountain belt caused by contractional deformation
during late Middle to Late Permian times (Helmcke & Kraikhong, 1982). But
we disagree with the,-interpretation that the influx of the chromian spinet is
due to the closure of a previously unknown suture which runs from the P .R.
of Laos via Loei in northeastern Thailand to the south. We still favour the
view that the evolution recorded in the sediments of the Nam Duk Formation
reflects the closure of the Nan- Uttaradit Suture (Chonglakmani, 1998,
Helmcke & Lindenberg, 1983). To substantiate our point of view we like to
reiterate and to reevaluate some previously published information by various
authors.
From Chiang Khan on the Mekong River to Wang Saphung
south of Loei an apparently important tectonic line can be drawn
which marks the western boundary of the region tentatively
described by Workman (1975) as a Hercynian Massif. Based on
fossil finds by Fontaine et al. (1981) and his own data,
Altermann et al. (1983) suggested that the main deformation in
this
region
can
be
dated
approximately
at
the
Devonian/Carboniferous boundary. The Carboniferous and
Permian strata are clearly much less deformed. The description
of the Loei area by Chairangsee et al_.(1990) does not highlight
the stratigraphic age of this main orogenic event. ,
But the data on the basement of the Khorat Basin (Kozar et
al., 1992) prove that the basin developed in a region affected by
an Early Carboniferous Variscan event, which is manifested in
an _ angular unconfonnity. The Variscan Unconformity divides
the Loei Group from the Saraburi Group (Mouret, 1994). Strata
of the Saraburi Group are distributed in most parts of the Khorat
Basin proving that the likely southern continuations of the Loei
ocean floor tholeiites and the Loei rhyolites dated by Intasopa &
Dunn (1994) could not have been eroded during Permian times.
Orogenic activity of this range in age (mainly Early
Carboniferous) is well known from regions in Vietnam (Fontaine
& Workman, 1978) and the ages reported by Intasopa & Dune
(1994) for the Loei ocean floor tholeiites and the Loei rhyolites
are not in conflict with the given interpretation. The ages
recorded in detrital muscovites of the Khorat red beds
mentioned by Heggemann (1994) support Devonian to
Carboniferous orogenic activity.
On the contrary to the above mentioned region. the Permian strata
of the Nam Duk Formation along the Lom Sak-Chum Phae highway
which contain the detrital chromian spinets recently reported by
Chutakositkanon et al. (1997, 1999), are severely affected by contra
ctional deformation. This deformation was first dated by Chonglakmani &
Sattayarak (1978). They discovered-a pronounced angular unconformity
between deformed Permian Nam Duk Formation and the Upper Triassic
Huai Hin Lat Formation approximately at km 34 of the above mentioned
highway (Chonglakmani & Sattayarak, 1978, Fig.15). In the following years
the stratigraphy and facies of the Nam Duk Formation were studied. The
youngest deformed fossiliferous strata found were dated by H.G.
Lindenberg (Fig.] 6, 17 in Helmcke & Kraikhong, 1982) and by R. Ingavat
(Fig.4 in Altermann et al., 1983) as Murgabian and very likely also part of
Midian. These data are now independently confirmed by Chutakositkanon
et al. (1997. 1999). Based on these data, the main orogenic event which
affected this region has been dated as approximately late Middle
Permian-early Late Permian. Only some K-Ar age determinations on the
fine mineral fractions (Ahrendt et al. 1993) support this interpretation. The
younger ages found are probably caused by younger thermal overprint or
the respectively younger intracontinental deformation.The pronounced
angular.unconformity (Chonglakmani & Sattayarak, 1978) between the
folded Permian strata and the Upper Triassic sediments cannot be
overlooked.
Paleocurrent indicators recorded in the siliciclastics are deposited by
turbidites and point to a sediment transport parallel to the axis of the basin
and gave therefore no conclugive result where to expect the source area.
If we discuss the possibility that the source area of the siliciclastics
deposited by turbidity currents of the Nam Duk Formaiton was to the east
as some authors suggested, we have to correlate the stratigraphic column
of the Nam Duk strata very carefully and in more detail.-Mouret (1994)
may serve as an example. He suggests that the sudden sand influx in the
Nam Duk Formation is caused by a major relative sea level fall which
occurred according to the data by Dawson et al. (1993) during the
Bolorian. This possible explanation cannot be substantiated by
stratigraphic results obtained in the Nam Duk Formation because they
indicate that the sudden influx of siliciclastics started not,earlier than the
late Kubergandian-Murghabian (R. Ingavat in Winkel et al., 1983, Fig.2).
However, the distribution of the Nan-Uttaradit ophiolite and the
geometry of the folds exposed in the Nam Duk strata suggest that the
subduction zone was located to the west. Therefore we expect the source
area of the newly discovered chromian spinel detritus in the more internal
zones of the rising mountain belt farther to the west. We regard the areas
to the east of the section along the highway Lom Sak-Chum Phae as
foreland areas and the possibility of major influx of detrital material during
the late Middle Permian from the foreland area seems to us quite unlikely.
If we accept the data by Intasopa & Dunn (1994) indicating a Loei
ocean, this ocean was already closed in pre-Permian times. If the Loei
suture `has a continuation to the south, then this continuation must be
searched for in the deformed basement of the Khorat Plateau. The
occurrence of the Paripteris flora (Laveine et al., 1993) in the Loei area
witnesses that this region was already fully integrated into the Northern
Continents in the Late Carboniferous time.
According to the data mentioned above we cannot accept the
interpretation of the "Loei suture" (exposed in the mountains east of Loei,
Intasopa & Dunn, 1994) as an important tectonic divide that runs from the
Mekong river via Loei towards south into the Phetchabun region. The
geodynamic evolution of the Phetchabun region is by all means
incompatible with the situation depicted in the area east of Loei.
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Geology, Mineral and Energy Resources of Southeast Asia. Abstracts.
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Chutakositkanon. V., Hisada, K., Ueno, K. & Charusiri, P., (1997) New
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tectonic evolution of central mainland Southeast Asia and the Loei
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The
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0
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