08 December 2009

Structures: Folds and Faults in West Kalimantan, Borneo

In West Kalirnantan, the E-W trending fold system is exemplified by the large synclinal structure that involves the Ketungau Basin sediments. It is a symmetrical fold with dips on both flanks around 30 degree. The situation is quite different in the Melawi Basin to the south, were the folding is asymmetric, with a steeply dipping north limb, and the dips decrease to the south. The fold axes extend NWSE. Similar trending folds have also affected Triassic to Cretaceous sedimentary formations to the west of the Melawi Basin.

In the northern part of Kalimantan, a number of thrust and normal faults have been identified trending E-W. The thrust faults may be associated with Late Cretaceous melange formation and were rejuvanated in the Early Miocene. The normal faults were formed after Oligocene time, probably in the Early Miocene.

There are north-trending faults in West Kalimantan, whose nature is ill defined. In Central Jawa, younger faults intersect the Plio-Pleistocene fold axes nearly perpendicularly.

A set of faults in West Kalimantan trends NE-SW, cutting the Cretaceous sediments and Boyan Melange. They are thought to be strikeslip.

20 November 2009

Diamond in Kalimantan, Borneo, Indonesia

Like gold, diamonds have been known to exist in Kalimantan since the 18th Century. Diamonds have been obtained by panning in the Lardak and Kapuas rivers (Sanggau Regency) since 1836. The largest diamond ever found weighs some 6 carats. All the Kalimantan diamonds are derived from alluvial deposits, and the ultimate source rocks have never been established.

The diamond-bearing alluvial sediments are clastic rocks of 2 to 12 meter thickness, whose clasts are of quartz (yellow to pink color), hornblende, corundum, schist, slate and igneous rock fragments, in addition to magnetite, mica and gold. The slate and schist clasts are known to be pre-Permian. The other rock clasts are Tertiary in age. It was formerly considered that the Pamali Breccia of Southeast Kalimantan represents the primary source of the diamonds. However, Bergman et al. (1987) have shown that this diamondiferous formation is a sedimentary conglomerate of local Bobaris ophiolite provenance.

In 1984 Anaconda Indonesia Inc., together with PT Aneka Tambang, carried out explorations over 4,882,500 hectares of West Kalimantan, under K.P. Number DU 574 by PT Aneka Tambang. Samples were collected from the Landak and Sekayam rivers and examined in Denver, but none showed a positive indication of primary diamond. Only one sample location contained diamonds.

Diamonds are found only in streams that drain the Plateau Sandstone. There is also a correlation between diamonds in the neighboring stream and corundum-bearing rocks occurring as rounded pebbles in the basal conglomerate of the Plateau Sandstone. Paleo-current analyses were made of the Plateau Sandstone, which generally indicated a provenance from the east, but such studies were unsuccessful in locating the primary source of the diamonds. 8 Ma old minette dykes occur at Linhaisai in the northern Barito Province, but they are not considered to be the source of the alluvial diamonds, and the search for the lamproite or kimberlite sources must continue in Central Kalimantan or adjacent Southeast Asia.

It is also possible that at least some of the diamonds were derived from the olivine basalts of Central Kalimantan, and from ophiolites occurring in the Suruk river area in West Kalimantan. The diamonds found in the Tertiary sediments and present day rivers of Kalimantan, Thailand, Burma and Sumatra are characteristically similar. The present geographical locations of the diamond deposits are likely to have resulted from multiple cycles of erosion and sedimentation.

13 November 2009

Geology of Sulawesi Island, Indonesia

Geologically, Sulawesi Island and its surrounding area is a complex region. The complexity was caused by con­vergence between three lithospheric plates: the northward-moving Australian plate, the west­ward-moving Pacific plate, and the south-southeast-moving Eurasia plate. The Makassar Strait, which sepa­rates the Sunda Platform (part of the Eurasia Plate) from the South Arm and Central Su­lawesi, formed by sea-floor spreading originat­ing in the Miocene. North of the island is the North Sulawesi Trench formed by the subduc­tion of oceanic crust from the Sulawesi Sea. To the southeast convergence has occurred between the Southeast Arm and the northern part of the Banda Sea along the Tolo Thrust. Both major structures (the North Su­lawesi Trench and Tolo Thrust) are linked by the Palu-Koro-Matano Fault system.

Based on lithologic association and tectonic development, Sulawesi and its surrounding is­lands are divided into 5 tectonic provinces:
  • The Tertiary Western Sulawesi Vol­canic Arc
  • Quarternary Minahasa-Sangihe Volcanic Arc
  • Cretaceous-Paleogene Cen­tral Sulawesi Metamorphic belt
  • Cretaceous Eastern Sulawesi Ophiolite Belt and its associ­ated pelagic sedimentary covers
  • Paleo­zoic Banda Micro-continental fragments derived from the Australian continent
The contacts between those provinces are faults.

10 November 2009

Coal Carbonization Process

Coal carbonization include the reform process with the state of anaerobic (without oxygen) at low temperatures 459-700 Celsius and at high temperatures produces 900-12000 Celsius and porous solid materials which are residues carbonization process called coke or charcoal and volatile gases (Tsai, 1980 ).

In general, the solid material consists of semi-coke is formed from the coal that is not experiencing maturation and coke derived from coal that has undergone maturation.

During the carbonization of coal through several stages of physical and chemical changes. Physical changes of softening, the flow of material, and hardening of the merger, while the chemical changes of cracking polymerization and evaporation. The factors above may affect the quality of coal in terms of petrography composition.

Coal type is characterized by variation maceral and mineral content in coal (Cook, 1975; Stach, 1985). The formation of this type are controlled by various factors, including the spatial and temporal variation of the ancient climate, geological age, tectonic processes, the ecological conditions of sedimentation environment and the coal-forming plants in its community. Type of coal occurs in phase biochemistry.

Rank or rank of coal is the maturity level of organic material that starts from the lowest level of lignite, sub-bituminous, bituminous, semi-anthracite, anthracite to meta-anthracite. Carbonization stage is dominated by geochemical processes, so that the most important factor in the formation of coal rank is the temperature, pressure and time.

Observations by petrography in coal basically covers two things namely the identification maceral abundance and composition of maceral vitrinite, inertinite and liptinite. Coal with high inertinite composition and low vitrinite will tend to produce low-power one while if vitrinite high and low inertinite it will have the moderate-power, but coal with high strength obtained when the composition shows inertinite content and vitrinite was balanced. Strength of coal can also affect the rank of coal. Through petrography, coal rank can be known through its vitrinite reflectance value. The best range of vitrinite reflectance value is 1.2-1.4. The coal with good vitrinite value obviously can produce coal with high strength quality.

Regional Tectonic of Timor Island, Indonesia

Arc-continent collision between Eastern Sunda Arc (Banda Arc) and Southwest Australia continent formed the southern boundary of the tectonic elements. This collision zone is part of the evolutionary stages of young or early and more to resemble aspects of normal trench-arc system.

In the eastern part of Sumba Island, Indian Ocean crust has a complete experience of intense subduction and Australia now has been raised above the Banda Arc due this. To the west of the collision zone, Sunda Arc moved to the edge of continental Southeast Asia which make up one of the classic collision system features, in which the crust of the Indian Ocean-Australian (about >150 Ma) forces down along the Sunda trench, given that the Indian Ocean Plate, Australia moved northward relative to the Eurasian Plate with a velocity of about 7.5 cm/year (according to Curray, 1989). The island of Java, Bali, Lombok and Sumbawa expected forming this through the formation of the volcanic arc on the southern edge of Sundaland that initially passive. Sumba represents the bedrock that uplifted front of the arc and was trapped in front of the arc current basin (Reed et al., 1986). Some evidence suggests that the development of Sumba geology can be parallel correlated with Doang Borderland located at the end of the edge of the Sunda Shield (Wytze et al., 1991). However, Lombok front arc basin lies to the west of Sumba marked by the opening structures on certain stratigraphy horizon.

Transition zone Sunda-Banda arc is clearly recorded the existence of two straight thrust fault zone, both located in the front of the arc itself. One is represented by Savu fault (thrust type), and the other were behind the arc is called Flores back arc fault (back-arc thrust type). Both systems are connected (Silver and Reed, 1987). Area behind the arc shows laterally discontinuous zones of the back arc fault structures and produced younger accretionary wedges.

Timor Island is located outside the non-volcanic arc islands of Indonesia, between the Australia plates that move toward the north and the outer Banda arc as part of the Eurasian plate. The Timor Island is made by deformation of the northern Australia plate which had being thrust faulted, especially the southern part around Timor Trough.

The Non-volcanic arcs consist of the underwater ridge of Java Trench, Timor Island, Tanimbar, Kei and Seram up to the east. During the Tertiary age, continuous trench system was fairly active in northwestern Sumatra, Java Trench, the Lesser Sunda Islands, Timor, Tanimbar, Kei and Seram, accompanied by active volcanic subduction that can be found on the West Coast of Sumatra, South Coast of Java, Lesser Sunda Islands (Katili, 1990).

Component of plate tectonics collision involved in this, namely the Asian plate lithosphere that appear shaped by the continental crust (Sunda Craton), sea-marginal (marginal sea) of the Banda Sea, and Australian-Irian lithosphere plate (Gondwana), made by the oceanic crust Indian and Australian continental crust include elements from the island of New Guinea, Buru, Obi and others.

Tectonic evolution that began at the age of the Upper End of Perm, Middle Jurassic, Early Cretaceous until the Late Cretaceous and Neogene basin formation resulting from Paleozoic basin which had trending oriented northwest-southeast direction which then formed again (overprinting) by later Mesozoic basin of northeast-southwest trending direction. Meanwhile, the sinistral transform fault was rejuvenated by Neogene normal fault were related both sides (N. Sitompul, S, Wijanto, J., Purnomo, 1993).

03 November 2009

Shape, Structure, and Volcanism Activity of Gunung Kelimutu (Kelimutu Mount), Flores Island, Indonesia

Shape and Structure 

This mountain is located in the Central Flores Island, Endeh District, also called Mount Geli or Mutu. It is at 1640 m above sea level. This mountain has 3 craters are: Tiwu Ata Mbupu, Tiwu Nua Muri Kooh Fai, Tiwu Ata Polo. Mount Kelimutu is belong to strato type volcano.

According to Neuman van Padang (1951) northeast caldera named Sukaria there is a compound volcano with a slope that can develop long straight lineament to the east. Granite buried here about 3 km to the north Kelido area and 2 km to the south of the Kelibara area which is height 1630 m.

Peak which extends 2 km to the west northwest direction, east southeast, and contains 3 pieces craters that all contain a lake.

Ata Mbupu Tiwu, northwest of the valley has a very steep wall of a crater with size of 850x700m rising in the east of an older crater with diameters of 600 m.

Double crater Nua Tiwu Kooh Fai and Tiwu Ata Polo surrounded by a dike ring with “C” shape. It is irregular with a diameter of 1200 m identified by Kemmerling (1929). In August 1932 Stehn (1940) found a large area of collapse sink outside the crater slopes of Tiwu Ata Mbupu and Tiwu Nua Muri Kooh Fai. Because of its embankment, the circle “C” shape is not present.

Kemmerling (1929) analyzed the rocks as follows:

1. A bomb from hyperstene alkaline andesite or basalt.
2. Obsidian.
3. Andesite lava flow or basalt hyperstene
4. Inclusion of the burned clay.

Tabel of Kelimutu Mount Details:

The size is based on Kemmerling (1929). The water color change from year to year, may be directly related to the magmatic activities. The color pattern is also caused by some kind of algae (Niloperbowo, 1972).

Eruption activity

According to old residents in the surrounding volcanoes, the three lakes have been there throughout history. Only the crater wall between the two eastern lakes was much wider and had the same height as the other wall. The eruption occurred between 1860-1870.

• 1938, in May-June occurred activities in Tiwu Nua Muri Kooh Fai. Neuman van Padang (1951) identify as phreatic eruption.
• 1967, in the September, water color of Lake Tiwu Nua Muri Kooh Fai changed from green to white. This is caused because more sulfur is deposited by fumarole uplifting or increasing its activity.
• 1968, Kusumadinata reported the eruption happened in water Tiwu Nua Muri Kooh Fai on June 3. This phenomenon is preceded by a hissing sound followed by a spray of blackish brown water in the west of the lake. Spray occurs in more than one place and reach the high altitude about 10 m.
• 1973, according Suryo there is no significant change, only the water of lake Tiwu Ata Mbupu look black.