Sumba island has a great and unique position respect to the Sunda Banda archipelagoes, it is one of the biggest island on the East Nusa Tenggara region beside Flores and Timor. 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.
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 has a unique culture and their social life. Sumbanese are traditionally divided into three level of social life : (Raja/King) - Maramba, Customary Official - Kabihu, and Slaves - Ata. Sumbanese are living from farming, cattle breeding, rice-field farming and trading. Ones owns cattle will contribute to their social status such as if they had more cattle giving them a higher social status.
Most Sumbanese are Christian (Catholic and Protestant), however, and part of them are still strongly keep their native and original religion called Marapu. Most cultural objects are related to the Marapu religion such as the shape of traditional houses, ceremonies, or kings' graves and tombs.
The Customary houses designed in high-peaked roof to store the heirlooms and store. It is divided into male and female section, and generally surrounded by impressive megalithic tombs. Their famous ceremony are the wedding and funerals. where they usually sacrificed animals pigs, buffaloes, cattle, and horses.
The Megalithic tombs are made from the hard stone forming the megalithic shape. This covered by rectangle flat stone supported by four pillars about 1,5 meters high. The Megalithic tombs are actually located in the front of their houses
A primitive Sumbanese art objects strongly related with a social functions of Merapu belief. The carved stones and wood statues are representing the death, Merapu, and as medium for their contact. Metal ornaments and jewelry are usually for wedding ceremonies, and are related to the social status
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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