dc.contributor.advisor |
Browne, P.R.L. |
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dc.contributor.author |
Suharno, 1962- |
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dc.date.accessioned |
2007-07-23T05:09:52Z |
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dc.date.available |
2007-07-23T05:09:52Z |
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dc.date.issued |
2003 |
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dc.identifier |
THESIS 04-011 |
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dc.identifier.citation |
Thesis (PhD--Geology)--University of Auckland, 2003 |
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dc.identifier.uri |
http://hdl.handle.net/2292/1045 |
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dc.description |
Full text is available to authenticated members of The University of Auckland only. |
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dc.description.abstract |
The Rendingan-Ulubelu-Waypanas (RUW) geothermal system, in the Tanggamus Regency, Lampung, Indonesia, is situated at the southern end of the Sumatra Fault Zone, The system is dominated by products of Quaternary and Tertiary volcanism (the Tanggamus volcanics) consisting mainly of andesitic lavas and pyroclastics. Thermal manifestations occur over a distance of more than 15 km within the Ulubelu graben and southwest of Mt. Waypanas. Hydrothermally altered rocks occur mostly around Pagaralam village in the middle of the study area. Six exploration wells (240 to 1200 m deep) encountered temperatures from 50 to 220 °C and penetrated rocks that mostly also occur at the surface, There are two major fault trends. Primary faults strike NW-SE, i.e. parallel to the Sumatra Fault Zone, and secondary faults strike NE-SW, associated with rectangular block movements along the Sumatra Fault Zone.
Microearthquake epicenters were determined using a random analysis method as velocity structures are not known. Gravity data were interpreted using 'iterative forward modeling' and deconvolution methods and gave consistent results. Ground magnetic data were upward continued to reduce noise and revealed the effects of deeper bodies. The Mt. Rendingan pyroclastics and andesite lavas, Mt. Kukusan basaltic andesite lavas and Mt. Kabawok pyroclastics are normally magnetised.
A microearthquake swarm in February 1993 was probably a result of fluid movement. Its epicenters were located within a fracture zone in the northern part of the area inferred from the gravity data which revealed the distribution and dimensions of subsurface lava and pyroclastic bodies. Magnetic interpretations suggest that hydrothermally demagnetised rocks are associated with the Rendingan manifestations in the north and the Ulubelu and Waypanas manifestations in the central and southern areas respectively. The magnetic interpretation, together with results from the mapping of surface manifestations, microearthquake study and previous Schlumberger resistivity surveys, show that the RUW geothermal system is a single unit, covering an area of about 150 km2.
Measured well temperatures and pressures, hydrothermal mineralogy, and the thermal characteristics of fluids trapped in inclusions indicate that in the central part of the system, perched meteoric water and steam condensate occurs above 250 m depth (450 m a.s.l.). Between about 250 m and 550 m depth (450 m and 150 m a.s.l.) the reservoir contains vapor with two phases occurring from about 600 m to 800 m depth (100 m a.s.l. to 100 m b.s.l.). Alkali chloride water with a near neutral pH and a low concentration of dissolved carbon dioxide occurs below 800 m depth (100 m b.s.l.). A pronounced temperature reversal in well UBLI indicates an inflow of cooler water at about 700 m depth; this is probably meteoric water descending a fault zone. Convection occurs below 800 m depth, consistent with the presence here of high permeability indicating minerals (i.e. adularia and albite). High temperature characteristic hydrothermal minerals (e.g. illite, wairakite, prehnite and epidote) in cuttings indicates the presence of water hotter than 210 °C, although these minerals may not represent the present thermal regime.
The dimensions of the RUW geothermal system have changed spatially and temporally during its life, but the sequence, chronology and directions of the changes are incompletely known. The mineralogical evidence, however, records some. The system has cooled since most hydrothermal alteration occurred. Alkali chloride waters close to boiling temperature and of neutral pH once discharged at the surface. Erosion allows some hydrothermal minerals (epidote, wairakite and prehnite) to occur closer to the surface than at the depths they formed within the geothermal reservoir during an early stage of activity. The piezometric surface likely dropped in response to caldera development. Such a lowering allowed steam condensate to occupy shallow levels in the reservoir and caused changes in surface activity so now discharging waters are clear with pHs between 2 and 4, and temperatures between 45 and 100 °C. |
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dc.language.iso |
en |
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dc.publisher |
ResearchSpace@Auckland |
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dc.relation.ispartof |
PhD Thesis - University of Auckland |
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dc.relation.isreferencedby |
UoA99119419514002091 |
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dc.rights |
Restricted Item. Available to authenticated members of The University of Auckland. |
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dc.rights |
Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. |
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dc.rights.uri |
https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm |
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dc.title |
Geophysical, geological and paleohydrological studies of the Rendingan-Ulubelu-Waypanas (RUW) geothermal system, Lampung, Indonesia |
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dc.type |
Thesis |
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thesis.degree.discipline |
Geology |
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thesis.degree.grantor |
The University of Auckland |
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thesis.degree.level |
Doctoral |
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thesis.degree.name |
PhD |
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dc.rights.holder |
Copyright: The author |
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dc.identifier.wikidata |
Q112859070 |
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