Дисертації з теми "Geology of Indonesia"

Galunggung volcano is located in West Java, Indonesia and covers an area about 275 km2. The volcano is very active and the slopes are highly populated (over 1.5 million people). There is therefore always the threat of volcanic disaster. This study investigates the character of past Galunggung volcanic activity and assesses likely future activity in order to advise on volcanic hazard and risk. The approach involves a study of stratigraphy, mineralogy and petrology of the Galunggung rocks, and the presentation of volcanic hazard zonation maps. Galunggung volcanic rocks are included within the Galunggung Group and can be divided into Old Galunggung Formation, Tasikmalaya Formation and Cibanjaran Formation. The first formation represents rocks of Old Galunggung stratovolcano (50,000 - 10,000 yrs. BP ?), the second formation covers rocks erupted during caldera formation (4200 ± 150 yrs. BP) and the third one comprises rocks erupted in 1822, 1894, 1918 and 1982-83. The Old Galunggung Formation consists mainly of pyroclastic flow, pyroclastic fall and lahar deposits and lava flows which have a total rock volume of about 56.5 km3. This activity ended with the intrusion of a cryptodome under the crater. The cryptodome blocked the existing vent and subsequent activity moved to the weakest part of the old cone to the ESE, resulting in the caldera forming-event. This destructive eruption formed a horseshoe-shaped caldera and ejected more than 20 km3 of material comprising debris avalanche, pyroclastic flow, pyroclastic fall, pyroclastic surge and lahar deposits. Historic eruptions separated by relatively long dormant periods produced less voluminous (< 0.4 km3) volcanic deposits. Galunggung volcanic rocks are basalt (49 - 53 % SiO2) to basaltic andesite (53 - 57 % SiO2) having porphyritic textures with medium sized phenocrysts (15 - 40 %), mainly plagioclase (av. 18 %) and clinopyroxene (1.6 %). Olivine is observed in basic rocks, whereas orthopyroxene and magnetite are present in the most evolved rocks. Amphibole is common in pyroclastic deposits and gabbro clasts ejected during caldera formation. On the basis of Mg contents, Galunggung rocks are divided into: 1. high-Mg basalt (12.5 10 % MgO) , 2. "Transitional" high-Mg basalt (9 - 6.5 % MgO) , 3. low-Mg basalt (< 6 % MgO), 4. high-Mg basaltic andesite (7 - 6 % MgO) and 5. low-Mg basaltic andesite (< 5 % MgO). The high-Mg basalts are subdivided into low-K high-Mg basalt (<0.4 % K2O) and medium-K high-Mg basalt (0.6 % K2O). Alkali and incompatible elements increase whereas Mg, Fe, Ca and compatible trace elements decrease with increasing SiO2. The high-Mg basalts are the most primitive Galunggung rocks with highest Mg# = 75 - 69, Ni (up to 193 ppm), and Cr (711 ppm) but lowest incompatible elements. The "primitiveness" of the basalts is also reflected by their 230Th/232Th ratio (= 0.68) which is one of the lowest ratios yet found. The Galunggung high-Mg basalts are considered to represent liquid compositions which have been derived from upper mantle peridotites. The low-K high-Mg basalt originate from spinel-peridotite by 15 % melting at about 50 km depth, and the medium-K high-Mg basalt from plagioclase-peridotite by 25 - 40 % melting at about 30 km depth. These primitive magmas probably rose rapidly to the surface as mantle "diapirs". During Old Galunggung volcanic activity, low-K high-Mg basalt magma moved upward diapirically and formed a magma chamber in the crust at a depth of about 10 km. Fractionation of this magma formed low-Mg basalts and basaltic andesites. This activity ended when a medium-K high-Mg basalt intruded as a cryptodome. Another low-K high-Mg basalt magma migrated into the crust and fractionated to produce low-Mg basalt basaltic andesite. Gas was trapped and high water pressure was attained; and amphibole gabbro solidified in the roof of the magma body. These rocks were erupted during the Galunggung caldera forming-event. In 1982-83, a new generation of low-K high-Mg basalt magma was erupted. Fractionation in a conduit system changed compositions at the top part but not significantly in the lower part of the magma body. During the eruptive sequence firstly low-Mg basaltic andesite, then high-Mg basaltic andesite, "transitional" high-Mg basalt, and finally the low-K high-Mg basalt were erupted. Rhyolite pumice erupted in September 1982 is considered to be a product of melting of Miocene dacite by the high temperature (1300ºC) Galunggung high-Mg basalt magma. Galunggung eruptions vary from non-violent effusive to destructive explosive events. These create hazards which are divided into four levels. First degree hazards are long-term and require further study. In this thesis hazard maps are presented for second, third and fourth degree hazards. Evacuation routes are suggested away from the volcano as all arrangements must be planned well in advance of an actual event.

Mapping and sediment sampling in reefs of the Pulau Seribu group (southwest Java Sea) shows the existence of ten physiographic zones and subzones represented by seven lithofacies. Reefs in the northern part of the archipelago are smaller, more closely spaced and morphologically sim pler than those in the south. This pattern is attributed to differences in subsidence rate. A th reedimensional model is proposed for the evo lution of these reefs but borehole data are requi red to test this model. Miocene limestones are described in detail from hydrocarbon reservoirs in the Batu Raja Formation of the same area. Brief comparisons a re made with surface outcrops of approximately coeval carbonate developments. The lithofacies developed within these limestones reflect variations in hydrodynam ic regime and basement topography . Ele\le.n diagenetic processes affected the Batu Raja limestones and the dist ribution of these is primarily related to sealevel fluctuations. Early diagenesis was marine and characterised by micritisation and preCipitation of fibrous and bladed cements. Dolomitisat ion occurred in the mixed- water zone and its variable intensity is attributed to the configuration of the carbonate body relative to this zone. Subsequently the limestones were subjected to freshwater phreatic zone diagenesis resulting in dissolution and cementation, and a t a late stage underwent burial compaction. Secondary porosity, which \ar9e1.y determines the suitability of these limestones as hydrocarbon reserVOirs, is a function of the variable intensity of dissolution and cementation, burial compaction, dolomitisation and possibly micrite neomorphism. The sedimentary processes that generated the Batu Raja buildups are inferred f rom comparisons with the Pulau Seribu and other Recent analogues. The contrasting pinnacle form of the Pulau Seribu patch reefs compared with the low relief of the Batu Raja buUdups results from differences in the initial substrate topography and subsequent subsidence rate

The islands of Halmahera, Morotai, Bacan, Obi and Waigeo lie in a zone of complex tectonics at the junction between the Eurasian margin and the Philippine Sea and Australian plates. New age data from the region using Sm-Nd, Rb-Sr and K-Ar systems and geochemical data are presented and are integrated with existing geological, geochemical and isotopic data to produce a regional geochronological framework. Continental metamorphic rocks of probable Palaeozoic age, derived from New Guinea, are found on Bacan and Obi. Sm-Nd model ages indicate that metamorphic protoliths contained Precambrian cratonic material which was subsequently mixed with younger mantle-derived material. Rb-Sr and K-Ar systematics give Neogene ages which relate to exhumation and emplacement of these rocks by strike-slip processes in the Sorong fault system. Ophiolitic rocks from Halmahera, Obi and Gag are of Philippine Sea plate origin and are interpreted to have formed an intra-oceanic forearc-arc-backarc system of Jurassic age based on Sm-Nd, K-Ar dating and geochemical and stratigraphic evidence. Subsequent Cretaceous to Tertiary arc activity has largely disturbed K-Ar ages of ophiolitic rocks. Cretaceous calc-alkaline arc activity formed the Gowonli and related volcaniclastic formations on Obi and Waigeo. Unusual amphibole-rich cumulates, hornblende gabbros and ultramafic rocks occur adjacent to continental metamorphic rocks. These yield Cretaceous and younger isotopic ages and are interpreted as the roots of a calc-alkaline island arc subsequently disrupted and uplifted by faulting in the Early Cretaceous and Neogene. Diorites and trondjhemites intruded into ophiolitic rocks on Halmahera and Obi date two phases of arc-related plutonic activity in the Middle to Late Cretaceous. One Paleocene diorite has also been dated. Isotopic ages from amphibolites, derived from basic protoliths, and biostratigraphic ages from sedimentary fault-related breccia deposits indicate deformation of ophiolitic rocks in the Late Cretaceous. Ar-Ar plateau ages and reset K-Ar ages suggest another period of deformation in the Paleocene. Isotopic dating shows that Tertiary arc activity occurred in three phases: a brief, Middle Eocene phase of diorite and andesite formation in eastern Halmahera; a dominantly Oligocene period of arc activity related to subduction beneath the Philippine Sea plate and a Neogene phase related to subduction of the Molucca Sea plate. Oligocene arc activity was terminated by Early Miocene collision of the Philippine Sea plate with the northern Australian margin. Convergence of the Philippine Sea plate with the Eurasian margin led to Neogene arc activity above an eastward-dipping Molucca Sea plate slab. Isotopic dating indicates that Neogene arc volcanism migrated northwards over time. Pliocene compressional deformation in Halmahera and Bacan caused a westward shift of the arc to its present position and may be related to collision events within the Sorong Fault system

Magma plumbing systems represent the physical framework of magma transport and storage from the source region in the mantle, through the crust, until reaching the surface in a volcanic eruption. Characterising the different aspects of magma plumbing, in particular the distribution of magma storage zones throughout the crust, is of key importance to better understand the behaviour of individual volcanoes. In particular, shallow crustal magma storage and associated magma-crust interaction processes could potentially explain some of the worlds most unpredictable and explosive volcanoes. This thesis studies magma plumbing architecture in the Sunda Arc (Indonesia), and the North Atlantic Igneous Province, based on elemental and isotope geochemistry, and derived petrological modelling. In this study, I have employed petrological models, so called geothermobarometers, to calculate pressures and temperatures (P-T) of crustal magma storage. Geothermobarometers are calibrated thermodynamic formulations based on the composition of magmatic minerals and their co-existing melt as a function of the P-T conditions of crystallisation. Using the calculated P-T estimates, I was able to derive the depth of magma storage, and thereby reconstruct the architecture of magma storage systems. A number of different geothermobarometers based on different mineral phases, including plagioclase, clinopyroxene and olivine, were used for this purpose, The geothermobarometric modelling was combined with additional elemental and isotope geochemical analyses, as well as collaborations with geophysical investigations. These additional approaches were used to corroborate the findings of the geothermobarometric modelling, and also to model and quantify magma-crust interaction processes that take place during crustal magma storage, such as assimilation of crustal lithologies into the magmatic system. The findings of this thesis build upon the growing body of evidence in support of the prevalence of shallow magma storage in different volcanic settings worldwide. This realisation is relevant to volcano monitoring and hazard mitigation worldwide.

Between 1981 and 1982 the Banjarmasin Quadrangle in South-East Kalimantan was mapped by the Geological Research and Development Centre, Bandung at the scale of 1 : 250,000. This thesis reports the results of a follow-up study to the mapping programme, which was directed towards determining the age, origin and tectonic evolution of the Pre-Tertiary rocks which form the Meratus Mountains in the eastern part of the Banjarmasin Sheet. The study consists of detailed field-mapping of Pre-Tertiary rocks in well exposed river sections at the scale of 1:10,000. Measured sections of sedimentary units were made and all structural features were recorded. A comprehensive collection of rock samples was made for laboratory studies. Thin sections were used to determine the composition and origin of sedimentary and igneous rocks. Macro-and microfossils have been examined to determine the depositional environments and the ages of the sedimentary units. From these studies the Pre-Tertiary rocks are divided into a number of tectonostratigraphic units, whose age, origin, structural and tectonic evolution has been determined as far as possible. This information has been used to compile a synthesis of the tectonic development of the Meratus Mountains in the context of plate tectonics and the development of the western Indonesian region. Isotopic and palaeontological dating has shown that the units exposed in the Meratus Mountains range in age from Early Cretaceous to Early Palaeocene. The oldest unit is the Paniungan Formation of Berriasian to Barremian age. It grades upward into the Upper Barremian to Lower Aptian Batununggal Formation. These formations are interpreted as shelf to slope sediments. It is suggested that shortly after deposition, most parts of the shelf to slope sediments were juxtaposed by strike-slip faulting with oceanic crust now represented by the Meratus Ophiolite Complex. Subduction generated a calcalkaline volcanic arc which then collided with the Sunda continent in the Cenomanian time. This collision zone was disrupted and sliced by strike-slip faults, forming a pull-apart basin within it. The absence of Palaeocene to Lower Eocene deposits reflects uplift, subsequently followed by rifting, regional subsidence and deposition of an Eocene-Miocene transgressive sequence. The present configuration of the Meratus Mountains resulted from late Middle Miocene and Plio-Pleistocene tectonic events.

Soputan volcano is one of the few basaltic volcanoes among 127 active volcanoes in Indonesia. It is part of the Sempu-Soputan volcanic complex located south of Tondano Caldera, North Sulawesi and commonly produces both explosive eruptions with VEI 2-3 and effusive lava dome and flow eruptions. Over the last two decades, Soputan had thirteen eruptions, the most recent in 2016. Most eruptions started explosively, followed by dome growth and in some cases pyroclastic flows. Our study focuses on understanding the magmatic system of Soputan and what processes are responsible for its highly explosive eruptions, which are typically uncommon for a basaltic magma composition. Our study includes tephra samples predating the 1911 eruptions, lava flow samples from the 2015 eruption, and ash from a 2015 fallout deposit. Our whole rock major and trace element composition are virtually identical to lava flow and select pyroclastic deposit compositions of Kushendratno et al. (2012) for the 1911-1912 and 1991-2007 eruptions. Bulk rocks contain 49 to 51 wt.% SiO2, whereas 2015 ash samples are slightly more silicic with 53 wt.% SiO2, consistent with segregation of groundmass from phenocrysts in the eruption cloud. Mantle normalized incompatible trace elements indicate strongly depleted HFSE (High Field Strength Elements) and REE (Rare Earth Elements) signatures but with spikes at Pb and Sr and mild enrichment of Rb and Ba. In comparison of data of this study with what was reported by Kushendratno et al. (2012), Fo68-79 olivine-hosted melt inclusions range from basaltic (48-52 wt.% SiO2) to basaltic andesite (54-55 wt.%) as compared to 54 - 65 wt.% SiO2 glass in Fo68-74 olivines. The compositional range of melt inclusions is consistent with 50% fractionation of multiple minerals including observed phenocrysts of olivine, plagioclase, pyroxene and oxides. Compositional trends with an inflection point likely reflect a change in the crystallizing assemblage, where early crystallization includes clinopyroxene and plagioclase, while later crystallization is dominated by plagioclase. New volatile concentration data from melt inclusions (S max. 0.35 wt.%, Cl max. 0.17%, H2O max. 5.2 wt.% from FTIR analyses) are higher than previously reported from younger samples (S max. ~0.07 wt.%, Cl max. 0.2%, H2O max. ~1 wt.%). H2O is relatively constant (~1-4 wt.%) for individual tephra samples (data by FTIR and water by difference method). Our inclusion data suggest that more volatile-rich magmas exist at depth and this is consistent with a model whereby recharge of deep, volatile-rich magmas into a more degassed and crystal-rich magma initiates a new, highly explosive eruption.

Porphyry and high sulfidation epithermal ore-forming systems are genetically associated with calc-alkaline volcanism in subduction zones, and where erosion has not been too deep, the volcanic rocks are still commonly exposed in close proximity to the deposits. Most models for porphyry copper and high sulfidation epithermal gold systems include a shallow magmatic reservoir (the porphyry stock), an overlying hydrothermal cell, its alteration paragenesis and a stratovolcano. Some investigations also discuss the importance of underlying granitoid batholiths as feeders for porphyry stocks and their hydrothermal systems. Although it is commonly believed that the ores deposit during the waning stages of volcanism, given the time span over which these deposits form (tens of thousands to several million years) and the undeniable existence of hydrothermal systems beneath volcanoes, it is quite probable that their formation is initiated at times when volcanoes are still active. Although currently mined ore deposits are excellent places to focus research, subduction zone stratovolcanoes provide important windows on the magmatic-hydrothermal processes at play.This thesis describes an investigation of the magmatic-hydrothermal environment that resides beneath Merapi volcano, Indonesia. The research involved sampling and chemical analysis of minuscule aliquots of evolving silicate and sulfide melts trapped as inclusions at different times and in different locations in growing crystals subsequently ejected during eruptions. The research also involved sampling and analysis of fumarolic gases (and their precipitates) emitted at Merapi volcano during times of quiescence and eruptive activity, as well as compilation of published compositional data for fumarolic gases from other arc volcanoes. These gases are the surface equivalents of ore-forming magmatic-hydrothermal fluids. Finally the research involved compilation from the literature of compositional data for fluid inclusions (micron-scale droplets of magmatic volatile phases) trapped in gangue minerals in porphyry copper deposits. The focus of the research was the behaviour of copper, nickel, cobalt, zinc, lead and molybdenum in magmatic hydrothermal systems.The research reported in Chapter 1 showed that injections of sulfide melt-saturated mafic magma into shallower, more evolved and more oxidized resident magma at Merapi volcano induced exsolution of a magmatic volatile phase from the mafic magma. This hydrothermal fluid dissolved the sulfide melt and became enriched in chalcophile (notably copper) and siderophile metals. An argument is presented that the overpressure generated by the exsolution of a fluid originating in this manner triggered an explosive eruption at Merapi volcano in 2006. This is supported by the observation that the metal content, particularly of copper, was higher in the volcanic gas sampled immediately after this eruption than during periods of quiescence and that metal ratios of the gas are remarkably similar to those of sulfide melt inclusions. In Chapter 2, it is shown that the mafic magma mixed poorly with the more felsic magma, that both magmas evolved via assimilation and fractional crystallization and, most importantly, that the magmatic volatile phase transferred base metals to the more felsic magma. In Chapter 3, the fluid inclusion and volcanic gas data are used to make inferences about the evolution of porphyry ore-forming systems and link mechanisms of ore-formation to those operative during the eruptive cycles of volcanoes. Finally, the thesis integrates the findings of this study into a model that provides new insights into the formation of porphyry copper deposits below stratovolcanoes.
Les gîtes de types porphyriques et épithermaux sont génétiquement associés au volcanisme des zones de subduction et les roches volcaniques cogénétiques à ces gisements sont souvent encore présentes. Tous les modèles actuels de mise en place de ces gîtes définissent un réservoir magmatique peu profond, lequel est coiffé d'une cellule hydrothermale et de sa séquence complexe d'altération, ainsi que d'un stratovolcan. Certains auteurs discutent aussi de l'importance de batholites sous-jacents ayant généré le porphyre et ses fluides hydrothermaux. Quoiqu'il soit généralement accepté que ces gîtes se forment durant le déclin du volcanisme, étant donné la longévité des périodes proposées pour la formation de ceux-ci (de dizaines de milliers à plusieurs millions d'années) et l'existence indéniable de systèmes hydrothermaux associés, il est fort probable que la formation de ces gîtes soit initiée alors que le volcanisme est encore actif. Les volcans situés en zones de subduction représentent d'importants points d'observation des processus magmatiques-hydrothermaux actuels.La présente recherche porte sur l'environnement magmatique-hydrothermal qui existe sous le volcan Mérapi, situé en Indonésie. Des échantillons de liquides silicatés et sulfurés piégés à l'intérieur de cristaux durant leur croissance à différents moments et endroits dans le magma et avant d'être éjectés hors des réservoirs magmatiques lors d'éruptions volcaniques ont été prélevés et dosés. Des gaz fumerolliens de haute température et leurs sublimats émis au volcan Mérapi durant des phases de dégazage passif et d'éruption explosive ont été échantillonnés et analysés. Des résultats similaires pour les gaz d'autres volcans, ainsi que des analyses d'inclusions fluides de systèmes hydrothermaux de porphyres cuprifères ont été compilés à partir de la littérature. Les gaz volcaniques analysés sont les équivalents superficiels des fluides magmatiques-hydrothermaux qui génèrent les gisements métallifères.Dans le premier chapitre, il a été démontré que des magmas mafiques d'origine profonde et saturés en liquide sulfuré ont été injectés dans le réservoir magmatique peu profond de Mérapi, celui-ci contenant un magma plus évolué et plus oxydé. La décompression qu'a subie le magma mafique a provoqué l'exsolution d'une phase magmatique volatile (un fluide hydrothermal) qui a dissous le liquide sulfuré et ses métaux chalcophiles et sidérophiles (notamment le cuivre). La surpression générée par l'exsolution de ce fluide hydrothermal a provoqué l'éruption explosive du volcan Mérapi de mars à août 2006. Ceci est corroboré par l'observation que certains métaux, particulièrement le cuivre, étaient enrichis dans les gaz volcaniques émis après l'explosion par rapport aux niveaux mesurés durant la phase de dégazage passif, et par le fait que les rapports des métaux dans ces gaz post-explosion étaient soudainement semblables à ceux mesurés dans les inclusions sulfurées, alors qu'ils étaient bien différents durant les phases de dégazage passif du volcan. Dans le second chapitre, je démontre que le magma plus mafique et le magma plus felsique ne se sont pas bien mélangés, que les deux magmas ont évolué via l'assimilation de roches encaissantes et la cristallisation fractionnée, et que la phase magmatique volatile qui s'est séparée du magma mafique et qui a dissous le liquide sulfuré a transféré ses métaux au magma plus felsique. Dans le troisième et dernier chapitre, les inclusions fluides et les gaz volcaniques ont été utilisés en conjonction avec les connaissances acquises et décrites dans les deux premiers chapitres afin de proposer un modèle pour l'évolution du système porphyrique et d'établir les liens qui existent entre les mécanismes de formation des gîtes porphyriques et épithermaux acides, et ceux qui opèrent durant les cycles éruptifs des volcans. Un modèle pour la formation des porphyres cuprifères sous les stratovolcans actifs des zones de subduction est finalement proposé.

Thesis (Ph. D.)--University of Texas at Austin, 1998.
Vita. Four folded plates in pocket. Includes bibliographical references (leaves 285-303). Available also in a digital version from Dissertation Abstracts.

The early human paleoanthropological site at Ngandong, Central Java, Indonesia has significant impact on the models for human migration and evolution out of the African continent. Located on an abandoned stream bank above the Solo River, Ngandong archaeological digs have uncovered fourteen Homo erectus fossils that, based on their unique shape, are believed to have lived more recently than any other known examples of Homo erectus. However, this hypothesis has not been substantiated by previous studies at Ngandong due to a general lack of understanding about the formation of the site as a whole. This study seeks to overcome the limits of these previous studies by thoroughly examining the grain size, grain shape, mineralogy, geochemistry, and stratigraphy of the site to understand how it formed, and in turn, provide a necessary geological context to the Ngandong Homo erectus fossils. The results outlined in this dissertation suggest the fossil-bearing layers were deposited at the site (at the time a channel bottom) over a short period of time and were sourced from the volcanic arc that forms the southern portion of Java island.

High-sulfidation epithermal deposits are genetically associated with calc-alkaline volcanism in subduction zones, and although these ore deposits are excellent places to focus research, subduction zone stratovolcanoes provide important windows on magmatic-hydrothermal processes that are not available from study of the corresponding ore deposits. There is general agreement that the hydrothermal alteration accompanying the high-sulfidation epithermal ores is the product of volcanic degassing, however, there is considerably less agreement on the nature and origin of the ore fluid. Opinion is divided over whether the ore fluid is a vapor or a liquid, and whether it is entirely volcanic or of mixed volcanic-meteoric origin.The research presented here details a field-based investigation of the magmatic-hydrothermal environment of Kawah Ijen volcano, an active stratovolcano (mainly andesitic pyroclastics and lavas) located in the Ijen Caldera Complex in Java, Indonesia. The Kawah Ijen crater is approximately one kilometer in diameter and contains a hyperacidic lake (pH ~ -0.5) and a small and actively degassing solfatara, which is surrounded by a much larger area of acid-sulfate alteration that was exposed during a phreato-magmatic eruption of the volcano in 1817; the eruption excavated the crater to a depth of 250 m. The research described in this thesis involved sampling and chemical analyses of the gases and their condensates (the surface equivalents of the ore-forming magmatic-hydrothermal fluids) collected from the solfatara and rock samples taken from the alteration center.Condensed fumarolic gases (pH ~ -0.5) released from the solfatara and sampled at temperatures between 330 and 495 °C contain up to 3 ppm Cu and 3.8 ppm As; the concentration of Ag is below detection. The alteration center is characterized by zones of residual silica, alunite-pyrite and kaolinite/dickite; based on alunite-pyrite geothermometry, the area formed at a temperature between 200 and 300 °C. High sulfidation epithermal mineralization occurs in this area in the form of massive and vein-hosted pyrite that contains up to 200 ppb Au, 9 ppm Ag, 6,800 ppm Cu, and 3,430 ppm As; these elements are invisible at the highest resolution of scanning electron microscopy, and thus occur either in the form of nano-particles or are in solid solution in the pyrite.The manuscript in Chapter 3 summarizes the observations detailed above to support a model in which highly acidic gases condensed ~ 250 m beneath the floor of the pre-1817 crater at Kawah Ijen volcano. In the area near the source of the vapors, the ratio of fluid to rock was extremely high and resulted in the leaching of elements from the andesitic host rock, leaving behind a residue of "vuggy silica." With increasing distance from the source, in an area of intermediate fluid/rock ratio, the condensed liquids replaced the primary minerals of the host with alunite and pyrite. The kaolinite/dickite zone formed in a rock-buffered environment (low fluid/rock ratio), in the zone furthest from the vapor source. Gold- silver- and copper-bearing phases were undersaturated in the condensed liquids, however, they were able to concentrate by adsorbing on the surfaces of the growing pyrite crystals, which developed p-type conductive properties as a result of the uptake of arsenic. The metals were incorporated in the pyrite either by their electrochemical reduction to form native metal nano-particles, through coupled substitutions with arsenic for iron and sulfur, or in the case of Cu, by direct replacement of Fe. This thesis provides new insight into the formation of high-sulfidation epithermal deposits, showing, in particular, that high sulfidation epithermal precious metal mineralization can form directly from condensed volcanic gases and that the processes of alteration and metallic mineralization occur synchronously.
Les dépôts épithermaux à forte sulfuration sont génétiquement associés au volcanisme calco-alkalin dans les zones de subduction, et bien que ces gisements métallifères soient intéressants pour la recherche, les stratovolcans des zones de subduction fournissent un bon aperçu quant aux procédés magmatiques et hydrothermaux, absent dans l'étude seule de ces gisements. Il existe un accord global sur le fait que le dégazage volcanique soit responsable de l'altération hydrothermale accompagnant les minerais épithermaux à forte sulfuration. Cependant l'avis est considérablement moins unanime sur la nature et l'origine des fluides du minerai. Le fluide minéralisateur pourrait être soit vapeur ou liquide, et son origine pourrait être soit entièrement volcanique ou soit un mélange volcanique-météorique. Cette étude présente les détails d'une étude sur l'environnement magmatique-hydrothermal du volcan Kawah Ijen, un stratovolcan actif (produisant principalement des pyroclastites andésitiques ainsi que des laves) situé dans le Complexe Ijen Caldera à Java en Indonésie. Le cratère Kawah Ijen a un diamètre d'environ un kilomètre et contient un lac hyper acide (pH ~ -0.5) ainsi qu'une petite solfatare en dégazage actif, entourée d'une aire d'altération acide-sulfate beaucoup plus grande qui était exposée durant l'éruption phréato-magmatique du volcan en 1817. L'étude décrite dans cette thèse comprend l'échantillonnage et l'analyse chimique des gaz et de leurs produits de condensation (l'équivalent de surface des fluides magmatiques hydrothermaux ayant formé le minerai) recueillis dans la solfatare et des échantillons de roche pris dans centre de l'altération. Les gaz de fumerolles condensés (pH ~ -0.5) émis par la solfatare et échantillonés à des températures entre 330 et 495 °C contiennent jusqu'à 3 ppm Cu et 3.8 ppm As. Le centre de l'altération est caractérisé par des zones de silice résiduelle, d'alunite-pyrite et de kaolinite/dickite; selon la géothermométrie de l'alunite-pyrite, la zone s'est formée à des températures entre 200 et 300 °C. La minéralisation épithermale à forte sulfuration survient à cet endroit sous la forme de pyrite massive dans la veine hôte, contenant jusqu'à 200 ppb Au, 16 ppm Ag, 6800 ppm Cu et 3340 ppm As; ces éléments sont invisibles sous la plus forte résolution du microcope à balayage électronique, et donc apparaissent soit sous la forme de nano-particules soit en solution solide dans la pyrite. Le manuscrit du chapitre 3 résume les observations décrites ci-haut, supportant un modèle dans lequel des gaz très acides ont été condensés à ~ 250 m sous le plancher du cratère pré-1817 du volcan Kawah Ijen. Dans la région près de la source de vapeur, le ratio fluide/roche était extrêmement élevé et a eu pour résultat le lessivage d'éléments de la roche hôte andésitique, laissant derrière un résidu de silice vacuolaire. En s'éloingnant de la source, vers une zone ou le ratio fluide/roche est intermédiaire, les liquides condensés ont remplacé les minéraux primaires de l'hôte avec de l'alunite et de la pyrite. La zone kaolinite/dickite s'est formée dans un environnement où la roche était en tampon (faible ratio fluide/roche), dans la zone la plus éloignée de la source de vapeur. Les phases contenant soit or, argent ou cuivre étaient sous-saturés en liquides condensés, cependant ils étaient aptes à se concentrer par adsorption sur les surfaces des cristaux de pyrite en croissance. Les métaux ont été incorporés dans la pyrite soit en formant des nanoparticules de métal, soit par substitutions couples, ou par remplacement direct du Fe (Cu seulement). Cette thèse procure une vision nouvelle quant à la formation de dépôts épithermaux à forte sulfuration, en montrant, en particulier, que la minéralisation épithermale à forte sulfuration de métaux précieux peut se former directement à partir des gaz volcaniques condensés, et que les procédés d'altération et de minéralisation métallifère peuvent se produire simultanément.

The Bowone and Binebase Au (Ag-Cu) deposits are related prospects, located 1 km apart on the volcanic island of Sangihe, Northeastern Indonesia. The deposits occur at the southern and oldest end of the island, and are hosted in Quaternary volcanic and volcaniclastic formations. Each deposit has a supergene and hypogene mineralized zone, although only the supergene zone of the Binebase deposit is of significant thickness. This thesis focuses on the hypogene zones of the deposits, and was undertaken with the goal of understanding the formation of high-sulphidation epithermal precious metal (Au, Ag) deposits. The hypogene mineralized zones at both Bowone and Binebase are spatially related to intense advanced (quartz, pyrite, pyrophyllite, natroalunite, alunite and kaolinite) and intermediate (quartz, pyrite, kaolinite, dickite and illite) argillic alteration that resulted in enhanced secondary porosity and silica-rich zones. However, vuggy or residual silica, which is characteristic of high-sulphidation epithermal deposits, is poorly developed. The mineralization occurred in three stages: 1) early gold-bearing pyrite (Pyrite I) in textural equilibrium with advanced and intermediate argillic alteration; 2) replacement and veining of massive gold-bearing Pyrite II and; 3) barite-enargite (Au and Ag bearing) veins. In each stage, gold and silver are hosted in pyrite and locally enargite, either in solid solution or as nanoparticles. The occurrence of gold-bearing pyrite in textural equilibrium with hydrothermal alteration minerals that are widely considered to have formed from condensed acidic vapours shows that the same fluids were also mineralizing, and transported gold (and other metals).The metals likely originated from an oxidizing felsic magma that was emplaced at high crustal levels and exsolved a low-density supercritical fluid into which the metals partitioned preferentially. The metals were transported by this fluid (which evolved to vapour on cooling) as hydrated species that ascended through the volcanic pile via fractures and zones of enhanced permeability. The fluid condensed at depths between 920 and 1260 m to form an acidic liquid with a pH between 0.5 and 4. The temperature ranged between 250 and 340°C and ∆ logfO2 (HM) was between -1 and +4. At high fluid/rock ratios, advanced argillic assemblages formed, whereas at low fluid/rock ratios, an intermediate argillic I and a distal intermediate argillic II alteration assemblage formed. The alteration also created porosity through the dissolution of minerals. The metals accumulated in zones of high fluid/rock ratios controlled by sub-vertical conduits and porosity of the sub-horizontal host rocks, where they were concentrated by adsorption onto the faces of pyrite crystals and incorporated in the pyrite through substitution for Fe or deposition as nanoparticles.Pyrite contains Ag, As, Au, Bi, Co, Cu, Fe, Ni, Pb, S, Sb, Se, Te and Zn. Pyrite I is host to an average of 1.1 ppm Au and 33.0 ppm Ag, pyrite II contains an average of 3.0 ppm Au and 80.6 ppm Ag, and enargite 0.53 ppm Au and 101.6 ppm Ag. Although there is a correlation between Au and As concentration, the absolute arsenic content is lower than in other deposits containing auriferous pyrite; it averages 329.7 ppm in Pyrite II. Pyrite II has the highest concentration of minor and trace elements overall, and contains up to 6.0 wt% Cu. Imaging by EMPA shows that growth and sector zones are common in Pyrite II. They are made evident by differences in the distribution of Cu and other elements. The anomalously high concentration of Cu and presence of both growth and sector zoning in Pyrite II enabled development of a tool for assessing relative changes in physicochemical conditions. Partition coefficients determined for Cu between paired sector zones in Pyrite II, showed that Cu, Au (and other metals) were preferentially incorporated in pyrite during periods when physicochemical conditions were stable.
Les gîtes d'or (cuivre-argent) Bowone et Binebase de l'île volcanique Sangihe, se trouvent à l'extrémité sud de l'île, sont associés aux formations volcaniques et volcano-sédimentaires quaternaires et sont géologiquement associés. Chaque gîte possède des minéralisations supergènes et hypogènes. Cette thèse porte principalement sur les zones hypogènes de chacun des gisements et a été réalisée dans le but de comprendre la formation des gîtes d'Au-Ag sulfato-acides. Les zones hypogènes minéralisées de Bowone et Binebase sont spatialement liées à une forte altération de style argileuse avancée (quartz, pyrite, pyrophyllite, natroalunite, alunite et kaolinite) et argileuse intermédiaire (quartz, pyrite, kaolinite, dickite et illite) qui ont produit des zones de porosité secondaire et des zones riches en silice. La minéralisation s'est effectuée en trois étapes : 1) formation de pyrite aurifère précoce (Pyrite I), en équilibre textural avec les altérations argileuses avancée et intermédiaire, 2) remplacement par la pyrite aurifère massive (Pyrite II), associé à la mise en place de veines, et 3) formation de veines de barite et d'énargite aurifères et argentifères. A chaque étape, l'or et l'argent sont associés à la pyrite et localement à l'énargite. La présence de la pyrite aurifère en équilibre textural avec des minéraux d'altération hydrothermale, qui sont considérés comme s'étant formés à partir de vapeurs acides condensées, montre que ces mêmes fluides ont également été minéralisant et ont transporté l'or et les autres métaux. Les métaux sont vraisemblablement issus d'un magma felsique oxydant. Ce magma aurait produit par exsolution un fluide supercritique de faible densité au sein duquel les métaux auraient été préférentiellement concentrés et par la suite été transportés par ce fluide, sous forme hydratée, à travers la séquence de roches volcaniques via les fractures et les zones de perméabilité accrue. Le fluide s'est condensé à des profondeurs entre 920 et 1260 m pour former un liquide acide avec un pH entre 0,5 et 4. La température a varié entre 250 et 340 °C pour un ∆ logfO2 (HM) compris entre -1 et +4. Pour des rapports fluide/roche élevés, les assemblages argileux avancés se sont formés, alors que pour des rapports fluide/roche faibles, l'altération a conduit à la formation d'assemblages argileuse intermédiaire et intermédiaire distale (I et II) et a également créé de la porosité par dissolution. Les métaux accumulés dans les zones de rapports fluide/roche élevés ont été contrôlés par la présence de conduits sub-verticaux et par la porosité sub-horizontale des roches encaissantes, où ils se sont concentrés, par adsorption sur les faces cristallines de la pyrite.La pyrite analyser contient les éléments suivants : Ag, As, Au, Bi, Co, Cu, Fe, Ni, Pb, S, Sb, Se, Te et Zn. La pyrite I se caractérise par un contenu moyen de 1,1 ppm Au et 33,0 ppm Ag, alors que la pyrite II contient en moyenne 3,0 ppm Au et 80,6 ppm Ag, et l'énargite 0,53ppm Au et 101,6 ppm Ag. Bien qu'il existe une corrélation entre les concentrations d'or et d'arsenic, la concentration absolue d'arsenic est plus faible que dans les autres dépôts contenant da la pyrite aurifère puisqu'elle est, en moyenne, de 329,7 ppm pour la pyrite II. La pyrite II montre la plus forte concentration d'éléments traces et contient, jusqu'à 6,0 % en poids de cuivre. L'imagerie par microsonde électronique montre que les zones de croissance et les zonations de secteur sont fréquentes dans la pyrite II. La concentration anormalement élevée de cuivre et la présence des zones de croissance et de secteur au sein de la pyrite II ont permis le développement d'un outil pour évaluer des changements relatifs de conditions physico-chimiques. Les coefficients de partage déterminés pour le cuivre entre les secteurs de la pyrite II montrent que les métaux ont été préférentiellement incorporés dans la pyrite pendant les périodes où les conditions physico-chimiques étaient stables.

In 1852, a five-minute long earthquake hit the Banda Arc region that was felt over most of Indonesia. It caused uplift of new islands and sent a tsunami across the Banda Sea that reached a height of 8 meters at Banda Neira and was also registered at Ambon, Saparua and other islands. Records of the 1852 earthquake at multiple locations provide the constraints needed to reconstruct the disastrous event through earthquake intensity analysis and numerical modeling of the tsunami. Using tsunami heights and arrival times as the major constraints, best fit numerical models of the tsunami were constructed using Clawpack. These models indicate that the earthquake was most likely a mega-thrust event along the Tanimbar Trough with a Mw of around 8.4. At least 10-15 meters of elastic strain energy has accumulated along the Tanimbar Through since the 1852 event, and the population in the region has increased exponentially. When another event occurs ≥ that in 1852, there will be many more people and treasure in harms way.

Improving our understanding of magma plumbing and storage remains one of the majorchallenges for petrologists and volcanologists today. This is especially true for explosivevolcanoes, where constraints on magma plumbing are essential for predicting dynamicchanges in future activity and thus for hazard mitigation. This study aims to investigate themagma plumbing system at Anak Krakatau; the post-collapse cone situated on the rim of the1883 Krakatau caldera. Since 1927, Anak Krakatau has been highly active, growing at a rateof ~8 cm/week. The methods employed are a.) clinopyroxene-melt thermo-barometry (Putirkaet al., 2003; Putirka, 2008), b.) plagioclase-melt thermo-barometry (Putirka, 2005), c.)clinopyroxene composition barometry (Nimis & and Ulmer, 1998; Nimis, 1999; Putirka,2008) and d.) olivine-melt thermometry (Putirka et al., 2007). Previously, both seismic(Harjono et al., 1989) and petrological studies (Camus et al., 1987; Mandeville et al., 1996a;Gardner et al., in review, J. Petrol.) have addressed the magma plumbing beneath AnakKrakatau. Interestingly, petrological studies indicate shallow magma storage in the region of2-8 km, while the seismic evidence points towards a mid-crustal and a deep storage, at 9 and22 km respectively.This study shows that clinopyroxene presently crystallizes in a mid-crustal storage region(8-12 km), a previously identified depth level for magma storage, using seismic methods(Harjono et al., 1989). Plagioclases, in turn, form at shallower depths (4-6 km), in concertwith previous petrological studies (Camus et al., 1987; Mandeville et al., 1996a; Gardner etal., in review, J. Petrol.). Pre-1981 clinopyroxenes record deeper levels of storage (8-22 km),indicating that there may have been an overall shallowing of the plumbing system over thelast ~40 years. The magma storage regions detected coincide with major lithologicalboundaries in the crust, implying that magma ascent and storage at Anak Krakatau is probablycontrolled by crustal discontinuities and/or density contrasts. Therefore, this study shows thatpetrology has the sensitivity to detect magma bodies in the crust where seismic surveys faildue to limited resolution. Combined geophysical and petrological surveys offer an increasedpotential for the thorough characterization of magma plumbing at active volcanic complexes.

Chapter 1-2:The Cassini RADAR mapper has imaged elevated blocks and mountains on Titan we term ‘ridges’. Two unresolved problems regarding Titan's surface are still debated: what is the origin of its ridges and was there tectonic activity on Titan? To understand the processes that produced the ridges, in this study, (1) we analyze the distribution and orientation of ridges through systematic geomorphologic mapping and (2) we compare the location of the ridges to a new global topographic map to explore the correlation between elevation and ridges and the implications for Titan's surface evolution. Globally, the orientation of ridges is nearly E-W and the ridges are more common near the equator than at the poles, which suggests a tectonic origin for most of the ridges on Titan. In addition, the ridges are found to preferentially lie at higher-than-average elevations near the equator. We conclude the most reasonable formation scenario for Titan's ridges is that contractional tectonism built the ridges and thickened the icy lithosphere, causing regional uplift. The combination of global and regional tectonic events, likely contractional in nature, plus enhanced fluvial erosion and sedimentation near the poles, would have contributed to shaping Titan's tectonic landforms and surface morphology to what we see today. However, contractional structures (i.e. thrusts and folds) require large stresses (8~10 MPa), the sources of which probably do not exist on Titan. Liquid hydrocarbons in Titan's near subsurface must play a role similar to that of water on Earth and lead to fluid overpressures, which enable contractional deformation at smaller stresses (< 1MPa) by significantly reducing the shear strength of materials. We show that crustal conditions with enhanced pore fluid pressures on Titan favor the formation of thrust faults and related folds, in a contractional stress field. The production of folds, as on Earth, is facilitated by the presence of crustal liquids to weaken the crust. These hydrocarbon fluids have played a key role in Titan's tectonic evolutionary history, leaving it the only icy body on which strong evidence for contractional tectonism exists. Chapter 3: Arthur Wichmann's ‘Earthquakes of the Indian Archipelago’ documents several large earthquakes and tsunami throughout the Banda Arc region that can be interpreted as mega-thrust events. However, the source regions of these events are not known. One of the largest and well-documented events in the catalog is the great earthquake and tsunami affecting the Banda islands on 1 August 1629. It caused severe damage from a 15-meter tsunami that arrived at the Banda Islands about a half hour after violent shaking stopped. The earthquake was also recorded 230 km away in Ambon, but no tsunami is mentioned. This event was followed by at least 9 years of uncommonly frequent seismic activity in the region that tapered off with time, which can be interpreted as aftershocks. The combination of these observations indicates that the earthquake was most likely a mega-thrust event. We use an inverse modeling approach to numerically reconstruct the tsunami, which constrains the likely location and magnitude of the 1629 earthquake. Only linear numerical models are applied due to the low-resolution of bathymetry in the Banda Islands and Ambon. Therefore, we apply various wave amplification factors (1.5 to 4) derived from simulations of recent, well-constrained tsunami to bracket the upper and lower limits of earthquake moment magnitudes for the event. The closest major earthquake sources to the Banda Islands are the Tanimbar and Seram Troughs of the Banda subduction/collision zone. Other source regions are too far away for such a short arrival time of the tsunami after shaking. Moment magnitudes predicted by the models in order to produce a 15 m tsunami are Mw of 9.8 to 9.2 on the Tanimbar Trough and Mw 8.8 to 8.2 on the Seram Trough. The arrival times of these waves are 58 minutes for Tanimbar Trough and 30 minutes for Seram Trough. The model also predicts 5 meters run-up for Ambon from a Tanimbar Trough source, which is inconsistent with the historical records. Ambon is mostly shielded from a wave generated by a Seram Trough Source.We conclude that the most likely source of the 1629 mega-thrust earthquake is the Seram Trough. Only one earthquake > Mw 8.0 is recorded instrumentally from the eastern Indonesia region although high rates of strain (50-80 mm/a) are measured across the Seram section of the Banda subduction zone. Enough strain has already accumulated since the last major historical event to produce an earthquake of similar size to the 1629 event. Due to the rapid population growth in coastal areas in this region, it is imperative that the most vulnerable coastal areas prepare accordingly.

L’intérêt de la télédétection appliquée aux volcans actifs et potentiellement dangereux a été démontré depuis longtemps dans la mesure où cette technique a participé à l’amélioration de la compréhension des processus éruptifs et des aléas volcaniques, amélioration qui permet une réduction des risques volcaniques. Nous avons entrepris plusieurs études volcanologiques reposant sur l’usage d’images de moyenne et haute résolution spatiale, qu’elles soient optiques (IKONOS, Pléiades, GeoEye, Quickbird and SPOT5), radar (ALOS-PALSAR) ou bien thermiques (ASTER et MODIS «hot spot»). Associées à l’analyse de MNTs et de photographies aériennes acquises par un drone, ces études ont consisté à appliquer des techniques de télédétection sur le Semeru et le Merapi, deux des volcans composites les plus actifs et les plus densément peuplés de l’ile de Java en Indonésie. Cette recherche fondée sur la télédétection a permis de mettre en évidence des structures géologiques et tectoniques, d’identifier, de classer et de cartographier des dépôts éruptifs sur les deux volcans et a servi à améliorer l’évaluation des risques à la suite des grandes éruptions de 2002-2003 au Semeru et de 2010 au Merapi. Nous avons également initié une étude afin de comprendre les interactions entre l’activité éruptive et le contexte sismo-tectonique régional en utilisant l’analyse des données MODIS avec la méthode MODVOLC. Nous avons remis à jour la carte géologique du volcan Semeru en y associant des données issues de l’interprétation d’images HSR récentes, des photographies aériennes, l’analyse de MNTs et des observations de terrain, notamment dans le réseau hydrograhique qui convoie des lahars. Nous avons décrit l’histoire éruptive postérieure à 2001 au Semeru en incluant la grande éruption à l’origine des écoulements pyroclastiques (EPs) en 2002-2003 et les éruptions effusives de 2012-2014, qui constituent un phénomène rarement observé sur ce volcan. Le Semeru a produit un volume de 2.5 ± 0.5 106m3 de coulées de lave provenant du cratère sommital entre 2010 et 2014, ce qui peut annoncer, pour la première fois depuis 1967 ou 1941, une modification profonde du style éruptif de ce volcan. Au moment de terminer cette thèse, le dome-coulée situé dans le cratère Jonggring-Seloko continue à croître et les coulées de lave dépassent 2 km de longueur dans la cicatrice majeure en pente raide sur le flanc SE ; leurs fronts pourraient s’effondrer et produire des EPs dont le volume moyen pourrait excéder les valeurs de 3 à 6.5 million de m3 mesurées sur la période 1967-2007. Les écoulements futurs pourront déborder des parois de la cicatrice vers l’aval et se propager vers les vallées des flancs est et sud-ouest. L’épisode éruptif du 26 octobre au 23 novembre 2010 s’est avéré l’événement majeur de l’activité du Merapi depuis 1872. Notre interprétation des images HSR démontre qu’à l’issue des éruptions explosives, le sommet du Merapi a perdu un volume de 10 x 106m3 et la gorge de Gendol orientée SSE a été élargie jusqu’à mesurer 1.3 x 0.3 x 0.2 km. Le nouveau cratère élargi et profond inclut le dome post-2010, qui a été fracturé en 2013, tandis que ses parois verticales instables peuvent être fragilisées par les explosions mineures de 2013 et 2014. Nous avons identifié et cartographié les dépôts pyroclastiques et de lahar de 2010 en appliquant plusieurs méthodes de classification aux images optiques HSR et aux données polarisées de Radar à Synthèse d’Ouverture (RSO). Les résultats démontrent la capacité de l’imagerie satellitaire HSR à capturer l’extension et les impacts de dépôts immédiatement après une grande éruption et avant tout remaniement. Cette technique met en exergue l’utilité de l’imagerie haute résolution et des données radar pour les volcans en activité persistante dont l’accès est souvent rendu impossible. (...)
Remote sensing has long been recognized as a tool for analysis at active and hazardous volcanoes because it can augment our understanding of the processes that underlie volcanic activity so as enable us to apply this understanding to volcanic risk reduction. This thesis presents a volcanological study using High-Spatial Resolution optical images (IKONOS, Pléiades, GeoEye, Quickbird and SPOT5 satellites), radar data (ALOS-PALSAR sensor) and thermal (ASTER satellite and MODIS hot spot) images. In association with DEMs and low-altitude aerial photographs, remote sensing techniques have been applied for tracing the evolution of activity at Semeru and Merapi, two of the most active and densely populated volcanoes in Java, Indonesia. This remotely sensing-based study has unraveled structures, geological features and erupted deposits of both volcanoes and has improved the existing hazard assessment after their most recent eruptions. The thesis also presents the first advance towards deciphering possible interactions between regional tectonic earthquakes and renewed stages of eruptive activity of Merapi and Semeru volcanoes based on the analysis of volcanic hotspots detected by the MODVOLC technique. The geological map of Semeru is updated, including additional data derived from the interpretation of the most recent satellite images, aerial photographs, DEM analysis and fieldwork. The post-2001 eruptive activity at Semeru, including the large PDC-forming eruption in 2002-2003 and uncommon lava flow eruptions in 2010-2014 are investigated. The fact that Semeru has produced several lava flows from the central summit vent between 2010 and 2014 may herald a profound change in eruption style for the first time since at least 1967. At the time of writing, a dome-fed coulée in the Jonggring-Seloko crater continues to grow and lava flows are extending to distances of >2 km down Semeru's SE-scar; their fronts may collapse and produce large-volume pyroclastic density currents (PDCs), perhaps exceeding the average (1967-2007) volume range of 3 to 6.5 million m3. Future dome-collapse PDCs may travel farther down the main SE scar and can spill over its lowermost rims towards the southwest and eastward radiating drainage network. The 26 October-23 November 2010 eruption was the Merapi’s largest event since 1872 (it attained VEI=4). The interpretation of HSR images shows that due to the explosive eruptions, the summit area lost about 10 x 106m3 and the SSE-trending Gendol Breach enlarged to reach 1.3 x 0.3 x 0.2 km in size. The new, enlarged and deep summit crater including the 2010 lava dome is extremely unstable having been weakened by the post-2010 explosive events. This instability is a result of the steep Gendol Breach below the mouth of the crater and the steep and unstable crater walls. The 2010 Merapi pyroclastic and lahar deposits have been identified by applying several classification methods to HSR optical images and dual-polarization synthetic aperture radar (SAR) data. The results show the ability of remotely sensed data to capture the extent and impacts of pristine deposits shortly after emplacement and before any reworking, and highlight the purpose of using high-spatial resolution imagery and SAR data on persistently active volcanoes where access for field survey is often impossible. The 2010 tephra and PDC deposits covered ca. 26 km2 in two catchments of Gendol and Opak Rivers on Merapi’s south flank, i.e. 60-75% of the total PDC deposit area and a total bulk volume of 45 x 106m3. The tephra-fall deposit covered an area of ca. 1300 km2 with a volume range of 18-21 x 106m3. Volumes of these deposits were estimated using the areas determined from remote sensing data and deposit thickness measured in the field. (...)
Penginderaan jauh telah lama dikenal sebagai suatu alat untuk analisis di gunungapi aktif dan berbahaya karena dapat meningkatkan pemahaman kita tentang proses yang mendasari aktivitas gunung berapi sehingga memungkinkan kita untuk menerapkan pemahaman ini dalam pengurangan risiko erupsi gunungapi. Disertasi ini menyajikan studi vulkanologi menggunakan citra satelit optik resolusi tinggi (IKONOS, Pléiades, GeoEye, Quickbird dan SPOT5), data radar (ALOS-PALSAR sensor) dan citra termal (satelit ASTER dan hotspot MODIS). Dalam kaitannya dengan DEM dan foto udara, teknik penginderaan jauh telah diterapkan untuk melihat evolusi aktivitas di Semeru dan Merapi, dua gunung berapi yang paling aktif dengan kepadatan penduduk yang tinggi terletak di Pulau Jawa, Indonesia. Studi berbasis penginderaan jauh ini telah mengkaji struktur, fitur geologi dan material erupsi dari kedua gunungapi tersebut dan telah mempertajam penilaian bahaya yang ada setelah erupsi terkini. Disertasi ini juga menyajikan kemajuan awal dalam menafsirkan kemungkinan interaksi antara gempa tektonik regional dan aktivitas gunungapi Merapi dan Semeru berdasarkan analisis hotspot vulkanik yang terdeteksi oleh MODVOLC. Peta geologi Semeru telah diperbaharui dengan memasukkan data tambahan yang berasal dari interpretasi citra satelit terbaru, foto udara, analisis DEM dan data lapangan. Aktivitas erupsi pasca-2001 di Semeru, termasuk erupsi dengan aliran pirokastik (Pyroclastic Density Current/PDC) besar pada tahun 2002-2003 dan erupsi tidak biasa dengan aliran lava pada 2010-2014, telah dikaji. Fakta bahwa Semeru telah menghasilkan beberapa aliran lava dari kawah di puncak antara tahun 2010 dan 2014, mengindikasikan perubahan besar dalam gaya erupsi untuk pertama kalinya setidaknya sejak 1967. Pada saat penulisan disertasi ini, sebuah kubah lava (Coulée) di kawah Jonggring- Seloko terus tumbuj dan aliran lava yang memanjang hingga jarak >2 km arah tenggara Semeru; ujung lava kemungkinan dapat runtuh dan menghasilkan aliran piroklastik yang mungkin melebihi volume rata-rata (tahun 1967 hingga 2007) dalam kisaran 3-6.5 juta m3. Aliran piroklastik yang akan datang mungkin mengalir sepanjang gawir utama ke arah tenggara dan dapat menyebar melampaui lereng paling bawah ke arah barat daya dan ke arah timur menyebar ke jaringan drainase. Erupsi yang terjadi pada 26 Oktober-23 November 2010 adalah erupsi terbesar Merapi (mencapai VEI 4) sejak 1872. Interpretasi citra resolusi tinggi menunjukkan bahwa daerah puncak kehilangan batuannya sekitar 10 juta m3 akibat erupsi eksplosif. Erupsi juga memperbesar “Gendol Breach” dengan orientasi tenggara menjadi berukuran 1.3x0.3x0.2 km. Kawah puncak yang baru, diperbesar dan dalam, termasuk juga kubah lava tahun 2010 sangat tidak stabil dan telah diperlemah oleh beberapa erupsi eksplosif pasca-2010. Ketidakstabilan ini diakibatkan oleh curamnya Gendol Breach di bawah mulut kawah dan kondisi dinding kawah yang curam dan tidak stabil. Deposit piroklastik dan lahar diidentifikasi dengan menerapkan beberapa metode klasifikasi terhadap citra optik resolusi tinggi dan data dual-polarisasi Synthetic Aperture Radar (SAR). Hasilnya menunjukkan kemampuan data penginderaan jauh untuk merekam jangkauan dan dampak dari deposit murni sesaat setelah pengendapan dan sebelum proses erosi, serta menyoroti tujuan penggunaan citra resolusi tinggi dan data SAR di gunungapi sangat aktif dengan akses untuk survei lapangan sering kali tidak memungkinkan. Endapan tephra dan PDC menutupi area sekitar 26 km2 di dua DAS, Kali Gendol dan Opak, di sisi selatan Merapi, atau 60-75% dari total luas endapan PDC, dan total volume 45 juta m3. Deposit tephra jatuh menutupi area seluas sekitar 1.300 km2 dengan volume 18-21 juta m3. Volume endapan vulkanik ini diestimasi menggunakan informasi luas yang ditentukan dari data penginderaan jauh dan ketebalan yang diukur di lapangan. (...)

Coral terrace surveys and U-series ages of coral and mollusk shells yield a surface uplift rate of ~0.6 m/ka for Kisar Island. The small island is located NE of Timor in the active Banda Arc of Indonesia. Based on this rate, Kisar first emerged from the ocean as recently as ~450 ka. Terrace surveys show warping that follows a pattern of east-west striking folds, which are along strike of thrust-related folds of similar wavelength imaged by a seismic reflection profile just offshore. This deformation shows that the emergence of Kisar can be attributed to forearc closure along the south-dipping Kisar Thrust. Terrace morphology and coral ages are best explained by recognizing major terraces as mostly growth terraces and minor terraces as mostly erosional into older growth terraces. All reliable and referable coral U-series ages are marine isotope stage (MIS) 5e (118-128 ka), which encrusted the coast up to 60 m elevation. All coral samples are found below 6 m elevation, but a tridacna (giant clam) shell in growth position at 95 m elevation yields an age of 195 +/- 31 ka, which corresponds to MIS Stage 7. Loose deposits of coral fragments found on top of low terraces between 8 and 20 m elevation yield ages of < 100 years and may represent paleotsunami deposits from previously undocumented seismic activity in the region. The metamorphic rocks of Kisar, Indonesia, which correlate with the Aileu Metamorphic Complex of East Timor, record the breakup of a supercontinent with associated rifting, metamorphism from arc-continent collision, and the growth and exhumation of a new orogenic belt. The protoliths of these rocks are mostly psammitic with minor basaltic and felsic igneous rocks. Geochemical analyses of mafic meta-igneous rocks show rift affinities that are likely related to rifting of Gondwana and later breakup in the Jurassic Period. The Aileu Complex is overlain by younger sedimentary rocks deposited on the northern passive margin of Australia, which collided with the Banda Arc in latest Miocene time. This collision caused metamorphism of the distal edge of the continental margin rocks at conditions of 600-700°C at 6-8 kbar and up to 700-850°C at 8-9 kbar locally, corresponding to depths from 25 to 30 km. These rocks were then rapidly uplifted and exhumed. U-Pb analysis of detrital zircons indicates a Permian to Late Jurassic age of the sedimentary sources and confirm an Australian provenance. The timing of metamorphism of the Aileu Complex is poorly constrained by previous studies, of which only a white mica cooling age of 5.36 +/- 0.05 Ma proved reliable. Prior apatite fission track studies show that all tracks are partially to completely annealed suggesting recent rapid cooling. A domal geometry of the island above the sea floor is expressed in the pinnacle shape. Foliations on Kisar Island generally strike parallel to the coastline, which is may be suggestive of doming. The Kisar Thrust, which is imaged in offshore seismic reflection data, may indicate that the doming corresponds to diapirism into the hinge of an active thrust-related anticline or diapirism of buoyant continental material along the thrust itself.

Grain size, 14C age, and X-ray diffraction (XRD) analyses of sediments indicate possible tsunami deposits on the southern coast of Java near Pangandaran and Adipala. Previous studies that have described known recent and paleotsunami deposits were used for comparison. Fining-upward grain size trends, interbedded sand and mud, sediment composition, and trends in heavy mineral abundances are among the characteristics used for tsunami deposit identification. At Batu Kalde, an archaeological site south of Pangandaran, a layer of aragonitic sand with marine fossils was found atop a layer of archaeological fragments at an elevation of ~2-5 m. It is likely this layer was deposited by a tsunami, potentially generated by a mega-thrust earthquake. Archaeological material remains suggest that the tsunami occurred ~1300 years ago. A bivalve with an age of 5584-5456 cal YBP was buried within the deposit, perhaps long after its death. At Goa Panggung, a cave east of Batu Kalde, fining-upward grain size trends, composition of sediments, and radiocarbon ages suggest the presence of at least one tsunami deposit. A 5040-4864 cal YBP piece of charcoal overlying modern organic matter suggest that the tsunami first scoured the cave floor, reworking existing material and making interpretation difficult. At Adipala, in western Central Java, fining-upward grain size, upward decrease in heavy mineral abundances, and lateral continuity of sand layers revealed the existence of two possible tsunami deposits buried within the sediments in a swale ~1.6 km from the ocean. Age of the deposits is undetermined.

Our paleotsunami surveys of the southern Java coast led to the discovery of five imbricate coastal boulder fields near Pacitan, Indonesia that may date to the mid-to-late 19th century or prior and two similar fields at Pantai Papuma and Pantai Pasir Putih that were tsunami-emplaced during the 1994 7.9 Mw event in East Java. Estimated ages for the fields near Pacitan are based on historical records and radiocarbon analyses of coral boulders. The largest imbricated boulders in fields near Pacitan and in East Java are similar in size (approximately 3 m^3) and are primarily composed of platy beachrock dislodged from the intertidal platform during one or several unusually powerful wave impactions. Hydrodynamic wave height reconstructions of the accumulations near Pacitan indicate the boulders were likely tsunami rather than storm-wave emplaced, as the size of the storm waves needed to do so is not viable. We evaluate the boulders as an inverse problem, using their reconstructed wave heights and ComMIT tsunami modeling to suggest a minimum 8.4 Mw earthquake necessary to dislodge and emplace the largest boulders near Pacitan assuming they were all deposited during the same tsunami event and that the rupture source was located along the Java Trench south of Pacitan. A combined analysis of historical records of Java earthquakes and plate motion measurements indicates a seismic gap with >25 m of slip deficit along the Java Trench. A 1000-1500 km rupture along the subduction interface of this segment is capable of producing a 9.0-9.3 Mw megathrust earthquake and a giant tsunami. However, evidence for past megathrust earthquake events along the this trench remains elusive. We use epicenter independent tsunami modelling to estimate wave heights and inundation along East Java in the event that the trench were to fully rupture. By translocating ComMIT slip parameters of Japan's 2011 9.1 Mw event along the trench offshore East Java, we demonstrate possible wave heights in excess of 20 m at various locations along its southern coasts. Approximately 300,000-500,000 people in low-lying coastal communities on the southern coasts of East Java could be directly affected. We recommend at-risk communities practice the "20/20/20 principle" of tsunami hazard awareness and evacuation.

Several laterally extensive candidate tsunami deposits are preserved along coastlines facing the eastern Java Trench, indicating it has experienced mega-thrust earthquakes in the past. We investigated 37 coastal sites in Bali, Lombok, Sumba and Timor islands, many of which preserve course sand and pebble layers that overlie sharp basal contacts with scour marks into the mud, fine upward in grain size, and have bimodal grain size distributions. Other unique features are the common occurrence of marine fossils and concentrations of heavy minerals. The occurrence of these high-energy deposits interlayered with clay-rich units indicates the coarse clastics are anomalous because they were deposited in what is normally a very low-energy depositional environment. The lateral extent and paucity of thin, coarse clastic layers with marine organisms are inconsistent with local stream flood event, and the proximity to the equator of the sites diminishes the possibility of marine flood events from cyclones. The sparse, but consistent, the occurrence of at least two candidate tsunami deposits at depths of 1 and 2 meters over 950 km along the strike of the Java Trench may reveal that mega-thrust earthquakes have occurred there and generated giant tsunamis in the recent past. Five widely scattered imbricated boulder deposits are also found on Bali, Lombok, and Sumba. The boulders consist of slabs of hardpan up to 2.5 m in length and 80 cm thick that was torn from a near-shore seabed and stacked on top of one another. Some of the boulders were carried over the erosional coastal bank and deposited up to 100 meters inland. Comparisons with imbricated boulder ridges formed during the 1994 tsunami in east Java indicate that these deposits are from one or multiple tsunamis sourced by the Java Trench. Experiments in effective ways to communicate and implement tsunami disaster mitigation strategies have led us to train local communities about the 20-20-20 rule. If coastal communities experience more than 20 seconds of shaking from an earthquake, even if it is not intense, they should evacuate the coast. The time delay between the earthquake and arrival of tsunami waves is around 20 minutes, which is the time window for evacuation. Some tsunami waves may be as high as 20 meters, which is the target elevation for evacuation. Adopting the 20-20-20 rule could save thousands of lives throughout the region, especially in Bali where nearly 1 million people inhabit likely tsunami inundation zones.

Le volcan merapi (java central, indonesie) menace continuement la ville de yogyakarta (1/2 million d'habitants) situee environ 30 km au sud. Les menaces directement eruptives sont principalement representees par des nuees ardentes associees a la croissance ou a la destabilisation gravitaire des domes. Ce travail consiste en une etude geologique detaillee des produits des eruptions depuis 1930 et une etude de reconnaissance des produits ante-1930 mais recents sur le flanc sud-ouest (actuellement menace). Une etude detaillee de la derniere eruption majeure (65 morts) a nuees ardentes, le 22 novembre 1994, a pu etre menee peu apres l'eruption, alors que les depots et les destructions etaient encore preserves. Nous montrons que l'essentiel des destructions est du a des deferlantes pyroclastiques qui se detachent des ecoulements grossiers restant canalises dans les vallees et se deplacent independamment, au devant des ecoulements canalises. Nous montrons que ce modele de detachement de deferlantes peut s'appliquer egalement aux destructions importantes decrites dans les eruptions de 1930, 1961 et 1969, dont nous avons identifies les depots jusqu'ici non reconnus. Sur le flanc sud-ouest, des depots de deferlantes encore plus volumineuses et de plus grande extension ont ete reconnus et dates par c14 d'age historique (posterieur a 1000 ad) ou anterieur. Les donnees mineralogiques et texturales obtenues sur les mesostases des laves produites depuis 1930 ne montrent pas de differences notables et systematiques d'une eruption a l'autre, en relation avec l'explosivite apparente ou la violence des nuees. Par contre, on observe que chaque eruption produit generalement plusieurs lithologies distinctes qui permettent de preciser la contribution des processus de construction (apport de nouveau magma) et de destruction dans la genese des nuees ardentes. Un suivi petrologique systematique du degazage des laves pourrait etre incorpore au dispositif de surveillance du volcan.

On etudie la diagenese des sediments deltaiques deposes sur plus de 4000m d'epaisseur du miocene inferieur a l'holocene a l'emplacement du delta actuel de la mahakam. On aborde les phenomenes de cimentation, de dissolution avec formation de porosite secondaire et de neoformations de kaolinite et illite a l'aide de la diffraction rx, de la microscopie electronique a balayage et a transmission, de la geochimie isotopique. On analyse les mecanismes d'illitisation ainsi que la formation de l'interstratifie illit nonesmectite en fonction de l'evolution thermique de la region

According to the Ade observation (Ade, W., pers. Comm.) “95% of all commercial oil fields in the Sumatra region occur within 17 km of seismically mappable structural grabens in the producing basins”. The Ade observation proposes a link between the subsidence of the source rocks (the Talang Akar Formation) in the grabens and the maturity of the organic material. To test the validity of the Ade observation, subsurface mapping of the region was carried out using geophysical logs. Using the well log information, the basement and the formation tops have been mapped with a special emphasis on Talang Akar and Air Benakat Formations. The isopach maps of these formations show that most of the producing wells on the Sunda shelf are in fact located in and around the major structural basins. Trends in the occurrence of the oil fields have also been observed which are analogous to the orientation of the grabens. Structural mapping of the basins have identified several wrench faults. These are of particular interest as wrench faults provide good structural traps for oil in the Los Angeles and the North Sumatra Basins and may prove to be very important for future exploration in southern Sumatra and northwest Java. In South Sumatra Basin, 77.78% of the potential oil fields are located in the 17 km margin from the grabens. For Sunda/Asri Basins and the Ardjuna Basin, it is 100 and 92 respectively. Identifying the source rocks in this 17 km window will enhance the success rate of oil exploration in the Sundaland Basins.
Department of Geological Sciences

The research involves mapping of subsurface at a scale of 1:25,000 the top of three geological formations in the Southern Part of Sumatra – the Airbenakat Formation, the top of the Talangakar Formation, and the top of structural basement in the Jambi Trough. Isopach maps of the formations will be constructed. These maps will form the basis of a basin analysis and hydrocarbon source rock assessment of the Jambi Trough using Basin Mod basin modeling software (Rockworks Software). The studies utilize the L. Bogue Hunt Southeast Asia database housed in the Department of Geological Sciences at Ball State University. Seismic record sections, geophysical logs, cutting descriptions, and paleontological reports will provide basic geological data to enable mapping of the three horizons. Although hydrocarbon accumulations are abundant in Central and Southern Sumatra, the nature of the source rocks is only partially understood. The proposed research will map the Airbenakat and Talangakar Formations while identifying the areas of thermally mature source rock is the main goal of the research. This study will identify characteristics which will enable the identification of thermally mature rocks in other regions of Sumatra. The area of the project is located at the Southeastern part of Asia in Indonesia and mainly the Jambi trough located in Southern Sumatra. Generally, the geology and tectonics of this area (Sumatra) is controlled by the subduction of the Indian plate towards the east and beneath the Eurasia plate.
Department of Geological Sciences

New Guinea has long been recognized by geologists as the location of geologically recent mountain building. This study combined field mapping, stratigraphic and remote sensing analysis along and near the Gunung Bijih (Ertsberg) mine road and mining district in order to analyze the geologic development of the collisional New Guinea orogen. As a result of the youthfulness and the quality of data, it is possible to constrain distinct parts of orogenic evolution to 1 or 2 m.y. The southern Central Range of New Guinea is located on the northern Australian continental margin. The southern one-third of the Central Range, exposed along the Gunung Bijih mine access road, is a 30-km-wide, north-dipping homocline exposing an apparently 18-km-thick Precambrian or Early Paleozoic to Cenozoic sequence. Following rifting in the early Mesozoic and until the Middle Miocene, the northern Australian continent was a passive margin. The Central Range of Irian Jaya formed when the Australian passive margin was subducted beneath and collided with a north-dipping subduction zone in the Middle Miocene. Litho- and biostratigraphic analysis of the New Guinea Limestone Group in the Gunung Bijih mining district and regional stratigraphic correlation indicates that the first evidence of subaerial exposure and erosion of the orogen is the widespread deposition of siliciclastic, synorogenic strata at ~12 Ma. I name this event the Central Range Orogeny. There is no evidence of an Oligocene orogenic event in the Irian Jaya region as has been described to the east in Papuan New Guinea. Deformation in the Central Range is dominated by ~12 to ~4 Ma southwest verging (210°-220°) contraction and minor east-west wrenching. This deformation is equally accommodated, there is no evidence for strain partitioning in the Central Range. Lithospheric-scale cross sections, incorporating field observations, predict the Central Range Orogeny is divided into a pre-collision and collisional stage. The pre-collision stage is the bulldozing of passive margin sediments in a north dipping subduction zone. The collision stage occurs when buoyant Australian lithosphere can not be subducted. The collision stage results in basement involved deformation and lithospheric delamination of the already subducted Australian plate.
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A geophysical and geological study utilizing high quality seismic and well log data was undertaken of a marginal basin in the Western Flores Sea, Indonesia, to document the evolution of Paleogene extensional basins and their transformation during the Neogene into compressional uplifts. These are referred to as inversion structures because they begin as extensional half-grabens and are transformed by compression into structural highs. The crust underlying the area is transitional between continental crust of the Sunda craton to the west and oceanic crust of the Banda back-arc region to the east. Half-grabens began to form in the middle Eocene by extensional reactivation of thrusts and bedding planes within the deformed and peneplained basement complex which was an accretionary prism during the Cretaceous. Extension and regional subsidence continued until early Miocene time, when compression began to reactivate the extensional bounding faults of the half-grabens as thrusts. Compressional growth of the inversion structures was most dramatic during the late Miocene and Pliocene and continues today. The Paleogene grabens appear to have resulted from essentially orthogonal extension, oriented roughly N-S with respect to present geography. During the Neogene, the axis of compression which caused the inversion of the extensional structures appears to have been essentially the same as that which caused the extensional structures. Seismic interpretation of the Neogene units attempted the resolution of individual depositional sequences related to changes in relative sea level. The sequences were recognized by their constituent lowstand, transgressive and highstand systems tracts, where present, as defined by stratal termination patterns, truncational relationships and incision. The number of Neogene sequences, their ages as constrained by biostratigraphic data, relative amounts of incision and truncation at specific sequence boundaries, and the stacking patterns of the sequences were compared to those predicted by the published, reputedly globally-correlative, sea level chart of Haq and others (1987). The comparison is generally favorable, with the greatest variances noted in the ages of individual sequences, and the greatest similarity noted in the long-term stacking patterns of the sequences, especially for tectonically quiescent parts of the basin.

This thesis aims to establish the correlation between gravity data and volcanic structure in Central Jawa, Indonesia. The study provides information on the major boundary which separates the Eocene sediment in the south from the younger sediment in the north. The results of this research may offer a better understanding of the major structural elements of island arcs.
Thesis (M.Sc.) -- University of Adelaide, Dept. of Geology and Geophysics, 1995?

The main objective of this research is to understand the seismic structure beneath Sumatra and its surrounding regions by using seismic tomography. The structure is interpreted as P wavespeed velocity anomalies relative to the ak135 model. The main data source is P wave traveltimes up to 2006 obtained from the International Seismological Centre with relocation using the EHB scheme. Summary rays are constructed for these ISC data to decrease the number of data and to give a more even rays distribution so that we obtain 1,750,070 ISC residuals. We also include arrivals reported to Geoscience Australia, data from RSES-ANU and the Indonesian Meteorological and Geophysical Bureau (BMG). The data recorded by the RSES arrays are analysed by using an adaptive stacking method and the BMG arrivals are picked by hand with an STA/LTA procedure used to speed up the analysis. The tomographic model using a 1{u00B0}x1{u00B0} degree grid parameterization extended from 70{u00B0}E to 193{u00B0}E and 45{u00B0}N to 45{u00B0}S which covers Himalaya to Tonga and Japan to Australia, is embedded inside a 2{u00B0}x2{u00B0} global model. Pseudo bending technique for 1D forward calculation is firstly performed and the conjugate least square is then applied to invert the residuals and obtain the velocity perturbation of the region. Subsequently, the 3D ray tracing and inversion scheme are reiterated to improve the 3D seismic structure of the region. This 1{u00B0}x1{u00B0} regional model is validated by resolution tests: with checkerboard and synthetic slab models. Within the region with sufficient ray coverage the checkerboard is resolved well. The 3D ray tracing and inversion reproduce the synthetic slabs well; even in complicated cases. This new regional model is very consistent with those produced by Widiyantoro et al., 1999 and Replumaz et al., 2004. In order to emphasize the understanding of the seismic structure beneath Sumatra and its surrounding regions a 0.5{u00B0}x0.5{u00B0} grid parameterization is embedded inside the 1{u00B0}x1{u00B0} regional model within the 2{u00B0}x2{u00B0} global model. The finer resolution model is chosen as the region from 80{u00B0}-125{u00B0}Eand 15{u00B0}S-l5{u00B0}N which covers Andaman, Sumatra, and eastern Indonesia. The 3D forward calculation and inversion are reiterated to obtain the smaller regional model with higher resolution. The higher resolution model offers better definition of the nature of the slabs and low velocity zones. Beneath the Aceh-Andaman region the old incoming lithosphere subducts steeply and terminates abruptly at ~500 km depth. A slab tear is found beneath this section that connects the Sumatran to the Himalayan subduction zone indicating a unified subduction zone a few million years ago. The Northern and Central Sumatran slabs dip shallowly with little deflection at ~500 km depth associated with younger, warmer incoming lithosphere. The slab-pull forces beneath Aceh-Andaman section may be less significant because the slabs terminate much shallower than beneath Sumatra. This behaviour may influence the frequency of large earthquakes. In the Java region with older lithosphere the slabs dip more steeply deflect backward and forward in the mantle transition zone.

abstract: Shallow earthquakes in the upper part of the overriding plate of subduction zones can be devastating due to their proximity to population centers despite the smaller rupture extents than commonly occur on subduction megathrusts that produce the largest earthquakes. Damaging effects can be greater in volcanic arcs like Java because ground shaking is amplified by surficial deposits of uncompacted volcaniclastic sediments. Identifying the upper-plate structures and their potential hazards is key for minimizing the dangers they pose. In particular, the knowledge of the regional stress field and deformation pattern in this region will help us to better understand how subduction and collision affects deformation in this part of the overriding plate. The majority of the upper plate deformation studies have been focused on the deformation in the main thrusts of the fore-arc region. Study of deformation within volcanic arc is limited despite the associated earthquake hazards. In this study, I use maps of active upper-plate structures, earthquake moment tensor data and stress orientation deduced from volcano morphology analysis to characterize the strain field of Java arc. In addition, I use sandbox analog modeling to evaluate the mechanical factors that may be important in controlling deformation. My field- and remotely-based mapping of active faults and folds, supplemented by results from my paleoseismic studies and physical models of the system, suggest that Java’s deformation is distributed over broad areas along small-scale structures. Java is segmented into three main zones based on their distinctive structural patterns and stress orientation. East Java is characterized by NW-SE normal and strike-slip faults, Central Java has E-W folds and thrust faults, and NE-SW strike-slip faults dominate West Java. The sandbox analog models indicate that the strain in response to collision is partitioned into thrusting and strike-slip faulting, with the dominance of margin-normal thrust faulting. My models test the effects of convergence obliquity, geometry, preexisting weaknesses, asperities, and lateral strength contrast. The result suggest that slight variations in convergence obliquity do not affect the deformation pattern significantly, while the margin shape, lateral strength contrast, and perturbation of deformation from asperities each have a greater impact on deformation.
Dissertation/Thesis
Doctoral Dissertation Geological Sciences 2016

The Kelian gold deposit, located 250 km west of the provincial capital of Samarinda, East Kalimantan, is Indonesia's principal gold producer. The deposit is an intrusive-related low sulphidation system, situated within the Central Kalimantan Continental Arc, which consists of andesitic to rhyolitic volcanics and intrusives of Miocene age. Hydrothermal activity produced extensive brecciation, porphyry- to epithermal-style alteration and gold and base metals mineralisation. The nature of genetic relations is the main aspect of this study and is approached through the geochemical evolution of the calc-alkaline suites in relation to the metallic mineralisation. Geochemical evolution in the Miocence calc-alkaline suites from the Kalimantan volcanic arc exhibit two distinctive trends of magmatic differentiation The first trend is defined by a series of "productive" igneous suites such as Kelian, Muyup and Ritan, and is a "typical" calc-alkaline series characterised by low Mg, moderate K, relatively high Ti and Al and depletion in Cr and Sc. The second trend is defined by the chemical variations of the Magerang-Imang and Nakan suites which have remarkably high concentrations of MgO. Major and trace element geochemistry of the high Mg andesites from MagerangImang and Nakan is comparable with that of low-Ca type-2 boninites. The Kelian Igneous Complex is characterised by positive Zr and Hf anomalies in the trace element patterns which is uncommon for calc-alkaline subduction zone magmas. The chemical diversity in the Magerang-Imang and Nakan suite might have been generated by a combined wallrock assimilation and fractional crystallisation process involving a parental basaltic magma and a Zr-rich cumulate. It is suggested that the Magerang-lmang and Nakan high Mg andesites were fed by magma chambers that formed deep in the crust, and were emplaced into pre-existing intrusions of felsic composition that formed as part of the Kelian Igneous Complex cycle. The shallow level stocks at Magerang-1.mang and Nakan were generated by intrusions that melted the walls and roofs of related, but pre-existing intrusions, and extracted abundant xenocrystic zircons during the assimilation process. This study represents the first Platinum Group Element data for a fractionated suite of calc-alkaline andesite. The technique developed in this study represents a breakthrough in our ability to monitor important ore elements in felsic igneous system. The PGE distribution patterns in the Magerang-lmang hornblende andesite are subparallel to each other over a range of concentrations that vary by about a factor of 20. All the Magerang-lmang samples are depleted in Ru, Ir and Os concentrations relative to Re, Pd, Pt and Rh concentrations and have Pd/Ir values of 15 to 54 and Ru/Ir - 1. The PGE concentrations decrease with increasing Si02, showing that they are depleted by fractional crystallisation. Gold is depleted by an order of magnitude and relative to Re and Pd. The low concentration of gold in the igneous rocks associated with the Kelian gold deposit is unexpected. Most metal deposits are found in association with rocks that are already enriched in the metal of interest. It is therefore surprising to find a major gold deposit in host rocks that are depleted in Au. It is also interesting that Au and PGE ratios change little during fractionation. This is surprising because it implies either that the partition coefficients for the PGEs into the sulphides are similar, which seems unlikely, or that Au and the PGEs are not being depleted by simple equilibriwn fractional crystallisation of sulphide. Alternatively, the gold and PGE fractionation are due to the assimilation of crustal material. This appears to be the most plausible process for the gradual depletion of Au and all of the PGE at Kellan. It is suggested that simple dilution with crustal material that contains no Au or PGE is the most likely process that will decrease the abundance of all of the PGE equally. Zircon U-Th-Pb isotope dates were determined in situ using excimer laser ablation ICP-MS. The two different bodies of the Magerang hornblende andesite yielded a single age of 19.38 ± 0.12 Ma and 19.62 ± 0.21 Ma, while the Nakan andesite gave an age of 20.01± 0.15 Ma. The Central Andesite porphyry at Kelian gave 3 populations of U-Pb zircon dates: 21.2 ± 0.32 Ma, 20.5 ± 0.12 Ma and 19.7 ± 0.12 Ma. The youngest date (19.7 Ma) is interpreted as the emplacement age and the two older zircon populations represent the age of inherited zircons coming from the previous thermal event that affected the source region of the andesite. The U-Pb zircon dating for the Runcing Rhyolite porphyry also yielded 3 distinctive date populations: the youngest date of zircon population (19.3 ± 0.1 Ma) is interpreted as the emplacement age and the other two populations (20.0 ± 0.2 Ma and 20.8 ± 0.1 Ma) represent the ages of inherited zircons. The emplacement age of the Magerang-Imang andesite implies that the highsulphidation Cu-Au mineralisation at Magerang is younger than the low-sulphidation Au deposit at Kelian. The Kelian and Magerang andesites have a relatively short interval of emplacement ages suggesting that the duration of magmatism and related epitbermal mineralisation in the larger Kelian region was between 0.5 - 1 Ma. During this period, the magmatic-hydrothermal system has produced 2 distinctive types of epithermal mineralisation: firstly, low-sulphidation Au deposit at Kelian and secondly highsulphidation Cu-Au mineralisation at Magerang-Imang. Detrital zircons from the Mahakam and Kelian rivers were dated to obtain the overall duration of volcanism in the region. These zircons are dominated by Pliocene, Miocene, Cretaceous, Triassic, Permian and Carboniferous zircons. The youngest detrital zircon from the Kelian river gave an age of 1.7 ± 0.1 Ma and the oldest one gave an age of 373 Ma. Within the Tertiary zircon population, there are age spectra peaks at Pliocene (from 1.7 Ma to 2.8 Ma) and Miocene (from 15.8 Ma to 21.7 Ma). The Cretaceous zircon population ranges from 67 .6 to 126.3 Ma and peaks at l 05 Ma. The gold mineralisation at Kelian occurs toward the end of the Miocene volcanism and took place locally within the Kelian region as this Miocene volcanism is not recorded in the zircon component from the larger Mahakam river. The two large inheritance populations in both the Central Andesite and Runcing Rhyolite lie within the time range of the Kelian igneous complex as defined by the KeJian River detrital zircons. They must be derived from crustal intrusions that formed as part of the Kelian cycle. It is suggested that both the Kelian Andesite and Runcing Rhyolite were fed by 2 magma chambers that formed deep in the crust, each of which were long lived. The magma chambers that fed the Kelian Andesite and Runcing Rhyolite were emplaced into pre-existing intrusions of similar composition that formed as part of the Kelian igneous complex. The abundance of xenocrystic zircons in both units suggests that these earlier intrusions were still hot, or perhaps even partially molten, at the time of magma emplacement. That is the shallow level stocks and diatremes at Kelian were fed by nested, cannibalistic intrusions deep in the crust that melted the walls and roofs of related, but pre-existing intrusions, and inherited abundant xenocrystic zircons in the process. Both the Kelian Andesite and the Runcing Rhyolite have two populations of inherited zircons, which indicate that the pre-existing intrusions formed in two distinct episodes, 0.7 to 0.8 m.y. apart. The difference between the emplacement age and the age of the oldest of the inherited zircon populations shows that this cannibalistic activity took place over 1.5 m.y. The interval of magmatic activity in these chambers corresponds to the period of peak activity in the Kelian igneous complex as defined by the detrital zircons.