Paleozoic-Mesozoic volcanic evidence based on petrographic analysis in Mengkarang area, Jambi Province, Indonesia (original) (raw)
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Indonesian Journal on Geoscience, 2020
Syn-sedimentary mafic volcanism has been identified within a rift setting (Eocene Tanjung Formation) in the Senakin Peninsula, southeast Kalimantan. Fine-grained, dark-grey basalt lava occurs and has prominent vertically oriented columnar jointing. Petrographically, the basalt is composed of small euhedral pyroxene, olivine, and lath-shaped plagioclase phenocrysts within a very fine-grained dark coloured groundmass. A volcaniclastic unit also occurs and in outcrop has sharp contacts with underlying and overlying sedimentary mudstone. The unit is composed of cm-scale clasts of fine-grained to glassy textured basalt with vesicles of varying size and abundance. Euhedral pyroxene phenocrysts are observed within the clasts, although some with overprinting alteration. Palagonite alteration on the margins of some clasts is noted and is indicative of mafic composition volcanic material that has come into contact with sea water. Presence of bivalve and coral fragments in sandstone and mudstone underlying the volcaniclastic unit indicates emplacement into a marine environment. Core description from 33 locations over an 18 km transect length show that both the basalt and volcaniclastic sediments are extensive throughout the east Senakin area. Lithological relationships and compositional similarities between the basalt and volcaniclastic sediment suggest they are related and were contemporaneous with sedimentation within the Tanjung Formation. It is proposed that the basalt unit is designated the Tanah Rata Basalt Member of the Tanjung Formation. If a wider distribution occurs for the volcaniclastic unit it is proposed that it is termed the Gumbil Volcaniclastic Member of the Tanjung Formation.
The geological history of the Latimojong region of western Sulawesi, Indonesia
Journal of Asian Earth Sciences, 2017
We present an updated geological map and revised stratigraphy of the Latimojong region of central-western Sulawesi. This work includes new biostratigraphic ages from the Latimojong Metamorphic Complex, Toraja Group, Makale Formation and Enrekang Volcanics, together with whole-rock geochemical data and sensitive highresolution ion microprobe (SHRIMP) U-Pb analyses from zircons extracted from igneous rocks in the region. Previous work on the study region and in other parts of Sulawesi have discussed the age and character of two different rock sequences with similar names, the Latimojong Complex and the Latimojong Formation. One would assume that the type location for these two sequences is in the Latimojong Mountains. However, there is considerable confusion as to the character and location of these sequences. We make a distinction between the Latimojong Formation and the Latimojong Complex, and propose that the Latimojong Complex be renamed the Latimojong Metamorphic Complex to minimise the confusion associated with the current nomenclature. The Latimojong Metamorphic Complex is an accretionary complex of low-to high-grade metamorphic rocks tectonically mixed with cherts and ophiolitic rocks, while the Latimojong Formation consists of Upper Cretaceous weakly deformed, unmetamorphosed sediments or very low-grade metasediments (previously interpreted as flysch or distal turbidites that unconformably overlie older rocks). Our work indicates that the Latimojong Formation must be restricted to isolated, unobserved segments of the Latimojong Mountains, or are otherwise not present in the Latimojong region, meaning the Latimojong Formation would only be found further north in western Sulawesi. Radiolaria extracted from chert samples indicate that the Latimojong Metamorphic Complex was likely assembled during the Cretaceous (Aptian-Albian) and was later metamorphosed. Ages obtained from benthic and planktonic foraminifera were used to differentiate and map the Toraja Group (Ypresian to Chattian: 56-23 Ma), Makale Formation (Burdigalian to Serravallian: 20.5-11.5 Ma) and Enrekang Volcanic Series (8.0-3.6 Ma) across the study area. U-Pb isotopic data collected from magmatic zircons record several phases of volcanism (~38 Ma, ~25 Ma and 8.0-3.6 Ma) in the region. Each phase of magmatism can be distinguished according to petrology and whole-rock geochemical data. The isotopic ages also show that dacites from the Enrekang Volcanic Series are contemporaneous with the emplacement of the Palopo Granite (6.6-4.9 Ma). Miocene to Proterozoic inherited zircons within these igneous rocks support earlier suggestions White et al., to be submitted to J. Asian Earth Sciences that Sulawesi potentially has a Proterozoic-Phanerozoic basement or includes sedimentary rocks (and therefore detrital zircons) derived from the erosion of Proterozoic or younger material. Some earlier work proposed that the granitic rocks in the region developed due to crustal melting associated with plate collision and radiogenic heating. Our observations however, support different interpretations, where the granites are associated with arc magmatism and/or crustal extension. The region was cross-cut by major strike-slip fault zones during the Pliocene. This deformation and the buoyancy associated with relatively young intrusions may have facilitated uplift of the mountains.
E3S Web of Conferences, 2019
Volcaniclastic rocks in East Johor Basin are found in a relatively great abundance comprising Sedili and Pengerang Formations excluding the metamorphics, siliciclastics, and granites. Since the volcaniclastic rocks are found in a different formation, this study aims to find out the characteristics of each rock. Geology, petrography, and geochemical analyses were elaborated to reveal the petrogenesis and depositional environment in the studied area on the basis of fieldwork data and 24 samples collected from outcrops. The Sedili and Pengerang Formations are dominated by acidic rocks of rhyolite, rhyodacite, ignimbrite, and lava classifiied into calc-alkaline magma series which indicates a subduction-related product. Moreover, those acidic rocks are grouped into active continental margin. Eventhough volcanic rocks in Sedili and Pengerang Formations exhibit similar characteristics, they are different in several major contents. Therefore, it is inferred that both Sedili and Pengerang Fo...
65 m.y.-long magmatic activity in Sumatra (Indonesia), from Paleocene to Present
Bulletin De La Societe Geologique De France, 2004
Kq wo s.-Ages (4K-'oAr), Calc-alkaline lavas, Island ar€, Sumatra, Java, Indonesia. Ab\tract.-Swn tra is th€ largest volcanic islatrd of the Indonesian archipelago. The oblique subduction of the lndian Ocean lithosphere below the Sundaland margin is responsible for the developmedt of a NW-SE trending volcanic arc, the location ofwhich coitrcides approxirnately with the Great Sumatratr Fault Zotre (CSFZ)-We preseat io this paper ca. 80 ne* onK-ooAt ages measured-on Cenozoic calc-alkaline to shoshonitic magmatic rocks sampled all along this arc ftorB Ac€h to Lampung. The results show that magmatic activity started duriog the Paleocene (ca. 63 Ma) all along rhe arc, aad was more or less permalrent urtil Present. However, its spatiel distribution increased at ca. 20 M8, a featwe po6sibly connected to the development of the Gr€at Surnatran Fault. The position of Plio-Quatemary magmatic rocks is shifted away from the tencb by a few tens of kilometres with rcspect to that of P.leocene to Miocene on€s, a feailue consiste[t with a sigBificant tectotric erosiotr of the Sundaland margia during the Celozoic' The studigd samples display opical subduction-related geochemical riglratures. However, w€ have been utrable to idefiiry cleai geocheDrical trends, either spatial or temporal. We sugg€st that the lack ofsuch regular variations teflects a complex igneous petrogenesis during which the contribution of the Sundaland contidental crust overpdnted those of the mantle wedge and the subducted slab.
Stratigraphy and Tectonics of the Sengkang Basin, South Sulawesi
Indonesian Journal on Geoscience, 2010
This study applies the charcoalification measurement method to infer the emplacement temperature of pyroclastic flow deposits erupted from the Sundoro Volcano, Indonesia. This pyroclastic flow partially covered the Liyangan archeological site, a site where Hindu temples were constructed approximately 1,000 years ago. Five samples of charcoal collected from this area were analyzed for reflectance and elemental composition. Charcoalification temperatures were determined based on mean random optical reflectance values (Ro) plotted on published Ro-Temperature curves. Charcoalification temperatures were also estimated using a published formula based on the charcoal's hydrogen to carbon (H/C) ratio. These two methods for determining pyroclastic flow deposition temperatures indicated that the pyroclastic deposits that entombed the Liyangan archeological site ranged from 295° to 487°C when they were deposited. This study used very simple, rapid, precise, and low-cost methods of charcoalification temperature measurement to infer the emplacement temperature of a pyroclastic deposit. This estimation procedure could be applied widely to predict emplacement temperatures in volcanic area in Indonesia to enhance volcanic hazard mitigation.
Geological Journal, 2017
The Early Permian (Asselian) Mengkarang Formation of the western Jambi Province, Sumatra, is well exposed in the valley of the Merangin River. No consensus regarding the depositional environment of this section had been reached hitherto. This section preserves abundant evidence of a Permian forest, named the Merangin Fossil Forest herein, which grew at the foot of an active volcano, where pyroclastic flows often made way and destroyed the vegetation and where epiclastic reworked pyroclastics rapidly entombed the vegetation. The present assessment is based on a detailed study of three localities using multiple lines of evidence, including petrography, silica typing including hot cathodoluminescence microscopy and spectroscopy, and palynofacies analysis. In situ Agathoxylon was near enough to the volcanic slope to be buried rapidly, shallow enough to avoid extreme crystallization in the lumina, and far enough from the metamorphic centre not to get recrystallized. All these combined contingencies make this a most unique find that provides significant insights into a rarely studied palaeoecological setting from the Early Permian.
Nucleation and Atmospheric Aerosols, 2018
Kampung Awah and Tasik Kenyir are geologically located in East Malaya Blocks. These block is also known as western margin of Indochina terrane. Apart from sedimentary formations, East Malaya Blocks is also dominated by plutonic and volcanic rocks of mafic to rhyolitic compositions. Petrography and geochemical data suggest that Kampung Awah and Tasik Kenyir are one of locations which consists of volcanic rocks of generally basaltic to basaltic andesite compositions. Volcanic rocks from both area consists of plagioclcase, clinopyroxene, orthpyroxene as main mineral constituents with minor occurrences of hornblende. Geochemical data also indicate that volcanic rocks from both area were formed during subduction of the Paleo-tethys oceanic underneath the East Malaya Block or Indochina terrane. Most of the samples are metaluminous which indicate the volcanics are derived from igneous origin. This paper will contribute new geochemical data of mafic volcanics from Kampung Awah and Tasik Kenyir with the support of petrographic and field evidence to deduce the magma evolution and the tectonic setting.
Indonesian Journal on Geoscience, 2016
Bayat Complex is usually used as a work field for students of geology and other geosciences. The study area is located in the southern part of the Bayat Complex. Administratively, it belongs to Central Java Province and Yogyakarta Special Province. The lithology of Bayat is very complex, composed of various kinds of igneous, sedimentary, metamorphic, and volcanic rocks. Most of previous researchers interpreted Bayat as a melange complex constructed within a subduction zone. Kebo-Butak is one of formations that forms the Bayat field complex. The formation is composed of basalt, layers of pumice, tuff, shale, and carbonaceous tuff. Most of them are known as volcanic rocks. These imply that volcanic activities are more probable to construct the geology of Bayat rather than the subducted melange complex. The geological mapping, supported by geomorphology, petrology, stratigraphy, and geological structures, had been conducted in a comprehensive manner using the deduction-induction method. The research encounters basalt, black pumice, tuff with basaltic glasses fragments, zeolite, argilic clay, as well as feldspathicand pumice tuff. Petrographically, the basalt is composed of labradorite, olivine, clinopyroxene, and volcanic glass. Black pumice and tuff contain prismatic clinopyroxene, granular olivine, and volcanic glasses. Feldspathic tuff and pumice tuff are crystal vitric tuff due to more abundant feldspar, quartz, and amphibole than volcanic glass. Zeolite comprises chlorite and altered glasses as deep sea altered volcanic rocks. The geologic structure is very complex, the major structures are normal faults with pyrite in it. There were two deep submarine paleovolcanoes namely Tegalrejo and Baturagung. The first paleovolcano erupted effusively producing basaltic sequence, while the second one erupted explosively ejecting feldspathic-rich pyroclastic material. The two paleovolcanoes erupted simultaneously and repeatedly.