Syn-sedimentary Mafic Volcanics in the Eocene Coal-bearing Tanjung Formation, Senakin Peninsula, South Kalimantan (Borneo), Indonesia (original) (raw)
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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.
Journal of geoscience, engineering, environment and technology, 2022
The Muria-Peninsula is a Quaternary volcano located in the northern Sunda arc. Its activity was controlled under high potassic and very high potassic magma series resulting in leucite-rich trachyte and pyroxene-rich basaltic-andesite. It is a strato-type volcano that is composed of lava, breccia, and tuff layers, and some dikes have some volcanic craters and maars varying in age and composition. The study area is covering the volcanoes of Muria, Genuk, and Patiayam. This paper aims to describe the petrology, mineralogy, and volcano-stratigraphy of the different volcanic materials. The data and materials were sourced from the primary and secondary data. The methods are field mapping, stratigraphy measurements, collecting samples, thin section analyses, and major element geochemistry using X-Ray fluorescence (XRF). The results describe two groups of volcanic rocks consisting of pyroxene-rich andesiticbasaltic volcanic materials and leucite-rich trachytic volcanic materials. Augite presents in the andesitic basalt together with small grains of olivine and a few anorthite and foid minerals. Aegirine (Na-Pyroxene) is present in the leucite-rich trachyte that is often associated with biotite and hornblende. Na-Ca Plagioclase such as labradorite-andesine is often present in the basaltic-trachy-andesite that is usually rarely leucite. The major elements show high-K volcanic rocks with % K2O is 4-5.9% and very high-K volcanic rocks (with % K2O is between 6-8.24%) and low-K volcanic rocks that contain % K2O is 2-3,9%. There are two groups of high-K to very high-K volcanic materials consisting of silicic-rich volcanic materials (~57-64% of SiO2) and low-silicic volcanic materials (~46-50%). The TAS diagram identifies tephrite, phonolite, and trachyte. Stratigraphic data identifies calcareous sediments of the Bulu Formation as the basement rocks of the Muria trachyandesite. Beds of pumice-rich volcanic breccia of the Ujungwatu Formation are the basement rocks of the basanite-tephrite of the Genuk Volcano, and the tuff of the Ujungwatu is also exposed consisting of the basanite-tephriticphonolite of the Patiayam Volcano. The leucite-like feldspars are very common in the andesite lava and dikes that compose the crater of Muria. Most of the Muria volcanic materials are rarely in leucite, while some maars contain pumice-rich pyroclastic flows and basaltic lava. The results of the major elemental analysis of the Muria materials indicate that the rock tends to be of medium to high K affinity (~2% K2O). The Genuk and older Muria are consisting of leucite-rich tephrite-phonolite. It was two periods of magmatic series developed in the Muria-Peninsula that was resulting in the high-K to very high-K magmatism and the medium K Kalk-alkaline magmatism.
Indonesian Journal on Geoscience, 2021
The study of tholeiitic basalt is a general-classic study from geotectonic MORB, ocean island (OIB), continental rift, volcanic-arcs {IAB or Active Continental Margin (ACM)}. However, the geotectonic study of the tholeiitic volcanic-arcs is still unclear at the moment. In general, the arc tholeiitic is directly pointed to an island-arc volcanic, and the result of google search engine defines no existence of tholeiitic geochemistry which is formed from continental-arc volcanic (ACM). The problem lies in the model of discrimination diagram which is not able to discriminate ACM from the island arc volcanic. The spider diagram shows relatively similar of patterns as well as in the use of the isotope 143Nd/144Nd versus 87Sr/86Sr. Tholeiitic Kebasen pillow lava exhibits a slightly hydrothermal alteration (propyilitic alteration) which consists of plagioclase (labradorite-bytownite), olivine, pyroxene (diopside), hornblende, volcanic glass and other secondary minerals (such as iddingsite, zeolite, carbonate, sericite and opaque minerals). The results of the interpretation using the overlay diagram of Mg# and FeO(t)/MgO, diagram Nb/La vs. La/Yb, the overlaid diagram between the diagram of Zr/Y vs. Zr, newly developed diagram for sedimentary recycling (Th/Ce vs. SiO2) reveal the Kebasen lava is a differentiated tholeiitic rock with relatively low of Mg# (Mg# < 55) which is generated from geotectonic forearc ACM (Active Continental Margin) and involves the sedimentary recycling (Th/Ce > 0.1); furthermore, the trace element constituent is interpreted based upon the melting of oceanic slab (Zr/Y ~ 3). The magmatism of Kebasen lava is potentially formed at temperature of ~ 1240 o C and a pressure of ~ 1.7 GPa at the depth of ~ 56 Km.
We subdivided volcaniclastic layers drilled during Leg 157 around Gran Canaria at distances up to 70 km from the shore of the island at Hole 953C, 955A, and 956B deposited between 14 and ~11.5 Ma into >100 volcaniclastic units at each site. Most volcaniclastic layers are <20 cm thick, but complex turbidite units up to 1.5 m thick make up 10% to 20% of all volcaniclastic units in Holes 953C and 956B. We distinguish several types of clasts: felsic vitroclasts, (1) bubble-wall/junction shards, (2) brown nonvesicular felsic shards, (3) welded tuff clasts, (4) pumice shards, and (5) sideromelane shards. Mineral phases comprise anorthoclase and lesser amounts of plagioclase, calcic and sodic amphibole (kaersutite, richterite, and edenite), clinopyroxene (titanaugite to aegirine), hypersthene, minor enstatite, phlogopite, Fe/Ti oxides, sphene, chevkinite, apatite, and zircon. Xenocrysts are dominantly titanaugite derived from the subaerial and submarine shield basalts. Lithoclasts are mainly tachylitic and crystalline basalt, the latter most common in Hole 953C, and fragments of felsic lava and ignimbrite. Bioclasts consist of open planktonic foraminifers and nannofossil ooze in the highly vitric layers, while filled planktonic foraminifers, benthic foraminifers, and a variety of shallow water calcareous and siliceous fossils and littoral skeletal debris are common in the basal coarser grained parts of turbidites.
K-rich Basalt in the Bukit Mersing area, Third Division, Sarawak
Bulletin of the Geological Society of Malaysia, 2006
The basalts exposed near Bukit Mersing, Sarawak are early Eocene in age, and li e conformably ove r the highly folded , imbricated metasediments of th e Rajang Group. Initi ally thought to be oph iolite, it lies close to the "Tatau-Bukit Mersing Line" , which was thought to be a major thrust fault or terrane suture, containi ng obducted ocean floor material. The one analysis published in 1957 showed a K 2 0 value of 2.82%, too high for ocean floor basalt produced at a spreading center. New ana lyses confirm that K contents in these rocks are high. The K is hosted in K-feld spar rims around pl agioclase phenocrysts. Based on the chemistry, and on field relation ships , the Tau Range basalt is not op hio lite, but is likely to be Oceanic Island basalt, developed over oceanic crust, caused by short-lived hot spot magmatism.
Journal of JTM, 2007
Hulusimpang Formation, volcanic products with Oligocene to Early Miocene in age, is mostly cropped out in southern part of Sumatera, particularly in Bengkulu and Lampung Provinces. Kota Agung is situated in the southernmost of Sumatera, in Lampung Province, at coast of Semangko Bay that is cut by southern segment of Sumatera Fault Zone. The Hulusimpang Formation around Kota Agung and surrounding areas shows bimodal magmatic composition consisting of basalt and dacite. They are classified as medium-K calc-alkaline volcanic type. The absence of andesitic rocks in the formation indicates that the change of magma composition from basaltic to dacitic is probably caused by contamination processes instead of a fractional crystallization or magmatic differentiation. Indicators of the contamination can be recognized in spider diagrams of their trace elements showing significant influences of subducting components that are rich on incompatible elements, such as Sr, Rb, Ba, K and Th compared to N-MORB.
Mengkarang area is part of Merangin National Geopark, Jambi Province, Indonesia. The area is mainly consisted of Permian and Jurassic rocks and known for its well-preserved fossils, where the occurrence of this fossils could demonstrate the massive extinction of Permian Age. Despite numerous studies on fossils of Mengkarang area have been published, only a few petrographical studies conducted on Mengkarang area. Such study is important in the future to better determine the petrotectonic setting of the Mengkarang area. We collected several igneous, volcaniclastic, and sedimentary rock samples from various rock formations in the study area. By combining the field observation and petrographic analyses, we made several assumptions that can link Mengkarang rocks to the Paleozoic-Mesozoic volcanic activity and deformation. The vitric tuff displays flow banding and welded features. Some of the petrographic samples show low-moderate argillic to intense propylitic alteration that related to volcanic activity, with several deformation evidence. Other samples show biotite minerals that altered to chlorite and deformed by the formational compaction. Furthermore, the rocks in the southern part of the Mengkarang area generally experienced stronger deformation compared to another part of the study area.
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.
Morphotectono-volcanic of Tertiary volcanic rock in Kulon Progo mountains area, Yogyakarta-Indonesia
IOP Conference Series: Earth and Environmental Science
Kulon Progo Mountains have very distinctive shapes, where they have form of circular structures of volcano that are still intact and the other is not been intact. This morphology is the morphology of the remaining volcanoes formed by tectonics and certain volcanisms. The study was conducted through a series of interpretations of volcanic body distribution, alignment interpretation on satellite imagery and field work. The formation of Kulon Progo Mountain morphology is strongly influenced by tectonic and volcanic processes. The process of tectonics which produces strike-slip fault structures, normal faults, and uplifts have formed the lineaments of the valleys and hills with various pattern directions. The volcanism that has occurred forms the structure of volcanic remains. Distribution of volcanic rocks form a circular or semicircle structures because of the normal fault structures that have occurred.