Analysis of granitoid type of Bukit Nunggal Village, Air Mesu, Central Bangka Regency

The research was conducted in Bukit Nunggal Air Mesu Village, Pangkalan Baru District, Central Bangka Regency, an IUP PT Tanjung Bukit Nunggal with a height of ± 210 meters. This study is to find out more details about the type of granitoid rock which is a unitary hill but it is estimated that it is the intrusion body of several types of granitoid rock. The research method includes analysis of mineralization content and geochemical analysis in the form of XRF. The steps to be taken include literature studies, field research, laboratory analysis including mineralogical analysis and microscopic observations as well as geochemical testing of rock samples using XRF. The sampling procedure for analysis is carried out based on the height and changes in rock texture, on the number of rock types / lithologies available to be observed and examined for their mineralization content. Regionally, the study area consists of a hill which is interpreted as a potential rock for construction mining. It is hoped that this research can produce an analysis of the existing granitoid types by studying the lithology / rock, geological structure and mineral textures. There are 2 types of granite found in Nunggal Hill, namely granite and granite alterated (gneiss), with its main minerals are quartz, feldspar, biotit, opaq and sericytic and chlorite minerals.

THE PETROLOGY CHARACTERISTIC OF GRANITOID ROCK BASED ON GEOCHEMICAL ANALYSIS OF BAJAU CAPE COAST AND ITS SURROUNDING, WEST KALIMANTAN

The aim of this study is to identify of petrology characteristic based on geochemical analysis in order to know the granitoid rock type. Administratively, the study area is in the City and District of Singkawang, West Kalimantan Province, at coordinate 108°48'30” - 109°1'30” E and 0°40'30” - 0°54'30” N and, situated ± 145 km to the north of Pontianak City. The outcrop of granitoid along Bajau Cape coast and its surrounding, had been analyzed petrographically and geochemically using AAS method. Based on analysis of five samples show that the ratio mole of Al2O3/(CaO+Na2O +K2O) > 1 ranged between 1.12 and 1.7, while the rest of three samples are moderately aluminous, with a ratio value between 0.5 and 1.0. The ratio between K2O and (K2O+Na2O+CaO) ranges 0.07 to 0.55 (moderate) that forms alkali feldspar normative ranges from 3.8 to 15.89 wt%. This ratio shows that granite alkali feldspar is classified to be calc-alkaline series. Petrographically, this rock is porfiritic texture, hollocrystalline, granular hypodiomorphic and biotite present as phenocryst, yellowish brown, euhedral, thin and platy. The content of oxides element (Na2O and MgO) tend to decrease, whereas of other oxides elements, namely Al2O3, TiO2, K2O, FeO and CaO increased, parallel with the raising of SiO2. Therefore, the Singkawang Granitoid can be grouped as alkali feldspar granite, syeno-granite and quartz monzonite. Keywords: petrography, geochemstry, major elements, calc-alcaline affinity, granitoid type and Bajau Coast, West Kalimantan. Penelitian ini bertujuan untuk mengidentifikasi karakteristik petrologi, berdasarkan analisa geokimia sehingga jenis batuan granitoidnya dikenali. Secara administratif, daerah penelitian termasuk ke dalam Kota dan Kabupaten Singkawang, Provinsi Kalimantan Barat, pada koordinat 108°48'30” - 109°1'30” BT and 0°40'30” - 0°54'30” LU dan terletak ± 145 km, arah utara dari Kota Pontianak. Singkapan batuan granitoid sepanjang pantai Tanjung Bajau dan sekitarnya telah dianalisis secara petrografi dan geokimia dengan menggunakan AAS. Berdasarkan 5 contoh yang dianalisa menunjukan perbandingan mol Al2O3/(CaO+Na2O +K2O) > 1, yakni berkisar antara 1,12-1,7, sedangkan 3 contoh sisanya bersifat peraluminus sedang, dengan nilai ratio antara 0.5-1.0. Perbandingan antara K2O dan (K2O+Na2O+CaO) berkisar antara 0,07-0,55 (sedang) yang membentuk alkali normatif feldspar berkisar 3,84 – 15,89% (berat). Perbandingan tersebut menunjukan batuan Granit alkali feldspar yang tergolong dalam seri batuan kalk-alkali. Secara petrografi, batuan tersebut menunjukkan tekstur porfiritik, holokristalin, hipidiomorfik granular dengan biotit hadir sebagai fenokris, coklat kekuningan, euhedral, pipih dan sedikit berlembar. Kandungan unsur oksida (Na2O dan MgO) cenderung mengalami penurunan, sedangkan unsur oksida lainnya, yaitu Al2O3, TiO2, K2O, FeO dan CaO mengalami kenaikan sejalan dengan makin bertambahnya SiO2. Maka dengan demikian Granitoid Singkawang dapat dikelompokan menjadi granit alkali feldspar, syenit-granit dan kuarsa-monsonit. Kata kunci: Petrografi, geokimia, senyawa utama, afinitas kalk-alkalin, batuan granitoid dan Pantai Bajau, Kalimantan Barat.

Petrogenetic interpretation of granitoid rocks using multicationic parameters in the Sanggau Area, Kalimantan Island, Indonesia

Granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram, based on major and trace element geochemistry and K-Ar dating. This shows that there is a different tectonic nature, rock affinity and suites. The basement granitoid rocks are ranging from diorite to granite composition. They appear to the products of crystallization differentiation of a calc-alkaline magma of island affinity and range to metaluminous granites, granodiorite and tonalite. The tectonic setting has two kinds which are subduction and post-subduction. The geochemical interpretation, origin and melting of mechanism and tectonic setting shows the types of granitoid are M and I-M type. The basement of granite and granodiorite are a segment of island arc that were happened the Sintang Intrusion as post subduction or syn-collision tectonic setting. Keywords: Petrogenetic, tectonic, affinity, Sintang Intrusion, Kalimantan

SHRIMP U-Pb zircon ages for Archaean granitoid rocks, Ataa area, north-east Disko Bugt, West Greenland

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Nutman, A. P., & Kalsbeek, F. (1999). SHRIMP U-Pb zircon ages for Archaean granitoid rocks, Ataa area, north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 49-54. https://doi.org/10.34194/ggub.v181.5111 _______________ Zircons from four samples of granitoid rocks from the Ataa area have been studied by SHRIMP ion microprobe. A trondhjemite from the Atâ intrusive complex (Atâ tonalite) yielded an age of 2803 ± 4 Ma, in agreement with earlier age determinations. A sample from the regional migmatitic biotite gneisses gave 2815 ± 4 Ma. A homogeneous granitoid rock, from field observations believed to be younger than the regional gneisses, has two main zircon populations, 2835 ± 4 Ma and c. 2800 Ma, respectively, and a granite that intrudes the Atâ complex yielded an age of 2758 ± 2 Ma.

Time of metamorphism beneath the Central Metasedimentary Belt boundary thrust zone, Grenville Orogen, Ontario: accretion at 1080 Ma?

New U–Pb zircon and titanite data from the Muskoka domain, Grenville Province, Ontario, provide protolith and metamorphic ages for the southwestern Central Gneiss Belt. Discordant analyses from a migmatitic orthogneiss and its leucosome form a linear array with an upper intercept age of 1457 ± 6 Ma and a lower intercept age of 1064 ±18 Ma. U–Pb analyses on metamorphic zircon from an amphibolite yield a set of concordant analyses with an average 207Pb/206Pb age of 1079 ± 3 Ma. A weakly migmatitic granitoid rock and a transecting charnockitic vein in the immediate footwall of the Central Metasedimentary Belt boundary thrust zone yielded a discordant array of analyses wth an upper intercept age of 1394 ± 13 Ma and a lower intercept age of 1066 ± 8 Ma. The charnockitic vein yielded concordant zircon ages of 1077 ± 2 Ma. The upper intercept ages are interpreted in terms of protolith crystallization, and the concordant and lower intercept ages as Grenviilian high-grade metamorphism and associated anatexis. We have found no evidence for a ca. 1190–1160 Ma metamorphic event in these rocks, as required by some regional tectonic interpretations. We conclude that emplacement of the Central Metasedimentary Belt over the Central Gneiss Belt, which caused high-grade metamorphism in the Muskoka domain, occurred at or shortly before ca. 1080 Ma, and that this marks the time of accretion of the Central Metasedimentary Belt to the southeast margin of Laurentia.