Petrogenetic Interpretation of Granitoid Rocks Using Multicationic Parameters in the Sanggau Area, Kalimantan Island, Indonesia
Total Page：16
File Type：pdf, Size：1020Kb
J. SE Asian Appl. Geol., Jan–Jun 2011, Vol. 3(1), pp. 45-53 PETROGENETIC INTERPRETATION OF GRANITOID ROCKS USING MULTICATIONIC PARAMETERS IN THE SANGGAU AREA, KALIMANTAN ISLAND, INDONESIA Kyaw Linn Zaw*1,2, Lucas Donny Setijadji1, I Wayan Warmada1, and Koichiro Watanabe3 1Department of Geological Engineering, Gadjah Mada University, Yogyakarta, Indonesia 2Department of Geology, Yangon University, Myanmar 3Department of Earth Resources Engineering, Kyushu University, Japan Abstract ern margin of the greater Eurasian plate. It is bounded to the north by the South China Sea Granitoid rock compositions from a range of tec- marginal oceanic basin, to the east by the Philip- tonic environments are plotted on a multicationic di- pine Mobile Belt and the Philippine Sea Plate agram, based on major and trace element geochem- and to the south by the Banda and Sunda arc istry and K-Ar dating. This shows that there is a dif- systems (Figure 1). It is bounded to the west ferent tectonic nature, rock affinity and suites. The by the Sunda Shelf and ultimately by Paleozoic basement granitoid rocks are ranging from diorite to and Mesozoic continental crust of the Malay granite composition. They appear to the products Peninsula. The Greater Kalimantan Block is of crystallization differentiation of a calc-alkaline surrounded to the north, east, and south by magma of island affinity and range to metalumi- plate boundaries and arc systems which are nous granites, granodiorite and tonalite. The tec- presently active or which have been active dur- tonic setting has two kinds which are subduction ing the Tertiary and it is bounded to the west and post-subduction. The geochemical interpreta- by an underexplored shelf region which possi- tion, origin and melting of mechanism and tectonic bly conceals a terrain boundary. setting shows the types of granitoid are M and I-M Based on petrological and geochemical char- type. The basement of granite and granodiorite are acteristics such as rock assemblage, petrogeo- a segment of island arc that were happened the Sin- chemistry, K-Ar age, studied petrogenesis of tang Intrusion as post subduction or syn-collision different stages of magmatism of the granitic tectonic setting. rocks from the Sanggau Area in Kalimantan. Keywords: Petrogenetic, tectonic, affinity, Sintang The magmatic activities of the Sanggau area Intrusion, Kalimantan can be divided into three stages. The Meso- zoic magmatism, induced by northern subduc- 1 Introduction tion of The Paleocene-Eocene magmatism was the most intensive, and resulted from a com- Sanggau area is located in the northwest part plex progress of Neotethyan oceanic slab, in- of West Kalimantan Province. The island of cluding subduction, rollback, and subsequent Kalimantan presently lies upon the southeast- breakoff. Neotethyan slab, was continuously developed, with two peak periods of Late Juras- *Corresponding author: K.L. ZAW, Department of Geological Engineering, Faculty of Engineering, Gadjah sic and Early Cretaceous. Mada University, Jl. Grafika 2 Yogyakarta, 55281, Indone- And the Oligocene-Miocene magmatism was sia. E-mail: [email protected] 45 ZAW et al. Figure 1: Location map and tectonic features of the Indonesia attributed to the convective removal of thick- margins of the granodiorite and tonalite of the ened lithosphere in an east-west extension set- Schwaner Batholiths, which in turn are consid- ting after India and Asia. ered to reflect the trend of a subduction zone active in Early Cretaceous times. The struc- 2 REGIONAL GEOLOGICAL SET- tural development of Sanggau was probably TING initiated in Triassic times with the subduction- related deformation of the igneous rocks of the The main elements of regional structure in Embuoi Complex, as recorded by K-Ar ages on West and Central Kalimantan and Sarawak biotite from foliated granitoids. The prevailing are the huge prism of upper Cretaceous to regional trend preserved in all these formations lower Tertiary greywacke in the north, and is west-northwesterly, which together with the the Lower to Upper Cretaceous subduction- orientation of belts of mélange in adjacent Sheet related Schwaner Batholith in the south. The areas reflects a convergent continental margin western part of this region is formed by pre- with the same orientation. Along this margin, Tertiary igneous, metamorphic, and deformed which was probably located to the south of sedimentary rocks (Figure 2), which constitute Sanggau deformation and accretion occurred the Northwest Kalimantan Domain of William intermittently from Triassic until early Tertiary et al. (1988). The Semitau ridge is the most times. important structural feature in Sanggau. It is an east-southeasterly trending structural 3 GEOCHEMISTRY ridge spanning outcrops of Permo-Triassic fo- liated igneous rocks of the Busang Complex Major elements in the east and Embuoi Complex in Sang- The numbers of schemes based on chem- gau (Doutche, 1992). The huge Schwaner ical composition have been applied for Batholith and its northwestern extension, the the classification and nomenclature of ig- Singkawang Batholith (Amiruddin, 1989), ap- neous rocks. The classification scheme of pear to be confined to the southern side of the De La Roche et al. (1980) involving the fundamental structure forming the Semitau whole rock chemical composition into cation ridge. The Semitau ridge parallels the northern 46 © 2011 Department of Geological Engineering, Gadjah Mada University PETROGENETIC INTERPRETATION OF GRANITOID ROCKS USING MULTICATIONIC PARAMETERS Figure 2: Regional geological map of the area proportions yields mixed result. The re- grouping of cations is such that the X-axis, [R1 = 4 Si − 11 (Na + K) − 2 (Fe + Ti)], of the diagram portrays variation in quartz content while the Y-axis, [R2 = 6 Ca + 2 (Mg + Al)], portrays variation in Mg/Fe ratio and An content of the constituent plagioclase. For basic rocks with common assemblage plagio- clase, pyroxene, and olivine, this classification scheme portrays their composition satisfactory. However, for basic and intermediate rocks con- taining cumulus amphibole, the R2 becomes unrealistically high, resulting in the classifica- tion of gabbroic rocks as ultrabasic and those of diorites as gabbros. In this scheme, the ana- lyzed samples of the area plot closely; three in the field of granodiorites, tonalite and diorite (Figure 3). On SiO2 vs. Na2O + K2O classification scheme of Cox et al. (1979), the basement Figure 3: Classification of the study rocks using samples as granite, granodiorite and diorite the parameters R1 and R2 (after De La Roche, (Figure 4). In O’Connor’s (1965) normative 1980), calculated from multication proportions An-Ab-Or diagram, the rocks plot in the field of tonalite, granodiorite and granite (Figure 5). © 2011 Department of Geological Engineering, Gadjah Mada University 47 ZAW et al. Figure 4: Plot of the rock samples from Sanggau area in the classification diagram of Cox et al., (1979) Figure 5: Ab-An-Or ternary plot classifying the silicic rocks (> 10% modal quartz) of the rocks. The rocks are essentially calc-alkaline on the Fields are after O’Connor (1965) with modifica- AFM diagram (Figure 6) of Irvine and Baragar tion of Barker (1979) (1971). Major Element variations The TiO2 and Na2O+K2O vs. SiO2 plots (Fig- ure 7) clearly discriminate samples contain vari- ation correlation of oxide elements. As noted that, the samples show little variation in SiO2 and while FeOt, TiO2, MgO and CaO exhibit negative correlation, P2O5 and K2O show posi- tive correlation with increasing in SiO2. A lack of iron-enrichment in the basement rocks with fractionation suggests their calc alkaline nature (Miyashiro 1977; Irvine and Baragar, 1971) 4 Petrogenesis and Tectonic Setting of Origin For assessing the petrogenetic associa- tion, the basement analyses are plotted in ACNK vs. ANK (where ACNK = molar Al2O3/[CaO+Na2O+ K2O], and ANK = mo- lar Al2O3/[Na2O+K2O]) diagram of Maniar Figure 6: AFM diagram showing the calc- and Piccoli (1989). alkaline character of the sample alalyzsis The analyzed samples of basement rocks (Irvine & Baragar, 1971) show metaluminous character (Figure 8). The AFM diagram is most commonly used to distin- 48 © 2011 Department of Geological Engineering, Gadjah Mada University PETROGENETIC INTERPRETATION OF GRANITOID ROCKS USING MULTICATIONIC PARAMETERS Figure 7: Binary plots showing behavior of major elements against SiO2 in granitoid rocks from Sanggau area © 2011 Department of Geological Engineering, Gadjah Mada University 49 ZAW et al. Figure 8: Classification of granitoid rocks from Figure 9: Samples showing the affinity of calc- Sanggau area on the basic of Shand’s molar in- alkaline and tholeiite series of the granitoid dices, ACNK= Al2O3 (CaO+Na2O+K2O) and rock analyses after Miyashiro (1974). ANK= Al2O3 (Na3O+K2O) (after Maniar and Piccoli,1989) of Sanggau is evident from major cation param- eters of Debon and Le Fort (1983), which essen- guish between tholeiitic and calc-alkaline dif- tially consist of biotite+ amphibole±pyroxene ferentiation trends in the sub-alkaline magma assemblage (Figure 11). The R1-R2 multica- series. Miyashiro (1974) presented dividing tion factors (De La Roche et al., 1980) classify lines separating the rocks of the calc-alkaline the samples as granodiorite and quartz mon- series and tholeiitic series. On this diagram zonite (Figure 5), corresponding to basement (Figure 9), the analyses plots in the field of rocks formed in pre-plate collision and Sintang most are calc-alkaline series. It was concluded Intrusions formed by syn-collision tectonic set- that the basement rocks evolved from magma ting (Figure 12). of calc-alkaline affinity. The calc-alkaline char- The basement rock is compared with gran- acter of the basement rocks is further substanti- ites and granodiorite from type tectonic settings ated by their metaluminous character revealed in terms of ocean ridge granite (ORG)- normal- by their high ANK ratio (1.2–3.9) relative to ized trace element patterns (Figure 13). The ACNK (0.62–1.0). rock from Sintang Intrusion has a spiked pat- Whereas the major element chemistry of the tern, which makes it different from all other basement rocks is of limited usage, restricted tectonic settings.