J. SE Asian Appl. Geol., Jan–Jun 2011, Vol. 3(1), pp. 45-53

PETROGENETIC INTERPRETATION OFGRANITOID ROCKS USING MULTICATIONICPARAMETERS 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, Indonesia2Department of Geology, Yangon University, Myanmar3Department of Earth Resources Engineering, Kyushu University, Japan

Abstract

Granitoid rock compositions from a range of tec-tonic environments are plotted on a multicationic di-agram, based on major and trace element geochem-istry and K-Ar dating. This shows that there is a dif-ferent tectonic nature, rock affinity and suites. Thebasement granitoid rocks are ranging from diorite togranite composition. They appear to the productsof crystallization differentiation of a calc-alkalinemagma of island affinity and range to metalumi-nous granites, granodiorite and tonalite. The tec-tonic setting has two kinds which are subductionand post-subduction. The geochemical interpreta-tion, origin and melting of mechanism and tectonicsetting shows the types of granitoid are M and I-Mtype. The basement of granite and granodiorite area segment of island arc that were happened the Sin-tang Intrusion as post subduction or syn-collisiontectonic setting.Keywords: Petrogenetic, tectonic, affinity, SintangIntrusion, Kalimantan

1 Introduction

Sanggau area is located in the northwest partof West Kalimantan Province. The island ofKalimantan presently lies upon the southeast-

*Corresponding author: K.L. ZAW, Department ofGeological Engineering, Faculty of Engineering, GadjahMada University, Jl. Grafika 2 Yogyakarta, 55281, Indone-sia. E-mail: klinzaw@gmail.com

ern margin of the greater Eurasian plate. It isbounded to the north by the South China Seamarginal oceanic basin, to the east by the Philip-pine Mobile Belt and the Philippine Sea Plateand to the south by the Banda and Sunda arcsystems (Figure 1). It is bounded to the westby the Sunda Shelf and ultimately by Paleozoicand Mesozoic continental crust of the MalayPeninsula. The Greater Kalimantan Block issurrounded to the north, east, and south byplate boundaries and arc systems which arepresently active or which have been active dur-ing the Tertiary and it is bounded to the westby an underexplored shelf region which possi-bly conceals a terrain boundary.

Based on petrological and geochemical char-acteristics such as rock assemblage, petrogeo-chemistry, K-Ar age, studied petrogenesis ofdifferent stages of magmatism of the graniticrocks from the Sanggau Area in Kalimantan.The magmatic activities of the Sanggau areacan be divided into three stages. The Meso-zoic magmatism, induced by northern subduc-tion of The Paleocene-Eocene magmatism wasthe most intensive, and resulted from a com-plex progress of Neotethyan oceanic slab, in-cluding subduction, rollback, and subsequentbreakoff. Neotethyan slab, was continuouslydeveloped, with two peak periods of Late Juras-sic and Early Cretaceous.

And the Oligocene-Miocene magmatism was

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Figure 1: Location map and tectonic features of the Indonesia

attributed to the convective removal of thick-ened lithosphere in an east-west extension set-ting after India and Asia.

2 REGIONAL GEOLOGICAL SET-TING

The main elements of regional structure inWest and Central Kalimantan and Sarawakare the huge prism of upper Cretaceous tolower Tertiary greywacke in the north, andthe Lower to Upper Cretaceous subduction-related Schwaner Batholith in the south. Thewestern part of this region is formed by pre-Tertiary igneous, metamorphic, and deformedsedimentary rocks (Figure 2), which constitutethe Northwest Kalimantan Domain of Williamet al. (1988). The Semitau ridge is the mostimportant structural feature in Sanggau. Itis an east-southeasterly trending structuralridge spanning outcrops of Permo-Triassic fo-liated igneous rocks of the Busang Complexin the east and Embuoi Complex in Sang-gau (Doutche, 1992). The huge SchwanerBatholith and its northwestern extension, theSingkawang Batholith (Amiruddin, 1989), ap-pear to be confined to the southern side of thefundamental structure forming the Semitauridge. The Semitau ridge parallels the northern

margins of the granodiorite and tonalite of theSchwaner Batholiths, which in turn are consid-ered to reflect the trend of a subduction zoneactive in Early Cretaceous times. The struc-tural development of Sanggau was probablyinitiated in Triassic times with the subduction-related deformation of the igneous rocks of theEmbuoi Complex, as recorded by K-Ar ages onbiotite from foliated granitoids. The prevailingregional trend preserved in all these formationsis west-northwesterly, which together with theorientation of belts of mélange in adjacent Sheetareas reflects a convergent continental marginwith the same orientation. Along this margin,which was probably located to the south ofSanggau deformation and accretion occurredintermittently from Triassic until early Tertiarytimes.

3 GEOCHEMISTRY

Major elements

The numbers of schemes based on chem-ical composition have been applied forthe classification and nomenclature of ig-neous rocks. The classification scheme ofDe La Roche et al. (1980) involving thewhole rock chemical composition into cation

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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 thediagram portrays variation in quartz contentwhile the Y-axis, [R2 = 6 Ca + 2 (Mg + Al)],portrays variation in Mg/Fe ratio and Ancontent of the constituent plagioclase. Forbasic rocks with common assemblage plagio-clase, pyroxene, and olivine, this classificationscheme portrays their composition satisfactory.However, for basic and intermediate rocks con-taining cumulus amphibole, the R2 becomesunrealistically high, resulting in the classifica-tion of gabbroic rocks as ultrabasic and thoseof diorites as gabbros. In this scheme, the ana-lyzed samples of the area plot closely; three inthe field of granodiorites, tonalite and diorite(Figure 3).

On SiO2 vs. Na2O + K2O classificationscheme of Cox et al. (1979), the basementsamples as granite, granodiorite and diorite(Figure 4). In O’Connor’s (1965) normativeAn-Ab-Or diagram, the rocks plot in the fieldof tonalite, granodiorite and granite (Figure 5).

Figure 3: Classification of the study rocks usingthe parameters R1 and R2 (after De La Roche,1980), calculated from multication proportions

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Figure 4: Plot of the rock samples from Sanggauarea in the classification diagram of Cox et al.,(1979)

The rocks are essentially calc-alkaline on theAFM diagram (Figure 6) of Irvine and Baragar(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 notedthat, the samples show little variation in SiO2and while FeOt, TiO2, MgO and CaO exhibitnegative correlation, P2O5 and K2O show posi-tive correlation with increasing in SiO2. A lackof iron-enrichment in the basement rocks withfractionation suggests their calc alkaline nature(Miyashiro 1977; Irvine and Baragar, 1971)

4 Petrogenesis and Tectonic Setting ofOrigin

For assessing the petrogenetic associa-tion, the basement analyses are plotted inACNK vs. ANK (where ACNK = molarAl2O3/[CaO+Na2O+ K2O], and ANK = mo-lar Al2O3/[Na2O+K2O]) diagram of Maniarand Piccoli (1989).

The analyzed samples of basement rocksshow metaluminous character (Figure 8). TheAFM diagram is most commonly used to distin-

Figure 5: Ab-An-Or ternary plot classifying thesilicic rocks (> 10% modal quartz) of the rocks.Fields are after O’Connor (1965) with modifica-tion of Barker (1979)

Figure 6: AFM diagram showing the calc-alkaline character of the sample alalyzsis(Irvine & Baragar, 1971)

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PETROGENETIC INTERPRETATION OF GRANITOID ROCKS USING MULTICATIONIC PARAMETERS

Figure 7: Binary plots showing behavior of major elements against SiO2 in granitoid rocks fromSanggau area

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Figure 8: Classification of granitoid rocks fromSanggau area on the basic of Shand’s molar in-dices, ACNK= Al2O3 (CaO+Na2O+K2O) andANK= Al2O3 (Na3O+K2O) (after Maniar andPiccoli,1989)

guish between tholeiitic and calc-alkaline dif-ferentiation trends in the sub-alkaline magmaseries. Miyashiro (1974) presented dividinglines separating the rocks of the calc-alkalineseries and tholeiitic series. On this diagram(Figure 9), the analyses plots in the field ofmost are calc-alkaline series. It was concludedthat the basement rocks evolved from magmaof calc-alkaline affinity. The calc-alkaline char-acter of the basement rocks is further substanti-ated by their metaluminous character revealedby their high ANK ratio (1.2–3.9) relative toACNK (0.62–1.0).

Whereas the major element chemistry of thebasement rocks is of limited usage, restrictedto classification, nomenclature, and assessmentof their petrological association, some samplewith full set of trace elements is of greater help,in determining the nature of the source mate-rial, and in deciphering the tectonic setting oforigin. Pearce et al., (1984) devised a variety ofdiagrams based on incompatible trace elementsfor distinguishing within-plate, collisional, vol-canic arc and oceanic-ridge granites. The vol-canic arc origin for the basement sample is sub-stantiated by Rb vs. Y + Nb plot of Pearce et al.,(1984) in Figure 10. The metaluminous nature

Figure 9: Samples showing the affinity of calc-alkaline and tholeiite series of the granitoidrock analyses after Miyashiro (1974).

of Sanggau is evident from major cation param-eters of Debon and Le Fort (1983), which essen-tially consist of biotite+ amphibole±pyroxeneassemblage (Figure 11). The R1-R2 multica-tion factors (De La Roche et al., 1980) classifythe samples as granodiorite and quartz mon-zonite (Figure 5), corresponding to basementrocks formed in pre-plate collision and SintangIntrusions formed by syn-collision tectonic set-ting (Figure 12).

The basement rock is compared with gran-ites and granodiorite from type tectonic settingsin terms of ocean ridge granite (ORG)- normal-ized trace element patterns (Figure 13). Therock from Sintang Intrusion has a spiked pat-tern, which makes it different from all othertectonic settings. However, a lower contentof HFSE, negative Nb anomaly, and not tooenriched abundance of LILE suggest a closermatch with island arc tholeiites and volcanicarc granites than with the within-plate granites.The basement rock from pre-plate collision andSintang intrusion is from syn-collision in termsof trace element spider diagram.

50 © 2011 Department of Geological Engineering, Gadjah Mada University

PETROGENETIC INTERPRETATION OF GRANITOID ROCKS USING MULTICATIONIC PARAMETERS

Figure 10: Rb vs. Y+Nb discriminant of the rockanalysis of the samples. Syn-collisional granite(syn-COLG), volcanic arc granite (VAG), withinplate granite (WPG) and ocean ridge granite(ORG) are after Pearce et al. (1984)

Figure 11: A-B diagram (Debon and LeFort, 1983) plotted for granitoid in present.Each of its six sectors, numbered from Ito VI, corresponds to a specific mineral as-semblage. I, II and III are peraluminoussectors, where I: muscovite>biotite (by vol-ume); II: biotite>muscovite; III: biotite (usu-ally alone, at times with a few amphi-boles); IV, V and VI are metaluminous sec-tors, where IV: biotite+ amphibole±pyroxene;V:clinopyroxene±amphibole±biotite; VI: un-usual rocks (e.g., carbonatites)

Figure 12: Classification and nomenclature ofgranitoid rocks using the parameters R1 and R2of De La Roche et al., (1980), calculated frommultication proportions

Figure 13: Comparison of the eight represen-tative samples from Sanggau area (ocean ridgegranite value after Pearce et al., 1984)

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5 Adakite Geochemistry

The term adakite comes from island of Adak(Aleutian Island, Alasaka) and was originallydefined to describe Cenozoic (<25 Ma) arc-related volcanic rocks with a a number of geo-chemical characteristics, including SiO2 ≥ 56wt.%, Al2O3 ≥ 5 wt.%, 3 wt.%≤ MgO≤ 6 wt.%,Y≤ 18 ppm, Sr≥ 400 ppm (Defant and Drum-mond, 1990). Contrary to normal, arc-relatedtholeiitic and calc-alkaline rocks that originatein the mantle wedge and later evolve by crystalfractionation or other processes, the adakiticrocks are derived from direct partial meltingof a subducting slab (Defant and Drummond,1990). These authors related the magma gen-eration to the melting of hot, young (<25 Ma)subducting lithosphere. Numerical and petro-logical models (Peacock et al., 1994) restrictthe process to even younger subducting litho-sphere (<5 Ma) at typically 60–80 km depth.

A graph of Sr/Y vs. Y (Figure 14) empha-sizes the difference between basement grani-toid rocks and Sintang Intrusive rock. Samplesfrom Sintang Intrusive rocks are within adakitefield. Partial melting of source would gener-ate melting curves that pass through the adakitefield toward high Sr/Y but low Y. Accordingto adakite geochemistry and trace element in-terpretation, Sintang Intrusive rocks may comefrom post subduction tectonic setting.

According to dating, in the correspond area,younger magmatic products of 28.1 ± 0.4 Ma in-dicate the chemical characters of adakitic mag-matism. These all of the above data show thatduring Oligo-Miocene time in Sintang areas, theprevious magmatic system giving the productshave been introduced by the back-arc magmaticsystem. The occurrence of Sintang adakitesthen may correlate rather to the collision thanto the subducted young oceanic plate, hence thecollision of Luconian continental block to Kali-mantan (Priadi, 2010).

6 Discussion and Conclusion

On the basis of geochemistry, the granite rocksare considered to be product of crystalliza-tion differentiation of a calc-alkaline magmawith pyroxene, biotite and amphibole playing

Figure 14: Y vs. Sr/Y binary diagram showingadakite field of the analyses

a major role in fractionation history of gran-ites. The trace element geochemistry of sam-ples collected from the basement is reflectiveof magmas typical of island arcs. In conclu-sion, the basement of granite and granodioriteare a segment of island arc that were happenedthe Sintang Intrusion as post subduction or syn-collision tectonic setting.

Acknowledgements

The author is very grateful to Dr. Lucas DonnySetijadji for his providing and allowing usingthe data and his kind guidance and suggestionfor academic support, as well as AUN/SEED-Net (JICA), Japan International Co-operationAgency, for financially support to process thisresearch work.

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