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Indonesian Journal on Geoscience Vol. 3 No. 3 December 2016: 197-216

INDONESIAN JOURNAL ON GEOSCIENCE Geological Agency Ministry of Energy and Resources

Journal homepage: hp://ijog.geologi.esdm.go.id ISSN 2355-9314, e-ISSN 2355-9306

Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin

Godang Shaban1, Fadlin2, and Bambang Priadi3

1Geochemist, Rare and REEs Researcher 2Geological Engineering, Jenderal Soedirman University (UNSOED) Jln. Mayjen. Sungkono Km 05, Blater, Purbalingga 3Department of Geology, Institute of Technology Bandung (ITB) Jln. Ganesha No.10, Bandung

Corresponding author: [email protected] Manuscript received: July 26, 2016; revised: October 24, 2016; approved: November 18, 2016; available online: December 7, 2016

Abstract - The Adang Volcanics represent a series of (ultra) potassic to sodic and tuffaceous rocks of predominantly trachytic composition, which forms the part of a sequence of Late Cenozoic high-K volcanic and associated intrusive rocks occurring extensively throughout Western Sulawesi. The tectonic setting and origin of these high-K rocks have been the subject of considerable debates. The Adang Volcanics have to mafitic-intermediate characteristics (SiO2: 46 - 56 wt%) and a wide range of high alkaline contents (K2O: 0.80 - 9.08 %; Na2O: 0.90 -

7.21 %) with the Total Alkali of 6.67 - 12.60 %. Al2O3 values are relatively low (10.63 - 13.21 %) and TiO2 values relatively high (1.27 - 1.91 %). Zr and REE concentrations are also relatively high (Zr: 1154 - 2340 ppm; Total REE (TREY = TRE): 899.20 - 1256.50 ppm; TRExOy: 1079.76 - 1507.97 ppm), with an average Zr/TRE ratio of ~ 1.39. The major rock forming minerals are leucite/pseudoleucite, /, and high temperature . Geochemical plots (major oxides and trace elements) using various diagrams suggest the Adang Volcanics formed in a postsubduction, within-plate continental extension/initial rift tectonic setting. It is further suggested was generated by minor (< 0.1 %) partial melting of depleted MORB mantle material (-lherzolite) with the silicate melt having undergone strong . Melt enrichment is reflected in the alkaline nature of the rocks and geochemical signatures such as Nb/Zr > 0.0627 and (Hf/Sm)PM > 1.23. A comparison with the Vulsini ultrapotassic volcanics from the Roman Province in Italy shows both similarities (spidergram pattern indicating affinity with Group III ultrapotassics volcanics) and differences (nature of mantle metasomatism). Keywords: Adang Volcanics, sodic and potassic/ultrapotassic, within-plate continental extension/initial rift, metasomatized silicate melts, leucite/pseudoleucite © IJOG - 2016. All right reserved

How to cite this article: Godang, S., Fadlin, and Priadi, B., 2016. Geochemical Signatures of Potassic to Sodic Adang Volcanics, West- ern Sulawesi: Implications for Their Tectonic Setting and Origin. Indonesian Journal on Geoscience, 3 (3), p.197-216. DOI: 10.17014/ijog.3.3.197-216

Introduction with associated intrusives and volcaniclastics. he volcanic rocks occurring in the central part Large parts of the Western Sulawesi Prov- of the province have been subdivided into four ince are covered by thick (up to 5000 m) piles units, these are Sekala Formation, Sesean, Adang, of Upper Cenozoic shoshonitic to ultra-potassic and Talaya Volcanics (Ratman and Atmawinata, and subordinate sodic volcanic rocks together 1993). The Adang Volcanics are the subject of

AccreditedIJOG/JGI by:(Jurnal - LIPI, Geologi valid AugustIndonesia) 2016 - -Acredited August 2021 by LIPI No. 547/AU2/P2MI-LIPI/06/2013. valid 21 June 2013 - 21 June 2016 - RISTEKDIKTI, valid May 2016 - May 2021 197 Indonesian Journal on Geoscience, Vol. 3 No. 3 December 2016: 197-216 this paper. Their locations are shown in Figure ous processes (e.g. Yuwono et al., 1. The unit consists of a sequence about 400 m 1985; Leterrier et al., 1990); thick of poorly bedded leucite-bearing lapilli 2. The volcanic rocks were formed in an Active , volcanic consisting of leucite Continental Margin (ACM) setting in which fragments embedded in leucite-bearing tuffaceous magma was generated from mantle melting in matrix, and leucite basalt flows (Ratman and At - the final stage of the subduction process (Pus - mawinata, 1993). Major element analyses carried pita et al., 2005), which involved subduction of out previously on a number of samples suggest microcontinental (Sukadana et al., 2015); the Adang Volcanics are mafic to intermediate in 3. The volcanics developed as the result of col- composition, ranging from to tephrite lision between the Banggai-Sula fragment and (Sukadana et al., 2015). Waele and and western Sulawesi (Bergman et al., 1996). Muharam (2014) describe the rocks as phlogopitic The goal of the research is to deduce from and leucitic volcanic rocks. The Adang Volcanics the magmatic typology of the Adang Volcanics, interfinger with the marine sedimentary Mamuju their tectonic setting, and the nature of submantle Formation, which has a latest Miocene to Early enrichment, using the geochemical approach. Pliocene age (Ratman and Atmawinata, 1993), The studied area is defined by the following and have yielded K/Ar ages of 5.4 and 2.4 Ma coordinates 118°45’11.10”E - 119°5’13.41”E (Bergman et al., 1996). The morphology of the and 2°33’28.27”S - 2°59’34.52”S, covering the volcanics is youthful, showing a volcanic centre Subregencies of Kalukku, Mamuju, Tabulahan, and several domal structures (Sukadana et al., Simboro, Tapalang, and Malunda. 2015). Opinions differ regarding the origin of these and other high-K rocks in the province: Materials and Methods 1. Magmatism took place in a postsubduction, continental-margin rift setting with the source For this purpose, six outcrop samples (loca- mantle having been metasomatized by previ- tions shown on Figures 1a, b, and 2) were sub-

b 120o E 124 o E a 2o N 2o N North Sulawesi Trench 9.715.000

9.710.000 Northern Sulawesi Palu - Koro Fault Koro - Palu Mamuju Sangihe Trench City 9.705.000

Batui Trust

9.700.000 Neogene NW sedimentary rocks

Makassar Strait o Paleogene o 2 S sedimentary rocks 2 S Mesozoic

9.695.000 Tma (Adang Volcanic), Rifting fault sedimentary rocks (Mid -- Late Miocene) Pliocene-Recent volcanics CW Matano Fault Neogene calc-alkaline volcanics

9.690.000 Kls Neogene potassive volcanics (Latimojong Easthern Sulawesi Formation) Paleogene volcanics

Tolo Trench

9.685.000 Intrusive rocks SW N Tmtv Metamoorphic rocks (Talaya Volcanic) Walanae Fault Tmpi Ophiolite 9.680.000 (Granitoid N Major thrust 0 6 12 km complex) 6o S 6o S Major strike-slip fault

695.000 700.000 705.000 710.000 715.000 720.000 725.000 730.000 735.000 120o E 100 km 124 o E

Figure 1. (a). Geological map of central Western Sulawesi (Ratman and Atmawinata, 1993) showing the location of the researched area and the six samples described in the text. Coordinate system UTM Zone 50S; (b). Simplified geological map of Sulawesi (modified after Sukamto, 1975b; Hamilton, 1979; Silver et al., 1983; Parkinson, 1991, in Van Leeuwen and Pieters, 2011). Western Sulawesi (dashed line) subdivided into NW (northwest; north part of Western Sulawesi), CW (central-west), and SW (southwest) Sulawesi.

198 Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin (Godang, S. et al.)

0 4.5 9 km Sample for Petrographic (GS1-0016-17)

9.715.000 N 9.710.000

Mamuju City 9.705.000

Rifting fault 9.700.000

1600 m 9.695.000 Tma 1500 m 1400 m 1300 m 1200 m 9.690.000 1100 m Kls 1000 m 900 m 800 m

9.685.000 700 m Sample for Petrographic 600 m (GS1-0607-10) Tmtv 500 m 400 m

9.680.000 300 m Sample for Petrographic Tmpi 200 m (GS1-0926-28) 100 m 0 m

695.000 700.000 705.000 710.000 715.000 720.000 725.000 730.000 735.000

Figure 2. Image of DEM-SRTM (ASTER 30m) and the position of sampling points. jected to major oxide, trace element, and rare weathering residue, trachytic fragments), vol- element (REE) analyses (Tables 1 and 2). caniclastics and intercalations of mafic/ The rocks were petrographically also studied in mafitic- (consisting of order to support the interpretation of the geo- leucite/pseudoleucite, diopside/aegirine and high chemical data. Geochemical analyses involved temperature phlogopite). Other rocks observed XRF and four acids digest (ICP-OES/MS, ICP- locally include peralkaline dyke, a mafic trachyte REE) assay methods, which were carried out at body, multiple dykes of mafic and leucitic intru- Intertek Laboratories in Jakarta and Perth. In sions, subvolcanic trachyte intrusion, addition, trace element data have been plotted intercalations of crystalline limestone, and other on various diagrams previously obtained from carbonate rocks. The limestone intercalations and 31 company drill core samples, and major oxide the presence of pillow lavas indicate the Adang data for 36 previously analyzed outcrop samples Volcanics were deposited in a marine environ- for which LOI contents were not determined. ment. Figures 3 and 4 show how the volcanics These samples were also analyzed in the Intertek occur in the field. Laboratories.

Field Relationships Analytical Results The field and petrologic observations indicate that the Adang Volcanics, covering an area of The of three samples in thin secton ~820 km2 (Ratman and Atmawinata, 1993), are is shown in Figures 5 - 7. Moreover, major and composed predominantly of leucite/pseudoleu- trace element results for the six samples presented cite-bearing trachytic tuff, lapilli-tuff, agglom- in Tables 1 and 2 respectively have a Mafic Index erate, volcanic , volcanic-sedimentary of Alteration (MIA(o)) ranging from 31.6 to 45.9 products (volcaniclatics consisting of trachytic (Figure 8). This suggests that all six samples were

199 Indonesian Journal on Geoscience, Vol. 3 No. 3 December 2016: 197-216

Table 1. Major Oxides (wt%) of Six Samples (Adang Volcanics)

No 28 75 82 99 121 1002 Sample_code GS1-0016-17 GS1-0481-85 GS1-0533-36 GS1-0607-10 GS1-0280-86 GS1-0926-28 Fine Leucitic Fine Rock_types Mafic Mafic Mafic Trachyte Trachyte Trachyte Trachyte Trachyte Trachyte Area Salu Dango Takandeang Ampalas Botteng Bebanga Tapalang

SiO2 (%) 55.48 49.28 54.86 50.79 49.15 53.74

TiO2 (%) 1.91 1.77 1.27 1.45 1.70 1.70

Al2O3 (%) 10.91 10.92 13.21 10.63 11.89 12.10

Fe2O3 (%) 11.78 10.80 7.50 9.82 12.80 11.42 FeO (%) 2.15 2.04 2.83 2.04 3.68 1.49 MnO (%) 0.25 0.19 0.12 0.14 0.18 0.14 MgO (%) 2.54 5.87 3.00 6.19 3.53 2.11 CaO (%) 2.03 6.98 3.83 7.25 4.57 3.32

Na2O (%) 3.52 0.90 5.52 1.40 1.89 7.21

K2O (%) 9.08 9.03 1.15 7.86 8.16 0.80 LOI (%) 0.90 1.32 5.70 1.21 1.20 4.32

P2O5 (%) 0.22 0.86 0.55 0.56 0.46 0.22 Total (%) 100.76 99.96 99.54 99.34 99.21 98.56

TA=Na2O+K2O 12.60 9.93 6.67 9.26 10.05 8.01

K2O/Na2O 2.58 10.03 0.21 5.61 4.32 0.11

Cr2O3 (%) 0.006 0.01 <0.005 0.04 0.04 <0.005 Radiometric 345 cps 255 cps 419 cps 200 cps 250 cps 210 cps fresh (after Nesbitt and Wilson, 1992), including concentrations are high (1,154.00 - two samples (No.82 and No.1002) with relatively 2,3440.00), the Total REE (TREY = TRE) ranges high LOI contents (4.3 - 5.7 wt%). This is sup- between 899.20 and 1256.50 ppm, and TRExOy ported by petrographic observations (Figures between 1079.76 and 1507.97 ppm (Table 2). The 7a, b). The Adang Volcanics samples are mafic/ percentage of LREE is 88.23 % (La–Sm) and mafitic - intermediate in composition with rela- that of HREE 11.77% (Eu–Y). The Th/U ratio is tively low SiO2 contents (46 - 56 wt%). Na2O and ~ 4.32/1, indicating a “Non-Uranium anomaly”,

K2O contents show a wide range of values, 0.90 - based on a Th/U ratio of ~ 3/1 {normal abundance 7.21 wt% and 0.80 - 9.08 wt%, respectively. Four of the earth crust : Th (6 ppm), U (1.8 ppm)} of the samples have high K O contents (7.86 and 2 (https://en.wikipedia.org). Relatively high radio- 9.08 wt%) and Na O contents varying between 2 metric signatures (200 - 419 cps) may be related 0.90 and 3.52 wt%, which classifies these rocks to relatively high contents of Zr, K, Th, U, and as ultrapotassic (Foley et al., 1987). The other two Ba (Figure 3g). samples have high Na2O contents (5.52 and 7.21 wt%) and low K O values, indicating they have 2 Interpretation of Results a sodic composition. It is these two samples that The analytical results on various diagrams also have high LOI contents, possibly indicating have been plotted in a diagram to classify the the presence of primary volatiles. Al O contents 2 3 Adang Volcanics, and to elucidate their tectonic are relatively low (10.63 - 13.21 wt%) and TiO2 contents relatively high (1.27 - 1.91 wt%) (typi- setting and the processes in the source mantle cal of nonsubduction volcanics {TiO > (-1.161 that led to their formation. 2 On the TAS diagram of Le Bas et al. (1986) + 0.1935 x Al2O3), (in wt%)} (Figure 9) (Muller and Groves, 1993 and 2000). most samples (including the 36 other samples)

200 Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin (Godang, S. et al.)

Table 2. Trace Element Concentrations (ppm) in Six Samples (Adang Volcanics)

No 28 75 82 99 121 1002 Sample_code GS1-0016-17 GS1-0481-85 GS1-0533-36 GS1-0607-10 GS1-0280-86 GS1-0926-28 Leucitic Rock_types Fine Trachyte Fine Trachyte Mafic Trachyte Trachyte Mafic Trachyte Mafic Trachyte Cr 5.00 56.00 30.00 197.00 5.00 5.00 Cu 128.00 144.00 122.00 104.00 199.00 96.00 Mn 1,600.00 1,320.00 831.00 965.00 1,150.00 838.00 Ni 14.00 46.00 35.00 116.00 17.00 11.00 P 900.00 3,740.00 2,410.00 2,510.00 2,020.00 870.00 S 90.00 <50 1,330.00 160.00 1,150.00 60.00 Sc 7.00 21.00 9.00 23.00 11.00 8.00 Ti 11,300.00 11,000.00 8,030.00 9,180.00 10,100.00 9,650.00 V 254.00 218.00 177.00 210.00 350.00 319.00 Zn 162.00 136.00 130.00 133.00 180.00 101.00 Ag <0.1 0.30 0.30 0.30 0.50 0.40 As 17.00 6.00 29.00 5.00 15.00 4.00 Ba >5000 2,450.00 4,970.00 4,270.00 >5000 >5000 Be 34.20 19.80 28.40 25.10 28.30 39.00 Bi 1.57 1.53 0.72 0.89 2.49 0.95 Cd 1.36 0.75 0.75 0.83 1.10 1.06 Co 22.00 33.00 23.00 30.00 28.00 17.00 Cs 32.30 57.70 50.60 68.20 31.60 214.00 Ga 21.40 20.20 23.70 20.10 24.30 23.00 Ge 0.40 0.60 0.40 0.80 0.20 0.60 Hf 61.50 36.60 35.20 31.90 45.30 47.20 In 0.07 0.08 0.06 0.08 0.11 0.10 Li 61.50 33.10 33.30 30.80 52.00 12.60 Mo 0.30 0.30 1.80 0.40 0.30 0.20 Nb 192.00 102.00 117.00 94.70 121.00 104.00 Pb 330.00 143.00 293.00 147.00 313.00 203.00 Rb 336.00 636.00 614.00 2,126.26 498.00 1,310.00 Sb 0.60 0.40 1.40 0.70 0.80 0.70 Re <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 Se <1 <1 <1 <1 <1 <1 Sn 29.80 18.10 24.00 15.60 25.70 31.00 Sr 699.00 1,350.00 930.00 1,300.00 1,410.00 769.00 Ta 10.00 5.83 6.38 4.82 7.30 8.44 Te <0.1 <0.1 <0.1 <0.1 0.10 <0.1 Th 310.00 154.00 266.80 167.80 230.30 324.10 Tl 4.84 2.66 1.48 3.43 5.52 12.90 U 62.80 32.60 68.10 45.80 51.30 75.50 W 3.00 4.50 18.40 3.20 8.60 2.30 Zr 2,340.00 1,384.00 1,269.00 1,154.00 1,549.00 1,651.00 Average % REE La 277.00 230.60 234.20 194.20 263.60 292.30 248.65 22.28% LREE= 88.23% Ce 552.00 445.40 429.70 371.90 513.70 469.00 463.62 41.54% Pr 59.60 52.90 47.50 44.30 58.20 63.10 54.27 4.86% Nd 194.00 196.60 166.70 159.70 191.20 211.00 186.53 16.71% Sm 32.30 32.80 27.40 26.20 33.70 37.70 31.68 2.84% Eu 5.80 6.10 4.90 4.70 6.50 7.20 5.87 0.53% HREE = 11.77% Gd 21.70 21.80 20.20 18.10 24.40 30.40 22.77 2.04% Tb 3.10 3.00 2.70 2.40 3.20 4.00 3.07 0.27% Dy 16.30 13.10 12.60 10.90 15.20 19.20 14.55 1.30% Ho 2.50 2.10 2.00 1.70 2.60 3.40 2.38 0.21% Er 7.10 5.40 5.40 4.90 6.40 8.90 6.35 0.57% Tm 0.90 0.80 0.90 0.60 0.90 1.20 0.88 0.08% Yb 5.70 4.20 4.60 3.70 5.40 7.40 5.17 0.46% Lu 0.70 0.30 0.60 0.60 0.80 1.00 0.67 0.06% Y 67.60 61.90 63.20 55.30 69.40 100.70 69.68 6.24% TRE 1,246.30 1,077.00 1,022.60 899.20 1,195.20 1,256.50 TREO 1,391.46 1,202.53 1,142.18 1,004.26 1,334.62 1,404.64 TRExOy 1,497.89 1,292.80 1,228.36 1,079.76 1,435.94 1,507.97

TRE2O3 1,464.03 1,265.29 1,201.96 1,056.78 1,404.32 1,478.70 dEu 0.67 0.70 0.64 0.66 0.69 0.65 *The average values of Th (242.17 ppm) and U (56.02 ppm); average Th/U ratio = 4.32/1, Zr/TRE (avg) = 1.39

201 Indonesian Journal on Geoscience, Vol. 3 No. 3 December 2016: 197-216

a b c

d e f

g h i

j k l

L

Figure 3. Field observation photos of Adang Volcanics. (a) Volcaniclastic rock (consists of trachytic fragments); (b) Boul- der of trachyte lava; (c) Crystalline limestone; overlies the Adang rocks, indicating that it formed after volcanic activ- ity had ceased; (d) Intercalation of heavy concentrate-rich sediment in Adang trachytic rock, indicating the volcanics were deposited in a submarine environment (drill sample A07_14-15m); (e) Pyroclastic sodic-rich fine-grained trachyte breccia (East Tapalang region); (f) Peralkaline dyke (silica and alumina undersaturated), sample of fine-grained trachyte No. 28 (GS1-0016-17); (g) Portable Dosimeter (Thermo Scientific tester), showing relatively high radiometric signature (255 cps) of mafic trachyte rock (sample GS1-0481-85, No.75)with low U (32.60 ppm), Th (154.00 ppm), high Zr (1384 ppm), Ba (2450 ppm), high K (K2O: 9.03 wt% and Na2O (0.90%); (h) The marine sedimentary rock (clastic carbonate; drill sample M01_14-15m); (i) Magnifier 40x manual close-up of zirc on crystal (tetragonal, yellow), drill sample C03_10-11m; (j) Magnifier 40x manual close-up of green diopside (monocli nic) in leucite trachyte; (k) Leucite trachyte (drill sampl e A29_22-23m) containing zircon crystal; (l) Magnifier 40x man ual close-up of zircon crystal (tetragonal, colorless) from (k) leucite trachyte. plot in the and basaltic- (after Peccerillo and Taylor, 1976) (Figure 11) the fields (Figure 10). The two sodic samples fall Adang Volcanics are represented by three series: under the basaltic-trachyandesite field, while the potassic alkaline, alkaline, and subalkaline. If the remaining “other samples” are in the tephrite and recently developed Godangs Trapezoid Geochem- istry Diagram (Godang, 2016) is used which also alkali-basalt fields. On the K 2O vs. SiO2 diagram

202 Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin (Godang, S. et al.)

a b c

leucite coarse-grained medium-grained (mela-trachyte) (leucite trachyte) (leucite trachyte)

d e f

medium-grained fine-grained sub-volcanic sanidine (leucite-rich mela-trachyte) (leucite trachyte phenocryst trachyte

g h i

fine-grained very fine-grained mafic trachyte (sodic-rich trachyte breccia) (peralkaline dyke)

Figure 4. Nature of the Adang textures, showing variation in: (a-f) trachytic textures, (g) mafic aphanitic texture (sample GS1-0481-85), (h) ‘pelitic like’ texture (sample GS1-0926-28), and (i) ‘green pelitic like’ texture (sample GS1-0016-17).

a mineralogy (GS1-0016-17) b Thin section mineralogy (GS1-0016-17) “Leucite (diopside) phlogopite Lamproite” Mineralogy (% volume): *Leucite: 52% * Pyroxene (diopside): 35% phlogopite phlogopite *Phlogopite: 12% phlogopite * : < 1% phlogopite Total = 100%

diopside needles diopside needles in groundmass pyroxene (diopside) in groundmass pyroxene (diopside)

leucite leucite

250 µm 250 µm

PPL XPL

Figure 5. (a) Petrographic (PPL) sample GS1-0016-17 (No. 28; fine-grained trachyte; peralkaline dyke); (b) Petrographic (XPL) sample GS1-0016-17 (No. 28; fine-grained trachyte; peralkaline dyke) showing abundant leucite (52%), interpreted as lamproite.

takes Al2O3 and NaO contents into consideration some in the ultrapotassic-series field. A plot on (Figure 12), most of the 43 samples plot in the the Rock Classification Diagram of Pearce (1996), sodic-series and shoshonitic-series fields, and which is based on relatively immobile trace ele-

203 Indonesian Journal on Geoscience, Vol. 3 No. 3 December 2016: 197-216

a Thin section mineralogy (GS1-0607-10) b Thin section mineralogy (GS1-0607-10)

Clinopyroxene Clinopyroxene Clinopyroxene Clinopyroxene

Vesicle filled Vesicle filled with zeolite pseudomorph with zeolite Diopside needles in groundmass Diopside needles Phlogopite in groundmass “Leucite pyroxene phlogopite ” Mineralogy (% volume): *Leucite: 40% * Clinopyroxene (diopside & aegirine): 20% * Phlogopite: 10% Phlogopite *Apatite: <<1% *Opaque grains/masses: 3% Amphibole *Glass materials (groundmass): 5% pseudomorph *Vesicles (voids): 10% Leucite *Clay minerals: 6% Leucite *Zeolite (secondary): 5% Total = 100%

PPL XPL

Figure 6. (a) Petrographic (PPL) sample GS1-0607-10 (No. 99; mafic trachyte dyke). (b) Petrographic (XPL) sample GS1- 0607-10 (No. 99; mafic trachyte dyke) showing abundant leucite (40%), intrepeted as lamprophyre.

a Thin section mineralogy (GS1-0926-28) b Thin section mineralogy (GS1-0926-28)

Pyroxene inclusions Pyroxene inclusions

Phlogopite Phlogopite Pyroxene (aegirine) Pyroxene (aegirine) needlesin groundmass needlesin groundmass

“Leucite? pyroxene (diopside/aegirine) phlogopite Lamproite” Mineralogy (5 volume): pseudoleucite * Pseudoleuctite: 70% pseudoleucite *Pyroxene (diopside/aegirire): 27% *Phlogopite: <1% *Nosean: <1% *Opaque: <1% Total = 100% Rock Class (Pearce, 1996): Sodic-rich fine-treachyte

SiO2 (53.74%), NA 2 O (7.21%, K 2 O (0.80%), Al 2 O 3 (12.10%)

125 µm 125 µm

PPL PPL

Figure 7. (a) Petrographic (PPL) sample GS1-0926-28 (No. 1002; sodic-rich fine-grained trachyte volcanic breccia) shows clearly unaltered condition. (b) Petrographic (XPL) sample GS1-0926-28 (sodic-rich fine-grained trachyte volcanic brec- cia) : pseudoleucite (70%): an intergrowth of albite, , ; interpreted as lamproite. ments, indicates that the rocks are of trachyte af- of potassic to ultrapotassic rocks, the plotting result finity (Figure 13), consistent with the TAS results. shows that the Adang Volcanic samples fall within As a comparison, data for a leucite phonolite the anorogenic within-plate field (Figures 9 and 14). have been plotted from the Vulsini , Roman In contrast, the Vulsini Volcanics appear to have Province, Italy (Santii et al., 2003) on Figure 11, formed in an arc-related tectonic setting (Alkaline which shows the rock belongs to the ultrapotas- Continental Arc; Supra-subduction Continental sic sub-alkaline series (alkaline-calcic character, ). Similar settings for the two units alumina oversaturated). It should be noted that its are suggested by plots on tectonic discriminant dia- alumina content (Al2O3: 19.97 - 20.37 %) is sig- grams for mafic rocks using trace elements shown nificantly higher than that of the Adang Volcanics on Figure 15 (after Hollocher et al., 2012b) (http://

(Al2O3: 10.63 - 13.21 %). minerva.union.edu), Figure 16 (after Wang et al., Using the diagram designed by Muller and 2001; modified in this paper), and Figure 17 (after Groves (1994) to discriminate the tectonic settings Sun et al., 2006; modified in this paper).

204 Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin (Godang, S. et al.)

Ternary Diagram of Weathered/Unweathered Mafic/Basaltic Rock C (Al2 O 3 +Fe 2 O 3 (t)) (after Nesbitt and Wilson, 1992), 0 100 modified by Babechuk et al., 2014 (MIA(o))

[Ternary : (Al2 O 3 +Fe 2 O 3 (t))-(CaO*+Na 2 O+K 2 O)-MgO (in molar)]

MIA(o)= Mafic Index of Alteration (oxidized) 10 90

Symbols: Adang Volcanics: : 20 80 Mafic Trachyte Fine-grained Trachyte .. Leucitic Trachyte Others Adang Trachytic rocks 30 70

Vulsini Volcanics (Roman, Italy) Altered (weathered)

40 60

50 50

60 40

70 30

Unaltered (unweathered) 80 20

90 10

A 100 0 B 0 10 20 30 40 50 60 70 80 90 100 (CaO*+Na2 O+K 2 O) MgO

Figure 8. Plots in Ternary Diagram of weathered/unweathered rock (after Nesbitt and Wilson, 1992), showing all Adang Volcanic samples (6), others Adang Trachytic rocks (36 outcrop samples) and Vulsini Volcanic samples (5) are fresh showing unweathered rocks.

4.5 Symbols: Adang Volcanics 4.0 Mafic Trachyte Fine-grained Trachyte Leucitic Trachyte 3.5 Others Adang Trachytic rocks

Vulsini Volcanics (Roman, Italy)

3.0 2O 3 Within-plate 2 2.5 2

Ti O (wt%) TiO = -1.1610 + 0.1935xAl

2.0

1.5

1.0 Arc-related

0.5

0 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Al2 O 3 (wt%)

Figure 9. Geotectonic diagram for within-plate vs. Arc-related (Muller and Groves, 1993 and 2000) suggesting the Adang Volcanics, others Adang trachytic rocks and Vulsini Volcanic rocks were formed in different tectonic settings.

Figures 18 and 19 are diagrams designed by drill core samples suggest that the rocks were La Fleche et al. (1998) for mafic rocks to identify formed by mantle metasomatism during the different metasomatic processes in the mantle. silicate melting processes, whereas the Vulsini Plots of the six Adang Volcanic outcrop and 31 Volcanics were derived from a hydrated mantle

205 Indonesian Journal on Geoscience, Vol. 3 No. 3 December 2016: 197-216

18 Note: Symbols : 17 Adang Volcanics: * ol = CIPW normative . 16 * P.I = Peralkaline Index (mol), Mafic Trachyte Saturation Line Fine-grained Trachyte 15 (Na2 O+K 2 O)/Al 2 O 3 Leucitic Trachyte phonolite 14 Others Adang Trachytic rocks. 13 Vulsini Volcanics (Roman, Italy) 12 alkali trachyte 11 (P.I > 0.875) alkali (P.I > 0.875) 10 foidite trachyte 9 vs. Subalkaline (Miyashiro, 1978) trachyandesite (P.I < 0.875) Alkaline 2 2 8 tephrite Na O+K O (wt %) (ol < 10%) - 7 basaltic rhyolite trachyandesite (P.I < 0.875) 6 basanite trachy (ol > 10%) basalt 5

4 alkali-basalt 3 picro- 2 basalt basaltic 1 basalt andesite 0 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81

Mafic Intermediate SiO2 (wt%)

Figure 10. Plot in TAS Diagram (after Le Bas et al., 1986) Vulsini Volcanics show peralkaline magma series (silica under- saturated), whereas Adang Volcanics and other Adang trachytic rocks show subalkaline to peralkaline series.

10 basalt (TAS) basaltic-andesite andesite (TAS) dacite and rhyolite (TAS)

9 Symbols: Adang Volcanics Mafic Trachyte Fine-grained Trachyte 8 Leucitic Trachyte Others Adang Trachytic rocks

Vulsini Volcanics (Roman, Italy) 7

., 2002) 6 et al 400 km Potassic alkaline (after Calanchi 2 Shoshonite series

K O (wt%) 5 350 km high-K rhyolite

300 km Alkaline vs. subalkaline (Keith, 1983) 4 Banakite high-K dacite high-K (Calc-alkaline series) 250 km Shoshonite 3 high-K andesite 200 km Absarokite medium-K (Calc-alkaline series) high-K 150 km basaltic-andesite medium-K rhyolite 2 medium-K dacite

high-K basalt medium-K 100 km medium-K andesite basaltic-andesite 1 low-K rhyolite medium-K basalt 50 km low-K dacite low-K (Tholeiitic series) low-K andesite low-K basalt low-K basaltic-andesite 0 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78

Mafic Intermediate Felsic SiO2 (wt %)

Figure 11. Volcanic rocks classification for orogenic zone (K2O vs. SiO2, wt%), (Peccerillo and Taylor, 1976). The depth to Benioff Zone 15 (modified by Fadlin and Godang, 2015 in( Godang, 2015; after Hatherton and Dickinson, 1969). The plotting result of Vulsini Volcanic (Table 3) shows ultrapotassic rocks whereas the Adang Volcanics and others Adang trachytic rocks showed medium-K calc-alkaline to potassic peralkaline.

source (subduction arc-related). This is reflected (Hf/Sm)PM < 1.00) of the Vulsini volcanic rocks in the relatively high Zr and REEs contents (Table 3).

(with geochemical signature (Hf/Sm)PM > 1.23) Figure 20 (diagram after Aldanmaz et al., of the Adang rocks, and low Zr contents rela- 2000; modified in this paper) suggests the tive to Total REE (with geochemical signature mantle source from which the Adang Volcanics

206 Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin (Godang, S. et al.)

Godangs Trapezoid Diagram (2016) Peralkaline

Discrimination of Alkaline type of Igneous rocks for Alkaline 1.05 Ultra-potassic-Potassic-Shoshonitic-Sodic-Calc-alkaline rocks. (after Shand, 1927 (alumina saturation), after Turner et al., 1996 Ab 1.00 (ultra-potassic and sodic series))

Calc-alkaline sub-group O = 1/2 (wt %) Albite 0.90 * Calc-alkaline (Sodic, Potassic) K2 O/Na 2 * Tholeiitic Nepheline Symbols : 0.80 Adang Volcanics Mafic Trachyte K2 O/Na 2 O = 1/1 Fine-grained Trachyte 0.70 Leucitic Trachyte

Others Adang Trachytic rocks. K2 O/Na 2 O = 1.24/1 Sanidine 0.60 Vulsini Volcanics (Roman, Italy) Anorthoclase K2 O/Na 2 O = 1.52/1 Madupitic Lamproite (Badgers Teeth, Leucite Hills) Sub-alkaline (Meta-Peraluminous) Nyiragongo 2002 lava & Older lavas, 0.50 Virunga Volcanics (East African Rift) K2 O/Na 2 O = 2/1 (alkaline-calcic) Sodic series Andesine Oligoclase Shoshobitic series

transition alkaline 2 2 3

0.40 Na O/Al O(molar) , Ab 50% (strong Na-) Potassic series Ultra-potassic series An 50% (strong Ca-) enrichment of Zr and/or REEs 0.30

Labradorite 0.20 Vulsini Volcanic : Sodic calc-alkaline Phlogopite Ultra-potassic Sub-alkaline ., 1963 (approx) Kalsilite Potassic calc-alkaline

(Calc-alkaliine sub-group) et al 0.10 Bytownite Microcline Mostly weathered/altered Leucite

Anorthite (or Potassic mafic rocks) after Deer An Or 0 0 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50

[Na2 O+K 2 O]/Al 2 O 3 , (molar)

Figure 12. Plots in Godangs Trapezoid Geochemistry Diagram (Godang, 2016). The Vulsini Volcanics show the ultrapo- tassic subalkaline (alkaline-calcic character, alumina oversaturated; higher Al2O3 contents), whereas Adang Volcanics and others Adang rocks show a contrast multimagmatic affinity (sodic series, shoshonitic, potassic, and ultrapotassic with alumina from oversaturated to undersaturated). Madupitic lamproite indicates ultrapotasic alkaline - peralkaline, whilst Virunga Volcanics are shoshonitic subalkaline - alkaline - peralkaline.

1.0

Alkali Rhyolite 0.5 Phonolite Trachyte

Evolved Rhyolite Dacite

Tephriphonolite 0.1

Z/Ti (ppm) Z/Ti Trachy-andesite 0.05

Andesite-basaltic

Intermediate Foidite

0.01 Symbols : Adang Volcanics Mafic Trachyte Alkali Basalt Fine -grained Trachyte 0.005 Leucitic Trachyte Basalt Others Adang Trachytic rocks

Basic Vulsini Volcanics (Roman, Italy) Madupitic Lamproite (Badgers Teeth, Leucite Hills) Nyiragongo 2002 lava & Older lavas, Virunga Volcanics (East African Rift)

0.001

0.01 0.05 0.1 0.5 1.0 5.0 10 50 100 0.01 Sub-alkaline Alkaline Ultra-alkaline Nb/Y (ppm)

Figure 13. Rock Classification Diagram (Pearce, 1996) showing Adang Volcanics, others Adang trachytic rocks and Vul- sini Volcanics to have trachytic composition, whereas Virunga Volcanics (East African Rift) and Madupitic lamproite (Leucite Hills) showing the foiditic composition.

207 Indonesian Journal on Geoscience, Vol. 3 No. 3 December 2016: 197-216

1.000 Symbols : Adang Volcanics: 500 Mafic Trachyte Fine-grained Trachyte Leucitic Trachyte Others Adang Trachytic rocks Within-plate ( anorogenic) Vulsini Volcanics (Roman, Italy)

100

50 2 3 2 3 Zr/Al O within-plate

Continental Arc (or ACM) arc-related (Zr in ppm, Al in ppm, (Zr O in wt %) + Post-collisional Arc 10

5

Initial oceanic arc, Late oceanic arc (Subduction Ocean crust-Ocean crust)

1 0.001 0.005 0.01 0.05 0.1 0.5 1

TiO2 / Al 2 O 3 (in wt%)

Figure 14. Tectonic discrimination diagram for high-K igneous rocks (Muller and Groves, 1994) suggesting the Adang Volcanics, other Adang trachytic rocks were formed in different tectonic settings.

Tholeiitic Transitional Calc-alkaline to alkaline (peralkaline)

La/Yb <3 La/Yb = 3 - 6 La/Yb > 6 5

4

3 Continental arcs (ACM) 2 (or alkaline arcs) Alkaline arcs 1 Oceanic arcs (or within-plate continental rift) (IAB)

Th/Nb = 0.67/1 Continental extensional zone/initial rift Th/Nb (in ppm) 0.5

Th/Nb = 0.27/1 (alkali basalts) lower HREE signature Lower crust

Intracontinental rift (La/Yb ~ 800). (tholeiitic) PM OIB Th/Nb - 0.11/1

0.1

Symbols: Adang Volcanics: Hawaiite Mafic Trachyte Fine-grained Trachyte 0.05 Leucitic Trachyte MORB Oceanic islands (or within-plate oceanic crust basalts) Trachytic rocks (company drill data)

Vulsini Volcanics (Roman, Italy) Madupitic Lamproite

La/Yb (in ppm) T-MORB, OIB, EMORB, (Badgers Teeth, Leucite Hills) 0.02 Nyiragongo 2002 lava & Older lavas, Virunga Volcanics (East African Rift) 0.4 0.5 1 5 10 50 100

Figure 15. Tectonic discrimination diagram for Basalts (after Hollocher et al., 2012b). Magmatic Affinity: ratio La\Yb for Tholeiitic--Transitional--Calc-alkaline to Alkaline (MacLean and Barrett, 1999), ratio Th/Nb (after Sun et al., 2006). Plot in Figure 15 and overlaying with Figure 14, the result showed Adang Volcanics were formed in within-plate continental extension zone/initial rift and Vulsini Volcanics formed in alkaline arcs, whereas Virunga Volcanics (East African Rift) were formed from within-plate oceanic island and the magma is possible generated from ‘mantle plume’? Madupitic lamproite (Leucite Hills) shows a lower HREE signature (La/Yb ~ 800).

208 Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin (Godang, S. et al.)

2

Symbols: Adang Volcanics: Ta/Th = 1/4 Mafic Trachyte Ta/Th = 1/1.6 Fine grained Trachyte 1 Leucitic Trachyte Within-plate enrichment Hawaiite Trachytic rocks (company drill data) (Melt-relatedSubduction enrichment) enrichment (Fluid-related enrichment) Vulsini Volcanics (Roman, Italy) Madupitic Lamproite V: Mantle plume basalts 0.5 (Badgers Teeth, Leucite Hills) Nyiragongo 2002 lava & Older lavas, Virunga Volcanics (East African Rift) IV-2: Intracontinental rift alkali basalts

Ta/Hf = 0.29 enriched mantle source

Ta/Th (ppm) Ta/Th (OIB, E-MORB, T-MORB) (or Alkaline arcs) III: Oceanic Intra-plateIntra Island IV-3: Continental extensional zone/ IV-1: Intracontinental rift Ta/Th = 0.131 (PM) initial rift basalts tholeiiticPM ---t r a n s i t i o n--- Ta/Hf = 0.1

0.1 slightly

II-2: Continental arc & Continental margin island-arc

0.05

I: N-MORB II-1: Island arc (Oceanic arc, IAB) (ACM) depleted mantle source 0.02 0.01 0.05 0.1 0.5 1 5 10 Th/Hf (ppm)

Figure 16. Tectonic discrimination diagram for basalts (after Wang et al., 2001; modified in this paper). Overlaying with Figure 14 suggesting the Adang Volcanics were formed in within-plate continental extension zone/initial rift, Vulsini Volcanics were formed in an arc-related (alkaline arcs; supra-subduction continental volcanic arc) and Virunga Volcanics were formed in mantle plume.

1.0

Symbols : Adang Volcanics: Mafic Trachyte Nb/Th = 1/0.27 Fine-grained Trachyte Nb/Th = 1/0.11 Nb/Th = 1/0.67 0.5 Leucitic Trachyte Within-plate enrichment Trachytic rocks (company drill data) (Melt-relatedSubduction enrichment) enrichment (Fluid-related enrichment) Vulsini Volcanics (Roman, Italy) Madupitic Lamproite Hawaiite (Badgers Teeth, Leucite Hills) Nyiragongo 2002 lava & Older lavas, Virunga Volcanics (East African Rift)

V: Mantle plume basalts Nb/Zr = 0.15 IV-1: Intracontinental rift tholeiitic (or Alkaline arcs)

enriched mantle source IV-2: Intracontinental rift alkali basalts IV-3: Continental extensional zone/initial rift basalts 0.1 (OIB, E-MORB, T-MORB) III: Oceanic Intra-plate Island Nb/Zr (ppm) Nb/Zr = 0.0627 (PM) PM

0.05 --- t r a n s i t i o n ---

slightly Nb/Zr = 0.04

I: N-MORB

(ACM) II-1: Island arc (Oceanic arc, IAB) II-2: Continental arc & Continental margin island-arc depleted mantle source

0.01 0.001 0.005 0.01 0.05 0.1 0.5 1.0 Th/Zr (ppm)

Figure 17. Tectonic discrimination diagram for basalts (after Sun et al., 2006; modified in this paper). Overlaying with Figure 14 suggesting the Adang Volcanics were formed in within-plate continental extension zone/initial rift, Vulsini Volcanics was formed in an arc-related (alkaline arcs; supra-subduction continental volcanic arc) and Virunga Volcanics (East African Rift) were formed in mantle plume, but the plot result of Madupitic lamproite (Leucite Hills) showed the difference tectonic setting (after Wang et al., 2001 and after Sun et al., 2006) is possible indicating to an interaction of two magma sources.

209 Indonesian Journal on Geoscience, Vol. 3 No. 3 December 2016: 197-216

5.0 Primitive Mantle Ta La Hf Sm

ppm 0.0370 0.6480 0.2830 0.4060 * Sun and McDonough (1995)

Melt-related subduction metasomatism (from mantle source metasomatized by silicated fluids)

MORB OIB DM (Depleted Mantle) 1.0 Hawaiite PM PM Lower crust

Fluid -related subduction metasomatism

(Hf/Sm) (from a hydrated mantle source) 0.5

Symbols: Adang Volcanics: Mafic Trachyte Fine-grained Trachyte Leucitic Trachyte

Trachytic rocks (company drill data). metasomatism Vulsini Volcanics (Roman, Italy) Madupitic Lamproite 0.1 (Badgers Teeth, Leucite Hills) Nyiragongo 2002 lava & Older lavas, Virunga Volcanics (East African Rift) 0.07 0.01 0.05 0.1 0.5 1.0 5.0

(Ta/La)PM

Figure 18. Metasomatism of Mafic Rocks Diagram (La Flèche et al., 1998). The plotting result showed Adang volcanics (‘Adang Volcanic Complex’) were formed by the silicate melt mantle metasomatism + a hydrated mantle source meta- somatism process and Vulsini Volcanics was formed by a hydrated mantle source metasomatized, whereas Madupitic lamproite (Leucite Hills) showed forming from a hydrated mantle source + carbonatite metasomatized.

DM (depleted mantle) weakly metasomatism moderately metasomatism strongly metasomatism enriched (0-10x) enriched (10-60x) enriched ( > 60x)

5.0 Low moderate high moderate For the six samples: Strongly metasomatized of silicate melts from mantle source. à High Zr signature (Zr/TRE (avg) = 1.39) Melt-related subduction metasomatism à REE rich (from mantle source metasomatized by silicated fluids) à Ratio (Hf/Sm)PM > 1.23

Hf/Sm)PM = 1.23 depleted mantle IAB MORB OIB Hawaiite 1.0 Chondrite PM Lower crust

Fluid-related subduction metasomatism Strongly metasomatized from PM (from a hydrated mantle source) a hydrated mantle source 0.5 à Low Zr signature (Zr/TRE (avg) = 0.85) à REE rich (Hf/Sm) 1.4346 x (Hf/Sm) or à Ratio (Hf/Sm)PM < 1.00

Strongly metasomatized from a hydrated mantle source + Carbonatite metasomatized à Lower Zr signature (Zr/TRE (avg) = 0.28) à REE rich

à Ratio (Hf/Sm)PM < 1.00

*Sun and McDonough (1989) Carbonatite metasomatism 0.1 Primitive Mantle (PM) Hf Sm ppm 0.2830 0.4060

1 5 10 50 100 500 1000 5000 TREY = (REE+Y)

Figure 19. Plot in metasomatism of Mafic Rocks Diagram (after La Flèche et al., 1998; modified in this paper) shows Adang Volcanics (‘Adang Volcanic Complex’) were formed by the silicate melt mantle metasomatism + a hydrated mantle source metasomatism process and Vulsini Volcanics was formed by a hydrated mantle source metasomatized, whereas Madupitic lamproite (Leucite Hills) formed from a hydrated mantle source metasomatism + carbonatite metasomatism (very low HREE signature, Figure 19) and Virunga Volcanics (East African Rift) were formed from moderate to strongly of the hydrated mantle metasomatism process.

210 Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin (Godang, S. et al.)

Table 3. Major Oxides (%) and Trace Elements (ppm) of Vulsini Volcanics - Roman, Italy (Santi et al., 2003)

Code# #1 #2 #3 #4 #5 Code# #1 #2 #3 #4 #5

Leucite Leucite Leucite Leucite Leucite Leucite Leucite Leucite Leucite Leucite Rock_type Rock_type phonolite phonolite phonolite phonolite phonolite phonolite phonolite phonolite phonolite phonolite

Sample_No# OSM 1 OSM 2 OSM 3 OSM 4 OSM 7 Sample_No# OSM 1 OSM 2 OSM 3 OSM 4 OSM 7

SiO2 55.51 55.03 55.44 56.21 56.31 La 173.00 182.00 189.00 176.00 169.00

TiO2 0.53 0.51 0.51 0.49 0.52 Ce 345.00 312.00 317.00 304.00 336.00

Al2O3 20.04 19.97 20.01 20.37 20.28 Pr 37.30 34.00 34.60 32.20 36.30

Fe2O3 4.19 4.08 4.13 3.92 4.18 Nd 124.00 112.00 114.00 106.00 116.00

FeO Sm 18.40 16.70 16.90 15.70 17.50

MnO 0.14 0.15 0.15 0.15 0.16 Eu 3.67 3.33 3.52 3.26 3.54

MgO 0.77 0.82 0.82 0.82 0.81 Gd 12.30 11.20 11.70 10.80 11.90

CaO 3.81 3.66 3.84 3.66 3.84 Tb 1.56 1.43 1.45 1.37 1.50

Na2O 3.42 2.83 3.89 2.69 3.07 Dy 8.01 7.28 7.35 6.89 7.62

K2O 8.46 9.18 9.01 9.78 9.11 Ho 1.47 1.34 1.35 1.26 1.38

LOI 2.34 3.05 1.32 1.93 1.75 Er 4.22 3.74 3.77 3.55 3.93

P2O5 0.13 0.13 0.11 0.13 0.13 Tm 0.62 0.55 0.57 0.51 0.57

Total 99.34 99.41 99.23 100.15 100.16 Yb 4.00 3.66 3.60 3.32 3.74

TA=Na2O+K2O 11.88 12.01 12.90 12.47 12.18 Lu 0.60 0.53 0.54 0.50 0.55

K2O/Na2O 2.47 3.24 2.32 3.64 2.97 Y 47.50 42.40 43.80 40.10 45.10

Radiometric ? cps ? cps ? cps ? cps ? cps TRE 781.65 732.16 749.15 705.46 754.63

V 131.00 130.00 129.00 121.00 129.00 TREO 873.08 817.72 836.73 787.87 842.88

Cr < 20 < 20 < 20 < 20 < 20 TRExOy 939.94 879.63 899.96 847.68 907.59

Co 6.00 6.00 6.00 6.00 6.00 TRE2O3 918.79 860.49 880.52 829.07 886.99

Ni < 20 < 20 < 20 < 20 < 20 dEu 0.75 0.74 0.77 0.77 0.75

Rb 298.00 395.00 292.00 350.00 294.00 Hf 12.30 10.90 11.20 10.40 11.70

Sr 2,130.00 1,900.00 2,140.00 2,020.00 2,150.00 Ta 2.79 2.44 2.53 2.35 2.62

Zr 677.00 610.00 626.00 584.00 657.00 Pb 183.00 157.00 200.00 217.00 192.00

Nb 49.50 46.60 47.90 45.80 51.40 Th 194.00 170.00 173.00 161.00 180.00

Ba 2,430.00 2,330.00 2,670.00 2,540.00 2,520.00 U 38.40 36.60 34.60 35.30 39.40

Tholeiitic Transitional Calc-alkaline to alkaline (peralkaline) La/Yb < 3 La/Yb = 3 - 6 La/Yb > 6 1

Remarks: *DMM = Depleted MORB Mantle. 0.1% *PM = Primitive Mantle. 0.5 *WAM = Western Anatolian Mantle, defined in Aldanmaz et al., 2000. spinel-lherzolite 0.1%

Symbols: Hawaiite Adang Volcanics: 0.1% Mafic Trachyte garnet-lherzolite 0.1% Fine-grained Trachyte OIB Leucitic Trachyte WAM

Nb/Zr (in ppm) Nb/Zr Trachytic rocks (company drill data). enriched mantle source

Nyiragongo 2002 lava & Older lavas, E-MORB Virunga Volcanics (East African Rift) garnet-lherzolite 0.1

spinel-lherzolite Lower crust 0.1% Nb/Zr = 0.0627 (PM) PM 0.1% Chondrite 0.05 Nb/Zr = 0.04 slightly s

MORB field N-MORB

depleted mantle garnet-lherzolite

spinel-lherzolite

IAB DMM

La/Yb (in ppm) depleted mantle source 0.01 0.1 0.5 1 5 10 50 100 150

Figure 20. curves of mantle source (after Aldanmaz et al., 2000; modified in this paper). magmatic affin- ity: ratio La\Yb (MacLean and Barrett, 1999), Depleted--slightly--enriched Mantle (after Le Roex et al., 1983 and after Sun et al., 2006), showing the genesis of the Adang Volcanics is related enrichment of DMM (garnet-lherzolite), whereas Virunga Volcanics are related enrichment of WAM (spinel-lherzolite).

211 Indonesian Journal on Geoscience, Vol. 3 No. 3 December 2016: 197-216 are derived was enriched (Nb/Zr > 0.0627) is similar to that of the Vulsini volcanic rocks and the magma was generated by small-scale (Figure 21a and b) and other Group III volcanics, partial melting (< 0.1 %) of Depleted MORB which are characterized by distinctly negative Mantle (DMM) composed of ultramafic (garnet- spikes in Ba, Nb-Ta, Ti, and P, whereas Rb, Th, lherzolite). and K are strongly enriched (Wilson, 1989). Lamproites of Group I and Group II rocks show a very different pattern (Figure 21b; Wilson, 1989). Discussion These differences may be caused by different genesis or metasomatism processes. Lamproites The results show that the Adang Volcanics of Group I (e.g. Leucite Hills rocks) were formed are represented by potassic and sodic magma from mixing between melts from metasomatized series, and consist predominantly of trachybasalt hydrated mantle and carbonatite sources (the and basaltic trachyandesite. Furthermore, they rocks have a lower Zr/TRE and very low HREE indicate that they were formed in a within-plate signatures) (Figures 19 and 21b) and Group II continental extension/initial rifting tectonic set- rocks {e.g. Virunga Volcanics (Nyiragongo, ting after subduction had ceased. East African Rift)} have a genesis from related The samples include ultrapotassic rocks. Foley enrichment of the Western Anatolian Mantle et al., 1987 (in Gupta, 2015) have subdivided the (WAM) from mantle material spinel-lherzolite within-plate ultrapotassic rocks into four groups, (Figure 20). While the patterns shown by the as follows: Adang and Vulsini volcanics are very similar, it 1. Group I: Lamproites. These rocks are not should be noted that the Adang rocks are more readily linked to subduction, although strongly enriched in Zr and Hf (~110–222x) than they may occur above a fossil subduction the Vulsini volcanic rocks (Zr 56x and Hf 38x). zone. Classic examples are Leucite Hills This difference can be explained by authors’ (, USA), West Kimberley, and interpretation that the high Zr-Hf signature Gaussberg. displayed by the Adang Volcanics is the result 2. Group II: Ultrapotassic rocks of continental of enrichment of the silicate melt from a source rift zones. Included in this group are , within the mantle itself, whereas the relatively olivine melilities, perovskite, kalsilite, and low Zr-Hf signature of the Vulsini volcanic rocks some micaceous . Type localities is linked to metasomatism by a hydrated mantle are in the East African Rift (e.g. Virunga source (see above; Figure 19). Volcanics, Nyiragongo; Cupaello and San Over the years a number of models have been Vananzo, Italy). proposed for the tectonic setting and origin of the 3. Group III: Ultrapotassic rocks of active oro- Late Cenozoic potassic to ultrapotassic volcanics genic zones. These rocks are a typical feature and associated intrusives in Western Sulawesi. of many Cenozoic volcanic provinces in the Most favour a post-subduction, within plate Mediterranean region, including the Roman extensional setting (cf. Maulana et al., 2016), Province of Central Italy. Group III rocks consistent with authors’ findings, which some show a strong association with active or re- authors based on similarities with the high-K cently active subduction systems. volcanics in the Roman Province (Leterrier et al., 4. Group IV: which cannot be included in either 1990). It is generally assumed that the of the three groups. The type examples of were derived from mantle previously metaso- group IV rocks are the potassic rocks of Na- matized by one ore more subduction events. As vajo , which lack mantle-derived mentioned above, the result suggests, however, . the magma that generated (at least part of) the The Adang Volcanics clearly belong to Group Late Cenozoic volcanics in Western Sulawesi III based on their spidergram pattern, which was metasomatized in a different way.

212 Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin (Godang, S. et al.)

20000 LILE LILE LILE Symbols: 10000 Adang Volcanics: HFSEHFSE HFSE HFSE HFSE HFSE Mafic Trachyte 5000 Fine-grained Trachyte Adang Volcanics (Trachyte affinity) : Leucitic Trachyte Tectonic setting : within-plate continental extension/initial rift. à Strongly metasomatized of silicate melts. Vulsini Volcanics (leucite phonolite lava; Roman, Italy) Geochemical Signature : High Zr -Hf 1000 (enriched ~ 110 - 222x)Hf (enriched ~ 110 - 222x) Madupitic Lamproite (Badgers Teeth, Leucite Hills) 500 strongly metasomatism

100

50 (Rock/Primitive mantle) Normalized concentration moderately

10

5 Vulsini Volcanic, Italy (leucite phonolite): Tectonic setting : Arc-related (Supra-subduction Volcanic Arc). Geochemical Signature: low Zr-Hf (enriched: Zr 56x and Hf 38x) weakly

Primitive Mantle (PM) 1

0.5 mantle

depleted mantle depleted

0.1 Rb Th Ba U NbLa* Ta P Ce* Sr Pr* Nd* Ti Sm* Eu* Hf Gd* Zr Tb* Dy* Ho* Er* Tm* Yb* Lu* Y* TREY

incompatible to compatible à ß compatible to incompatible increasing compatibility decreasing compatibility

20000 LILE LILE LILE 10000 HFSEHFSE HFSE HFSE HFSE HFSE

5000 Symbols: Adang Volcanics (6 samples)

Virunga Volcanics (East African Rift : Group II)

1000 Madupitic Lamproite (Badgers Teeth, Leucite Hills : Group I) Vulsini Volcanics (leucite phonolite, Roman-Italy : Group III) 500 strongly metasomatism

100

50 (Rock/Primitive mantle) Normalized concentration moderately 10

5 weakly

Primitive Mantle (PM) 1

0.5 mantle depleted mantle depleted

0.1 Rb Th Ba U NbLa* Ta P Ce* Sr Pr* Nd* Ti Sm* Eu* Hf Gd* Zr Tb* Dy* Ho* Er* Tm* Yb* Lu* Y* TREY

incompatible to compatible à ß compatible to incompatible increasing compatibility decreasing compatibility

Figure 21. (a) Incompatible to compatible multitrace elements diagram Normalized to Primitive Mantle (the inco patibility sequence: after Zhang, 2014; depleted–weakly–moderately–strongly metasomatism: after La Flèche et al., 1998 (Figure 19); modified in this paper) showing plots of the Adang Volcanics, Vulsini Volcanics (leucite phonalite), and Madupitic lamproite (Leucite-Hills); (b) Plots of the Adang Volcanics, Group I (Madupitic lamproite, Leucite-Hills), Group II (Virunga Volcanics: Nyiragongo, East African Rift system) and Group III (Vulsini Volcanics: leucite phonalite, Roman-Italy).

Conclusion and Suggestion diagrams, is that the Adang Volcanics consist of (ultra) potassic to sodic rocks of predominantly The main conclusion of this study, involv- trachytic composition, that were formed by minor ing petrographic and geochemical analyses, the partial melting (<0.1 % by volume) which has results of which have been plotted on a series of been enriched DMM (Depleted MORB Mantle)

213 Indonesian Journal on Geoscience, Vol. 3 No. 3 December 2016: 197-216 of garnet-lherzolite composition. Metasomatic chemical constraints on the Cenozoic, OIB- processes accompanying silicate melting caused type alkaline volcanic rocks of NW Turkey : the strong enrichment in Na, K, Zr, and REEs Implications for mantle sources and melting (with a geochemistry signature of (Hf/Sm)PM processes. Lithos 86 p.50-76, Elsevier. DOI: > 1.23). The magmatism that gave rise to the 10.1016/j.lithos.2005.04.003 Adang volcanic complex took place during a Anthony R., Philpotts, and Ague, J.J., 1989. within-plate rifting event. The presence of both (2nd edition): Principles of Petrography of potassic and sodic volcanic rocks possibly indi- Igneous and Metamorphic Rocks. Cambridge cates magma was generated from more than one University Press (Fig. 15.10 : Depth to Benioff mantle reservoir. zone, Hatherton and Dickinson, 1969. DOI: It would be of great interest to carry out a 10.1017/CBO9780511813429 comparative study on the ultrapotassic leucite/ Babechuk, M.G., Widdowsonc, M., and Kamber, pseudoleucite-bearing volcanics from Gunung B.S., 2014. Quantifying chemical weathering Muria and Bawean Island (Central Java) with intensity and trace element release from two the aim to establish whether or not those rocks contrasting basalt profiles, Deccan Traps, were formed by similar processes as the Adang India. Chemical Geology, 363, p.56-75. Volcanics and in a similar tectonic setting. It is (modified of Weathering Ternary Diagram further recommend to carry out U/P zircon dat- of Mafic/Basaltic from Nesbitt & Wilson ing on a suite of representative samples from the (1992), MIA(o)). DOI: 10.1016/j.chem- Adang Volcanics in order to better constrain the geo.2013.10.027 age of this unit, including the temporal relation- Bergman, S.C., Coffield, D.Q., Talbot, J.P., and ship between the potassic and sodic series. Garrard, R.A., 1996. Tertiary Tectonic and Magmatic Evolution of Western Sulawesi and the Makassar Strait, Indonesia - Evi- Acknowledgements dence for a Miocene Continent-Continent Collision. In: (eds Hall, R. and Blundell, The authors express their gratitude to Dr. Nur- D. J.(Eds.), Tectonic evolution of Southeast chayo Indro Basuki (ITB) for petrographic ad- Asia. Geological Society of London, Special vise and useful discussions pertaining to leucite/ Publication, 106, p.391-429. DOI: 10.1144/ pseudoleucite, Dr. Ade Kadarusman for valuable GSL.SP.1996.106.01.25 input regarding the partial melting of mantle, Dr. Deer W.A. and Andrew R., 2001. (2nd edi- rer. nat. Arifudin Idrus (UGM) for his help and tion). Rock-Forming Minerals: Framework support in writing this manuscript, and Theo Van Silicates (), Volume 4A. Published Leeuwen for his constructive review. by The Geological Society. p.46 (Ternary solid solution An-Ab-Or). DOI: 10.1017/ CBO9780511813429 References Foley, S.F., Venturelli, G., Green, D.H., and Toscani, L., 1987. The ultrapotassic rocks : Aldanmaz, E., Pearce, J.A., Thirlwall, M.F., and Characteristics, classification and constraints Mitchell, J.G., 2000. Petrogenetic evolution for petrogenetic models. Earth Science of late Cenozoic, post-collision volcanism Reviews, 24, p.81-134. DOI: 10.1016/0012- in western Anatolia, Turkey. Journal of 8252(87)90001-8 Volcanology and Geothermal Research 102 Godang, S., 2015a. Introduction of Godangs p.67-95. Elsevier. DOI: 10.1016/S0377- Trapezoid Geochemistry for Determining 0273(00)00182-7 Magmatic Classification, Review & Dis- Aldanmaz, E., Koprubasi, N., Gurer, O.F., Kay- cussion with Unsoed’s Geo-academician & makci, N., and Gourgaud, A., 2006. Geo- Geo-colleger.

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