Sains Malaysiana 50(1)(2021): 9-21 http://dx.doi.org/10.17576/jsm-2021-5001-02

Petrology and Geochemical Features of Volcanic Rocks, South-east , (Ciri Petrologi dan Geokimia Batuan Volkano Semporna, Tenggara Sabah, Malaysia)

ELVAENE JAMES*, AZMAN ABDUL GHANI, OLUWATOYIN O. AKINOLA & JUNAIDI ASIS

ABSTRACT The volcanic rocks in , Sabah, Malaysia forms parts of the Miocene subjected slab during the Miocene-Pliocene orogeny. This study presents new petrographic and geochemical data of volcanic rocks in Semporna area. The volcanic rocks range in composition from basaltic , andesite, dacite to , with most of the volcanic shows calc-alkaline affinity with a minor tholeiitic feature. The trace elements shows enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE) suggesting that the volcanic rocks have similar geochemical patterns and might come from similar magma source. The petrochemical data suggests that volcanic rocks of Semporna shows characteristic of subduction zone (negative Nb, Ta, and Ti). Decreasing magnitude of Europium anomalies from intermediate to acid lavas suggests an important role of plagioclase in the fractional crystallization. Negative Ce anomaly in part of Semporna volcanic rocks suggest that those volcanic rocks may related with emergence of oxygenated deep-sea environment. Tectonic diagrams showed that the Semporna volcanic rocks were formed in an island arc setting. Keywords: Calc-alkaline; island arc; Semporna; subduction; volcanic rocks

ABSTRAK Batuan volkano Semporna di Semenanjung Semporna, Sabah, Malaysia dihasilkan oleh sebahagian daripada bidur subduksi Miosen semasa orogeni Miosen-Pliosen. Kajian ini membentangkan penemuan baru mengenai data petrografi dan geokimia batuan volkano Semporna daripada batuan pertengahan hingga asid di Semporna. Batuan volkano terdiri daripada andesit , andesit, dasit dan riolit serta semua batuan menunjukkan dominasi kalkalkali dengan sebahagian kecil menunjukkan ciri tholeitik. Unsur-unsur surih menunjukkan pengayaan Unsur Litofil Ion Besar (LILE) dan Unsur Nadir Bumi Ringan (LREE) mencadangkan batuan volkano Semporna mempunyai corak geokimia yang sama serta kemungkinan datang daripada sumber magma yang serupa. Data petrokimia mencadangkan bahawa batuan volkano Semporna menunjukkan ciri-ciri zon benam (anomali Nb, Ta dan Ti negatif). Penurunan anomali Europium daripada lava pertengahan hingga lava berasid menunjukkan peranan penting plagioklas dalam penghabluran berperingkat magma yang berasal daripada mantel. Penurunan Ce anomali pada sebahagian batuan volkano Semporna mencadangkan batuan tersebut mungkin berkaitan dengan kemunculan persekitaran laut dalam yang beroksigen. Rajah tektonik menunjukkan bahawa batuan volkano Semporna terbentuk dalam sekitaran arka kepulauan. Kata kunci: Arka kepulauan; batuan volkano; benam; kalkalkali; Semporna

INTRODUCTION INTRODUCTION to the Mesozoic is located in the eastern part of Sabah (Semporna and ), and is part of a basement River Sabah is located on the northern part of and surrounded by the South China Sea to the west, the Sulu complex that comprised of various types of igneous and Sea to the north-east and the to the south- metamorphic rocks (Dhonau & Hutchison 1966; Kirk east (Figure 1). It is surrounded by the Eurasian plate, 1968; Reinhard & Wenk 1951). Extension related to slab Indian-Australian plate, Pacific plate, and the roll back during subduction of the Sulu Arc had generated plates (Balaguru & Hall 2009; Hall 2012; Tongkul granite magmatism which is emplaced as Kinabalu granite 1999). In northern Borneo, the oldest rocks dated back during Miocene by break-off of a subjected slab beneath 10

Sabah or the possibility of delamination of lithospheric Borneo trough is situated in southern part of the South root underneath the (Hall 2013; Rangin et China Sea and extends into southern continental margin al. 1990). Volcanic activity eastern part of Sabah began of the Dangerous Ground and Reed Bank (Hall 2013). in the Early Miocene to Pleistocene in Semporna and Dent Semporna Peninsula categorizes into three morphotectonic Peninsula (Bellon & Rangin 1991; Bergman et al. 2000; units; the Mesozoic oceanic crust, the Middle Miocene Haile et al. 1965; Kirk 1962, 1968; Rangin et al. 1990; , and the Plio-Pleistocene volcanic arc Swauger et al. 1995; Takashima et al. 2005). The Semporna (Sanudin et al. 1995). Semporna is in eastern part of the Peninsula consists of areas that includes Semporna, Semporna Peninsula and extends offshore into Pulau , and . The occurrences of volcanic rocks Gaya (Hutchison 2007; Lee 1988). The highest elevation in Semporna area are believed to be south-west onshore in this area is Mount Conner situated at about 96 km south continuation of the Sulu Arc from Zamboanga which of Semporna (Figure 1) which composed of dacitic and formed by the subduction of the Celebes Sea (Hall 2013; rhyolitic rocks. Recent isotopic and geochemical studies Rangin & Silver 1991). The Sulu Arc volcanism in eastern suggest that volcanic rocks on the Semporna Peninsula part of Sabah, which are Semporna and Dent Peninsula shows an ocean-island basalt (OIB) signature as a result commenced from Early-Late Miocene (Bellon & Rangin of the Miocene subduction which produced an upwelling 1991; Haile et al. 1965; Kirk 1962, 1968; Rangin & Silver of OIB-like magma in the upper mantle into a lithospheric 1991; Swauger et al. 1995) based on evidence of closely thin spot (Lee 1988). association with Kalumpang Formation in Semporna Between Eocene to Early Miocene, the Proto- Peninsula (Kirk 1968; Tjia et al. 1992). South China Sea has subducted southwards beneath Previous petrological and geochemical studies of the northern Borneo (Hall 2012) and caused a collision the volcanic rocks were focused only in Tawau and Kunak during the Early Miocene between and the area with less study in Semporna vicinity (Bellon & Rangin continental margin of south China (Hall & Wilson 2000; 1991; Bergman et al. 2000; Macpherson et al. 2010; Hutchison et al. 2000). Northern Borneo began to emerge Sanudin et al. 2010). This paper presents new petrographic by the end of the Early Miocene, while most of the and geochemical data for the Semporna volcanic rocks, west and eastern parts were still subside below sea level using the major and trace elements analysis to investigate (Balaguru et al. 2003). The volcanic arc in south Sabah the magmatic processes and tectonic environments of the formed after the northward subduction of the Celebes Sea. study area. The subduction has initiated on the opening of the back arc basin followed by slab roll back towards south- GEOLOGICAL SETTING east (Hall 2013). However, the arc activity terminated Northern Borneo lies at a critical junction between the during the late Pliocene (Garwin et al. 2005). Recent north-west Borneo Trough offshore north-west Sabah study shows the Semporna Peninsula volcanic rocks along the former Palawan mountains and Proto-Sulu Arc exhibit the characteristic of subduction-related, OIB-like 118°20'0"E 118°30'0"E 118°40'0"E and1 18MORB°50'0"E (James et al. 2019). towards offshore of north-east118°20 '0"ESabah. 1The18°30'0"E north-west118°40'0"E 118°50'0"E 118°20'0"E 118°30'0"E 118°40'0"E 118°50'0"E N N " " 0 0 ' N ' N " 0 " 0 0 5 0 ' 5 ' ° °

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FIGURE 1. (a) Simplified geological map of Semporna located in Sabah and sampling locations in this study. Modified from Kirk (1968), (b) Extention of Zamboanga Peninsula toward Semporna

MATERIALS AND METHODS higher LOI (>4%) and might experience alteration. They Among all the collected samples from Semporna, a total are classified under Winchester and Floyd (1977) and of 16 fresh volcanic rocks samples were carefully selected range from basaltic andesite, andesite, and dacite (Figure for petrographic and geochemical analysis (Figure 1). 2(b)). Basaltic andesite contains phenocrysts of plagioclase Petrographic analyses and thin section preparation were and clinopyroxene enclosed by fine grained plagioclase, conducted at the Department of Geology, Faculty of clinopyroxene and minor iron oxide groundmass (Figure Science, University of Malaya. Geochemical analysis that 3(a)). Plagioclase phenocrysts (0.1-0.4 mm in diameter) include both major and trace elements compositions were are subhedral and make up almost 70% of the rocks. analysed at the Bureau Veritas Laboratories, Vancouver, Majority of the clinopyroxene (0.1-0.3 mm) were altered Canada for major and trace elements composition (Table to uralite with inclusions of iron oxide in some of the 1). Major elements were determined using the X-ray clinopyroxene. The brown cryptocrystalline minerals in fluorescence (XRF) method. Rock samples were crushed, the groundmass consists of secondary minerals including and pulverized. Samples were mixed with lithium borate chlorite and sericite. inside a platinum crucible then fused at 1100 to 1200 Andesite shows a fine-grained and porphyritic °C. After fusion, samples are transferred into a mould to texture with phenocryst assemblages of plagioclase, form beads. The fusion beads were analysed using Philip clinopyroxene, hornblende, and biotite. Plagioclase occur PW 1404/10 X-ray fluorescence spectrometer. Trace as a major phenocryst phase (0.1-1.6 mm) as well as in elements and rare earth elements (REE), were measured via the groundmass. Plagioclase forms a weak alignment inductively coupled plasma mass spectrometry (ICP-MS) indicate the lava flow (Figure 3(b)). Plagioclase zoning (Perkin-Elmer Elan 9000). The loss on ignition (LOI) for is commonly seen in the andesitic unit. Hornblende each sample were determined by weight difference after phenocrysts (0.1-1.0 mm) are subhedral, strongly ignition at 1000 °C. Analytical error for major and trace pleochroic and brown in colour. Minor clinopyroxene elements are less than 3 and 7.5%, respectively. (augite) and biotite are also observed in andesite. The occurrence of iron oxide is common in the groundmass and are accompanied by quartz, plagioclase, and pyroxene. RESULTS Dacite and rhyolite were found in the same outcrop and shared common textural characteristics in hand CLASSIFICATION AND PETROGRAPHIC DESCRIPTION specimens (Figure 3). The only difference between them Based on TAS classification after Le Maitre et al. (1989), is that rhyolite contains more cavities filled with secondary Semporna volcanic rocks range from basaltic andesite, minerals such as chalcedony (0.2-2.0 mm) compared with andesite, dacite, and rhyolite and fall under Subalkaline/ dacite. Amygdale texture is common in rhyolite (Figure Tholeiitic series (Figure 2(a)). Rocks samples contain 3(d)) and filled cavities contain mineral of secondary 12 origin with a low-temperature alteration. Phenocrysts plagioclase is evident in both dacite and rhyolite (Figure of plagioclase (0.4-2.0 mm) are colorless, subhedral to 3). Groundmass texture is mostly glassy associated with euhedral, and show polysynthetic twinning. Zoning of minor iron oxide, quartz, plagioclase, and alkali feldspar.

TABLE 1. Major, trace, and rare elements of the Semporna volcanic rocks

Sample Basaltic andesite Andesite 10 L2 13 L9 13 L11 9 L4 9 L5 10 L1 10 L4 11 L3 Major element

SiO2 (wt. %) 52.34 57.32 53.16 59.08 57.3 60.18 61.46 62.29

TiO2 0.85 0.67 0.68 0.52 0.87 0.59 0.40 0.57

Al2O3 21.3 17.42 18.04 16.55 17.07 16.33 14.83 14.28 FeO* 5.31 1.63 9.73 5.95 7.35 5.94 4.52 4.22 MnO 0.02 0.01 0.18 0.07 0.15 0.11 0.14 0.21 MgO 1.44 0.06 4.04 2.60 2.48 2.57 1.01 1.33 CaO 7.45 0.32 8.28 5.40 6.70 5.95 4.90 5.01

Na2O 2.60 1.36 2.67 2.22 2.81 2.53 2.56 3.45

K2O 0.18 1.89 1.30 1.03 2.04 2.36 2.65 1.66

P2O5 0.25 0.26 0.19 0.13 0.30 0.17 0.14 0.13 LOI 8.10 18.80 1.50 6.30 2.80 3.10 7.30 6.70

Total 99.84 99.74 99.77 99.85 99.87 99.83 99.91 99.85

Trace element Ba (ppm) 87 742 233 415 281 366 458 340 Be 2 0 0 0 1 0 2 1 Co 11.4 0.6 23.3 15.2 12.6 12.7 10.6 5.4 Cs 0.2 0 2.7 4.8 1.7 6.1 5.8 3.1 Ga 23.2 9.9 16.4 16.7 17.1 15.2 13.7 15.6 Hf 2 2.3 1.8 3 3 2.8 2.2 4.4 Nb 1.9 2.2 1.4 3.1 3.3 2.9 1.8 5.1 Rb 4.1 4.3 44.7 32.1 40.4 86.1 88.6 74.8 Sn 1 4 0 0 0 0 0 1 Sr 528 440.9 35.5 292.1 340.3 296.7 219.3 213.1 Ta 0.1 0.2 0.1 0.3 0.1 0.2 0.2 0.3 Th 2.6 8.1 4.6 8 3.5 6.7 8.7 6.3 U 0.5 1.5 1 1.2 0.9 2 2.1 1.4 V 166 177 184 117 131 121 52 55 W 1.1 9 0 0 0.5 1.2 1 0.6 Zr 72.9 81.1 63.4 106.3 102.3 99.2 77 169.9 Y 39.7 6.4 16 47.8 32.6 20.5 37.1 36.7 La 39.9 31.2 13.5 21 17.2 16.2 29.1 22.9 Ce 22.9 59.7 28.1 32.6 36.9 31.7 42.5 41.2 13

Pr 9.85 6.62 3.59 4.32 4.7 4.05 6.22 5.04 Nd 43.3 25.3 15.6 18.3 20 16 25 19.9 Sm 9.25 4.38 3.11 3.71 4.9 3.59 6.23 4.5 Eu 2.88 1.25 1.04 0.99 1.5 0.87 2.23 1.13 Gd 9.39 3.31 3.06 4.39 5.74 3.69 7.36 4.96 Tb 1.28 0.37 0.48 0.65 0.93 0.56 1.14 0.84 Dy 7.54 1.65 2.91 4.41 5.72 3.52 6.92 5.5 Ho 1.39 0.25 0.64 1.05 1.18 0.73 1.51 1.2 Er 3.77 0.69 1.89 3.36 3.6 2.15 4.25 3.84 Tm 0.43 0.11 0.25 0.42 0.5 0.33 0.55 0.55 Yb 2.64 0.74 1.68 2.74 3.4 2.34 3.73 3.54 Lu 0.38 0.11 0.26 0.45 0.51 0.34 0.6 0.6

LaN/SmN 2.71 4.48 2.73 3.56 2.21 2.84 2.94 3.20

GdN/LuN 3.07 3.73 1.46 1.21 1.40 1.35 1.53 1.03 Eu/Eu* 0.94 1.00 1.03 0.75 0.86 0.73 1.01 0.73 Table 1 continued Sample Andesite Dacite Rhyolite 11 L11 13 L10 9 L1 9 L3 11 L1A 13 L8 9 L2 11 L1B Major element

SiO2 (wt. %) 56.95 61.32 69.22 64.66 66.63 64.53 74.8 70.97

TiO2 0.67 0.54 0.38 0.37 0.42 0.50 0.44 0.43

Al2O3 15.61 16.65 13.06 15.81 14.08 14.28 13.29 13.87 FeO* 5.38 5.65 3.54 4.61 3.24 3.83 3.01 3.39 MnO 0.15 0.11 0.07 0.10 0.03 0.09 0.04 0.04 MgO 1.72 2.64 0.77 1.48 0.47 1.02 0.20 0.57 CaO 7.29 5.28 3.64 3.78 2.82 4.35 0.24 1.67

Na2O 3.93 2.92 2.47 3.70 2.86 3.09 3.02 3.34

K2O 0.83 2.16 2.15 2.52 2.64 1.14 2.83 3.98

P2O5 0.13 0.17 0.13 0.13 0 0.09 0.05 0.01 LOI 7.20 2.40 4.50 2.70 6.60 6.90 1.90 1.60

Total 99.86 99.84 99.93 99.86 99.79 99.82 99.82 99.87 Trace element Ba (ppm) 138 341 341 399 801 422 947 436 Be 0 2 0 2 3 0 4 0 Co 12.3 16.4 4.3 8 3.1 5.3 2.4 4 Cs 5.9 2.4 12.9 6.5 23.7 4.7 18.9 1.6 Ga 16.9 15.9 12.2 16 16.6 13.5 12.9 17.2 Hf 3.1 2.4 2 2.7 6.1 5.6 4.7 5.5 Nb 1.5 3.2 1.9 2.1 6.6 5.7 5.4 6.2 Rb 17.1 63.8 86.1 97.7 279.1 37.3 57.7 99.3 Sn 0 0 0 0 2 2 2 2 Sr 715.9 377.4 176.1 319.2 324.8 253.1 163.1 111.9 14

Ta 0.1 0.2 0 0.2 0.3 0.3 0.4 0.4 Th 2.5 8.6 7.9 9.1 9.4 7.8 7.7 9.4 U 0.8 2.1 1.7 2.1 2.1 2.3 1.9 2.9 V 118 111 51 63 32 34 19 36 W 0 0.9 0.8 1 0 0.6 0.8 0.7 Zr 104.5 93.5 69.4 90.3 220.4 202.9 195.5 217.6

Y 32.2 28.7 12.8 10.8 43.5 39.6 51.2 63 La 10 28.7 14.1 17.1 32.3 22.7 64.6 40.2 Ce 21.4 45.8 25.4 32.2 35.3 45.4 133.9 42.3 Pr 3.21 6.78 2.94 3.52 8.87 5.78 16.66 11.73 Nd 14.7 26.9 11.1 12.9 36.4 23.8 59.1 49.4 Sm 3.81 6.19 2.35 2.35 8.33 5.74 12.19 12.06 Eu 1.13 2.24 0.67 0.7 1.85 1.29 2.28 2.07 Gd 4.75 6.49 2.37 2.11 7.58 6.28 9.62 11.87 Tb 0.79 1.05 0.35 0.29 1.25 1.06 1.54 1.93 Dy 5.12 5.87 2.27 1.81 7.66 6.55 9.32 11.65 Ho 1.14 1.17 0.45 0.36 1.69 1.42 1.89 2.45 Er 3.3 3.31 1.31 1.14 5.06 4.62 5.97 7.4 Tm 0.47 0.45 0.18 0.15 0.72 0.63 0.9 1.09 Yb 3.21 2.99 1.34 1.18 4.95 4.36 6.05 7.19 Lu 0.46 0.39 0.2 0.17 0.76 0.69 0.96 1.08

LaN/SmN 1.65 2.92 3.77 4.58 2.44 2.49 3.33 2.10

GdN/LuN 1.28 2.07 1.47 1.54 1.24 1.13 1.25 1.37 Eu/Eu* 0.81 1.08 0.87 0.94 0.71 0.66 0.64 0.53

Nb Y − Zr TiO2 plot (Winchester and Floyd 1977) 0 0 5 .

B Comendite Phonolite A Pantellerite 0 0 5 . 0 Rhyolite

Trachyte

2 Rhyodacite/Dacite O i T 11 L1A r Trachy− 0 5 Z . 13 L8 0 Andesite andesite 11 L3 9 L410 L4 9 L1 11 L11 13 L9 Basanite Andesite/Basalt10 L2 Nephelinite 5 0 0 . Alk−Bas SubAlkaline Basalt 0 1 0 . 0 0.01 0.05 0.10 0.50 1.00 5.00 10.00 Nb/Y 10 L2,11 L11,9 L4,10 L4,11 L3,13 L9,9 L1,11 L1A,13 L8

FIGURE 2. (a) Na2O wt. % + K2O wt. % vs. SiO2 wt. % diagram for the Semporna volcanic samples (after Le Maitre et al. (1989)). (b) Zr/TiO2 vs Nb/Y diagram (after Winchester and Floyd (1977)) 15

FIGURE 3. Photomicrograph of Semporna volcanic rocks, (a) Subhedral plagioclase and altered clinopyroxene with cryptocrystalline groundmass in basaltic andesite, (b) Zoned plagioclase and subhedral hornblende in andesite and weak alignment shows by smaller size plagioclase, (c) Zoned and polysynthetic twinning plagioclase as phenocryst in dacite, (d) Amygdoloidal texture composed of quartz chalcedony and plagioclase phenocryst enclosed by glass groundmass in rhyolite

MAJOR ELEMENTS AND TRACE ELEMENTS increasing SiO2 indicating the fractionation of plagioclase

SiO2 contents for basaltic andesite range from 52.34 and hornblende (Liu 2005), while TiO2 and P2O5 also

- 57.32 wt. % and total alkali from 2.78 - 3.97 wt. %. portray a decreasing trend with increasing SiO2, which

Andesite have range of SiO2 contents from 56.95 - 62.29 might be related to the fractional crystallization of apatite, wt. %, with total alkali from 3.25 - 5.21 wt. %. The SiO2 rutile, and ilmenite during magma evolution (Liu 2005). content for dacite range from 64.53 - 69.22-wt. %, with Scattered pattern shown in plot of Na2O vs SiO2 suggest total alkali from 4.23 - 6.22 wt. % (Table 1). Rhyolite yield post magmatic alteration (Liu 2005) which supported by relatively high SiO2 and total alkali compared to basaltic presence of alteration minerals observed in thin section. andesite, andesite and dacite which ranges from 70.97 - Continuous pattern shown that Semporna volcanic rocks 74.80 wt. % and 5.85 - 7.32 wt. %, respectively (Table 1). are formed from a co-magmatic series.

There is a positive correlation between K2O and SiO2, The Semporna volcanic rocks ranging from basaltic and the volcanic rocks range from tholeiite series to high-K andesite to rhyolite display a significant variation of calc-alkaline series. Most of the units are plotted within the LILE (Large-Ion Lithophile Elements). Ba and Rb show calc-alkaline series, except for some andesite and rhyolite, positive correlation with increasing SiO2 which clearly which fall under the high-K calc-alkaline series and one indicate enrichment of alkali feldspar and biotite (Di basaltic andesite (10L2) in the tholeiite series (figure not Vincenzo et al. 1996; Imeokparia 1981). In contrast, Sr shown). All the Semporna volcanic rocks show both shows negative correlation with increasing SiO2. Multi- increasing and decreasing trends from basaltic andesite elements spider-plot (Figure 5(a)) shows that most of to rhyolite on Harker diagrams (Figure 4). Major elements the volcanic rocks in the study area are characterized by: such as TiO2, Al2O3, FeO(t), MgO, CaO, and P2O5 shows negative Nb, Ta, Ti anomalies, enrichment of LILE (Ba, Sr, negative correlation, while K2O show a positive correlation and Rb), and slightly positive to negative Zr anomalies. with SiO2. Decreasing trends shown by Al2O3 and CaO with Volcanic rocks that occur in subduction-related domains 16

are usually depleted in HFSE (Nb, Ta, and Ti) and = 1.65 - 3.73). Most Semporna volcanic rocks exhibits enrichment in LILE (Stolz et al. 1996; Xia & Li 2019). weak negative Eu anomalies (Eu/Eu* = 0.53 - 0.93), Observation in primitive mantle normalised Semporna except four samples (10L4, 13L9, 13L10, and 13L11) volcanic rocks show signatures that are similar pattern which show absent or small positive Eu anomalies (Eu/ to typical subduction zones (e.g. enrichment of LILE Eu* = 1.00 - 1.08) (Figure 5(b); Table 1). Slightly positive and a depleted Nb, Ta, and Ti) and are comparable to the Eu anomalies may suggest accumulation of plagioclase Mariana Arc (Sarbas 2008) which exhibits subduction- and negative Eu anomalies indicating that plagioclase related features. Enrichments of LILE (e.g. Ba, Sr, and fractionation played a significant role during evolution of Rb) and depletion of Nb, Ta, Z, and Ti in primitive mantle these magmas (Zhou & Mukasa 1997). In REE patterns, normalised Semporna volcanic rocks are consistent with noticeable negative Ce anomaly present slightly in transportation of fluid-soluble elements into the mantle andesite (9L4, 10L4, 11L1A, and 11L11), dacite (11L1A) wedge source region in subduction zone magmas (Stern and rhyolite (11L1B), while strong negative Ce anomaly 2002; Tastumi & Eggins 1995). Th and Be are relatively observed in basaltic andesite (10L2) (Figure 5(a)), showing low in Semporna volcanic rocks. This suggest less that those volcanic rocks may related with emergence sediment involvement in the subduction processes (Stern of oxygenated deep-sea environment (Kato et al. 2002). 2002) since Th and Be are highly soluble in hydrous The weak Ce anomaly in andesite, dacite and rhyolite silicate melt (Zheng 2019). in Semporna may indicate near-shore and ocean margin Chondrite-normalized REE plot (Figure 5(b)) seawater settings (Johannesson et al. 2006) while basaltic

shows Semporna volcanic rocksMultM idisplaypulelt ipplloet po slightlof tS oiOf S2 enrichmentivOs2. vTsiO. T2,iO A2l,2 OA l32,O M3,andesiteg MOg, OC,a COa, OoccursN,a N2Oa2,O K in, 2KO 2the,O P, 2 PmodernO2O5, 5F, eFOeOt opent ocean setting (Tostevin 9 9 2 2 . . 5 5 2 2 0 of light rare earth element 0 (LREE) (La/SmN = 1.65 - 4.58) et al. 2016). Semporna volcanic rock REE patterns suggest 8 8 . . 0 0 0 4 0

compared to heavy rare earth elements (HREE) (Gd/LuN the rocks are co-magmatic.4 2 2 7 7 , , , , , , , . . Multiple plot of SiO2 vs. TiO2 Al2O3 MgO CaO Na2O K2O P2O5 FeOt 0 0 Multiple plot of SiO vs. TiO , Al O , MgO, CaO, Na O, K O, P O , FeOt 2 8 2 2 3 2 2 2 5 8 3 3 9 , , , , , , , 2 1

Multiple plot of SiO vs. TiO A1 l O MgO CaO Na O K O P O FeOt . 2 3 2 2 3 2 2 2 5 3 5 2 2 2 9 0 O 2 O . 6 6 O 5 O . O . 9 g O 2 g 2 2 0 i 2 i . l 5 l 0 0 2 T 0 T M M A 8 MuMltiuplteip plelo pt oloft S oifO S iOvs . vTsiO. T ,i OA l, OAl, ,OM g, OM,g C,O a,O C, aN,O a, ONa, ,K OO, K, P,O O, P, F,O eO, Ft e, Ot 6

. 2 2 2 22 32 3 2 2 2 2 2 5 2 5 Multiple plot of SiO2 vs. T6 iO2 Al2O3 MgO CaO Na2O K2O P2O5 FeOt 2 2 0 8 1 0 1 4 . ● ● 5 2 5 0 8 . 9 . 9 0 . 4 9 2 ● 2 2 .

. ● 2 . 5 0 5 0 5 0 0 4 2 2 ● 2 ● 0 0 2 7 0 . 7 0

4 ● 4 . ● 8 ● 1 1

7 4 ● ● 4 ● ●

● 3 1 0 1 . . . 1 8 8 8 8 3 . 2 . 0 . 3 ● ● 0 0 O 1 ● 8 0

● 0 3 0 6 O 0 3 0 ● 0 2 ● 4 4 . 4 O ● ● g 1

2 O ● i 3 2 2 ● 2 6 l O 2 0 . O � g O 2 T i 6 M � O l A � 3 3 0 . ) O 2 g 2 6 2 . i . ) T 0 M ) 0 l 7 2 7 A 0 7 1 1 1 . 6 . 0 T 0

. ● M 5 A 2 . 6 0 1 0

0 ● . %

● 2 5 8 8 . % 8 0 1 . % . ● 3 3 t 3 5 ● ● 1 t 1 3 t . 1 0 3 3 2 50 5060● 6070 7080 80 50 50 60 60 70 70 80 80 5050 6060 7070 8080 2 ● 2 O 0 O 6 O 4 w

O ●

6 ● 6 O . w O O ● 1 g w 4 . ● O

● 2 . i ( O g 1

2 4 ● g . i l 2 � ( i 0 l ( ● 1 l 4 ● 0 ● 4 0 � ● � T

1 ● 0 M . 2 T 1

A ● M T 4 ● ● ● M A 1 3 A 6

. ● ● 0 ● 6 2 SiO ●SiO 6 SiO SiO SiOSiO● 2 2 2 2 O 2 2 2 ● 0

● 1 2 O ● ●

● 1 5 1 ● O i ● ● ● 5 g .

3 ● 5

2 ● . .

● 2 . 0

3 T ● 0 l 2 ● 1 0 0 . 0 0 ● 0 0 0 0 3 . . 2 ● 4 4 1 .

M ● 0 0 1 1 A 4 1 4 0

4 ● 1 4 ● ● 4 ●

● 4 ● 1 50 60 70 80 50 60● 70 80 1 50 60 70 80 .

4 ● ● ● 1

4 ● ● 1 ● ● . 50 60 70 80 1 50 60 70 80 50 60 70 80 . ● 0 5 50 60 70 80● 5 50 60 70 80 50 60 70 ●80 0 ● . .

0 ● ●● ● ● ● 3 ● 3 ● 8 8 ● ● ●

3 SiO2 SiO2 SiO2 2 3 3 . 3 SiO SiO 0 SiO 2

3 2 2 2 . 1 2 0 SiO SiO 0 SiO . 2 2 2 0 0 ● 0

1 ● . 0 . 1 0 0

0 ● ● . 3 3 4 0

0 ● ● 1 .

0 ● 4 ● 4 0 6 6 .

1 50 60 70 80 50 60 70 80 50 60 70 80 4 4 1

50 60 70 80 4 50 60 70 80 50 60 70 80 O 50 60 70 80 O 50 60 70 80 50 60 70 80 O O

5 ● O ● O 5 ● 2 2 . . 2 5 ● 2 a 2 2 a a . a ● ● ● 5 2 2 K . 5 K C 3 C 8 N . ● N

● SiO 3 SiO SiO

8 2 2 2 ) 3 � 4 8 4 SiO2 SiO2 3 SiO2 ) SiO ● SiO 3 SiO � ● 2 0 2 2 0 %

● � ● 3 . 0 . .

) ● . ) t 0 0

0 ● 2 2 0 . . ● ● 4 3 . 0 . % w ●● 1 ● ● ● ● 0 3 % 4 ● 0 ● . ( % 6 1 0 3 4

1 ● t . . ●

4 ● 1 . 6 ● 4 6 1 t O 4 2 2 5 t O 5 O 5 ● ● O 2 . . w O . O O 5 2 ● 2 a 2 O 5

5 O ● a . 2 ( 1 ● w 1 2 2

. ● a 2 . � w 2 2 a a ● ● K C 2 a (

5 ● N 2 3 ( K � 8 C

● 5 . K � C N . N

4 ● ● O 3 4 8 ● 3 0 4 3 2 0 O 0 8 ● O ● . . . 0 0 ● 0

0 ● 0 0 3

● . 0 2 a

. 1 ● 2 3 1 .

2 ● ● 2 ● 0 K 3 C a ● ● ● 1 N ● ● 0 . ● ●

● 1 . 1 6 ● 2 3 50 60 70 80 5 50 60 70 80 50 ● 60 70 80

2 50 60 70 80 3 50 60 70 80 50 60 ● 70 80 . 5 2 ● 5 O

6 ● . O

. ●

5 O ● 1 6 2 . 1 2 2 1 a O a ● O 2 O 5 O ● 2 K O C . O 5 ● 2 2 2 a N .

● a 0 2

● 2 a

SiO 2 SiO SiO

2 . 2 2 SiO a 0 SiO SiO 4

0 ● 2 2 K 2 0 0 2 C .

. , , , , , , , 0 0 N K 0 0

● 1 Multiple plot of SiO vs. Ba Rb Sr Zr Y La Ce U C 2 ● ● 0 N 1 1 ● . 4 0 0 0 4

● 2 0 0 0 3 ● 0 3 ● 0 . ● . ● ● 0 1 . 50 60 70 80 50 60 70 80 50 60 70 80 0 1 . 1

50 60 70 80 50 60 70 80 0 50 60 70 80

50 60 70 80 2 50 60 70 80 50 60 70 80 0 0 3 2

● 1 ● 2 5 ● ● ● 1 . 1 0 1 0 2 5 0 2 SiO . SiO SiO � 0 2 5 2 2 SiOSiO SiO SiO SiO SiO 5

2 8 2 2

2 2 2 7 . 8 1 0 2

) ● 1 ) 0 8 0 � � 0 0 . % 0 0 0 0 m ) 3 ) ) 0 0 0 . % 3 3 . 1 t . 0 1 . 2 . 1 1 2 0 t . p ) 0 . . 0 0 0 0 w 0 0 % 0 . ( 0 0 0 0 1 2 . % . p m 6 ( w 6 0 1 0 ( t t t 50 60 70 80 50 60 70 80 p 50 60 70 80 5 t 5 � 0 p 6 O ( O 0 O 5 8 r a O w w 8 b a 8 2

50 60 70 80 e 50 60 70 80 50 60 70 80 2 5 e ( ( S �

50 � 60 70 80 50 60 70 80 50 60 70 80 B R B F P 1 t F P ● ● 5 0 0 0 ● ●SiO S●iO 0 SiO 2 4 ● 2 2 4 2 ● 2 0 2 0 . O . 0 ● . O 0 1

● 4 0 0 1 0 . 2

0 ● e

SiO 6 SiO SiO 6 . 2 2 ● 2 6 ● 0

● 0 ● 0 t t 0 SiO SiO SiO ●

3 ● 5 5 2 ● t 2 ● 2

5 ● 0 F P ● 1 . 0 1 ● O O O O O 0 0 O 3 2 0 2 e e 2 2 0 e 0 3 2 ● 0 . F P 0 F P 1 F P 3 ● ●● ● ● ● 0 . ● 2 0 1 4 ●

4 ● 5 4 0 0 0 0 ● 1 8

1 ● ● 1 ● . ● . 0 . ● ● 0 ● ● 0 ● ● 0 ● 0

0 ● ● 0 0

0 , , , ,, ,, ,, , , , , , . 0 MultiMplueltpiplolet oplfoSt ioOf0 2SviOs.2 Bvsa. BRab RSbr SZr ZYr LYaLCaeCUe U . 8 0 0 0 0 2 2 0 0 0 8 1 2 2 . 0 0 0 0 0 0 0 0 0 6 0 50 60 70 80 50 60 70 80 3 3 0 t

2 50 60 70 80 50 60 70 80 1 5 1 50 60 70 80 50 60 70 80 50 60 70 80 . ● ● 2 0 0 O 0 . 0 0 O 0 0 0 0 6 0 2 0 0 e 0 0 . 0 0 0 0 5 0 t . 5 . 5 6 7 7 0 F P (wt.%) 0 2 0 2 t ● ● 0 0 S●iO ● S(wiOt.%) 5 2 2 (wt.%) SiO O SiO 8 O 2 2 ● 4 8 SiO2 SiO2 SiO2 0 2

O SiO (wt.%) � � e ) O 50 60 70 80 50 60 70 80 2� � 0 0 ) ) 1 2 50 5060 6070 7080 80 e 50 50 60 60 70● 70 80 80 F P . m 0

0 ● ● ● 0 F P 0

p ● ● 0 4 0 2

● 0 0 2 ● ● m 0 m 0 5 0 0 ● 0 4 7 7 ( p 0 0 1 2 6 0

6 ● p p

. SiO SiO 0 2

2 5 2 r 0 5

b ● a 1 SiO r SiO

b SiO SiO a ● 2 2 ● 2 2 . 0 5

p ● p 5

S ● B R S

B Basaltic andesite R 0 1

● ( ( 0

1 ● 0 0 � � ● 0 ● 6

0 ● 2 6 r

0 ●

● b 0 0 0 4 0 2 4 S

● 0 ● 0 0 0 ● 0 R ● 0

0 ● Andesite 0 . ● ● ● 1 ● 2 0 1 ● 0

● 5 0 0 3 0 3 0 0

● 5

0 ● 0 0 0 0 ● 0 0 2 . 50 60 70 80 50 60 70 80 2 0 5 0 5 Dacite 0 0

. ● ● ● ● 4 ● 0 r 0 a 0 5 Y 0 Z L 4 0

50 60 70 80 50 60 70 80 1 0 0 0 0 0 0 SiO2 0 SiO2 Rhyolite 50 60 70 80 1 50 60 70 80 3 1 ● 50 60 70 80 50 60 70 80 50 60 70 80 0

50 60 70 80 50 60 70 80 50 60 70 80 3 SiO SiO 0 2 2 0 2

SiO2 SiO2 0

1 ● ● SiO2 SiO2 SiOSi(Ow2 t.%) ● 0 SiO2 SiO S(iOw2 t.%) 2� SiO2 � 0 2� � ● 2

1 ● 0 ● 0 0 0 5

0 0 ● 7 7 5 2 7 7 0 0 2 0 5 1 0 0 ● 0 6

● 0 6 6 6 0 FIGURE 4. Harker diagrams of major elements and selected50 trace60 70 80 50 60 70 80 50 60 70 80 0 ● 0

● 0 0 2 0 5 2 0 5 0 5

● elements of5 Semporna volcanic rocks

0 ● SiO2 SiO2 SiO2

0 ● 4 0

r ● 4 a 0 0 5 r Y a 0 Z 0 L 4 0 5 Y 1 Z . L 4 0 4 1 0 3 3 1

3 ● 0 ● 0 3 0 0 0 3 0 2 2 0 5 0 2 . 1 0 1 ●

● 2 0 1 ● ● ● 0 0 ● ● 2 0 1 ● 0 ● 2 ●

● 1

● 0 ● ●

1 ● ● ● 0 0 0 . 0 5 1 0 0 2 0 5 1 e 0 U 8 50 60 70 80 50 60 70 80 50 60 70 80 C 50 60 70 80 50 60 70 80 50 60 70 80 ● 5 . 1 SiO2 SiO2 SiO2 0 SiO2 SiO2 SiO2 6 0 0 0 . . 4

0 ● 0 0 3 . 1 1 4 4 3 1 ●

0 ● 2 5 0

. ● 5 1 0 2 5 . 2 . 1 2 0 2 ● 0

0 ● 0

1 ● ● 0 0

. 50 60 70 80 50 60 70 80

1 ● ● 0 2 . e 2 0 U 8 C

e ● 0 U 8

5 SiO SiO C ● 2 2 . 5 1 . 0 1 6 0 6 0

● . 0 1 0 .

4 ●

0 ● 1

4 ● ● ● ● 5 0 .

2 ● 0 5 0 . 2 50 60 70 80 0 50 60 70 80 50 60 70 80 50 60 70 80

SiO2 SiO2 SiO2 SiO2 17 SpideSrp pidloetr − p lPort im− i tPivreim mitaivnet lme (aMntcleD (oSMnpociduDegorhn p o alountg d−h S aPunrnidm 1995 iStiuven ) m1995antl)e (McDonough and Sun 1995) 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 Basaltic andesite A Spider plot − PrimitiveA mndeasnitele (McDonough and Sun 1995) Dacite 0 0 0 0 0 0 0 0 ● ● ● 0 0 0 0 0 1 1 1 Rhyolite 1 ● ● ● ● ● ● Mariana Arc

● ● ● e e e − l l ● l Spider plot Primitive mantle (McDonough and Sun 1995) t t ● t ● Castillo et al. 2007 n n ● ● n ●

● 0

a ● ● a a 0 0 0 0 ● ● 0 ● ● ● ● ● 0 ● ● ● Sajona et al. 1996 & 0 0 0 ● ● 0 ● 0 m m ● ● m ● 1 0 1 1

● ● 1 ● 1 e

e Castillo et al. 2007 ● ● ● ● e ● ● ● v v v i i ● ● ● i ● ● ● t t t ● i i ● i ● ● ● ● ●

m m m ● ● ● ● i i i ● e ● ● ● ● ● l r r r ● ● ● ● t ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● P P P n

● ● ● ● ● ● ● / / / ● ● a ● ● ● 0 ● ● ● 0 ● ● ●

0 ● 0 0

0 ● ● e e e ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● 0 l l l ● ● 1

0 ● ●

1 ● ● 1 ● ● ● ● m ● ● ● ● ● ● ● ● ● ● 1 ● ● ● ● ●

● 1 ● ● ● ● ●

p ● ● p ● ●p ● ● ● ● ● ● ● e ● ● ● ● ● ● ● ●

m ● m m ● ● ● ●v ● ● i ● ● ● a a a t ● ● ● ● ●

i ● ● ● ● S S S ● ● ● ● ● ● ● ● ● ● ● m ● ● ● ● ● ● ● ● ● ● ● i e ● ● ● ● ● ● ● ● ● ● ● l ● ● ● ● ● ● r

t ● ● ● ● ● ● ● ● ● ● P ● ● n ● ● ● / ● a ● ● 0 ● ●

0 ● e ● ● ● ● 1

0 ● ● 1 1

l ●

1 ● m ● ● ● ● ● ● 1 ● ● ● ● p ● ● ● ● e ● ● ● ●

m ● v ● i ● ● ● a t ●

i ● ●

S ● ● ● ● m ● ● ● ● ● i ● ● ● ● ● ● r ● ● ● ● ● ● ● ● P Dy ● Cs Ba U Ta Ce Pr P Zr Eu ● Yb ●

/ Dy Dy Cs Ba U Ta Ce Cs Pr Ba P U Zr Ta Eu Ce P●r Y●b P Zr ● Eu Yb 1 1 1

0 ● e . ● . . ● ● ● 1 l

1 ● ● 0 ● ● ● 0 0 ● ● ● ● ● p ● ● Rb Th Nb La Pb Sr Nd Sm ● Ti Y Lu Rb Th Nb La Pb Rb Sr Th Nd Nb Sm La Ti Pb Y Sr L●u Nd ● Sm Ti Y Lu m ● ● a ● ●

SpideSSrSp pipSdildoiepdetrie d r−S pr ep lpRorlo ltpoE t−l tEo− − tR cR −REhE oEREnE c dc hEcrhioh tcoenohn dn(odrBdnirtroiedtiety re(in t( Be(tBoBo (onyoBy ny1984ontnoytotnon tn1984o )1984 n1984 1984))) ) ● ● ● ● ● ● ● ● ● ● ● 0 0 0 0 0 ● 0 0 0 0 0 Dy

0 0 0 0 Cs U Ce 0 Ba Ta Pr P Zr Eu Yb 1 1 1 1 1 1 . 1 0 Basaltic andesite B Rb Th Nb La Pb Sr Nd Sm Ti Y Lu Andesite Dacite Cs Ba U Ta Ce Pr P Zr Eu Dy Yb 1 .

0 Rhyolite Rb Th Nb La Pb Sr Nd Sm Ti Y Lu

Castillo et al., 2007 0 0 0 0 0 e e e e e

0 0 ●0 0 0 ●●● ● t t t t t 1 1 1 1 1 i i i i i r r r r r Sajona et al. 1996 & d d d d d ● ●●● ● ● ●●● ● n

n n n n ● ●●● ● Castillo et al. 2007 o o o o o ● ●●●● ● ●●● ● h h h h h ● ●●● ● ● ●●● ● c c c c c ● ●●● ● ● ●●● ●

● ●●● ● ● ●●● ● E E E E E ● ●●● ● E E E E E ● ●●● ● ● ●●● ● ● ●●● ● ● ●●● ● ● ●●● ● R R R R R ● ●●● ● ● ●●● ● ● ●●●● ● ●●●● ● ●●● ● ● ●●●● ● ●●● ●

● ●●● ● ● ●●●● ● ●●● ● / / / / / ● ●●● ● ● ●●● ● ● ●●●● ● ●●● ● ● ●●●● ● ●●● ● e e e e e ● ●●● ● l l l l l ● ●●● ● p p p p p m m m m m ● ●●● ● 0 0 0 a 0 0 a a a a 1 1 1 1 1 ● ●●● ● S S S S S ● ●●●● ● ●●● ● ● ●●● ● ● ●●●● ● ●●● ● ● ●●● ● ● ●●●● ● ●●● ● ● ●●●● ● ●●● ● ● ●●● ● ● ●●●● ● ●●●● ● ●●● ● ● ●●● ● ● ●●● ● ● ●●● ●

La LaLLaaLa Pr PPrPrr Pr Pm PPmPmmPm Eu EEuEuuEu Tb TTbTbbTb Ho HHoHooHo Tm TTmTmmTm Lu LuLLuuLu 1 1 1 1 1 Ce CCeCeeCe Nd NNdNddNd Sm SSmSmmSm Gd GGdGddGd Dy DDyDyyDy Er EErErr Er Yb YYbYbbYb

FIGURE 5. (a) Primitive mantle-normalized patterns for the Semporna volcanic rocks, (b) Chondrite-normalized patterns for the Semporna volcanic rocks

DISCUSSION rock exhibit typical subduction-related characteristics evidenced by enrichment of LILE and depletion of Nb, MAGMA DIFFERENTIATION AND TECTONIC SETTING Ta, and Ti. Major and trace elements signatures for Semporna Even though Semporna volcanic rocks show some volcanic rocks show: Variation in trends of major elements attributes of subalkaline/tholeiitic series, however, most of the rocks plotted in the calc-alkaline series (figure against SiO2 indicating magma differentiation (SiO2 vs. TiO , Al O , FeO(t), MgO, CaO, K O, and P O ) and not shown here). In the surrounding regions, Semporna 2 2 3 2 2 5 volcanic rocks shared a similar calc-alkaline and tholeiitic dominance of plagioclase fractionation (SiO2 vs. Al2O3 and CaO; negative Eu anomalies); the increasing fractionated distribution with magma suites from Dent Peninsula (Bergman et al. 2000), north-eastern Sulu Arc (Castillo et REE patterns (Figure 5(b)) ((LaN/YbN) = 2.10 - 28.48) and negative Eu anomalies in Semporna lavas indicate that al. 2007; Sajona et al. 1996), central Sulu basaltic andesite the magma has experienced magma differentiation and (Castillo et al. 2007) and eastern (Sonntag et fractional crystallization from basaltic andesite to andesite al. 2011), where all rocks had formed at convergent and later to more evolved dacite and rhyolite; and all the margin in the Sulu Sea. In addition, their chemical 18

characteristics (e.g. enrichment of LILE and LREE, using Hf/3-Th- Nb/16 and Hf/3-Th-Ta (Figure 6(c) and depleted HFSE, and typical subduction-related signature) 6(d)) shows Semporna volcanic rocks fall into island arc relatively complement each other. The distribution of Sulu calc-alkaline basalt. The Semporna volcanic rocks might Arc which can be traced in eastern Sabah (Chiang 2002) have formed in a back-arc basin, or marginal basin since might originated from Sulu Arc regions since Semporna the Sulu Sea also formed in these settings and currently Peninsula located at the end of NE-SE Sulu Arc. Recent subducted underneath the Sulu Arc (Pubellier et al. 1991; zircon U-Pb dating of Semporna volcanic rocks showed Rangin & Silver 1991). After the subduction of Celebes sea the age of Semporna dacite (12.46 ± 0.28 Ma) is much beneath the Sulu Arc (Chiang 2002), the Sulu Sea back- older than Semporna andesite (10.49 ± 0.11 Ma) (James & arc basin was formed followed by subduction rollback Azman 2019). Although the U-Pb age reflects that dacite is towards the south-east (Hall 2013). The volcanic activity older than the andesitic unit, the overall REE patterns for was generated by the subduction along Sulu Ridge from Semporna lavas still indicates similar magmatic sources. Zamboanga Peninsula to southern Sabah during Early to Tectonically, Semporna volcanics are plotted into Late Miocene (Rangin & Silver 1991). The Sulu Arc slowly island arc lavas tectonic discrimination diagram of Ti vs. emerged from sea level and then collapsed during Mid- Zr diagram (Figure 6(a)). Other tectonic discrimination Miocene. Most of the Sulu Sea is an extension of former diagrams Nb/Yb versus Th/Yb (Figure 6(b)) show volcanic arc and not an oceanic crust (Hutchison 1992). majority Semporna volcanic rocks plotted within oceanic The subduction of the Celebes Sea was first suggested by arcs with one basaltic andesite (13L9) full under active Rangin (1989) and then supported by geochemical data continental margin and alkaline oceanic arcs. Only three (Chiang 2002) and structural data (Hall & Wilson 2000). rocks samples (dacite = 9L1 and 9L3; basaltic andesite = Nevertheless, Pre-Neogene volcanic rocks are uncommon 13L9) plotted under island arc Shoshonites while the rest in west and central Sabah and more common in eastern of the Semporna volcanic rocks plotted under island arc part of Sabah. calc-alkaline basalt. More specific discrimination diagrams

� 0 0 . 0

0 B A 1 Oceanic�arcs� Ac ve�con nental�margin�� +�Alkaline�oceanic�arcs� 0 � 0 . 0 1 SHO� ICA� � b � 0 Y 0 . / 1 h

T ICA� Castillo et al. 2007 IAT� � Sajona et al. 1996 & 0 1

. Castillo et al. 2007 0 IAT – Island Arc Tholeiites ICA – Island Arc Calc-alkaline

� SHO – Island Arc Shoshonites 1

Triangular diagrams of the Th−Hf−Ta−Zr−Nb system, Wood0 1980 .

0 Triangular diagrams of the Th−Hf−Ta−Zr−Nb system, Wood 1980 0.1� 1.0� 10.0� 100.0� 1000.0� Nb/Yb�

C D Hf/3 Hf/3 Hf/3 Zr/117 Hf/3 Zr/117

N− N− N− N− N− N− MORB MORB MORB MORB MORB MORB

IAT IAT IAT IAT IAT IAT

E−MORB, E−MORB, E−MORB, E−MORB, E−MORB, E−MORB, WPT WPT WPT WPT WPT WPT

CAB CAB CAB CAB CAB CAB ● ● ● ● ● ● ● WPA ● WPA ● ●WPA WPA ● WPA ● WPA

● ● ● ● ● ● ● ● ● ●

Th Ta Th Nb/16 Th Th Ta Nb/16 Th Nb/16 Th Nb/16

FIGURE 6. Plot of (a) Ti (ppm) vs. Zr (ppm) (after Pearce (1982)), (b) Nb/Yb (ppm) vs. Th/Yb (ppm) diagram (after Pearce (2008)), (c) Hf/3-Th- Nb/16 diagram (after Wood (1980)), and (d) Hf/3-Th-Ta diagram (after Wood (1980)) 19

CONCLUSION peraluminous crdierite-bearing granite: The San Basilio Semporna volcanic rocks are composed of basaltic Intrusion (Central Sardinia, Italy). Journal of Petrology andesite, andesite, dacite, and rhyolite based on 37(5): 1175-1206. geochemical classification. Semporna volcanic lavas are Garwin, S., Hall, R. & Watanabe, Y. 2005. Tectonic setting, formed within island arc tectonic environment shows geology, and gold and copper mineralization in Cenozoic magmatic arcs of Southeast Asia and the West Pacific. calc-alkaline with minor tholeiitic feature. Geochemical Economic Geology 100th Anniversary Volume 891: 930. features showed fractionation trends and co-magmatic Hall, R. 2013. Contraction and extention in northern Borneo relationship exist between the basaltic andesite and driven by subduction rollback. Journal of Asian Earth rhyolite. Large lithophile elements and light rare earth Sciences 76: 399-411. elements enrichment indicated a subduction zone Hall, R. 2012. 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Oluwatoyin O. Akinola *Corresponding author; email: [email protected] Department of Geology Faculty of Science Received: 29 February 2020 Ekiti State University Accepted: 3 July 2020 Ado-Ekiti Nigeria

Junaidi Asis Faculty of Science and Natural Resources University Malaysia Sabah 88400 , Sabah Malaysia