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Origin and tectonic significance of the metamorphic rocks associated with the Ophiolite, ,

SHARIFF A. K. OMANG 1 & A. J. BARBER 2 1 Department of Earth Sciences, Faculty of Science and Natural Resources, Universiti Kebangsaan Malaysia, Sabah Campus, Locked Bag No 62, 88996 , Sabah, Malaysia 2 SE Asia Research Group, Department of Geology, Royal Holloway, University of London, Egham TW20 OEX, UK

Abstract: Banded hornblende gneiss, foliated amphibolite, hornblende, chlorite and siliceous schist form lenses in an 8 km wide belt within the Darvel Bay Ophiolite Complex. Foliation in the belt is generally steep to vertical, striking parallel to the trend of the belt and lineations are sub-horizontal. Mineral and geochemical studies show that the metamorphic rocks represent banded and isotropic , plagiogranites, doleritic and basaltic dykes, basaltic volcanics and cherts formed at a spreading ridge in a supra- zone environment, which were deformed at high temperatures but low pressures along a transform fault. Incorporation of supracrustal cherts indicates that the transform extended for hundreds of kilometres between spreading centres. Garnet and amphibolites found as clasts in Miocene volcanic agglomerates formed at high pressures, and temperatures are interpreted as derived from a metamorphic sole underlying the complex, formed during subduction of ocean crust and the emplacement of the ophiolite complex on Sabah.

Ophiolite outcrops are distributed throughout the (Rangin et al. 1990). Cherts from the Chert- eastern part of Sabah, East Malaysia, from Banggi Formation have yielded radiolaria of Lower Island in the north to and and the Cretaceous age (Leong 1977; Rangin et al. 1990; area in the south (Fig.l, inset). The Aitchison 1994). Massive limestones associated Darvel Bay Ophiolite Complex in the south is the with the Chert-Spilite Formation contain most extensive outcrop, extending 100 km west- Cretaceous foraminifera (Leong 1974). The Chert- wards from Darvel Bay. The greater part of the Spilite Formation is interpreted as representing complex consists of , largely serpen- ocean floor sediments which were deposited on top tinized, but it also includes cumulate pyroxenites, of the ophiolite (Hutchison 1975), and carbonate layered and massive gabbros and diorites, meta- cappings to seamounts. Since the underlying morphosed to varying degrees. The complex is also is unlikely to be much older than the cut by dolerite dykes, although these are never so oldest overlying sediments, the Early Jurassic K-Ar abundant to be termed a sheeted dyke complex. ages are regarded as spurious (Hutchison 1988). These rock types are closely associated with out- Fragments of ophiolitic rocks are found as clasts crops of the Chert-Spilite Formation, composed of in Eocene sediments (Newton-Smith 1967; Rangin pillow , banded ribbon chert, turbiditic sand- et al. 1990), suggesting that the ophiolite complex stones, mainly volcaniclastic but with some rare had been obducted onto Sabah either in the latest sandstones, and a few occurrences of Cretaceous or earliest Palaeogene. In the early massive limestone. Miocene the ophiolite complex formed the base- The ophiolite complex has been well described ment to a volcanic arc, possibly related to continued in the publications of the Geological Survey of subduction of the Proto-South China Sea. Mitchell Malaysia (Reinhard & Wenk 1955; Fitch 1955; et al. (1986) and Rangin (1989) have suggested Dhonau & Hutchison 1966; Koopmans 1967). The that, as a result of continued compression, the complex has been interpreted as a segment of ocean complex was backthrust over the Celebes Sea floor floor, either of a Proto-South China Sea (Holloway to the south. 1981; Rangin et al. 1990) or of the Celebes Sea The ophiolite complex is surrounded by chaotic (Hutchison 1988). A wide range of K-Ar age dates melange deposits (Fig. 1) which contain fragments has been obtained from the rocks of the ophiolite of all the rock units represented in the complex complex from 210Ma (Leong 1971) to 137 Ma and the Chert-Spilite Formation, as well as

From Hall, R. & Blundell, D. (eds), 1996, TectonicEvolution of Southeast Asia, 263 Geological Society Special Publication No. 106, pp. 263-279. Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014 264 s.A.K. OMANG (~ A. J. BARBER

0 5 10 r' Km Ophiolite Complex E~ Felsite ~ RecentAIluvium ~ ~'~] Metamorphic rocks E~ Chert-Spilite • " '* '° "~ "* "* "* "* "° "° "° ". "° "... - , ~ '. ". "° '. ". ". "° ". Formation ~'.'~**,' i**: (foliated metabasites ) ~~::*:i*" []'EI Sheared D Neogene , ,, ,, ,,, ,, ,, -° "4 "° . "° "° .o .° .° ...... sediments , ', ', ', ', ', ', "°,:*.:*.:*.:°.:*,:*,:°,:*,:*, ~ Gabbros & Cumulates [~ M6langes "°"°' ' °"°' l Peridotite ~ Thrust fault (mainly serpentinised) - - " Fault ~!~:i:ii!i:i:i:!...i.i~.:i:i:i!!iiii!i!iiiiiiiiiiiiiiii!i!iiiii!i!ii!iii!::ii!i!~ii:!:!:!:!:i: l: 8" 20' E. ::::::::::::::::::::::::::::::::::::::::::::::::::::: ======~~:i.i:i:i:i!ii!i!i!iii!iiiiii!iiiiiiii!!!iii!!!iliiiiiiiiiii

*Dolerite dyke PSI2 D~:: PS6

Irtl Pulau Sakar , ~ ~PT3 Pulau "~;K4 ! I ! rl~l ! ! ! ! | ruiau~, ' %,• ~l9 Katung- / ~1 i i : • ~. Saddle/ % Kalungan-.L l.ll.l~.l~.ll. 1.1~.13.11.1~.1~I~. ~ ~ -.L Cumulate D i i i i i i i pi--.~.,1-.-~ ,,.z.~ p C rocks Darvel Bay

E t 7 4* 58'N Pulau SARAWAK 1 "~ ~, Bohayan Pulau Tabauwan _/'f / ~, P ~ f V~Silumpat / ~':*'i*' 118" 10' E. E --/- 118"20' E Dolerite dyke I Fig. 1. Geological map of the Darvel Bay Ophiolite Complex near Lahad Datu showing location of samples used in this study. Inset map shows distribution of ophiolite complexes in Sabah. B, ; R, Ranau; T, Telupid; DB, Darvel Bay. younger sediments and volcanic rocks. Clennell Metamorphic rocks (1991) considered that the melanges were formed by processes of sedimentary slumping and Although the rocks forming the Darvel Bay diapirism, coincident with the collision of micro- Ophiolite Complex are variably metamorphosed continental blocks with the north Sabah margin and throughout, dynamically metamorphosed rocks the extension of the arc basement related to the are concentrated in an E-W belt c. 8 km wide development of the in late early and early extending westwards from Lahad Datu on the north mid Miocene times. The ophiolite complex and side of Darvel Bay (Fig.l) which can be traced for the melanges are overlain unconformably by Late c. 40 km to the west. Metamorphic rocks are well Miocene to Pliocene sediments of the 'circular exposed in coastal sections around the shores of basins' and in the Quaternary again formed the Darvel Bay and particularly around the small basement to a volcanic arc which extends from islands within the bay, where they have been Mindanao in the Philippines, through the Sulu described previously by Dhonau & Hutchison archipelago to the Dent and peninsulas (1966) and Hutchison & Dhonau (1969, 1971) from of Sabah. the north side of the bay, and by Koopmans (1967) Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014 DARVEL BAY OPHIOLITE, SABAH 265

from the south. Inland exposures are poor, apart schistosity increases in localized shear zones. The from road-cuts, quarries and scarce river sections. banding is commonly folded into tight intrafolial The metamorphic rocks have been described as isoclinal folds which may show the closed eyed metagabbros, amphibolites, hornblende gneisses outcrop pattern characteristic of sheath folds. and schists. Reinhard & Wenk (1955) described Where folds are present the schistosity is parallel to the dynamically metamorphosed rocks as the axial planes of the folds. In the more intensely 'Crystalline Schists' and Koopmans (1967) identi- deformed shear zones aligned hornblende and fied them as the 'Crystalline Basement Complex', crystals define a mineral lineation, lying with the implication that they were the oldest rock in the plane of the schistosity. unit in Sabah. However, K-Ar dating reported by Dhonau & Hutchison (1966) showed that these Amphibolite metamorphic rocks are of Cretaceous age, the same age as the Darvel Bay Ophiolite Complex, and form Amphibolites are commonly found associated with an intrinsic part of the complex the banded gneisses in the field. These may form The structure of the dynamically metamorphosed extensive outcrops, as on the northern side of Sakar belt has been fully described by Dhonau & Island or as smaller bodies which may show cross- Hutchison (1966). The metamorphic rocks are cutting, intrusive relationships to the hornblende typically banded, schistose and lineated. Through gneisses. The grain size of these amphibolitic rocks most of the belt the banding and schistosity are is variable. Coarse grained amphibolites show the vertical or steeply dipping and strike E-W, parallel characteristic distribution of white feldspathic and to the general trend of the belt, swinging round to a black or green ferromagnesian minerals which more NW-SE trend in the islands of Darvel Bay. indicate that they have been derived from gabbros The lineation is sub-horizontal, lying in the plane (metagabbro). Medium and finer grained of the schistosity and plunges at low angles either amphibolites may show relict ophitic textures in to E or W. From their mapping of the structure thin section and large euhedral plagioclase pheno- in the metamorphic rocks, Dhonau & Hutchison crysts or polycrystalline aggregates pseudo- (1966) identified two large-scale open post- morphing plagioclase which indicate an origin as metamorphic monoclinal flexures on E-W axes hypabyssal intrusive rocks (metadolerite). Fine affecting the foliation in the islands of Pulau grained amphibolites without these features may Saddle, Pulau Bohayan and Pulau Silumpat. represent basaltic volcanic rocks (metabasalts). This paper gives an account of the field relations, Like the banded gneisses the amphibolites show petrography, mineral chemistry, geochemistry and varying degrees of deformation. Where they cross- K-At isotopic dating of the metamorphic rocks cut the banding in the gneisses, the amphibolites associated with the Darvel Bay Ophiolite Complex generally show a less intensely developed and discusses their origins and significance in the schistosity than the associated gneisses. In coarse tectonic evolution of Sabah. A separate occurrence grained amphibolites the gabbroic texture may be of is found among Miocene flattened in the foliation, in finer grained rocks volcanics at Tungku, 50 km to the east of Lahad minerals may be recrystallized in the schistosity Datu (Reinhard & Wenk 1955). Garnet amphibolite to form hornblende schists. Where the coarser from this locality was also included in the present amphibolites cross-cut the banding of the gneisses, study. no clear chilled margins are evident and the schistosity crosses the contact between the gneisses Banded hornblende gneiss into the amphibolites, although it is generally not as intensively developed in the latter. Finer grained The dominant metamorphic rock type in the meta- amphibolites often have a dyke-like form, ranging morphic belt within the Darvel Bay Ophiolite in width from a few metres to tens of centimetres Complex is a banded gneiss, the 'Silumpat Gneiss' and show varying angular relationships with the of Dhonau & Hutchison (1966) and Hutchison & banding of the gneiss. Sometimes they are con- Dhonau (1971), with alternating bands of white cordant, and then generally have a well developed feldspathic and black or dark greenish ferro- schistosity with a similar intensity to that in the magnesian bands, well exposed on the north shore adjacent gneisses. Where amphibolite dykes cut the of Darvel Bay, west of Lahad Datu and in road cuts banding at a high angle, the schistosity is generally along the Silam Road. The bands range in thick- less well developed than in the surrounding gneiss. ness from tens of centimetres to millimetres. The Evidently some of the dykes were intruded into banding is paralleled by a schistosity, with the already deformed gabbros, but deformation con- alignment of feldspathic and ferromagnesian aggre- tinued after dyke emplacement, indicating that gates which may also be elongated to form a the dykes were intruded into a zone of active rodding type of lineation. The intensity of the deformation. Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014 266 s.A.K. OMANG t~ A. J. BARBER

twinning. Microprobe analysis shows that where Mineralogy plagioclase is associated with it has a In the less highly deformed and altered hornblende composition of An68-An74 (labradorite to gneisses and metagabbros the ferromagnesian bytownite) representing an igneous relic, but more component includes relict crystals of pale green commonly is An 6 -An32 (oligoclase to andesine) or colourless pyroxene. These may form the cores of metamorphic origin (Hutchison 1978). In the to brownish-green amphibole crystals and show amphibolites, and especially in highly deformed alteration along their margins and along internal rocks, the plagioclase is An 3 -An 5 (albite). In cracks to aggregates of small blue-green amphibole many samples of hornblende gneiss and amphibo- crystals. Microprobe analysis shows that they are lite the plagioclase has been completely pseudo- clinopyroxenes of salite to augite composition morphed by low grade alteration products (En40.5 Fst3 Wo47-En45.5 Fs]2.7 Wo28), with Xrvlg (saussurite). values of 90-97 and an Na20-content of 0.5 wt%. is a common constituent of the gneisses Plagioclase crystals have a grain size up to and amphibolites as an alteration product of plagio- 4 ram, and form tabular crystals with albite clase , but in occurrences at the western

Tschermakite Pargasite

II Edenite Hornblende • Metagabbro d- Metadolerite Tremotite I 0 0.5 1.0 (a)

Glaucophane

2.0 1 1.8 ]4)Si(IV) = Ca(M4)Ai(IV) 1.6 t Sodic-am~hibole Na[M4] 1.4 ...... II 1.2 Winchite a.0 Barroisite aramite Sodic-Calcicamphibole 0.8 ....

Calcic-amphibole 0.2 ~ + Metadolerite I 0.0 0 2 Actinolite Hornblende Tschermakite AI[IV] (b) Fig. 2. (a) Composition of amphiboles in metagabbro and metadolerite from Darvel Bay on diagram of Deer et al. (1966). (b) AI[IV] versus Na[M4] plot of amphibole compositions in metagabbro and metadolerite from Darvel Bay, isobars after Brown (1977). Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014 DARVEL BAY OPHIOLITE, SABAH 267

end of Pulau Sakar and in Pulau Katung Kalungan hornblende schists these actinolitic hornblendes there are amphibolites in which epidote is a major form a major component of the rock and are aligned component of the rock. These rocks are distin- to form the schistosity and lineation. guished in the field by their yellowish colour where they occur as bands among more normal amphibo- lites. In thin section they are foliated, with large Metamorphic histo:y crystals of epidote, colourless or pale pink in a matrix of blue-green amphibole and plagioclase. As far as may be determined the primary minera- The plagioclase is albite or is represented by an logical composition of the banded and isotropic aggregate of sericite and calcite. Microprobe gabbros, now found as banded hornblende gneiss analysis of the epidote crystals show that it is an and amphibolite, was clinopyroxene, hornblende -rich variety (Xps27_33). The Fe 3+ content is (cf. Hutchison 1978), labradorite/bytownite and very high (1.5- 2.0 atoms per unit cell) and the ilmenite. Olivine and orthopyroxene may have XFe 3+ (1.0) gives an estimated temperature of been present in some rocks, as olivine and noritic formation of c. 400°C (Nakajima et al. 1977). gabbros occur elsewhere in the Darvel Bay Amphiboles in the amphibolites occur either as Ophiolite Complex (Omang 1993), but all evidence large brownish-green or as small blue-green of their previous existence has been destroyed. The crystals which may be randomly oriented or aligned gabbros were recrystallized in a high temperature, to form foliar and linear structures. The larger low pressure metamorphic environment where amphibole crystals are 2-4 mm in size and are pyroxene was replaced by brownish-green horn- greenish-brown in colour. Some of the brown blende and plagioclase by oligoclase/andesine. hornblende has been interpreted by Hutchison Alignment of brown hornblende and plagioclase (1978) on textural and mineral chemical grounds crystals with foliar and linear structures indicate as of relict igneous origin. However, where they that recrystallization took place in a high tempera- enclose pyroxene relics, or where they are aligned ture dynamic environment; continued dynamic in the foliation and lineation, hornblende crystals metamorphism under lower temperature amphibo- are clearly of metamorphic origin. Electron micro- lite facies conditions are indicated where green probe analyses plotted on the (Na+ K)/A1TM amphiboles are aligned with the schistosity and diagram of Deer et al. (1966) show that the amphi- lineation. Later recrystallisation under hydro- bole composition lies between the hornblende and thermal conditions at lower temperatures resulted pargasitic hornblende fields (Fig. 2a) (cf. Hutchison in the local replacement of plagioclase by 1978, fig. 6). On the AlIV/Na (M4) plot of Brown saussurite and the alteration of pyroxene and (1977) compositions extend from the calcic hornblende to chlorite. amphibole towards the sodic-calcic amphibole field, corresponding to pressures of about 5 kbar (Fig.2b). On the AllY/A1vI plot of Fleet & Barnett Geochemistry (1978) the amphiboles lie in the low pressure field (Fig. 3a) and on the Na + K/A1TM plot of Jamieson Whole rock major element and trace element (1981) follow the high temperature/low pressure analyses of hornblende gneisses and amphibolites trend (Fig. 3b). The Ti content of the amphiboles are shown in Table 1. On an AFM plot (Fig. 4) (0.04-0.3 atoms per formula unit) indicates that these metabasites lie in the tholeiite and oceanic crystallization of the amphiboles took place in the gabbro (MORB) field of Kirst (1976). AlzO3]TiO2 temperature range 550-650°C under low pressure ratios also fall in the MORB field (Fig. 5) of Sun conditions in the lower amphibolite facies (Spear & Nesbitt (1978). Trace element analyses show that 1981). Using the semi-empirical geothermometer high field strength (HFSE) elements (e.g. Zr, Y) proposed by Plyusnina (1982) for plagioclase/ have a high concentration relative to large ion hornblende pairs, core compositions of crystals lithophile (LILE) elements. The Cr-Y plot (Pearce from the amphibolites give temperatures of et al. 1984b) and Ti-Zr-Y diagram (Pearce & Cann 580-600°C and pressures of 3-4 kbars for R T 1973) also suggest a MORB-like character. conditions at the time of crystallization. On the basis of spider diagrams the samples can Small blue-green amphibole crystals commonly be divided into three groups. The metadolerite occur in the banded gneisses and amphibolites dykes (Fig. 7a), are a suite of basaltic rocks with marginal to pyroxene or brown hornblende crystals. moderate LILE enrichment but are with a clear In the study by Hutchison (1978), microprobe negative Nb anomaly relative to the light rare earth analyses of blue-green amphiboles from the Darvel elements (LREE). One group of metagabbros Bay Ophiolite Complex showed that their com- (Fig. 7b) is very similar to the metadolerites, but position lay mainly in the actinolitic hornblende with more primitive compositions, indicated by field with some actinolite. In highly deformed high Cr and Ni, and with much lower contents of Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014 268 s.A.K. OMANG (~ A. J. BARBER

Pargasite Tschermakite 2

~-'l'/ High-pressure ~i~'l~/ CT"amphib°lez°ne Ed~...... Homilende ...... AI[IV] 1 Low-pressure Actinolite ole zone 0 Glaucophane 0 2 (a) AI[Vl] Glaucophane

2.01.51 High-pressuretrend

Na+KEckermakite 1 / Ede ite Pargasite + .= [ High-temperature i d

0.0 Tremolite/A~tinolit? ~ , Tschermakite

0.0 0.5 1.0 1.5 2.0 (b) Ai[IV] Fig. 3. (a) AI[VI] v. AI[IV], and (b) AI[IV] v. (Na + K) of amphibole compositions in metagabbro and metadolerite from Darvel Bay; boundary between low and high pressure calcic amphiboles in (a) is from Fleet & Barnett (1978); high and low pressure trends in (b) from Jamieson (1981).

K, Rb and Ba. The other group of metagabbros (Fig. 7c) includes samples which have very spiky Felsic rocks profiles. They are extremely depleted in most The hornblende gneisses and amphibolites are incompatible elements, particularly Nb, LREE, P frequently cut by felsic veins on the outcrop scale. and Zr; K and Rb are conspicuously low, and only These veins may be concordant, parallel to the Ba and Sr are at MORB levels in some samples. foliation and schistosity and are then boudinaged, In view of their textures and the field relation- or are cross-cutting. Cross-cutting veins may be ships, the metabasic rocks are interpreted as part straight or folded in a ptygmatic style, and un- of a single ophiolite suite, with geochemical data deformed veins may cut earlier folded veins. indicating MORB-like compositions, but Nb Where the veins are folded, the schistosity in the deficient and show a mild LILE enrichment. The surrounding rocks has an axial plane relationship metadolerites represent an original liquid, with a to the folds. These relationships provide clear chemistry suggesting a supra-subduction zone evidence of multiple intrusion of felsic rocks into setting for their environment of formation. The a zone of active deformation. group of metagabbros which resemble the meta- At several localities within the metamorphic belt dolerites on spider diagrams are suggested to be larger bodies of felsic rock are found. On the north former isotropic gabbros, while the other group shore of Pulau Sakar a felsic body, identified as of metagabbros probably represent cumulate rocks trondhjemite (Specimen PS12c) has been intruded, which have lost an evolved inter-cumulus liquid with an irregular contact and without a chilled fraction enriched in incompatible elements. margin, into metadolerites. A weak schistosity is Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014

Table 1. Whole rock geochemical analyses for metagabbros and metadolerites of the Darvel Bay Metamorphic Complex

Metagabbro Metadolerite

Sample Element JS4a JS L JSp KS2 PS2 PS 3a PS6 PS 12d PS 11 PS 11 b PS 12a PS 12b PS 13d PT3a

SiO 2 44.22 48.07 47.55 49.73 46.42 48.82 50.11 48.52 51.42 51.24 49.28 48.82 51.43 51.42 TiO 2 1.70 1.63 1.55 0.62 0.97 0.23 0.57 1.28 1.61 1.64 1.34 1.63 1.61 1.55 A1203 15.86 15.25 15.62 14.17 17.87 19.99 15.49 15.05 14.87 14.30 15.64 15.40 14.67 15.32 Fe203* 12.38 11.70 11.55 8.58 9.83 5.58 6.57 10.60 12.10 12.07 10.96 11.37 11.27 13.94 MgO 9.13 8.60 8.59 10.53 8.83 8.50 9.96 6.52 6.44 6.86 8.45 9.29 7.22 4.64 MnO 0.22 0.18 0.19 0.15 0.18 0.14 0.13 0.18 0.20 0.19 0.17 0.19 0.20 0.23 CaO 15.01 11.40 11.95 13.41 13.52 14.28 14.85 14.74 8.45 9.00 10.22 9.52 8.18 8.18 Na20 0.99 2.94 2.75 2.38 2.01 1.96 2.07 2.26 4.46 3.84 3.58 3.12 4.62 4.10 K20 0.03 0.06 0.04 0.25 0.12 0.12 0.03 0.06 0.28 0.26 0.18 0.15 0.19 0.20 P205 0.13 0.15 0.13 0.02 0.02 0.01 0.02 0.12 0.16 0.15 0.17 0.14 0.15 0.21 Total 99.67 99.98 99.92 99.84 99.78 99.63 99.79 99.33 99.98 99.54 100.0 99.62 99.53 99.79 LOI 3.44 1.83 1.80 1.39 2.56 2.73 1.59 1.31 1.47 1.87 1.51 2.02 1.23 2.60

A1203/TiO2 9.33 9.36 10.08 22.86 18.42 86.91 27.18 11.76 9.24 8.72 11.67 9.45 9.11 9.88 CaO/TiO 2 8.83 6.99 7.71 21.63 13.94 62.09 26.05 11.52 5.25 5.49 7.63 5.84 5.08 5.28 mg c. 59 c. 59 c. 59 c. 71 c. 64 c. 75 c. 75 c. 55 c. 52 c. 53 c. 61 c. 62 c. 56 c. 40 Ni 115 71 105 127 206 159 128 103 52 45 113 136 92 11 Cr 338 364 368 487 413 243 886 269 80 74 282 296 273 5 V 355 336 331 228 392 120 214 303 354 345 308 314 295 386 Sc 56 57 53 60 69 41.6 63 41 49 49 43 43 46 35 Pb 0.7 n.d. n.d. n.d. 0.6 n.d. 0.3 0.6 1.1 0.4 1.3 n.d. 0.3 1.2 Sr 155.6 160.9 168.6 130.0 333.1 493.2 103.1 283.6 105.5 170.6 196.8 126.4 109.0 158.6 Rb 0.6 0.4 0.3 4.9 0.6 0.9 0.2 0.4 2.9 4.1 1.8 1.5 2.0 1.9 Ba 10 1 1 8 36 45 3 8 14 32 22 24 26 20 Th n.d. n.d. n.d. n.d. 0.2 n.d. n.d. 0.4 0.6 0.7 1.7 0.3 0.3 0.8 Zr 77.9 84.5 82.7 25.0 29.1 6.7 21.9 78.8 104.0 105.3 95.0 110.4 107.7 67.6 Nb 1.4 1.2 1.9 0.4 0.8 0.1 0.4 1.0 2.0 1.8 1.7 1.7 1.7 0.9 Y 38.8 34.6 34.7 15.6 19.3 8.8 16.7 27.4 35.9 36.0 29.6 32 35.1 35.1 La 2 2 2 0.3 1 1 1 2 3 2 7 3 2 1 Ce 10 9 11 0 4 1 2 9 12 6 20 10 11 5 Nd 12 10 12 2 6 4 3 7 10 8 13 10 11 8 Cu 60 100 64 5 8 32 60 17 35 64 46 18 83 43 Zn 142 97 158 53 90 42 48 69 102 93 99 98 99 121 C1 n.d. 219 161 359 33 n.d. 614 104 n.d. 44 121 n.d. 33 88 Ga 17 17 17 12 14 14 13 18 16 15 17 16 13 19

Oxides as wt%, trace elements in ppm. Data presented on a volatile-free basis; mg =Mg[Mg +Fe2+], Mg =MgO/40; Fe203 ×0.9/72; total iron as Fe203 t,~ (Fe203* = Fe203 + FeOxI.III); n.d., below detection limit; LOI, loss on ignition at 1100°C. Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014 270 s.A.K. OMANG • A. J. BARBER

F

/L I+gabr°s M°ta"°l°rTMe 1

A M

I~ Oceanicgabbro (Kirst 1976)~ Amphibolitesfrom Vema | FractureZame ] A M (blonnorezet at. 1984) J

Fig. 4. Metamorphic rocks from Darvel Bay plotted on an AFM diagram compared with gabbros and amphibolites from the Vema Fracture Zone, equatorial Mid-Atlantic; the tholeiite calc-alkaline boundary is from Irvine & Baragar (1971).

developed in the felsic body, parallel to the schis- internal schistosity of the crystal at a high angle, tosity in the surrounding metabasites. Thin section indicating that the rocks have been subjected to study shows that the rock is fine grained with multiple deformation (Omang 1993, pl. 5.7D). elongated crystals of quartz and feldspar defining Whole rock major element and trace element the schistosity. Minor constituents are acicular analyses of felsic rocks are listed in Table 2, and amphibole, epidote, apatite, chlorite, sphene, zircon are compared to ocean ridge granites (ORG) on and Fe-Ti oxides. the spider diagram of Fig. 7d. These analytical data A block (1 m × 1.2 m) of felsic rock, identified show that although the felsic rocks are not true as tonalite (Specimen PK4a), occurs enclosed in granites they are comparable to ORG in their amphibolite on the foreshore on the south coast incompatible element concentrations and resemble of Pulau Sakar. The block probably represents a acid rocks fore other ophiolites, interpreted as xenolith incorporated in a basic intrusion, but now co-genetic with basic rocks (Pearce et al. 1984a). forms a boudin with a schistosity parallel to that in the surrounding metabasite. Thin section study shows that this rock is composed predominantly Metatuff of quartz and plagioclase feldspar with subsidiary actinolitic hornblende. The rock has recrystallized, Chloritic schists are exposed at Km 134 north of with the growth of porphyroblastic feldspar and Kampong Silam on Jalan Silam, where they are hornblende crystals; granophyric texture in the in contact with sheared serpentinite, and near quartz-feldspar matrix may represent an original Kampong Lok Bikin on the coast of the mainland igneous texture or be due to partial melting of the opposite Pulau Sakar where they are interbedded tonalite. The hornblende porphyroblasts contain with metacherts. At the locality on Jalan Silam the trails of small inclusions of quartz, feldspar and schists are folded by small-scale open folds on ENE Ti-oxides defining an internal schistosity. The (060°-070 °) axes with a low angle of plunge porphyroclasts are enclosed in augen structures and (10-12 °) and steep axial planes indicating a the external schistosity in the matrix cuts across the southerly vergence. Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014 DARVEL BAY OPHIOLITE, SABAH 271

100 In thin section the schistosity is defined by fine grained chlorite flakes and small feldspar laths 80 diverging around larger euhedral to subhedral ophiolite plagioclase crystals showing albite and Carlsbad .C..•60 twinning (Fig. 8a). These schists have the composition of tholeiitic 40 and are therefore interpreted as tuffaceous .< MORB rocks belonging to the ophiolite sequence, as 2O • hyaloclastic tufts forming part of the ocean floor Arc assemblage, which has been intensely deformed

! and metamorphosed under greenschist facies ! ", 1 1 2 3 4 conditions. (a) TiO2 (wt.%) Metachert Thin bedded red-brown ribbon cherts occur exten- 80 sively in the northern and southern areas of the 70 Darvel Bay Ophiolite Complex (Fig. 1). In the 60 northern part of the area cherts occur as blocks in the Kuamut Melange (Clennell 1991; Aitchison ophiolite 1994). In the southern area bedded cherts folded '° and imbricated with basaltic pillow lavas, forming ~ 3a an accretionary complex, crop out along Jalan 20 ~ ~ Im MORB Silam. A • Near Kampong Diam, south of Lahad Datu, dis- 10 4-__ Arc ¥~I I continuous exposures of greenish-white chert with o I ! a bedded appearance outcrop along the shore. In o ~ 2 3 4 thin section these cherts are composed almost (b) TiO2 (wt.%) entirely of microcrystalline quartz. The quartz crystals are elongated and have a strong preferred Fig. 5. (a).TiO 2 v. A1203frio2; (b) TiO 2 v. CaO/TiO2 plots of Darvel Bay metamorphic rocks; fields from orientation with a mylonitic texture (Fig. 8b). The Sun & Nesbitt (1978). apparent bedded appearance is a schistosity pro- duced by deformation. Concordant quartz and epidotic veins extend along the schistosity which is cut by calcite veins.

TfflO0 1000 .J. JDI A MORB: Mid-ocean ridge basalts Cr PK3a f / ~ IAATB ~ sla~d_alI ~ alt~°~e~iatesSalt s (ppm) i/ b

II \~ i 100 I I / / \ I + Metad°'eri e | } I : JD6 Zrt/ (~ ~o'nAT~A Amphib°lites,~,3 I h ~ IAT

..... ! .i.'t ,,, 10 Y(ppm) 100 (a) (b)

Fig. 6. Tectonic discriminant diagrams. (a) Y/Cr after Pearce et al. (1984b); (b) Zr-Ti/100-Y after Pearce & Cann (1973). Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014

272 s.A.K. OMANG • A. J. BARBER lO.00 1°°/ kssllsllcR

1.0(3 0.00 PS12a

o.1( 1.

0.0 i 0 i ! i i i i ! 0 i a 0.10 Sr K Rb Ba Nb La Ce Nd P Zr Ti Y Sc Cr K Rb Ba Th Nb Ce Zr Y (a) (a)

10.00 10.OO Metagabbros (Cumulates)

1.0£

0

0,10 OlO] ~ T • V • ~_~ I • X JSp I &, PS12d I

0.01 o D i o o o I o a I u 0011 q i I I I I I I I I I I Sr K Rb Ba Nb La Ce Nd P Zr Ti Y Sc Cr Sr K Rb Ba Nb La Ce Nd P Zr Ti Y Sc Cr (b) (e)

Fig. 7. (a)-(c) MORB-normalized chemical plots for metadolerites and metagabbros from the Darvel Bay Ophiolite listed in Table I; normalized values from Pearce et al. (1984b). (d) ORG-normalized ocean-ridge granite chemical plot for felsic rocks listed in Table 2; normalized values from Pearce et al. (1984a).

Epidote crystals from the veins analysed by Datu (Reinhard & Wenk 1955). Garnet amphibo- microprobe are of XpSl8_25. XFe 3+ (0.9) is rela- lites from the Tungku River were analysed during tively high, corresponding to temperatures of the present study. In thin section the amphibolites formation of 450-500°C (Nakajima et al. 1977), commonly show mylonitic textures with crystals of i.e. in the greenschist facies. garnet, pyroxene and hornblende enclosed in augen These mylonitic quartz schists have been formed structures, enclosed in a fine grained matrix of by the deformation of bedded cherts in an active hornblende and plagioclase (Fig. 8c). shear zone and affected by calcium P, T estimates from amphiboles and from in a hydrothermal system, in which the fluids were garnet-pyroxene pairs in the present study (Omang enriched in calcium carbonate, under greenschist 1993), and an earlier study of garnet facies metamorphic conditions. from the same locality by Morgan (1974), give the conditions of formation of these rocks as T > 850°C at P > 5 kbar. Garnet amphibolite Bulk rock geochemistry, rare earth and trace Fragments of high grade metamorphic rocks element geochemistry of the garnet amphibolites including garnet pyroxenites and garnet amphibo- show that they are MORB tholeiites and represent lites occur in volcanic conglomerates in the oceanic crustal materials. These rocks were meta- Tungku and Pungulupi Rivers 50 km east of Lahad morphosed as pyroxene granulites and garnet Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014 DARVEL BAY OPHIOLITE, SABAH 273

Table 2. Whole rock geochemical analyses for felsic and sediments. This association of rock types is rocks from the Darvel Bay Metamorphic Complex characteristic of the ocean floor and its under- lying mantle. The basic rocks have a tholeiitic Sample No. LD5 PK4a PS 12c composition and fall predominantly in the MORB field of discriminant diagrams, showing that they Sit 2 60.14 61.46 67.27 originated by partial melting of mantle peridotite in Tit 2 0.438 1.461 0.370 AI203 17.90 15.38 16.60 a mid-ocean ridge environment. Chemical analyses Fe203* 5.16 9.43 2.89 show depletion in HFS elements, enrichment in MgO 2.01 2.22 1.06 LIL and LREE, positive Sr and negative Nb and Ce MnO 0.120 0.120 0.044 anomalies, characteristic of tholeiites, Cat 8.89 4.77 3.52 indicating that the mid-ocean ridge was generated Na20 4.73 4.76 7.68 above an active subduction zone. K20 0.333 0.091 0.044 In map view (Fig. 1), in cross-section (Fig. 9) P205 0.250 0.308 0.149 and also on an outcrop scale the rocks are Total 99.98 100.00 99.62 distributed in lenticular slivers elongated parallel to LOI 4.73 1.30 0.73 mg c. 44 c. 32 c. 42 the E-W trend of the metamorphic belt. The slab of mantle peridotite forming Silam Hill is juxtaposed Ni 19 5 5 along the northern shore of Darvel Bay against the Cr 13 2 2 'Silumpat Gneiss', representing deformed cumulate V 75 94 26 gabbro, and with amphibolite and hornblende Sc 10 24 4 schist, representing isotropic gabbro or doleritic Pb 3.4 3.4 0.3 Sr 537 169 125 and basaltic dykes, from higher levels of the ocean Rb 7.9 1.2 0.5 crust. On the northern side of Silam Hill mantle Ba 206 23 188 peridotite is juxtaposed with felsic rocks, repre- Th 2.9 0.3 2.9 senting K-deficient silicic differentiates from Zr 273.3 169.6 188.0 tholeiitic which were intruded into oceanic Nb 3.2 3.9 5.5 crust at a high structural level. Chloritic schists at Y 22.9 53.9 25.1 Jalan Silam and Lok Bikin, identified as deformed La 19 6 15 and recrystallized volcaniclastic rocks, represent Ce 40 20 37 Nd 21 17 21 tufts or hyaloclastics, and mylonitic quartz-schists, Cu 84 4 38 identified as banded cherts, represent the ocean Zn 56 15 19 floor and its sedimentary cover. All these rocks C1 8 35 179 are now at the same structural level as the mantle Ga 22 19 13 peridotite. Most of the metamorphic rocks in the belt are Oxides in wt%, trace elements in ppm. Total iron as foliated, sometimes intensely, to form schists, and Fe203(FeeO3 + FeOxI.III); mg = [100Mg/(Mg + Fe)], frequently show mineral lineations. The foliation or where Mg = MgO/40 and Fe = F203 x 0.9/72. Data schistosity is generally steeply inclined or vertical presented on a volatile-free basis; LOI, loss on ignition at 1100°C. and the lineation is subhorizontal. Both foliation and lineation are orientated parallel to the E-W trend of the belt. Preferred orientation of minerals in the gneisses and schists defining foliation, schis- amphibolites at temperatures and pressures charac- tosity and mineral lineation, and rotated inclusion teristic of the and were deformed trails in hornblende porphyroblasts in the tonalite and recrystallized with mylonitic textures in the from Pulau Sakar, indicate that the metamorphic amphibolite facies. These features are consistent rocks recrystallized syntectonically. Compositions with deformation and recrystallization of oceanic of amphiboles and amphibole/plagioclase pairs crustal rocks carried down in a subduction zone. indicate that this recrystallization occurred under high temperature but low pressure conditions in the Origin of metamorphic rocks in the amphibolite and greenschist metamorphic facies. Darvel Bay Ophiolite Complex No clear metamorphic gradation across the belt was recognized in our study, different facies being Protoliths of rocks which form the belt of meta- randomly juxtaposed (cf. Hutchison 1975). morphic rocks in the Darvel Bay Ophiolite Basaltic dykes and felsic veins cutting the meta- Complex extending westwards from Lahad Datu morphic rocks show varying relationships to the can be identified as mantle , cumulate foliation and schistosity. Dykes and veins may be pyroxenites and gabbros, isotropic gabbros, plagio- concordant to the foliation or schistosity in the granites, doleritic and basaltic dykes, volcanics country rocks, or may cut across these structures Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014

t~

(a) ~)

1 mm 4

Fig.8. (a) Photomicrograph of chlorite schist, deformed crystal tuff, Jalan Silam Km 134, Darvel Bay, Sabah. (b) Photomicrograph of siliceous schist (metachert) with epidote bands and cross-cutting quartz veins, Kampong Diam, Lahad Datu, Sabah. (e) Photomicrograph of garnet amphibolite (Specimen EKc) showing a fractured garnet crystal with alteration to hornblende enclosed in a fine grained mylonitic hornblende-plagioclase matrix to form an augen structure. Pebble from Tungku River, , Sabah. Scale bar 1 mm. (c) Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014 DARVEL BAY OPHIOLITE, SABAH 275

I SECTION A-A' ]

Bukit Silam South 3000 3000 Feet 2000 2000 1000 1000 0 0

Distance A-A' ~ 35 Km [

] SECTION B- B' I South Bukit Silam North 3000 " ~ ~~ _ SilamDam 3000 Feet 2000- Silam Road ~ ~ Sg. Telewas ~ e ..... 2000 1000" ~ 1000 0 Distance B-B' - 29 Km

I SECTION C-C' I SECTION D - D'[ South Kampong North South dolerite dyke North _ 1,,,~ P. Gifford Silam Kg. Sepagaya Pulau Sakar k, v~ Veer tmo I000 L~.~" 1000 0 0 Feet 0 i o

[ Distance C-C': - 17 Km] I Distance D-D':D-I3 ~ 17 Kml South [ SECTION E" E'i North 10IN) 1000 Feet 0 0 Sea-level

[ Distance E-E' : ~ 11 Km I

Fig. 9. Schematic cross-sections across the metamorphic belt in the Darvel Bay Ophiolite Complex Sabah. Lines of section and key to ornaments are shown on Fig. 1.

with varying degrees of obliquity. Hutchison & These features indicate that some of the dykes Dhonau (1971) reported a xenolith of 'Silumpat were intruded into rocks which had already been Gneiss' (i.e. foliated banded gabbro) enclosed in a deformed, but that deformation continued after basaltic 'sill' on Pulau Silumpat. Within the dykes, dyke emplacement. Deformation of the felsic veins schistosity may be developed with varying degrees is indicated by boudinage where they are con- of intensity; in general the more concordant the cordant, and folding where they are cross-cutting. dyke the more intense the schistosity within it. Boudinaged and folded veins are frequently cut Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014 276 s.A.K. OMANG • A. J. BARBER by veins which are completely undeformed. The parallel to the sense of movement within the fault relationships of basaltic dykes and felsic veins zone. to the foliation and schistosity demonstrate that At the time of formation the grade of meta- deformation and intrusion of igneous rocks were morphism will decrease across the fault zone, from going on continuously during the development pyroxene and hornblende granulite against the of the metamorphic belt. hotter younger crustal segment, declining to Metamorphic rocks associated with ophiolite greenschists and unmetamorphosed rocks towards complexes from many parts of the world have been the older colder segment and vertically towards the attributed either to processes of deformation and ocean floor. As has already been stated, no simple metasomatism which affect ocean floor materials gradation of metamorphic facies has been recog- shortly after their formation in the mid-ocean ridge nized in the metamorphic belt at Darvel Bay. environment, or to the processes of subduction However, in an active fault zone any such simple which lead to the emplacement of the ophiolite arrangement is likely to be disrupted by continual on a . It has been suggested that movement along the fault, juxtaposing unrelated foliated rocks may be formed at the crust-mantle fault slices of different metamorphic grades and boundary in the region of a mid-ocean ridge by from different crustal levels, as has been described gravitational spreading of the ridge (Smewing et al. from Darvel Bay. No sedimentary infills, com- 1984; Gibbons & Thompson 1991). Foliated meta- posed of clastic debris flows formed by submarine morphic rocks within ophiolites have also been erosion, as reported from the Arakapas Transform interpreted as having originated along transform in (Simonian & Gass 1978; McLeod & fault zones (Karson & Dewey 1978; Saleeby 1978; Murton 1993) have been recognised as associated Simonian & Gass 1978; Prinzhofer & Nicholas with the Darvel Bay Transform, suggesting that 1980; Karson 1984). Foliated metamorphic rocks several kilometres have been removed by erosion which occur along the basal thrust of an ophiolite since the emplacement of the ophiolite on Sabah. complex have been interpreted as a 'metamorphic The mylonitic quartz-schists described from sole' formed during subduction and emplacement Kampong Diam, and identified as deformed of the ophiolite on a continent (Davies 1971; banded cherts, are an unexpected component of Williams & Smyth 1973; Jamieson 1980; Searle & an assemblage of rocks incorporated in a fossil Malpas 1980; Spray & Williams 1980; Ghent & transform fault zone. Cherts are deposited on the Stout 1981; Moores 1982). ocean floor only after it has subsided beneath On the basis of the characteristics detailed above, carbonate compensation depth, some millions of the rocks of the metamorphic belt within the Darvel years after the ocean crust formed at the mid-ocean Bay Ophiolite are interpreted as having formed ridge. The presence of chert among the deformed along a transform fault zone. Throughout the rocks indicates that a much older segment of ocean oceans, mid-ocean ridge systems are offset along crust was juxtaposed against an active spreading transform faults at intervals of a few hundred kilo- ridge, implying that the transform fault extended metres. In these zones segments of ocean crust over several hundreds of kilometres. Karson & are moving past each other between active ridge Dewey (1978) came to a similar conclusion segments. As the two crustal slices move past each regarding the Coastal Complex transform associ- other, oceanic materials along the fault are ated with the Bay of Islands Ophiolite in deformed, producing foliated peridotites, banded Newfoundland, and pointed to present day gneisses from cumulate gabbros and foliated and examples where very long transform faults separate schistose amphibolites from gabbros and sheeted short ridge segments, in the Gulf of and dykes. In transform fault zones at the time of the Andaman Sea. Continued movements over a their formation the foliation surfaces will be set long distance through transtensional and trans- vertically, parallel to the trend of the fault zone and pressional fault segments increases the likelihood lineation will be sub-horizontal representing the of the juxtaposition of uplifted mantle peridotite, direction of movement along the fault. In an active with downfaulted crustal materials including fault zone crustal slices on either side of the fault supracrustal volcanics and metasediments, as seen will be of different ages. On one side of the fault the in Silam Hill and along Jalan Silam. crust will have been formed recently at the ridge The garnet pyroxenites and garnet amphibolites axis and will be at a high temperature; on the other from the Tungku and Pungulupi rivers described the crust will be older and will have cooled and earlier in this account are not compatible with a subsided as it moved away from the ridge axis. transform fault origin. As previously concluded the Deformation and shearing of the oceanic crustal high pressures and temperatures of formation of rocks along the fault, with the ingress of water, will these rocks, combined with their mylonitic textures induce recrystallization of hydrous phases which are consistent with their formation in a subduction are aligned to form schistose and linear structures zone. These rocks are therefore considered to Downloaded from http://sp.lyellcollection.org/ at Royal Holloway, University of London on March 25, 2014 DARVEL BAY OPHIOLITE, SABAH 277 represent fragments of a metamorphic sole which subduction of Proto-South China Sea crust led to must be present at depth below the Darvel Bay the and uplift of the ophiolite by under- Ophiolite of the Dent Peninsula. A K-Ar age of thrusting of Upper Cretaceous and Lower 76+ 21 Ma obtained from garnet amphibolite Palaeogene turbidites of the Crocker Formation. during the present study coincides with the Late Hutchison (1988), from the occurrence of Cretaceous-Palaeogene age of subduction beneath Oligocene granitoid intrusions in the Long Laai the Darvel Bay Ophiolite inferred from the area SW of Darvel Bay, suggests that the sub- stratigraphic evidence. duction of may also have been These metamorphic sole rocks, which must involved. Fragments of ophiolitic rocks in Eocene underlie the whole of the ophiolite complex, were conglomerates show that the ophiolite had been intersected by Miocene volcanics and carried to obducted, uplifted and was subject to erosion by the surface, to be incorporated with andesitic frag- Eocene times (Newton-Smith 1967). ments, ophiolitic rocks and sandstones in volcanic It has been demonstrated in the foregoing and conglomerates during the formation account that the major occurrence of metamorphic of the Sulu Volcanic Arc. rocks associated with the Darvel Bay Ophiolite represents a fossil transform fault, while fragments of high pressure metamorphic rocks in overlying Tectonic setting and emplacement of the volcanics indicate that the ophiolite is underlain by a metamorphic sole related to subduction and Darvel Bay Ophiolite the obduction of the ophiolite in Sabah. Evidence given in this account confirms the The work described in this paper was presented as a interpretation of the Darvel Bay Ophiolite Complex thesis by SAKO for the award of the PhD degree of as a segment of oceanic crust and upper mantle the University of London, sponsored by the Universiti originating at a mid-ocean spreading ridge. Kebangsaan Malaysia (UKM) and the Government of Evidence has also been given that the spreading Malaysia. Bulk rock geochemistry was determined in the ridge was developed above a subduction zone in geochemical laboratories at Royal Holloway, University a back-arc basin. The belt of metamorphic rocks, of London using a Philips PW1480 XRF Spectrometer which occurs within the complex and extends under the supervision of Drs M F Thirlwall and G F westwards from Lahad Datu, is interpreted as a Marriner and Mr Ceil Jenkins. Mineral analyses were car- ried out on a JEOL Superprobe 733 electron microprobe fossil transform fault. at Birkbeck College under the supervision of Prof Robert Radiometric ages and biostratigraphic ages from Hall, University College and mineral compositions were radiolarian cherts and foraminiferal pelagic lime- recalculated using a suite of programs developed by Prof stones in the Chert-Spilite Formation indicate a Hall who also gave general advice on the interpretation of Lower Cretaceous age for the origin of the the chemical data. K-Ar isotopic dating was carried out at ophiolite. Shallow-water limestones with Upper the NERC Isotope Geosciences Laboratory at Keyworth, Cretaceous fossils, interpreted as the carbonate Nottingham under the supervision of Dr C. C. Rundle. cappings to seamounts, indicate that the ophiolite Mr David Lee, Director of the Geological Survey of still formed part of the ocean floor at this time. Malaysia, Kota Kinabalu, provided the samples of garnet amphibolite from the Tungku River used in this study. Hamilton (1979), Holloway (1981) and Rangin Attendance at the Conference on the 'Tectonic Evolution et al. (1990) have suggested that the Darvel Bay of Southeast Asia' held at the Geological Society, London Ophiolite, together with other ophiolite fragments was sponsored by UKM. Presentation has been greatly in eastern Sabah, originally formed part of a Proto- improved by careful and constructive reviews by Prof. South China Sea crust. In this scenario, southward C. S. Hutchison and Dr J. E. Dixon.

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