Sabah, Easter

https://doi.org/10.1130/G48126.1 Manuscript received 14 May 2020 Revised manuscript received 10 July 2020 Manuscript accepted 12 January 2021 © 2021 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 22 March 2021 New zircon radiometric U-Pb ages and Lu-Hf isotopic data from the ultramafic-mafic sequences of Ranau and Telupid (Sabah, eastern Malaysia): Time to reconsider the geological evolution of Southeast Asia? Basilios Tsikouras1, Chun-Kit Lai1, Elena Ifandi1, Nur’Aqidah Norazme1, Chee-Hui Teo1 and Xiao-Ping Xia2 1 Physical and Geological Sciences, Faculty of Science, Universiti Brunei Darussalam, Gadong BE1410, Brunei Darussalam 2 State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China ABSTRACT China Sea continental crust beneath the Sabah New zircon U-Pb geochronology from a peridotite suite near Ranau and the Telupid active margin, resulting in the Sabah orogeny ophiolite in Sabah, eastern Malaysia, contradict previous studies, which assumed that the (Hutchison, 1996). However, for the post–early Sabah mafic-ultramafic rocks are largely ophiolitic and Jurassic–Cretaceous in age. We show Miocene evolution of Sabah and north Borneo, that these rocks formed during a magmatic episode in the Miocene (9.2–10.5 Ma), which is there are conflicting views interpreting compres- interpreted to reflect infiltration of melts and melt-rock reaction in the Ranau subcontinental sional (e.g., Rangin et al., 1990; Hesse et al., peridotites during extension, and concurrent seafloor spreading forming the Telupid ophiol- 2009; Morley et al., 2011; Sapin et al., 2011) ite further south. Older zircons from the Ranau peridotites have Cretaceous, Devonian, and or extensional (Hall, 2013) tectonics. Neoproterozoic ages. Zircon Lu-Hf isotopic data suggest their derivation from a depleted We present new U-Pb zircon geochronology mantle. However, significant proportions of crustal components have been incorporated data with Lu-Hf isotopic data from mafic and in their genesis, as evidenced by their less-radiogenic Hf signature compared to a pristine ultramafic rocks from central Sabah, indicating mantle reservoir. The involvement of a crustal component is consistent with our interpreted much younger ages than previously thought. continental setting for the Ranau peridotite and formation in a narrow backarc basin for These provide a robust basis for a radical change the Telupid ophiolite. We infer that the Sulu Sea, which was expanding throughout much of of ideas concerning the geological evolution of the Miocene, may have extended to the southwest into central Sabah. The Telupid oceanic Sabah, which may help distinguish between con- strand formed during the split, collapse, and rollback of the Sulu arc due to the subduction flicting hypotheses. of the Celebes Sea beneath Sabah. Incorporation of the Sulu arc in the evolving Miocene oceanic basin is a potential source to explain the involvement of crustal material in the zircon GEOLOGICAL BACKGROUND evolution of the Telupid ophiolite. The oldest unit (“Crystalline Basement”) in Sabah comprises Triassic–Jurassic granitic INTRODUCTION of central Sabah has never been dated but has and metamorphic rocks in the Darvel Bay and Present-day Southeast Asia was assembled also been assumed to be of similar Mesozoic age, Segama areas (Leong, 1998; Graves et al., from Gondwana continental blocks, volcanic supported by radiolarian ages from the Chert- 2000, Burton-Johnson et al., 2020). Sabah is arcs, and ophiolites and includes young ocean Spilite Formation in this area (Jasin, 1992). dominated by the highly deformed Eocene to basins such as the South China and Sulu Seas Several authors have suggested genetic early Miocene Crocker and Trusmadi Forma- (Hall, 1996, 2013; Hutchison et al., 2000, models for the opening and evolution of a Cre- tions, consisting of deep-water sandstones with Hutchison, 2005, 2010; Hall et al., 2008). It is taceous oceanic basin in Sabah to explain the minor shales and argillaceous beds (Tongkul, widely considered that sedimentary basins of origin of the ophiolite (e.g., Tongkul, 1994; 1994, 1997; Hall, 1996, 2013; Hall and Wilson, Sabah, northern Borneo (Malaysia), were depos- Jasin and Tongkul, 2013; Wang et al., 2016). 2000; Hutchison et al., 2000, Hutchison, 2005; ited on an ophiolitic “basement” (including what Morley and Back (2008) suggested that Sabah Morley et al., 2008, 2011; van Hattum et al., is described as the “Chert-Spilite Formation”). has been a dynamically exhuming area since the 2013). They are interpreted as an accretionary Radiometric data (K-Ar) from the ophiolitic Miocene, and Paleogene to Neogene compres- prism formed during subduction of the proto– rocks of Darvel Bay, eastern Sabah, as well as sional events have been linked to the opening South China Sea beneath Sabah (van Hattum radiolaria from cherts of the Chert-Spilite Forma- of the South China Sea (Tongkul, 1994, 1997; et al., 2006). The Sabah orogeny created the tion, suggest Middle Jurassic to Early Cretaceous Morley and Back, 2008; Morley et al., 2011; early Miocene Top-Crocker unconformity and ages (Rangin et al., 1990; Jasin, 1992; Leong, Wang et al., 2016). There is a general agree- was followed by the deposition of neritic and 1999, and references therein; Hutchison, 2005; ment on early Miocene collision in Sabah as a fluvial formations, preserved in eastern Sabah Jasin and Tongkul, 2013). The Telupid ophiolite consequence of subduction of the proto–South (Hutchison, 2005; Hall, 2013). CITATION: Tsikouras, B., et al., 2021, New zircon radiometric U-Pb ages and Lu-Hf isotopic data from the ultramafic-mafic sequences of Ranau and Telupid (Sabah, eastern Malaysia): Time to reconsider the geological evolution of Southeast Asia?: Geology, v. 49, p. 789–793, https://doi.org/10.1130/G48126.1 Geological Society of America | GEOLOGY | Volume 49 | Number 7 | www.gsapubs.org 789 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/49/7/789/5335951/g48126.1.pdf by guest on 02 October 2021 the mafic samples rather than the ultramafic ones. Most of the zircons display oscillatory zoning, and a few show planar zoning and are variably luminescent under cathodolumines- cence (Fig. S2). Table 1 presents concordant ages (<15% discordance) from two Ranau peridotites (34 spots from 29 zircon crystals), and one diabase (8 spots from 7 crystals) and two basalts (29 spots from 27 crystals) from the Telupid ophiolite. Excluding the inherited ages, 54 spots (out of 71) from all samples yielded consistently Miocene ages (Fig. 2). From the subcontinental Ranau peridotites, sample SB 120B yielded 12 spots with inherited Cenomanian and two spots with inherited Early to Middle Devonian ages. Sample SB 120A has one inherited Neo- proterozoic age. The vast majority of the zircons in the Telupid ophiolitic basalts and diabases are Miocene. The basaltic pillow lava SB 130C had two spots with inherited Middle Triassic ages. Lutetium-Hafnium Isotopic Data The Lu-Hf isotopic data for the 57 zircon spots with concordant U-Pb ages are listed in Table S2. The analytical methodology is described in Appendix S3. The Miocene zircons from the Ranau peridotites (samples SB 120A and SB 120B) yielded a large variation in Figure 1. Simplified geological map of central Sabah, eastern Malaysia, compiled from Yin their εHf(t) values (−5.2 to +3.5) and Nd depleted (1985), Tongkul (1997), and our observations. mantle model, TDM2, ages (868–1427 Ma). An outlier has εHf(t) = −16.8 and a TDM2 = 2164 Ma Our extensive fieldwork in central Sabah The Telupid ophiolite includes variably ser- (Fig. 2E). A Cretaceous (Aptian–Turonian) age was focused on the mafic and ultramafic rocks, pentinized peridotites dominated by lherzolites is recorded in zircons from sample SB 120B including widespread monotonous perido- with minor harzburgites and replacive dunites with narrower ranges of εHf(t) (+5.9 to +9.6) tites near Ranau town and a complete ophio- (Fig. 1). Local pods of magmatic dunite with and TDM2 model ages (543–778 Ma) relative lite suite in the Telupid area (Fig. 1). The subordinate chromite occur in these perido- to the Miocene ones. An outlier of this age Ranau peridotites are intensely lateritized and tites, which are crosscut by a few rodingitized group shows εHf(t) = +2.3 and an older TDM2 dominated by varieties of lherzolite with rare gabbroic dikes. The mafic members are dis- of 1016 Ma. Two Devonian zircon spots have harzburgite (see Appendix S1 in the Supple- membered and comprise layered and isotropic more radiogenic εHf(t) of +8.4 and +13.1 and 1 mental Material ). The lherzolites are com- gabbros, sheeted dikes, as well as pillow and TDM2 model ages of 851 and 554 Ma, respec- monly impregnated by dunite bodies ranging massive basalts. Petrographic and geochemical tively. One zircon core in sample SB 120A has from microscopic veins to cylindrical or tabular details of the Telupid ophiolite lithologies are a Neoproterozoic age, a highly radiogenic εHf(t) bodies. Scarce blocks of mafic rocks are struc- presented in Appendices S1 and S2. The ophi- (+15.1) similar to the depleted mantle value, turally trapped in the peridotites. There are a olitic rocks have normal fault contacts with the and a TDM2 model age of 668 Ma (Fig. 2E). few rodingitized gabbroic dikes. Garnet-bear- surrounding sedimentary formations. The Miocene zircons of the diabase SB 127 ing peridotites from Sungai Mensaban, close to display a narrow range of εHf(t) (+6.6 to +9.2) Ranau, are interpreted as subcontinental mantle RESULTS and TDM2 (504–673 Ma). One exception has (Imai and Ozawa, 1991). Our petrographic and Uranium-Lead Radiometric Dating εHf(t) = −1.9 and TDM2 = 1216 Ma. The Miocene geochemical data support the idea that the whole The methodological details for the U-Pb zircons of the basaltic sample SB 125 have a gen- range of Ranau peridotites comprises subcon- dating are described in Appendix S3.

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