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Journal ArticleDOI

Adakites without a slab: Remelting of hydrous basalt in the crust and shallow mantle of Borneo to produce the Miocene Sintang Suite and Bau Suite magmatism of West Sarawak

TL;DR: In this paper, geochronological and geochemical data for Neogene magmatism from West Sarawak were presented, showing that the geochemical diversity is consistent with the Bau and West SARawak Sintang suites representing mixtures of mafic, mantle-derived magma with felsic magma derived from remelting of hydrous basaltic rocks in the crust.
About: This article is published in Lithos.The article was published on 2019-11-01 and is currently open access. It has received 22 citations till now. The article focuses on the topics: Adakite & Mafic.

Summary (3 min read)

1. Introduction

  • Subduction zones have been major sites of crustal processing since at least the Neoproterozoic.
  • Thus, several different processes – some involving slab melting, some not – have been proposed to explain the generation of the adakitic chemical signature.
  • The authors explore the temporal, petrological, and geochemical development of a suite of Neogene magmatic rocks from Borneo that includes adakitic rocks.
  • These were generated in a setting that had lacked subduction during, at least, the preceding 50 million years, and where there is no evidence of substantial crustal thickening.

2. Regional background

  • Geochemically similar rocks from Kalimantan and West Sarawak (Kirk, 1968; Williams and Harahap, 1987) are predominantly of Late Oligocene to Early Miocene age, and have been referred to as the Sintang Intrusives, the Sintang Intrusive Suite or the Sintang Suite (e.g. Doutch, 1992; Moss et al., 1998; Hutchison, 2005, 2010).
  • Compositions are predominantly dacitic, granodioritic, or subordinately dioritic to granitic, with Itype character (Williams and Harahap, 1987).
  • Whole-rock, biotite, and hornblende K-Ar dating of 12 samples collected near Sintang in NW Kalimantan (Williams and Harahap, 1987) yielded two distinct age groups: an older group of 30.4 to 23 Ma in the Melawi Basin near Sintang (type locality), and a younger group of 17.9 to 16.4 Ma in the Ketungau Basin.

3. Methodology

  • 1. Sampling Fresh rocks or rocks with minimal alteration were sampled (TB samples) from outcrops or nearby float in West Sarawak (Fig. 3).
  • An example of pellet reproducibility, and comparison between XRF and isotope dilution data, are given in the web link referred to above.
  • Grains were mounted in epoxy resin blocks and AC C EP TE D M AN U SC R IP T polished to expose mid-grain sections.
  • Tera-Wasserburg plots were used to identify individual peaks or visually assess outliers (e.g. lead loss, inheritance and common lead) within the population which were then excluded from the weighted mean age calculation.

4. Petrography

  • Intrusive rocks Micro-tonalites/granodiorites (TB33, TB148a, STB36c, and STB61b) dominate the intrusive West Sarawak Sintang Suite.
  • Plagioclase and alkali feldspar form large idiomorphic to hypidiomorphic phenocrysts.
  • Biotite is often replaced by sericite, chlorite and titanite.
  • Idiomorphic volcanic quartz commonly has a bipyramidal shape, embayments and inclusions of sericite, biotite and plagioclase.
  • Plagioclase is zoned and forms idiomorphic to subidiomorphic crystals (Fig. 4k).

5. Geochemistry

  • Intrusive rocks of the West Sarawak Sintang Suite are predominantly felsic with a range of SiO2 contents from 56 to 70 wt. %, classified as granodiorite, monzodiorite and gabbro-diorite (Supplementary Fig. 1).
  • Major element variations in the West Sarawak Sintang intrusive rocks are also coherent with those of Sintang intrusive rocks from Kalimantan (Fig. 5a).
  • This means that their trace element ratios broadly resemble volcanic AC C EP TE D M AN U SC R IP T arc or post-collision rocks (Supplementary Fig. 1).
  • This makes the Bau Suite more similar to Kalimantan’s Central Sintang group than the Northern or Southern groups (Fig. 5).

6. U-(Th)-Pb zircon geochronology

  • Intrusive rocks Sample TB63b TB63b is a granodioritic sill intruding the Kayan Sandstone at Tanjung Santubong.
  • Simple internal zoning is evident in most grains.
  • Concentric, patchy and sector zoning are rare.
  • Two outliers of Miocene age were excluded from the weighted mean age calculation because of lead-loss, resulting in a unimodal population (Fig. 9a) of 81 Miocene ages (98% of total Miocene ages) that cluster between 19 and 23 Ma with a weighted mean age of 21.1 ± 0.2 Ma (MSWD = 3.5).

Sample TB58

  • TB58 is a stock that intrudes sediments of the Silantek Formation sampled from a granodiorite boulder in a small gully from Bukit Kelambi .
  • Zircons are angular, with a euhedral to subhedral or anhedral shape.
  • Simple internal zoning is evident in most grains.
  • A single Miocene age was excluded because of high common lead.
  • The population is predominantly Early Miocene (43 ages) with 7 inherited zircons of Mesozoic to Permian age, ranging from 114 to 267 Ma. 7 outliers of Miocene ages (grey in Fig. 8b) have either lead-loss or inheritance, and were excluded from the weighted mean age calculation.

Sample TB33

  • Simple internal zoning is evident in most grains.
  • Two ages were excluded because of partial ablation of the resin mount.
  • Six Miocene outliers, including a small population of inherited Miocene zircons at around 24 Ma and a number of zircons affected by lead-loss, were identified and excluded from the weighted mean age calculation.

Sample TB209a

  • Sample TB209a was sampled from a rhyolite boulder field near Bukit Buwaya.
  • Inherited zircons are subrounded to anhedral, usually with sector or oscillatory zoning.
  • Two inherited ages were excluded for failing the 10% discordance criteria and two Miocene ages were also excluded because of abundant common lead.
  • Of the valid ages 19 are Miocene, with three Miocene outliers either affected by lead-loss or inheritance (marked in grey) and excluded from the weighted mean age calculation, leaving a unimodal population which includes 16 of 19 (84% of all).

Sample TB61

  • Sample TB61 is a micro-granodiorite collected from the Bukit Stapok quarry in Batu Kawa near Kuching that contains euhedral, elongate zircons with simple or oscillatory zoning.
  • Larger zircons are anhedral, can be easily distinguished from elongate varieties, and are inherited.
  • The sample has one concordant inherited Proterozoic age around 850 Ma.

7. Discussion

  • West Sarawak Sintang Suite The authors U-Pb dating of zircons in volcanic and intrusive rocks from West Sarawak yielded a restricted range of ages (Fig. 10a), suggesting relatively short-lived Miocene magmatic episodes.
  • A single, slightly older, zircon age of c. 19 Ma in TB61, indistinguishable from the age of West Sarawak Sintang rocks (Fig. 10a) suggests Early Miocene magmatism in the Bau area.
  • Thus, melting of hydrated basalt in the mid- to deep-crust below Borneo could produce much of the major element variation character of non-adakitic rocks of West Sarawak, and in the Northern and Southern groups of the Kalimantan Sintang Suite.
  • The presence of such rocks among the Sintang Suite has two important implications.
  • Instead, the authors have identified that emplacement of these suites was accompanied by contemporaneous, mafic, mantle -derived magmatism.

Conclusions

  • Inherited zircons in the West Sarawak Sintang Suite suggest magmatism was active by c. 24 Ma. 2. The Neogene magmatism was not related to active subduction.
  • Geochemistry shows an adakite character for the Bau Suite while the Sintang Suite samples plot predominantly outside the adakite field.
  • The geochemical character of both suites is consistent with remelting of hydrous mafic rocks in the lithosphere of Borneo that were emplaced as arc basalt tens or hundreds of millions of years previously.
  • The mechanisms that generated this magmatism could have provided the heat to re-melt the crust, which yielded the intermediate and evolved intrusive rocks of the Sintang and Bau suites.
  • These may have been relicts from the extension which formed the Melawi and Ketungau basins and/or products of contemporaneous extension/transtension.

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Citations
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01 Dec 2008
TL;DR: In this paper, the East Philippine Arc was studied and local variations in lithosphere thickness suggest that thinning is rapid and may be piecemeal, and the evolution of the arc lithosphere has been observed over time.
Abstract: The Philippine Trench marks a nascent plate margin where subduction initiation is propagating from north to south. Magma compositions in the East Philippine Arc record thinning of arc lithosphere as it is eroded from below. Lithosphere is thicker beneath the younger, southern part of the arc, causing basaltic magma to stall and fractionate garnet at high pressure. In the mature, northern section, basaltic magma differentiates at shallower levels, at pressures where garnet is not stable. Local variations in lithosphere thickness suggest that thinning is rapid and may be piecemeal. Fluctuations in arc lithosphere thickness throughout the history of this margin appear to control spatial and temporal variations in magma fluxes into the arc crust. Varying fractionation depths of hydrous basalt may help to explain the andesitic composition of bulk continental crust.

51 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented new geochemistry, zircon U-Pb and 40Ar/39Ar age data from igneous and metamorphic rocks from the Schwaner Mountains to investigate their tectono-magmatic histories.
Abstract: The Schwaner Mountains in southwestern Borneo form a large igneous province with a complex magmatic history and poorly known tectonic history. Previously it was known that Cretaceous granitoids intruded metamorphic rocks of the Pinoh Metamorphic Group assumed to be of Paleozoic age. Jurassic granitoids had been reported from the southern Schwaner Mountains. Most ages were based on K-Ar dating. We present new geochemistry, zircon U-Pb and 40Ar/39Ar age data from igneous and metamorphic rocks from the Schwaner Mountains to investigate their tectono-magmatic histories. We subdivide the Schwaner Mountains into three different zones which record rifting, subduction-related and post-collisional magmatism. The Northwest Schwaner Zone (NWSZ) is part of the West Borneo Block which in the Triassic was within the Sundaland margin. It records Triassic to Jurassic magmatism during early Paleo-Pacific subduction. In contrast, the North Schwaner Zone (NSZ) and South Schwaner Zone (SSZ) are part of the SW Borneo (Banda) Block that separated from NW Australia in the Jurassic. Jurassic granitoids in the SSZ are within-plate (A-type) granites interpreted to have formed during rifting. The SW Borneo (Banda) Block collided with eastern Sundaland at c. 135 Ma. Following this, large I-type granitoid plutons and arc volcanics formed in the NWSZ and NSZ between c. 90 and 132 Ma, associated with Cretaceous Paleo-Pacific subduction. The largest intrusion is the c. 110 to 120 Ma Sepauk Tonalite. After collision of the East Java-West Sulawesi (Argo) Block, subduction ceased and post-collisional magmatism produced the c. 78 to 85 Ma Sukadana Granite and the A-type 72 Ma Sangiyang Granite in the SSZ. Rocks of the Pinoh Metamorphic Group mainly exposed in the NSZ, previously assumed to represent Paleozoic basement, contain abundant Early Cretaceous (110 to 135 Ma) zircons. They are interpreted as volcaniclastic sediments that formed contemporaneously with subduction-related volcanic rocks of the NSZ subsequently metamorphosed during intrusion of Cretaceous granitoids. There are no igneous rocks older than Cretaceous in the NSZ and older than Jurassic in the SSZ and there is no evidence for a continuation of a Triassic volcanic arc crossing Borneo from Sundaland to the east.

40 citations


Cites background from "Adakites without a slab: Remelting ..."

  • ...The youngest ages around 20 to 25 Ma belong to zircons probably derived from the Neogene Sintang Suite that intruded the Schwaner granitoids (Breitfeld et al., 2019)....

    [...]

Journal ArticleDOI
TL;DR: In this article, the authors show that partial melting of mafic rocks can generate adakitic magmas under pressure, temperature, and hydrous conditions of 1.2-3.0 GPa, 800-1000°C, and 1.5-6.0 wt.% H2O.
Abstract: Adakitic rocks are intermediate-acid magmatic rocks characterized by enrichment in light rare-earth elements, depletion in heavy rare-earth elements, positive to negligible Eu and Sr anomalies, and high La/Yb and Sr/Y ratios. Cenozoic adakitic rocks generated by partial melting of subducted oceanic crust (slab) under eclogite-facies conditions (i.e., the original definition of “adakite”) occur mainly in Pacific Rim volcanic arcs (intra-oceanic, continental, and continental-margin island arcs), whereas those generated by partial melting of thickened lower crust occur mainly in Tethyan Tibetan collisional orogens. In volcanic arcs, adakitic melts derived from the melting of subducted oceanic crust metasomatize the mantle wedge to form a unique rock suite comprising adakite-adakite-type high-Mg andesite-Piip-type high-Mg andesite-Nb-rich basalt-boninite. This suite differs from the basalt-andesite-dacite-rhyolite suite formed from mantle wedge metasomatized by fluids derived from subducted oceanic crust. Previously published data indicate that partial melting of mafic rocks can generate adakitic magmas under pressure, temperature, and hydrous conditions of 1.2–3.0 GPa, 800–1000°C, and 1.5–6.0 wt.% H2O, respectively, leaving residual minerals of garnet and rutile with little or no plagioclase. Cenozoic Au and Cu deposits occur proximally to adakitic rocks, with host rocks of some deposits actually being adakitic rocks. Adakitic rocks thus have important implications for both deep-Earth dynamics and Cu-Au mineralization/exploration. Although studies of Cenozoic adakitic rocks have made many important advances, there remain weaknesses in some important areas such as their tectonic settings, petrogenesis, magma sources, melt-mantle interactions of pre-Cenozoic adakitic rocks, and their relationship with the onset of plate tectonics and crustal growth. Future research directions are likely to involve (1) the generation of adakitic magmas by experimental simulations of partial melting of different types of rock (including intermediate-acid rocks) and magma fractional crystallization at different temperatures and pressures, (2) the relationship between magma reservoir evolution and the formation of adakitic rocks, (3) the tectonic setting and petrogenesis of pre-Cenozoic adakitic rocks and related geodynamic processes, (4) interactions between slab melts and the mantle wedge, (5) the formation of Archean adakitic tonalite-trondhjemite-granodiorite and its link to the onset of plate tectonics and crustal growth, and (6) the relationship between the formation of adakitic rocks and metal mineralization in different tectonic settings.

29 citations

Journal ArticleDOI
TL;DR: The Segama Valley Felsic Intrusions (SVFI) of Sabah, north Borneo, shows them to be arc-derived tonalites; not windows or partial melts of a crystalline basement beneath Sabah as mentioned in this paper.

19 citations

Journal ArticleDOI
TL;DR: In this article, the Nyalau Formation (Biban sandstone Member and Upper Nyalua Member), Kakus Unit, and Merit-Pila Formation are divided into Oligocene to Lower Miocene sequences.

18 citations


Additional excerpts

  • ...11 and 14) reported by Hennig-Breitfeld (2019)....

    [...]

References
More filters
Journal ArticleDOI
TL;DR: In this article, the authors present a compilation of trace element data from approximately sixty published works for NIST SRM 611 and NISTSRM 613 and provide useful new working values for these reference materials.
Abstract: Microanalytical trace element techniques (such as ion probe or laser ablation ICP-MS) are hampered by a lack of well characterized, homogeneous standards. Two silicate glass reference materials produced by National Institute of Standards and Technology (NIST), NIST SRM 610 and NIST SRM 612, have been shown to be homogeneous and are spiked with up to sixty one trace elements at nominal concentrations of 500 μg g-1 and 50 μg g-1 respectively. These samples (supplied as 3 mm wafers) are equivalent to NIST SRM 611 and NIST SRM 613 respectively (which are supplied as 1 mm wafers) and are becoming more widely used as potential microanalytical reference materials. NIST however, only certifies up to eight elements in these glasses. Here we have compiled concentration data from approximately sixty published works for both glasses, and have produced new analyses from our laboratories. Compilations are presented for the matrix composition of these glasses and for fifty eight trace elements. The trace element data includes all available new and published data, and summaries present the overall average and standard deviation, the range, median, geometric mean and a preferred average (which excludes all data outside ± one standard deviation of the overall average). For the elements which have been certified, there is a good agreement between the compiled averages and the NIST data. This compilation is designed to provide useful new working values for these reference materials.

2,487 citations

Journal ArticleDOI
01 Jan 2005-Lithos
TL;DR: In this article, an analysis of an extensive adakite geochemical database identifies two distinct compositional groups: high-SiO2 adakites (HSA) which represent subducted basaltic slab-melts that have reacted with peridotite during ascent through mantle wedge and low-Si O 2 adakitic mantle wedge.

2,125 citations


"Adakites without a slab: Remelting ..." refers background in this paper

  • ...The deviation from experimental slab melt compositions cannot be due to interaction between slab melts and mantle (Kay, 1978; Martin, 1999; Martin et al., 2005; Yogodzinski et al., 2001) since the Borneo rocks do not display the systematic decrease in the aluminium saturation index (molar [Al / Ca + K + Na]) with only a small change in SiO2 that Rapp et al....

    [...]

OtherDOI
01 Jan 1979
TL;DR: The plate-tectonic evolution of a region can be deduced by following the as-sumptions that subduction zones are characterized by ophiolite, melange, wildflysch, and blueschist, that intermediate and silicic calc-alkaline igneous rocks form above Benioff zones, and that truncations of orogenic belts indicate rifting as mentioned in this paper.
Abstract: The plate-tectonic evolution of a region can be deduced by following the as­ sumptions that subduction zones are characterized by ophiolite, melange, wildflysch, and blueschist, that intermediate and silicic calc-alkaline igneous rocks form above Benioff zones, and that truncations of orogenic belts indicate rifting. Interrelatioships provide cross­ checks, as do marine geophysical data. Southeast Asia and "Sundaland" are an aggregate of small continental fragments. Late Paleozoic subduction westward beneath Malaya and Thailand (recorded by granites in eastern Malaya, and by melanges in western Laos and Cambodia) ended when Indochina collided with them. Early and Middle Triassic subduction was eastward, beneath the west side of the aggregate. Late Triassic and Jurassic subduction from the north ended in collision of the aggregate with China. Early Cretaceous subduction was again from the west. Late Cretaceous subduction was beneath the east side of the aggregate and followed continental rifting there. Cenozoic subduction, from the west once more, ended in the north when the aggregate collided with India, but subduction still continues in the south. Borneo similarly reflects changing subduction patterns. The Philippines, Sulawesi, and Halmahera consist wholly of upper Mesozoic(?) and Cenozoic island-arc subduction and magmatic complexes and lack old continental founda­ tions. The scrambled fragments of the Philippines came from several arc systems, including two extending to Borneo. Sulawesi and Halmahera record primarily subduction from the east and may be rifted and contorted fragments initially continuous with southeast Borneo and central Java. In the early Tertiary, Australia and New Guinea, which then had a stable-shelf northern margin, moved northward until they collided with a southward-migrating island arc, behind which had formed the Caroline oceanic plate. Late Cenozoic tectonics in New Guinea have been dominated by southward subduction fo the Caroline oceanic plate beneath the Austra­ lian New Guinea continent, and by left-lateral strikeslip faulting. Such faulting tore the Sula Islands from northwest New Buinea and carried them to Sulawesi. The islands of the outer Banda arc are formed of melanges of the shallow-water sedi­ ments of the New Guinea and Australian continental shelf, which is now disappearing be­ neath the active arc.

1,603 citations

Journal ArticleDOI
TL;DR: In this paper, a set of experiments on natural, hydrous basalts at 1-4 GPa constrain the composition of "unadulterated" partial melts of eclogitized oceanic crust within downgoing lithospheric slabs in subduction zones, where these same adakite melts are allowed to infiltrate and react with an overlying layer of peridotite.

1,492 citations


"Adakites without a slab: Remelting ..." refers background in this paper

  • ...In panel b) only experimental equilibration of slab melt with peridotite (AB-1 + AVX; Rapp et al., 1999)....

    [...]