朱作飞, 闫 义, 赵 奇

古南海俯冲过程: 婆罗洲晚白垩世‒渐新世地层沉积记录

朱作飞1, 2, 3, 闫 义1, 2, 4, 5*, 赵 奇1, 2, 4, 5

(1. 中国科学院 广州地球化学研究所边缘海与大洋地质重点实验室, 广东 广州 510640; 2. 中国科学院 深地科学卓越创新中心, 广东 广州 510640; 3. 中国科学院大学 地球与行星科学学院, 北京 100049; 4. 南方海洋科学与工程广东省实验室(广州), 广东 广州 511458; 5. 中国科学院南海生态环境工程创新研究院, 广东 广州 510301)

古南海的俯冲消亡是深入揭示南海扩张机制和重塑东南亚中新生代构造演化的关键, 然而目前对于古南海的俯冲过程仍存在诸多争议。马来西亚婆罗洲出露完整的晚白垩世‒渐新世沉积地层, 是研究古南海构造演化的重要窗口。本文通过碎屑矿物组成、元素地球化学及Nd同位素分析, 对婆罗洲晚白垩世‒渐新世地层沉积物来源进行示踪, 反演区域古地理格局及构造演化。结果显示, 晚白垩世‒古新世Rajang群沉积物主要来源于古太平洋俯冲形成的岩浆岩带, 马来半岛与印支陆块南缘对古新世‒晚渐新世地层沉积贡献明显增加, 暗示古太平洋板块俯冲的影响持续到早古新世(～60 Ma)。晚始新世, 随着澳大利亚板块持续向北漂移, 婆罗洲逆时针旋转引起残余海盆剪刀式闭合。～37 Ma, 曾母陆块与婆罗洲碰撞, Rajang群抬升剥蚀。渐新世, 古南海在婆罗洲东北部沙巴开始俯冲, 对应于南海的打开。古南海自西向东斜向俯冲消亡, 婆罗洲的逆时针旋转与沿卢帕尔线的走滑使Rajang群与Kuching超级群叠置。

古南海; 古太平洋; 婆罗洲; 物源; 构造演化

0 引 言

“古南海”这一概念最早是由Hinz et al. (1991)依据前人研究资料提出, 用来描述位于华南大陆南缘至加里曼丹的晚中生代古海洋。而Taylor and Hayes (1983)及Hall and Breitfeld (2017)认为古南海是西太平洋的一个残留海湾, 古南海的消亡与南海的打开几乎同步(Holloway, 1982; Taylor et al., 1983), 因此古南海的演化与南海的扩张息息相关。理清古南海消亡过程不仅可以揭示南海扩张机制, 而且有助于重塑东南亚中新生代构造演化历史。

三叠纪‒晚白垩世, 古太平洋板块沿华南与巽他大陆边缘俯冲, 形成了一条北到日本、南至苏门答腊延伸数千千米的晚中生代岩浆岩带(Hutchison, 2010; Xu et al., 2016; Li et al., 2018; Breitfeld et al., 2020a; Wang et al., 2021b)。晚白垩世, 由于古太平洋板块俯冲后撤(孙卫东等, 2008; Li et al., 2014; Wang et al., 2021c), 华南和巽他大陆边缘经历了明显的拉张, 发育一系列裂陷盆地(Li et al., 2014)。渐新世, 南海开始扩张, 推动古南海向南俯冲消亡于婆罗洲‒巴拉望一带(Li et al., 2014)。古太平洋俯冲与古南海俯冲在时间上是否连续？空间上是否重叠？这一系列问题至今还存在诸多争议: Hutchison (1996, 2005)认为古南海俯冲始于晚白垩世, 由大陆岛弧的施瓦纳山(Schwaner Mountains)(Hutchison, 2005)、弧前盆地的Kuching超级群(Williams et al., 1988)以及古俯冲带和增生楔的卢帕尔线(Lupar Line)和Rajang群(Hutchison, 2005)构成了完整的沟弧盆系统。在该模式中, Rajang群晚始新世由深海沉积转变成陆相沉积标志着俯冲的结束, 拉让不整合(Rajang Unconformity)代表着曾母陆块(Luconia block)与婆罗洲的碰撞(Hutchison, 1996, 2005)。然而, 这一模式遭到了不少研究者质疑, 施瓦纳山岩浆活动仅持续到约72～80 Ma (Moss, 1998; Davies et al., 2014; Breitfeld et al., 2020a), 且Hennig-Breitfeld et al. (2017)指出施瓦纳山岩浆岩与西婆罗洲同时期岩浆岩地球化学特征相似, 应与古太平洋俯冲有关。锆石及重矿物特征也显示Kuching超级群并非弧前盆地(Breitfel and Hall, 2018; Breitfeld et al., 2018), Rajang群只是被卢帕尔走滑断层与Kuching超级群分割的被动大陆边缘沉积(Galin et al., 2017; Breitfeld and Hall, 2018; Breitfeld et al., 2018)。因此, Hall and Breitfeld (2017)认为古太平洋板块在婆罗洲的俯冲止于晚白垩世。澳大利亚板块北移引起的区域板块重组事件导致Rajang群在晚始新世抬升形成拉让不整合。也有研究者认为古太平洋俯冲结束于古新世(Moss, 1998; Fyhn et al., 2010; Hutchison, 2010; Madon et al., 2013; Wang et al., 2016)。Zhao et al. (2021a)通过Lubok Antu混杂岩和Lupar组自生伊利石定年, 获得～60 Ma和36 Ma的变形年龄, 分别对应俯冲结束时间和拉让不整合的形成时间。晚始新世, 古南海在婆罗洲北部西巴兰姆线(West Baram Line)以东的沙巴‒卡加延地区开始俯冲。地球物理手段显示沙巴‒菲律宾地块下方的P波高速异常体可能为古南海俯冲板片残留(Hall and Spakman, 2015; Wu and Suppe, 2018)。中‒晚始新世沙巴地区沉积环境由深水向陆相转变, 且渐新世地层中大量火山碎屑对应于古南海的俯冲(Hall and Breitfeld, 2017)。中中新世, 南沙陆块与婆罗洲碰撞(Hall, 2013)。

南海南部婆罗洲出露完整的晚白垩世‒中新世沉积地层(Liechi et al., 1960; Haile, 1974; Hutchison, 2005), 是研究古南海演化历史绝佳的窗口。晚白垩世‒始新世沉积地层自婆罗洲西北部的古晋带、西布带呈弓形延伸至东北部的沙巴地区, 分别是古晋带的Kuching超级群、西布带的Rajang群以及沙巴地区的Crocker群(图1)。有研究者也将西布带的Rajang群与沙巴同时期地层合称为“Rajang-Crocker群”(图2;van Hattum et al., 2006, 2013)。对于巨厚的Rajang-Crocker群沉积物来源还存在很大争议, 支持远源观点的研究者认为该时期巨厚沉积物来源于印支半岛(Hamilton, 1979)或是华南(Moss, 1998; Moss and Chambers, 1999),通过流经华南以及印支的主要河流, 如古湄公河, 将较老陆块的沉积物搬运至巽他陆架(Hutchison, 1996; Hall, 1996; Métivier et al., 1999)。然而Hennig-Breitfeld et al. (2018)通过对越南南部地层碎屑锆石分析认为古湄公河流向为自南向北, 与现今具有较大差异。碎屑锆石以及重矿物结果指示沉积物搬运距离较近, 源区可能为婆罗洲西南部的施瓦纳山和马来半岛(van Hattum et al., 2006, 2013; Galin et al., 2017; Breitfeld et al., 2018)。除物源争议外, Rajang-Crocker群的构造属性也不清楚。Hutchison (1996, 2005)认为整个Rajang群具有增生楔属性, 为古南海晚白垩世‒晚始新世俯冲形成。Moss (1998)提出晚白垩世‒古新世Rajang群为俯冲增生的产物, Rajang群上部地层为残余海盆沉积。而Hall and Breitfeld (2017)则认为Rajang群与Kuching超级群均为被动大陆边缘的正常沉积地层。渐新世‒早中新世地层主要分布在米里带(Miri)和沙巴地区, 与下伏Rajang-Crocker群呈不整合接触。该不整合代表沙捞越(Sarawak)地区区域隆升事件, Hutchison (2005)称之为曾母陆块与婆罗洲碰撞引起的“沙捞越造山运动”; 也有研究者认为这一事件代表着古南海俯冲的开始(Hall and Breitfeld, 2017; Hennig-Breitfeld et al., 2019)。本文通过对Rajang-Crocker群进行详细的野外观察、镜下矿物鉴定、元素地球化学和Nd同位素分析, 结合区域岩浆及构造演化研究成果, 重建婆罗洲晚白垩世‒渐新世的构造演化过程。

1 区域地质概况

婆罗洲由众多微陆块拼贴而成, 可分为西南婆罗洲(SW Borneo)、古晋带、西布带、米里带和东婆罗洲(East Borneo)五个部分(图1)。西南婆罗洲于晚侏罗世从冈瓦纳大陆裂离, 并在早白垩世拼贴于巽他大陆东南缘(Metcalfe, 2009, 2011; Hennig- Breitfeld et al., 2017)。施瓦纳山北部为白垩纪变质岩(Davies et al., 2014; Breitfeld et al., 2020a); 南部为侏罗纪板内花岗岩、85～135 Ma I型花岗岩(Setiawan et al., 2013; Davies et al., 2014; Hennig et al., 2017; Breitfeld et al., 2020a), 以及72～85 Ma碰撞后花岗岩。施瓦纳山以北为古晋带, 古晋带西部属于巽他大陆基底, 出露有三叠纪岩浆岩, 同时也有零星的三叠系Sadong组、Kuching组以及白垩系Pedawan组沉积地层出露。东部主要为晚白垩世‒晚始新世巨厚陆相沉积地层——Kuching超级群(图1; Breitfeld et al., 2018; Breitfeld and Hall, 2018), 分为Kayan群和Ketungau群, 主要由砂岩、泥岩和砾岩构成, 部分地层含火山碎屑。沿古晋带北部边界, 卢帕尔线分布有Lubok Antu混杂岩以及Sambas-Mangkaliat花岗岩带(图1; Tan, 1982; William et al., 1988; Hutchison, 1996; Amiruddin, 2009)。碎屑锆石U-Pb年龄显示, Lubok Antu混杂岩最大沉积年龄为105～115 Ma (Zhao et al., 2021a)。Sambas-Mangkaliat岩浆岩年龄为74.9～80.6 Ma, 被认为是古南海俯冲后撤导致岩浆岩带北移的结果(Amiruddin, 2009)。卢帕尔线以北为西布带(图1), 被巨厚的Rajang群深海复理石沉积覆盖, 基底没有出露, 性质不清。有限的微体古生物化石显示区内地层时代为晚白垩世‒晚始新世, 且由南向北逐渐变年轻(Liechti et al., 1960; Hutchison, 2005)。Rajang群分为Lupar组和Belaga组, 其中Belaga组又分为五个段, 分别是Layar段、Kapit段、Pelagus段、Metah段以及Bawang段。Rajang群主要由深海浊积砂岩、粉砂岩、泥岩以及页岩组成的韵律层, 可观察到鲍玛序列的Tc～Te段(图3a); 地层倾角大甚至直立, 滑塌、褶皱现象普遍(图3b、e、f、g), 其中Layar段和Kapit段经历一定程度的变质作用(图3c、d)。Galin et al. (2017)和Hennig-Breitfeld et al. (2019)根据碎屑锆石和重矿物特征将Rajang群分为四个单元, 其中Lupar组、Layar段以及下Kapit段归为一单元, 上Kapit段、Pelagus段为二单元, Metah段与出露在米里带的Bawang段分别为三单元和四单元(图2)。米里带由武吉‒米辛线(Bukit-Mersing Line)与西布带分隔(图1), 区内大部分被渐新世‒中新世陆相地层覆盖, 出露少量古新世地层。渐新世Tatau组不整合覆盖在Rajang群之上, 地层倾角较缓且变形较小。Tatau组底部为砾岩, 向上为砂岩, 砂岩中含煤层, 指示沉积环境已由深海相转变为沼泽相(图3h)。米里带西南部Nyalau组为河流‒三角洲沉积相, 厚度巨大; 东北部Satap Shale组为深海黑色泥页岩。沙巴位于米里带以及东婆罗洲北部(图1), 发育较为完整的白垩纪‒新生代沉积地层。基底出露于基纳巴卢山(Kinabalu Mountains)以及南部达卫湾(Darvel Bay), 为角闪石片岩、片麻岩以及超镁铁质岩组成的蛇绿岩, 时代为中侏罗世‒早白垩世(Hutchison, 1989; Rangin et al., 1990; Macpherson et al., 2010)。上白垩统世‒中始新统Trusmadi组和Sapulut组主要为一套深海相浊积岩, 不整合覆盖于基底之上, 对应于沙捞越地区的Rajang群(Hutchison, 1996)。浊积岩局部可见交错层理、爬升层理以及鲍玛序列(图3i), 滑塌、褶皱等构造现象普遍(图3j), 岩层中常见虫洞以及生物扰动痕迹(图3k)。Hutchison (1996)称Trusmadi组和Sapulut组为“下Crocker群”。“上Crocker群”为Crocker组(图3l), 沉积时代为始新世‒早中新世, 厚度超过10 km。早中新世前, 沙巴地区一直处于深海沉积环境, Trusmadi组和Crocker组向西逐渐变年轻(van Hattum et al., 2013)。东婆罗洲南端出露白垩纪基性岩和深海相地层(图1), 被认为与苏拉维西海向婆罗洲的俯冲有关, 其他大部分区域被中新世‒第四纪沉积物覆盖。

图1 婆罗洲地质简图(据Haile, 1974; Hutchison, 2010; Wang et al., 2016修改)

图2 婆罗洲晚白垩世‒渐新世地层柱状图(据van Hattum et al., 2013; Galin et al., 2017; Breitfeld and Hall, 2018; Breitfeld et al., 2018; Hennig-Breitfeld et al., 2019修改)

(a) Lupar组浊积砂岩, 显示鲍玛序列Tc～Te段以及包卷层理; (b) Lupar组滑塌和褶皱构造; (c) Layar段千枚岩; (d) Kapit段轻微变质形成铅笔构造; (e) 砂岩滑塌进入泥岩层中; (f) Metah段板岩; (g) Bawang段块状砂岩滑塌进入泥岩中; (h) Bawang段与Tatau组不整合接触; (i) Sapulut组浊积砂岩, 显示鲍玛序列Tb和Te段; (j) Trusmadi组砂岩因滑塌形成的褶皱; (k) Crocker组砂岩表面生物扰动痕迹; (l) Crocker组砂泥岩互层。

2 婆罗洲沉积物来源

作为世界上最大的海底沉积扇之一, 婆罗洲深水扇沉积规模类似于现今的孟加拉扇(Moss, 1998)。位于沙捞越中部的西布带Rajang群宽度可达200 km,晚白垩世‒中新世沉积地层厚度至少达上万米(表1)。Zhu et al. (2021)估算婆罗洲晚白垩世‒晚始新世沉积量约达10.9×105～19.5×105km3。

2.1 碎屑矿物组成

选取Rajang群和Tatau组14个新鲜的中‒粗砂岩样品进行镜下矿物鉴定及碎屑组分统计, 每个样品统计颗粒为300～500颗。与Kuching超级群和Crocker群相似(van Hattum et al., 2006, 2013; Ferdous and Farazi, 2016; Galin et al., 2017; Breitfeld and Hall, 2018), Rajang群碎屑矿物组成以石英为主, 含有大量燧石以及少量岩屑与长石。重矿物主要有锆石、金红石、石榴石、电气石、绿帘石、尖晶石等。Lupar组和Layar段具有相似的特征, 以隐晶质‒微晶长英质及黏土为基质, 矿物碎屑整体颗粒较小, 分选性差且磨圆度低。石英大多为单晶石英, 占70%～80%, 多晶石英占4%～10%, 长石含量很少, 燧石较为常见。单晶石英偶尔可见火山岩成因的港湾状构造(图4a)。部分薄片可见石英、长石等矿物受剪切作用定向排列, 形成眼球状、云母鱼等构造形态(图4b)。Kapit段和Pelagus段整体粒度较为均一, 矿物颗粒磨圆度较差。多晶石英含量增加, 约为7%～13%, 长石含量为2%～6%, 且燧石、长石等绢云母化严重(图4c)。重矿物自型程度高, 具很高的正突起, 矿物的边缘粗而黑(图4d)。火山岩屑主要由交织的板条状斜长石与基质组成, 斜长石微晶定向排列。沉积岩岩屑多为粉砂岩岩屑, 填隙物以黏土矿物为主(图4e)。Metah段多晶石英以及长石含量明显增加, 多晶石英含量高达20%, 长石占总体含量的8%, 以具卡氏双晶的斜长石为主(图4f), 偶尔可见具格子双晶的微斜长石。石英晶体大多被压扁拉长, 具齿状变晶结构, 为片状石英岩岩屑, 也有少量粒状变晶结构的变质石英岩岩屑。重矿物(锆石)边角被磨圆呈圆弧状(图4g), 具环带结构。含少量碳质板岩岩屑, 主要由碳质以及呈定向排列的绢云母等组成, 具板状构造。拉让不整合上下Bawang段与Tatau组砂岩薄片呈现截然不同的特征, Bawang段砂岩显微镜下特征与Kapit段和Pelagus段相似, 但颗粒磨圆度更高; 而Tatau组砂岩矿物颗粒具有很好的磨圆度且颗粒较大(图4h), 均在200～400 μm, 部分石英颗粒可观察到自生加大边现象(图4i), 表明为沉积再循环的产物。

Q-F-L图显示Rajang群和Tatau组样品均位于再旋回造山区; Qm-F-Lt图中, 除一个Bawang段和一个Tatau组样品落入混合区外, 其余样品落入石英质再旋回和过渡型再旋回区域(图5a)。该结果与前人对婆罗洲晚白垩世‒渐新世地层碎屑组成统计结果一致(van Hattum et al., 2013; Galin et al., 2017; Breitfeld and Hall, 2018; Hennig-Breitfeld et al., 2019)。Rajang群石英‒长石‒岩屑以及多晶石英‒单晶石英含量显示一定的规律性: Pelagus段和Metah段长石含量较下伏地层明显增加, 岩屑随着地层沉积年代的减小而略微增多(图5b)。由于婆罗洲地处热带, 伴随着强烈的化学风化作用, 辉石、角闪石等基性矿物以及长石等不稳定矿物容易在后期风化作用中溶解, 可能导致统计结果产生偏差。抗风化能力较强的石英类矿物统计结果显示, 单晶石英随着地层变年轻占比逐渐减少; 而多晶石英则相反, 表明变质碎屑输入增加(图5c)。

2.2 主量、微量元素特征

晚白垩世‒渐新世沉积物稀土元素配分模式呈现右倾特点, 伴随着Eu元素的亏损; 微量元素也显示出极强的Sr负异常(图6a、b; Ferdous and Farazi, 2016; Ahmed et al., 2020; Ramasamy et al., 2021; Baioumy et al., 2021; Zhao et al., 2021b; Zhu et al., 2021)。TiO2-Zr物源判别图中, Lubok Antu混杂岩和Rajang群沉积物落入长英质以及中性物质源区, 其中Lubok Antu混杂岩样品与Rajang群下部Lupar组和Layar段样品均更靠近中性物质区域, 而上部地层沉积岩样品大部分落于长英质区域内(图6c)。TiO2-Al2O3物源判别图也显示Lubok Antu混杂岩与Rajang群下部地层集中落于花岗闪长岩和花岗岩二者交界处, 而Rajang群上部地层样品数据点则零散分布在花岗闪长岩和花岗岩区域范围内(图6d)。Rajang群样品地球化学特征随时间变化, 表现为晚白垩世‒古新世地层(Lupar组、Layar段和下Kapit段)相比上覆地层含有更多的中‒基性物质, 随着地层逐渐年轻, 酸性物质含量逐渐增加。Kuching超级群和Rajang群均来自于花岗闪长岩以及花岗岩。Kuching超级群中的Kayan群、Ketungau群与Rajang群地球化学特征相似, 物源判别图均位于长英质花岗岩‒花岗闪长岩区域, 但相较于Rajang群具有更低的TiO2和Al2O3值(图6d)。

表1 婆罗洲晚白垩世‒中新世沉积地层厚度统计

(a) Lupar组单晶石英、燧石, 石英具溶蚀港湾状边缘表明来自喷出岩; (b) Layar段单晶石英, 矿物定向排列; (c) Kapit段多晶石英、燧石, 燧石绢云母化; (d) Pelagus段单晶石英、多晶石英、锆石; (e) Pelagus段沉积岩屑; (f) Metah段斜长石、燧石; (g) Metah燧石以及次圆状锆石; (h) Bawang段单晶石英、多晶石英; (i) Tatau组单晶石英、多晶石英、燧石, 石英加大边显示再旋回特征。矿物代号: Qm. 单晶石英; Qp. 多晶石英; Ch. 燧石; Kfs. 钾长石; Plg. 斜长石; Lm. 变质岩屑; Ls. 沉积岩屑。

2.3 Nd同位素地球化学特征

Lubok Antu混杂岩143Nd/144Nd值为0.512306～ 0.512498, 对应Nd值为−6.5～−2.7。Rajang群下部的Lupar组和Layar段143Nd/144Nd值为0.512346～0.512457, 对应的Nd值高达−5.7～−3.5, 上部古新世‒晚始新世地层Nd值减小到−9.7～−5.7。拉让不整合之上Tatau组地层Nd值则稳定在−7.9～−7.7之间(图7)。沉积物中Nd的相对高值表明有年轻的地壳物质加入(Li et al., 2003; Yan et al., 2007)。相较于南海现代沉积物Nd值而言, Lubok Antu混杂岩与Rajang群下部样品具有异常高Nd值(图8), 说明同时期近源存在大面积火山喷发或是年轻岩浆岩岩体出露和剥蚀。由于婆罗洲晚白垩世‒古新世火山活动较少, 且在镜下未观察到大量火山碎屑, 因此认为近源出露的大面积岩浆岩是晚白垩世‒古新世Rajang群沉积物的主要物质来源。古新世后, 沉积物中Nd值开始逐渐减小到−9.7～−5.7, 这一变化表明物源由年轻的岩浆岩转变为古老的大陆物质。

2.4 婆罗洲沉积物源演化过程

前人通过古水流、碎屑锆石和重矿物研究认为Rajang群沉积物主要来自施瓦纳山和马来半岛(Tan, 1982; Hutchison, 2005; van Hattum et al., 2006, 2013; Galin et al., 2017; Breitfeld and Hall, 2018; Breitfeld et al., 2018), 且Galin et al. (2017)以及Breitfeld and Hall (2018)认为此期间Rajang群与Kuching超级群经历了两次物源转变, 晚白垩世‒古新世沉积物主要来源于施瓦纳山和马来半岛, 古新世‒早/中始新世沉积物几乎全部来自于施瓦纳山, 中始新世‒晚始新世物源则受马来半岛以及施瓦纳山共同影响。但是Zhu et al. (2021)认为施瓦纳山和马来半岛的剥蚀量远小于Rajang-Crocker群巨大的沉积量。从矿物组成、主量和微量元素、Nd同位素数据来看, 古新世前后Rajang群物源发生明显变化。晚白垩世‒古新世Rajang群沉积物具有近源特征, 且由大面积年轻的中‒酸性花岗岩剥蚀沉积, 分布于越南南部至婆罗洲西南部中生代岩浆岩带可能是晚白垩世‒古新世Rajang群的主要物源区。地表露头与钻孔等资料显示环太平洋花岗岩具有相似的年龄以及地球化学特征(图8; Katili, 1973; Li and Li, 2007; Hutchison, 2010; Shellnutt et al., 2013; Hennig et al., 2017; Li et al., 2018; Breitfeld et al., 2020a; Hennig-Breitfeld et al., 2021), 且经历了晚白垩世‒古新世快速风化剥蚀(Areshev et al., 1992; 周蒂等, 2005; Cuong and Warren, 2009)。越南南部Dalat花岗岩Nd值为−2.8～+0.6 (Shellnutt et al., 2013), 分布于Kuching带的白垩纪火山岩及花岗岩Nd值同样高达+0.9～+3.6(Wang et al., 2021b)。这一花岗岩带的剥蚀使Rajang群晚白垩世‒古新世沉积物具有相对较高的Nd同位素组成(Shellnutt et al., 2013; Nong et al., 2021; Waight et al., 2021; Hennig-Breitfeld et al., 2021; Wang et al., 2021b)。古新世后, 马来半岛及印支陆块逐渐成为主要物源区, 具较低Nd值(−10.8～−5.6; Wang et al., 2021a)的酸性物质逐渐成为Rajang群的物源。古新世‒早始新世, Kapit段、Pelagus段沉积物地球化学特征反映的物源区与Galin et al. (2017)研究的差异, 可能是由于采样位置以及测试手段引起。进行沉积物地球化学分析的细粒粉砂岩‒泥岩样品主要位于沙捞越西北部, 受马来半岛影响较大, 而中部砂岩中碎屑锆石更可能受施瓦纳山影响(Zhu et al., 2021)。Rajang群物源区由晚中生代岩浆岩带向马来半岛的转变, 可能与岩浆岩带的裂解(Shellnut et al., 2013)以及巽他大陆的整体抬升(Morley, 2012; Cottam et al., 2013)有关。渐新世, Tatau组样品Nd同位素值稳定在−7.9～−7.7之间, 强烈的再循环特征表明Tatau组是由Rajang群抬升剥蚀沉积。

(a) Rajang群砂岩Q-F-L和Qm-F-Lt图解, Trusmadi组引自van Hattum et al. (2013), Kuching超级群引自Ferdous and Farazi (2016); Breitfeld and Hall (2018), Rajang群引自Galin et al. (2017), Tatau组引自Hennig-Breitfeld et al. (2019); (b) 石英‒长石‒岩屑组分变化图; (c) 单晶石英‒多晶石英占碎屑组分比值变化图。矿物代号: Q. 石英颗粒; F. 长石; L. 岩屑; Qm. 单晶石英; Qp. 多晶石英。

(a) 球粒陨石标准化稀土元素配分图(标准化值据Sun and McDonough, 1989); (b) 上地壳标准化微量元素蛛网图(标准化值据Rudnick and Gao, 2003); (c) TiO2-Zr二元判别图(底图据McLennan et al., 1980); (d) TiO2-Al2O3二元判别图(底图据McLennan et al., 1980)。

图8 婆罗洲周缘Nd同位素及年龄分布图(据Wei et al., 2012; Breitfeld et al., 2020a修改)

3 婆罗洲晚中生代构造演化

在Th-Zr/10-Co构造背景判别图中, Rajang群底部Lupar组、Layar段位于大陆岛弧构造背景, 其余样品大多落入主动大陆边缘区域内, Tatau组样品则在主动大陆边缘和被动大陆边缘之间的区域内(图9a)。log(K2O/Na2O)-SiO2二元构造判别图中, 西布带Rajang群样品都落入主动大陆边缘和被动大陆边缘区域, Tatau组样品则完全落于被动大陆边缘范围(图9b)。同时我们搜集Kuching超级群、Lubok Antu混杂岩以及沙巴始新世Trusmadi组沉积地层地球化学数据(Burgan et al., 2008; Ferdous and Farazi, 2016; Khan et al., 2017; Zhu et al., 2021; Zhao et al., 2021b)并进行对比, 发现古晋带、西布带、米里带以及沙巴样品反映的构造背景自西向东呈现出时空差异。古晋带上白垩统‒上始新统Kayan群、Ketungau群样品完全处于被动大陆边缘, 同沉积期的Rajang群则大多处于主动大陆边缘和被动大陆边缘之间(图9a、b), 而位于沙巴地区的中/上始新统Trusmadi组则完全处于主动大陆边缘背景(图9b)。

三叠纪‒晚白垩世, 古太平洋沿华南‒婆罗洲俯冲形成安第斯型岛弧。古晋带白垩系Pedawan组作为弧前盆地沉积接受来自周缘岩浆弧的物质供给(Breitfeld et al., 2017), 古晋带沉积环境由深海相Pedawan组向陆相Kayan组转变, 形成Pedawan不整合(Morley, 1998; Breitfeld et al., 2017), 标志着古太平洋板块在古晋带的俯冲作用于90 Ma左右停止(Breitfeld et al., 2018; 赵帅等, 2019)。西沙捞越地区古晋带上白垩统‒上始新统Kayan群、Ketungau群构造背景相对稳定。然而, 沿Lupar线出露的Lubok Antu俯冲混杂岩以及西布带出露的Rajang群底部的Lupar组、Layar段具有较高的Nd同位素比值, 主量、微量元素特征显示二者含有更高的中‒基性物质, 构造背景相对活跃, 说明古太平洋板块于婆罗洲的俯冲可能持续到古新世。晚白垩纪‒始新世时期, 地球化学特征显示古晋带稳定的构造背景与西布带较为活跃的构造背景之间的差异, 可能是由于古太平洋在沙捞越地区的俯冲后撤造成。当古太平洋沿卢帕尔线俯冲停止并向东后撤时, 古晋带远离俯冲带而靠近内陆地区, 构造背景相对稳定, 由深海沉积环境转变为陆相沉积环境, Kuching超级群开始沉积。而西布带深海相Rajang群作为增生楔沉积了同时期的Lupar组与Layar段, 具有明显的俯冲背景信号。古晋带内发育的77～80 Ma具有火山弧花岗岩性质的Pueh和Gading侵入体(Hennig et al., 2017)也可能对应俯冲带的后撤。～60 Ma, 古太平洋板块在西北婆罗洲的俯冲停止(Zhao et al., 2021a)。另外, 俯冲后撤引起区域挤压应力向区域伸展应力转变, 发育一系列区域性伸展构造(Shellnutt et al., 2013; Liu et al., 2016), 位于巽他陆架的岩浆岩带坍塌裂解, 使得Rajang群源区由近源岩浆岩带向马来半岛迁移, 大量具有较低Nd同位素组成且更具酸性的沉积物为Rajang群提供物质来源。～37 Ma, 曾母陆块与婆罗洲碰撞(Fuller et al., 1999; Madon et al., 2013; Advokaat et al., 2018), Rajang群变形抬升(Hutchison, 2010; Zhao et al., 2021a), 且由于后期板块边界重组及婆罗洲逆时针旋转, 最初具有缝合线性质的卢帕尔线转变为走滑断层。婆罗洲的逆时针旋转及沿卢帕尔线的走滑使Rajang群与Kuching超级群叠置。渐新世, 深海相Rajang群被陆相Tatau组和Nyalau组地层不整合覆盖, Tatau组Nd同位素比值稳定且位于Rajang群Nd同位素比值范围内, 主量、微量元素反映的此时构造背景由活跃转变为稳定, 且碎屑矿物形态证明沉积物来源于早期Rajang群的物质循环(图4); Nyalau组碎屑锆石及矿物形态也反映出一致的循环特征(Breitfeld et al., 2020b)。同时古南海在西巴兰姆线以东的沙巴地区开始俯冲, Trusmadi组具有强烈的主动大陆边缘沉积地球化学信号(图9b), 沙巴南部中新世砂岩中发现少量的始新世‒早中新世岩浆锆石(22～48 Ma), 暗示沙巴地区存在与古南海俯冲相关的火山活动(Suggate, 2011), 这与沙巴南部渐新世砂岩中含有大量火山岩屑一致(van Hattum et al., 2013)。此外, 古南海向南俯冲形成卡加延火山岛弧(Holloway, 1982; 金康辰, 1989; Hinz et al., 1991; Rangin and Silver, 1991; Spadea et al., 1996; Keenan et al., 2016; Hall and Breitfeld, 2017), 卡加延弧钻井样品定年结果为14～26 Ma, 甚至更老, 表明其很可能向西南连接至沙巴山打根(Sandakan)附近, 共同代表与古南海俯冲相关的岩浆活动事件(Kudrass et al., 1990; Rangin and Silver, 1991)。而渐新世‒中新世深水Crocker组更被认为是古南海俯冲于沙巴‒巴拉望过程中的产物(Taylor and Hayes, 1983; Hall, 1996, 2013; Hutchison et al., 2000)。

(a) Th-Zr/10-Co构造背景判别图(底图据Bhatia and Crook, 1986); (b) Log(K2O/Na2O)-SiO2构造背景判别图(底图据Roser abd Korsch, 1986)。AM. 主动大陆边缘; PM. 被动大陆边缘; OIA. 大洋岛弧; CIA. 大陆岛弧。

4 结 论

(1) Rajang群沉积物来源在古新世前后经历了一次较为明显的变化。晚白垩世‒早古新世Rajang群沉积物具有近源特征, Nd同位素比值相对较高, 其物源主要来自巽他大陆边缘晚中生代岩浆岩岩带。早始新世‒晚始新世物源区向马来半岛迁移。

(2) 晚白垩世, 位于古晋带的俯冲停止, 然而西部带的俯冲持续到～60 Ma。Rajang群底部的Lupar组和Layar段与Lubok Antu俯冲混杂岩为古南海俯冲增生产物。古新世后, 卢帕尔线由缝合线转变为走滑断层, 婆罗洲的逆时针旋转及沿卢帕尔线的走滑使Rajang群与Kuching超级群叠置。

(3) ～37 Ma, 曾母陆块与婆罗洲碰撞, Rajang群抬升剥蚀。渐新世, 古南海在婆罗洲东北部沙巴地区开始俯冲, 对应于南海的打开。

致谢:两位匿名审稿专家对本文提出的宝贵建议及意见, 在此表示衷心的感谢。

金康辰. 1989. 在西太平洋边缘盆地的钻探——ODP第124 航次. 海洋地质译丛, (5): 81, 77.

孙卫东, 凌明星, 汪方跃, 丁兴, 胡艳华, 周继彬, 杨晓勇. 2008. 太平洋板块俯冲与中国东部中生代地质事件. 矿物岩石地球化学通报, 27(3): 218–225.

吴世敏, 周蒂, 刘海龄. 2004. 南沙地块构造格局及其演化特征. 大地构造与成矿学, 28(1): 23–28.

赵帅, 李学杰, 姚永坚, 解习农, 肖苏芸, 何西, 邓雨恬, 石梦临, 周末. 2019. 南海南部造山运动及其与古南海俯冲的成因联系. 海洋地质与第四纪地质, 39(5): 147–162.

周蒂, 刘海龄, 陈汉宗. 2005. 南沙海区及其周缘中‒新生代岩浆活动及构造意义. 大地构造与成矿学, 29(3): 354–363.

Advokaat E L, Marshall N T, Li S H, Spakman W, Krijgsman W, van Hinsbergen D J. 2018. Cenozoic rotation history of Borneo and Sundaland, SE Asia revealed by paleoma­gnetism, seismic tomography, and kinematic reconstruction., 37(8): 2486–2512.

Ahmed N, Siddiqui N A, Ramasamy N, Ramkumar M, Jamil M, Usman M, Sajid Z. 2020. Geochemistry of Eocene Bawang Member turbidites of the Belaga Formation, Borneo: Implications for provenance, palaeoweathering, and tectonic setting., 56(5): 2477– 2499.

Amiruddin A. 2009. Cretaceous orogenic granite belts, Kalimantan, Indonesia., 19(3): 167–176.

Areshev E G, Dong T L, San N T, Shnip O A. 1992. Reservoirsin fractured basement on the continental shelf of southern Vietnam., 15(4): 451–464.

Baioumy H, Salim A M A, Ahmed N, Maisie M, Al-Kahtany K. 2021. Upper Cretaceous-Upper Eocene mud-dominated turbidites of the Belaga Formation, Sarawak (Malaysia): 30 Ma of paleogeographic, paleoclimate and tectonic stability in Sundaland., 126(1), 104897.

Balaguru A, Nichols G. 2004. Tertiary stratigraphy and basin evolution, southern Sabah (Malaysian Borneo)., 23(4): 537–554.

Bhatia M R, Crook K A. 1986. Trace element characteristics of greywackes and tectonic setting discrimination of sedimentary basins., 92(2): 181–193.

Breitfeld H T, Davies L, Hall R, Armstrong R, Forster M, Lister G, Thirlwall M, Grassineau N, Hennig-Breitfeld J, van Hattum M W. 2020a. Mesozoic Paleo-Pacific subduction beneath SW Borneo: U-Pb geochronology of the Schwaner granitoids and the Pinoh Metamorphic Group., 8, 568715.

Breitfeld H T, Hall R, Galin T, BouDagher-Fadel M K. 2018. Unravelling the stratigraphy and sedimentation history of the uppermost Cretaceous to Eocene sediments of the Kuching Zone in West Sarawak (Malaysia), Borneo., 160: 200–223.

Breitfeld H T, Hall R, Galin T, Forster M A, BouDagher- Fadel M K. 2017. A Triassic to Cretaceous Sundaland- Pacific subduction margin in West Sarawak, Borneo., 694: 35–56.

Breitfeld H T, Hall R. 2018. The eastern Sundaland margin in the latest Cretaceous to Late Eocene: Sediment provenance and depositional setting of the Kuching and Sibu Zones of Borneo., 63: 34–64.

Breitfeld H T, Hennig-Breitfeld J, BouDagher-Fadel M K, Hall R, Galin T. 2020b. Oligocene-Miocene drainage evolution of NW Borneo: Stratigraphy, sedimentology and provenance of Tatau-Nyalau province sediments., 195(15), 104331.

Burgan A M, Ali C A, Tahir S H. 2008. Chemical compositionof the Tertiary black shales of West Sabah, East Malaysia., 27(1): 28–35.

Collenette P. 1965. The geology and mineral resources of the Pensiangan and Upper Kinabatangan area, Sabah., 12: 150.

Cottam M A, Hall R, Ghani A A. 2013. Late Cretaceous and Cenozoic tectonics of the Malay Peninsula constrained by thermochronology., 76: 241–257.

Cuong T X, Warren J K. 2009. Bach ho field, a fractured granitic basement reservoir, Cuu Long Basin, offshore SE Vietnam: A “buried-hill” play., 32(2): 129–156.

Davies L, Hall R, Armstrong R. 2014. Cretaceous crust in SW Borneo: Petrological, geochemical and geochro­nolo­gical constraints from the Schwaner Mountains // 38thAnnual Convention and Exhibition. Jakarta, Indonesia: Indonesian Petroleum Association: 21–23.

Ferdous N, Farazi A H. 2016. Geochemistry of Tertiary sandstones from southwest Sarawak, Malaysia: Implications for provenance and tectonic setting., 35(3): 294–308.

Fuller M, Ali J R, Moss S J, Frost G M, Richter B, Mahfi A. 1999. Paleomagnetism of Borneo., 17(1–2): 3–24.

Fyhn M B, Pedersen S A, Boldreel L O, Nielsen L H, Green P F, Dien P T, Huyen L T, Frei D. 2010. Palaeocene- early Eocene inversion of the Phuquoc-Kampot Som Basin: SE Asian deformation associated with the suturing of Luconia., 167(2): 281–295.

Galin T, Breitfeld H T, Hall R, Sevastjanova I. 2017. Provenance of the Cretaceous-Eocene Rajang Group submarine fan, Sarawak, Malaysia from light and heavy mineral assemblages and U-Pb zircon geochronology., 51: 209–233.

Haile N S. 1974. Borneo.,,, 4(1): 333–347.

Hall R. 1996. Reconstructing Cenozoic SE Asia.,,, 106(1): 153–184.

Hall R. 2013. Contraction and extension in northern Borneo driven by subduction rollback., 76: 399–411.

Hall R, Breitfeld T. 2017. Nature and demise of the proto- South China Sea., 63: 61–76.

Hall R, Spakman W. 2015. Mantle structure and tectonic history of SE Asia., 658: 14–45.

Hamilton W. 1979. Tectonics of the Indonesian region., 6: 3–10.

Hennig-Breitfeld J, Breitfeld H T, Hall R, BouDagher-Fadel M, Thirlwall M. 2019. A new upper Paleogene to Neogene stratigraphy for Sarawak and Labuan in northwestern Borneo: Paleogeography of the eastern Sundaland margin., 190: 1–32.

Hennig-Breitfeld J, Breitfeld H T, Hall R, Nugraha A S. 2017. The Mesozoic tectono-magmatic evolution at the Paleo-Pacific subduction zone in West Borneo., 48: 292–310.

Hennig-Breitfeld J, Breitfeld H T, Sang D Q, Vinh M K, Van Long T, Thirlwall M, Cuong T X. 2021. Ages and character of igneous rocks of the Da Lat Zone in SE Vietnam and adjacent offshore regions (Cuu Long and Nam Con Son basins)., 218, 104878.

Hennig-Breitfeld J, Breitfeld T, Gough A, Hall R, Long T V, Kim V M, Quang S D. 2018. U-Pb zircon ages and provenance of upper Cenozoic sediments from the Da Lat Zone, SE Vietnam: Implications for an intra-Miocene unconformity and paleo-drainage of the proto-Mekong River., 88(4): 495–515.

Hinz K, Block M, Kudrass H R, Meyer H. 1991. Structural elements of the Sulu Sea, Phillipines.,, 127: 483–506.

Holloway N H. 1982. North Palawan block — Its relation to Asian mainland and role in evolution of South China Sea., 66: 1355–1383.

Honza E, John J, Banda R M. 2000. An imbrication model for the Rajang Accretionary Complex in Sarawak, Borneo., 18: 751–759.

Hutchison C S, Bergman S C, Swauger D A, Graves J E. 2000. A Miocene collisional belt in north Borneo: Uplift mechanism and isostatic adjustment quantified by thermochronology., 157(4): 783–793.

Hutchison C S. 1989. Geological Evolution of South-east Asia. Oxford, United Kingdom: Clarendon Press: 376.

Hutchison C S. 1996. The ‘Rajang accretionary prism’ and ‘Lupar Line’ problem of Borneo.,,, 106(1): 247–261.

Hutchison C S. 2005. Geology of North-West Borneo: Sarawak, Brunei and Sabah. Elsevier.

Hutchison C S. 2010. Oroclines and paleomagnetism in Borneo and south-east Asia., 496(1–4): 53–67.

Katili J A. 1973 Geochronology of west Indonesia and its implication on plate tectonics., 19(3): 195–212.

Keenan T E, Encarnación J, Buchwaldt R, Fernandez D, Mattinson J, Rasoazanamparany C, Luetkemeyer P B. 2016. Rapid conversion of an oceanic spreading center to a subduction zone inferred from high-precision geochronology., 113(47): E7359–E7366.

Khan A A, Abdullah W H, Hassan M H, Iskandar K. 2017. Tectonics and sedimentation of SW Sarawak basin, Malaysia, NW Borneo., 89(2): 197–208.

Kudrass H R, Müller P, Kreuzer H, Weiss W. 1990. Volcanic rocks and Tertiary carbonates dredged from the CagayanRidge and the Southwest Sulu Sea, Philippines.,, 124: 51–63.

Li C F, Xu X, Lin J, Sun Z, Zhu J, Yao Y, Zhao X X, Liu Q S, Kulhanek D K, Wang J, Song T R, Zhao J F, Qiu N, Guan Y X, Zhou Z Y, Williams T, Bao R, Briais A, Brown E A, Chen Y F, Clift P D, Colwell F S, Dadd K A, Ding W W, Almeida I H, Huang X L, Hyun S, Jiang T, Koppers A A P, Li Q Y, Liu C L, Liu Z F, Nagai R H, Peleo-Alampay A, Su X, Tejada M L G, Trinh H S, Yeh Y C, Zhang C L, Zhang F, Zhang G L. 2014. Ages and magnetic structures of the South China Sea constrained by deep tow magnetic surveys and IODP Expedition 349.,,, 15(12): 4958–4983.

Li F C, Sun Z, Yang H F. 2018. Possible spatial distribution of the Mesozoic volcanic arc in the present-day South China Sea continental margin and its tectonic implications.:, 123(8): 6215–6235.

Li J H, Zhang Y Q, Dong S W, Johnston S T. 2014. Cretaceoustectonic evolution of South China: A preliminary synthesis., 134: 98–136.

Li X H, Wei G J, Shao L, Liu Y, Liang X L, Jian Z M, Sun M, Wang P. 2003. Geochemical and Nd isotopic variations in sediments of the South China Sea: A response to Cenozoic tectonism in SE Asia., 211(3–4): 207–220.

Li Z X, Li X H. 2007. Formation of the 1300-km-wide intracontinental orogen and postorogenic magmatic province in Mesozoic South China: A flat-slab subduction model., 35(2): 179–182.

Liechti P, Roe F W, Haile N S. 1960. The geology of Sarawak, Brunei and the western part of North Borneo, British Territories of Borneo., 3, 360.

Liu L, Xu X S, Xia Y. 2016. Asynchronizing paleo-Pacific slab rollback beneath SE China: Insights from the episodic Late Mesozoic volcanism., 37: 397–407.

Macpherson C G, Chiang K K, Hall R, Nowell G M, Castillo P R, Thirlwall M F. 2010. Plio-Pleistocene intra-plate magmatism from the southern Sulu Arc, Semporna peninsula, Sabah, Borneo: Implications for high-Nb basalt in subduction zones., 190: 25–38

Madon M, Ly K C, Wong R. 2013. The structure and stratigraphy of deepwater Sarawak, Malaysia: Implicationsfor tectonic evolution., 76: 312–333.

McLennan S M, Nance W B, Taylor S R. 1980. Rare earth element-thorium correlation in sedimentary rocks and the composition of the continental crust., 44: 1833–1839.

Metcalfe I. 2009. Late Palaeozoic and Mesozoic tectonic and palaeogeographical evolution of SE Asia.,,, 315(1): 7–23.

Metcalfe I. 2011. Palaeozoic-Mesozoic history of SE Asia.,,, 355(1): 7–35.

Métivier F, Gaudemer Y, Tapponnier P, Klein M. 1999. Mass accumulation rates in Asia during the Cenozoic., 137(2): 280–318.

Morley C K. 2012. Late Cretaceous-Early Palaeogene tectonic development of SE Asia., 115: 37–75.

Morley R J. 1998. Palynological evidence for Tertiary plant dispersals in the SE Asian region in relation to plate tectonics and climate // Hall R, Holloway J D. Biogeography and Geological Evolution of SE Asia. Backhuys Publishers:211–234.

Moss S J. 1998. Embaluh Group turbidites in Kalimantan: Evolution of a remnant oceanic basin in Borneo during the Late Cretaceous to Palaeogene., 155(3): 509–524.

Moss S J, Chambers J L C. 1999. Tertiary facies architecture in the Kutai basin, Kalimantan, Indonesia., 17(1–2): 157–181.

Nong A T, Hauzenberger C A, Gallhofer D, Dinh S Q. 2021. Geochemistry and zircon U-Pb geochronology of Late Mesozoic igneous rocks from SW Vietnam-SE Cambodia: Implications for episodic magmatism in the context of the Paleo-Pacific subduction., 390, 106101.

Pieters P E, Sanyoto P. 1993. Geology of the Pontianak/ Nangataman Sheet area, Kalimantan 1∶250,000. GeologicalResearch and Development Centre, Bandung, Indonesia.

Ramasamy N, Franz L K, Jong J, Muthuvairavasamy R, Muhammad A A, Dayong V, Shanmugarajah L, Vusak N, Sivanasvaran K, Kinanthi D. 2021. Geochemistry of the Palaeocene-Eocene Upper Kelalan Formation, NW Borneo: Implications on palaeoweathering, tectonic setting, and provenance., 56(5): 2500–2527.

Rangin C, Bellon H, Benard F, Letouzey J, Müller C, Tahir S. 1990. Neogene arc-continent collision in Sabah, N. Borneo (Malaysia)., 183: 305–319.

Rangin C, Silver E A. 1991. Neogene tectonic evolution of the Celebes Sulu basins: New insights from Leg 124 drilling.,, 124: 51–63.

Roser B P, Korsch R J. 1986. Determination of tectonic setting of sandstone-mudstone suites using SiO2content and K2O/Na2O ratio., 94: 635–650.

Rudnick R, Gao S. 2003. Composition of the continental crust // Holland H D, Turekian K K. Treatise on Geochemistry. Amsterdam: Elsevier Scientific Publishing Company: 3: 1–64.

Setiawan N I, Osanai Y, Nakano N, Adachi T, Setiadji L D, Wahyudiono J. 2013. Late Triassic metatonalite from the Schwaner Mountains in West Kalimantan and its contribution to sedimentary provenance in the Sundaland., 12(28): 4–12.

Shellnutt J G, Lan C Y, Van Long T, Usuki T, Yang H J, Mertzman S A, Lizuka Y, Chung S L, Wang K L, Hsu W Y. 2013. Formation of Cretaceous Cordilleran and post-orogenic granites and their microgranular enclaves from the Dalat zone, southern Vietnam: Tectonic implicationsfor the evolution of Southeast Asia., 182: 229–241.

Spadea P, D’Antonio M, Thirlwall M F. 1996. Source characteristics of the basement rocks from the Sulu and Celebes Basins (Western Pacific): Chemical and isotopic evidence., 123(2): 159–176.

Suggate S. 2011. Provenance of Neogene sandstones of Sabah, northern Borneo. PhD Thesis, Royal Holloway University of London: 441.

Sun S S, McDonough W. 1989. Chemical and isotopic systematics of oceanic basalts: Implications for mantle composition and processes.,,, 42: 313–345.

Tan D N K. 1982. Lubok Antu Melange, Lupar Valley, West Sarawak: A Lower Tertiary subduction complex. Bulletin., 15: 31–46.

Taylor B, Hayes D E. 1983. Origin and history of the South China Sea basin., 27: 23–56

van Hattum M W A, Hall R, Pickard A L, Nichols G J. 2013. Provenance and geochronology of Cenozoic sandstones of northern Borneo., 76: 266–282.

van Hattum M W, Hall R, Pickard A L, Nichols G J. 2006. Southeast Asian sediments not from Asia: Provenance and geochronology of north Borneo sandstones., 34(7): 589–592.

Waight T, Fyhn M B, Thomsen T B, Van Tri T, Nielsen L H, Abatzis I, Frei D. 2021. Permian to Cretaceous granites and felsic volcanics from SW Vietnam and S Cambodia: Implications for tectonic development of Indochina., 219, 104902.

Wang P C, Li S Z, Guo L L, Jiang S H, Somerville I D, Zhao S J, Zhu B D, Chen J, Dai L M, Suo Y H, Han B. 2016. Mesozoic and Cenozoic accretionary orogenic processes in Borneo and their mechanisms., 51: 464–489.

Wang Y J, Qian X, Zhang Y Z, Gan C S, Zhang A M, Zhang F F, Feng Q L, Cawood P A, Zhang P Z. 2021a. Southern extension of the Paleotethyan zone in SE Asia: Evidence from the Permo-Triassic granitoids in Malaysia and West Indonesia., 398, 106336.

Wang Y J, Wu S N, Qian X, Cawood P A, Lu X H, Gan C S, Junaidi B A, Zhang P Z. 2021b. Early Cretaceous subduction in NW Kalimantan: Geochronological and geochemical constraints from the Raya and Mensibau igneous rocks., 101: 243–256.

Wang Y J, Zhang A M, Qian X, Asis J B, Feng Q L, Gan C S, Zhang Y Z, Cawood P A, Wang W T, Zhang P Z. 2021c. Cretaceous Kuching accretionary orogenesis in MalaysiaSarawak: Geochronological and geochemical constraintsfrom mafic and sedimentary rocks., 400, 106425.

Wei G J, Liu Y, Ma J L, Xie L H, Chen J F, Deng W F, Tang S. 2012. Nd, Sr isotopes and elemental geochemistry of surface sediments from the South China Sea: Implications for provenance tracing., 319: 21–34.

Williams P R, Johnston C R, Almond R A, Simamora W H. 1988. Late Cretaceous to early Tertiary structural elementsof West Kalimantan., 148(3–4): 279–297.

Wu J, Suppe J, Lu R Q, Kanda R. 2017. Philippine Sea and East Asian plate tectonics since 52Ma constrained by new subducted slab reconstruction methods.:, 121: 4670–4741.

Wu J, Suppe J. 2018. Proto-South China Sea plate tectonics using subducted slab constraints from tomography., 29(6): 1304–1318.

Xu C H, Shi H S, Barnes C G, Zhou Z Y. 2016. Tracing a late Mesozoic magmatic arc along the Southeast Asian marginfrom the granitoids drilled from the northern South China Sea., 58(1): 71–94.

Yan Y, Xia B, Lin G, Carter A, Hu X Q, Cui X J, Liu B M, Yan P, Song Z J. 2007. Geochemical and Nd isotope composition of detrital sediments on the north margin of the South China Sea: Provenance and tectonic implications., 54(1): 1–17.

Zhao Q, Yan Y, Tonai S, Tomioka N, Clift P D, Hassan M H A, Aziz J H B A. 2021a. A new K-Ar illite dating application to constrain the timing of subduction in West Sarawak, Borneo., 134(1–2): 405–418.

Zhao Q, Yan Y, Zhu Z F, Carter A, Clift P D, Hassan M H A, Yao D, Aziz J H A. 2021b. Provenance study of the Lubok Antu Mélange from the Lupar valley, West Sarawak, Borneo: Implications for the closure of eastern Meso- Tethys?, 581, 120415.

Zhou J, Jiang Y H, Xing G F, Zeng Y, Ge W Y. 2013. Geochronology and petrogenesis of Cretaceous A-type granites from the NE Jiangnan Orogen, SE China., 55(11): 1359–1383.

Zhu Z F, Yan Y, Zhao Q, Carter A, Hassan M H A, Zhou Y. 2021. Geochemistry and paleogeography of the Rajang Group, Northwest Borneo, Malaysia., 137, 105500.

Subduction Processes of the Proto-South China Sea: Evidence from the Late Cretaceous-Oligocene Stratigraphic Record in Borneo

ZHU Zuofei1, 2, 3, YAN Yi1, 2, 4, 5*, ZHAO Qi1, 2, 4, 5

(1. CASKey Laboratory of Ocean and Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, Guangdong, China; 2. Center for Excellence in Deep Earth Science, Chinese Academy of Sciences, Guangzhou 510640, Guangdong, China; 3. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China; 4. Southern Marine Science and Engineering Guangdong Laboratory, Guangzhou 511458, Guangdong, China; 5. Innovation Academy of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences, Guangzhou 510301, Guangdong, China)

The subduction and extinction of the Proto-South China Sea is the key to reveal the expansion mechanism of the South China Sea and to reconstruct the Meso-Cenozoic tectonic evolution of Southeast Asia. However, there are still many controversies about the subduction process of the Proto-South China Sea. The overall Late Cretaceous-Oligocene sedimentary strata are outcropped in Borneo, Malaysia, which are important window for studying the tectonic evolution of the Proto-South China Sea. Detrital mineral composition, sedimentary geochemistry and Nd isotope analysis have been used to trace the origin of sediments from the Late Cretaceous-Oligocene strata in Borneo, and reconstruct the regional palaeogeographic pattern. The results show that the magmatic rock belt formed by subduction of the Paleo-Pacific Plate was the main source area for the Late Cretaceous-Paleocene sediments of the Rajang Group, and the sedimentary contribution of the Malay Peninsula and Southern margin of the Indochina were increased during Paleocene-Late Eocene, indicating that the influence of the Paleo-Pacific Plate subduction continued into the Early Paleocene (. 60 Ma). During the Late Eocene, the counterclockwise rotation of Borneo caused the scissor-like closure of the residual basin as the Australian Plate continued to drift northward. About 37 Ma, the Luconia block collided with Borneo, leading the uplift and erosion of the Rajang Group. During the Oligocene, the Proto-South China Sea started to subduct under Sabah, which located in Northeast Borneo, corresponding to the opening of the South China Sea. The Proto-South China Sea subducted obliquely from west to east, the rotation of Borneo and the strike-slip along the Lupar Line superimposed the Rajang Group over the Kuching Supergroup.

Proto-South China Sea; Paleo-Pacific Ocean; Borneo; provenance; tectonic evolution

2021-12-10;

2022-02-14

国家自然科学基金委(NSFC)–广东联合基金项目(U1701641)、南方海洋科学与工程广东省实验室(广州)人才团队引进重大专项 (GML2019ZD0205)联合资助。

朱作飞(1994–), 男, 博士研究生, 构造地质学专业。E-mail: zhuzuofei94@163.com

闫义(1973–), 男, 研究员, 从事海洋地质方面研究。E-mail: yanyi@gig.ac.c

P588.21

A

1001-1552(2022)03-0552-017

10.16539/j.ddgzyckx.2022.03.010