沙巴地区新生代碎屑岩物源分析及构造意义:锆石年代学和Lu-Hf同位素组成约束

Provenance and Tectonic Significance of the Cenozoic Sandstones in Sabah:Constraints from Zircon Geochronology and Lu-Hf Isotope

沙巴地区位于印度‒澳大利亚、太平洋和菲律宾海板块交汇区,其发育的新生代沉积对理解婆罗洲北部的沉积‒构造演化具有重要意义。本文对沙巴北部始新世‒中新世碎屑岩开展岩石学、锆石U-Pb年代学及Lu-Hf同位素研究,结果表明:该套碎屑岩包括岩屑石英砂岩和长石岩屑石英砂岩,其中始新统Trusmadi组碎屑锆石年龄主要峰值为160 Ma和120 Ma,对应年龄群(185~145 Ma和140~100 Ma)的εHf(t)值分别为–15.6~+14.8和+0.6~+12.2,表明源区新生地壳物质贡献明显。始新统‒中新统Crocker组碎屑锆石年龄主要峰值为248 Ma,次要峰值为1860 Ma、438 Ma、280 Ma和120 Ma,主要年龄群(265~220 Ma)的εHf(t)值为–11.9~+9.9。中新统Kudat组的碎屑锆石年龄集中在120 Ma、εHf(t)值(+1.8~+9.0)均为正值,次要峰值174 Ma。本次研究认为Trusmadi组砂岩物源主要受控于越南大叻带和婆罗洲西部中生代花岗质岩及古晋带再循环沉积物,Crocker组主要源自婆罗洲西部和马来半岛东部中生代火成岩,以及沙巴本身。Kudat组砂岩物源主要来自沙巴蛇绿岩及部分巴拉望陆块的再循环沉积物。此外,少量始新世岩浆成因碎屑锆石暗示沙巴地区存在始新世与古南海板块俯冲相关的岩浆作用。

Sabah in Borneo is located in the junction region of the Indo-Australian,Pacific,and Philippine Sea plates,and experienced complex tectonic evolution.The Cenozoic sedimentary strata in Sabah preserved important fingerprints for understanding the sedimentary-tectonic evolution of Northern Borneo.This paper presents petrographic and detrital zircon U-Pb geochronological results,as well as zircon in-situ trace elemental and Lu-Hf isotopic results for the Eocene-Miocene sandstones in Northern Sabah.These results indicate that the sandstones are characterized by lithic quartz sandstone and feldspar lithic quartz sandstone.Detrital zircons from the Eocene Trusmadi Formation show two main age peaks at ca.160 Ma and ca.120 Ma,withεHf(t=185–145 Ma and 140–100 Ma)ranging from–15.6 to+14.8 and+0.6 to+12.2,indicative of significant juvenile crustal materials in the provenance.The detrital zircon from the Eocene-Miocene Crocker Formation has a main peak at ca.248 Ma and four secondary age peaks at ca.1860 Ma,ca.438 Ma,ca.280 Ma,and ca.120 Ma,and the correspondingεHf(t=265–220 Ma)values range from–11.9 to+9.9.Detrital zircon apparent ages for the Miocene Kudat Formation yielded a major age peak of ca.120 Ma and a secondary age-peak of ca.174 Ma,with positiveεHf(t=140–100 Ma)values of+1.8–+9.0,indicating that juvenile crustal materials were the main contributor to the provenance.Our results indicate that the Trusmadi sandstone was sourced from Mesozoic intermediate-acid igneous rocks in the Vietnam Dalat Zone and Western Borneo and recycled sediments from the Sarawak Kuching zone.The Crocker sandstones are mainly Mesozoic igneous rocks from Western Borneo and East Malaya,along with associated rocks from Sabah.The Kudat sandstones were mainly from the Sabah ophiolitic mélange and partially recycled sediments from the Palawan continental terrane.Our results also suggest the existence of Eocene magmatism associated with subduction of the Proto-South China Sea in Sabah.