哈尔滨宾县砂砾石剖面沉积物组成及碎屑锆石U-Pb测年:对沉积环境和区域构造演化的指示

Sedimentary composition and detrital zircon U-Pb dating of the sand-gravel profile in Binxian County,Harbin:Indications for sedimentary environment and regional tectonic evolution

黑龙江宾县宁远镇中阳村剖面的砂砾石堆积过去被认为是哈尔滨地区第四纪下限的罗家窝棚组地层,对于其地层属性和沉积环境方面的研究较为薄弱。本文在野外考察的基础上,利用沉积学、矿物学、地球化学和碎屑锆石U-Pb测年对这套砂砾石堆积剖面进行研究,对其化学风化特征、源岩性质、沉积环境以及构造背景进行讨论。结果表明,这套砾石地层分选和磨圆较差,风化程度较低,无定向性排列,砾石以花岗岩(63%)、石英砂岩(22%)为主;钛铁矿(22.5%)是最主要重矿物,其次是锆石(17.4%)、赤褐铁矿(13.4%),其它重矿物含量较少。元素地球化学揭示,沉积物中的细颗粒组分经历了中-低等的化学风化过程,大部分沉积物经历了首次循环。砾石岩性和地球化学组成共同揭示了沉积物主要来源于长英质母岩。元素地球化学的迁移与富集以及古气候判别图解指示沉积物是干热气候条件下的近距离搬运的冲洪积物。碎屑锆石U-Pb年龄分布在较窄的范围(208~129 Ma,峰值年龄~180 Ma),与周围潜在源区锆石年龄对比,结合地貌位置,确定其物源区位于张广才岭余脉哈尔滨东南部低山丘陵带。早侏罗世源区受到古太平洋板块俯冲作用的影响,形成大陆边缘的构造背景,哈尔滨东南低山丘陵带经历了隆升和岩浆活动。与罗家窝棚组标准地层的沉积学特征对比存在明显差异,推测宁远剖面形成时间要晚于罗家窝棚组,与白土山组大致相当。这项研究对于哈尔滨地区第四纪地层的划分具有重要意义。

The sandstone accumulation in Zhongyangcun section,Ningyuan Town,Binxian County,Heilongjiang Province was considered to be the Luojiawopeng Formation at the lower limit of Quaternary in Harbin area,and the research on its stratigraphic properties and sedimentary environment was relatively weak.On the basis of field investigation,sedimentology,mineralogy,geochemistry and detrital zircon U‐Pb dating are used to study this set of sandstone accumulation profiles,and the chemical weathering characteristics,nature of source rock,sedimentary environment and tectonic setting are discussed.The results show that this set of gravel stratum has poor sorting and rounding,low weathering degree and no directional arrangement.The gravel is mainly granite(63%)and quartz sandstone(22%).Ilmenite(22.5%)is one of the main heavy minerals,followed by zircon(17.4%),hemlimonite(13.4%),and other heavy minerals are less.Elemental geochemistry reveals that the fine‐grained components in the sediments underwent a moderate to low chemical weathering process,with most of the sediments undergoing the first cycle.The lithology and geochemical composition of the gravel together reveal that the sediments are mainly derived from felsic parent rocks.The geochemical migration and enrichment of elements and the paleoclimate discrimination diagram indicate that the sediments are alluvial sediments transported in close distance under hot and dry climate conditions.The U‐Pb ages of detrital zircons are distributed in a relatively narrow range(208~129 Ma,with a peak age of~180 Ma),and the peak age is in the Early Jurassic.By comparing the zircon ages with the surrounding potential source areas,combined geomorphic location,the provenance area of detrital zircons is located in the low hill belt southeast of Harbin,the residual mountain range of Zhangguangcai Range.Under the influence of the subduction of paleo‐Pacific Plate,the Early Jurassic source area formed the tectonic setting of the continental margin.The low mountain belt southeast of Harbin experienced uplift and magmatic activity.It is inferred that the formation time of the section is later than Luojiawopeng Formation and roughly equal to that of Baitushan Formation.This study is of great significance to the division of Quaternary stratigraphy in Harbin area.