华北临汾盆地中部柴庄上新世—更新世剖面沉积学特征及其构造意义

SEDIMENTATION OF THE PLIOCENE-PLEISTOCENE CHAIZHUANG SECTION IN THE CENTRAL OF LINFEN BASIN,NORTH CHINA AND ITS TECTONIC SIGNIFICANCE

临汾盆地位于华北克拉通汾渭地堑系中南部,是典型的受控于北东—南西向和近东西向正断层的晚新生代断陷盆地。沉积相、古水流和重矿物综合分析表明,盆地中部的柴庄新生界剖面除顶部的风成黄土之外,可以划分为3个岩性段,分别具有不同的物源,反映了不同时期的构造背景。第一岩性段为上新统（5.0-2.6 Ma）,冲积扇和风成红黏土沉积,冲积扇碎屑物源为盆地周缘的灰岩等沉积岩类;第二岩性段为更新统下部（2.6-1.0 Ma）,三角洲相沉积,沉积物来自盆地南缘中条山北部和东缘太行山西部的太古宇—下元古界的花岗片麻岩和片麻岩、上元古界—古生界的碳酸盐岩、中生界的陆源碎屑岩及少量不同时代的花岗岩;第三段为更新统中上部（〈1.0 Ma）,河流相沉积,主要物源为盆地北东缘太行山的花岗岩类、少量沉积岩和变质岩。结合区域应力演化过程认为,距今5.0-2.6 Ma期间,受北西—南东向伸展作用影响,北东—南西向正断层为盆地的主控断层;距今2.6-1.0 Ma时期,主要受到北东—南西伸展应力的影响,近东西向断层开始活动;距今1.0 Ma以来,沉积环境由三角洲和湖泊相转为河流相沉积,指示盆地发育的减弱,可能与后一期伸展应力的减弱有关。上述结果表明,受青藏高原向北东扩展的影响,汾渭地堑系至少经历了中新世晚期—上新世早期（〉5 Ma）、2.6 Ma和1.0 Ma等主要构造转换时代。

Linfen Basin is located in middle-southern part of the Fenwei Graben systems,North China Craton. As a late Cenozoic rift basin,it was defined by the northeast-striking and east-striking normal faults. Comprehensive constraints of sedimentary facies and provenance of the Chaizhuang section in the middle part of the basin indicating that the section can be divided into three units with different source areas,with some loess on the top of the section. This may provide important clues for exploring the tectonic setting of the basin evolution. Unit 1 in Pliocene（ 5 ~ 2. 6 Ma） was deposited in alluvial fan and eolian environment with the nearby sedimentary rocks（ i. e.limestone） to be the main source rocks. Unit 2 in the lower part of the Pleistocene（ 2. 6 ~ 1. 0 Ma）was deposited in a delta environment with mixed source rocks shed from Taihang Mountains and Zhongtiao Mountains on the eastern and southeastern of the basin,which include the ArcheanPalaeoproterozoic granitic gneiss and gneiss, Neoproterozoic-Paleozoic carbonatite, Mesozoic terrigenous clastic rocks and some granitoids. Unit 3 in the upper part of the Pleistocene（ 〈1.0 Ma） was deposited in a fluvial environment with the acidic magmatic rocks derived from the Taihang Mountains on the northeastern of the basin. Combined with the late Cenozoic regional regime evolution of the Shanxi Graben,we proposed that the northeast-striking normal faults were strongly active in Pliocene and influenced by the transtensional stress regime under NW-SE extension. The east-striking faults seem to be active in early Pleistocene（ 2. 6 ~ 1. 0 Ma） and were influenced by the NE-SW extension. From 1. 0 Ma,the fluvial replaced the delta and lacustrine sedimentary environments. This indicates that the basin evolution is not as strong as in early Pleistocene which may be a result of the weakening of the extension. All these clues indicate that the main tectonic transition ages in Fenwei Graben systems influenced by the Tibetan in PliocenePleistocene may include Late Miocene-early Pliocene（ 5. 0 Ma）,2. 6 Ma and 1. 0 Ma.