中国东部四明山古夷平面遗迹特征与演化
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摘要
古夷平面研究在地貌演化和新构造运动研究中占有极其重要的地位,但由于遭受构造运动和剥蚀作用的影响,很多古夷平面遗迹已无从清晰辨识。浙江四明山顶古近纪夷平古风化壳面的发现,为研究浙江东部甚至华东地区的新生代地貌演化提供了重要地质信息,同时为始新世和中新世时的古气候、古环境研究提供了重要物质证据。通过详细的野外地质调查,系统采集了该区5个点位的20个古风化壳样品和7个点位的15个现代风化壳样品,开展黏土矿物分析和玄武岩K-Ar年龄测试。研究确认四明山地区发育有2期古夷平面遗迹,即古近纪(E)和新近纪(N)古夷平面遗迹:第一期夷平面发育时间为65. 0～32. 2 Ma,解体和古夷平面遗迹保存时间为32. 2～21. 7 Ma;第二期夷平面发育时间为21. 7～10. 5 Ma,解体和古夷平面遗迹保存时间为10. 5～3. 0 Ma。研究区2期火山活动喷发所形成的玄武岩盖层有效保护了该区的古风化壳,从而使四明山古夷平面遗迹具有空间展布完整、剖面信息清晰等特征,呈现出由古夷平面(古风化壳)与玄武岩堆积面(现代风化壳)组成的"双风化壳"现象,为观察古夷平面遗迹特征提供了最佳场所。
Ancient planation surface plays an important role in the research of geomorphological evolution and neotectonics. However,many ancient planation surfaces are hard to be identified due to the influence of tectonics and erosion. The Paleogene planation surface at the top of Siming Mountain reveals important geological information on the Cenozoic geomorphological evolution of eastern Zhejiang or even East China,as well as important evidence for the research of the paleoclimate and paleoenvironment during the Eocene and Miocene. Based on detailed field investigation,this work collected 20 ancient planation surface samples from 5 sites and 15 modern planation surface samples at 7 sites to conduct clay mineral analysis and K-Ar dating of basalt. It confirms that there are two stages of ancient planation surfaces in this area,which were formed in the Paleogene( E) and Neogene( N),respectively. The first stage of planation surface was developed during 65. 0-32. 2 Ma,and disintegrated and preserved during 32. 2-21. 7 Ma; the second stage of planation surface was developed during 21. 7-10. 5 Ma and disintegrated and preserved at 10. 5-3. 0 Ma. The overlying basalt layers,formed during the 2 volcanic activities,have effectively protected the ancient weathered crusts,such that the relics of ancient planation surfaces have a complete spatial distribution and clear section information. The double-weathered crusts,composed of ancient planation surface( ancient weathered crust) and basalt layers( modern weathered crust),become a perfect site for studying the relics of ancient planation surface.
Ancient planation surface plays an important role in the research of geomorphological evolution and neotectonics. However,many ancient planation surfaces are hard to be identified due to the influence of tectonics and erosion. The Paleogene planation surface at the top of Siming Mountain reveals important geological information on the Cenozoic geomorphological evolution of eastern Zhejiang or even East China,as well as important evidence for the research of the paleoclimate and paleoenvironment during the Eocene and Miocene. Based on detailed field investigation,this work collected 20 ancient planation surface samples from 5 sites and 15 modern planation surface samples at 7 sites to conduct clay mineral analysis and K-Ar dating of basalt. It confirms that there are two stages of ancient planation surfaces in this area,which were formed in the Paleogene( E) and Neogene( N),respectively. The first stage of planation surface was developed during 65. 0-32. 2 Ma,and disintegrated and preserved during 32. 2-21. 7 Ma; the second stage of planation surface was developed during 21. 7-10. 5 Ma and disintegrated and preserved at 10. 5-3. 0 Ma. The overlying basalt layers,formed during the 2 volcanic activities,have effectively protected the ancient weathered crusts,such that the relics of ancient planation surfaces have a complete spatial distribution and clear section information. The double-weathered crusts,composed of ancient planation surface( ancient weathered crust) and basalt layers( modern weathered crust),become a perfect site for studying the relics of ancient planation surface.
引文
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徐义刚,魏静娴,邱华宁,等,2012.用火山岩制约南海的形成演化:初步认识与研究思想[J].科学通报,57(20):1883-1878.
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Zhou Xinmin,Li Wuxian,2000.Origin of Late Mesozoic igneous rocks in Southeastern China:implications for lithosphere subduction and underplating of mafic magmas[J].Tectonophysics,326(3/4):269-287.
Zou Haibo,Zindler A,Xu Xisheng,et al.,2000.Major,trace element,and Nd,Sr and Pb isotope studies of Cenozoic basalts in SE China:mantle sources,regional variations,and tectonic significance[J].Chemical Geology,171(1/2):33-47.
Zhou Xinmin,Sun Tao,Shen Weizhou,et al.,2006.Petrogenesis of Mesozoic granitoids and volcanic rocks in South China:a response to tectonic evolution[J].Episodes,29(1):26-33.
崔之久,李德文,冯金良,等,2001.夷平面研究的再评述[J].科学通报,46(21):1761-1768.
邓焰平,洪汉烈,殷科,等,2010.兰州盆地永登剖面晚古新世-早渐新世沉积物中黏土矿物的特征及其古气候指示意义[J].现代地质,24(4):793-800.
冯金良,崔之久,朱立平,等,2005.夷平面研究评述[J].山地学报,23(1):1-13.
洪汉烈,于娜,薛惠娟,等,2007.临夏盆地晚更新世沉积物黏土矿物的特征及其古气候指示[J].现代地质,21(2):406-414.
洪汉烈,王朝文,徐耀明,等,2010.青藏高原新生代以来气候环境演化的黏土矿物学特征[J].地球科学,35(5):728-736.
卢炳生,张环,林金波,2013.四明山夷平面特征及成因[J].现代矿业,29(3):56-57.
潘保田,高红山,李吉均,2002.关于夷平面的科学问题:兼论青藏高原夷平面[J].地理科学,22(5):520-526
任雪梅,陈忠,罗丽霞,等,2003.夷平面研究综述[J].地理科学,24(1):107-111.
师育新,戴雪荣,宋之光,等,2005.我国不同气候带黄土中黏土矿物组合特征分析[J].沉积学报,23(4):690-695.
单莉莉,张晋飚,许红根,等,2010.四明山夷平面与玄武岩复合台地景观特征与开发研究[J].山西农业科学,38(8):41-44,83.
徐义刚,魏静娴,邱华宁,等,2012.用火山岩制约南海的形成演化:初步认识与研究思想[J].科学通报,57(20):1883-1878.
浙江省区域地质调查大队,1980.1∶20万宁波幅、余姚幅等五幅区域地质调查报告[R].杭州:浙江省地质调查院.
曾罡,郑丽波,陈立辉,等,2017.南海洋脊抽吸作用对其周边新生代玄武质岩浆活动的影响[J].高校地质学报,23(3):373-382
Li Zhengxiang,Li Xianhua,2007.Formation of the 1 300-kmwide intracontinentalorogen and postorogenic magmatic province in Mesozoic South China:A flat-slab subduction model[J].Geology,35(2):179-182.
Steiger R H,Jger E,1977.Subcommission on geochronology:convention on the use of decay constants in geo-and cosmochronology[J].Earth and Planetary Science Letters,36(3):359-362.
Yu Xun,Chen Lihui,Zeng Gang,[2015-11-19].Growing magma chambers control the distribution of small-scale flood basalts[J/OL].Scientific Reports,5:16824.doi:10.1038/srep16824.https://www.nature.com/curticls/srep16824.
Zhou Xinmin,Li Wuxian,2000.Origin of Late Mesozoic igneous rocks in Southeastern China:implications for lithosphere subduction and underplating of mafic magmas[J].Tectonophysics,326(3/4):269-287.
Zou Haibo,Zindler A,Xu Xisheng,et al.,2000.Major,trace element,and Nd,Sr and Pb isotope studies of Cenozoic basalts in SE China:mantle sources,regional variations,and tectonic significance[J].Chemical Geology,171(1/2):33-47.
Zhou Xinmin,Sun Tao,Shen Weizhou,et al.,2006.Petrogenesis of Mesozoic granitoids and volcanic rocks in South China:a response to tectonic evolution[J].Episodes,29(1):26-33.