本文主要研究内容
作者陈冠旭（2019）在《鄂尔多斯地块西南部元古宙地质建造的构造意义研究》一文中研究指出：在华北地块西南部出露的元古宙地层主要由长城系熊耳群(ChX)、高山河群(ChG)、蓟县系官道口群(JxG)和少量震旦系罗圈组(Zl)组成,这些地层的出露范围不大,但是它们与华北地块南部熊耳山、崤山和小秦岭一带出露的同时代地层在岩石组合、形成环境、形成时代和软沉积变形等方面都有显著差异,这种差异是由什么原因造成的?为什么在鄂尔多斯地块西南部会零星出露这些元古宙地层?反映何种构造意义?论文针对这些问题对鄂尔多斯地块西南部出露的熊耳群、高山河群和官道口群地层分别进行了岩石学、地质年代学、地球化学和软沉积变形等方面的研究。地学界目前对震旦系罗圈组的认识相对比较一致,本文没有对震旦系罗圈组开展相关研究。论文以鄂尔多斯地块西南部岐山县庙坡里和凤翔县长青地区(也即千阳县冯家山水库南侧)出露的元古宇熊耳群、高山河群和官道口群为研究对象,在野外地质调查的基础上,通过对各岩石地层单元详细的岩石学、岩相学、地球化学、软沉积变形构造和锆石U-Pb年代学研究,结合前人研究成果和区域大地构造背景分析,进一步确定研究区元古宇的空间分布特征与形成时的构造环境特点,进而探讨华北地块西南部的元古宙构造演化史,为进一步深化地学界对华北地块元古宙构造演化的现有认识提供新资料。为了把鄂尔多斯地块西南部的熊耳群与华北地块南部经典的熊耳群区别开来,本文把鄂尔多斯地块西南部原熊耳群中的绿片岩系称为长青绿片岩,把原熊耳群中浅变质碎屑岩-碳酸盐岩称为长青浅变质碎屑岩-碳酸盐岩。论文主要取得了以下研究成果:(1)通过对长青绿片岩的岩石学、地球化学和地质年代学研究,确定这套绿片岩的原岩为大陆拉斑玄武岩,形成时代为晚三叠世-早侏罗世,反映晚三叠世-早侏罗世鄂尔多斯地块西南部处于强烈的伸展构造环境。绿片岩与周围地层以断层接触,论文通过对绿片岩的锆石U-Pb测年和绿片岩中粉砂岩夹层的碎屑锆石U-Pb测年并结合区域地质资料间接确定绿片岩的形成时代。对绿片岩中36粒锆石进行的U-Pb LA-ICP-MS测年得到年龄2455~393Ma,对绿片岩中两层粉砂岩夹层进行的碎屑锆石U-Pb LA-ICP-MS测年分别得到年龄2462~206Ma和3039~194Ma,结合区域地质资料和其他研究者的相关研究成果,论文认为将绿片岩原岩的形成时代确定为晚三叠-早侏罗世比较合适。绿片岩出露区位于六盘山南段,推断早白垩世在六盘山构造带整体沉降的背景下在玄武岩之上沉积了巨厚的下白垩统六盘山群碎屑岩,在研究区西边不远处的宝鸡市县功镇现今仍残存累计厚度超过3678m的六盘山群碎屑岩,玄武岩由于深埋而遭受绿片岩相变质作用。晚白垩世,绿片岩由于六盘山断裂带斜向走滑被抬升,同时上覆下白垩统被剥蚀殆尽,整个六盘山构造带缺失上白垩统。从玄武岩到绿片岩的另外一种可能机制是六盘山断裂带内的动力变质作用。虽然本文的地质年代学数据将玄武岩的形成时代指向晚三叠-早侏罗世,但是从玄武岩到绿片岩的变质机制仍然是一个值得进一步研究的问题。(2)通过对长青浅变质碎屑岩进行的碎屑锆石LA-ICP-MS U-Pb测年将这套浅变质碎屑岩划归南华系,这可能是华北地块南部首次揭露南华系地层信息。对浅变质碎屑岩进行的碎屑锆石U-Pb测年分别获得年龄2708~753Ma、2507~854Ma和2735~1444Ma,说明浅变质碎屑岩的沉积时间应该晚于753Ma。考虑到官道口群之上被震旦系罗圈组以平行不整合覆盖,而且震旦系之上整合覆盖着寒武-奥陶系,推断浅变质碎屑岩的沉积时间应该在753Ma之后、震旦纪之前,这个时间段对应新元古代南华纪。这套南华系浅变质岩系与上三叠统-下侏罗统绿片岩之间以正断层接触,绿片岩位于正断层上盘。南华系浅变质碎屑岩-碳酸盐岩的底界未出露,出露厚度约600m。南华系浅变质碎屑岩-碳酸盐岩建造应该形成于大陆边缘的海槽环境,从下向上反映海水变浅的沉积序列。(3)根据长青浅变质碎屑岩中碎屑锆石U-Pb LA-ICP-MS测年结果探讨了这套浅变质碎屑岩的物源特征。碎屑锆石年龄谱系与鄂尔多斯基底在华北地块基底克拉通化(~1.9-1.8Ga)之前的年龄谱系具有很大的相似性,但是在克拉通化之后就有比较大的差异,说明鄂尔多斯地块西南部在华北地块基底克拉通化之后受到周围邻区大地构造单元的明显影响,这与该地区处于多个大地构造单元交汇部位的大地构造环境是一致的。(4)详细研究了岐山县庙坡里剖面蓟县系官道口群碳酸盐岩中的软沉积变形构造,并在其中识别出震积构造。庙坡里剖面官道口群碳酸盐岩中的软沉积构造根据成因可以分为两大类:(1)由成岩作用形成的软沉积构造;(2)由地震活动造成的软沉积构造,即震积构造。由成岩作用造成的软沉积构造包括火焰构造、燧石层球形化和包卷层理等。由地震活动造成的软沉积变形构造包括微断层、自碎屑角砾岩和球枕构造。由于官道口群的岩石成分相对比较单一(碳酸盐岩夹燧石团块或燧石条带),沉积物的密度差比较小,各向异性比较弱,由此导致官道口群碳酸盐岩中震积构造的种类相对比较少,强度也相对比较弱。震积构造反映当时该地区受到邻区地震作用和震积事件的显著影响,意味着该地区当时应该紧邻构造活动带。据区域地质资料推断,蓟县系官道口群沉积之时很可能受到南方宽坪洋盆活动的影响。(5)对官道口群碳酸盐岩和南华系浅变质碎屑岩-碳酸盐岩沉积环境的分析表明,这些地层在沉积之时受到邻区构造活动的影响比较明显,说明研究区在官道口群和南华系沉积之时就处于鄂尔多斯地块的边缘部位。换句话说,现今的鄂尔多斯地块西南边界在官道口群和南华系沉积之时就是鄂尔多斯地块的西南边界。岐山县庙坡里剖面与冯家山水库西南部官道口群剖面相距并不太远(约41km),但是沉积环境差异明显,前者形成于碳酸盐岩台地环境,而后者形成于大陆边缘环境。庙坡里剖面官道口群中的震积构造反映受到邻区构造活动影响比较明显,沉积区距离鄂尔多斯地块边缘不太远。南华系碎屑岩中大量出现周边大地构造单元的岩浆锆石,这些都反映研究区在新元古代时就处于鄂尔多斯地块的边缘部位。(6)作者和项目组成员在野外地质调查过程中,在前人认为应该是长城系高山河群(ChG)出露的多条剖面上并没有观察到高山河群,为此论文质疑在鄂尔多斯地块西南部的露头区是否存在高山河群。根据前人的资料,鄂尔多斯地块西南部高山河群露头区的范围并不大,作者和项目组成员在前人资料中标注的高山河群露头区考察了4条地质剖面,但是我们均未观察到高山河群典型的岩石组合,我们在所谓的高山河群露头区观察到绿片岩,而绿片岩应该是原熊耳群的组成部分(也就是本文的长青绿片岩)。关于在鄂尔多斯盆地西南部露头区是否存在高山河群的问题有待以后进一步研究确认。
Abstract
zai hua bei de kuai xi na bu chu lou de yuan gu zhou de ceng zhu yao you chang cheng ji xiong er qun (ChX)、gao shan he qun (ChG)、ji xian ji guan dao kou qun (JxG)he shao liang zhen dan ji luo juan zu (Zl)zu cheng ,zhe xie de ceng de chu lou fan wei bu da ,dan shi ta men yu hua bei de kuai na bu xiong er shan 、xiao shan he xiao qin ling yi dai chu lou de tong shi dai de ceng zai yan dan zu ge 、xing cheng huan jing 、xing cheng shi dai he ruan chen ji bian xing deng fang mian dou you xian zhe cha yi ,zhe chong cha yi shi you shen me yuan yin zao cheng de ?wei shen me zai e er duo si de kuai xi na bu hui ling xing chu lou zhe xie yuan gu zhou de ceng ?fan ying he chong gou zao yi yi ?lun wen zhen dui zhe xie wen ti dui e er duo si de kuai xi na bu chu lou de xiong er qun 、gao shan he qun he guan dao kou qun de ceng fen bie jin hang le yan dan xue 、de zhi nian dai xue 、de qiu hua xue he ruan chen ji bian xing deng fang mian de yan jiu 。de xue jie mu qian dui zhen dan ji luo juan zu de ren shi xiang dui bi jiao yi zhi ,ben wen mei you dui zhen dan ji luo juan zu kai zhan xiang guan yan jiu 。lun wen yi e er duo si de kuai xi na bu qi shan xian miao po li he feng xiang xian chang qing de ou (ye ji qian yang xian feng jia shan shui ku na ce )chu lou de yuan gu yu xiong er qun 、gao shan he qun he guan dao kou qun wei yan jiu dui xiang ,zai ye wai de zhi diao cha de ji chu shang ,tong guo dui ge yan dan de ceng chan yuan xiang xi de yan dan xue 、yan xiang xue 、de qiu hua xue 、ruan chen ji bian xing gou zao he gao dan U-Pbnian dai xue yan jiu ,jie ge qian ren yan jiu cheng guo he ou yu da de gou zao bei jing fen xi ,jin yi bu que ding yan jiu ou yuan gu yu de kong jian fen bu te zheng yu xing cheng shi de gou zao huan jing te dian ,jin er tan tao hua bei de kuai xi na bu de yuan gu zhou gou zao yan hua shi ,wei jin yi bu shen hua de xue jie dui hua bei de kuai yuan gu zhou gou zao yan hua de xian you ren shi di gong xin zi liao 。wei le ba e er duo si de kuai xi na bu de xiong er qun yu hua bei de kuai na bu jing dian de xiong er qun ou bie kai lai ,ben wen ba e er duo si de kuai xi na bu yuan xiong er qun zhong de lu pian yan ji chen wei chang qing lu pian yan ,ba yuan xiong er qun zhong jian bian zhi sui xie yan -tan suan yan yan chen wei chang qing jian bian zhi sui xie yan -tan suan yan yan 。lun wen zhu yao qu de le yi xia yan jiu cheng guo :(1)tong guo dui chang qing lu pian yan de yan dan xue 、de qiu hua xue he de zhi nian dai xue yan jiu ,que ding zhe tao lu pian yan de yuan yan wei da liu la ban xuan wu yan ,xing cheng shi dai wei wan san die shi -zao zhu luo shi ,fan ying wan san die shi -zao zhu luo shi e er duo si de kuai xi na bu chu yu jiang lie de shen zhan gou zao huan jing 。lu pian yan yu zhou wei de ceng yi duan ceng jie chu ,lun wen tong guo dui lu pian yan de gao dan U-Pbce nian he lu pian yan zhong fen sha yan ga ceng de sui xie gao dan U-Pbce nian bing jie ge ou yu de zhi zi liao jian jie que ding lu pian yan de xing cheng shi dai 。dui lu pian yan zhong 36li gao dan jin hang de U-Pb LA-ICP-MSce nian de dao nian ling 2455~393Ma,dui lu pian yan zhong liang ceng fen sha yan ga ceng jin hang de sui xie gao dan U-Pb LA-ICP-MSce nian fen bie de dao nian ling 2462~206Mahe 3039~194Ma,jie ge ou yu de zhi zi liao he ji ta yan jiu zhe de xiang guan yan jiu cheng guo ,lun wen ren wei jiang lu pian yan yuan yan de xing cheng shi dai que ding wei wan san die -zao zhu luo shi bi jiao ge kuo 。lu pian yan chu lou ou wei yu liu pan shan na duan ,tui duan zao bai e shi zai liu pan shan gou zao dai zheng ti chen jiang de bei jing xia zai xuan wu yan zhi shang chen ji le ju hou de xia bai e tong liu pan shan qun sui xie yan ,zai yan jiu ou xi bian bu yuan chu de bao ji shi xian gong zhen xian jin reng can cun lei ji hou du chao guo 3678mde liu pan shan qun sui xie yan ,xuan wu yan you yu shen mai er zao shou lu pian yan xiang bian zhi zuo yong 。wan bai e shi ,lu pian yan you yu liu pan shan duan lie dai xie xiang zou hua bei tai sheng ,tong shi shang fu xia bai e tong bei bao shi dai jin ,zheng ge liu pan shan gou zao dai que shi shang bai e tong 。cong xuan wu yan dao lu pian yan de ling wai yi chong ke neng ji zhi shi liu pan shan duan lie dai nei de dong li bian zhi zuo yong 。sui ran ben wen de de zhi nian dai xue shu ju jiang xuan wu yan de xing cheng shi dai zhi xiang wan san die -zao zhu luo shi ,dan shi cong xuan wu yan dao lu pian yan de bian zhi ji zhi reng ran shi yi ge zhi de jin yi bu yan jiu de wen ti 。(2)tong guo dui chang qing jian bian zhi sui xie yan jin hang de sui xie gao dan LA-ICP-MS U-Pbce nian jiang zhe tao jian bian zhi sui xie yan hua gui na hua ji ,zhe ke neng shi hua bei de kuai na bu shou ci jie lou na hua ji de ceng xin xi 。dui jian bian zhi sui xie yan jin hang de sui xie gao dan U-Pbce nian fen bie huo de nian ling 2708~753Ma、2507~854Mahe 2735~1444Ma,shui ming jian bian zhi sui xie yan de chen ji shi jian ying gai wan yu 753Ma。kao lv dao guan dao kou qun zhi shang bei zhen dan ji luo juan zu yi ping hang bu zheng ge fu gai ,er ju zhen dan ji zhi shang zheng ge fu gai zhao han wu -ao tao ji ,tui duan jian bian zhi sui xie yan de chen ji shi jian ying gai zai 753Mazhi hou 、zhen dan ji zhi qian ,zhe ge shi jian duan dui ying xin yuan gu dai na hua ji 。zhe tao na hua ji jian bian zhi yan ji yu shang san die tong -xia zhu luo tong lu pian yan zhi jian yi zheng duan ceng jie chu ,lu pian yan wei yu zheng duan ceng shang pan 。na hua ji jian bian zhi sui xie yan -tan suan yan yan de de jie wei chu lou ,chu lou hou du yao 600m。na hua ji jian bian zhi sui xie yan -tan suan yan yan jian zao ying gai xing cheng yu da liu bian yuan de hai cao huan jing ,cong xia xiang shang fan ying hai shui bian jian de chen ji xu lie 。(3)gen ju chang qing jian bian zhi sui xie yan zhong sui xie gao dan U-Pb LA-ICP-MSce nian jie guo tan tao le zhe tao jian bian zhi sui xie yan de wu yuan te zheng 。sui xie gao dan nian ling pu ji yu e er duo si ji de zai hua bei de kuai ji de ke la tong hua (~1.9-1.8Ga)zhi qian de nian ling pu ji ju you hen da de xiang shi xing ,dan shi zai ke la tong hua zhi hou jiu you bi jiao da de cha yi ,shui ming e er duo si de kuai xi na bu zai hua bei de kuai ji de ke la tong hua zhi hou shou dao zhou wei lin ou da de gou zao chan yuan de ming xian ying xiang ,zhe yu gai de ou chu yu duo ge da de gou zao chan yuan jiao hui bu wei de da de gou zao huan jing shi yi zhi de 。(4)xiang xi yan jiu le qi shan xian miao po li pou mian ji xian ji guan dao kou qun tan suan yan yan zhong de ruan chen ji bian xing gou zao ,bing zai ji zhong shi bie chu zhen ji gou zao 。miao po li pou mian guan dao kou qun tan suan yan yan zhong de ruan chen ji gou zao gen ju cheng yin ke yi fen wei liang da lei :(1)you cheng yan zuo yong xing cheng de ruan chen ji gou zao ;(2)you de zhen huo dong zao cheng de ruan chen ji gou zao ,ji zhen ji gou zao 。you cheng yan zuo yong zao cheng de ruan chen ji gou zao bao gua huo yan gou zao 、sui dan ceng qiu xing hua he bao juan ceng li deng 。you de zhen huo dong zao cheng de ruan chen ji bian xing gou zao bao gua wei duan ceng 、zi sui xie jiao li yan he qiu zhen gou zao 。you yu guan dao kou qun de yan dan cheng fen xiang dui bi jiao chan yi (tan suan yan yan ga sui dan tuan kuai huo sui dan tiao dai ),chen ji wu de mi du cha bi jiao xiao ,ge xiang yi xing bi jiao ruo ,you ci dao zhi guan dao kou qun tan suan yan yan zhong zhen ji gou zao de chong lei xiang dui bi jiao shao ,jiang du ye xiang dui bi jiao ruo 。zhen ji gou zao fan ying dang shi gai de ou shou dao lin ou de zhen zuo yong he zhen ji shi jian de xian zhe ying xiang ,yi wei zhao gai de ou dang shi ying gai jin lin gou zao huo dong dai 。ju ou yu de zhi zi liao tui duan ,ji xian ji guan dao kou qun chen ji zhi shi hen ke neng shou dao na fang kuan ping xiang pen huo dong de ying xiang 。(5)dui guan dao kou qun tan suan yan yan he na hua ji jian bian zhi sui xie yan -tan suan yan yan chen ji huan jing de fen xi biao ming ,zhe xie de ceng zai chen ji zhi shi shou dao lin ou gou zao huo dong de ying xiang bi jiao ming xian ,shui ming yan jiu ou zai guan dao kou qun he na hua ji chen ji zhi shi jiu chu yu e er duo si de kuai de bian yuan bu wei 。huan gou hua shui ,xian jin de e er duo si de kuai xi na bian jie zai guan dao kou qun he na hua ji chen ji zhi shi jiu shi e er duo si de kuai de xi na bian jie 。qi shan xian miao po li pou mian yu feng jia shan shui ku xi na bu guan dao kou qun pou mian xiang ju bing bu tai yuan (yao 41km),dan shi chen ji huan jing cha yi ming xian ,qian zhe xing cheng yu tan suan yan yan tai de huan jing ,er hou zhe xing cheng yu da liu bian yuan huan jing 。miao po li pou mian guan dao kou qun zhong de zhen ji gou zao fan ying shou dao lin ou gou zao huo dong ying xiang bi jiao ming xian ,chen ji ou ju li e er duo si de kuai bian yuan bu tai yuan 。na hua ji sui xie yan zhong da liang chu xian zhou bian da de gou zao chan yuan de yan jiang gao dan ,zhe xie dou fan ying yan jiu ou zai xin yuan gu dai shi jiu chu yu e er duo si de kuai de bian yuan bu wei 。(6)zuo zhe he xiang mu zu cheng yuan zai ye wai de zhi diao cha guo cheng zhong ,zai qian ren ren wei ying gai shi chang cheng ji gao shan he qun (ChG)chu lou de duo tiao pou mian shang bing mei you guan cha dao gao shan he qun ,wei ci lun wen zhi yi zai e er duo si de kuai xi na bu de lou tou ou shi fou cun zai gao shan he qun 。gen ju qian ren de zi liao ,e er duo si de kuai xi na bu gao shan he qun lou tou ou de fan wei bing bu da ,zuo zhe he xiang mu zu cheng yuan zai qian ren zi liao zhong biao zhu de gao shan he qun lou tou ou kao cha le 4tiao de zhi pou mian ,dan shi wo men jun wei guan cha dao gao shan he qun dian xing de yan dan zu ge ,wo men zai suo wei de gao shan he qun lou tou ou guan cha dao lu pian yan ,er lu pian yan ying gai shi yuan xiong er qun de zu cheng bu fen (ye jiu shi ben wen de chang qing lu pian yan )。guan yu zai e er duo si pen de xi na bu lou tou ou shi fou cun zai gao shan he qun de wen ti you dai yi hou jin yi bu yan jiu que ren 。
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