华北克拉通北缘的中元古代多旋回复合盆地及其地质意义：来自碎屑锆石U-Pb年龄的统计学证据*

钟焱 相振群 初航**

1. 中国地质调查局天津地质调查中心，天津 3001702. 中国地质调查局前寒武纪地质研究中心，天津 300170

中、新元古代的华北克拉通主要存在4个张裂程度和发育时序均有不同的沉积盆地(图1a，翟明国等，2014)，其中，新元古界主要发育在北缘和东缘盆地，中元古界则以熊耳、燕辽和北缘盆地保存较好。燕辽盆地的蓟县剖面具有地层连续性好、后期改造弱、出露和保存程度俱佳的优势，因此长期以来一直是我国中、新元古界划分与对比的标准剖面(陈晋镳等，1980)。根据近年来的一系列年代地层学研究成果(详见Lietal., 2013；苏文博，2016)，2014版《中国地层表》(全国地层委员会，2014)将我国的晚前寒武系年代地层序列，自下而上修订为：中元古界长城系(1.80～1.6Ga)、蓟县系(1.6～1.4Ga)、待建系(1.4～1.0Ga)和新元古界青白口系(1.0～0.78Ga)、南华系(780～635Ma)、震旦系(635～541Ma)。此后，我国的中元古代综合地层学研究出现了三个亟待解答的新问题：即查明各盆地的发育与演化机制、寻找长城系下部1.8～1.65Ga岩石地层单元、完善1.4～1.0Ga待建系标准剖面(耿元生和陆松年，2014)。

图1 华北克拉通晚前寒武纪沉积盆地(a, 据Zhai et al., 2015)和采样区地质简图(b,据Zhong et al., 2015修改)[1]熊耳裂谷；[2]北缘裂谷系；[3]燕辽裂谷；[4]东缘裂谷Fig.1 Late Precambrian basins in the North China Craton (a, after Zhai et al., 2015) and simplified geologic map of the sampling area (b, after Zhong et al., 2015)[1] Xiong’er rift; [2] Northern marginal rift system; [3] Yanliao rift; [4] Eastern marginal rift

与国际地层表建议的1.6Ga不同，我国地质学界坚持将古、中元古代的界限置于1.8Ga，这一主张继承自“华北陆块1.8Ga以后进入稳定地台演化阶段(赵宗溥，1993)”的传统认识。随着蓟县剖面长城群的沉积时代被修订为1.65～1.60Ga(全国地层委员会讨论通过，耿元生和陆松年，2014)，我国的中元古界标准剖面——蓟县剖面自此缺失1.80～1.65Ga的沉积记录。对此，已有学者提出“华北南部的熊耳群火山岩系是发育时代早于燕辽地区长城群的地层单元，填补了(华北克拉通)从结晶基底形成到接受稳定盖层沉积的转折期地质记录空白”(赵太平等，2015)。查明华北其他地区是否存在这一时期的沉积作用记录，将为理解华北克拉通1.80～1.65Ga的构造演化状态(稳定地台或过渡阶段)提供直接依据。已有研究显示，渣尔泰群的下部存在～1.75Ga的火山岩(Lietal., 2007)，暗示北缘盆地可能是开展中元古代早期阶段沉积、岩浆作用研究的关键地区。

我国前寒武纪地层学研究近年来最显著的进展之一是将下马岭组沉积时代修订至1.40～1.35Ga(Lietal., 2013)，其主要依据一是发现了数层时代为1.38～1.36Ga的斑脱岩或凝灰岩夹层(高林志等，2007，2008a, b；Suetal., 2008, 2010)，另一依据则是～1.32Ga基性侵入岩的识别(李怀坤等，2009b；Zhangetal., 2012)。这一进展打破了燕辽盆地从长城纪到青白口纪近于连续沉积的传统认识、促成了“待建系”地层单元的建立(耿元生和陆松年，2014)。华北南缘地区洛峪群顶部1.64～1.61Ga凝灰岩夹层的发现，使得洛峪群及其下部汝阳群的地层时代被调整至长城纪(苏文博等，2012；李承东等，2017)，这一成果势必导致华北南缘地区中元古代地层对比格架的重大变革，同时也说明熊耳盆地、至少是其北部地区(即渑池-确山地层小区)，并未参与蓟县纪-待建纪的盆地演化过程。至于华北北部，燕辽盆地缺失除下马岭组之外的大部分待建系地层，表明燕辽地区在1.35Ga以后可能处于隆起区。与上述地区相比，尽管华北克拉通北缘的白云鄂博群、化德群分别被1.34Ga辉绿岩(周志广等，2016)、1.33～1.31Ga花岗岩(Shietal., 2012；Zhangetal., 2012)侵入，但华北北缘是否存在待建系地层？其时代、分布范围和盆地演化过程如何？这些问题目前尚无系统研究。

华北克拉通晚前寒武纪盆地的发育机制和演化过程长期以来存在多种解释。例如对于熊耳盆地的构造属性即有裂谷/拗拉槽(孙枢等，1981，1982；Zhaoetal., 2002b；Houetal., 2008)、地幔柱(Pengetal., 2008)或安第斯型大陆边缘(Zhaoetal., 2009; Heetal., 2010)等不同认识；对于燕辽盆地的大地构造属性，除多数学者认同的裂谷模式外，也有观点提出该盆地的发育与华北克拉通北部古元古代造山事件后的伸展过程有关(Zhangetal., 2007; Wangetal., 2015)；相对而言，有关北缘盆地成因的争议不大，我国地质学界普遍认为中、新元古代的华北克拉通北缘长期处于“陆缘裂谷系”的大地构造背景(王楫等，1992)。关于晚前寒武纪裂谷事件的成因，目前存在两种主要观点，其一认为“裂谷事件是华北克拉通对元古宙超大陆裂解过程的响应(Zhaoetal., 2004; Zhangetal., 2009, 2012, 2017a, b)”；而另一种观点，即“中、新元古代多期裂谷事件”模式则认为，长期持续的伸展过程或者指示华北克拉通一直位于超大陆的边缘位置、或者说明元古宙超大陆的演化过程可能并不具有全球性(翟明国等，2014；Zhaietal., 2015)。北缘盆地的区位优势对于厘清上述争议十分关键，但目前的研究资料并不足以精细刻画这一地区的中元古代构造演化过程。

作为碎屑岩中最常见的副矿物，锆石具有较稳定的U-Pb同位素体系，碎屑锆石年代学统计结果因此常被用于约束最大沉积时代、反映源区物质年代学组成和识别沉积间断等(Fedoetal., 2003)。本研究对北缘盆地渣尔泰群、白云鄂博群的部分层位进行了碎屑锆石U-Pb同位素分析，同时归类整理了白云鄂博群、渣尔泰群和化德群现有的碎屑锆石年代学数据。参考Cawoodetal.(2012)和Couttsetal.(2019)的分析方法，本文对新取得的和前人已发表的锆石年代学数据进行了统计分析，结果显示：北缘盆地中元古界记录的构造属性存在从碰撞体系到伸展体系的转变，这说明中元古代的北缘盆地可能是在长城纪造山后伸展盆地之上、叠加了蓟县-待建纪裂谷事件而成的多旋回复合盆地。

1 华北北缘的晚前寒武系研究概况

从地球系统科学的角度，国际地科联提出了“以关键地质事件为界、建立前寒武纪自然主义年表”的研究理念(苏文博，2014)。中、新元古代地球系统演化过程的具体表现形式，可能是超大陆聚合、拼贴、裂解事件的往复，即Columbia-Rodinia超大陆旋回假说(Oggetal., 2016)。与全球其他地区类似，近年来华北克拉通北缘盆地的中、新元古代研究普遍围绕着“查明沉积、岩浆、变质和成矿作用是否与超大陆旋回有关”展开。根据已出露中、新元古代沉积岩的分布范围，华北的北缘盆地大体上是南沿武川-固阳一线、北至白云鄂博-四子王旗等地、东起商都、西至乌拉特后旗的带状区域，相应的岩石地层单元自西向东依次为狼山群、渣尔泰群、白云鄂博群(腮林忽洞群)和化德群。

化德群出露于商都、康保、张家营等地，该群的变形、变质程度较高，原岩沉积序列不易识别，前人曾将其解释为华北克拉通在古元古代向北增生的产物(郑建民等，2004)。通过区域对比，李承东等(2005)重新厘定了化德群的原岩序列、并将该群自下而上划分为毛忽庆组、戈家营组和三夏天组。在此基础上，后续研究发现化德群顶部的三夏天组被～1.3Ga的A型花岗岩脉侵入(Shietal., 2012; Zhangetal., 2012)、同时群内各组均发现了年轻于1.8Ga的碎屑锆石(胡波等，2009；Liuetal., 2014，2018)，化德群的沉积时限因此被限定在1.8～1.3Ga的某一阶段、归属晚前寒武系。

北缘盆地中段的固阳至白云鄂博一带，由南至北分别出露渣尔泰群、腮林忽洞群和白云鄂博群，这些地层的时代归属曾有较大争议：早期的生物地层学研究认为这些地层含有早古生代的化石组合(孙淑芬，1992；陈从云，1993；谭励可和石铁铮，2000)，近期的微生物岩和生物地层学研究再次提出，白云鄂博群与腮林忽洞群是可对比的早古生代地层(乔秀夫等，1997；章雨旭等，2008，2012)；然而，多数区域地质和年代地层学研究者认为，这些变质、变形程度较低的沉积或火山-沉积序列普遍不整合于早前寒武纪变质基底之上，应属元古界(王楫等，1992；梁玉左等，1993；梁玉左和王楫，1994；高劢等，1995；张宗清等，1997)。新近取得的研究资料充分支持了“元古界”观点，例如：腮林忽洞群顶部微晶丘的成因可能与拉张背景的海底热液活动有关(孙剑和朱祥坤，2015)、白云鄂博群下部与腮林忽洞群具有相同的源区物质组成(马铭株等，2014)、白云鄂博群下部的沉积下限晚于1.82Ga(胡波等，2009；Zhongetal., 2015)但又早于1.4Ga(Fanetal., 2014)、白云鄂博群由可与蓟县剖面对比的下部长城系、中部蓟县系和上部青白口系组成(王楫等，1992；贾和义等，2002)；仅携带早前寒武纪碎屑锆石记录的渣尔泰群，其初始沉积时代近于或略早于1.75Ga(Lietal., 2007；公王斌等，2016)等等。

北缘盆地的西段地区，出露于东升庙一带的“狼山群”曾被作为中元古界渣尔泰群的西延部分。近来已有研究指出，北缘西段地区缺失中元古代的火山-沉积记录，狼山群实际上是一套新元古代的裂谷型火山-沉积建造(彭润民等，2010；Huetal., 2014)，其所代表的裂谷事件可能与Rodinia超大陆的裂解过程有关(彭润民等，2010)。

华北北缘发育多种类型的金属、非金属矿床，如白云鄂博REE-Nb-Fe矿床(见Yangetal., 2017综述)、东升庙-甲生盘矿集区铅锌硫矿床(彭润民等，2000；付超等，2010)、赛乌苏-浩尧尔忽洞金矿床(Liuetal., 2016b)和大乌淀石墨矿(姜高珍等，2017)等。尽管成矿机制和矿化时代各有不同，但上述矿床的成矿物质普遍与围岩中的中、新元古代火山-沉积建造关系密切。早期研究认为，北缘地区中、新元古界的沉积相序和岩石组合特征指示了裂陷槽或被动陆缘背景(乔秀夫等，1991)。王楫等(1992)随后提出，北缘地区沉积-岩浆-成矿作用的特征和分布样式符合裂谷盆地的数种要素，并据此判断北缘盆地是由陆缘裂谷(白云鄂博群)和陆内裂谷(渣尔泰群)组成的陆缘裂谷系。与单纯讨论沉积体系的分布样式和盆地类型相比，陆缘裂谷系模式的突出贡献是从各个方面综合阐述了晚前寒武纪华北北缘的构造演化过程。众所周知，除了关联聚合阶段的造山带以外(Rogers and Santosh, 2002；Zhaoetal., 2002a)，裂解阶段基性岩墙群和沉积盆地的形态学恢复，也是重建超大陆地理格局的重要依据(Houetal., 2008)。Zhaoetal.(2003)认为，形成于1.6～1.2Ga的北缘裂谷系，是华北克拉通从Columbia超大陆裂解而出的关键证据。其后至今，“Columbia超大陆裂解引发陆缘裂谷事件”一直是相关研究引用的主要模型，已报道的相关裂谷事件包括：中段渣尔泰山地区～1.75Ga的基性岩浆活动(Lietal., 2007)、白云鄂博地区～1.67Ga、1.34Ga、1.23Ga的基性岩浆(Yangetal., 2011；周志广等，2016)和1.4Ga、1.3Ga的碳酸岩浆活动(Fanetal., 2014；Zhangetal., 2017b)、以及东段化德地区～1.30Ga的花岗岩侵位事件(Shietal., 2012; Zhangetal., 2012)等。

图2 华北克拉通北缘中段化德群(据李承东等，2005)、白云鄂博群(据Zhong et al., 2015)和渣尔泰群(据乔秀夫等，1991)的岩性柱状图和沉积-岩浆序列Fig.2 Sedimentary-magmatic timing sequences and lithologic columns of the Huade Group (after Li et al., 2005), Bayan Obo Group (after Zhong et al., 2015) and Zhaertai Group (after Qiao et al., 1991) in the middle part of the northern margin of NCC

2 区域地质背景

中、新元古代的沉积-岩浆作用记录在华北克拉通北缘的时空分布并不均匀，较明确的新元古代沉积记录发育在西段，包括狼山地区的青白口系狼山群(彭润民等，2010；Huetal., 2014)和千里山、贺兰山地区的南华系-震旦系黄旗口组、王全口组和正目观组(彭澎等，2018)；中元古代相关地质记录则主要分布在固阳至察右后旗地区，但其内的白云鄂博群(腮林忽洞群)和渣尔泰群中是否存在新元古代物质记录，目前仍无定论(Zhongetal., 2015；公王斌等，2016)。本文重点讨论华北克拉通北缘的中元古代构造演化过程，研究区位于北缘盆地的中、东段地区(图1b)。除晚前寒武系外(图2)，区内典型前寒武纪地质体包括：新太古代至古元古代的变质基底(王凯怡等，2001；范宏瑞等，2010；刘健等，2011；公王斌等，2016；Wuetal., 2018)、古元古代基性岩墙(周志广等，2016)、中元古代基性岩墙和碳酸岩墙(Yangetal., 2011; Fanetal., 2014; 周志广等，2016; Zhangetal., 2017b)、赋存REE-Nb-Fe矿床的碳酸岩/碳酸盐岩(成矿和成岩时代仍有前寒武纪或显生宙的争议，Zhuetal., 2015; Laietal., 2016; Yangetal., 2017; Songetal., 2018)等。

白云鄂博群自下而上包括：下亚群都拉哈拉组-尖山组、中亚群哈拉霍圪特组-比鲁特组、上亚群白音宝拉格组-呼吉尔图组，本群与下伏变质基底角度不整合接触、与上覆下古生界断层接触，群内各亚群之间为平行不整合接触(王楫等，1992；贾和义等，2002)。白云鄂博群累计厚度大于7000m，主体以海相地层为主(王楫等，1992)，底部未见冲积扇或河流相沉积序列，显示该群缺失裂谷早期阶段常见的河流相沉积。腮林忽洞群仅见于白云鄂博镇南东地区(图1b)，是一套可与白云鄂博群对比的浅变质碎屑岩-碳酸盐岩建造(乔秀夫等，1997；章雨旭等，2008；马铭株等，2014；孙剑和朱祥坤，2015；苏文博，2016)。渣尔泰群自下而上依次为：书记沟组碎屑岩、增隆昌组碎屑岩-碳酸盐岩、阿古鲁沟组碎屑岩夹碳酸盐岩、刘鸿湾组碎屑岩，其中书记沟组角度不整合于太古宙基底岩石之上，刘鸿湾组被二叠系砾岩角度不整合覆盖。渣尔泰群累积厚度大于2500m，主体由滨、浅海相沉积序列组成，陆相地层不发育、过渡相(三角洲相)仅见于书记沟组下部(王楫等，1992)；该群沉积环境以碳酸盐岩台地和台后盆地为主，相应层序地层特征指示了被动陆缘背景(乔秀夫等，1991)。化德群顶、底均不可见，累积厚度大于10000m，底部毛忽庆组以长石石英岩为主，中部戈家营组可见变粒岩、透辉岩、透辉大理岩，上部三夏天组主体为石英岩(李承东等，2005)；戈家营组的原岩为一套石英砂岩、钙质泥砂岩和不纯的碳酸盐岩，反映滨浅海相沉积环境(刘超辉和刘福来，2015)，而三夏天组中可见变余的纹层状构造、冲洗交错层理和浪成波痕，指示滨海潮间带沉积环境(李承东等，2005)。

由于缺乏来自火山岩夹层年龄的有效约束，研究区中、新元古代年代地层格架的建立依据主要来自碎屑锆石年代学结果(表1)。白云鄂博群都拉哈拉组-尖山组时代被大致限定在1820～1670Ma(Zhongetal., 2015；杨奎锋等，2012；马铭株等，2014；周志广等，2016；Liuetal., 2017)、哈拉霍圪特组-比鲁特组的时代约在1730～1342Ma之间(Zhongetal., 2015; 周志广等，2016)；此后比鲁特组的时代被进一步限定在1580～1350Ma(Liuetal.，2017)或1560～1350Ma(Zhouetal.，2018)，该组黑色岩系的全岩Re-Os等时线年龄则给出～1450Ma的成岩时代(Liuetal., 2016a)；白音宝拉格组-呼吉尔图组的最大沉积时代约为1250Ma(钟焱，2015)。渣尔泰群的初始沉积可能近于或早于1.75Ga(Lietal., 2007)，书记沟组碎屑锆石的年龄组成以2.5Ga为主、1.9～1.8Ga物质记录仅见于该组上部；阿古鲁沟组、刘鸿湾组的源区组成相似，主体为1.90～1.75Ga、可见2.6～2.4Ga年龄信息(公王斌等，2016)。化德群的最大沉积时代为～1.8Ga(胡波等，2009)，毛忽庆组、戈家营组源区物质的年龄组成近似一致且呈双峰式分布，主要峰值为1.95～1.90Ga、次要峰值为2.55～2.50Ga(Liuetal., 2014)；除1.9Ga和2.5Ga的峰值外，三夏天组碎屑锆石的年龄分布中还存在1.72Ga、1.58～1.50Ga、1.35Ga的显著峰值(胡波等，2009；Liuetal., 2014, 2018)。

表1 碎屑锆石U-Pb测年样品信息汇总表

Table 1 Summary of information of the samples for detrital zircon U-Pb dating

样品号采样层位岩性测试方法GPS位置参考文献渣尔泰群NOR250-4书记沟组一段底部变砾岩LA-ICP-MSN41°11'10″、E109°28'36″公王斌等,2016NOR255-1书记沟组二段底部石英砂岩N41°10'38″、E109°31'27″公王斌等,2016NOR265-2书记沟组二段中部石英砂岩N41°11'49″、E109°28'50″公王斌等,201609NM65书记沟组底部含砾石英砂岩N41°11'20″、E109°28'22″本文09NM66书记沟组下部细砂岩N41°11'21″、E109°28'23″本文09NM72书记沟组中部长石砂岩N41°3'31″、E110°1'35″本文NOR258-1阿古鲁沟组一段中部粉砂质板岩N41°11'20″、E109°31'35″公王斌等,2016NOR259-1刘鸿湾组二段下部砂岩N41°11'42″、E109°30'47″公王斌等,2016NOR260-1刘鸿湾组三段中部石英片岩N41°12'33″、E109°29'8″公王斌等,2016白云鄂博群(含腮林忽洞群)10991腮林忽洞群底部中粗粒砂岩SHRIMPN41°37'48″、E110°9'42″马铭株等,201410912-1都拉哈拉组底部中粗粒砂岩SHRIMPN41°49'24″、E110°1'6″马铭株等,201412BY48都拉哈拉组底部含砾粗砂岩LA-ICP-MSN41°44'12″、E110°04'27″Zhong et al., 201506SD01都拉哈拉组长石石英砂岩胡波等,200912JS07都拉哈拉组中部石英砂岩N41°49'26″、E110°00'16″Zhong et al., 2015PM11-1TW1都拉哈拉组中部含砾石英砂岩N41°45'18″、E111°25'30″Zhou et al., 201809NM80都拉哈拉组上部石英砂岩N41°47'8″、E109°54'7″本文10B10尖山组H4石英砂岩杨奎锋等,201201B148石英砾岩?N41°48'58″、E110°00'49″Fan et al., 2014DJP01-TW1尖山组不等粒石英砂岩N41°45'18″、E111°24'30″Zhou et al., 201812BY02尖山组底部杂砂岩N41°49'31″、E110°00'10″Zhong et al., 201512JS01尖山组上部石英砂岩N41°49'29″、E109°58'7″本文06SD12哈拉霍圪特组石英岩胡波等,200913ZB34-3哈拉霍圪特组板岩N41°50'44″、E109°31'44″Liu et al., 201713ZB38-1哈拉霍圪特组石英砂岩夹层N41°39'56″、 E110°10'21″Liu et al., 201713ZB40-1哈拉霍圪特组石英砂岩夹层N41°42'33″、E110°5'48″Liu et al., 201713ZB74-1哈拉霍圪特组石英长石砂岩N41°50'17″、E110°35'46″Liu et al., 201712BY07哈拉霍圪特组中部钙质砂岩N41°49'27″、E109°58'2″Zhong et al., 201512BY05哈拉霍圪特组下部杂砂岩N41°48'57″、E109°56'36″本文09NM78哈拉霍圪特组中部砂质板岩N41°43'11″、E110°7'6″本文09NM84哈拉霍圪特组中部长石石英砂岩N41°40'16″、E109°35'53″本文09NM85哈拉霍圪特组中部长石石英砂岩N41°39'36″、E109°35'30″本文13ZB72-1比鲁特组粉砂岩N41°43'56″、E111°20'16″Liu et al., 2017HMM-TW1比鲁特组细粒石英砂岩N41°46'24″、E111°23'15″Zhou et al., 2018DJP-TW2白音宝拉格组中细粒石英砂岩N41°49'36″、E111°17'30″Zhou et al., 2018DM-3白音宝拉格组石英砂岩王子风,2015GSS-3白音宝拉格组石英砂岩王子风,2015GJT-1白音宝拉格组石英砂岩王子风,201512BY31白音宝拉格组上部石英砂岩N41°53'44″、E109°50'31″本文13ZB49-2呼吉尔图组石英长石砂岩N41°49'10″、E110°15'15″Liu et al., 201713ZB51-2呼吉尔图组粉砂岩N41°48'44″、E110°17'27″Liu et al., 201713ZB53-1呼吉尔图组砾岩N41°47'57″、E110°18'21″Liu et al., 201713ZB77-1呼吉尔图组钙质砂岩N41°48'8″、E112°32'38″Liu et al., 2017化德群06HD01毛忽庆组含砾长石石英砂岩LA-ICP-MS胡波等,200906KB18三夏天组石英岩胡波等,200911HD10-1毛忽庆组上部石英片岩Liu et al., 201411HD01-2葛家营组下部石英岩Liu et al., 201411HD07-1葛家营组中部细粒石英岩Liu et al., 201411HD06-1三夏天组下部细粒绢云母石英岩Liu et al., 201411HD16-1三夏天组中部细粒石英片岩Liu et al., 201411HD31-1呼吉尔图组下部绢云母石英片岩Liu et al., 2014NOD-030-2三夏天组板岩Liu et al., 2018NOD-030-4三夏天组石英片岩Liu et al., 2018

依据沉积相与层序地层特征、成矿专属性以及不整合面的性质、数量等方面的证据，早期研究认为白云鄂博群和渣尔泰群具有同时异相性质、且均可与中-上元古界蓟县剖面良好对比(乔秀夫等，1991；王楫等，1992；贾和义等，2002)。然而，通过碎屑锆石年龄谱系的对比研究，公王斌等(2016)认为渣尔泰群仅相当于白云鄂博群的都拉哈拉组-尖山组部分。Liuetal.(2018)则提出，渣尔泰群阿古鲁沟组和化德群戈家营组应与白云鄂博群的哈拉霍圪特组-比鲁特组对比。此外，有学者认为白云鄂博群的白音宝拉格组-呼吉尔图组和化德群的三夏天组，可能是华北克拉通参与Rodinia超大陆聚合和裂解过程的地质记录(Liuetal., 2014, 2017; Zhouetal., 2018)。

3 样品和测试方法

本研究共采集了10个碎屑岩样品用于进行锆石U-Pb同位素分析(图1b)，其中3个样品采自渣尔泰群，其余样品采自白云鄂博群(表1)。样品09NM65为渣尔泰群书记沟组底部含砾石英砂岩、09NM66采自该组下部变质玄武岩之上的细砂岩、09NM72采自该组中部长石砂岩；样品09NM80采自白云鄂博群都拉哈拉组上部石英砂岩，12JS01采自尖山组上部石英砂岩，12BY05采自哈拉霍圪特组下部杂砂岩，09NM78、09NM84、09NM85分别采自哈拉霍圪特组中部的砂质板岩和长石石英砂岩，12BY31采自白音宝拉格组上部的石英砂岩。

碎屑岩样品采用常规方法破碎后，通过重液浮选和电磁分离法进行分选，各样品分选出的锆石颗粒均大于500粒，在双目镜下挑选出未见矿物包裹体的、不同形态的锆石颗粒粘在双面胶上，然后用无色透明的环氧树脂固定，待环氧树脂充分固化后，对其表面进行抛光至锆石内部暴露，然后进行锆石显微(反射光和透射光)照相和阴极发光(CL)图像研究，依据观测结果对锆石的无裂纹部位进行原位的U-Pb同位素分析。

样品12BY05、12JS01、12BY31的锆石分选工作由河北省廊坊市科大岩石矿物分选技术服务有限公司完成，锆石CL图像在在中国科学院地质与地球物理研究所Cameca SX51电子探针仪器上完成，分析电压为15kV，锆石U-Pb同位素测试工作在西北大学大陆动力学国家重点实验室完成，测试仪器为搭载Geolas 200M激光剥蚀系统的Agilent 7500a ICP-MS仪器，U-Pb同位素组成分析采用91500标准锆石作为外标，元素含量的计算采用NIST SRM610作为外标，29Si作为内标，激光束班直径为32μm。详细的仪器参数设置与分析技术见柳小明等(2007)。其余7个样品的锆石分选工作在河北省廊坊区域地质调查所实验室完成，锆石CL照相、同位素测试均在中国地质调查局天津地质调查中心实验室测试完成，利用NIST612玻璃标样作为外标计算锆石样品的Pb、U、Th含量，分析数据采用GJ-1作为外部锆石年龄标准进行U、Pb同位素分馏校正，采用208Pb校正法对普通铅进行校正，数据处理由ICPMSDataCal程序(Liuetal., 2008)和Isoplot程序(Ludwig，2012)完成。详细的仪器参数设置与分析技术可参考李怀坤等(2009a)。

锆石U-Th-Pb同位素数据的年龄计算及谐和图成图采用Isoplot程序完成(Ludwig, 2012)，谐和数据(不谐和度<10%)的207Pb/206Pb年龄累积频率曲线通过Density Plotter程序中的KDE法绘制(Vermeesch, 2012)。样品的碎屑锆石U-Pb同位素分析结果见表2，样品典型锆石的CL图像见图3。

4 测试结果

4.1 渣尔泰群书记沟组

样品09NM65中锆石的长轴约120～300μm不等，主体大于200μm；长宽比以2:1～3:1为主，近1:1者少见；锆石颗粒圆度普遍较低，以棱角状-次棱角状为主，滚圆状颗粒罕见。锆石颗粒的形态特征显示较低的磨蚀程度，指示近源、快速堆积的沉积特征。锆石CL图像普遍可见具较宽同心环带的核-幔结构，少见具冷杉叶状、板状结构的变质锆石，普遍发育较窄的高亮变质边。对32颗锆石测试了40个分析点，其中35组数据的谐和度较高，207Pb/206Pb年龄集中在2441～2543Ma之间(图4a)，核、幔部位的年龄结果在误差范围内基本一致。

样品09NM66中的锆石多呈长柱状，长宽比普遍大于2:1、少数自形程度较高者可达4:1；锆石长轴以120～250μm为主。锆石颗粒多为次棱角状-次圆状，棱角状偶见、滚圆状未见，指示沉积物经历了有限的搬运和再循环过程。锆石的内部结构以震荡环带为主，显示岩浆成因特征；此外可见板状、冷杉叶状分带结构的变质锆石。较窄的高亮变质增生边在岩浆、变质结构锆石均有发育。对22颗锆石进行了24组测试分析，分析数据不谐和度均小于5%，207Pb/206Pb年龄集中于2478～2534Ma之间(图4a)；对两颗核、幔结构的岩浆锆石分别进行了同位素分析(分析点21.1、21.2和22.1、22.2)，结果显示核部年龄为～2.5Ga、幔部年龄为2.3Ga左右。

表2 渣尔泰群、白云鄂博群碎屑岩样品LA-ICP-MS锆石U-Pb分析结果

Table 2 LA-ICP-MS zircon U-Pb dating results of the clastic samples from the Zhaertai Group and Bayan Obo Group

测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)09NM6511556190.250.44110.002410.19670.09130.16770.001423551324532225341482645800.110.43550.00269.90680.09330.16500.001423301424262325071483.160515730.380.35140.00206.88750.06340.14220.0012194111209719225415163.21233700.330.38850.00218.92630.08340.16660.0015211611233022252415194.1207315441.340.31290.00177.28040.06560.16880.0014175510214619254514454.2782240.350.69080.007415.46420.19240.16240.00143385362844352480142752737320.370.43640.002410.13910.09160.16850.001423351324482225431496475670.080.59620.004120.94550.26820.25480.0025301521313640321515771563880.400.44440.002510.24530.09370.16720.0014237013245722253014781173230.360.44060.00249.93170.08880.16350.001423531324282224921469.179651.210.47440.002510.37670.10570.15870.001525031324692524411629.21351450.930.44220.002410.08160.09100.16540.0014236013244222251114610168618820.900.24720.00135.82570.05190.17090.00141424819501725671480111102190.500.47550.002611.94700.10790.18220.0015250814260023267314712246515651.580.26530.00306.22870.08180.17030.001415171720082625611469134223461.220.44500.002410.15020.09130.16540.00142373132449222512146142745600.490.43170.00239.79170.08830.16450.0014231312241522250314815747860.090.44220.00249.94530.08970.16310.001423601324302224881451671130.060.44550.002410.22410.09280.16640.00142375132455222522146173237830.410.43280.00279.78570.09250.16400.0014231814241523249714818.1673750.180.48710.002610.79720.09660.16080.0014255813250622246414418.242612220.350.43200.00249.54140.08580.16020.0013231513239222245814619.11303830.340.44680.002510.03520.09180.16290.0014238113243822248614419.21311660.790.45970.00259.49930.08590.14990.0013243813238722234515420.1174011981.450.45020.002410.15710.09000.16360.0014239613244922249414420.21063100.340.48530.003010.79600.10140.16140.001425501625062424701432112511740.110.43160.00239.61220.08600.16150.00142313122398212472147223835150.740.44240.00259.89130.08980.16220.00142361142425222478145233816880.550.43550.00239.67110.08650.16110.00142330122404212467146242686330.420.44540.00249.94460.08850.16190.001423751324302224761442519708292.380.44640.00259.99560.09120.16240.001423791324342224811442637913920.270.44830.00249.98840.08870.16160.001423881324342224721442730421250.140.43130.00239.50750.08460.15990.0013231212238821245414628.11292900.440.43820.00259.88150.09230.16360.0014234313242423249314628.2255817261.480.21820.00245.04320.06150.16760.00141272141827222534149929.11663630.460.46560.002810.50930.09840.16370.0014246415248123249414129.21491501.000.48020.002710.55450.10180.15940.00142528142485242449153301615310.300.45910.002510.29170.09250.16260.00142435132461222483142311311980.660.47530.002810.90710.10240.16640.00142507152515242522141322668390.320.45050.002810.19440.09700.16410.0014239715245323249914409NM6613432771.240.45780.002810.30190.08360.16320.0011243015246220248911222962331.270.45530.002710.18260.08000.16220.0011241914245119247912231241740.710.46640.002810.55550.08440.16420.0011246815248520249912142261891.200.46030.003010.31870.09030.16260.0011244116246422248312259604372.200.46990.003010.57730.08740.16320.0011248316248721249011064895520.890.47000.003710.50480.09790.16210.0011248419248023247812074202241.870.47230.003510.65380.09640.16360.001124941924932324931208681580.430.47530.004210.80030.11000.16480.00112507222506262505120

续表2Continued Table 2测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)92101711.230.47070.003610.87560.10010.16760.00122487192513232534122109119021.010.47380.004110.67160.10730.16330.0011250022249525249111011551920.280.46540.003510.44060.09410.16270.00112463182475222484121121423900.370.46380.002810.41520.08370.16290.00112456152472202486111134483641.230.45910.002910.47480.08360.16550.00112436152478202512113141222290.530.47320.002810.83970.08480.16610.00112497152509202519111156136340.970.46860.002410.66890.07610.16510.00112477122495182509111163797040.540.47150.002410.82680.07700.16660.00112490122508182523111174289170.470.47660.002310.96840.07720.16690.00112513122520182527111181843940.470.45580.002710.26950.07980.16340.0011242114245919249111319253920.060.45150.002710.16060.07950.16320.0011240214245019248911420791370.570.44080.00289.91120.08550.16310.0012235415242721248812621.12925220.560.46180.002610.36930.07750.16290.0011244814246818248511221.21341171.150.44220.00229.18130.07800.15060.0012236112235620235314022.15418630.630.46190.003210.50570.08540.16490.0011244817248020250711222.21783320.540.40960.00258.24460.07070.14600.0010221313225819229912409NM7212241601.400.45440.003110.51290.07710.16780.0010241516248118253610523503530.990.43040.00339.91400.08110.16710.00092308182427202528101031696380.260.46120.003010.62560.07490.16710.000924451624911825299343284330.760.47360.002910.78590.07250.16520.0009250015250517250910056200.300.48970.003711.54490.12490.17100.0016256919256828256716061101170.940.47340.002910.72840.07680.16440.0010249816250018250110072133420.620.47450.002910.68360.07010.16330.0009250315249616249010183539660.370.41880.00289.46420.06760.16390.00092255152384172496101192112980.710.42890.00279.46000.06520.16000.00092301152384162456107103994060.980.43990.00289.84080.06750.16220.00092350152420172479105114322861.510.44890.002910.05480.06900.16240.00092390152440172481104123323370.980.45380.002910.21470.07030.16320.00092412162454172490103131554440.350.48660.003412.42960.09310.18530.0010255618263720270096141181600.740.45760.003010.54990.08370.16720.0010242916248420253010415952250.420.46050.002910.66930.07270.16800.00102442152495172538104163752831.330.45620.003010.42860.07270.16580.0009242316247417251510417981860.530.44870.002810.26620.07030.16590.00092389152459172517105182791811.540.45420.002910.39050.07140.16590.0010241415247017251710419111760.060.45660.002910.63330.07270.16890.00102424152492172547105202676680.400.39090.00268.88650.06290.16490.0009212714232616250691821542210.240.47290.003410.79240.08340.16550.0009249618250519251310122381080.350.43630.00299.96470.07370.16560.00102334162432182514108232601621.600.46800.003011.20720.07740.17370.00102475162541182593105241471890.780.44900.002910.09170.07040.16300.00092391162443172487104251861481.260.46860.003011.13920.07640.17240.001024781625351725811042611317640.060.41040.00329.25520.07980.16360.00092217172364202493101227845940.140.44050.00289.91930.06740.16330.0009235315242716249010628.129611290.260.41910.00299.48900.07010.16420.0009225716238618249991128.21503240.460.47300.003010.83750.08510.16620.0010249716250920251910129.1277134160.810.17830.00394.24110.08470.17250.001010582316823425821014429.22082690.770.46640.003510.31980.08340.16050.0010246818246420246111030602350.260.43420.00279.81360.06580.16390.00092325142417162496107

续表2Continued Table 2测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)313325990.550.46000.003110.61790.07670.16740.0009243917249018253294321442380.610.45710.003010.42680.07210.16550.00092427162473172512104332327510.310.43750.00289.89980.06760.16410.00092340152425172498107341221660.740.44770.002810.12290.07050.16400.001023851524461724971053569720.960.43880.00289.94510.07160.16440.0010234515243017250111736.11062710.390.43800.00309.97790.07230.16520.0010234216243318251010736.22679290.290.34470.00317.71610.07040.16230.00091909172198202480103037.12962261.310.45510.002810.25860.06830.16350.0009241815245816249210337.22424270.570.42180.00279.52200.06530.16370.00092269152390162494101038.11004700.210.39250.00267.59590.06520.14040.0009213414218419223211538.2872190.400.47630.003010.94480.07480.16660.0010251116251817252410139.1991590.620.40650.00358.56620.08920.15280.0010219919229324237811839.256711630.490.43580.00419.76030.10140.16240.0009233222241225248110640.181801.010.47770.003810.97330.09200.16660.0011251720252121252411040.24793501.370.44420.002910.10870.06960.16500.0009236915244517250810609NM801.12455930.410.48030.003611.03290.11950.16660.001525281925262725241501.2275830.050.35420.00315.84690.06290.11970.001119551719532119521702.12944290.680.40330.00227.55880.07120.13590.001221841221802121761602.2952200.430.41240.00598.07680.13490.14210.004122263222403722525013.12814850.580.40050.00227.38850.06990.13380.001221711221602021481613.2577200.080.34940.00195.66490.05360.11760.00101932101926181920161452980.530.47500.002910.76300.10740.16430.001525051525032525011505991400.710.48610.002511.22490.10970.16750.001525541325422525331516.12005390.370.44440.00309.28510.10280.15150.001423701623672623631506.21178890.130.40470.00427.70410.14060.13810.001621902321974022032017.1662110.310.39710.00287.35320.07790.13430.001221561521552321551607.2273730.070.34650.00205.55200.05480.11620.001119181119091918991618.1406330.060.35630.00225.89370.06130.12000.001119651219602019561608.2217390.030.34270.00275.51820.05930.11680.001019001519032019081609.13104290.720.40070.00237.37780.07130.13350.001221721221582121451619.2913300.280.37640.00336.60090.08120.12720.0012206018205925205916010.11002070.480.47420.003010.65980.10660.16300.0015250216249425248715110.2454570.100.37980.00356.74300.09850.12880.0013207519207830208117011.181310.060.47540.002510.71170.10150.16340.0015250713249824249115111.2195380.030.26910.00604.32210.09640.11650.00141536351698381903212412.11202480.480.47320.002710.78240.10540.16520.0015249814250524251015012.2252780.090.37540.00247.67970.08850.14840.00142055132194252327171313.11753100.560.47870.002710.97090.10660.16620.0015252214252124252015013.2161480.110.33580.00295.15150.12610.11130.0033186616184545182055214.1741030.710.40370.00237.60740.07530.13670.0013218612218622218616014.284480.020.32530.00225.11560.05510.11410.0010181512183920186516315.1993470.290.47550.002610.83530.10470.16530.0015250814250924251015015.2111670.070.34590.00455.79170.06850.12140.0020191525194523197729316.1661850.360.48090.002711.08570.10580.16720.0015253114253024253015016.2316870.040.33020.00255.46800.06620.12010.0011183914189623195816614.11123020.370.40480.00227.68230.07340.13760.0012219112219521219815017.21465170.280.37110.00576.53170.13610.12770.0013203531205043206618218.1115020.020.41510.00388.43790.14290.14740.00172238212279392316193

续表2Continued Table 2测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)18.2107260.010.32010.00285.12120.06590.11600.0011179016184024189616619.11023550.290.45780.00329.88810.11790.15660.0015243017242429242016019.296340.010.34100.00215.52720.05600.11750.0010189212190519191916120.1761730.440.39520.00217.48480.07060.13740.0012214711217120219416220.2514670.110.31710.00225.19910.05840.11890.00111776131852211940169212016230.320.38550.00257.02830.07610.13220.00122102142115232128161221553630.430.39860.00227.42080.07220.13500.0012216212216321216516023655510.120.35410.00206.04050.06000.12370.00111954111982202011163241063060.350.40790.00237.69150.07370.13670.00122205122196212186151251392170.640.39610.00217.50180.07160.13730.00122151122173212194162261022240.450.46770.002410.32370.09670.16010.00142474132464232456151271115420.200.37110.00276.58180.08510.12860.00122035152057272079172283794800.790.44950.002510.05200.09890.16220.00142393142440242478154292393050.780.47220.002410.72480.09980.16470.00152493132500232505150301174620.250.39510.00207.28860.06830.13380.0012214711214720214816031811660.490.39930.00217.44850.07010.13530.0012216611216720216816032441090.400.39460.00207.40610.07130.13610.0013214411216221217816233971690.570.39640.00217.42970.07040.13590.00122153112165212176161341532950.520.45640.002410.39760.09750.16520.00152423132471232510154351232480.490.38990.00207.33960.06870.13650.0012212311215420218315336501540.330.47210.002410.78210.10090.16560.00152493132505232514151375095830.870.32580.00215.45640.05490.12150.0011181812189419197816938441330.330.38780.00346.96590.08910.13030.00122113182107272102161391152430.480.38890.00227.27400.06930.13570.00122118122146202173163401664110.400.39340.00217.51100.07080.13850.00122139112174212208153411153040.380.43500.003010.30560.11710.17180.00162328162463282576151142125540.020.33590.00175.53900.05170.11960.00111867101907181950164431871861.000.45520.002410.58460.10010.16860.00152418132487242544155441454330.330.46310.002410.68900.09990.16740.00152453132496232532153451413540.400.47020.002611.10820.10570.17130.0015248514253224257115346843190.260.40040.00227.55760.07250.13690.0012217112218021218815112JS01-1661680.390.35770.00525.32910.07580.10800.001719712418741217661010-2705990.120.36350.00425.25900.04590.10490.00101999201862717121414-3482270.210.35300.00465.12930.06080.10540.001319492218411017201212-456800.700.34850.00625.23280.10440.10890.0024192730185817178088-5572290.250.33990.00445.06990.05750.10810.0013188621183110176866-611488611.330.31160.00364.47520.03870.10410.001017481817267169933-71301530.850.48980.006810.65400.12140.15770.0019257029249311243155-81042350.440.34280.00435.11040.05430.10810.001219002118389176877-955750.740.53610.008613.23940.18860.17910.0027276736269713264444-1051620.830.49850.007710.82930.14990.15750.00232607332509132429127-111083910.280.34690.00405.11180.04360.10680.0010192019183871746109-1239920.420.35470.00555.22190.08530.10680.001919572618561417451311-13673830.170.34180.00405.03430.04410.10680.0010189519182571746108-153553660.970.33140.00404.91640.04590.10760.0011184519180581759105-161071810.590.47420.005810.19590.08920.15590.0014250225245382412104-172403070.780.33190.00395.22170.04670.11410.0011184819185681865101-182363670.650.34700.00405.34340.04340.11170.0010192019187671827105

续表2Continued Table 2测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)-19772180.350.32530.00404.76560.04750.10630.0011181519177981736104-20821620.510.33980.00445.03150.05680.10740.00131886211825101756117-21812220.360.34570.00425.15430.05010.10810.0011191420184581768108-223173181.000.48840.005610.71820.07960.15920.0012256424249972447105-2311730.150.36490.00546.06920.08590.12060.00182005251986121965122-241061070.990.46250.00749.93770.14720.15580.00252450332429142411122-251103150.350.31710.00434.74780.06000.10860.00151775211776111776110-26543010.180.32960.00394.94560.04480.10880.0011183719181081780103-271632020.810.34090.00435.03380.05310.10710.0012189120182591751107-282368740.270.46250.00509.88860.06080.15510.0010245122242462402102-293013060.990.33260.00394.94440.04470.10780.0010185119181081763105-30189682.760.34300.00545.08970.08340.10760.00191901261834141760137-31511890.270.32540.00444.88920.06250.10900.00151816221800111782112-323093180.970.32870.00405.09700.04980.11250.0012183219183681840100-331803500.510.36530.00425.91660.04770.11750.0010200720196471918104-34562990.190.33670.00405.09470.04590.10980.0011187119183581795104-35847320.110.31300.00354.74330.03460.10990.0008175517177561798102-361717570.230.33980.00385.07390.03680.10830.0008188618183261771106-3727181.550.30030.00824.27210.15190.10320.00401693411688291682311-3823490.470.35770.00635.94880.11110.12060.00251971301968161965150-392202450.900.46170.006110.10130.10490.15870.00172447272444102442100-40881610.550.38500.00516.89550.07800.12990.00162099242098102097100-4139670.580.47720.008510.51230.18060.15980.00292515372481162453142-421252110.590.48630.005910.81780.09540.16130.0015255526250882470103-43891760.500.35200.00465.64630.06350.11640.00141944221923101901102-441903250.590.40740.00487.23440.06230.12880.0012220322214182082105-4532670.480.35070.00585.27700.09350.10920.00211938271865151785148-46823950.210.37170.00435.74240.04910.11210.00102037201938718331010-47401700.230.45750.00609.91900.10270.15730.00172429262427102426100-481512710.560.48550.005810.76910.09030.16090.0014255125250382465103-49511540.330.49230.006410.65980.10930.15710.00172581282494102424106-501322140.620.34080.00435.15290.05600.10970.0013189121184591794105-51903900.230.36640.00435.80470.05090.11490.0011201320194781878107-52876170.140.34260.00395.22850.04040.11070.0009189919185771811105-5321350.590.49240.009610.34860.20290.15250.00322581412466182374158-541591151.390.28980.00453.91830.06770.09810.00181640231617141588143-55422080.200.35520.00575.80990.09580.11860.00211960271948141936131-56522380.220.47580.007010.72500.13580.16350.00222509302500122492111-5733820.410.49050.007111.12850.13660.16460.00212573302534112503113-58741990.370.35830.00515.38020.07340.10890.001619742418821217811210-592746040.450.35190.00437.14730.06400.14730.00141944202130823151019-603123071.020.48630.005710.72020.08560.15990.0013255525249972454104-61681680.410.34500.00485.13020.06740.10790.00151911231841111763118-62812060.390.33980.00465.30700.06740.11330.00161886221870111853112-631262210.570.46600.005810.07790.09400.15690.0015246626244292422102-64703180.220.34190.00415.19540.05010.11020.0011189620185281803105-65654400.150.34550.00415.27820.04650.11080.0010191319186581813105-66992140.460.34650.00455.32450.06160.11150.00141918221873101823115-67714930.140.34290.00415.24550.04790.11100.0011190120186081815105

续表2Continued Table 2测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)-681381630.850.49020.006510.99670.11720.16270.00182571282523102484103-69723180.230.35510.00445.43930.05630.11110.0012195921189191818107-70821550.530.50030.006911.26770.12920.16340.00202615302546112491115-713633611.000.49020.005911.09160.09620.16410.0015257226253182498103-7235530.650.50510.009611.53930.21540.16570.00332635412568172515155-732611981.320.35290.00495.46430.07190.11230.00161948231895111837116-741062090.500.50970.006711.41070.11900.16240.00182655292557102481107-751152830.410.36130.00475.58000.06430.11200.00141988221913101832118-76693250.210.34950.00465.53290.06380.11480.00141932221906101877103-77502600.190.36080.00475.58380.06490.11230.00141986221914101836118-78623000.210.35760.00465.52190.06230.11200.00141971221904101832107-79501330.380.50010.007211.20830.13990.16250.00212614312541122482115-801123440.330.36450.00475.59600.06310.11130.0013200422191510182110912BY05-11963940.500.32940.00524.83890.07940.10630.0019183525179214173755-21282280.560.47160.00859.07680.16070.13930.002624903723461622181111-3322740.120.32990.00624.88930.10290.10730.0025183830180018175455-4601420.420.30790.00754.60150.13570.10810.0035173137175025176822-5933320.280.31140.00574.32050.08990.10040.0023174728169717163277-6821170.700.40000.00896.30680.16010.11410.003121694120192218661414-7831140.730.35900.00925.39810.16710.10880.003719774418852717801010-81182590.450.33710.00614.94580.09900.10620.0023187329181017173577-91182300.510.29330.00623.94830.10100.09740.0027165831162421157655-101671371.220.43890.00889.06670.18140.14950.00322346392345182341160-111452370.610.28670.00603.91200.09830.09880.00271625301616201601211-12802960.270.30040.00554.13940.08830.09980.00231693271662171619184-131421650.870.42890.00888.65520.18150.14610.00332301402302192301160-141832590.710.42310.00738.47700.14230.14510.00262274332283152288131-155015930.840.29070.00443.96780.06370.09880.00171645221628131602133-163404340.780.43510.00638.94170.11350.14880.00202329282332122332110-173043011.010.30070.00574.30330.09300.10360.00251695281694181689180-18581020.570.42720.01128.47950.23880.14370.00442293502284262272221-191462200.660.38600.00746.94690.13960.13030.00292104342105182102160-201673940.420.43280.00658.84950.11790.14810.00212318292323122324110-214325100.850.30390.00494.36290.07450.10400.00201711241705141696141-221084700.230.29240.00464.07410.06940.10090.00191653231649141641141-231782900.620.29780.00514.20320.07950.10220.00211680251675161665161-2425360.690.35650.01005.35200.18260.10870.004119654718772917782810-2553810.660.43500.01028.88150.21630.14790.00392328462326222321190-261142180.520.29260.00594.09070.09700.10120.00271655291652191647200-2718450.400.55690.012112.27430.26480.15960.003628545026262024521714-28802860.280.29530.00574.16250.09300.10210.00251668281667181662190-29664550.140.29190.00454.08010.06660.10120.00181651221650131647140-3028010560.260.42420.00498.45050.07010.14430.0013227922228182279100-311711571.090.31690.00674.75750.11810.10880.00301775331777211779200-321002340.430.40830.00717.78000.13540.13800.00262207332206162203140-3341760.540.43070.01258.31520.26820.13990.00492309572266292225254-34691970.350.28770.00613.96650.10270.09990.00291630311627211622220-351793610.490.30170.00504.32750.07730.10390.00211700251699151695150

续表2Continued Table 2测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)-362862301.240.30520.00584.42370.09570.10500.00251717281717181714180-371403280.430.28620.00483.93100.07510.09950.00211623241620151615160-381403380.410.42190.00678.33650.12420.14320.00232269302268142266120-3948790.610.42480.01128.44020.24220.14390.00452282512280262275220-401132230.510.29330.00604.11320.10010.10160.00271658301657201654200-4136750.480.43670.01088.92950.23210.14820.00422336482331242325200-42713550.200.31170.00504.58750.07820.10670.00201749241747141743140-432363540.670.28440.00483.90420.07400.09950.00211613241615151614160-441914820.400.29100.00454.05650.06840.10100.00191647231646141643140-451011570.640.29900.00654.25820.11110.10320.00301686321685211683220-462743610.760.40260.00567.60680.09420.13690.00192181262186112188110-47662250.290.29610.00544.19760.08700.10270.00241672271674171674170-48682910.230.29380.00504.10220.07950.10120.00221660251655161646161-491932370.810.29440.00584.14580.09680.10210.00261663291663191662190-501772440.730.29150.00583.83330.09330.09530.00261649291600201534217-51791060.750.40870.01007.77620.20560.13790.00402209462205242201210-52493650.130.29250.00484.03050.07370.09990.00201654241640151622152-532101191.760.40660.00877.69040.17600.13710.00342199402195212191180-54322190.140.29570.00564.14840.09140.10170.00251670281664181655181-551186070.190.29130.00404.06760.05690.10120.00161648201648111647120-561182700.440.29000.00494.04240.07850.10100.00221642251643161643160-571343000.450.45520.00659.81510.12330.15630.00212418292418122416110-581703700.460.30050.00474.28790.07370.10350.00201694231691141687140-59676760.100.29040.00394.07240.05520.10170.00151643201649111655121-60521350.390.28470.00683.90100.11780.09940.00331615341614241612260-611463330.440.29610.00494.15670.07660.10180.00211672241666151657151-6248840.570.28200.00833.83210.14770.09850.00421601421600311596340-632041661.230.28560.00653.90840.11120.09930.00311619331615231610241-64982060.480.28450.00683.91450.11730.09980.00331614341617241620260-651052080.500.29200.00663.92310.11110.09740.00301651331618231576245-66614590.130.28360.00413.89570.05920.09960.00171610201613121617130-671751790.980.28910.00574.03450.09530.10120.00261637291641191646201-6868950.720.28150.00783.81350.13770.09830.00391599391596291591311-691298740.150.30110.00384.31790.05120.10400.00141697191697101697100-701622180.740.28470.00553.91220.09070.09960.00261615281616191617190-71151320.110.28310.00713.85290.12510.09870.00351607361604261600280-72411430.290.27750.00693.73870.11810.09770.00341579351580251581270-731795220.340.30780.00454.48350.06940.10570.00181730221728131726130-7435850.410.30810.00684.38030.11880.10310.00311731331709221681233-751959920.200.25480.00443.20840.06820.09140.00221463231459161454181-761932030.950.32330.00954.87850.17770.10950.00441806461799311791301-77912870.320.32510.00784.97810.14590.11110.00361815381816251817240-781201950.610.29840.00614.22700.10380.10280.00281683301679201675210-79532650.200.28500.00643.86700.10910.09840.00311617321607231594241-802862851.010.43720.00808.88340.16500.14740.00302338362326172316141-81762150.350.28450.00763.87800.13430.09890.00381614381609281603301-821382570.540.30410.00694.44310.12180.10600.0032171134172023173223109NM781991650.600.47580.002710.68790.07180.16290.00102509142496172486101

续表2Continued Table 2测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)214510.270.49070.002811.61200.09340.17160.001225741525742125741102.2344670.070.55610.003512.50090.09530.16300.00102851182643202487101331157470.150.47560.002810.69000.07340.16300.0009250815249717248710141834380.420.32960.00195.05140.03390.11120.00061836111828121819111527800.330.49900.002812.25490.08390.17810.001126091526241826351016673520.190.36200.00205.94750.04080.11920.00071992111968141944112771980.040.47560.002710.57710.07020.16130.00092508142487172469102837730.510.47770.002710.82290.07570.16430.0010251714250818250010191925040.380.32740.00184.98940.03270.11050.00061826101818121808111102857500.380.46930.002610.40140.06830.16070.00092481142471162463101111726130.280.47900.002710.96720.07220.16610.0010252314252017251810012685800.120.46400.002610.40360.06760.16260.000924571424711624831011330970.310.40500.00227.95560.05460.14250.0009219212222615225811314471150.410.46130.002610.63020.07080.16710.00102445142491172529103151174130.280.34280.00205.65860.03800.11970.0007190011192513195210316281770.160.47570.002611.25410.07350.17160.00102509142544172573103174659250.500.44870.002610.18640.06740.16460.0009239014245216250410518.117327510.060.33720.00317.04550.07430.15150.00091873172117222363102618.22987360.410.38710.00328.86120.12440.16600.00212109182324332518211919.1671400.480.46340.002610.81220.07250.16920.0010245514250717255010419.23763451.090.42300.00439.35430.10700.16040.0010227423237327246011820.147813670.350.45620.002610.28640.06930.16350.0009242314246117249310320.21791741.020.39190.00308.68350.08410.16070.00102131162305222463101621.1451340.330.48140.002911.09260.07970.16710.0010253315253118252910021.21133410.330.41300.00569.33710.13640.16400.00102229302372352497101222.11062430.430.47840.002810.98030.07370.16650.0010252015252117252310022.21483700.400.47850.002911.01000.07660.16690.0010252115252418252710023.11362130.640.45950.002810.58330.07410.16700.0010243715248717252810423.21251710.730.47070.002910.57780.07500.16300.0010248715248718248710024.11451510.960.47830.002711.00580.07730.16690.0011252014252418252711024.21652780.590.42370.00499.52930.12880.16310.0010227726239032248811925891740.510.49310.002711.34450.07430.16690.0010258414255217252610226721160.620.48610.002912.44790.17740.18570.00202554152639382705186273025180.580.33400.00195.25550.03480.11410.00071858111862121866100284244211.010.40350.00239.08450.06130.16330.000921851323471624901014295436010.900.42930.00279.71250.06930.16410.00102303152408172498108307476801.100.46070.002710.38010.07000.16340.0009244314246917249110231342550.130.31950.00194.99910.03430.11350.000717871018191218561143213710110.140.34160.00205.52780.03770.11740.00071894111905131917101332002870.700.46200.002710.54970.07150.16560.001024481424841725141033446312080.380.47240.003111.48290.13970.17630.001524941725633126181453548713550.360.42780.00299.66510.07230.16390.0010229615240318249610936.11092730.400.44530.002610.03730.06700.16350.0009237414243816249210536.21254210.300.44700.003810.07740.09530.16350.0009238220244223249210537564410.130.45370.002610.30810.06770.16480.0010241214246316250510438641010.630.46340.002610.80580.07320.16910.0010245414250717254910439711500.470.47980.002711.38840.07470.17220.00102526142555172579102402013700.540.48070.002711.13420.07230.16800.00102531142534162538100411705410.310.44940.002610.20360.06780.16470.00102393142453162504105

续表2Continued Table 2测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)422915520.530.32310.00195.10460.03570.11460.0007180511183713187411443791880.420.45560.002610.41020.07030.16570.00102420142472172515104442124300.490.33090.00195.30630.03510.11630.000718431018701219001034525132810.080.31080.00184.72680.03160.11030.00061744101772121805103462034120.490.47650.002710.88820.07160.16570.00102512142514172515100471544740.330.44600.002610.04570.06840.16340.0009237714243917249110509NM841734700.160.32680.00435.03520.07010.11170.000818232418252518281301.220813530.150.33180.00215.08730.04450.11120.000818471218341618191222.11608600.190.45720.002910.07170.08950.15980.001124271624412224531212.2804010.200.46520.004510.61120.12430.16540.001824622424902925121823.13912240.030.33340.00255.52240.05690.12010.000918551419042019581363.24016200.020.33680.00195.22940.04490.11260.000818711118571618421324.1371600.230.49050.008011.90730.18330.17610.001525734225974026161424.22324130.560.47350.003310.82420.10530.16580.001224991825082425161215.122512930.170.47220.002710.70410.09300.16440.001224931424982225021205.2793950.200.57680.004412.38560.12520.15570.0011293622263427241012186.1523560.150.47450.003410.84450.09920.16580.001225031825102325151206.22125950.360.47710.002710.91930.09080.16600.001225151425162125181207.121515070.140.42100.00249.11520.07510.15700.001122651323501924241277.21023990.260.46510.002610.38040.08500.16190.001124621424692024751118.1882780.320.44590.00267.48300.06160.12170.0008237714217118198112178.26310840.060.33720.00195.37230.04320.11550.000818731118801518881219.11215950.200.60850.004015.16520.14300.18080.0013306420282627266011139.21139980.110.50520.002912.37320.09970.17760.0012263615263321263111010.1203190.060.42370.00299.17490.09300.15710.0012227716235624242413610.23728670.430.47350.002910.71680.09120.16410.0011249915249921249911021482080.230.33420.00205.24260.04380.11380.00081859111860161861120223185710.560.47220.003610.57150.11160.16240.001124931924862624801212314516910.090.36310.00227.22210.07000.14430.0011199712213921227913142427023030.120.33820.00196.13680.05000.13160.00091878111996162120121325291350.210.54110.003214.36310.11770.19250.00132788162774232764111262375870.400.43070.00259.23000.07600.15540.00102309132361192406114271182450.480.47330.002810.76210.08900.16490.00112498152503212507110281164820.240.47520.003110.78440.09480.16460.0011250616250522250311029722440.290.48310.002711.09620.09010.16660.001125411425312125241113030010010.300.46750.002610.51330.08390.16310.0011247314248120248811131881770.500.47460.002710.62700.08700.16240.0011250414249120248111132331250.260.49110.003011.66020.09950.17220.0012257515257822257911033872240.390.48020.002710.97240.08840.16570.0011252814252120251511134611910.320.35650.00205.92230.04840.12050.0008196611196516196312035402200.180.35750.00215.92120.04960.12010.0008197012196416195812136431280.340.46180.003710.64410.10950.16720.0011244720249326253011337942310.410.49630.002811.44170.09330.16720.001125981525602125301133813560.230.43460.002710.20890.09160.17040.00122327152454222561121039832530.330.49420.002711.74760.09430.17240.0012258914258421258111040722220.320.44100.002610.14210.08380.16680.0011235514244820252611741872580.340.45050.002510.17750.08150.16390.0011239713245120249611442571220.470.51090.002912.12080.09780.17210.00122660152614212578113

续表2Continued Table 2测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)43604830.120.35850.00205.81840.04680.11770.00081975111949161922123441413260.430.47740.002910.74850.09240.16330.0011251616250222249011145491310.370.49450.003311.79710.10430.17300.0012259017258823258711046531960.270.46740.003310.34840.09420.16060.00112472172466222462110472113840.550.47300.004910.72490.12820.16450.0011249726250030250211048671410.480.47160.002910.66900.09060.16410.0011249115249521249811049691380.500.46330.002910.12560.08900.15850.00112454152446222440121501412820.500.43960.00279.71570.08030.16030.0011234914240820245911551641100.580.46610.002610.26630.08400.15970.00112467142459202453121522855250.540.44310.00259.68120.07770.15850.0011236513240519243911353561790.310.47710.002810.87790.09240.16540.00112514152513212511110541574370.360.46970.002710.53370.08530.16260.00112482142483202483110551974290.460.46890.002710.47550.08440.16200.001124791424782024771105620630.310.49360.002811.54590.10050.16960.00132586142568222554121571023330.310.46940.002910.40810.08830.16080.0011248115247221246411158801350.590.35240.00227.78510.06800.16020.00111946122206192458112659851280.660.47120.002810.50780.08770.16170.0011248915248121247412160521000.520.47590.003710.81870.10750.16490.0011250920250825250611061543170.170.44880.00279.79690.08550.15830.0011239014241621243812262874090.210.42660.00329.47370.09000.16110.00112290172385232467118633005430.550.46420.002610.28850.08250.16070.0011245814246120246411064551220.450.47770.002710.94100.09100.16610.0012251714251821251912009NM851862650.320.47390.002810.76440.08580.16470.0011250115250320250511023249080.360.47390.002710.74680.08510.16450.0011250114250120250211043997480.530.47390.002710.70890.08470.16390.0011250114249820249611055788060.720.45900.002810.79750.08680.17060.0011243515250620256411582054990.410.47400.002710.72840.08390.16420.0011250114250020249911091142540.450.48110.002710.91980.08460.16460.00112532142516202504111102034950.410.47120.002710.56890.08350.16270.00112489142486202484110112820750.010.35010.00195.59030.04330.11580.00081935111915151892122121122790.400.47510.002710.81800.08550.16510.00112506142508202509110131858020.230.44330.003310.20480.09520.16700.001123651724542325281171428922680.130.47820.002710.77320.08450.16340.001125191425042024911111524621790.110.34830.00207.17340.05790.14940.00101927112133172339112116832630.320.48540.002811.36340.09010.16980.00112551152553202556110171333520.380.47490.002710.93270.08990.16700.00112505142517212528121181654330.380.47410.002710.84470.08490.16590.0011250114251020251711119264140.060.47520.002610.78970.08450.16470.0011250614250520250411020842550.330.48390.002711.11090.08810.16650.00112544142532202523121211583800.420.46670.002710.66890.08570.16580.001124691424952025161122230311570.260.45530.002710.38430.08280.16540.001124191424702025121142340217450.230.36090.00206.18120.04840.12420.00081987112002162017122241984940.400.47380.002610.89780.08480.16680.00112500142514202526111251553740.410.48730.002811.17460.08830.16630.00112559152538202521111261834240.430.47600.002610.89770.08510.16610.00112510142514202518110271724290.400.48570.003211.25870.09520.16810.001125521725452225391112839890.430.48250.002911.28520.09580.16960.0012253815254722255412129513750.140.46960.002710.77090.08470.16640.00112482142504202521112

续表2Continued Table 2测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)306340.170.49720.002911.95510.10570.17440.001426021526012326001303126611190.240.47630.002610.77840.08340.16410.0011251114250419249811132143580.040.49690.003011.88630.09700.17350.00122600152595212592110331494670.320.47700.002610.84930.08480.16500.0011251414251020250711034801930.420.47880.002710.94960.08660.16590.00112522142519202516120351446030.240.46340.002610.85680.08780.16990.00122454142511202557124362085210.400.47190.002710.85520.08800.16680.00112492142511202526111371374730.290.46940.003210.58890.09670.16360.0011248117248823249311138832900.290.46870.002610.70740.08360.16570.00112478142498192514111391504140.360.47360.002810.80420.08970.16540.00112500152506212512110401263540.360.47620.002710.82820.08510.16490.0011251114250820250711041661260.520.47240.002710.72970.08580.16470.001124941425002025051104230860.350.46940.003310.51190.09870.16240.0012248117248123248112043289540.030.46550.002610.32050.08110.16080.0011246414246419246411044311060.300.44790.00269.53520.07660.15440.0011238614239119239512045221290.170.49300.002811.65310.09450.17140.0012258414257721257212046932450.380.45650.00269.88820.07820.15710.0011242414242419242511012BY31-01176 266 0.66 0.4592 0.0064 9.7191 0.1144 0.1535 0.0019 2436282409112385112-02116 153 0.76 0.2086 0.0047 2.3343 0.0777 0.0812 0.0030 1221251223241225330-03327 333 0.98 0.3120 0.0048 6.6819 0.0972 0.1553 0.0025 17512420701324051237-04186 440 0.42 0.2317 0.0032 3.4006 0.0477 0.1064 0.0016 13431715051117391229-05196 533 0.37 0.2403 0.0039 3.8906 0.0672 0.1174 0.0023 13882016121419171438-06104 248 0.42 0.6395 0.0083 23.0138 0.2114 0.2610 0.0024 318733322893253102-07125 105 1.19 0.4252 0.0078 8.7097 0.1623 0.1485 0.0030 2284352308172329152-0850 69 0.72 0.3260 0.0061 5.0082 0.1092 0.1114 0.0026 1819301821181823180-09128 173 0.74 0.4695 0.0070 10.6165 0.1409 0.1640 0.0023 2481312490122497111-1021 83 0.26 0.4186 0.0076 9.1519 0.1651 0.1585 0.0031 2254352353172440148-11229 388 0.59 0.2276 0.0030 3.5022 0.0423 0.1116 0.0015 13221615281018251138-12200 332 0.60 0.2644 0.0035 4.0868 0.0503 0.1121 0.0015 15121816521018341121-13104 290 0.36 0.3232 0.0044 4.9289 0.0622 0.1106 0.0015 1805211807111809110-14117 501 0.23 0.2263 0.0029 3.7900 0.0554 0.1215 0.0024 13151515911219783550-1544 63 0.69 0.3501 0.0087 5.6977 0.1707 0.1180 0.0039 1935411931261926240-1625 46 0.55 0.4720 0.0103 10.5545 0.2386 0.1622 0.0039 2493452485212478171-17132 241 0.55 0.2944 0.0039 4.5866 0.0561 0.1130 0.0015 16632017471018481111-1868 113 0.60 0.4804 0.0072 11.1564 0.1476 0.1684 0.0024 2529312536122542111-19151 170 0.89 0.3247 0.0050 5.1950 0.0835 0.1160 0.0020 1813251852141896135-201994 1196 1.67 0.0774 0.0010 1.0476 0.0138 0.0982 0.0015 48067287159011231-2184 406 0.21 0.2149 0.0027 3.7028 0.0390 0.1250 0.0015 1255141572820281062-2273 282 0.26 0.3591 0.0044 8.0098 0.0737 0.1618 0.0016 1978212232824741025-23117 152 0.77 0.4299 0.0057 9.1069 0.0990 0.1536 0.0018 2305262349102387104-2455 274 0.20 0.3285 0.0042 5.0908 0.0552 0.1124 0.0013 183120183591838100-25165 325 0.51 0.2944 0.0037 4.5581 0.0491 0.1123 0.0013 1663181742918371010-26124 258 0.48 0.3104 0.0039 4.7968 0.0501 0.1121 0.0013 174319178491833105-2791 270 0.34 0.3272 0.0040 5.0389 0.0503 0.1117 0.0012 182519182681827100-28143 332 0.43 0.3158 0.0045 4.7113 0.0662 0.1082 0.0017 1769221769121769120-29128 435 0.29 0.2357 0.0029 3.7200 0.0393 0.1145 0.0013 1364151576818711037-30288 593 0.49 0.1880 0.0023 3.4657 0.0339 0.1337 0.0015 1110131519821471093-31147 286 0.51 0.3314 0.0041 5.1418 0.0523 0.1125 0.0012 184520184391841100

续表2Continued Table 2测点号含量(×10-6)ThUTh/U同位素比值年龄(Ma)不谐和度206Pb238U1σ207Pb235U1σ207Pb206Pb1σ206Pb238U1σ207Pb235U1σ207Pb206Pb1σ(%)-32218 335 0.65 0.2699 0.0033 3.9343 0.0417 0.1057 0.0012 1540171621917271012-33218 483 0.45 0.1821 0.0022 2.5061 0.0269 0.0999 0.0012 1078121274816211050-3473 254 0.29 0.2817 0.0036 4.2871 0.0495 0.1104 0.0014 16001816911018061013-35127 460 0.28 0.3024 0.0036 4.5834 0.0426 0.1099 0.0011 170318174681798106-36197 555 0.35 0.2037 0.0024 3.0029 0.0283 0.1069 0.0011 1195131408717471046-37185 419 0.44 0.2960 0.0035 4.4653 0.0405 0.1094 0.0011 167117172581790107-38190 405 0.47 0.2740 0.0033 5.0292 0.0465 0.1331 0.0013 1561171824821391037-39142 221 0.64 0.3048 0.0039 4.6583 0.0521 0.1108 0.0013 171519176091813106-4061 72 0.85 0.4320 0.0068 9.6053 0.1377 0.1613 0.0025 2315302398132469127-4158 121 0.48 0.4579 0.0064 10.0138 0.1178 0.1586 0.0020 2430282436112441110-42159 186 0.86 0.4099 0.0054 8.9356 0.0962 0.1581 0.0018 22142523311024361010-43217 406 0.54 0.2271 0.0028 3.1956 0.0329 0.1021 0.0012 1319141456816621026-4434 54 0.63 0.3081 0.0056 4.8320 0.0983 0.1138 0.0025 1731271790171860167-45226 437 0.52 0.3194 0.0037 6.0153 0.0508 0.1366 0.0012 1787181978721851022-46145 266 0.55 0.4444 0.0056 9.7438 0.0946 0.1590 0.0016 237025241192445103-47578 857 0.67 0.0940 0.0012 1.5218 0.0159 0.1174 0.0014 57979396191710231-48275 274 1.00 0.3628 0.0044 9.8153 0.0829 0.1962 0.0018 1996212418827951040-4986 117 0.73 0.3084 0.0043 4.6255 0.0623 0.1088 0.0016 1733211754111780113-5048 86 0.56 0.4164 0.0060 9.2838 0.1167 0.1617 0.0022 22442723661224741110-5189 458 0.19 0.2609 0.0030 4.0012 0.0348 0.1112 0.0010 1494151634718201022-52306 418 0.73 0.3406 0.0042 7.1798 0.0676 0.1529 0.0016 1889202134823791026-53318 329 0.97 0.2378 0.0029 3.4933 0.0373 0.1066 0.0012 1375151526817411027-5481 158 0.51 0.3245 0.0043 4.9921 0.0608 0.1116 0.0015 1811211818101826111-55352 502 0.70 0.2302 0.0028 3.4962 0.0341 0.1101 0.0012 1336141526818021035-56245 207 1.18 0.4849 0.0059 15.4701 0.1299 0.2314 0.0021 2548262845830621020-57109 106 1.02 0.4555 0.0067 10.0849 0.1297 0.1606 0.0022 2419302443122462112-581117 1110 1.01 0.0600 0.0008 0.6451 0.0102 0.0780 0.0014 37655056114714205-5987 131 0.66 0.4528 0.0058 9.7775 0.1003 0.1566 0.0017 240726241492420101-6075 409 0.18 0.3209 0.0037 4.8319 0.0412 0.1092 0.0010 179418179071786100-61224 194 1.16 0.4288 0.0053 11.5367 0.1045 0.1952 0.0019 2300242568827861021-62154 212 0.73 0.2991 0.0038 4.5098 0.0515 0.1094 0.0014 168719173391789106-6390 82 1.10 0.4400 0.0064 9.5808 0.1218 0.1579 0.0022 2351292395122434114-6487 121 0.72 0.3910 0.0052 7.1260 0.0834 0.1322 0.0017 2127242127102127100-6596 311 0.31 0.2732 0.0034 3.9446 0.0422 0.1047 0.0012 1557171623917101010-66554 554 1.00 0.1613 0.0019 2.1877 0.0227 0.0984 0.0011 964111177715941065-67106 163 0.65 0.4577 0.0059 10.1139 0.1033 0.1603 0.0017 242926244592459101-68178 375 0.47 0.2489 0.0030 3.8225 0.0370 0.1114 0.0012 1433151597818221027-6970 286 0.25 0.3185 0.0038 4.8210 0.0465 0.1098 0.0011 178219178981796101-7079 179 0.44 0.3215 0.0042 4.8971 0.0579 0.1105 0.0014 1797201802101807111-71117 106 1.10 0.3298 0.0047 5.1620 0.0711 0.1135 0.0017 1838231846121856121-7264 161 0.40 0.4350 0.0055 9.2281 0.0919 0.1539 0.0016 232825236192389103-73188 461 0.41 0.2256 0.0027 3.3028 0.0318 0.1062 0.0011 1312141482717351032-74195 252 0.77 0.3580 0.0044 7.6505 0.0703 0.1550 0.0016 1973212191824021022-75146 468 0.31 0.2463 0.0029 3.7590 0.0349 0.1107 0.0011 1419151584718111028-7641 341 0.12 0.3106 0.0037 4.6321 0.0429 0.1081 0.0011 174418175581768101-7774 364 0.20 0.3079 0.0036 4.6590 0.0435 0.1097 0.0011 173018176081795104-78387 349 1.11 0.2663 0.0032 3.9539 0.0395 0.1077 0.0012 1522161625817611016-7981 243 0.33 0.3063 0.0037 5.3146 0.0523 0.1258 0.0014 1723181871820401018-8048 98 0.49 0.2926 0.0045 4.3234 0.0717 0.1072 0.0020 1654231698141752146

图3 年代学样品典型锆石CL图像分析点位置和点号由图中黄色圆圈和相邻数字表示，测试结果见图中黑色数字，单位“Ma”Fig.3 CL images of the typical zircons from the dating samplesLocations and numbers of the analyzing spots on the typical zircon grains are illustrated as circles and numbers in yellow, and the dating results are presented by the numbers in black without their units in “Ma”

图4 渣尔泰群、白云鄂博群样品锆石U-Pb测年结果Fig.4 Zircon U-Pb dating results of the samples form the Zhaertai Group and Bayan Obo Group

样品09NM72中的锆石长轴可见120～150μm和200～300μm两类，长宽比以1.5:1～2:1为主，普遍呈短柱状；锆石颗粒圆度较高，棱角-次棱角状少见，多为次圆状-滚圆状；CL图像中可见具板状、均一状分带结构的锆石，但仍以发育清晰震荡环带的岩浆型锆石为主。对40颗锆石进行了47个分析点的测试，其中41组数据的不谐和度小于10%，207Pb/206Pb年龄大多集中在2456～2567Ma之间(图4a)；另有2个位于锆石幔部的分析点显示了2232Ma和2378Ma的207Pb/206Pb年龄(分析点38.1和38.1)。

上述样品数据共同组成的谐和图中可见，谐和数据点和大部分不谐和锆石所组成的不一致线上交点均位于2.5Ga左右，显示书记沟组源区物质以2.5Ga的岩浆岩为主，与前人结果一致。选取不谐和度小于10%的锆石年龄进行207Pb/206Pb年龄累计频率分析、并与该组已发表的所有碎屑锆石数据(不谐和度<10%，数据来源见表1，下同)进行频率峰值的对比作图(图5a)，上述样品未见前人在该组上部砂岩中测得的～1.92Ga峰值(公王斌等，2016)。

图5 渣尔泰群、白云鄂博群样品锆石207Pb/206Pb年龄累计频率分布灰色曲线和文字代表该组前人已发表锆石207Pb/206Pb年龄累计频率分布Fig.5 Cumulative proportion curves of the zircon 207Pb/206Pb age of the dating samples from the Zhaertai Group and Bayan Obo GroupCurves and texts in grey represent the pioneers’ data in the same formation

4.2 白云鄂博群都拉哈拉组

样品所含碎屑锆石粒径主体为120～150μm，长宽比2:1～3:1，以次圆状为主，滚圆状颗粒少见，总体表现为磨蚀程度中等的自形特征；CL图像显示岩浆型锆石比例高于变质型锆石，内部结构可见震荡环带和扇状、均一状等类型；部分锆石具有明显核、边结构。对46颗锆石进行了同位素测试，分析点共计64个，其中61组数据谐和度较高，207Pb/206Pb年龄分布区间为1820～2571Ma(图4b)。锆石207Pb/206Pb年龄累计频率曲线存在～2.2Ga的主要峰值，这一信息在该组中是首次发现；此外，还可见2.50Ga、1.95Ga的2个次要峰值，这与前人报道结果一致(图5b)。

4.3 白云鄂博群尖山组

样品12JS01所含锆石长轴多为80～120μm，长宽比变化不大，普遍为1:1～2:1；颗粒圆度较高，均呈次圆状-滚圆状。在锆石CL图像中，可见震荡环带、板状分带和均一状等内部结构类型。共对80颗锆石进行了U-Pb同位素测试，其中75组分析结果具有较高谐和度，207Pb/206Pb年龄主要分布于1682～2515Ma之间(图4c)；在207Pb/206Pb年龄累积频率图中，本样品出现了约1.8～1.7Ga的主要峰值和约1.85Ga、2.52～2.40Ga的次要峰值，其主要峰值的分布特征与该组已发表数据存在显著差异(图5c)。

4.4 白云鄂博群哈拉霍圪特组

样品12BY05所含锆石形态差异较大，颗粒长轴变化范围50～200μm，长宽比1.5:1～3:1不等，普遍呈次棱角-次圆状；CL图像显示，具有震荡环带内部结构的岩浆型锆石比例较高，而具有板状、冷杉叶状和均一状内部结构的变质型锆石略低。对81颗锆石进行了同位素测试，分析点总计82个，其中79组数据谐和度较高(图4d)，207Pb/206Pb年龄主要分布于1576～2341Ma之间，其累计频率曲线显示两组主要的年龄区间，即1.70～1.58Ga和2.4～2.2Ga，与该组中、上部已发表年龄存在显著不同，这种差异可能与样品层位和岩性对应新一轮沉积旋回早期阶段的近源快速堆积有关(图5d)。

样品09NM78中的锆石以长轴100～200μm的颗粒为主，长宽比多为1:1～2:1，普遍呈次圆状至滚圆状，少量呈次棱角状；锆石内部结构以震荡环带和板状分带结构为主，少数锆石具有云雾状和均一状结构类型。样品09NM84中的锆石颗粒长宽比普遍为2:1～3:1，长轴变化较大，粒径范围80～200μm不等，以次圆状-次棱角状为主；锆石内部结构主要存在震荡环带和冷杉叶状、板状分带等类型。样品09NM85中锆石的长轴粒径主体为100～180μm，可见大于250μm颗粒；颗粒普遍呈长宽比大于2:1的柱状形态；CL图像中以震荡环带结构为主，其次为冷杉叶状和板状结构。对样品09NM78的47颗锆石进行了56个分析点测试，其中50组数据谐和度较好；在样品09NM84的64个测试点中(54颗锆石)，58组谐和度较高；样品09NM85的48颗锆石的43组有效数据中，42组数据谐和度较高(图4e)。上述样品所有谐和数据的207Pb/206Pb年龄主要分布于1805～2635Ma之间，累计频率曲线显示了2.5Ga左右的主峰和2.0～1.8Ga的次峰组成，频率曲线形态学特征与前人结果基本吻合(图5e)。

4.5 白云鄂博群白音宝拉格组

样品12BY31中锆石颗粒的长轴粒径普遍小于150μm，主要分布于80～120μm；颗粒长宽比为1.5:1～2:1，多为次圆状-次棱角状；锆石内部结构类型可见震荡环带、板状、扇状、冷杉叶状以及均一状等。对80颗锆石进行的80个点位的U-Pb同位素分析中，有45组数据的不谐和度小于10%(图4f)。除了1颗～1.23Ga的锆石以外，本样品锆石分为两类：第一类磨蚀程度较低，不谐和锆石组成的不一致线上交点年龄为1826±18Ma(n=19)，与谐和锆石(不谐和度<5%)的加权平均年龄1811±13Ma(n=23)在误差范围内一致；第二类为圆度较高的锆石颗粒，其不谐和锆石组成的不一致线上交点年龄为2451±22Ma(n=11)，与谐和锆石(不谐和度<5%)的加权平均年龄2437±31Ma(n=13)在误差范围内一致。本样品45组谐和数据的207Pb/206Pb年龄累积频率曲线仅显示出～2.45Ga和～1.80Ga两个主要峰值，与前人数据曲线的形态学差异较大，这可能与本样品分析点较少或者本样品的源区组成相对简单有关(图5f)。

图6 渣尔泰群、白云鄂博群和化德群各组的最大沉积时代估算结果(a1)书记沟组、(a2)阿古鲁沟组、 (a3)刘鸿湾组；(b1)都拉哈拉组、(b2)尖山组、(b3)哈拉霍圪特组、(b4)比鲁特组、(b5)白音宝拉格组、(b6)呼吉尔图组；(c1)毛忽庆和戈家营组、(c2)三夏天组Fig.6 Maximum depositional age (MDA) results of the formations from the Zhaertai, Bayan Obo and Huade groups(a1) Shujigou Fm., (a2) Agulugou Fm., (a3) Liuhongwan Fm.; (b1) Dulahala Fm., (b2) Jianshan Fm., (b3) Halahuogete Fm., (b4) Bilute Fm., (b5) Baiyinbaolage Fm., (b6) Hujiertu Fm.; (c1) Maohuqing and Gejiaying Fms., (c2) Sanxiatian Fm.

5 统计学分析方法和结果

新成物质组分在沉积岩中的比例通常与盆地构造属性密切相关。通过盆内或盆缘岩浆作用类型及其活动频率、新成物质保存潜力和蚀源区地域范围的综合对比，对于已知沉积时代的地层序列，Cawoodetal.(2012)提出了一种利用碎屑锆石年龄判别盆地构造属性的统计方法。然而，前寒武纪地层的沉积时代一般较难判定，这限制了Cawoodetal.(2012)方法的推广和应用。采用大数据对比的方式，Couttsetal.(2019)最近评估了在不同样本数量下，各种已知的碎屑锆石年龄统计分析方法给出的最大沉积时代与真实沉积时代的百分误差。由上推测，综合运用Cawoodetal.(2012)和Couttsetal.(2019)的统计分析方法，有可能查明前寒武纪哑地层的时代及其盆地发育过程。因此，本文对白云鄂博群、渣尔泰群和化德群的碎屑锆石年龄数据，以组为单位进行了统计分析。需要强调的是，本研究是对现有数据的集成和利用，因此下文的分析和讨论是具有时代局限性的，但其结果对于验证Cawoodetal.(2012)和Couttsetal.(2019)的统计学模型能否适用于前寒武纪沉积序列，具有指示意义。

5.1 “逼近法”与最大沉积时代

前人曾提出了多种借助碎屑锆石年龄限定哑地层最大沉积时代(Maximum depositional age，MDA)的方法，例如最年轻单粒锆石法(YSG)、最年轻频率峰值法(YPP)、1σ误差内最年轻锆石组法(YGC 1σ)、2σ误差内最年轻锆石组法(YGC 2σ)、最年轻碎屑锆石法(YDZ)、3颗最年轻锆石加权平均年龄法(Y3Zo或Y3Za)和最年轻统计组法(YSP)等，此外还有AgePick法、TuffZirc 6+法、τ法等，这些方法的原理和文献出处可见Couttsetal.(2019)的综述。通过不同方法MDA计算结果的对比，Couttsetal.(2019)提出，在所有数据均可信的前提下，对于数据样本库N=50～120、N=200～300和N>500的不同情况，YSG法和YDZ法给出的MDA计算结果与真实的沉积时代最为接近。本文采用YDZ法进行现有数据的MDA计算，计算软件为Isoplot(Ludwig, 2012)，如果样本库中最年轻锆石的207Pb/206Pb年龄与第二年轻锆石的年龄在1σ误差范围内一致，则视其可信；否则将该锆石从样本库中剔除并重新进行筛选流程；本文将上述分析流程概括为“逼近法”，其计算结果可暂时用于估算已经有一定碎屑锆石数据积累(N>200)的前寒武系哑地层的最大沉积时代。

需要明确的是，逼近法给出的计算结果可能与真实沉积时代相差甚远，例如：燕辽地区青白口系长龙山组和景儿峪组碎屑锆石的最小峰值年龄为1.75Ga左右(Wanetal., 2011；Sunetal., 2012)，据此计算的MDA应为1.8～1.7Ga之间；但目前普遍认为青白口系的沉积时代应晚于1.0Ga，在此极端情况下，MDA结果与真实沉积时代的误差可达800Ma以上。因此，在利用逼近法建立年代地层序列的同时，要结合其他区域地质要素，如野外接触关系、区内岩浆作用事件、地层叠覆关系等，综合判断MDA计算结果的真实性和可信性。

采用“逼近法”计算北缘盆地渣尔泰群、白云鄂博群和化德群各组的最大沉积时代，参与计算的所有锆石数据不谐和度均小于10%(表2)，各组总数据库、参与计算数据样本库和计算结果见图6。MDA估算结果显示：1)渣尔泰群书记沟组为1822Ma、(增隆昌组无数据)、阿古鲁沟组为1763Ma、刘鸿湾组为1723Ma；2)白云鄂博群都拉哈拉组为1723Ma、尖山组为1688Ma、哈拉霍圪特组为1492Ma、比鲁特组为1458Ma、白音宝拉格组为1171Ma、呼吉尔图组为942Ma；3)化德群毛忽庆组+戈家营组为1779Ma、三夏天组为1323Ma。

5.2 盆地构造属性判别

Cawoodetal.(2012)分析方法的具体流程是：对于已知沉积时代的地层单元，通过碎屑锆石年龄与地层沉积时代的差值的累积频率分布，识别聚合背景(如弧前、弧后盆地)、碰撞背景(如前陆盆地)和伸展背景(如裂谷、被动陆缘盆地)等盆地类型。由于不同背景的投图区域各有重合，该方法给出了两个更加重要的统计学判别指标(图7)：在时代差值的累积频率分布曲线上，若5%累积频率的时代差值大于150Ma，指示该地层为伸展背景产物；小于150Ma时，则以30%累积频率的时代差值是否大于100Ma而定，即大于100Ma指示碰撞背景、小于100Ma指示聚合背景。

图7 渣尔泰群、白云鄂博群和化德群各组碎屑锆石年龄的盆地属性判别图解红色五角星为代表累积频率5%，蓝色五角星代表累积频率30%Fig.7 Detrital zircon ages diagrams for tectonic setting of individual formation from the Zhaertai, Bayan Obo and Huade groupsRed stars represent the 5% points of the cumulative curves and blue stars represent the 30% points

根据MDA估算结果，对华北北缘中、东段晚前寒武系各组分别进行盆地构造属性的统计分析，参与统计的碎屑锆石年龄数据不谐和度均小于10%，结果显示：渣尔泰群书记沟组、阿古鲁沟组和刘鸿湾组，均为碰撞背景的盆地构造属性；白云鄂博群下部都拉哈拉组和尖山组为碰撞背景，其上各组则显示伸展背景特征；化德群毛忽庆组+戈家营组为碰撞背景、顶部三夏天组为伸展背景(图7)。上述结果表明，渣尔泰群的构造属性未发生变化，始终处于碰撞背景；而白云鄂博群、化德群的盆地构造属性则存在从碰撞背景到伸展背景的转换。

6 讨论

6.1 可信性论证

碎屑锆石年代学研究通常以不谐和度小于5%或10%作为评判数据是否有效的标准，因此本文选取不谐和度小于5%的锆石年龄数据作为对照组进行了统计分析(图略)。结果显示，不谐和度小于10%和小于5%的两个数据库，逼近法计算的各组MDA完全一致；以MDA结果进行的盆地属性判别，大部分层位给出了一致的判别结果，仅有比鲁特组和呼吉尔图组给出了“碰撞型”的不一致结果，这与对照组参与分析的数据点总量锐减有关(分别降低了24.5%和37.5%)。由此判断，以碎屑锆石年代学数据判别盆地构造属性的统计方法，结果可信性与单点数据的精度(即谐和度)无关、而与分析点总量呈正相关关系。由于各组最年轻碎屑锆石(1颗或数颗)的不谐和度普遍小于5%，对照组未能揭示不谐和度对MDA计算结果的影响，但基于不同批次数据实验条件截然不同的必然性(包括系统误差和人为偏差等)，本文认为降低单点精度要求以谋求更大样本库的统计原则，同样适用于MDA的计算过程。

本文各组的MDA估算结果，与现有的沉积、岩浆事件序列基本一致(图2)，在取得有效年龄约束之前，可暂将其视为各组的真实沉积时代。研究区晚前寒武系从碰撞到伸展的构造属性转换，同样与区内约1.9～1.23Ga构造-热事件的期次和性质一致。

6.2 多旋回复合盆地

根据各组的MDA和盆地属性判别结果(图6、图7)、结合区内已知的岩浆事件(图2)，华北克拉通北缘盆地的中元古代构造演化过程大致可分为四个阶段(时代上限中的粗斜体数字为图2中所示各层位中最早期侵入岩时代、“？”表示目前缺乏有效约束)：

(1)造山后伸展阶段：沉积记录包括渣尔泰群(1822～？Ma)、白云鄂博群下部都拉哈拉组(1723～1670Ma)和尖山组(1688～？Ma)、化德群下部毛忽庆组和戈家营组(1779～？Ma)。这些地层单元普遍为碰撞型构造属性(图7a中a1～a3、7b中b1～b2、7c中c1)，属于同一构造演化阶段沉积的、可大致对比的地层记录，这与碎屑锆石源区分析取得的结论一致(公王斌等，2016)；北缘各主要沉积盆地呈近东西向展布，其成因很可能与～1.9Ga南北向的俯冲、拼贴、碰撞(张华锋等，2009；Wanetal., 2015; Wuetal., 2018)及其后在～1.82Ga前完成的快速抬升过程有关(Wanetal., 2015)。综上推测，北缘地区自1.82Ga起进入造山后伸展阶段，期间发生了～1.75Ga和1.67Ga两次幔源岩浆活动(Lietal., 2007；周志广等，2016)。本次盆地发育过程结束的标志是一次区域性的抬升事件，对应尖山组、戈家营组顶部的平行不整合面(贾和义等，2002)。

(2)早期伸展阶段：沉积记录仅见于白云鄂博地区，即白云鄂博群的哈拉霍圪特组(1492～？Ma)和比鲁特组(1458～1342Ma或1458～1400Ma)，相应沉积序列是北缘地区进入伸展型构造体制后的第一套沉积记录(图7b中b3, b4)。考虑到比鲁特组黑色岩系的全岩Re-Os等时线年龄为1447±42Ma(Liuetal.，2016a)，并且白云鄂博地区与裂谷事件有关的基性岩浆和碳酸岩浆活动在1.4Ga以后才开始频繁发育(Yangetal., 2011；Zhangetal., 2012, 2017b； Fanetal., 2014)，本文认为以1.4Ga为界划分同一伸展体系下的早期伸展阶段和裂谷峰期阶段更为合理。

(3)裂谷峰期阶段：沉积记录只有化德群的三夏天组(1323～1313Ma)，是一套持续时间小于10Myr的巨厚粗碎屑岩，该组具伸展型盆地构造属性(图7c中c2)。与短暂、快速的堆积过程不同，本阶段的幔源岩浆活动自1.4Ga开始(Fanetal., 2014)、间断性持续到1.23Ga左右(Yangetal., 2011)，前人认为1.3Ga是北缘地区中元古代岩浆活动的峰期(Shietal., 2012；Zhuetal., 2015；周志广等，2016; Songetal., 2018)、可与克拉通北部的燕辽大火成岩省事件对比(Zhangetal., 2012, 2017b)。待建纪沉积记录在华北克拉通的分布十分局限，已经查明的下马岭组(1.4～1.35Ga)在燕辽地区普遍呈孤岛状或串珠状分布(Zhangetal., 2012)，显示这一时期的区域构造样式应以大面积抬升和局部沉降为主。前人提出华北克拉通在1.4～1.35Ga期间的区域抬升与1.33～1.3Ga燕辽大火成岩省有关，即“岩浆活动前的构造抬升事件”(Zhangetal., 2017a)。三夏天组的局限分布和快速堆积特征，显示了与燕辽盆地下马岭组类似的盆地演化过程，即：受到1.3Ga大规模幔源岩浆事件的影响，北缘盆地在1.4～1.3Ga为整体隆升区，仅在化德及其周边地区，发育了一个规模有限、演化周期极短的过渡相沉积盆地。

(4)第二次裂谷阶段(?)：白云鄂博群的白音宝拉格组(1171～？Ma)和呼吉尔图组(942～？Ma)在研究区的其他地区并不发育，本研究未能明确这套沉积序列的地层归属(待建系顶部、青白口系或南华-震旦系)。前人曾提出这套沉积序列中晚于1.6Ga、特别是呼吉尔图组中1.3～1.0Ga碎屑锆石的出现(王子风，2015；Liuetal., 2017；Zhouetal., 2018)，表明华北克拉通参与了Rodinia超大陆的汇聚、拼贴和裂解过程。然而本文认为，虽然这套地层显示了伸展型的构造属性(图7b中b5, b6)，但区内尚未发现特征性的岩浆作用记录，因此较难判断这一时期北缘地区的构造背景(裂谷？被动陆缘？或是克拉通内凹陷？)。

6.3 华北克拉通北部的中元古代构造演化

以蓟县系顶、底的两条平行不整合面所代表的时、空界限为界，华北克拉通北部地区至少存在三次“有间断、无闭合”的盆山耦合过程：

(1)构造反转期(1.82～1.60Ga)：本阶段的盆地沉降和基性岩浆活动在北缘地区首先发育，而在燕辽地区则表现出明显的滞后性，例如：北缘的渣尔泰群下部存在～1.75Ga的变质基性岩(Lietal., 2007)、白云鄂博群被～1.67Ga基性岩侵入等(周志广等，2016)；燕辽盆地长城群的初始沉积时代不早于1.67Ga(Lietal., 2013)、且～1.64Ga才开始出现大规模的基性岩浆活动(张拴宏等，2013)。在正视不整合面穿时性的前提下(Catuneanuetal., 2005)，依据燕辽地区的年代学研究结果，通过平行不整合面的区域对比，本阶段的结束时代可大致限定在1.6Ga。

本次伸展和沉降过程是由北部陆缘向陆内逐步发展的，在地球动力学和板块构造环境两方面，均呈现出不同于陆内裂谷的演化特征(刘和甫，2001)。结合北缘盆地构造属性的分析结果，本研究认为1.82～1.60Ga实际上是一个构造反转期，代表华北克拉通北部从约1.90～1.82Ga的挤压(俯冲、碰撞)环境向伸展体系的转变。需要注意到，约1.72～1.62Ga是华北克拉通著名的非造山岩浆活动期，相关岩浆岩多具有“类岛弧地球化学特征”，以持续的、脉动的形式广布于华北北部地区(翟明国等，2014)，表明构造反转期华北北部岩石圈的物质和热状态，已经被彻底改造。就此而言，本文认为至少在华北北部地区，仍以1.8Ga作为古、中元古代的界线是合理的，它是华北陆块完成终极克拉通化之后、开始向稳定地台转化的起点。

(2)陆内伸展阶段(1.6～1.4Ga)：本阶段燕辽盆地的张裂较早，堆积了本区地层厚度最大的蓟县系，持续沉积时代至少为1.58～1.44Ga(Suetal., 2010；李怀坤等，2010；田辉等，2015)，上、下限合理延展后即为我国蓟县纪的标准时代1.6～1.4Ga；本阶段北缘盆地的沉积作用时限为约1.5～1.4Ga、相应沉积记录仅见于白云鄂博地区。除了少量的火山岩夹层外，华北克拉通北部地区不发育1.6～1.4Ga的岩浆活动。Mengetal.(2011)认为，以1.63～1.56Ga的穿时性平行不整合为界，蓟县纪以来的华北克拉通已经进入到陆块漂移的演化阶段，此后的华北北部应长期处于被动陆缘环境。然而，本阶段北缘盆地构造属性的判别结果结合沉降中心、初始破裂均发生在燕辽地区的证据显示，1.6～1.4Ga的华北北部似仍处于陆内伸展的早期阶段。另外，与之前的构造转换期相比，本阶段华北克拉通的壳幔物质交换强度和频率显著降低，因此本阶段盆地的发育机制应以力学沉降和热沉降为主(刘和甫，2001)。

(3)裂谷作用阶段(1.4～1.3Ga)：待建纪华北克拉通北部基本的盆山格局是：早期短暂的局部沉降和此后长期的大面积抬升剥蚀区(Zhangetal., 2017a)。现有数据可将北缘盆地三夏天组的沉积时代精确限定在1.32～1.31Ga，置于1.4～1.35Ga的下马岭组之上(Lietal., 2013)。始于1.4Ga、以1.33～1.30Ga的燕辽大火成岩省为峰期、持续到1.23Ga左右的基性和碳酸岩浆活动，成因背景普遍与裂谷事件有关(Yangetal., 2011；Zhangetal., 2012, 2017a, b；Shietal., 2012；Fanetal., 2014； 周志广等，2016)。

(4)沉积间断(1.3～1.0Ga)：1.3Ga的裂谷峰期岩浆事件结束后，除少数地区可能存在的岩浆活动外，华北北部彻底结束了中元古代的盆山耦合过程；与之类似，整个华北克拉通在1.3～1.0Ga也处于长期的沉积间断状态。然而，这次间断是与克拉通整体抬升或是沉积物供给受限等其他因素有关，仍需深入研究。

综上，华北克拉通北部地区中元古代的盆山耦合过程，是在古元古代北缘造山事件的影响下，由中元古代早期北缘地区的造山后伸展开始，经过非造山岩浆活动对整个陆块壳、幔的长期改造，最终发展出了以燕辽地区为中心的、具有“早期陆内伸展沉降+峰期巨量岩浆活动”特征的大型被动裂谷盆地。

致谢 本文主要认识源自翟明国研究员的指导和彭澎研究员的启发、成型于与马旭东博士的长期讨论，在此对诸位师长表达敬意和感谢。李怀坤研究员对本研究给予了大力支持，李承东研究员与笔者进行了有益讨论；张阔、任云伟、田辉等同事参与了部分样品的测试和数据处理工作；专辑召集人赵太平研究员、副主编俞良军博士、审稿专家胡健民研究员、张华锋博士和祝禧艳博士对本文提出了宝贵建议和具体意见。在此一并表示感谢。