关于中国元古宙地质年代划分几个问题的讨论

本文简略回顾了我国元古宙划分的进展和问题,在我国地质文献中,元古宙通常以２．５Ｇａ,１．８Ｇａ,１．０Ｇａ和０．５７Ｇａ为年代界线划分为在早,中和晚元古代。本文建议以古,中和新元古代代替早,中和晚元古代的命名,古元古代介于２．５Ｇａ至１．８Ｇａ之间,可包含三个纪,内部年代界线置于２．３Ｇａ和２．０５Ｇａ,文中对三个纪的名称和代表悸地层单元提高明确的建议,中元古代通常包含长城纪和蓟县纪,纪的界线置于     

吉林省前寒武纪地层

吉林省前寒武纪地层可见有太古宙变质表壳岩系、古元古代中深变质火山-沉积岩系、吉南新元古代陆源碎屑岩-碳酸盐岩组成的盖层沉积岩系和吉北造山带新元古代变质火山-沉积岩系4种类型.其中太古宙地层龙岗陆块具有多陆块拼贴的特点,可划分为龙岗岩群(四道砬子河岩组、杨家店岩组)、夹皮沟岩群(三道沟岩组、老牛沟岩组)、板石沟岩群、南岗岩群(鸡南岩组、官地岩组)、清原岩群.分别代表白山镇地块、夹皮沟镇地块、板石沟地块、和龙地块和清原地块的变质表壳岩系,其中除龙岗岩群可能为中太古代外,其余地质体的时代均为新太古代.古元古代地层有集安岩群、光华岩群和老岭岩群,前两者为古元古代早期裂谷环境沉积,分别可进一步划分为蚂蚁河岩组、荒岔沟岩组、大东岔岩组、双庙岩组和同心岩组,沉积时限为2 300～2 100Ma;后者为古元古代晚期内克拉通凹陷沉积,可进一步划分为林家沟岩组/达台山岩组、珍珠门岩组、花山岩组、临江岩组和大栗子岩组,沉积时限为1 900～1 800Ma.吉南新元古代地层的岩石地层学属性基本清楚,按新元古代三分的观点,其中细河群及其以下地层时代为青白口纪.浑江群时代为震旦纪,吉南地区缺失南华系.吉林省北部造山带中沿色洛河-海沟-青龙村-江域一线的元古宙地层事实上为不同时代、不同性质的构造岩片堆叠体,属于构造地层学范畴;具有层状地层特征的仅有敦化地区的塔东岩群、蛟河地区的新兴岩组、九台地区的机房沟岩群、辽源地区的西保安岩组以及安图地区的万宝岩组,时代可暂置于新元古代.     

太古宙—元古宙过渡分界及成矿动力体制转换

太古宙与元古宙之间分界时限较窄、测年数据偏新和混乱, 极大遏制了地球早期基础地质的深入研究.通过太古宙与元古宙分界标志和过渡标志的确定, 将太古代—元古代间动力体制转换类型划分为4种: 挤压体制向扩张体制转换; 垂直运动与水平运动间转换; 水平主压应力场转换; 地幔柱体制向板块构造体制转换.太古代与元古代间动力体制转换产物主要为真核生物、放射性元素、岩浆、矿产, 各自形成时限可达(3~5) × 108 a.太古宙与元古宙之间分界不应以单一年代划分, 而是一个渐变过渡的界线, 可初步确定在2.2 0~2.80Ga之间.太古宙—元古宙界线的划分应与地球动力学和构造体制等重大事件相联系, 此研究为探求早期深部成矿作用带来新的启迪      

从哥伦比亚超大陆裂解事件论古/中元古代的界限

国际前寒武纪地层表中始终把古/中元古代的界线置于1. 6Ga,我国则一直将这一界线置于1. 8Ga。存在认识分歧的根本原因是对1. 8Ga前后时期地质事件及其性质的理解与认识的差异或偏颇。本文通过阐述1. 8～1. 6Ga期间地质事件及其性质,重点分析和讨论古/中元古代(界)界限的划分及相关地质事件的标志与意义。大量的地质资料显示,超大陆从1. 8～1. 75Ga开始裂解,形成一系列的陆内盆地,如北美(劳伦古陆)的Thelon盆地、澳大利亚北部的Leichhardt超级盆地、南美巴西圣弗兰西斯科盆地、华北南缘的熊耳裂谷盆地以及扬子地块西南缘的东川盆地等。在这些盆地形成的早期沉积了冲积扇相、河流相的碎屑岩,之后伴有较广泛的火山岩喷发,中晚期从河流相、湖相碎屑岩沉积过渡到浅海碳酸盐台地沉积,反映一个拉伸裂解的过程。在复原的哥伦比亚超大陆内,广泛分布有1. 78～1. 72Ga的非造山花岗岩,包括AMCG组合(斜长岩、纹长二长岩、紫苏花岗岩和花岗岩)、环斑花岗岩、A型花岗岩等,以及广泛分布的基性岩墙群。这些岩浆岩都反映了拉伸裂解的地球动力学背景。在1. 8～1. 6Ga,不论是沉积事件还是岩浆事件,绝大部分与超大陆的拉伸裂解有关,并未显示造山作用、大陆固结和克拉通化的特点,用固结纪来概括这一阶段地质事件的性质并不合适。哥伦比亚超大陆上的许多盆地在1. 6Ga左右经历了一次广泛的抬升,使沉积作用短时间间断,之后原有盆地继续发展,接受了更广泛的沉积,这种沉积作用可以一直延续到1. 4～1. 3Ga左右。与裂解有关的岩浆事件也以幕式方式从1. 78Ga一直断续持续到1. 4～1. 32Ga左右。从1. 8Ga(或1. 78Ga)到1. 4～1. 3Ga,不论是盆地的沉积事件还是与裂解有关的岩浆事件,基本是连续的。以1. 6Ga作为年代界线划分古/中元古代,人为地隔断了连续的沉积事件和岩浆事件,显然与"尽可能少地截断沉积作用、火成侵位或造山运动的主要序列"的前寒武纪地层划分原则相悖。连续的裂谷盆地沉积事件和非造山岩浆事件可以追溯到1. 8Ga(或1. 78Ga)。因此,我们建议将古/中元古代的界线置于1. 8Ga或1. 78Ga。考虑到裂谷作用的本质是在已有超大陆或克拉通的基础上盖层的发育过程,因此我们建议将～1. 8Ga或1. 78～1. 4Ga都归入盖层系。     

江西中部新元古代潭头群的建立

江西中部在元古代神山群黑色千枚岩之上,早震旦世古家组砾岩或含砾千枚岩之下,有一套以火山碎屑岩夹酸性火山熔岩为主的地层,这套地层命名为潭头群,自下而上划分为田东组,火峡岭组,上施组,总厚达２０００ｍ。上部２个组产丰富的微古植物化石,时代大部分属于蓟县纪－震旦纪。下部田东组的熔岩测得锆石Ｕ－Ｐｂ年龄为（１０２７±３６）Ｍａ。根据上述情况,确认潭头群属于新元古代,时限为１０５０￣７４０Ｍａ之间。     

江西中部新元古代潭头群的建立

江西中部在元古代神山群黑色千枚岩之上,早震旦世古家组砾岩或含砾千枚岩之下,有一套以火山碎屑岩夹酸性火山熔岩为主的地层。这套地层命名为潭头群,自下而上划分为田东组、火峡岭组、上施组,总厚达２０００ｍ。上部２个组产丰富的微古植物化石,时代大部分属于蓟县纪—震旦纪;下部田东组的熔岩测得锆石ＵＰｂ年龄为（１０２７±３６）Ｍａ。根据上述情况,确认潭头群属于新元古代,时限为１０５０～７４０Ｍａ之间。     

来自国际地层委员会前寒武纪分会的消息报道

天津地质矿产研究所所长,中国地质学会前寒武纪专业委员会主任、国际地层委员会前寒武纪分会（SPS）投票委员陆松年先生最近收到了SPS的最新简报,其中部分内容需即时向国内同行介绍。1．太古富和元古宙的四分SPS于1998年12月在巴西召开了第11届会议。会上正式通过了太古宙的四分方案。即始太古代（＞3．6Ga）、古太古代（3．6～3．2Ga）、中太古代（3．2～2．8Ga）和新太古代（2．8～2．SGa）,并决定报请国际地层委员会正式批准,准备工作正在进行。此外,会议注意到部分委员对元古宙四分的提议,认为现在划分的古元古代（2．5～1…     

新疆中—新元古代古地理

1 前言 研究某一时期的古地理,首先要确定该时期的时限和层序。新疆中、新元古界时限、层序研究程度很差,尤其是"时限",全区无一个系统的同位素年龄测定剖面。本次编图为了与国际地层研究接轨,按国际地科联规定的"地层时代表（1989年）"划分：即中元古代的时限为1 650～1 050 Ma;新元古代为1 050～570 Ma;其中800～570 Ma为震旦纪。地层层序方面,近20年来有较大进展,在该时代地层中,获得较多同位素年龄、叠层石、微古植物资料及少量古地磁数据,岩石地层学及区域地层学方面也有不少新的认识。层序研究较清楚的地区有库鲁克塔格、…     

中朝板块元古宙板内地震带与盆地格局

地史中发生的强地震事件在地层中留下固定的记录 (图 1～ 3) ,这些记录在区域上呈带状分布 ,代表地史中的地震带。中朝板块元古宙目前可识别出两个板内地震带 (图 5 )。中元古代板内地震带 (170 0～ 12 0 0Ma)西起太行山北段 ,经燕山山脉、辽宁西部、穿越辽河平原至辽宁北部的泛河流域分布 ,即燕山—泛河地震带 ,现今呈NEE向延伸。新元古代震旦纪地震带沿吉林南部、辽东半岛、山东中部及苏皖北部现今呈NNE走向分布 ,即古郯庐地震带 (6 5 0～ 6 0 0Ma)。上述两个板内地震带是元古宙不同时期超大陆裂解的响应。中元古代与新元古代两个不同方向的地震断裂带分别控制着两个时期的盆地边界。燕山泛河地震断裂带构成中元古代海盆南界 (指现在的位置 ) ,形成向北开放的海域。古郯庐地震断裂带将中朝板块裂解为华北块体与胶辽朝块体。古郯庐地震断裂带构成震旦纪海域的边界 ,震旦纪海盆通过朝鲜半岛与当时的外海相连接 ,华北块体则为陆源剥蚀区。文内四幅古地理图 (图 6～ 9)是以地震灾变思想为指导 ,以新的地层研究、对比为基础编制的 ,侧重反映了盆地的格局及其变化。根据地震、同沉积断裂新的思路 ,可提供地质学家重新认识与解释某些沉积矿床的成因 ,它们的成矿元素均来自地球深部而非地表风化作用。文中编制     

北秦岭前寒武纪地壳组成及其构造演化

北秦岭主要发育元古宙构造岩石地层单位,包括古元古代秦岭岩群,中元古代峡河岩群,宽坪岩群和武关岩群,中元古代晚期松要地沟蛇绿岩构造岩片,新元古代丹凤岩群和二郎坪岩群的下部地层单位以及晋宁期强烈的构造岩浆活动。北秦岭广泛存在晋宁期强烈构造－岩浆－变质地质事件,且是新元古代主体形成的古老造山带,晋宁期的强烈地质事件可能代表了地块,北秦岭微地块中秦岭地块与扬子地块之间的俯冲碰撞拼合。震旦纪之后又逐渐开始发     

A New Progress of the Proterozoic Chronostratigraphical Division

The Precambrian, an informal chronostratigraphical unit, represents the period of Earth history from the start of the Cambrian at ca. 541 Ma back to the formation of the planet at 4567 Ma. It was originally conceptualized as a "Cryptozoic Eon" that was contrasted with the Phanerozoic Eon from the Cambrian to the Quaternary, which is now known as the Precambrian and can be subdivided into three eons, i.e., the Hadean, the Archean and the Proterozoic. The Precambrian is currently divided chronometrically into convenient boundaries, including for the establishment of the Proterozoic periods that were chosen to reflect large-scale tectonic or sedimentary features(except for the Ediacaran Period). This chronometric arrangement might represent the second progress on the study of chronostratigraphy of the Precambrian after its separation from the Phanerozoic. Upon further study of the evolutionary history of the Precambrian Earth, applying new geodynamic and geobiological knowledge and information, a revised division of Precambrian time has led to the third conceptual progress on the study of Precambrian chronostratigraphy. In the current scheme, the Proterozoic Eon began at 2500 Ma, which is the approximate time by which most granite-greenstone crust had formed, and can be subdivided into ten periods of typically 200 Ma duration grouped into three eras(except for the Ediacaran Period). Within this current scheme, the Ediacaran Period was ratified in 2004, the first period-level addition to the geologic time scale in more than a century, an important advancement in stratigraphy. There are two main problems in the current scheme of Proterozoic chronostratigraphical division:(1) the definition of the Archean–Proterozoic boundary at 2500 Ma, which does not reflect a unique time of synchronous global change in tectonic style and does not correspond with a major change in lithology;(2) the round number subdivision of the Proterozoic into several periods based on broad orogenic characteristics, which has not met with requests on the concept of modern stratigraphy, except for the Ediacaran Period. In the revised chronostratigraphic scheme for the Proterozoic, the Archean–Proterozoic boundary is placed at the major change from a reducing early Earth to a cooler, more modern Earth characterized by the supercontinent cycle, a major change that occurred at ca. 2420 Ma. Thus, a revised Proterozoic Eon(2420–542 Ma) is envisaged to extend from the Archean–Proterozoic boundary at ca. 2420 Ma to the end of the Ediacaran Period, i.e., a period marked by the progressive rise in atmospheric oxygen, supercontinent cyclicity, and the evolution of more complex(eukaryotic) life. As with the current Proterozoic Eon, a revised Proterozoic Eon based on chronostratigraphy is envisaged to consist of three eras(Paleoproterozoic, Mesoproterozoic, and Neoproterozoic), but the boundary ages for these divisions differ from their current ages and their subdivisions into periods would also differ from current practice. A scheme is proposed for the chronostratigraphic division of the Proterozoic, based principally on geodynamic and geobiological events and their expressions in the stratigraphic record. Importantly, this revision of the Proterozoic time scale will be of significant benefit to the community as a whole and will help to drive new research that will unveil new information about the history of our planet, since the Proterozoic is a significant connecting link between the preceding Precambrian and the following Phanerozoic.     

中国金矿床成矿时代及其特征

根据 70 4个主要金矿床的成矿时代研究 ,将中国金矿床划分为古元古代、中新元古代、早古生代、晚古生代、三叠纪、侏罗 -白垩纪、新生代 7个成矿期。统计分析了各成矿期形成的金矿床数量、储量及矿床类型 ,总结了各成矿期金矿床的分布特征。     

Geochronological Framework and Geodynamic Implications of Mafic Magmatism in the Liaodong Peninsula and Adjacent Regions, North China Craton

Mafic rocks are widespread on the Liaodong Peninsula and adjacent regions of the North China Craton. The majority of this magmatism was originally thought to have occurred during the Pre-Sinian, although the precise geochronological framework of this magmatism was unclear. Here, we present the results of more than 60 U–Pb analyses of samples performed over the past decade, with the aim of determining the spatial and temporal distribution of mafic magmatism in this area. These data indicate that Paleoproterozoic–Mesoproterozoic mafic rocks are not as widely distributed as previously thought. The combined geochronological data enabled the subdivision of the mafic magmatism into six episodes that occurred during the middle Paleoproterozoic, the late Paleoproterozoic, the Mesoproterozoic, the Late Triassic, the Middle Jurassic, and the Early Cretaceous. The middle Paleoproterozoic (2.1–2.2 Ga) mafic rocks formed in a subduction-related setting and were subsequently metamorphosed during a ca. 1.9 Ga arc–continent collision event. The late Paleoproterozoic (ca. 1.87–1.82 Ga) bimodal igneous rocks mark the end of a Paleoproterozoic tectono-thermal event, whereas Mesoproterozoic mafic dike swarms record global-scale Mesoproterozoic rifting associated with the final breakup of the Columbia supercontinent. The Late Triassic mafic magmatism is part of a Late Triassic magmatic belt that was generated by post-collisional extension. The Middle Jurassic mafic dikes formed in a compressive tectonic setting, and the Early Cretaceous bimodal igneous rocks formed in an extensional setting similar to a back-arc basin. These latter two periods of magmatism were possibly related to subduction of the Paleo-Pacific plate.     

A subdivision of the Precambrian of China

Precambrian rocks are widely distributed in China. The Precambrian is divided into two time units, i.e., the Archaean and Proterozoic Eon, each of these is separated into three chronological intervals, also with the status of eras, with the prefixes early, middle or late. The time boundary between the Archaean and Proterozoic Eon is placed at ～ 2500 Ma.According to the present isotopic data, the proposed subdivision for the Archaean of China is two-fold. The age of the Fuping Group is younger than 2800–2900 Ma, and that of the Qianxi Group and the corresponding stratigraphic units of eastern Liaoning are older than 2800 Ma, so that 2800+ Ma is selected as the boundary between the early—middle and late Archaean.Based on the representative stratigraphic units, the Wutai and Huto Groups, and an intervening major unconformity formed by the Wutaiian orogeny at 2200–2300 Ma, the early Proterozoic is further divided into two periods, with a time demarcation at 2200+ Ma. A major episode of orogeny known as the “Luliangian Movement” occurred at the end of the early Proterozoic at ～ 1900 Ma. This disturbance was very extensive and is, in a way, responsible for the difference in geological conditions between the lower and middle—upper Proterozoic in China. The boundary (1900 Ma) that relates to the Luliangian Movement is more important than the boundary corresponding to the age of 1600 Ma, which is recommended as the time boundary between Proterozoic I and II, so we propose to use 1900 Ma as the boundary between the early and middle Proterozoic in China.The time boundary between the middle Proterozoic, including the Changcheng System and the Jixian System, and the late Proterozoic, which is composed of the Qingbaikou and Sinian Systems, is ～ 1000 Ma. The age for the boundary between Cambrian and Precambrian, based upon the recent isochron data, is inferred to be 610 Ma.     

甘新蒙北山地区构造格局及演化

甘新蒙北山地区地处天山东段、北山及阿拉善地区 ,为古生代哈萨克斯坦板块、塔里木板块和华北板块交汇地带。可分为 7个二级构造单元 (构造区 )、2 6个三级构造单元 (地块、褶皱带 )。该区构造演化史漫长而复杂。太古宙时期 ,是古陆核形成萌芽阶段 ,古元古代初陆壳开始生成 ,出现薄壳结构的宽广的裂陷活动带 ,到了中、新元古代后期显露出板块构造运动 ,新元古代晚期经历重大热事件———晋宁运动 ,发生陆块间汇聚—碰撞并形成了榴辉岩—花岗岩岩浆带。震旦纪在晋宁期的拼合古陆上再一次裂解 ,经历了板块构造演化史。晚古生代 ,本区主体转入板内构造时期 ,以开合构造为主 ,花岗岩浆活动广泛发育。中、新生代进入板内造山和现今的盆山构造格局时期     

新疆北部前寒武系划分和对比

库鲁克塔格是新疆北部前寒武系分布较广,地层层序相对完整的地区.作者以库鲁克塔格为地层模型区,以同位素第龄为格架,初步确定了本区群级地层单元的界线及归属.在岩石地层、生物地层、化学地层等各种方法相互印证的基础上,建立并完善了前寒武纪的地层层序.     

扬子板块东北缘的随县－应山地区早古生代沉积盆地演化

位于扬子板块和大别变质地体之间的随－应地区，早古生代是一被动大陆边缘扩张盆地。根据沉积盆地基底、地层层序、沉积体系和火山岩亲缘关系，随一应地体的发展史可追溯到晚元古代，并划分为４个阶段：（１）晚元古代至早震旦世地壳上拱和拉伸阶段；（２）晚震旦世至早寒武世被动大陆边缘阶段；（３）中寒武世至奥陶纪海底扩张阶段；（４）志留纪至泥盆纪盆地充填回返阶段。本区沉积盆地发育模式是由大陆边缘裂谷盆地转化为前陆盆地模式。     

敦煌复合造山带前寒武纪地质体的组成和演化

敦煌复合造山带位于塔里木克拉通东端,是连接塔里木克拉通和华北克拉通的重要纽带。近年来,敦煌基础地质研究取得了重大进展。本文简要回顾了敦煌基础地质研究历史和现状,系统归纳了区内前寒武纪地质单元时空分布特征及前寒武纪构造-热事件序列,初步讨论了前寒武纪大陆地壳形成和演化规律、前寒武纪结晶基底亲缘性及构造演化过程,提出:(1)敦煌造山带前寒武纪结晶基底形成于ca.3.1~1.6Ga,构造-热事件主要划分为新太古代(ca.2.7~2.6Ga和2.6~2.5Ga)、古元古代晚期(ca.2.0~1.8Ga)和中元古代早期(1.8~1.6Ga)三个阶段;(2)新太古代早期(ca.2.7~2.6Ga)和新太古代晚期(2.6~2.5Ga)是敦煌造山带大陆地壳形成的主要阶段;古元古代晚期(ca.2.0~1.8Ga)和中元古代早期(1.8~1.6Ga)主要是古老大陆地壳物质再循环阶段,也有少量新生陆壳物质的形成;(3)敦煌造山带前寒武纪结晶基底最初拼合事件可能发生在新太古代末期(~2.5Ga),之后经历了古元古代晚期(ca.2.0~1.8Ga)汇聚、碰撞造山过程,直到中元古代早期(1.8~1.6Ga),造山活动结束,前寒武纪结晶基底最终固结,进入稳定发展阶段;(4)前寒武纪结晶基底最终稳定固结之后,即～1.6Ga之后,敦煌前寒武纪结晶基底可能进入长达12亿年的静寂期,一直处于稳定状态,目前没有发现相关的岩浆-变质-沉积记录(类似于地盾状态),直至古生代志留纪开始活化(～440Ma),卷入古亚洲洋南缘俯冲、碰撞造山过程并被强烈改造。     

中国晚元古代古构造与古地理

本文所指晚元古代时限为距今1000-600百万年。中国晚元古代可分为两个阶段,自1000-800百万年一段暂不建纪,因为这一时期的地层在全国的对比还存在很多问题,生物面貌远不明确,所以我们仍称青白口群,不用青白口系。自800-600百万年这一段即现称震旦纪。根据地层沉积类型和分区,我们编制了三幅古构造古地理图(图1-3)。     

Tectonic Development of the Proterozoic Continental Margins in East Qinling and Adjacent Regions

The East Qinling and adjacent cratonic regions belong to two geotectonicunits,the Sinokorean Subdomain including the Sinokorean Platform and itssouthern continental margin the North Qinling Belt,and the YangtzeanSubdomain comprising the Yangtze Platform and its northern continental mar-gin the South Qinling Belt.The Qinling region may thus be subdivided into twocontinental margin belts separated from each other by the Proterozoic Qinlingmarine realm,which did not disappear until Late Triassic.The convergentcrustal consumption zone,the megasuture between the two belts,lies betweenthe Fengxian-Shangnan line in the north and the Shanyang-Xijia line in thesouth and was much deformed and displaced through Mesozoic intracratoniccollision and compression.In the northern subdomain the Lower Proterozoic is representedby protoaulacogen volcano-sediments,the inner Tiedonggou Group and theouter marginal Qinling Group,which were folded and metamorphosed in theLuliangian orogeny,a general process of aggregation and s