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1.
华北克拉通太古宙研究若干进展   总被引:11,自引:0,他引:11  
华北克拉通存在3.8 Ga以上的地质演化历史。本文对近年来我们在鞍本、冀东、鲁西、胶东和阴山地区研究取得的进展作了简要介绍。在鞍山,深沟寺杂岩获得~3770 Ma,3600–3660 Ma,~3450 Ma,3310–3330 Ma和~3120 Ma锆石年龄,与白家坟杂岩和东山杂岩的岩浆事件十分类似。在冀东,对曹庄杂岩副变质斜长角闪岩和石榴黑云片麻岩定年,发现大量3.5–3.8 Ga碎屑锆石,并获得~2.5 Ga变质锆石年龄,冀东地区很可能存在始太古代岩石,可把曹庄杂岩形成时代限定在2.5 Ga和3.4 Ga之间。在鲁西,把太古宙基底从东北到西南依次划分为A、B、C三个岩带:A带主要为新太古代晚期的壳源花岗岩,B带主要为新太古代早期的岩石,C带主要为新太古代晚期的新生岩浆岩。鲁西是华北克拉通新太古代早期岩石分布最广泛的地区,也是华北克拉通确认新太古代早期和晚期表壳岩系共存的唯一地区。在胶东,规模巨大的2.9 Ga岩浆热事件被识别出来,它是强烈地幔添加作用的产物。可能作为岩浆板底垫托作用的结果,2.9 Ga岩石与2.7 Ga岩石一道,在新太古代晚期(~2.5 Ga)遭受强烈变质改造。在阴山地块,除2.5 Ga表壳岩和侵入岩外,还存在2.7 Ga英云闪长岩和2.6 Ga花岗岩。新获得的资料表明阴山地块与华北克拉通东部陆块具有类似的早前寒武纪地质演化历史。还对华北克拉通太古宙变质基底的锆石年龄和Hf同位素组成及全岩Nd同位素组成进行了统计研究。结合前人工作,初步总结了华北克拉通太古宙地质演化特点。认为华北克拉通与其它克拉通类似,新太古代早期—中太古代晚期是陆壳形成增生的主要时期,但最强烈广泛的构造热事件存在于新太古代晚期。在我们新提出的构造区划中,划分出了三个古陆块(2.6 Ga),即东部古陆块、南部古陆块和中部古陆块。  相似文献   

2.
黄道袤  董春艳  万渝生 《地球科学》2020,45(9):3330-3340
为了探讨华北克拉通南缘早前寒武纪形成演化,对华北克拉通南缘小秦岭地区早前寒武纪变质基底花岗质片麻岩开展了SHRIMP U-Pb锆石定年、Hf同位素组成及地球化学组成研究,获得了2个TTG片麻岩样品~2.50 Ga的岩浆锆石年龄和时代相近的变质锆石年龄,岩浆锆石εHf(t)值为0.71~4.37;1个花岗质片麻岩样品的岩浆锆石年龄为~2.30 Ga,εHf(t)值为-1.21~0.11.它们也记录了古元古代晚期变质锆石年龄或显示古元古代晚期构造热事件影响的存在.岩石以轻重稀土强烈分异为特征,大离子亲石元素相对富集,Nb、P、Ti相对亏损.在小秦岭地区首次发现新太古代晚期TTG岩石,并识别出新太古代晚期构造热事件.现有资料支持华北克拉通南缘与华北克拉通其他地区具有类似的早前寒武纪形成演化历史的认识.但是,华北克拉通南缘以2.3 Ga左右岩浆作用十分发育而显示出独特性.   相似文献   

3.
第五春荣 《岩石学报》2021,37(2):317-340
太古宙约占地球已有演化历史的三分之一强,这一时期涉及到大陆地壳起源、陆壳的巨量生长和稳定以及板块构造作用的启动、建立等诸多最根本的全球性重大地质事件。太古宙岩石在华北克拉通南部的涑水、登封、太华、霍邱和五河等杂岩中广泛出露,这为解析上述重大科学问题提供难得的素材。近十年来,在华北克拉通南部古生代-中生代火山岩或早前寒武纪变沉积岩中陆续发现冥古宙-古太古代的捕获/碎屑锆石,暗示南部地块依然尚存地球形成最初期的陆壳物质。根据华北克拉通南部太古宙岩石年龄统计结果显示有2850~2700Ma和2580~2480Ma两个突出年龄区间,对应的峰值年龄分别为~2.76Ga和~2.52Ga。其中~2.76Ga的岩石主要出露于南部的鲁山、霍邱、五河和中条山地区。此外,在华北克拉通诸多地区,诸如怀安、阜平、五台、中条等地区的花岗质片麻岩和变质沉积岩中也均发现年龄为~2.76Ga的碎屑锆石或者继承锆石,暗示华北克拉通2.85~2.70Ga岩石的分布似乎比现今出露范围更为广泛。与整个华北克拉通类似,2.58~2.48Ga岩石亦在克拉通南部广泛分布,尤其是嵩箕地区的登封杂岩几乎全部是由新太古代晚期的岩石组成。~2.52Ga是华北克拉通南部,乃至整个克拉通太古宙地壳演化最突出、最重要的岩浆-构造事件,明显有别于全球其它诸多典型克拉通。已有的同位素资料研究表明华北克拉通南部,乃至整个克拉通在太古宙经历了两期明显的地壳生长事件:一期发生在2.85~2.70Ga左右,以形成于此时期的涑水杂岩中花岗质岩石和鲁山太华片麻岩系中深成侵入岩和斜长角闪岩为代表;另一期发生在2.58~2.48Ga,以登封杂岩、涑水杂岩以及小秦岭地区太华杂岩中~2.52Ga各类花岗质岩石和变基性岩为代表。华北克拉通正是经过这两期陆壳巨量生长事件之后完成初始的克拉通化。我们在登封杂岩中识别出形成于俯冲汇聚环境的TTG质片麻岩、类似于赞岐岩的变闪长岩和具有N-MORB地球化学特征的变基性火山岩,提出其构成"新太古代构造混杂岩",标志着新太古代末期具有现代体制的板块构造在华北克拉通南部已经开始启动。最近,在登封杂岩中识别出的新太古代双变质带也支持上述观点。  相似文献   

4.
在对一些重点地区新太古代早期—中太古代晚期(2.6~3.0 Ga)岩石的空间分布、岩石类型和形成时代作简要介绍基础上,文章总结了华北克拉通这一时代花岗质岩石的年龄分布模式、地球化学和Nd-Hf-O同位素组成特征。新太古代早期—中太古代晚期变质基底具有如下特征:①新太古代早期—中太古代晚期岩浆作用在华北克拉通几乎连续分布,峰期为2.70~2.75 Ga;②新太古代早期—中太古代晚期岩石在华北克拉通广泛存在,主要分布在东部古陆块、中部古陆块和南部古陆块中;③新太古代早期—中太古代晚期侵入岩以英云闪长岩为主,存在奥长花岗岩和花岗闪长岩及其他类型岩石;④新太古代早期—中太古代晚期表壳岩规模很小,零星分布于花岗质岩石中,岩石类型主要为变玄武质岩石,一些地区存在变质科马提岩、变质安山质?英安质火山岩和变质碎屑沉积岩;⑤2.6 Ga可作为华北克拉通新太古代早期和晚期的界线;⑥TTG岩石的Sr/Y和La/Yb比值存在很大变化,在Sr/Y-Y和La/Yb-Yb图中位于高压、中压和低压TTG分布区;除少量富钾花岗岩外,华北克拉通新太古代早期—中太古代晚期岩石大都具有亏损Nd-Hf同位素组成特征;岩浆锆石O同位素组成与全球太古宙岩浆锆石类似;⑦许多地区都具有类似地质特征,但一些地区显示出较大的独特性。新的研究进一步支持了这样的认识:与全球其他许多典型克拉通类似,新太古代早期—中太古代晚期是华北克拉通最重要的陆壳增生时期,主要区别是华北克拉通叠加了强烈的新太古代晚期岩浆构造热事件。   相似文献   

5.
正本期论文"华北克拉通南缘约2.5Ga构造变质事件及意义"(曹正琦等),对于探讨华北克拉通太古宙晚期的构造演化具有重要意义.华北克拉通新太古代末期到早元古代早期构造-岩浆热事件的性质,是中国早前寒武纪地质学领域的重大科学问题和区域热点之一.华北克拉通约2.5Ga构造岩浆热事件广泛发育,但  相似文献   

6.
肖玲玲  刘福来  张健 《岩石学报》2019,35(2):325-348
新太古代早期是全球地质历史上一个重要的地壳生长时期,世界众多克拉通中广泛存在2. 7Ga左右的岩浆年龄记录。华北克拉通最主要的岩浆事件发生在新太古代晚期,这与世界其他克拉通广泛存在~2. 7Ga的构造热事件明显不同。但全岩Nd和锆石Hf同位素研究表明,华北克拉通~2. 5Ga的岩石主体来自于中太古代晚期-新太古代早期大陆物质的重熔或再造。因此,厘定~2. 7Ga地质事件在华北克拉通的空间分布对深入理解新太古代地壳形成与演化具有重要科学意义。华北克拉通已识别出的~2. 7Ga的花岗质岩石主要分布在胶东、鲁西、武川、赞皇和太华等少数杂岩区,中部带的恒山、阜平和中条杂岩中亦有零星出露。左权变质杂岩位于中部带中南段,赞皇杂岩西南,初步地球化学和锆石年代学研究表明,该地区有多种岩石类型记录了~2. 7Ga的年龄信息,包括副片麻岩、长英质浅色体、磁铁矿角闪片麻岩和TTG片麻岩。其中,TTG片麻岩的原岩为英云闪长岩,锆石发育明显的核边结构,核部具有清晰的岩浆环带,两个不同LA-ICP-MS实验室获得的不一致线上交点年龄分别为2727±14Ma和2731±12Ma,代表了TTG岩浆岩的结晶年龄。同时,左权变质岩石中较好地保存了新太古代晚期的岩浆和变质年龄记录,推测其所代表的构造热事件与华北克拉通~2. 5Ga所经历的大规模幔源岩浆的底侵作用有关。  相似文献   

7.
石强  马龙  陈湘智  徐仲元  李世超  徐进贵  陈开运 《地质论评》2023,69(6):2023060007-2023060007
华北克拉通北缘西部陆块早前寒武纪基底分布广泛,现有的研究普遍认为经历 2.5 Ga,2.45~2.37 Ga,1.95 Ga和1.85 Ga变质热事件影响。华北克拉通北缘阴山陆块中2.5 Ga的紫苏花岗岩研究已经成为了揭示华北克拉通北缘早前寒武纪构造演化的一个热点,但孔兹岩带中却鲜少有新太古代晚期构造热事件的相关报道。近年来,相继从大青山地区的孔兹岩带石榴黑云母片麻岩中分辨出一期具有2.45~2.37 Ga变质锆石年龄的大青山表壳岩,同时出露与其成因关系密切的深熔石榴花岗岩,但其深熔成因的模式存在争议。本文对大青山地区新发现的新太古代晚期紫苏花岗岩、石榴花岗岩及其围岩的野外空间产出关系和锆石年代学进行对比分析,为探究深熔石榴花岗岩成因模式提供重要的启示。  相似文献   

8.
华北克拉通具有3.8Ga以上的演化历史,TTG是其地质记录的最重要载体。华北克拉通太古宙(特别是中太古代以前)地质演化在很大程度上与TTG岩石密切相关。在华北克拉通,始太古代(3.6~4.0Ga)TTG岩石仅在鞍本地区被发现,但冀东地区已在多种变质碎屑沉积岩中发现大量3.6~3.88Ga碎屑锆石;古太古代(3.2~3.6Ga)TTG岩石在鞍本、冀东、信阳地区被识别出来;中太古代(2.8~3.2Ga)TTG岩石在鞍本、冀东、胶东、鲁山等地存在;可把新太古代(2.5~2.8Ga)进一步划分为早期和晚期两个阶段:新太古代早期(2.6~2.8Ga)TTG岩石已在10余个地区被发现,新太古代晚期(2.5~2.6Ga)TTG岩石几乎在每一个太古宙基底岩石出露区都存在。野外地质、锆石定年、元素地球化学和Nd-Hf同位素组成研究表明,中太古代以前TTG岩石局部存在,主要分布于Wan et al.(2015)所划分的三个古陆块中;新太古代TTG岩石广泛分布,是陆壳增生最重要时期岩浆作用的产物。TTG岩石类型随时代变化,3.1~3.8Ga和2.7~2.9Ga TTG岩石分别主要为奥长花岗岩和英云闪长岩;2.5~2.6Ga期间花岗闪长岩大规模出现,并有壳源花岗岩广泛分布,表明这时陆壳已有相当的成熟度。奥长花岗岩轻重稀土分异程度从弱到强的时间出现在~3.3Ga;2.5~3.3Ga的TTG岩石轻重稀土分异程度变化很大,表明其形成条件存在很大差异。TTG岩石主要为新生地壳,但也有相当部分为壳内再循环产物或形成过程中受到陆壳物质影响。华北克拉通中太古代以前的主要构造机制是板底垫托或地幔翻转作用,新太古代晚期板块构造体制可能已起作用。  相似文献   

9.
鲁西是华北克拉通太古宙基底典型分布区之一,存在新太古代早期到晚期长期连续的地质演化的记录。在泰山地区黄前水库北侧,我们对相互关系十分清楚的不同类型和时代TTG岩浆岩进行了详细野外地质观察和锆石SHRIMP U-Pb定年。早期片麻状英云闪长岩为望府山杂岩的一部分,具有深熔特征,岩浆锆石和变质锆石年龄分别为2695±7 Ma和2630±10 Ma。早期片麻状英云闪长岩被奥长花岗岩脉切割,后者的两组锆石年龄分别为2626±8 Ma和2689±12 Ma,分别代表了其形成时代和捕获锆石年龄。之后,它们又被晚期弱片麻状英云闪长岩(线峪岩体)侵入,其岩浆锆石年龄为2547±7 Ma,存在2.6~2.7 Ga捕获锆石。这些不同时代岩浆岩的形成过程是鲁西地区新太古代地质演化的一个缩影。  相似文献   

10.
华北克拉通南部早前寒武纪基底形成与演化   总被引:4,自引:3,他引:1  
张瑞英  孙勇 《岩石学报》2017,33(10):3027-3041
简要总结了华北克拉通南部鲁山地区、小秦岭地区、登封及中条山地区的早前寒武纪地质事件序列及其地质意义,并对各地区地质特征和变质演化特点进行对比。结合前人研究工作,初步探讨了华北克拉通南部早前寒武纪基底的演化特点、陆壳形成的主要时期和华北南部基底的构造区划等问题,提出几点认识:1)华北克拉通南部鲁山、中条山、小秦岭等地区均有2.7~2.9Ga岩石记录,以英云闪长质-奥长花岗质-花岗闪长质(TTG)岩石为主,它们共同构成华北南缘的古老结晶基底,并经历了新太古代晚期~2.5Ga构造-热事件,标志着华北克拉通南部在新太古代末期可能已经形成统一基底;2)华北克拉通南部主要的陆壳形成时期为中太古代晚期-新太古代,与全球其他主要克拉通一致,而古元古代早-中期则以地壳再循环为主;3)综合地质、地球化学等特点,将华北南部鲁山-小秦岭地区和中条山等地区划归为"南部古陆块",并提出该陆块呈现为一个大型的倾伏向斜构造,可能在新太古代晚期已经形成,其枢纽向南东倾斜。"南部古陆块"在新太古代末期与其它微陆块拼合,并发生了变质作用和陆壳的活化与再循环,共同指示新太古代晚期华北克拉通统一基底的形成。  相似文献   

11.
华北克拉通南缘太华杂岩组成及演化   总被引:1,自引:4,他引:1  
第五春荣  刘祥  孙勇 《岩石学报》2018,34(4):999-1018
太华杂岩位于华北克拉通南部,其组成复杂,记录了几乎所有早前寒武纪各阶段重要的地质事件;此外,由于其所处特殊地理位置,研究太华杂岩对于华北克拉通早前寒武纪地壳形成和演化、构造单元划分和基底拼合等都具有举足轻重的科学价值。本文综合已有的岩石学、变质作用、地球化学以及同位素年代学等诸多研究工作,得到以下阶段性结论和认识:1)将鲁山地区太华划分为以深成侵入岩为主的片麻岩系和以变质沉积-火山岩为主的表壳岩系;前者形成于中太古代晚期-新太古代早期,后者形成于古元古代晚期。而小秦岭地区太华杂岩中变质深成侵入岩形成时间跨度较大,为中太古代晚期-古元古代早期;而其上覆的火山-沉积岩可与鲁山太华杂岩的表壳岩类比,形成时间亦为古元古代晚期。2)中太古代-新太古代(2.91~2.50Ga)为华北克拉通南部大陆最主要的地壳形成时期。提出太华杂岩在太古宙经历了两期明显的地壳生长时间,一期发生在2.85~2.70Ga,以鲁山太华片麻岩系中的深成侵入岩和斜长角闪岩为代表;另一期发生在~2.50Ga,以小秦岭华山和崤山地区太华杂岩中各类花岗质岩石为代表。3)太华杂岩在所谓的全球陆壳生长"沉寂期(2.45~2.20Ga)"岩浆活动异常发育,推测这一时期的岩石形成于古元古代俯冲-汇聚环境,可能是与华北克拉通南部太古宙陆块和其他陆块汇聚-碰撞相关。4)太华杂岩在古元古代晚期普遍遭受了强烈的变质和变形,其变质程度主体为高角闪岩相,局部可达麻粒岩相,且记录了包含近等温降压退变质片段的顺时针变质作用P-T轨迹,经历了一个漫长的变质演化过程(1.97~1.80Ga),变质作用的时限跨度可达150Myr。5)提出华北克拉通南部曾经为一个统一基底,称之为"南部太古宙地块",此地块形成时间为新太古代末期(~2.5Ga)。该古老陆块经历了如下5个构造-演化阶段:(1)冥古宙-始太古代初始陆核形成;(2)中太古代-新太古代陆壳快速生长;(3)古元古代早期(~2.3Ga)岩浆活动异常活跃;(4)古元古代(2.30~1.97Ga)陆内拉伸-破裂;和(5)古元古代末期(1.97~1.80Ga)陆块最终拼合。  相似文献   

12.
The Dashiqiao Formation on the Liaodong Peninsula constitutes an important component within the Jiao–Liao–Ji Belt, North China Craton. It is composed dominantly of dolomitic marbles intercalated with minor carbonaceous slates and mica schists, hosting one of the largest magnesite deposits on Earth. This study presents zircon cathodoluminescence (CL) images and U–Pb–Hf isotope data, as well as single-mineral geochemical data for the staurolite–garnet–mica schist from the Dashiqiao Formation, in order to constrain its protolith age and provenance, and further to discuss the early Precambrian tectono-thermal events of the North China Craton. U–Pb isotopic dating using the LA–ICP–MS method on detrital zircons from the schist preserves at least three age populations ranging in age from 2.99 to 2.02 Ga, and grains as old as ca 4087 Ma. The dominant Neoarchean detrital zircons were most probably sourced from the basement within the Longgang and Nangrim blocks, while the minor Mesoarchean zircons were only sourced from the Longgang Block. The subordinate middle Paleoproterozoic zircons are consistent with ages of the regionally distributed coeval Liaoji granites and volcanics within the Jiao–Liao–Ji Belt. Zircon U–Pb dating yields a metamorphic age of 1930 Ma for the sample, interpreted to represent the peak stage of epidote amphibolite facies metamorphism. Thus, the depositional age for the protolith of the schist was proposed in the period between 2.01 and 1.93 Ga. LA–MC–ICP–MS Lu–Hf isotopic data show that all Archean (2.45–2.55) detrital zircons possess positive εHf(t) values from +?0.7 to +?7.5 with juvenile depleted mantle model ages, suggesting a significant crustal growth event during the Neoarchean in the North China Craton. The Paleoproterozoic detrital zircons possess variable εHf(t) values (??5.5–+?8.3) and depleted mantle model ages from Mesoarchean to Paleoproterozoic. The zircons with negative εHf(t) values implies the Mesoarchean to Neoarchean crust undergoing a recycling event in the period 2.40–2.01 Ga, while those with positive εHf(t) value suggest some indication of juvenile addition to the crust during the Paleoproterozoic. Using regional geological and new detrital zricon U–Pb–Hf isotopic data, the early Precambrian tectono-thermal events can be subdivided into the following episodes: Mesoarchean, late Neoarchean, middle Paleoproterozoic, and late Paleoproterozoic times.  相似文献   

13.
Zircons from granulite xenoliths entrained in a Late Cretaceous mafic dike in the Jiaodong Peninsula, North China Craton (NCC), show three distinct U-Pb age populations. Part of the old zircon grains yield discordant data that project to ages of about 2.4 to 2.5 Ga, a few grains indicate growth at about 2.0 Ga and a third group yield Cretaceous ages with peaks at 120 and 90 Ma. The oldest zircons give Hf TDM model ages of 2.6-2.8 Ga. These results demonstrate the existence of original Archean lower crust in the Jiaodong region. Zircons of 2.0 Ga have similar Hf TDM model ages as the Neoarchean-Paleoproterozoic grains, suggesting that these zircons were products of metamorphic recrystallization due to thermal event without juvenile input. Early Cretaceous zircons yield εHf(t) values of − 21 to − 12 and Late Cretaceous zircons large variable εHf(t) from + 4 to − 50. These data suggest that magmatic underplating occurred in the Neoarchean to Earliest Proterozoic lower crust of the NCC, both in the Early and Late Cretaceous. It is suggested that the Mesozoic magma underplating, which also provided the heat source for the voluminous Mesozoic magmatism in the NCC, significantly modified the composition of the Archean to Paleoproterozoic lower crust of the NCC.  相似文献   

14.
Santunying is an important area for revealing nature of the late Neoarchean tectono-magmato-thermal events in the eastern Hebei part of the North China Craton. It is mainly composed of meta-intrusive rocks. Supracrustal rocks sporadically occur in the meta-intrusive rocks. The meta-intrusive rocks are subdivided into the Santunying tonalitic gneiss, Qiuhuayu tonalitic-trondhjemitic gneiss, Xiaoguanzhuang dioritic gneiss and Qingyangshu meta-gabbro. Respectively, SHRIMP U–Pb zircon dating on fourteen samples yielded weighted mean 207Pb/206Pb ages of 2525–2537, 2532–2546, 2530–2544 and ∼2531 Ma for magmatic zircons from them. Dioritic gneiss of the Xiaoguanzhuang gneiss contain abundant 2544–3487 Ma xenocrystic zircons. SHRIMP U–Pb dating on a garnet-biotite gneiss sample yielded a weighted mean 207Pb/206Pb age of 2537 Ma for detrital zircons. All rocks underwent strong metamorphism, deformation and anatexis, resulting in formation of leucosomes and residues, with some leucosomes concentrating to form large veins. They record a strong late Neoarchean event by metamorphic zircon ages of 2489–2519 Ma. Some rocks also record metamorphic zircon ages of 1772–1843 Ma. Magmatic zircons from the magmatic rocks show large variations in εHf(t) values ranging from −1.7 to +8.7. Combined with early studies, conclusions are: 1) Intrusive rocks with the involvement of mantle-derived materials have a narrow range of magmatic zircon ages from 2525 to 2546 Ma, and supracrustal rocks were formed during the same period. 2) Ancient crustal remnants (>2600 Ma) are present, consistent with the late Neoarchean arc magmatism involving older continental crust, similar to Phanerozoic Andean margins. 3) The Archean basement underwent a strong tectonothermal event at the end of the Neoarchean, with the metamorphic zircon ages being 10–30 million years younger than the timing of magmatism, a common feature of the North China Craton. 4) A late Paleoproterozoic tectonothermal event widely occurred in the western part of eastern Hebei, which is linked with regional ductile deformation.  相似文献   

15.
The Miyun area of Beijing is located in the northern part of the North China Craton(NCC)and includes a variety of Archean granitoids and metamorphic rocks.Magmatic domains in zircon from a tonalite reveal Early Neoarchean(2752±7 Ma) ages show a small range in ε_(Hf)(t) from 3.1 to 7.4and t_(DM1)(Hf) from 2742 to 2823 Ma,similar to their U-Pb ages,indicating derivation from a depleted mantle source only a short time prior to crystallization.SHRIMP zircon ages of granite,gneiss,amphibolite and hornblendite in the Miyun area reveal restricted emplacement ages from 2594 to2496 Ma.They also record metamorphic events at ca.2.50 Ga,2.44 Ga and 1.82 Ga,showing a similar evolutionary history to the widely distributed Late Neoarchean rocks in the NCC.Positive ε_(Hf)(t) values of 1.5 to 5.9,with model ages younger than 3.0 Ga for magmatic zircon domains from these Late Neoarchean intrusive rocks indicate that they are predominantly derived from juvenile crustal sources and suggest that significant crustal growth occurred in the northern NCC during the Neoarchean.Late Paleoproterozoic metamorphism developed widely in the NCC,not only in the Trans-North China Orogen,but also in areas of Eastern and Western Blocks,which suggest that the late Paleoproterozoic was the assembly of different micro-continents,which resulted in the final consolidation to form the NCC,and related to the development of the Paleo-Mesoproterozoic Columbia or Nuna supercontinent.  相似文献   

16.
How the earth's crust formed and evolved during the Precambrian times is one of the key questions to decipher the evolution of the early Earth. As one of the few cratons containing well-preserved Eoarchean to Neoarchean basement on Earth, the North China Craton is an ideal natural laboratory to unravel the early crustal evolution. It is controversial whether the Archean tectonothermal events in this area represents reworking or growth of the continental crust. To solve this issue, we have compelled field-based mapping, zircon U–Pb dating by SHRIMP RG and LA–ICP–MS U–Pb, zircon SHRIMP SI oxygen and LA–MC–ICP–MS Hf isotope, and whole-rock Nd–O isotope analyses from the Archean granitoids in northern Liaoning, North China Craton. On the basis of zircon U–Pb isotopic dating and measured geological section investigation, two distinct magmatic suites as enclaves in the Jurassic granites are recognized, viz. a newly discovered 3.0 Ga crustal remnant and a 2.5 Ga granitoid. The Mesoarchean zircons from the 3.0 Ga granodioritic gneisses exhibit heterogeneous Hf isotopic compositions, with the most radiogenic analysis (εHf(t) = +3.8) following the depleted mantle evolution array and the most unradiogenic εHf(t) extending down to −3.4. This implies that both ancient continental crust at least as old as 3.4 Ga and depleted mantle contributed to the magma source of the protoliths of the Mesoarchean gneisses. The εHf(t) values of the Neoarchean zircons from these gneisses overlap the 3.4–3.0 Ga zircon evolution trend, indicating that the ancient crustal materials have been reworked during the late Neoarchean. The Neoarchean zircons from the 2.5 Ga granitoids have a relatively small variation in the Hf isotope and are mainly plotted in the 3.0–2.8 Ga zircon evolution field. However, taking all the εHf(t) values of the Neoarchean zircons into the consideration, we find that the Hf model age of the Neoarchean zircon does not represent the time of crustal growth or reworking but are artifacts of magma mixing. The interaction between the magmas derived from the ancient crustal materials and the depleted mantle is also supported by zircon O isotopic data and Hf–O isotopic modeling of the Neoarchean granitoids. Both Mesoarchean and late Neoarchean tectonothermal events involved synchronous crustal growth and reworking, which may be applicable to other parts of the world.  相似文献   

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