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1.
为了探讨华北板块北缘晚古生代的隆升历史和古亚洲洋的闭合过程,利用碎屑岩的锆石U-Pb年代学、Hf同位素和锆石微量元素组成对北京周口店太平山南坡晚石炭世-早二叠世地层进行物源分析,并判定源区的大地构造背景.5件样品的碎屑锆石U-Pb年龄主要分布在3个时代:显生宙（285~425 Ma）、古元古代（1 700~2 450 Ma）和新太古代（2 500~2 747 Ma）.前寒武纪的锆石年龄主要集中在2.5 Ga和1.8 Ga,与华北克拉通的前寒武纪基底岩石相似.显生宙的锆石年龄主要集中在308~297 Ma,最年轻的峰值年龄在299~291 Ma,在误差范围内与地层沉积年龄相似,因此这些最年轻的碎屑锆石属于早二叠世同沉积锆石.29颗同沉积锆石的Hf同位素结果显示,原始176Hf/177Hf比值介于0.282 021~0.282 318,εHf（t）值介于-20.1~-9.6.显生宙锆石的年龄谱特征以及Hf同位素组成与内蒙古隆起同期的岩浆锆石特征十分相似,因此显生宙碎屑锆石可能来源于内蒙古隆起,并伴随有少量来自北侧兴蒙造山带南部的早古生代岛弧碎屑的输入.二叠纪同沉积锆石的微量元素特征表明锆石结晶的岩浆源区具有大陆岛弧的构造属性.上述数据表明:（1）华北板块北缘在晚石炭世-早二叠世为活动大陆边缘;（2）晚古生代古亚洲洋向华北北缘的持续俯冲消减导致了内蒙古隆起的快速隆升;（3）古亚洲洋闭合的时间应晚于早二叠世. 相似文献
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大陆造山运动：从大洋俯冲到大陆俯冲、碰撞、折返的时限——以北祁连山、柴北缘为例 总被引：20，自引：8，他引：12
北祁连山和柴北缘是典型的早古生代大陆造山带,分别发育有北祁连山大洋型俯冲缝合带和柴北缘大陆型俯冲碰撞带.作为早古生代大洋冷俯冲的典型代表,北祁连山经历了从新元古代-寒武纪大洋扩张、奥陶纪俯冲和闭合及早泥盆世隆升造山的过程.高压变质岩变质年龄为490～440Ma,证明古祁连洋经历了至少50m．y．的俯冲过程.柴北缘超高压变质带是大陆深俯冲的结果,岩石学、地球化学和同位素年代学表明,柴北缘超高压变质带中榴辉岩的原岩分别来自洋壳和陆壳两种环境.高压/超高压变质的蛇绿岩原岩的年龄为517±11Ma,与祁连山蛇绿岩年龄一致.榴辉岩早期的变质年龄为443～473Ma,与祁连山高压变质年龄一致,代表大洋地壳俯冲的时代,而柯石英片麻岩和石榴橄榄岩所限定的超高压变质时代为420～426Ma,代表大陆俯冲的年龄.从大洋俯冲结束到大陆俯冲最大深度的转换时间最少需要20m．y．.自420Ma起,俯冲的大洋岩石圈与跟随俯冲的大陆岩石圈断离,大陆地壳开始折返,发生隆升和造山.北祁连山和柴北缘两个不同类型的高压-超高压变质带反映了早古生代从大洋俯冲到大陆俯冲、隆升折返的造山过程. 相似文献
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Yamirka Rojas-Agramonte Daniel Herwartz Antonio García-Casco Alfred Kröner Dmitriy V. Alexeiev Reiner Klemd Stephan Buhre Matthias Barth 《Contributions to Mineralogy and Petrology》2013,166(2):525-543
High-pressure and ultrahigh-pressure (UHP) eclogite-bearing metamorphic assemblages in the North Tianshan of Kyrgyzstan are known from the Aktyuz and Makbal areas, where eclogites and garnet amphibolites are associated with continental rocks such as granitoid gneisses in Aktyuz and shallow-water clastic (passive margin?) metasediments in Makbal. We present the first Lu–Hf isotope data for an eclogite and two garnet amphibolite samples from the two metamorphic terranes which, combined with petrological analysis, tightly constrain the age of high-pressure metamorphism in the Kyrgyz North Tianshan. A five-point isochron for an Aktyuz eclogite sample provides a Lu–Hf age of 474.3 ± 2.2 Ma, and a four-point isochron on a Makbal sample corresponds to 470.1 ± 2.5 Ma. A prograde, subduction-related path is inferred for both samples with peak P–T conditions ranging from 1.4 to 1.6 GPa and 610–620 °C. A further Makbal sample provided a significantly older Lu–Hf age of 486 ± 5.4 Ma, most likely due to late alteration in the sample (late addition of unradiogenic Hf). We conclude that garnet growth in all three samples occurred around ca. 474 Ma and that these rocks likely experienced UHP metamorphism contemporaneously. Our results support previous geochronological evidence for an Early Ordovician collision belt in the North Tianshan and allow refinement of a tectonic model involving subduction of thinned continental crust to considerable depth along the margin of a small microcontinent. 相似文献
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《International Geology Review》2012,54(5):539-561
ABSTRACTThere are voluminous ultrahigh pressure-related orthogneisses and minor metamorphic supracrustal rocks in the northeastern Sulu UHP terrane (NSL), East China. The tectonic affinities of the supracrustal rocks are crucial for unravelling the deep continental subduction processes and locating the tectonic suture between the South China (SCB) and North China (NCB) blocks. In this contribution, we report new zircon U–Pb ages and Hf isotope data for the supracrustal rocks and metagabbros in the Zeku region of the NSL. In the Zeku region, the supracrustal rocks are spatially associated with granitic gneisses, metagabbros, and eclogites. Detrital zircon U–Pb analyses yield ages between 3.39 and 0.65 Ga that cluster as three major age populations including (1) 2.15–1.68 Ga with two subpeaks at ~1.83 Ga and~1.97 Ga, (2) 2.45–2.15 Ga with a peak at ~2.37 Ga, and (3) 0.79–0.65 Ga. In addition, there is a small age population between 3.39 and 2.61 Ga. The youngest age population of 0.79–0.65 Ga indicates that the Zeku supracrustal rocks must have been deposited after 650 Ma rather than during the Palaeoproterozoic as previously thought. The 210–190 Ma metamorphic ages suggest that the Zeku rocks were affected by Triassic collision–subduction and exhumation. Most of the Archaean-Palaeoproterozoic zircons have negative εHf(t) values and two-stage Hf model ages concentrating at 2.4–3.4 Ga (peak at ~2.9 Ga), indicating that source rocks of these zircons were mainly derived from recycling of ancient crustal material. These ages, together with the Hf isotopic compositions and rock assemblages, indicate that the Zeku supracrustal rocks were mainly derived from the Precambrian basement rocks of the northern Yangzte Block and have a tectonic affinity to the SCB, rather than the NCB. Our results, together with previously published data, suggest that there are two types of supracrustal rocks with different zircon U–Pb ages and tectonic affinities in the NSL. On the basis of new data, we suggest that the surface boundary between the SCB and NCB in the Jiaodong Peninsula is a complicated tectonic mélange zone rather than a single fault. 相似文献
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塔里木盆地东南缘(阿尔金山)"变质基底"记录的多期构造热事件:锆石U-Pb年代学的制约 总被引：23，自引：16，他引：7
塔里木盆地东南缘的阿尔金山被认为是塔里木克拉通变质基底的主要出露地区之一。 本文通过阿尔金山北坡不整合在太古代-古元古代变质基底之上的安南坝群中的碎屑岩和中南阿尔金中深变质岩石(原定为阿尔金岩群)的锆石U-Pb年代学研究,来确定塔里木盆地东南缘变质基底的性质及所经历的多期构造热历史。研究结果显示,塔里木盆地东南缘的安南坝群中含砾砂岩的碎屑锆石年龄集中在1.92Ga左右,少量在2.0~2.4Ga,表明其碎屑物质主要来源于下伏的太古代-早元古代米兰岩群和相关的深成侵入体。在中阿尔金地块和南阿尔金俯冲碰撞杂岩带的深变质岩石中,锆石U-Pb年代学数据表明其记录有新元古代早期(920~940Ma)、新元古代晚期(760Ma左右)和早古生代(450~500Ma)三期构造热事件,新元古代早期的构造热事件与塔里木(或晋宁)造山作用有关,它普遍存在于塔里木盆地周缘的和南中国地块(扬子克拉通)的变质基底岩石中,与Rodinia超级大陆汇聚相关;新元古代晚期的构造热事件也同样广泛存在于塔里木盆地周缘和扬子克拉通之中,被认为与Rodinia超大陆的裂解作用有关。因此,在新元古代时期,阿尔金的地质演化历史与扬子克拉通非常相似,而与华北则有很大的不同,锆石U-Pb测定还表明中南阿尔金的深变质岩石普遍遭受了早古生代的变质作用的改造,显示它们普遍卷入了早古生代的碰撞造山事件之中,成为早古生代碰撞造山带的组成部分。 相似文献
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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
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8.
胶北太古宙早期锆石U-Pb定年及Hf同位素研究：华北克拉通古老陆壳增生及再循环的证据 总被引：5，自引：4，他引：1
古老陆壳物质的发现与鉴别是探索地球早期陆壳形成与演化历史的重要内容之一,锆石U-Pb年龄结合Hf同位素研究是该研究的重要手段。本文通过对胶北地体内一个长英质副片麻岩中的锆石开展系统的原位U-Pb定年和微量、稀土元素分析,获得了多个太古宙早期的锆石。根据这些锆石的阴极发光图像、Th/U比值及稀土元素球粒陨石标准化配分模式,它们具有典型岩浆锆石的特征,其中2个分析点给出了3413Ma和3400Ma(~3.4Ga)的锆石U-Pb年龄,7个分析点给出3547±19Ma(MSWD=1.16)的锆石U-Pb年龄,指示太古宙早期的陆壳岩浆事件;结合华北克拉通其它地区的类似研究结果,暗示华北克拉通可能曾经存在比现今出露面积更大的太古宙早期的古老陆壳。这些古老锆石的Hf同位素分析显示,它们的εHf(t)值在-6.19~0.95之间,平均为-2.54,两阶段Hf模式年龄在3737~4353Ma之间,平均值为~4.1Ga,远大于锆石的U-Pb年龄,指示华北克拉通存在~4.1Ga的地壳增生作用及古老陆壳(3.55Ga)的再循环。 相似文献
9.
胶北地体地壳演化：玲珑黑云母花岗岩继承锆石U-Pb年龄、微量元素和Hf同位素证据 总被引：6，自引：5，他引：1
胶北地体晚侏罗世下地壳重熔的玲珑黑云母花岗岩大面积出露,其中残留有大量继承锆石,记录了多期热事件,为复杂的地壳演化过程提供了重要线索。论文通过分析玲珑黑云母花岗岩中继承锆石的U-Pb年龄、微量元素和Hf同位素组成,探讨了胶北地体的地壳演化历史。结果显示胶北地体前寒武纪经历了~2.9Ga和~2.7Ga两期主要的地壳生长事件,~2.5Ga和2.2~1.8Ga两期地壳重熔改造事件,~2.5Ga和1.95~1.8Ga两期变质事件。~2.9Ga的岩浆作用形成于岛弧环境,~2.7Ga岩浆活动与下地壳基性物质的部分熔融有关,~2.5Ga发生的岩浆和变质事件与地幔柱底侵作用有关,并有同时期的表壳岩组合-胶东岩群形成。~2.1Ga地壳处于拉张状态,伴有与裂谷活动有关的双峰式岩浆作用,荆山群和粉子山群开始沉积,而后1.95~1.8Ga发生碰撞造山运动,胶北所有早前寒武纪岩石单元卷入此次事件,并发生变质作用。自此之后,直至二叠纪末,胶北处于岩浆活动的沉寂期,但于~1.7Ga和~1.0Ga发生沉积作用,形成芝罘群和蓬莱群。二叠纪末扬子板块向北俯冲于华北克拉通之下,并于三叠纪与华北克拉通发生陆陆碰撞作用,致使扬子板块北缘新元古代花岗岩发生超高压变质,形成苏鲁超高压变质带,之后超高压变质岩发生折返。玲珑黑云母花岗岩复杂的继承锆石组成可能表征了前寒武纪岩石卷入陆-陆碰撞事件而发生再循环作用。 相似文献
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The Qilian Orogen of north western China records mid-Paleozoic collisional suturing of arc and continental blocks onto the south western margin of the North China craton. Silurian strata from the retroarc foreland basin mark the transition from ocean closure and northward subduction to the initiation of collision suturing. Detrital zircons were analysed from the western and eastern parts of the basin and show a spectrum of ages from Archean to Paleozoic with major age concentrations at around 2.5 Ga, 1.6 Ga, 1.2 Ga, 0.98 Ga, 0.7 Ga and 0.45 Ga. Archean age grains are derived from the North China craton, whereas the Central Qilian Bloc, which lies to the south provides the likely source for the bulk of the Proterozoic detritus. Paleozoic grains are restricted to Early Silurian samples from the western part of the basin and are considered to have been derived from the magmatic arc related to ocean closure and ultimate collision of the Central Qilian Belt with the North China craton. 相似文献
11.
白云鄂博位于华北克拉通北缘,是阴山地块的重要组成部分。本文对该区变质基底的5个花岗质岩石样品进行了锆石SHRIMP U-Pb定年,获得了2.63Ga和1.89~2.20Ga的岩浆锆石年龄以及2.47~2.51Ga和1.86~1.94Ga的变质锆石年龄。新太古代早期片麻状英云闪长岩的岩浆锆石εHf(t)值和tDM2(CC)(Hf)年龄分别为3.57~8.36和2.59~2.88Ga,古元古代中晚期花岗质岩石的岩浆锆石εHf(t)值和tDM2(CC)(Hf)年龄分别为-17.20~8.58和2.11~3.70Ga。变质锆石与岩浆锆石具有类似的Hf同位素组成。结合前人研究成果,表明:白云鄂博地区存在新太古代早期到古元古代晚期岩浆作用;在每一岩浆作用过程中,地幔添加和壳内再循环都起了重要作用;白云鄂博地区变质基底经历了新太古代晚期-古元古代早期和古元古代晚期构造热事件;阴山地块与南侧孔兹岩带具有类似的早前寒武纪地质演化历史。 相似文献
12.
鄂尔多斯盆地周缘地壳形成与演化历史:来自锆石U-Pb年龄与Hf同位素组成的证据 总被引：4，自引：0，他引：4
锆石U-Pb定年及Hf同位素测定结果表明,鄂尔多斯盆地周缘的华北板块北缘、兴蒙造山系及扬子板块-秦岭-大别-苏鲁造山带等构造单元系统具有明显不同的形成与演化历史。华北板块北缘锆石年龄平均值为1 837 Ma,最强烈的岩浆活动出现于2 200~1 800 Ma,该期锆石约占全部的40%;次为强烈的岩浆活动在2 800~2 200 Ma,其众数在全部锆石中约占30%;1 500~1 200 Ma、500~100 Ma这两个阶段形成的锆石在全区所占比例各约为15%。华北板块北缘最突出的特征是基本不含1 000~700 Ma期间形成的锆石,>3 000 Ma的锆石在全区分布极为有限。锆石Hf同位素亏损地幔模式年龄表明华北板块北缘平均值为2.55 Ga,较U-Pb平均年龄老,说明2 200~1 800 Ma期间形成的锆石含有较多的古老地壳再循环组分。Hf亏损地幔模式年龄最强峰值约为2.8 Ga,与全岩Nd亏损地幔模式年龄的峰值相一致,Hf模式年龄为3.0~2.25 Ga的颗粒占全部的近95%,证明华北板块北缘的地壳增生主要在太古宙至古元古代期间。Hf同位素亏损地幔模式年龄>3.0 Ga的锆石颗粒所占比例不到0.1%,另外近5%锆石的模式年龄分布于中元古代。晚古生代-中生代所形成的锆石均是先存地壳组分,尤其是中元古代增生地壳的熔融作用形成。兴蒙造山系中锆石U-Pb年龄平均值为497 Ma,最强峰分布于石炭纪(约320 Ma),石炭纪-二叠纪末(350~250 Ma)形成的锆石所占比例达30%以上。新元古代至早古生代(600~440 Ma)形成的锆石占全部锆石的55%以上,而中元古代末-新元古代期间(1 200~600 Ma)形成的锆石在全区仅占4%。中元古代以前形成的锆石非常有限,说明该区最早形成的地壳组分在兴蒙造山系的形成过程中较充分地参与到后期的岩浆作用过程中。兴蒙造山系中锆石相应的Hf同位素亏损地幔模式年龄平均为1.13 Ga,明显较相应的U-Pb年龄老,最强峰值出现于约0.6 Ga。Hf亏损地幔模式年龄为0.7~0.28 Ga的颗粒在兴蒙造山系所占比例达57%,证明该区最强烈的地壳增生发生于新元古代至古生代期间。Hf同位素亏损地幔模式年龄分布于1.5~0.7 Ga的锆石在全区约占38%,说明此期间也是该区地壳较强烈的增生期。Hf亏损地幔模式年龄大于1.5 Ga的锆石所占比例不到5%,古生代以后兴蒙造山系也基本没有明显的地壳增生。扬子与秦岭-大别-苏鲁造山带构造单元中的锆石U-Pb年龄平均为799 Ma,年龄为1 300~750 Ma的锆石在全部锆石中约占70%。晚古生代-燕山期形成的锆石约占20%。年龄在3 500~2 650 Ma、2 118~1 680 Ma的锆石在该区各约占5%。结合扬子与秦岭-大别-苏鲁造山带平均为1.56 Ga的Nd亏损地幔模式年龄特征,说明1 300~750 Ma期间该区较强烈的岩浆作用事件中有较多的古老地壳组分加入其中。锆石U-Pb年龄及Hf同位素组成均说明鄂尔多斯盆地周缘各构造单元具有不同的形成演化历史。地壳是幕式增长的,但各构造单元每幕发生的时间、强度存在明显差别。因此,由盆地中不同时代地层中碎屑锆石U-Pb年龄及Hf同位素组成及全岩Nd同位素特征的系统研究可反演盆地物源供给与周围构造单元之间的关系。 相似文献
13.
Saijun Sun Trevor R Ireland Lipeng Zhang Rongqing Zhang Chanchan Zhang 《International Geology Review》2018,60(8):1061-1072
The early tectonic evolution of the Lhasa Terrane remains poorly understood, although evidence for a substantial prehistory has been reported recently. We have carried out in situ zircon U–Pb dating and Hf–O isotopes of late Early Cretaceous monzogranites and get a surprising package of inherited zircons, not only because of their age profile, but also because the oldest Palaeoarchaean zircons are euhedral. The discovery of Palaeoarchaean euhedral zircons in the region suggests the presence of extremely old rocks in Tibet. Zircons from the Nagqu monzogranite yield five age peaks at ~3.45 Ga, ~2.56 Ga, ~1.76 Ga, ~900 Ma, and ~111 Ma. They have large variations in εHf(t) values (?45.1–9.2) and old Hf model ages (924–3935 Ma), with variable δ18O values of ?5.80–9.64. Palaeoarchaean zircons (~3.20–3.45 Ga) are euhedral with magmatic zircon characteristics. One of the grains has negative εHf(t) value (?4.8), old Hf model age (3935 Ma), and high positive δ18O value (7.27), which suggests an ancient crustal origin. The source of Palaeoarchaean euhedral zircons should be proximal to prevent long-distance transport and abrasion, whereas the late Early Cretaceous monzogranites are I-type. Thus, Palaeoarchaean euhedral zircons are most likely captured from the country rocks by assimilation at depth or may be relics of previous magmatic zircons. Notwithstanding their exact history, Palaeoarchaean euhedral zircons indicate Palaeoarchaean materials near Nagqu in the Tibetan Plateau. The inherited zircons also experienced a Late Palaeoproterozoic event (~1.76 Ga) likely related to the evolution of the India block. The peak at ~900 Ma suggests affinity to the Qiangtang and Himalaya blocks. 相似文献
14.
《International Geology Review》2012,54(1):29-56
We conducted in situ U–Pb and Lu–Hf isotope analyses of 401 detrital zircons collected from the Songpan–Ganzi Triassic turbidite complex in an attempt to understand the provenance variations of the siliciclastic rocks and the crustal growth history of central China. These detrital zircons exhibit a wide age spectrum with three major peaks at 1.7–2.0 Ga, 750–1050 Ma, and 210–500 Ma. They are dominated by negative ?Hf(t) values with a large range. Synthesis of the zircon U–Pb and Lu–Hf isotopic data indicate that the Triassic Songpan–Ganzi turbiditic succession could have been derived dominantly from the Tibetan terrains + the Kunlun and Qinling orogens. Our samples are characterized by a common, prominent group of Hf crust formation model ages at 0.8–4.1 Ga with a peak at 2.7–3.4 Ga. This fact indicates that (1) Phanerozoic magmatism in central China could have been predominantly products of crustal reworking with insignificant formation of juvenile crust and (2) the Neoarchaean was an important period of continental growth in central China. In addition, our data set also reveal that three widespread tectonothermal events could have occurred in the region during the late Mesoproterzoic, Palaeozoic, and early Mesozoic, respectively. 相似文献
15.
本文收集大量锆石U-Pb年代学数据,通过制作年龄-频数图谱,简略探讨了西伯利亚克拉通、华北克拉通、东北地区微地块以及内蒙古大石寨地区的演化史,并对大石寨二叠系与其周边块体的锆石年龄作比较分析,进而探讨了大石寨地区二叠系的物源问题。碎屑锆石年龄-频数图表明,大石寨地区二叠系碎屑锆石年龄可以划分出古生代年龄段(500~250 Ma),中—新元古代年龄段(1.6~0.8 Ga),新太古一古元古代年龄段(2.6~1.7 Ga)。华北克拉通北缘与西伯利亚克拉通南缘基底年龄均1.6 Ga,其二者都不能反映大石寨地区二叠系物源年龄信息,而大石寨地区二叠系碎屑锆石年龄峰值与东北地区地块年龄峰具有很好一致性,说明二者锆石年龄峰值反映的构造岩浆事件一致,表明大石寨地区二叠系物源应来源于东北地块而不是华北克拉通和西伯利亚克拉通。同时,东北地区大量古老基底锆石年龄数据的存在,暗示东北地块可能独立于上述两大板块而存在,并响应中亚造山带内存在古老微大陆的观点;东北地块由诸多微小块体拼贴而成,并分别与西伯利亚克拉通和华北克拉通碰撞拼接,缝合线分别是贺根山一黑河缝合带与西拉木伦缝合带。 相似文献
16.
The Neoproterozoic-Early Cambrian evolution of peri-Gondwanan terranes (e.g. Avalonia, Carolinia, Cadomia) along the northern (Amazonia, West Africa) margin of Gondwana provides insights into the amalgamation of West Gondwana. The main phase of tectonothermal activity occurred between ca. 640–540 Ma and produced voluminous arc-related igneous and sedimentary successions related to subduction beneath the northern Gondwana margin. Subduction was not terminated by continental collision so that these terranes continued to face an open ocean into the Cambrian. Prior to the main phase of tectonothermal activity, Sm-Nd isotopic studies suggest that the basement of Avalonia, Carolinia and part of Cadomia was juvenile lithosphere generated between 0.8 and 1.1 Ga within the peri-Rodinian (Mirovoi) ocean. Vestiges of primitive 760–670 Ma arcs developed upon this lithosphere are preserved. Juvenile lithosphere generated between 0.8 and 1.1 Ga also underlies arcs formed in the Brazilide Ocean between the converging Congo/São Francisco and West Africa/Amazonia cratons (e.g. the Tocantins province of Brazil). Together, these juvenile arc assemblages with similar isotopic characteristics may reflect subduction in the Mirovoi and Brazilide oceans as a compensation for the ongoing breakup of Rodinia and the generation of the Paleopacific. Unlike the peri-Gondwanan terranes, however, arc magmatism in the Brazilide Ocean was terminated by continent-continent collisions and the resulting orogens became located within the interior of an amalgamated West Gondwana. Accretion of juvenile peri-Gondwanan terranes to the northern Gondwanan margin occurred in a piecemeal fashion between 650 and 600 Ma, after which subduction stepped outboard to produce the relatively mature and voluminous main arc phase along the periphery of West Gondwana. This accretionary event may be a far-field response to the breakup of Rodinia. The geodynamic relationship between the closure of the Brazilide Ocean, the collision between the Congo/São Francisco and Amazonia/West Africa cratons, and the tectonic evolution of the peri-Gondwanan terranes may be broadly analogous to the Mesozoic-Cenozoic closure of the Tethys Ocean, the collision between India and Asia beginning at ca. 50 Ma, and the tectonic evolution of the western Pacific Ocean. 相似文献
17.
Tong-Tong Huang Jian-Lin Chen Jian-bin Wu Yun-Chuan Zeng 《International Geology Review》2017,59(2):166-184
The subduction polarity and related arc–magmatic evolutional history of the Bangong–Nujiang Ocean, which separated the South Qiangtang terrane to the north from the North Lhasa terrane to the south during the Mesozoic, remain debated. This study tries to reconstruct the subduction and evolution of the Bangong–Nujiang Ocean on the basis of U–Pb and Hf isotopic analyses of detrital zircons in samples from sedimentary rocks of the middle-western section of the Bangong–Nujiang suture zone in Gerze County, central Tibet. The Middle Jurassic Muggargangri Group in the Bangong–Nujiang suture zone was deposited in a deep-sea basin setting on an active continental margin. The Late Jurassic strata, such as the Sewa Formation, are widely distributed in the South Qiangtang terrane and represent deposition on a shelf. The Early Cretaceous Shamuluo Formation in the Bangong–Nujiang suture zone unconformably overlies the Muggargangri Group and was probably deposited in a residual marine basin setting. The detrital zircons of the Muggargangri Group contain seven U–Pb age populations: 2.6–2.4 Ga, 1.95–1.75 Ga, 950–900 Ma, 850–800 Ma, 650–550 Ma, 480–420 Ma, and 350–250 Ma, which is similar to the age populations in sedimentary rocks of the South Qiangtang terrane. In addition, the age spectra of the Shamuluo Formation are similar to those of the Muggargangri Group, indicating that both had a northern terrane provenance, which is conformed by the north-to-south palaeocurrent. This provenance indicates northward subduction of the Bangong–Nujiang oceanic crust. In contrast, two samples from the Sewa Formation yield variable age distributions: the lower sample has age populations similar to those of the South Qiangtang terrane, whereas the upper possesses only one age cluster with a peak at ca. 156 Ma. Moreover, the majority of the late Mesozoic detrital zircons are characterized by weakly positive εHf(t) values that are similar to those of magmatic zircons from arc magmatic rocks in the South Qiangtang terrane. The findings, together with information from the record of magmatism, indicate that the earliest prevalent arc magmatism occurred during the Early Jurassic (ca. 185 Ma) and that the principal arc–magmatic stage occurred during the Middle–Late Jurassic (ca. 170–150 Ma). The magmatic gap and scarcity of detrital zircons at ca. 140–130 Ma likely indicate collision between the Qiangtang and Lhasa terranes. The late Early Cretaceous (ca. 125–100 Ma) magmatism on both sides of the Bangong–Nujiang suture zone was probably related to slab break-off or lithospheric delamination after closure of the Bangong–Nujiang Ocean. 相似文献
18.
鄂尔多斯(地块)盆地南缘唐王陵砾岩的沉积时代长期存在晚前寒武纪(或震旦纪)与奥陶纪之争,沉积环境和物源组成也存在不同认识,是盆地南缘海相沉积地层及构造古地理研究关注的热点争议问题。本文采用碎屑锆石U-Pb年代学和岩石地球化学研究方法,综合分析探讨了唐王陵砾岩的沉积时代、物源组成及其构造古地理环境。结果表明:唐王陵砾岩自下而上三个组段的砂岩夹层样品、共计396颗碎屑锆石U-Pb谐和年龄数据主要分布在2531～2364Ma(n=25)、2120～1618Ma(n=268)、1230～940Ma(n=29)和905～744Ma(n=10)等四个年龄区间,相应的峰值年龄分别为2440Ma、1800Ma、1090Ma和810Ma,各组段样品单颗粒锆石最小年龄为829±11Ma、820±17Ma和744±8Ma。这一测年结果与盆地西南缘的震旦系正目观组和罗圈组碎屑锆石U-Pb年龄分布基本相似,但明显缺少其近邻剖面奥陶系平凉组碎屑锆石接近454Ma的高频年龄组分,表明唐王陵砾岩的沉积时代更接近新元古代晚期或震旦纪。碎屑锆石年龄谱物源示踪与岩石地球化学、沉积建造特征等综合分析结果揭示,唐王陵砾岩沉积具有来自(华北)鄂尔多斯陆块与祁连-北秦岭(杂岩)地体的双向混合物源特征,总体属于含有多套滑塌和水下扇堆积的滨浅海相碳酸盐岩和碎屑岩沉积建造组合体,主体形成于鄂尔多斯地块南缘新元古代晚期的被动大陆边缘伸展断陷海盆环境。唐王陵砾岩碎屑锆石测年数据接近1. 09Ga和0. 81Ga的年轻峰值年龄组分,提供并支持祁连-北秦岭地区存在格林威尔期Rodinia大陆聚合-裂解相关的构造岩浆活动事件,指示(华北)鄂尔多斯陆块与北秦岭地体至少在唐王陵砾岩沉积之前的格林威尔期曾经历过拼贴聚合-陆缘增生作用;随后受Rodinia大陆裂解事件的影响,鄂尔多斯地块南缘拼贴增生型大陆边缘发育形成了包括唐王陵砾岩在内的新元古代晚期陆缘滨浅海滑塌-碎屑流沉积。 相似文献
19.
《International Geology Review》2012,54(4):492-507
Numerous Triassic granitoids in the Qinling orogenic belt related to the Late Triassic collision between the North China Craton (NCC) and the Yangtze Block (YB) are important for determining the crustal composition at depth and the geodynamic processes by which the orogen formed. Most of the Triassic plutons in the Qinling orogen were emplaced between 205 and 225 Ma. The granitoid rocks from the southern margin of the NCC, North Qinling, South Qinling, and the northern margin of the YB that were emplaced during this interval have two-stage Hf model ages of 0.60–2.52 Ga (average 2.19 Ga), 0.90–2.66 Ga (average 1.29 Ga), 0.41–3.04 Ga (average 1.48 Ga), and 1.00–1.84 Ga (average 1.34 Ga), respectively, and mean εHf(t) values of ?14.5, ?0.32, ?1.36, and ?3.98, respectively. The Hf isotope compositions of the granitoids in different tectonic units differ significantly, mirroring the diverse history of crustal growth of the four units.The temporal and spatial distribution and Hf isotope compositions of the granitoids suggest that there was a unified geodynamic process that triggered the magmatism. Formation of the Triassic granitoid plutons at 225–205 Ma was a consequence of slab break-off or E–W-striking slab tearing, related to slab rollback in the west part of the Qinling orogen and oblique continental collision in the east. Upwelling of the asthenospheric mantle led to partial melting of the subcontinental lithospheric mantle and the lower crust, and mixing and/or mingling of the resulting magmas resulted in the formation of granitoids with diverse geological and geochemical characteristics. 相似文献
20.
We review the geology of the Gyeonggi Massif, Gyeonggi Marginal Belt, and Taebaeksan Basin of the Korean Peninsula, which are relevant to the 2018 Winter Olympic sites. Neoarchaean–Palaeoproterozoic gneisses and schists of the Gyeonggi Massif underwent two distinct collisional orogenies at the Palaeoproterozoic (1.88–1.85 Ga) and Triassic (245–230 Ma). These basement rocks are structurally overlain by a suite of Mesoproterozoic to Early Permian supracrustal rocks of the Gyeonggi Marginal Belt, consisting primarily of medium-pressure schists and amphibolites metamorphosed at ~270–250 Ma. In contrast, sedimentary successions in the Taebaeksan Basin, commonly fossiliferous, consist primarily of Early Cambrian–Middle Ordovician Joseon Supergroup and Late Carboniferous–Early Triassic Pyeongan Supergroup. The ‘Great Hiatus’ between the two supergroups is characteristic for the North China Craton. The marked contrast in tectonometamorphic evolution between the Taebaeksan Basin and Gyeonggi Marginal Belt suggests an existence of major suture in-between, which is most likely produced by the Permian–Triassic continental collision between the North and South China cratons. Finally, recent tectonics of the Korean Peninsula is governed by the opening of East Sea/Sea of Japan during the Late Oligocene–Early Miocene. This back-arc rifting event has resulted in an exhumation of the Taebaek Mountain Range, estimated to be 22 ± 3 Ma on the basis of apatite (U–Th)/He ages. Thus, high topography in the 2018 Winter Olympic sites is the consequence of Tertiary tectonics associated with the opening of a back-arc basin. 相似文献