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1.
云开地块中生代构造演化是华南地区的研究热点之一.通过对云开地块变质基底中的混合岩、片麻岩（5个样品）和花岗岩（1个样品）开展锆石LA-ICP-MS U-Pb定年,获得440.3±3.3 Ma、230.2±2.9 Ma、230.7±1.3 Ma、459.5±2.7 Ma、431.5±4.3 Ma、229.2±5.4 Ma、229.7±2.7 Ma 7组变质（深熔）或岩浆年龄和2组（样品1432-1和ID7-3）碎屑锆石年龄,碎屑锆石年龄范围均为太古代-新元古代,且具有~1.0 Ga年龄主峰,与天堂山岩群和云开群碎屑锆石年龄谱相似.区域资料表明云开地块天堂山岩群和云开群具有相似的物质组成,均形成于早古生代-新元古代,存在变质程度和物质面貌的差异;在加里东期构造-热事件的基础上,广泛叠加了印支期区域变质（深熔）-构造-流体作用影响.4个样品中（1431-1、1432-1、D116-3和ID7-3）锆石原位Lu-Hf同位素组成显示,加里东期变质和深熔锆石Lu/Hf同位素组成基本一致,应继承了原岩的同位素组成特征.印支期变质和深熔锆石Lu/Hf同位素组成不同,可能主要由变质作用和深熔作用的差异所致.以古-中元古代为主的地壳物质参与了加里东期和印支期变质-深熔作用,在加里东期和印支期深熔作用过程中,均有少量幔源物质的加入,印支期幔源物质的贡献相对显著. 相似文献
2.
Protolith and metamorphic ages of the Haiyangsuo Complex, eastern China: a non-UHP exotic tectonic slab in the Sulu ultrahigh-pressure terrane 总被引：8，自引：0，他引：8
J. G. Liou T. Tsujimori W. Chu R. Y. Zhang J. L. Wooden 《Mineralogy and Petrology》2006,88(1-2):207-226
Summary The Haiyangsuo Complex in the NE Sulu ultrahigh-pressure (UHP) terrane has discontinuous, coastal exposures of Late Archean
gneiss with amphibolitized granulite, amphibolite, Paleoproterozoic metagabbroic intrusives, and Cretaceous granitic dikes
over an area of about 15 km2. The U–Pb SHRIMP dating of zircons indicates that theprotolith age of a garnet-biotite gneiss is >2500 Ma, whereas the granulite-facie
metamorphism occurred at around 1800 Ma. A gabbroic intrusion was dated at ∼1730 Ma, and the formation of amphibolite-facies
assemblages in both metagabbro and granulite occurred at ∼340–460 Ma. Petrologic and geochronological data indicate that these
various rocks show no evidence of Triassic eclogite-facies metamorphism and Neoproterozoic protolith ages that are characteristics
of Sulu-Dabie HP-UHP rocks, except Neoproterozoic inherited ages from post-collisional Jurassic granitic dikes. Haiyangsuo
retrograde granulites with amphibolite-facies assemblages within the gneiss preserve relict garnet formed during granulite-facies
metamorphism at ∼1.85 Ga. The Paleoproterozoic metamorphic events are almost coeval with gabbroic intrusions. The granulite-bearing
gneiss unit and gabbro-dominated unit of the Haiyangsuo Complex were intruded by thin granitic dikes at about 160 Ma, which
is coeval with post-collisional granitic intrusions in the Sulu terrane. We suggest that the Haiyangsuo Complex may represent
a fragment of the Jiao-Liao-Ji Paleoproterozoic terrane developed at the eastern margin of the Sino-Korean basement, which
was juxtaposed with the Sulu terrane prior to Jurassic granitic activity and regional deformation. 相似文献
3.
华北地台北缘集宁地区古元古代片麻状石榴花岗岩的深熔成因及地质意义 总被引：3，自引：3，他引：0
本文对华北克拉通北缘集宁地区空间上密切共生的片麻状石榴花岗岩和孔兹岩系富铝片麻岩的岩相学、地球化学及年代学特征进行了对比研究。SHRIMP锆石U-Pb定年方面,在富铝片麻岩中获得了1910±10Ma和1839±13Ma变质锆石年龄,在片麻状石榴花岗岩中获得了1919±17Ma的变质重结晶锆石年龄。在石榴花岗岩的石榴石包裹体中识别出与富铝片麻岩相对应的进变质阶段(M1)和峰期阶段(M2)的矿物组合,由此确认富铝片麻岩的变质作用和导致石榴花岗岩形成的深熔作用是同一构造热事件的产物。通过对二者变质作用演化及特征变质矿物的对比,认为深熔作用主要发生在峰期后等温降压阶段(M3),石榴花岗岩中的石榴石为深熔作用过程中的残留矿物相或转熔矿物相,而石榴花岗岩则是混合有大量残留矿物相的熔体结晶的产物。对片麻状石榴花岗岩和富铝片麻岩的地球化学组成特征进行了对比分析,片麻状石榴花岗岩既有一定的继承性,又有十分明显的变异性。变异性表现为:1)石榴花岗岩主量和微量元素含量分布极不均匀,微量元素含量普遍低于源岩(Cs、Rb、Th、U、Nb、Ta、Zr、Hf等);2)大离子亲石元素Cs和生热元素U、Th亏损明显,Sr相对富集;3)高场强元素Nb、Ta、P、Ti的明显亏损;4)铕异常变化大,存在铕富集型、铕平坦型和铕亏损型共存的稀土配分曲线的岩石,这是深熔成因石榴花岗岩最突出的表现,也可能是原地-半原地深熔花岗岩的主要地球化学标志。综合区域上的地质资料,认为深熔作用与碰撞后伸展构造背景下基性岩浆底侵事件有关。 相似文献
4.
中国东北~500Ma泛非期孔兹岩带的确定及其意义 总被引：14，自引：7，他引：7
东北地区的变质基底,如佳木斯地块的麻山群、兴安地块的兴华渡口群等岩石组合是以(含石墨)大理岩、夕线石榴片麻岩、斜长角闪岩等为主要标志的孔兹岩系。在额尔古纳、兴安和佳木斯-兴凯地块的夕线石榴片麻岩分别得到锆石U-Pb年龄,证明这些高级变质岩的原岩年龄以新元古代(600~850Ma)为主,变质年龄为~500Ma,因此东北地区的变质基底记录了从Rodinia 到 Gondwana大陆的聚合与离散的过程。泛非期高级变质岩及其同期岩浆岩在额尔古纳、兴安、松辽、佳木斯 和兴凯地块等断续分布,总体出露范围>1300km,并沿虎头、鸡西、萝北、兴华渡口和漠河一线总体北西向沿黑龙江断续分布,因此我们命名为"中国东北泛非期孔兹岩带"。 "中国东北泛非期孔兹岩带"的提出和进一步研究, 对深入探讨东北地区各地块基底组成的异同性以及陆块聚合的过程,以及东北地区的构造演化历史及其在Gondwana大陆重建中的位置都具有重要的科学意义。 相似文献
5.
中国东北麻山杂岩晚泛非期变质的锆石SHRIMP年龄证据及全球大陆再造意义 总被引：43，自引：1，他引：43
中国东北地区佳木斯地块南部麻山杂岩正、副片麻岩 7个样品的锆石 SHRIMP年龄数据首次明确地表明 ,东北地区存在 500 Ma的晚泛非期高级变质作用事件。峰期麻粒岩相变质导致柳毛地区 (502± 10)Ma (2σ )深熔花岗岩的形成。正、副片麻岩变质年龄的一致性表明它们已在变质前发生了构造叠置。西麻山副片麻岩中含有在后期麻粒岩相变质过程中未重结晶的碎屑锆石，由此形成从协和一致的 550 Ma到弱不一致 1 900 Ma的较大 207Pb/206Pb年龄变化范围，表明其原岩具有从新元古代到中元古代-古元古代的年龄。柳毛地区变质的片麻状闪长岩中所含的古老锆石的 207Pb/206Pb年龄为 546～ 1 460 Ma表明，该闪长岩大约在 1 400 Ma就位，并受到 500 Ma变质事件的影响，从而说明柳毛地区存在中元古代基底。然而，与以前的认识相反，麻山杂岩不存在具有太古宙基底的同位素证据。晚泛非期变质事件年龄的确定对重塑晚前寒武纪-显生宙早期麻山杂岩和佳木斯地块的古地理位置具有重要意义。根据目前获得的有关证据，认为佳木斯地块可能曾经位于冈瓦纳大陆北缘的华北克拉通附近。 相似文献
6.
北天山温泉群的地质特征、时代和构造意义 总被引：1，自引：0，他引：1
北天山温泉群长期以来被认为是古元古代的变质岩。最新的野外调查和锆石SHRIMP U-Pb 测年结果表明,温泉群可
以划分为三个岩石构造单元：（1）前早新元古代变质火山岩和变质沉积岩,主要包括斜长角闪岩、云母片岩、石英片岩、
黑云母片麻岩、大理岩等;（2）早新元古代混合岩和正片麻岩;（3）早古生代未变质变形的辉长岩和闪长岩。上述三种岩
石组合类型均被后期二云母花岗岩（脉）所侵入。温泉县以南的混合岩和花岗片麻岩中锆石的SHRIMP U-Pb 年龄分别为
926±12 Ma 和907±11 Ma,与天山地区出露的新元古代花岗岩类的时代基本一致。结合前人对花岗片麻岩Nd 同位素组成
的研究,花岗片麻岩应为古老地壳物质部分熔融的产物,而同期的混合岩化作用则是新元古代地壳加厚和部分熔融的直接
地质证据。辉长岩和闪长岩侵入到温泉群花岗片麻岩和斜长角闪岩中,其中闪长岩的锆石SHRIMP U-Pb 年龄为452±7 Ma,
并含有1.1 Ga 和1.4 Ga 的继承锆石。根据前人的研究成果,本区早古生代辉长岩和闪长岩具有岛弧岩浆岩的地球化学特征,
可能与准噶尔-巴尔喀什洋的俯冲作用有关,这一俯冲增生作用最终导致伊犁北部与哈萨克斯坦陆块在志留纪拼贴造山,
并使温泉群前寒武纪变质岩与侵入岩发生变质变形作用。 相似文献
7.
Fernando Corfu Alan Crane Desmond Moser Graeme Rogers 《Contributions to Mineralogy and Petrology》1998,133(4):329-345
The Gruinard Bay area of the mainland Lewisian complex comprises a metamorphosed suite of Archaean trondhjemites and minor
granites enclosing remnants of older tonalitic gneiss and mafic to ultramafic enclaves. The U-Pb zircon dating yields ages
of 2731 ±14 Ma and 2728 ±2 Ma for two trondhjemite and 2732 ±4 Ma for one granite sample, also revealing the presence of large
amounts of inherited xenocrystic zircons. Although the region has been pervasively overprinted by retrogressive events in
amphibolite to greenschist facies, the textural relations between biotite, hornblende, quartz and titaniferous minerals indicate
that these minerals are pseudomorphs of pyroxene and high-Ti amphibole formed in hornblende-granulite facies. Structural relations
link this metamorphism to a steep northeast-trending fabric coeval with the intrusion of the trondhjemites, dated at 2730 Ma.
Dating of zircon in amphibolite and tonalite enclaves yields complex internal isotopic relations with apparent ages ranging
from 2825 to 2740 Ma. This age range reflects new growth during the 2730 Ma metamorphic/metasomatic events, superimposed on
older zircon phases which include combinations of xenocrystic cores, and magmatic and/or metamorphic growth phases whose mode
of formation cannot clearly be resolved by imaging techniques (e.g. cathodoluminescence) alone. A pegmatitic vein that escaped
the D3 strain and related isotopic disturbances yields a precise age of 2792 ±2 Ma, which constrains to some degree the earliest
orogenic events in the area. Age relationships displayed in the central block at Scourie–Badcall, and in the Gruinard Bay
area indicate that petrogenetic events in both areas were comparable about 2800 Ma and that both areas underwent trondhjemitic
magmatism about 2730 Ma. In contrast, at Gruinard Bay there is no isotopic evidence for a period of high-grade metamorphism
and magmatism at 2490–2480 Ma that drastically affected the Scourie block indicating that at this stage the two regions occupied
different levels of the crust.
Received: 23 October 1997 / Accepted: 20 July 1998 相似文献
8.
滇西高黎贡山群变质岩的锆石年龄及其构造意义 总被引：11，自引：5，他引：6
被认为是腾冲-梁河地块前寒武纪结晶基底的滇西高黎贡山群变质岩系,其原岩及变质时代长期争论不休。岩相学和地球化学表明,组成高黎贡山群的黑云二长片麻岩、黑云角闪斜长片麻岩和变粒岩的原岩均为岩浆岩。首次对这些变质岩进行原位锆石U-Pb定年,分别获得497.8±7.2Ma～500±14Ma、83.5±0.9Ma的岩浆结晶年龄和459±5Ma、55.2±1.1Ma的变质年龄。结合相邻区碎屑锆石年龄及其区域对比分析,认为腾冲-梁河地块高黎贡山群中以石英片岩、石英岩为主体的原始沉积岩系可能形成于新元古代,应与拉萨地块有密切的亲缘关系。在早古生代环冈瓦纳大陆周缘造山过程中被寒武纪花岗岩侵入并发生变质作用;在新特提斯俯冲过程中,经历了晚中生代的安第斯型造弧作用;在印度与欧亚大陆碰撞过程中,又经历了新生代的岩浆作用、变质作用以及走滑剪切形成糜棱岩化作用。 相似文献
9.
《Precambrian Research》2001,105(2-4):115-128
The Aasivik terrane is a ∼1500 km2 complex of gneisses dominated by ∼3600 Ma components, which has been discovered in the Archaean craton of West Greenland, ∼20–50 km south of the Paleoproterozoic Nagssugtoqidian orogen. The Aasivik terrain comprises granulite facies tonalitic to granitic gneisses with bands of mafic granulite, which include disrupted mafic dykes. Four gneiss samples of the Aasivik terrain have given imprecise SHRIMP U–Pb zircon ages of 3550–3780 Ma with strong loss of radiogenic lead and new growth of zircon probably associated with a granulite facies metamorphic event(s) at ∼2800–2700 Ma. To the Southeast, the Aasivik terrane is in tectonic contact with a late Archaean complex of granitic and metapelitic gneisses with apparently randomly distributed mafic and ultramafic units, here named the Ukaleq gneiss complex. Two granitic samples from the Ukaleq gneiss complex have U–Pb zircon ages of 2817 ± 10 and 2820 ± 12 Ma and tzircon εNd values of 2.3–5.4. Given their composition and positive εNd values, they probably represent melts of only slightly older juvenile crust. A reconnaissance SHRIMP U–Pb study of a sample of metasedimentary rock from the Ukaleq gneiss complex found ∼2750–2900 Ma zircons of probable detrital origin and that two or more generations of 2700–2500 Ma metamorphic zircons are present. This gneiss complex is provisionally interpreted as a late Archaean accretionary wedge. A sample of banded granulite facies gneiss from a complex of banded gneisses south of the Aasivik terrain here named the Tasersiaq gneiss complex has yielded two zircon populations of 3212 ± 11 and 3127 ± 12 Ma. Contacts between the three gneiss complexes are mylonites which are locally cut by late-post-kinematic granite veins with SHRIMP U–Pb zircon ages of ∼2700 Ma. The isotopic character and the relationships between the lithologies from the different gneiss complexes suggest the assembly of unrelated rocks along shear zones between 2800 and 2700 Ma. The collage of Archaean gneiss complexes were intruded by A-type granites, here named the Umiatsiaasat granites, at ∼2700 Ma, later than the tectonic intercalation of the gneiss complexes. 相似文献
10.
喜马拉雅造山带东部错那县麻玛沟地区发育多种类型的花岗片麻岩和淡色花岗岩。锆石SHRIMP U-Pb地质年代学研究结果表明：花岗片麻岩（MM15）原岩结晶年龄为500.7±4.5Ma,含石榴子石淡色花岗岩中携带的继承性核部锆石年龄为498.6±3.4Ma,表明该地区经历了早古生代的岩浆作用事件。淡色花岗岩的结晶年龄区间为15.7~25.1Ma之间,为白云母脱水熔融的产物,可能是晚元古代-早古生代花岗质岩石发生低程度部分熔融的结果。锆石形态学表明该区的花岗片麻岩和淡色花岗岩均为过铝质花岗岩,并相对富集Cs、Rb、U、Pb,亏损Zr、Hf和低Nb/Ta比值,属于造山型花岗岩,支持该区域古生代岩浆作用事件与俯冲-碰撞造山作用相关,不是被动大陆边缘构造背景。结合前人数据推断：（1）从晚元古代末期开始,原特提斯洋向印度大陆的初始俯冲为自东向西的俯冲扩展模式;和（2）喜马拉雅造山带中新世淡色花岗岩为白云母脱水熔融和水致白云母熔融共同作用的结果,岩浆活动至少存在五个相。 相似文献
11.
Ian S. Buick Robert Frei Ian Cartwright 《Contributions to Mineralogy and Petrology》1999,135(2-3):244-254
Lower Calcsilicate Unit metasediments and underlying migmatitic Napperby Gneiss metagranite at Conical Hill in the Reynolds
Range, central Australia, underwent regional high-grade (∼680 to 720 °C), low-pressure/high-temperature metamorphism at 1594 ±
6 Ma. The Lower Calcsilicate Unit is extensively quartz veined and epidotised, and discordant grandite garnet + epidote quartz
veins may be traced over tens of metres depth into pegmatites that pooled at the Lower Calcsilicate Unit-Napperby Gneiss contact.
The quartz veins were probably precipitated by water-rich fluids that exsolved from partial melts derived from the Napperby
Gneiss during cooling from the peak of regional metamorphism to the wet granite solidus. Pb stepwise leaching (PbSL) on garnet
from three discordant quartz veins yielded comparable single mineral isochrons of 1566 ± 32 Ma, 1576 ± 3 Ma and 1577 ± 5 Ma,
which are interpreted as the age of garnet growth in the veins. These dates are in good agreement with previous Sensitive
High Resolution Ion Microprobe (SHRIMP) ages of zircon and monazite formed during high-temperature retrogression (1586 ± 5
to 1568 ± 4 Ma) elsewhere in the Reynolds Range. The relatively small age difference between peak metamorphism and retrograde
veining suggests that partial melting and melt crystallisation controlled fluid recycling in the high-grade rocks. However,
PbSL experiments on epidote intergrown with, and partially replacing, garnet in two of the veins yielded isochrons of 1454 ± 34
and 1469 ± 26 Ma. The ∼100–120 Ma age difference between intergrown garnet and late epidote from the same vein suggests that
the vein systems may have experienced multiple episodes of fluid flow.
Received: 24 April 1998 / Accepted: 17 December 1998 相似文献
12.
Jian-Bo Zhou Simon A. Wilde Guo-Chun Zhao Chang-Qing Zheng Wei Jin Xing-Zhou Zhang Hong Cheng 《Precambrian Research》2008,160(3-4):323-340
Archean basement gneisses and supracrustal rocks, together with Neoproterozoic (Sinian) metasedimentary rocks (the Penglai Group) occur in the Jiaobei Terrane at the southeastern margin of the North China Craton. SHRIMP U–Pb zircon dating of an Archean TTG gneiss gave an age of 2541 ± 5 Ma, whereas metasedimentary rocks from the Neoproterozoic Penglai Group yielded a range in zircon ages from 2.9 to 1.8 Ga. The zircons can be broadly divided into three age populations, at: 2.0–1.8 Ga, 2.45–2.1 Ga and >2.5 Ga. Detrital zircon grains with ages >2.6 Ga are few in number and there are none with ages <1.8 Ga. These results indicate that most of the detrital material comes from a Paleoproterozoic source, most likely from the Jianshan and Fenzishan groups, with some material coming from Archean gneisses in the Jiaobei Terrane. An age of 1866 ± 4 Ma for amphibolite-facies hornblende–plagioclase gneiss, forming part of a supracrustal sequence within the Archean TTG gneiss, indicates Late Paleoproterozoic metamorphism. Both the Archean gneiss complex and Penglai metasedimentary rocks resemble previously described components of the Jiao-Liao-Ji orogenic belt and suggest that the Jiaobei Terrane has a North China Craton affinity; they also suggest that the time of collision along the Jiao-Liao-Ji Belt was at 1865 Ma. 相似文献
13.
14.
在新疆西南天山科桑溶洞地区,新厘定出一套斜长角闪岩-花岗岩地质单元:侵入斜长角闪岩中的新元古代白云母花岗岩(片麻状构造)、以及侵入上述古老岩石单元的早奥陶世花岗岩(块状构造)。片麻状白云母花岗岩中锆石具有热液锆石边、岩浆锆石幔和碎屑锆石核(边-幔-核结构),剔除被热液锆石和碎屑锆石混染的SHRIMP测点,获得岩浆锆石幔的加权平均年龄752.3±5.1Ma(MSWD=0.95),代表岩浆的结晶年龄。块状花岗岩的锆石具有边-核结构,热液锆石边的U-Pb年龄(419.5±5.7Ma)明显偏低。剔除热液锆石和碎屑锆石,获得岩浆锆石的平均U-Pb年龄481.1±4.4Ma(MSWD=0.88),代表花岗岩的结晶年龄。早奥陶世早期,岩浆侵入新元古代片麻状白云母花岗岩中。在晚志留世或者更晚时期,两类花岗岩共同经受了变质热液改造,变质流体交代岩浆锆石,导致锆石溶蚀再生长。 相似文献
15.
Bodo Weber Alexander Iriondo Wayne R. Premo Lutz Hecht Peter Schaaf 《International Journal of Earth Sciences》2007,96(2):253-269
The histories of the pre-Mesozoic landmasses in southern México and their connections with Laurentia, Gondwana, and among
themselves are crucial for the understanding of the Late Paleozoic assembly of Pangea. The Permian igneous and metamorphic
rocks from the Chiapas massif as part of the southern Maya block, México, were dated by U–Pb zircon geochronology employing
the SHRIMP (sensitive high resolution ion microprobe) facility at Stanford University. The Chiapas massif is composed of deformed
granitoids and orthogneisses with inliers of metasedimentary rocks. SHRIMP data from an anatectic orthogneiss demonstrate
that the Chiapas massif was part of a Permian (∼ 272 Ma) active continental margin established on the Pacific margin of Gondwana
after the Ouachita orogeny. Latest Permian (252–254 Ma) medium- to high-grade metamorphism and deformation affected the entire
Chiapas massif, resulting in anatexis and intrusion of syntectonic granitoids. This unique orogenic event is interpreted as
the result of compression due to flat subduction and accretionary tectonics. SHRIMP data of zircon cores from a metapelite
from the NE Chiapas massif yielded a single Grenvillian source for sediments. The majority of the zircon cores from a para-amphibolite
from the SE part of the massif yielded either 1.0–1.2 or 1.4–1.5 Ga sources, indicating provenance from South American Sunsás
and Rondonian-San Ignacio provinces. 相似文献
16.
《International Geology Review》2012,54(14):1754-1768
The Wudaogou Group in eastern Yanbian, Northeast China, plays a key role in constraining the timing and eastward termination of the Solonker–Xra Moron River–Changchun Suture, where the Palaeo-Asian Ocean closed. The Wudaogou Group consists of schist, gneiss, amphibolite, metasedimentary, and metavolcanic rocks, all of which underwent greenschist- to epidote–amphibolite-facies regional metamorphism, with some hornfels resulting from contact metamorphism. To determine the age of deposition, the timing and grade of metamorphism, and the tectonic setting of the Wudaogou Group, we investigated the petrography and geochronology of the metamorphic rocks in this group. Zircons from the metasedimentary rocks of this group can be divided into metamorphic zircons and detrital zircons of magmatic origin. U–Pb ages of metamorphic zircons dated by LA-ICP-MS vary from 249 ± 4 to 266 ± 4 Ma, approximating the age of regional metamorphism in the eastern Yanbian area. Detrital zircons yield U–Pb ages ranging from 253 ± 5 to 818 ± 5 Ma, and indicate that the provenance of the Wudaogou Group experienced four tectonic–thermal events between 818 and 253 Ma: Neoproterozoic (ca. 818–580 Ma), Cambro–Ordovician (ca. 500–489 Ma), Devonian–Carboniferous (ca. 422–300 Ma), and middle–late Permian (ca. 269–253 Ma). The youngest detrital zircon, with a U–Pb age of 253 ± 5 Ma, defines the maximum depositional age of the Wudaogou Group. The presence of the Cambro-Ordovician and Neoproterozoic detrital zircons implies that the source of the Wudaogou Group had an affinity with Northeast China, which leads us to conclude that the Solonker–Xra Moron River–Changchun Suture extends from Wangqing to Hunchun in eastern Yanbian, and that the Palaeo-Asian Ocean may have closed at the end of the Permian or Early Triassic period. 相似文献
17.
北山地区出露大量古硐井群,其地层时代主要依据区域地层对比和上覆、下伏地层中获得的Sm-Nd全岩等时线年龄确定,没有高精度的年龄数据。为了获得并限定古硐井群的时限,采用LA-ICP-MS和SHRIMP测试方法,对北山地区出露大量古硐井群石英岩中的碎屑锆石进行U-Pb同位素年龄测试,获得最年轻的碎屑锆石年龄为1213±24Ma,可以作为古硐井群的下限年龄(中元古代中晚期)。获得3110±6Ma、2786±7Ma等碎屑锆石年龄,暗示甘蒙北山微地块存在古老的地壳残留,表明古硐井群是北山地区的变质基底之一。连续的3个峰值年龄1750Ma、1580Ma和1470Ma,表明古硐井群石英岩的沉积物大部分来自经历过晋宁运动的源区。研究结果为完善北山地区的地层格架提供了有利依据。 相似文献
18.
点苍山变质杂岩新生代变质-变形演化及其区域构造内涵 总被引：3，自引：2，他引：1
点苍山变质杂岩体是哀牢山-红河韧性剪切带四个变质杂岩体之一,遭受了多期多阶段变质-变形作用改造。本文重点针对点苍山杂岩的新生代变质-变形作用,尤其是以富铝质高级变质岩即夕线石榴黑云片麻岩和侵位于其中的糜棱岩化细晶花岗质岩石开展了深入研究。对夕线石榴黑云片麻岩的显微构造分析与矿物共生组合研究,确定了高角闪岩相和低角闪岩相变质矿物共生组合,分别为:石榴石(Grt)+夕线石(Sil)+钾长石(Kfs)+黑云母(Bi)+斜长石(Pl)±石英(Q)和夕线石(Sil)+白云母(Ms)+黑云母(Bi)+石英(Q)。对其中的变质锆石进行SHRIMP U-Pb测试,获得了新生代三个阶段的变质作用年龄,即54.2±1.7Ma、31.5±1.5Ma和27.5±1.2Ma.本文还深入研究了侵位于高级变质岩中的一个花岗岩质糜棱岩的宏观与显微构造特点,其LA-ICP-MS年龄为24.4±0.89Ma,代表着同剪切就位花岗质岩浆侵位和结晶年龄。夕线石榴黑云片麻岩中变质锆石从2150～27Ma多期多阶段表观年龄的发育,表明点苍山变质杂岩体具有复杂的构造演化史。点苍山杂岩的多阶段新生代构造-热演化归咎于印度-欧亚板块会聚与碰撞作用(约54Ma)、造山后伸展作用(大约40～30Ma)和沿着哀牢山-红河剪切带大规模左行走滑变形作用(约27～21Ma)。 相似文献
19.
Hannes K. Brueckner Jane A. Gilotti Allen P. Nutman 《Contributions to Mineralogy and Petrology》1998,130(2):103-120
High-pressure metamorphic assemblages occur in mafic, ultramafic and a few intermediate rocks in a gneiss complex that covers
an area of approximately 400 × 100 km in the North-East Greenland Caledonides. Detailed petrologic and geochronologic studies
were carried out on three samples in order to clarify the P-T-t evolution of this eclogite province. Geothermobarometry yields temperature estimates of 700–800 °C and pressure estimates
of at least 1.5 GPa from an eclogite sensu stricto and as high as 2.35 GPa for a garnet websterite. The eclogite defines a garnet-clinopyroxene-amphibole-whole rock Sm-Nd isochron
age of 405 ± 24 Ma (MSWD 0.9). Isofacial garnet websterites define garnet-clinopyroxene-orthopyroxene-amphibole-whole rock-(biotite)
ages of 439 ± 8 Ma (MSWD =2.1) for a coarse-grained sample and 370 ± 12 Ma (MSWD=0.6) for a finer-grained variety. Overgrowths
on zircons from the fine-grained pyroxenite and the eclogite give a pooled 206Pb/238U SHRIMP age of 377 ± 7 Ma (n=4). Significantly younger Rb-Sr biotite ages of 357 ± 8, 330 ± 6 and 326 ± 6 agree with young Rb-Sr, K-Ar and 40Ar/39Ar mineral ages from the gneiss complex and indicate slow cooling of the eclogitic rocks. High-pressure metamorphism may have
been at least 439 Ma old (Siluro-Ordovician) with cooling through amphibolite-facies conditions in the Devonian and continued
crustal thinning and exhumation well into the Carboniferous. Sm-Nd whole rock model ages indicate the eclogite protoliths
are Early Proterozoic in age, while 207Pb/206Pb SHRIMP ages of 1889 ± 18 and 1981 ± 8 from anhedral zircon cores probably reflect Proterozoic metasomatism. The samples
have negative ɛNd values (−5 to −16) and elevated 87Sr/86Sr ratios (0.708–0.715), consistent with field evidence that the eclogite protoliths were an integral part of the continental
crust long before Caledonian metamorphism. The presence of a large Caledonian eclogite terrane in Greenland requires modification
of current tectonic models that postulate subduction of Baltica beneath Laurentia during the Caledonian orogeny.
Received: 9 October 1996 / Accepted: 7 July 1997 相似文献
20.
Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea Zone (Southern Alps) 总被引：52，自引：2，他引：50
Gerhard Vavra Rolf Schmid Dieter Gebauer 《Contributions to Mineralogy and Petrology》1999,134(4):380-404
Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone
(IZ) are distinguished and attributed to magmatic, metamorphic and fluid-related events. Anatexis of pelitic metasediments
in the IZ produced prograde zircon overgrowths on detrital cores in the restites and new crystallization of magmatic zircons
in the associated leucosomes. The primary morphology and Th-U chemistry of the zircon overgrowth in the restites show a systematic
variation apparently corresponding to the metamorphic grade: prismatic (prism-blocked) low-Th/U types in the upper amphibolite
facies, stubby (fir-tree zoned) medium-Th/U types in the transitional facies and isometric (roundly zoned) high-Th/U types
in the granulite facies. The primary crystallization ages of prograde zircons in the restites and magmatic zircons in the
leucosomes cannot be resolved from each other, indicating that anatexis in large parts of the IZ was a single and short lived
event at 299 ± 5 Ma (95% c. l.). Identical U/Pb ages of magmatic zircons from a metagabbro (293 ± 6 Ma) and a metaperidotite
(300 ± 6 Ma) from the Mafic Formation confirm the genetic context of magmatic underplating and granulite facies anatexis in
the IZ. The U-Pb age of 299 ± 5 Ma from prograde zircon overgrowths in the metasediments also shows that high-grade metamorphic
(anatectic) conditions in the IZ did not start earlier than 20 Ma after the Variscan amphibolite facies metamorphism in the
adjacent Strona–Ceneri Zone (SCZ). This makes it clear that the SCZ cannot represent the middle to upper crustal continuation
of the IZ. Most parts of zircon crystals that have grown during the granulite facies metamorphism became affected by alteration
and Pb-loss. Two types of alteration and Pb-loss mechanisms can be distinguished by cathodoluminescence imaging: zoning-controlled
alteration (ZCA) and surface-controlled alteration (SCA). The ZCA is attributed to thermal and/or decompression pulses during
extensional unroofing in the Permian, at or earlier than 249 ± 7 Ma. The SCA is attributed to the ingression of fluids at
210 ± 12 Ma, related to hydrothermal activity during the breakup of the Pangaea supercontinent in the Upper Triassic/Lower
Jurassic.
Received: 7 July 1998 / Accepted: 4 November 1998 相似文献