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1.
As for the metamorphic rock series distributed on the “Faku Faulted Convex (FFC)”[1] of the northern Liaoning, the earliest geologic investigation divided it into the Langzishan, Dashiqiao and Gaixian forma-tions1) and considered it to be equivalent to the Liaohe Group in the eastern Liaoning, whereas Liaoning Bu-reau of Geology and Mineral Resources (LBGMR) included it into the Lower Proterozoic basement[1]. Recent 1︰50000 scale geological mapping2) reveals that this deformed and …  相似文献   

2.
For lack of reliable isotopic chronological data, the metamorphic rock series in the Faku region of northern Liaoning has long been regarded as the platform basement. Recent studies reveal that these deformed and metamorphosed rocks, with a variety of protoliths of plutonic intrusions and supracrustal volcanic and sedimentary rocks, were genetically related to later ductile shearing events, and they, together with the syntectonic intrusions, constituted the large-scale Faku tectonites. In this paper, we report new 40Ar/39Ar data on hornblende, biotite, and K-feldspar from typical granitic mylonites in this suite of tectonites. The plateau age 256 Ma of FK53 hornblende and the high-temperature plateau age 262 Ma of Fk51-1 biotite should represent the cooling ages when the granites, formed as a result of Paleozoic oceanic crustal subduction beneath the continental crust or collision of multiple micro-continental blocks, were exhumed into shallow crustal levels. The plateau age 231 Ma of FK51-1 boitite and the apparent age 227 Ma of Fk51-2 K-feldspar are interpreted to record the time of ductile deformation occurring under greenschist facies conditions, i.e. the formation age of the Faku tectonites, while the age gradient from 197 Ma to 220 Ma of Fk51-2 K-feldspar probably record the subsequent stable uplift-cooling process. The tectonic exhumation event indicated by the plateau age 180 Ma of Fk51-2 K-feldspar may be associated with the onset of paleo-Pacific subduction beneath the North China plate. In addition, the U-Pb dating of FK54 zircon from later-intruded granite yields the age of crystallization of this super-unit intrusion at 159 Ma, thus establishing an upper limit for the formation age of the Faku tectonites, while the plateau age 125 Ma of Fk54 K-feldspar most likely corresponds to the rapid cooling and tectonic denudation event associated with the final collision between the Siberian plate and the North China plate. These isotopic ages provide important geochronological constraints for re-evaluating the tectonic essence of the Faku Faulted Convex and ascertaining the suturing boundary between the North China Platform and the Xingmeng Fold System.  相似文献   

3.
The Helong block, located in southeastern Jilin Province, was thought to be an Archean geological unit in the most northeast part of the North China Craton (NCC)[1,2]. Previous geological survey sug-gested that this block is mainly composed of two parts: Jinchengdong Archean metamorphic supracrustal rocks intruded by Archean TTG complex[3―5], and the Bailiping granite[6,7] distributed in the Shiliping-Bai- liping-Guangping area. Both of them were thought as the Jinchengdong (or Helong…  相似文献   

4.
Researches over the last 20 years show that the orogenic belt remains rather active after plate colli-sion[1,2]. A complete orogenic cycle in the last period of the Wilson cycle can be defined by three stages of development[3]: (1) horizontal contraction and crustal thickening due to collision, as well as formation of topography and the crustal and lithospheric root; (2) eclogite facies metamorphism of the crustal root; and (3) delamination of the crustal root or lithospheric mantle, extension…  相似文献   

5.
皖南谭山岩体的锆石定年及地质意义   总被引：1，自引：0，他引：1  
皖南地区广泛分布燕山期岩浆岩,但其年代学方面的工作较为薄弱。为厘定该地区燕山期岩浆岩年代学格架,本文利用LA-ICP-MS锆石U-Pb定年方法对皖南谭山岩体的正长花岗岩进行了锆石U-Pb年代学研究,两个样品的206Pb/238U加权平均年龄分别为128．5±1．7Ma和128．3±1．5Ma,基本一致,为早白垩世岩浆活动的产物。结合本地区高精度年代学数据,皖南地区中生代岩浆岩可划分为三个峰期：第一峰期为142～139Ma;第二峰期为133～130Ma;第三峰期为128～125Ma。  相似文献   

6.
Zircon U-Pb thermal ionization mass-spectrometer (TIMS) and secondary ion mass-spectrometer (SIMS) dating, mica and amphibole 40Ar-39Ar dating and mineral Sm-Nd isotopic compositions of Huangzhen Iow temperature eclogite and country granitic gneiss are carried out. The zircon U-Pb weighted average SIMS age is (231.6±9.7) Ma for one eclogite.The mica 40Ar-39Ar isochron age is (232.6±2.1) Ma and the lowest plateau age is (221.7±2.4)Ma from same sample. U-Pb TIMS concordant ages from other eclogite zircons are from (221.3± 1.4) Ma to (222.5±2.3) Ma. U-Pb SIMS low intercept age from country granitic gneiss is (221±35) Ma. The retrograde amphibole 40Ar-39Ar isochron age is (205.9± 1.0) Ma. Except for mica,which may contain excess 40Ar, all the ages represent peak and retrograde metamorphism of low temperature eclogites. It is indicated that the Huangzhen low temperature eclogites differ from Xiongdian low temperature eclogites of north of the Northern Dabie Terrain in metamorphic ages.Huangzhen low temperature eclogites share one coherent HP-UHP terrain with high temperature eclogites from Southern Dabie Terrain and they may have differences in subduction depth and cooling rates during exhumation.  相似文献   

7.
The NE-trended Mesozoic granodioritic intrusions are spatially and temporally associated with the copper multi-metal mineralization in southeastern Hunan Province, South China. U-Pb dating result of single-grained zircons of four samples respectively from Shuikoushan, Baoshan, western Tongshanling and eastern Tongshanling intrusions reveals that their crystallization age spans a range from 172 Ma to 181 Ma, which also represents the oldest age of the regional copper multi-metal mineralization. Some of the zircon grains give an upper intercept age of about 1753 Ma and 207Pb/206Pb apparent age of (1752 ± 4) Ma, implying the involvement of the pre-Cambrian metamorphic (possible Middle Proterozoic) basement in their genesis. The presence of such a kind of zircon grains in these granodiorites indicates either that the parental magmas were assimilated by basement rocks during magma ascent or that lower/middle crustal rocks were one of the important components during the melting process.  相似文献   

8.
The petrographic characteristics of Jingshan "migmatitic granite" and the occurrence of the magmatic zircons indicate that the granite was formed by normal crystallization of felsic melts. All zircons in the granite have inherited cores and fine-scale oscillatory zoning rims of magmatic origin. It is realized that the granite was formed at 160.2±1.3 Ma through dating magmatic zircons. The generation of the granitic magma could be related to the lithospheric mantle and/or lower crust delamination after the ultrahigh pressure metamorphism (UHPM) in Triassic. Most inherited zircons yield the ages of 217.1±6.6 Ma, which is consistent with the peak UHPM in the Dabie-Sulu orogenic belt. Some of the inherited zircons (433-722 Ma) constitute a discordia line with the upper intercept age of 850+85/-68 Ma and a lower intercept age of 261+100/-140 Ma. These ages imply that the granite could be derived from the partial melting of the crustal materials of the South China Block that was intensively superimposed by t  相似文献   

9.
新疆库鲁克塔格新元古代花岗岩年龄和地球化学   总被引：3，自引：0，他引：3  
本文报道了新疆塔里木北缘库鲁克塔格地区新元古代孤山岩体（或太阳岛岩体）的岩石学、锆石U-Pb年龄及地球化学组成。研究表明：该岩体主要由英云闪长岩、奥长花岗岩及正长花岗岩组成，结晶的时间为795 Ma。其地球化学特征表现为富Na、LREE、LILE及亏损HREE、HFSE，因此具有高的（La/Yb）N及Sr/Y比值，与现代的艾达克岩相似。然而该岩体具有低的Nd初始值及太古代的Nd模式年龄，因此推测其岩浆来自太古代基性下地壳的重熔。鉴于在库鲁克塔格地区发育有800 Ma左右的蛇绿岩，因此我们推测该岩体是碰撞造山引起的加厚的下地壳重熔的结果，代表了塔里木地块前寒武纪基底的最终形成。  相似文献   

10.
SHRIMP U-Pb zircon age, geochemical and Nd isotopic data are reported for the Neoproterozoic Guandaoshan pluton in the Yanbian region, SW Sichuan. This pluton is of typical I-type granite and emplaced at (857±13) Ma. Geochemical and Nd isotopic characters suggest that the pluton was generated by partial melting of pre-existing, young (late Mesoproterozoic to early Neoproterozoic) low-K tholeiitic protolith within an intraplate anorogenic setting. The Guandaoshan pluton probably records the earliest magmatism induced by the proposed ca. 860-750 Ma mantle superplume beneath the supercontinent Rodinia.  相似文献   

11.
A dating of two biotite samples taken from the meso- and low-temperature mylonites within the Shangyi-Chicheng fault belt on the north of the North China Craton yields 40Ar/39Ar isotopic ages of (399 ± 1) Ma and (263 ± 2) Ma, respectively. These data reflect an Early Devonian deformation and a Late Carboniferous retrograde metamorphism event along the fault, suggesting that the tectonic activities of the North China Craton in Paleozoic should be reconsidered.  相似文献   

12.
Granitoids in the Hida region of Japan encompass two main rock types: younger type‐1 granites and older type‐2 granites. Sensitive high mass‐resolution ion microprobe (SHRIMP) U–Pb zircon dating of older type‐2 granites collected from the Tateyama area show similar ages of 245 ± 2 Ma and 248 ± 5 Ma for two gneissose granites, while a significantly younger intrusion age of 197 ± 3 Ma was determined for the younger type‐1 granites collected from the Hayatsukigawa River which belongs to the Okumayama pluton. A felsic gneiss sample (07HI‐3) collected from the right bank of the Hayatsukigawa River yielded multiple complex ages at 330 ± 6 Ma, indicating the timing of the Hida regional tectono‐thermal events that formed the Hida gneisses; 243 ± 8 Ma, representing the timing of intrusion of the augen granite; and 220 Ma, indicating the timing of regional dextral ductile shearing that caused a repeated recrystallization of metamorphic rocks in the study area. Considering the geochronological data, the rock types and assemblages, basement, and Sr–Nd isotopic constraints, we propose that the Hida Belt separated from the Jiamushi massif, which is located in the eastern margin of the Central Asian Orogenic Belt.  相似文献   

13.
扬子板块东北缘中元古代的大地构造划分   总被引：1，自引：0，他引：1  
扬子板块东北缘存在四条主要的中元古代变质带,自南向北依次为江南变质带、沿江变质带、云台一张八岭变质带和连云港一泗阳变质带。它们分别为中元古代的古弧后盆地、火山岛弧、裂谷及弧前盆地,扬子板块东北缘中元古代为活动大陆边缘构造体系。苏（北）胶（南）变质造山带应解体,其中一部分属扬子大陆边缘体系。  相似文献   

14.
The SHRIMP zircon U-Pb geochronology of three typical samples, including two monzo nitic granites from the Lincang batholith and a rhyolite from the Manghuai Formation are presented in the southern Lancangjiang, western Yunnan Province. The analyses of zircons for the biotite monzonitic granites from the northern (02DX-137) and southern (20JH-10) Lincang batholith show the single and tight clusters on the concordia, and yield the weighted mean 206Pb/238U ages of 229.4 ± 3.0 Ma and 230.4 ± 3.6 Ma, respectively, representing the crystallized ages of these granites. The zircons for the rhyolitic sample (02DX-95) from the Manghuai Formation give a weighted mean 206Pb/238U age of 231.0 ± 5.0 Ma. These data suggest that the igneous rocks from the Lincang granitic batholith and Manghuai Formation have a similar crystallized age. In combination with other data, it is inferred that both were generated at a narrow age span (~230 Ma) and were originated from the postcollisional tectonic regime. An early Proterozoic 206Pb/238U apparent age of 1977±44 Ma is additionally obtained from one zircon from the biotite monzonitic granite (southern Lincang batholith), indicative of devel- opment of the early Proterozoic Yangtze basement in the region. These precisely geochronological data provide important constraints on better understanding the Paleozoic tectonic evolution of the Tethys, western Yunnan Province.  相似文献   

15.
本文对新疆巴里坤红石滩铜矿区出露的石英闪长斑岩进行LA-ICP MS锆石U-Pb年龄测定,结果表明红石滩石英闪长斑岩形成年龄为403.1±3.8 Ma,形成时代为早泥盆世.此外,测得的两个锆石U-Pb同位素年龄为895 Ma左右,表明研究区可能存在早元古代基底.红石滩石英闪长斑岩体与铜矿关系密切,是寻找斑岩型铜多金属矿的有利场所,为今后在该区寻找同类型铜矿提供重要依据.  相似文献   

16.
The Japanese archipelago underwent two arc–arc collisions during the Neogene. Southwest Honshu arc collided with the Izu‐Bonin‐Mariana arc and the northeast Honshu arc collided with the Chishima arc. The complicated geological structure of the South Fossa Magna region has been attributed to the collision between the Izu‐Bonin‐Mariana arc and the southwest Honshu arc. Understanding the geotectonic evolution of this tectonically active region is crucial for delineating the Neogene tectonics of the Japanese archipelago. Many intrusive granitoids occur around the Kofu basin, in the South Fossa Magna region. Although the igneous ages of these granitoids have been mainly estimated through biotite and hornblende K–Ar dating, here, we perform U–Pb dating of zircon to determine the igneous ages more precisely. In most cases, the secondary post‐magmatic overprint on the zircon U–Pb system was minor. Based on our results, we identify four groups of U–Pb ages: ca 15.5 Ma, ca 13 Ma, ca 10.5 Ma, and ca 4 Ma. The Tsuburai pluton belongs to the first group, and its age suggests that the granite formation within the Izu‐Bonin‐Mariana arc dates back to at least 15.5 Ma. The granitoids of the second group intruded into the boundary between the Honshu arc and the ancient Izu‐Bonin‐Mariana arc, suggesting that the arc–arc collision started by ca 13 Ma. As in the case of the Kaikomagatake pluton, the Chino pluton likely corresponds to a granodiorite formed in a rear‐arc setting in parallel with the other granodiorites of the third group. The U–Pb age of the Kogarasu pluton, which belongs to the fourth group, is the same as those of the Tanzawa tonalitic plutons. This might support a syncollisional rapid granitic magma formation in the South Fossa Magna region.  相似文献   

17.
The North Dabie complex unit(NDC)is a widely exposed petro-tectonic unit.To understand post-orogenic uplift history and mechanism of the Dabie orogenic belt,many samples of granite,granodiorite,diorite,and alkali feldspar granite with precise zircon U-Pb ages were collected for electron microprobe analysis of hornblende.Emplacement pressure values were then calculated by using an Al-in-hornblende geobarometer.The result shows that total Al(AlT)values in hornblende range from 1.17to 1.97 p.f.u.,XFe(=Fe/(Fe+Mg))from 0.4 to 0.65,and corresponding pressure values from 256.8 to 676.2 MPa for AlT greater than 1.17.It is suggested that although the main mechanism for the uplift is tectonic extension,inhomogeneous uplift related to the pluton emplacement is also important during post-orogenic evolution of the Dabie orogenic belt.Emplacement depth distribution of the plutons shows that uplift in the NDC is affected by horst-graben structures since 120 Ma.  相似文献   

18.
Once a mafic intrusive rock has become altered, it is generally difficult to obtain a reliable intrusion age using conventional isotopic dating methods. To overcome this problem, this study used zircon fission track (ZFT) thermochronometry to determine the timing of crystallization of altered mafic intrusions. ZFT dating was carried out on samples of baked granite country rock adjacent to dolerite dikes (5–10 m thick) in the Takato area of central Japan. Three granite samples collected within 8 mm of a dike contact yielded consistent ZFT ages of 17–16 Ma, with confined track lengths indicative of the complete annealing of pre‐existing tracks by reheating due to dike intrusion. An older ZFT age was obtained for one granite sample collected within 20 mm of the contact, but confined track length measurements indicate that this is an incompletely reset age that lies between the ZFT age of the unbaked granitic country rocks (ca. 55 Ma) and the emplacement age of the dike. Petrographic examinations suggest that post‐intrusion hydrothermal activity did not influence the ZFT ages. We conclude that the 17–16 Ma ZFT age represents the emplacement age of the dikes. Our results show that ZFT dating of baked country rock is an effective tool for dating altered mafic intrusions, for which other dating techniques are not applicable. In the eastern part of Southwest Japan, dispersed volcanic activity occurred in the late Early to early Middle Miocene (18–15 Ma), and the volcanic belt extended into the forearc. This pulse of activity was possibly related to the injection of asthenospheric material into the trench‐side mantle wedge beneath the Japan arc. We also present young apatite fission track ages (ca. 4 Ma) that may reflect a Middle Miocene or later thermal event associated with local magmatic activity near the Takato area.  相似文献   

19.
The structural mapping and section study indicate that the "greenstone belts" in the southern to central parts of Hengshan were intensively sheared and transposed mafic dyke swarm,which originally intruded into the Neoarchean grey gneiss and high-pressure granulite terrain(HPGT).The HPGT is characterized by flat-dipping structures,to the south it became steep and was cut by the Dianmen mafic dyke swarm.After high-pressure granulite-facies metamorphic event,the mafic dyke swarm occurred,and was associated with the extensional setting and reworked by the late strike-slip shearing.The zircon age dating proves that the Dianmen mafic dyke swarm was emplaced during the period between 2499±4 Ma and 2512±3 Ma,followed by late tectonothermal reworking.The Dianmen mafic dyke swarm further documents the extensional episode in the central to northern parts of North China Craton(NCC),providing the important constraint for the limit between Archean and Proterozoic and correlation between NCC and other cratonic blocks of the world.  相似文献   

20.
Abstract Gneiss samples were collected from the Shandong Peninsula, eastern China, in order to carry out Rb-Sr dating using whole rock powder and biotite mineral separates. Middle Proterozoic whole rock age (1808 ± 71 Ma) and Middle to Late Proterozoic biotite ages (1312 and 729 Ma) were obtained for country gneisses in the northwestern part of the peninsula. Late Proterozoic whole rock age (707 ± 61 Ma) and Mesozoic biotite ages (172 and 222 Ma) were obtained for orthogneisses in the southeastern part of the peninsula. These new age data, as well as recent petrological results and published radiometric data, support the subdivision of the Shandong Peninsula into two geological districts: (i) a northwestern area of Proterozoic age represented by a low- and middle-pressure metamorphic sequence belonging to the Sino-Korean craton; and (ii) a southeastern area of Late Proterozoic and Mesozoic age accompanied by ultra-high pressure eclogite.  相似文献   

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