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1.
The Lake District terrane of northern England comprises Upper Cambrian–Silurian sediments and volcanics accumulated at the northern margin of the Avalonian Plate during growth and demise of the Iapetus Ocean. Ocean closure and suturing resulted in Late Ordovician and Acadian tectonism and were accompanied by emplacement of a large regional batholith. Palaeomagnetic study of intrusive igneous rocks, including application of thermal demagnetization, field tests and principal component analysis, identifies a history of Ordovician to Devonian magnetization. Late plutons (Shap and Skiddaw granites and/or aureoles) record a shallow dipolar (A3) axis (mean declination/inclination (D/I=278/+17°) dating from emplacement in late Early Devonian times (c. 395 Ma). Although this axis is recorded as a sporadic overprint in older rocks, no pervasive remagnetization is attributable to batholith emplacement. Instead, the Carrock Fell Complex Layered Gabbros have a mid- to late Ordovician (A1) remanence (D/I)=17·4/−58·1°, 36 samples, α95=4·8°) predating regional F2 folding. Later events in this igneous complex comprise the Carrock Fell Granophyre with a post-folding Ordovician remanence, and Round Knott Dolerite with a remanence linked to hydrothermal alteration late in the Ordovician magmatic episode. A Late Ordovician (Ashgill) palaeofield is also defined by remanence (A2) in the Threlkeld–St John's Microgranite and aureole (438 Ma, D/I=236·5/63·3°, 41 samples, α95=4·7°). Other intrusions carrying a remanence predating the Acadian deformation include the Great Cockup Picrite (458 Ma, D/I=43·2/−31·8°, 31 samples, α95=7·7°) and basic intrusives in the aureole of the Eskdale Granite (429 Ma, D/I=174·5/25·8°, 32 samples, α95=8·8°). Collectively the palaeomagnetic data from this terrane identify a hairpin in the apparent polar wander path during Late Ordovician (Caradoc–Ashgill) times corresponding to ‘soft’ closure of the Iapetus suture and accompanying deformation. The same motion is recognized in contemporaneous data from the Welsh Caledonides where declinations are rotated by c. 55° relative to contemporaneous results from the Lake District. Adjustment for this (probable late Acadian) rotation beings fold trends of the Paratectonic Caledonides into alignment and identifies a parallel mid- to late Ordovician destructive plate margin comprising forearc (Lake District) and backarc (North Wales). This arc was oriented latitudinally in mid-southerly latitudes during formation and the bulk of the magmatism occurred during a single normal-polarity chron. The relationships between magnetization and folding in both the Lake District and Welsh Borderlands identify the importance of Late Ordovician deformation along this arc during collision of Avalonia and Laurentia. Arc-related volcanism was succeeded in Silurian times by parallel foreland basins embracing the Welsh Basin and southern Lake District as the Laurentian Plate overrode the Avalonian Plate. © 1997 John Wiley & Sons, Ltd.  相似文献   

2.
Alternating field and thermal demagnetization of igneous rocks of the Malvern Hills identifies a number of magnetite-held components which are characterized by a high blocking temperature (M2) component D = 283°, I = 47°, and lower blocking temperature (M3) component D = 269°, I = −43° which is of complex origin or more than one age. Two subordinate components are (M1) D = 7°, I = 56° and (M4) D = 174°, I = 51° in later dolerites. A pervasive hematite-held remanence with a mean D = 186°, I = −5° is linked to Hercynian palaeofield directions and the uplift/folding of the Malvernian axis. The similarity of the magnetization directions in the Stanner–Hanter (702 Ma) and Malvernian (681 Ma) rocks suggests that folding of the Palaeozoic rocks in the Malvern Hills was achieved by upthrust of the basement and involved little folding of the latter. The Old Radnor sediments possess a post-folding remanence D = 117°, I = −13° of probable Cambrian age and a subordinate remanence which may be Hercynian in age. The late Precambrian–Cambrian palaeomagnetic record (ca. 700–500 Ma) of England and Wales is compared with data from the Armorican Massif. Although the apparent polar wander (a.p.w.) paths are widely dissimilar prior to 550 Ma, the two regions had similar latitudes and went through similar palaeolatitudinal movements throughout this interval. The palaeomagnetic data support models involving tectonic rotations but little closure across this part of the Hercynian Belt.  相似文献   

3.
纸房花岗岩体位于新疆东准噶尔卡拉麦里构造带北侧。该岩体侵入的最新地层为中-上奥陶统荒草坡群, 并被晚志留世及早泥盆世地层不整合覆盖。对纸房花岗岩进行锆石SHRIMP U-Pb定年, 获得的206Pb/238U加权平均年龄为(463±7)~(436±4) Ma, 表明该岩体形成于晚奥陶世-早志留世, 是早古生代岩浆活动的产物。对已有的区域地质资料、岩体侵位时代及其与围岩接触关系进行综合分析后认为, 纸房花岗岩体的形成时代大致对应于卡拉麦里构造带内区域性角度不整合的形成时间, 推测该岩体为早古生代造山过程中形成的花岗质岩石。高Sr、低Yb、弱的Eu负异常等地球化学特征也显示其为埃达克型同造山花岗岩。纸房地区早古生代同造山花岗岩的存在为东准噶尔卡拉麦里构造带早古生代造山作用的确认提供了证据。   相似文献   

4.
Four distinct components of natural remanent magnetization were isolated from a single site in welded tuffs in the Upper Cretaceous Kisin Group of the Sikhote Alin mountain range, Russia. In order to contribute toward a basis for an interpretation of multicomponent magnetization, rock magnetic experiments were performed on the welded tuffs. All four magnetization components essentially reside in magnetite. The lowest-temperature component up to 300 °C (component A: D=349.3°, I=60.9°, α95=7.3°, N=7) is a present day viscous magnetization. The third-removed component (component C: D=41.4°, I=51.8°, α95=3.5°, N=8), isolated over the temperature range of 450–560 °C, is a primary remanence. The second- and fourth-demagnetized components (component B: D=174.7°, I=−53.1°, α95=21.2°, N=3 and component D: D=188.1°, I=−64.5°, α95=4.0°, N=8, respectively) are secondary magnetizations related to a thermal event in Sikhote Alin between 66 and 51 Ma. Components B and D were acquired through different remagnetization processes. Component B is ascribed to a thermoviscous remanent magnetization carried by single-domain magnetite, and component D is a chemical remanent magnetization.  相似文献   

5.
巴什尔希岩体分布在东昆仑西段白干湖断裂和阿尔金断裂之间,岩性主要为二长花岗岩和钾长花岗岩,其中二长花岗岩与白干湖钨、锡多金属矿床关系密切。对锆石内部结构、阴极发光图像特征和Th/U比值的研究表明,二长花岗岩中的锆石为岩浆锆石。锆石LA-ICP-MSU-Pb同位素分析结果显示,二长花岗岩形成年龄为(458.0±9.0)Ma。结合前人对巴什尔希钾长花岗岩的锆石U-Pb定年(432.3±0.8)Ma,初步认为该岩体为晚奥陶世—早志留世侵入体。元素地球化学特征显示,巴什尔希花岗岩为弱准铝质或弱过铝质A型花岗岩,是东昆仑地区加里东期局部弧后盆地拉张过程中,地幔底侵导致地壳物质熔融的产物。  相似文献   

6.
The Zhongchuan district is an important component of the metallogenic belt in the Western Qinling. The Zhongchuan granite pluton occurring in the centre of the Zhongchuan metallogenic area has been poorly constrained, though the Triassic granite in Western Qinling has been well documented. In‐situ zircon U–Pb ages, Hf isotopic compositions and whole‐rock geochemical data are presented for host granite and mafic microgranular enclaves (MMES) from the Zhongchuan pluton, in order to constrain its sources, petrogenesis and tectonic setting of the pluton. The distribution of major, trace and rare earth elements apparently reflect exchange between the MMES and the host granitic rocks mainly due to interactions between coeval felsic host magma and mafic magma. The zircon U–Pb age of host granite (231.6 ± 1.5 to 235.8 ± 2.3 Ma) has overlapping uncertainty with that of the MMES (236.6 ± 1.3 Ma), establishing that the mafic and felsic magmas were coeval. The Hf isotopic composition of the MMES (εHf(t) = −13.4 to 4.0) is distinct from the host granite (εHf(t) = −15.7 to 0.0), indicating that both enriched subcontinental lithosphere mantle (SCLM) and crustal sources contributed to their origin. The zircons have two‐stage Hf model ages of 1064 to 1798 Ma for the host granite and 858 to 1747 Ma for the MMES. This suggests that the granitic pluton was likely derived from partial melting of a Late Mesoproterozoic crust, with subsequent interaction with the SCLM‐derived mafic magmas in tectonic affinity to the South China Block. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

7.
《International Geology Review》2012,54(13):1666-1689
ABSTRACT

The Wulonggou area in the Eastern Kunlun Orogen (EKO) in Northwest China is characterized by extensive granitic magmatism, ductile faulting, and orogenic gold mineralizations. The Shidonggou granite is located in the central part of the Wulonggou area. This study investigated the major as well as trace-element compositions, zircon U–Pb dates, and zircon Hf isotopic compositions of the Shidonggou granite. Three Shidonggou granite samples yielded an average U–Pb zircon age of 416 Ma (Late Silurian). The Late Silurian Shidonggou granite is peraluminous, with high alkali contents, high Ga/Al ratios, high (K2O + Na2O)/CaO ratios, and high Fe2O3T/MgO ratios, suggesting an A-type granite. The Shidonggou granite samples have zircon εHf(t) values ranging from ?7.1 to +4.4. The Hf isotopic data suggest that the Late Silurian granite was derived from the partial melting of Palaeo- to Mesoproterozoic juvenile mantle-derived mafic lower crust. Detailed geochronological and geochemical data suggest that the Late Silurian granite was emplaced in a post-collisional environment following the closure of the Proto-Tethys Ocean. Combining data of other A-type granitic rocks with ages of Late Early Silurian to Middle Devonian, such post-collisional setting related to the Proto-Tethys Ocean commenced at least as early as ~430 Ma (Late Early Silurian), and sustained up to ~389 Ma (Middle Devonian) in the EKO.  相似文献   

8.
A paleomagnetic study of subsurface core samples from dolomitized carbonates of two producing reservoirs in the Upper Ordovician Trenton Formation, collected from four wells in southwestern Ontario yielded a paleomagnetic direction of D = 152.3°, I = − 12.3° (N = 49, α95 = 8.7). This characteristic remanent magnetization (ChRM) direction was azimuth-corrected by aligning the viscous remanence magnetization (VRM) with the present Earth's magnetic field direction. A drilling-induced magnetization (VRMdi) was present in less than half the specimens sampled in this study. In addition, where the VRM correction could not be made, a paleolatitudinal arc calculated from the inclination-only mean of I = − 9.0° (N = 34, α95 = 3.0°) intersected the apparent polar wander path in the Late Permian–Early Triassic. These paleodirections are similar to the paleomagnetic directions observed in Ordovician Trenton carbonates from the Michigan Basin and New York State, U.S.A., suggesting a related regional late Paleozoic remagnetization.  相似文献   

9.
Paleomagnetic studies of thick lava series are one of the most reliable sources of data on the ancient geomagnetic field. However, most of such data are younger than 5 Ma, with much fewer results on the rest of the Cenozoic and the Mesozoic. Two wholesome results are available for the Precambrian but none for the Paleozoic. Late Permian basalts and rhyolites from northeastern Kazakhstan were studied to obtain first estimates of the geomagnetic-field characteristics during that period. We present preliminary results on part of the collection (66 flows (sites)) from a section ~ 1600 m thick. The characteristic component of reversed polarity was isolated by stepwise demagnetization at all the sites with a slight error. This component is of prefolding age and, most likely, primary. No abnormal magnetization direction is observed in the data, and the average directions of the characteristic component at the sites are tightly clustered (D = 243.3°; I = − 57.0°; k = 79.1; α95 = 2.0°; 65 sites). As compared with the published data on Cenozoic and Mesozoic thick lava series, secular variation was much weaker in the Late Permian than in the Mesozoic or Cenozoic, and the geomagnetic field was less disturbed. Secular-variation models based on the Late Cenozoic data show even more dramatic differences.  相似文献   

10.
This work presents the results of U–Pb geochronological studies of alkaline granites of the Aralaul complex of Northern Kazakhstan, which allow one to substantiate their Late Silurian (420 ± 4 Ma) age. Taking into consideration the previously obtained data, we propose a new development scheme of Paleozoic granitoid magmatism in Northern Kazakhstan, which includes Late Ordovician granite–granodiorite (Zerenda and Krykkuduk), Early Silurian granite–leucogranite (Borovoe and Karabulak), Late Silurian granosyenites–granite (Aralaul), and Early Devonian (Balkashino and Orlinogorsk) complexes.  相似文献   

11.
《Tectonophysics》1987,134(4):331-338
From the island of Cres and the fold belt north of autochthonous Istria 260 light-grey Cretaceous limestone samples were collected at 25 localities. Stepwise thermal demagnetization was employed to clean the remanence up to max. 525 °C. About two-thirds of the samples were successfully cleaned and the locality means were calculated from the characteristic remanences. The locality means significantly deviate from the present field direction both before and after tectonic correction: the mean inclination is about 15° lower than the present inclination and the declination is rotated counterclockwise i.e. it basically fits the pattern so far observed in the Periadriatic region.Unfolding barely influences the scatter of the directions (Cres: D = 308°, I = 45°, k = 26, α95 = 13.3°, before tilt correction, and D = 330°, I = 48°, k = 33, α95 = 11.9° after tilt correction; fold belt north of autochthonous Istria: D = 309°, I = 48°, k = 17, α95 = 11.9°, before tilt correction, and D = 336°, I = 41°, k =13, α95 = 14.0°, after tilt correction. In view of the inconclusive fold test, the magnetization cannot be dated precisely and thus does not yield sufficient information concerning possible relative movements between autochthonous Istria-Gargano and the fold belt studied. Nevertheless, the counterclockwise rotated declinations of the area studied are in contrast with the clockwise rotated declinations of the Ionian Zone of Western Greece. The large angular difference in declination between two parts of the Dalmatian-Ionian Zone with similar tectonic trends casts doubt on the continuity of the fold belt.  相似文献   

12.
This paper presents new SHRIMP zircon U–Pb chronology, major and trace element, and Sr–Nd–Hf isotopic data of two Early Paleozoic granitic plutons (Yierba and North Kudi) from the western Kunlun orogen, in attempt to further constrain the Proto-Tethys evolution. SHRIMP zircon U–Pb dating shows that the Yierba pluton was emplaced in the Middle Cambrian (513?±?7 Ma) and the North Kudi pluton was emplaced in the Late Silurian (420.6?±?6.3 Ma). The Yierba pluton consists of quartz monzodiorite, quartz monzonite and granodiorite. These granitoids are metaluminous and potassic, with initial 87Sr/86Sr ratios of 0.7072–0.7096, εNd (T) of ?0.2 to ?1.6 and εHf (T) (in-situ zircon) of ?1.2. Elemental and isotopic data suggest that they were formed by partial melting of subducted sediments, with subsequent melts interacting with the overlying mantle wedge in an oceanic island arc setting in response to the intra-oceanic subduction of Proto-Tethys. The North Kudi pluton consists of syenogranite and alkali-feldspar granite. These granites are metaluminous to weakly peraluminous and potassic. They show an affinity of A1 subtype granite, with initial 87Sr/86Sr ratios of 0.7077–0.7101, εNd (T) of ?3.5 to ?4.0 and εHf (T) (in-situ zircon) of ?3.9. Elemental and isotopic data suggest that they were formed by partial melting of the Precambrian metamorphic basement at a shallow depth (<30 km) during the post-orogenic regime caused by Proto-Tethyan oceanic slab break-off. Our new data suggest that the subduction of the Proto-Tethyan oceanic crust was as early as Middle Cambrian (～513 Ma) and the final closure of Proto-Tethys was not later than Late Silurian (～421 Ma), most probably in Middle Silurian.  相似文献   

13.
The zircon SHRIMP dating of the Zhangtiantang granite gave an age of 159±7 Ma., which shows that the granite was produced at the early Late Jurassic. The Ar-Ar plateau ages of biotite and K-feldspar from the Zhangtiantang pluton are 153.2±1.1 Ma and 135.8±1.2 Ma, respectively. The Ar-Ar anti-isochrone ages of biotite and K-feldspar are 152.5±1.7Ma and 135.4±2.7Ma, respectively. The ages represent the isotopic closure ages of minerals in the pluton. The Zhangtiantang granites are regarded as peraluminous crust-derived type granites to possess the typical geochemical characteristics of calc-alkaline rocks on continental margin, with enriched Si, K, Al (average value of A/CNK as 1.18), HREE, Rb, U, and Th, heavily depleted V, Cr, Co, Ni, Ti, Nb-Ta, Zr, Sr, P, and Ba, strongly negative Eu and common corundum normative (average value of C as 1.84). The εNd(t) values of the Zhangtiantang granite are −5.84 to −7.79, and t 2DM values are 1.69 to 1.83 Ga, which indicates partial melting of continental-crust metamorphic sedimentary rocks during the Middle Proterozoic. The cooling history of the Zhangtiantang granitic pluton indicates that the cooling velocity of pluton was faster (about 67°C/Ma) from zircon (158 Ma) to biotite (152 Ma), and was slower (about12°C/Ma) from biotite (152.5 Ma) to K-feldspar (135.8 Ma). It can be deduced that the temporal gap (about 10 Ma) between the granite formmation and W-Sn mineralization in South China may be related to ordinary magma-hydrothermal processes by the variational cooling curve of the pluton. The Zhangtiantang pluton was formed in a compressive setting, with differentiation evolution and mineralization occurring in a relative relaxation setting.  相似文献   

14.
The Kejie pluton is located in the north of the Changning-Menglian suture zone. The rock types are mainly biotite-granite. Zircon LA-ICP-MS U-Pb dating indicates that the Kejie pluton emplaced at about 80–77 Ma, Late Cretaceous. The Kejie pluton samples are characterized by high SiO2(71.68%–72.47%), K2O(4.73%–5.54%), total alkali(K2O + Na2O = 8.21%–8.53%), K2O/Na2O ratios(1.36–1.94) and low P2O5(0.13%–0.17%), with A/CNK of 1.025–1.055; enriched in U, Th, and K, depleted in Ba, Nb, Sr, Ti, P and Eu. They are highly fractionated, slightly peraluminous I-type granite. The two samples of the Kejie pluton give a large variation of εHf(t) values(-5.04 to 1.96) and Hf isotope crustal model ages of 1.16–1.5 Ga. Zircon Hf isotopes and zircon saturation temperatures of whole-rock(801°C–823°C) show that the mantle-derived materials maybe have played a vital role in the generation of the Kejie pluton. The Kejie pluton was most likely generated in a setting associated with the eastward subduction of the neo-Tethys ocean, where intrusion of mantle wedge basaltic magmas in the crust caused the anatexis of the latter, forming hybrid melts, which subsequently experienced high-degree fractional crystallization.  相似文献   

15.
南岭成矿带加里东期大花岗岩基的钨锡成矿潜力是近年来地质学家关注的热点。本文以湖南省彭公庙岩体为研究对象,精确厘定了产于彭公庙岩体内部的石牛仙钨矿的形成时代,同时厘定了彭公庙岩体中粗粒黑云母花岗闪长岩形成时代,分析了其地球化学特征,并与典型的成钨锡矿花岗岩进行对比,以此评估其钨锡成矿潜力。黑云母花岗闪长岩LA-ICP-MS锆石和独居石U-Pb年龄分别为436.1±2.5 Ma(MSWD=1.9,n=19)和436.8±2.8 Ma(MSWD=2.7,n=20),指示其侵位于早志留世。石牛仙钨矿床白云母39Ar/40Ar同位素坪年龄为150.2±1.2 Ma(MSWD=0.42),成矿时代与彭公庙成岩时代明显不同。彭公庙岩体分异程度不高,成矿元素W和Sn含量低,主要来源于上地壳贫粘土的变质砂岩,与南岭典型的成钨、成锡花岗岩分异程度高、成矿元素含量高、来源于富粘土的上地壳物质部分熔融区别明显,说明其成矿潜力有限。最后,在综合前人研究成果的基础之上,指出应综合地球物理、地球化学、构造蚀变信息等资料,重点评价彭公庙岩体内部及周缘晚期晚侏罗世花岗岩岩脉或...  相似文献   

16.
The Taurides, the southernmost of the three major tectonic domains that constitute present‐day Turkey, were emplaced following consumption of the Tethyan Ocean in Late Mesozoic to mid‐Tertiary times. They are generally assigned an origin at the northern perimeter of Gondwana. To refine palaeogeographic control we have investigated the palaeomagnetism of a range of Jurassic rocks. Forty‐nine samples of Upper Jurassic limestones preserve a dual polarity remanence (D/I=303/−9°, α95=6°) interpreted as a primary magnetization acquired close to the equator and rotated during emplacement of the Taurides. Result from mid‐Jurassic dolerites confirm a low palaeolatitude for the Tauride Platform during Jurassic times at the Afro–Arabian sector of Gondwana. Approximately 4000 km of Tethyan closure subsequently occurred between Late Jurassic and Eocene times. Although related Upper Jurassic limestones and Liassic redbeds preserve a sporadic record of similar remanence, the dominant signature in these latter rocks is an overprint of probable mid‐Miocene age, probably acquired during a single polarity chron and imparted by migration of a fluid front during nappe loading. This is now rotated consistently anticlockwise by c. 30° and conforms to results of previous studies recording bulk Neogene rotation of the Isparta region following Lycian nappe emplacement. The regional distribution of this overprint implies that the Isparta Angle (IA) has been subject to only small additional closure (<10°) since Late Miocene time. A smaller amount (c. 6°) of clockwise rotation within the IA since Early Pliocene times is associated with an ongoing extensional regime and reflects an expanding curvature of the Tauride arc produced by southwestward extrusion of the Anatolian collage as a result of continuing northward motion of Afro–Arabia. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

17.
Analyses of primary and early diagenetic fluid inclusions in the halite from the Late Ordovician Mallowa Salt, Canning Basin, Western Australia indicate a Ca‐rich composition and high concentration of parent brines in the basin which were close to sylvite and carnallite precipitation. The salt‐bearing series in the sampled interval was overheated up to 62 °C. The recorded differences in gas compositions result from the input of several gas sources including dispersed organic matter in the salt series and hydrocarbon deposits in the underlying rocks. The high concentration of the brines in fluid inclusions does not allow quantitative reconstruction of the chemical composition of Late Ordovician parent seawater. Using the information from Early Cambrian and Late Silurian basins as a proxy, however, the new data indicate that Late Ordovician seawater was undoubtedly Ca‐rich and, in comparison with modern seawater, had a similar K content, considerably lower Mg content (c. 30%), approximately three times the Ca content and one‐third the SO4 content.  相似文献   

18.
We report a new paleomagnetic pole for the Black Range Dolerite Suite of dykes, Pilbara craton, Western Australia. We replicate previous paleomagnetic results from the Black Range Dyke itself, but find that its magnetic remanence direction lies at the margin of a distribution of nine dyke mean directions. We also report two new minimum ID-TIMS 207Pb/206Pb baddeleyite ages from the swarm, one from the Black Range Dyke itself (>2769 ± 1 Ma) and another from a parallel dyke whose remanence direction lies near the centre of the dataset (>2764 ± 3 Ma). Both ages are slightly younger than a previous combined SHRIMP 207Pb/206Pb baddeleyite weighted mean date from the same swarm, with slight discordance interpreted as being caused by thin metamorphic zircon overgrowths. The updated Black Range suite mean remanence direction (D = 031.5°, I = 78.7°, k = 40, α95 = 8.3°) corresponds to a paleomagnetic pole calculated from the mean of nine virtual geomagnetic poles at 03.8°S, 130.4°E, K = 13 and A95 = 15.0°. The pole's reliability is bolstered by a positive inverse baked-contact test on a younger Round Hummock dyke, a tentatively positive phreatomagmatic conglomerate test, and dissimilarity to all younger paleomagnetic poles from the Pilbara region and contiguous portions of Australia. The Black Range pole is distinct from that of the Mt Roe Basalt (or so-called ‘Package 1’ of the Fortescue Group), which had previously been correlated with the Black Range dykes based on regional stratigraphy and imprecise SHRIMP U–Pb ages. We suggest that the Mt Roe Basalt is penecontemporaneous to the Black Range dykes, but with a slight age difference resolvable by paleomagnetic directions through a time of rapid drift of the Pilbara craton across the Neoarchean polar circle.  相似文献   

19.
华南早三叠世的古地磁学与大地构造   总被引：50，自引：0，他引：50       下载免费PDF全文
从华南几个具代表性地点的下三叠统灰岩中,获得了有意义的古地磁学初步结果。这些结果支持华南存在分离板块的设想。根据新近获得的地质与古地磁学证据,推断华南存在4个岩石图板块。它们是扬子(D=232.4°,I=-11.8°,K=28.2,α95=5.5°),湘桂(D=198.0°,I=32.2°,α95=12.9°),华夏(D=88.0°,I=13.0°,K=20.1,α95=9.1°)和海南(上二叠统D=338.2°,I=15.9°,K=10.2,α95=14.3°)板块。4个板块的古地磁极位分散,纬度差明显,并存在碰撞后的局部与区域性的旋转作用,尤其是顺时针旋转。华南早中生代的大地构造可理解为4个来自古特提斯和冈瓦纳的岩石圈碎块与欧亚大陆聚合作用的产物。  相似文献   

20.
笔者等对东昆仑造山带西段克其克孜苏花岗岩开展岩石学、岩石地球化学及LA-ICP-MS锆石U-Pb年代学研究,探讨岩体的形成时代、成因及地质意义.研究表明,克其克孜苏花岗岩中的锆石U-Pb加权平均年龄为442.3±4.4 Ma(MSWD=2.7),为晚奥陶世—早志留世,是区域上新解体出的早古生代花岗岩.花岗岩SiO2含量...  相似文献   

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