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1.
In this paper we present complex geological, petrographic and geochronological data of the study of intermediate and acid composition intrusive and volcanogenic rocks from the Porozhnaya massif of the South Yenisei Ridge. For the first time in the Yenisei Ridge Devonian and Triassic U-Pb age values (SHRIMP method) have been obtained for leucogranites—387 ± 5 Ma and alkaline trachytes—240 ± 3 Ma, which allows us to attribute them to two different complexes, despite the fact that these rocks were formed within the same Severnaya riftogenic structure. Geochronological Ar-Ar data (392–387 Ma) for micas from paragneisses and leucogranitic dikes of the Yenisei suture zone on whose extension the Severnaya riftogenic structure is located are also given in this study. These data on Devonian tectonic-magmatic events in the South Yenisei Ridge agree well with coeval events of continental rifting—the formation of intrusive and volcanogenic rocks of the Agul graben in the Prisayan region and the Minusa basin in the Altai-Sayan folded area. The forming of alkaline trachytes and alkaline syenites of the Severnaya riftogenic structure, for which an age of 240 ± 3 Ma has been established, is related to the trap magmatism of the Siberian platform.  相似文献   

2.
The formation and evolution conditions for alkaline magmatism and associated igneous rocks in the western framing of the Siberian craton are shown by the example of alkaline and subalkaline intrusive bodies of the Yenisei Ridge. Here we present petrographic, mineralogical, geochemical, and geochronological data for the rocks of the Srednetatarka and Yagodka plutons located within the Tatarka–Ishimba suture zone. Ferroan and metaluminous varieties enriched with rare elements (Nb, Ta, Zr, Hf, and REE) are making up most of the studied rocks. They formed at the stages of fractional crystallization of alkaline magma in a setting of active continental margin in the west of the Siberian craton in the Late Neoproterozoic (710–690 Ma). As differentiates of mantle magmas, these rocks associate with Nb-enriched rocks—A-type leucogranites and carbonatites. Sm/Nd and Rb/Sr isotopic data imply a predominance of the mantle component in the magmatic sources of the mafic and intermediate rocks as well as contamination processes of various volumes of continental crustal material by this magma.  相似文献   

3.
Neoproterozoic carbonatites and related igneous rocks, including A-type granites in the Tatarka-Ishimba suture zone of the Yenisey Ridge are confined to a horst-anticlinal structure that was formed in a transpression setting during the oblique collision between the Central Angara terrane and the Siberian craton. The carbonatites, associating mafic (including alkaline) dikes as well as the Srednetatarka nepheline syenites are the oldest igneous formations of the Tatarka active continental margin complex. Geochronological data indicate that magmatic evolution continued in the studied anticline for nearly 100 m.y. On the earliest stage carbonatites were formed and on the last stage — the emplacement of mantle-crustal A-type Tatarka granites took place. According to new U/Pb zircon studies, the earliest rocks in the Tatarka pluton are A-type leucogranites aged 646 ± 8 Ma. The younger 40Ar/39Ar ages of carbonatites obtained for phlogopites (647 ± 7 and 629 ± 6 Ma) are related to the last tectonic events in the studied region of the Tatarka-Ishimba suture zone, which are coeval with the formation of the A-type granitoids (646–629 Ma).  相似文献   

4.
The discovery of glaucophane relicts in the high-pressure tectonites of the Yenisei suture zone of the Yenisei Ridge suggests the manifestation of the “Chilean-type” convergent margin on the western Siberian Craton, which was controlled by subduction of oceanic crust beneath the continental margin. These rocks are restricted to the tectonic suture between the craton and the Isakovka ocean-island terrane and experienced two metamorphic stages. Petrogeochemical characteristics of the mafic tectonites indicate that their protoliths are N-MORB and E-MORB basalts. More primitive N-MORB basalts were formed at the initial spreading stages through melting of the upper depleted mantle. Higher Ti basalts were formed by melting of enriched mantle protolith at the later spreading stages. U–Pb zircon age of 701.6 ± 8.4 Ma of the metamorphosed analogues of normal basalts marks the initiation of oceanic crust in the region. Revealed sequence of spreading, subduction (640–620 Ma), and shear deformations (~600 Ma) records the early stages in the evolution of the Paleoasian ocean in its junction zone with the western margin of the Siberian craton: from formation of fragments of oceanic crust to the completion of accretionary–subduction events.  相似文献   

5.
Studies of gneisses from the Yenisei regional shear zone (YRSZ) provide the first evidence for Mesoproterozoic tectonic events in the geologic history of the South Yenisei Ridge and allowed the recognition of several stages of deformation and metamorphism spanning from Late Paleoproterozoic to Vendian. The first stage (~ 1.73 Ga), corresponding to the period of granulite-amphibolite metamorphism at P = 5.9 kbar and T = 635 °C, marks the final amalgamation of the Siberian craton to the Paleo-Mesoproterozoic Nuna supercontinent. During the second stage, corresponding to a hypothesized breakup of Nuna as a result of crustal extension, these rocks underwent Mesoproterozoic dynamic metamorphism (P = 7.4 kbar and T = 660 °C) with three peaks at 1.54, 1.38, and 1.25 Ga and the formation of high-pressure blastomylonite rocks in shear zones. Late-stage deformations during the Mesoproterozoic tectonic activity in the region, related to the Grenville-age collision processes and assembly of Rodinia, took place at 1.17-1.03 Ga. The latest pulse of dynamic metamorphism (615–600 Ma) marks the final stage of the Neoproterozoic evolution of the Yenisei Ridge, which is associated with the accretion of island-arc terranes to the western margin of the Siberian craton. The overall duration of identified tectonothermal processes within the South Yenisei Ridge during the Riphean (~ 650 Ma) is correlated with the duration of geodynamic cycles in the supercontinent evolution. A similar succession and style of tectonothermal events in the history of both the southern and the northern parts of the Yenisei Ridge suggest that they evolved synchronously within a single structure over a prolonged time span (1385–600 Ma). New data on coeavl events identified on the western margin of the Siberian craton contradict the hypothesis of a mantle activity lull (from 1.75 to 0.7 Ga) on the southwestern margins of the Siberian craton during the Precambrian. The synchronous sequence and similar style of tectonic events on the periphery of the large Precambrian Laurentia, Baltica, and Siberia cratons suggest their spatial proximity over a prolonged time span (1550–600 Ma). The above conclusion is consistent with the results of modern paleomagnetic reconstructions suggesting that these cratons represented the cores of Nuna and Rodinia within the above time interval.  相似文献   

6.
The geodynamic nature of the Late Neoproterozoic island-arc dacites (691 ± 8.8 Ma) and rift basalts (572 ± 6.5 Ma) of the Kiselikhinskaya Formation, Kutukasskaya Group, in the Isakovskii terrane is inferred from geochemical data and U–Pb zircon (SHRIMP-II) dates. The volcanic rocks were produced during the late evolutionary history of the Yenisei Range, starting at the origin of oceanic crustal fragments and their accretion to the Siberian craton to the postaccretionary crustal extension and the onset of the Caledonian orogenesis. The reproduced sequence of geological processes marks the early evolution of the Paleo- Asian Ocean in its junction zone with the Siberian craton. The data refine the composition and age of volcanic rocks in the trans-Angara part of the Yenisei Range and specifics of the Neoproterozoic evolution of the Sayan–Yenisei accretionary belt.  相似文献   

7.
This paper presents the results of geochemical, isotopic (Sm-Nd), and geochronological (U-Pb and Ar-Ar) investigations of leucogranites from the Garevka massif in the Transangara segment of the Yenisey Ridge. The most distinctive geochemical characteristics of these A-type granitoids are the enrichment in silica, potassium, iron, and fluorine and a considerable depletion in europium. Using U-Pb zircon geochronology, the age of the Garevka leucogranites was estimated as 752 ± 3 Ma, which allowed us to attribute them to a previously established Neoproterozoic tectonic event related to the collision of the Central Angara terrane and the Siberian craton. The parental melts of the granitoids were probably derived by melting of a mixed source composed of continental crustal rocks of Paleoproterozoic and Mesoproterozoic and (or) Neoproterozoic ages. Based on the obtained petrological, geochemical, and geochronological data, the leucogranites of the Garevka massif were assigned to the Neoproterozoic postcollisional Glushikha complex.  相似文献   

8.
中蒙边境中段花岗岩时空分布特征及构造和找矿意义   总被引：30，自引：1，他引：29  
本文精确地厘定了中蒙边境中段白乃庙片麻状石英闪长岩(459-454 Ma)、锡林浩特代托吉卡山中粒晶洞正长花岗岩(268±6.9 Ma)、镶黄旗巴音察汗灰白色中细粒角闪黑云母花岗闪长岩(261.7±6.1 Ma)、镶黄旗二长花岗岩(262.7±6.0 Ma)、镶黄旗哈达庙黑云母石英闪长岩(277.2±2.9 Ma)、锡林浩特白音锡勒中细粒正长花岗岩(231.1±7.6 Ma)、苏尼特左旗(东苏)二长花岗岩(216.9±5.4 Ma)、苏尼特左旗沙尔塔拉碱长花岗岩(152.1±2.5 Ma)的时代。并在前人工作的基础上, 总结了本地区花岗岩的时空分布规律: 区内花岗岩空间上呈3条近东西向的条带分布, 时间上可划分为5个重要期次:早-中古生代(490-387 Ma)、石炭纪(342-302 Ma)、二叠纪(282-257 Ma)、三叠纪(249-204 Ma)和晚中生代(152-118 Ma), 峰期间隔约为40 Ma, 并存在两条巨型碱性花岗岩带(东乌珠穆沁旗一带的二叠纪碱性岩带、华北板块北缘的晚三叠世碱性正长岩带), 岩浆活动呈现不对称性。结合区域地质、岩石、年代学等证据说明, 北部贺根山蛇绿岩与南部索伦山-西拉木伦蛇绿岩代表两个洋盆体系, 贺根山洋闭合早于中二叠世, 而索伦山-西拉木伦缝合带所代表残留古亚洲洋关闭, 中朝板块与西伯利亚板块最终碰撞拼合的时代应在晚二叠世-早三叠世。同时, 区内与花岗岩有关的矿产发育, 包括铜、钨、锌等矿种, 多产于造山后伸展或岩石圈拆沉, 区域大规模伸展环境。  相似文献   

9.
Collisional granitoid magmatism caused by the Early Neoproterozoic orogeny in the west of the Siberian craton is considered. New data on the petrogeochemical composition, U-Pb (SHRIMP II), Ar-Ar, and Sm-Nd isotopic ages of the Middle Tyrada granitoid massif in the northwestern Yenisei Ridge are presented. Plagiogranites, granodiorites, and quartz diorites of the massif are of calcareous and calc-alkalic composition. The elevated alumina contents and presence of accessory garnet permit them to be assigned to S-type granitoids. Their spidergrams show Rb, Ba, and Th enrichment, minimum Nb, P, and Ti contents, and no Sr depletion. The granitoids formed through the melting of plagioclase-enriched graywacke source, obviously Paleoproterozoic metaterrigenous rocks of the Garevka Formation and Teya Group (TNd(DM) = 2.0-2.5 Ga), judging from the isotope composition of the granitoids (TNd(DM-2st) = 2200 Ma and 8Nd(T) = − 6.0) and the presence of ancient zircon cores (1.80-1.85 Ga). Formation of granitoids took place in the final epoch of the Grenville collision events in the late Early Neoproterozoic (U-Pb zircon age is 857.0 ± 9.5 Ma). In the Late Neoproterozoic, the granitoids underwent tectonothermal reworking caused by Vendian accretion and collision events on the southwestern margin of the Siberian craton, which explain the younger K-Ar biotite age, 615.5 ± 6.3 Ma.  相似文献   

10.
The petrology, geochronology and geochemistry of the mafic enclaves in the Mid-Late Triassic Jiefangyingzi pluton from Chifeng area, southern Inner Mongolia, in China are studied to reveal their petrogenetic relationship with the host pluton. Furthermore, the coeval magmatic assemblage and its petrogenesis on the northern margin of the North China craton(NCC) are studied synthetically to elucidate their tectonic setting and the implications for the destruction of the NCC. Zircon U-Pb dating reveals that the mafic enclaves formed at 230.4 ± 2.2 Ma, which is similar to the age of the host pluton. The most basic mafic enclaves belong to weak alkaline rocks, and they display rare earth element(REE) and trace element normalized patterns and trace element compositions similar to those of ocean island basalt(OIB). In addition, they have positive εNd(t) values(+3.84 to +4.94) similar to those of the Cenozoic basalts on the northern margin of the NCC. All of these geochemical characteristics suggest that the basic mafic rocks originated from the asthenosphere. Petrological and geochemical studies suggest that the Jiefangyingzi pluton and the intermediate mafic enclaves were formed by the mixing of the asthenosphere-derived and crust-derived magmas in different degrees. The Mid-Late Triassic magmatic rocks on the northern margin of the NCC could be classified into three assemblages according to their geochemical compositions: alkaline series, weak alkaline–sub-alkaline series and sub-alkaline series rocks. Petrogenetic analyses suggest that the upwelling of the asthenosphere played an important role in the formation of these Mid-Late Triassic magmatic rocks. Basing on an analysis of regional geological data, we suggest that the northern margin of the NCC underwent destruction due to the upwelling of the asthenosphere during the Mid-Late Triassic, which was induced by the delamination of the root of the collisional orogeny between Sino-Korean and Siberian paleoplates in Late Permian.  相似文献   

11.
Geological, petrologeochemical, and geochronological studies of the rocks from the Shivei alkali-granitic pluton were conducted. A pluton about 500 km2 in area is a part of the larger (more than 30 000 km2) Kaakhem magmatic area. The data obtained allow us to characterize the magmatic complex of the Shivei pluton as a bimodal association with picrobasalts, subalkali basalts, and subalkali and alkali granitic rocks differentiated from syenites to leucogranites. The SHRIMP_II zircon dating from quartz syenites and alkali granites indicate the Permian age of the pluton (293.8 ± 3.8 Ma and 297.1 ± 3.8 Ma, respectively). Mafic-alkali-granitic associations similar in age and type, which are traced in the meridional direction along the Eastern Sayan toward the Siberian Platform, were distinguished as the Eastern Sayan zone of the Late Paleozoic alkaline magmatism. Its location corresponds to the western periphery of the Angaro-Vitim batholite and fits well into the zonal structure of the Barguzin magmatic province. We relate the geodynamic position of the Barguzin province with the mantle plume that was overlapped by the edge of the Siberian Pale-ocontinent in the course of its Paleozoic migration above the African hot spot.  相似文献   

12.
We report data from the Khadarta, Khoboi, and Orso metamorphic complexes of the Olkhon terrane in the western Baikal region. High-grade rocks in the three complexes may have been derived from active continental margin rocks (island arc–backarc basin system). The backarc basin history possibly began at 840–800 Ma, according to SHRIMP-II U-Pb zircon ages of the Orso gneiss. Many tectonic units in the Olkhon terrane belonged to the active margin of the Barguzin microcontinent which rifted off the Aldan province of the Siberian craton in the early Neoproterozoic. The accretion of the microcontinent to the craton was accompanied by high-grade metamorphism recorded in the Khadarta and Khoboi granulites. The 507 ± 8 Ma and 498 ± 7 Ma SHRIMP-II U-Pb zircon ages of the latter complexes, respectively, may refer to the earliest evolution stage of the Olkhon metamorphic terrane. New data for the Olkhon terrane agree well with the ages of other high-grade complexes along the southern Siberian craton (Slyudyanka, Kitoikin, Derba) and correspond to the initiation of the Central Asian orogen. With these data, the Olkhon metamorphic terrane has been interpreted as an Early Paleozoic collisional collage of fragments of the microcontinent’s Neoproterozoic active margin.  相似文献   

13.
The Late Vendian (540–550 Ma) U–Pb zircon age of postcollisional granitoids in the Osinovka Massif was obtained for the first time. The Osinovka Massif is located in rocks of the island-arc complex of the Isakovka Terrane, in the northwestern part of the Sayany–Yenisei accretion belt. These events stand for the final stage of the Neoproterozoic history of the Yenisei Ridge, related to the completing accretion of the oceanic crust fragments and the beginning of the Caledonian orogenesis. The petrogeochemical composition and the Sm–Nd isotopic characteristics support the fact that the granitoid melt originated from a highly differentiated continental crust of the southwestern margin of the Siberian Craton. Hence, the granite-bearing Late Riphean island-arc complexes were thrust over the craton margin at a distance considerably exceeding the dimensions of the Osinovka Massif.  相似文献   

14.
Late Vendian (540–550 Ma) U–Pb age was established for zircon from postcollisional granites of the Osinovsky Massif located among island-arc complexes of the Isakovka terrane in the northwestern Sayan–Yenisei accretionary belt. The granites were formed 150 Ma after the formation of the host island-arc complexes and 50–60 Ma after the beginning of their accretion to the Siberian Craton. These events mark the final stage of the Neoproterozoic history of the Yenisei Ridge related to the end of accretion of oceanic fragments and the beginning of the Caledonian Orogeny. The granites are subalkaline leucoractic Na–K rocks enriched in Rb, U, and Th. The petrogeochemical and Sm–Nd isotope data (TNd(DM)-2st = 1490–1650 Ma and εNd(T) from–2.5 to–4.4) indicate that their source was highly differentiated continental crust of the SW margin of the Siberian Craton. Therefore, the host Late Riphean island-arc complexes were thrust over the craton margin for distance significantly exceeding the size of the Osinovsky Massif.  相似文献   

15.
Comprehensive geochemical and geochronological studies were carried out for two-mica granites of the Biryusa block of the Siberian craton basement. U-Pb zircon dating of the granites yielded an age of 1874 ± 14 Ma. The rocks of the Biryusa massif correspond in chemical composition to normally alkaline and moderately alkaline high-alumina leucogranites. By mineral and petrogeochemical compositions, they are assigned to S-type granites. The low CaO/Na2O ratios (< 0.3), K2O - 5 wt.%, CaO < 1 wt.%, and high Rb/Ba (0.7-1.9) and Rb/Sr (3.9-6.8) ratios indicate that the two-mica granites resulted from the melting of a metapelitic source (possibly, the Archean metasedimentary rocks of the Biryusa block, similar to the granites in £Nd(t) value) in the absence of an additional fluid phase. The granite formation proceeded at 740-800 °C (zircon saturation temperature). The age of the S-type two-mica granites agrees with the estimated ages of I- and A-type granitoids present in the Biryusa block. Altogether, these granitoids form a magmatic belt stretching along the zone of junction of the Biryusa block with the Paleoproterozoic Urik-Iya terrane and Tunguska superterrane. The granitoids are high-temperature rocks, which evidences that they formed within a high-temperature collision structure. It is admitted that the intrusion of granitoids took place within the thickened crust in collision setting at the stage of postcollisional extension in the Paleoproterozoic. This geodynamic setting was the result of the unification of the Neoarchean Biryusa continental block, Paleoproterozoic Urik-Iya terrane, and Archean Tunguska superterrane into the Siberian craton.  相似文献   

16.
中国西秦岭碎屑锆石U-Pb年龄及其构造意义   总被引：5，自引：1，他引：4  
西秦岭是北接华北克拉通、西接祁连与柴达木、南接松潘—甘孜地块的东秦岭造山带的西延。文中研究了该区从前寒武纪到三叠纪的碎屑沉积岩。这些碎屑沉积岩中分离出的锆石由LA-ICPMS(激光剥蚀等离子体质谱)进行了U-Pb定年。全岩Nd亏损地幔模式年龄类似于扬子克拉通年龄,主要分布于1.55~1.98Ga,峰值为1.81Ga,而与华北克拉通主要为古元古代与太古宙的模式年龄形成明显的对比。泥盆系中的碎屑锆石930~730Ma的U-Pb年龄指示其与扬子克拉通具亲缘性。930~730Ma是源区地壳的强烈增长阶段。二叠系—三叠系的碎屑沉积岩主体以含老于1600Ma的碎屑锆石为特征。碎屑锆石U-Pb年龄与Sm-Nd同位素组成指示此时华北克拉通南缘的基底岩石成为二叠系—三叠系碎屑沉积岩的重要物源。扬子克拉通在三叠纪时与华北克拉通拼接。西秦岭二叠系—三叠系碎屑沉积岩含有高达50%的华北克拉通南缘的基底岩石。  相似文献   

17.
A study of gneisses and schists from the Yenisey regional shear zone (Garevka complex) at the western margin of the Siberian Craton has provided important constraints on the tectonothermal events and geodynamic processes in the Yenisey Ridge during the Riphean. In situ U-Th-Pb geochronology of monazite and xenotime from different garnet growth zones and the calculation of P-T path derived from chemical zoning pattern in garnet were used to distinguish three metamorphic events with different ages, thermodynamic regimes and metamorphic field gradients. The first stage occurred as a result of the Grenville orogeny during late Meso-early Neoproterozoic (1050–850 Ma) and was marked by low-pressure zoned metamorphism at ～4.8–5.0 kbar and 565–580°C and a metamorphic field gradient with dT/dH = 20–30°C/km typical of orogenic belts. At the second stage, the rocks experienced Late Riphean (801–793 Ma) collision-related medium-pressure metamorphism at ～7.7–7.9 kbar and 630°C with dT/dH ≤ 10°C/km. The final stage evolved as a syn-exhumation retrograde metamorphism (785–776 Ma) at ～4.8–5.4 kbar and 500°C with dT/dH ≤ 12°C/km and recorded a relatively fast uplift of the rocks to upper crustal levels in shear zones. The range of exhumation rates at the post-collisional stage (500–700 m/Ma) correlates with the duration of exhumation and the results of thermophysical numerical modeling of metamorphic rocks within orogenic belts. The final stages of collisional orogeny are marked by the development of rift-related bimodal dyke swarms associated with Neoproterozoic extension (797 ± 11 and 7.91 ± 6 Ma; U-Pb SHRIMP II zircon data) along the western margin of the Siberian craton and the beginning of the breakup of Rodinia. Post-Grenville metamorphic episodes of regional evolution are correlated with the synchronous succession and similar style of the later tectono-metamorphic events within the Valhalla orogen along the Arctic margin of Rodinia and support the spatial proximity of Siberia and North Atlantic cratons at about 800 Ma, as indicated by the latest paleomagnetic reconstructions.  相似文献   

18.
古亚洲洋不是西伯利亚陆台和华北地台间的一个简单洋盆,而是在不同时间、不同地区打开和封闭的多个大小不一的洋盆复杂活动(包括远距离运移)的综合体.其北部洋盆起始于新元古代末-寒武纪初(573~522Ma)冈瓦纳古陆裂解形成的寒武纪洋盆.寒武纪末-奥陶纪初(510~480Ma),冈瓦纳古陆裂解的碎块、寒武纪洋壳碎块和陆缘过渡壳碎块相互碰撞、联合形成原中亚-蒙古古陆.奥陶纪时,原中亚-蒙古古陆南边形成活动陆缘,志留纪形成稳定大陆.泥盆纪初原中亚-蒙古古陆裂解,裂解的碎块在新形成的泥盆纪洋内沿左旋断裂向北运动,于晚泥盆世末到达西伯利亚陆台南缘,重新联合形成现在的中亚-蒙古古陆.晚古生代时,在现在的中亚-蒙古古陆内发生晚石炭世(318~316Ma)和早二叠世(295~285Ma)裂谷岩浆活动,形成双峰式火山岩和碱性花岗岩类.蒙古-鄂霍次克带是西伯利亚古陆和中亚-蒙古古陆之间的泥盆纪洋盆,向东与古太平洋连通,洋盆发展到中晚侏罗世,与古太平洋同时结束,其洋壳移动到西伯利亚陆台边缘受阻而向陆台下俯冲,在陆台南缘形成广泛的陆缘岩浆岩带,从中泥盆世到晚侏罗世都非常活跃.古亚洲洋的南部洋盆始于晚寒武世.此时,华北古陆从冈瓦纳古陆裂解出来,在其北缘形成晚寒武世-早奥陶世的被动陆缘和中奥陶世-早志留世的沟弧盆系.志留纪腕足类生物群的分布表明,华北地台北缘洋盆与塔里木地台北缘、以及川西、云南、东澳大利亚有联系,而与上述的古亚洲洋北部洋盆没有关连,两洋盆之间有松嫩-图兰地块间隔.晚志留世-早泥盆世,华北地台北部发生弧-陆碰撞运动,泥盆纪时,在松嫩地块南缘形成陆缘火山岩带,晚二叠世-早三叠世华北地台与松嫩地块碰撞,至此古亚洲洋盆封闭.古亚洲洋的南、北洋盆最后的褶皱构造,以及与塔里木地台之间发生的直接关系,很可能是后期的构造运动所造成的.  相似文献   

19.
Metamorphic and magmatic rocks are present in the northwestern part of the Schwaner Mountains of West Kalimantan. This area was previously assigned to SW Borneo (SWB) and interpreted as an Australian-origin block. Predominantly Cretaceous U-Pb zircon ages (c. 80–130 Ma) have been obtained from metapelites and I-type granitoids in the North Schwaner Zone of the SWB but a Triassic metatonalite discovered in West Kalimantan near Pontianak is inconsistent with a SWB origin. The distribution and significance of Triassic rocks was not known so the few exposures in the Pontianak area were sampled and geochemical analyses and zircon U-Pb ages were obtained from two meta-igneous rocks and three granitoids and diorites. Triassic and Jurassic magmatic and metamorphic zircons obtained from the meta-igneous rocks are interpreted to have formed at the Mesozoic Paleo-Pacific margin where there was subduction beneath the Indochina–East Malaya block. Geochemically similar rocks of Triassic age exposed in the Embuoi Complex to the north and the Jagoi Granodiorite in West Sarawak are suggested to have formed part of the southeastern margin of Triassic Sundaland. One granitoid (118.6 ± 1.1 Ma) has an S-type character and contains inherited Carboniferous, Triassic and Jurassic zircons which indicate that it intruded Sundaland basement. Two I-type granitoids and diorites yielded latest Early and Late Cretaceous weighted mean ages of 101.5 ± 0.6 and 81.1 ± 1.1 Ma. All three magmatic rocks are in close proximity to the meta-igneous rocks and are interpreted to record Cretaceous magmatism at the Paleo-Pacific subduction margin. Cretaceous zircons of metamorphic origin indicate recrystallisation at c. 90 Ma possibly related to the collision of the Argo block with Sundaland. Subduction ceased at that time, followed by post-collisional magmatism in the Pueh (77.2 ± 0.8 Ma) and Gading Intrusions (79.7 ± 1.0 Ma) of West Sarawak.  相似文献   

20.
We present detailed geochronological, geochemical and Sr-Nd-Pb isotopic data for late Mesozoic mafic intrusions in the Taili region (western Liaodong Province) of the eastern North China Craton (NCC). We obtained laser-ablation inductively-coupled plasma mass spectrometry U-Pb zircon ages from lamprophyres with ages ranging from 139 to 162 Ma and diorites with clusters of ages at 226 ± 11 Ma, 165 ± 5.8 Ma and 140 ± 4.8 Ma. We interpret the Triassic zircons in diorites to be inherited from the Paleo-Asian Ocean slab. Both the lamprophyres and diorites contain abundant inherited grains (2644–2456 Ma) that were likely derived from the ancient NCC basement, reflecting a contribution from old lower crustal material. Like contemporaneous late Mesozoic mafic rocks in the Jiaodong and Liaodong Peninsula areas of the NCC, the Taili lamprophyres reveal a strong subduction signature in their normalized trace element patterns, including depletion of high field strength elements and enrichment of large ion lithophile elements. The rare-earth element patterns of the Taili intermediate-mafic intrusions are best explained if they were principally derived from partial melting of amphibole-bearing lherzolite in the spinel-garnet transition zone. Slab-derived melts likely contributed to the formation of late Mesozoic mafic rocks along three margins of the craton: due to accretion of the Yangtze Block along the southern margin of the craton, subduction of the Paleo-Asian Ocean along the northern margin, and subduction of the Paleo-Pacific oceanic plate along the eastern margin of NCC. We present a synthesis of the geochemical, spatial, and temporal patterns of magmatic rocks and periods of deformation that contributed to decratonization of the NCC in response to the Mesozoic tectonic evolution of adjacent plates along its northern, southern, and eastern margins.  相似文献   

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