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1.
The Ghanzi-Makunda area exposes three main Proterozoic assemblages. The oldest rocks belong to the Palaeoproterozoic (Eburnian) Okwa Basement Complex, which consists of porphyritic rhyolitic felsite and granitoids emplaced at 2055±4 Ma. A volcanic sequence named the Kgwebe volcanic complex consists of metarhyolites and metabasalts with interbedded tuff and agglomerate. These metavolcanic rocks represent a bimodal suite of continental tholeiites and high K rhyolites linked to the evolution of the Mesoproterozoic Kibaran orogenic system. Siliciclastic and carbonate rock successions of the Neoproterozoic to early Palaeozoic Ghanzi-Chobe Belt unconformably overlie the Mesoproterozoic Kgwebe volcanic complex. The Ghanzi-Chobe Supergroup comprises the Ghanzi Group and the Okwa Group. In Namibia, felsic lavas with UPb zircon ages of ca 750 Ma occur at the top of lithological units correlated to the Ghanzi Group. The deposition of the Ghanzi Group occured after 1020 Ma and before 750 Ma. In the Okwa Group, detrital zircons extracted from Neoproterozoic sedimentary rocks of the Takatswaane Formation yielded the following dates: 1887±14 Ma, 1246±4 Ma, 1054±5 Ma, 627±6 Ma and 579±12 Ma. The age of 579 ± 12 Ma is considered to represent the maximum depositional age of the Okwa Group. Based on the data in this paper, as well as lithological similarities, the Ghanzi Group is correlated with the Nosib Group of the Damara Belt, while the Okwa Group is correlated with the Nama Group in Namibia.  相似文献   

2.
A new National Geological Map of Botswana incorporates data acquired from a variety of sources; the map is produced as a 1:1 million hardcopy as well as in digital format. The new map shows the pre-Kalahari Group geology. The oldest rocks are exposed in eastern Botswana where three Archaean terranes are recognised: the western parts of the Kaapvaal and Zimbabwe Cratons and the western part of the Limpopo Mobile Belt. All three terranes are lithologically similar but differ in their structural styles and in the timing of major thermal events. The oldest (pre-3.0 Gal high-grade metamorphic rocks are found in the Kaapvaal Craton, and the youngest in the Limpopo Mobile Belt, which appears to record Palæoproterozoic ductile shearing. Proterozoic orogenic belts, mostly concealed beneath Karoo rocks, define the western limits of the Archaean terranes and pprogressively young westwards away from the Archaean rocks. The Palwoproterozoic Magondi and Kheis Belts are well-defined by regional magnetic maps, but both are very poorly exposed in Botswana. The Kheis Belt trends due north from South Africa into central Botswana to define the western edge of the Kaapvaal Craton. The western part of the Magondi Belt, as well as all of a Mesoproterozoic (Kibaran) belt and rift are overprinted by the Neoproterozoic Damara Belt; all have pronounced northeasterly trends. During the Palæoproterozoic, there was also significant intraplate magmatism, sedimentation and deformation within the Archæan terranes. Some of the magmatism (in southeastern Botswana) was contemporaneous with, and lithologically similar to, the Bushveld Igneous Complex of South Africa. The main feature of the Mesoproterozoic geology of Botswana is a northeast trending rift that extends right across the northwest of the country and which is partly infilled with ca 1 106 Ma volcanic rocks. Neoproterozoic sedimentary rocks overlie the volcanics within the rift. The various rocks are exposed along the Ghanzi Ridge and to the northeast in the Chobe District.New detailed airborne magnetic surveys in northwest Botswana (Ngamiland) show the detailed geology of the northeast trending inland branch of the Damara Belt and exactly define its northwestern and southeastern boundaries. The southeastern part of the Damara Belt comprises the Mesoproterozoic volcanics of the Kgwebe Formation and the Neoproterozoic Ghanzi Group sedimentary strata. The full extent of the volcanics, and of the three formations recognised in the Ghanzi Group, is shown on the new map. Deformation of these rocks increases to the northwest where they are bounded by the tectono-stratigraphical Roibok Group. To the northwest of the Roibok Group are poorly dated granitoid rocks separated into several units that are locally overlain by carbonate-dominated sequences. A cover sequence of metasedimentary rocks with northnorthwest trending folds lies northwest of the Damara Belt. These sediments may overlie the southernmost part of the Congo Craton in the extreme northwest of Botswana. Neoproterozoic/ Lower Palæozoic sediments of the Nama Group partly infill a foreland basin to the south of the Damara belt in western Botswana.Karoo strata deposited within the Kalahari Basin underlie central Botswana. The distribution of the four major sedimentary groups, as well as of the capping basalts, is shown. The total thickness of the sediments is < 2000 m and the basalts are up to 1000 m in thickness. The sediments comprise a lower sequence (Dwyka and Ecca Groups) related to regional sagging and an upper sequence (Beaufort and Lebung Groups) that succeeded regional uplift that created intra-Karoo unconformities. Karoo sedimentation commenced towards the end of the Carboniferous Period and the basalts were extruded at about 180 Ma before Present. Wherever there have been detailed studies undertaken on the Karoo rocks, they show intense faulting that may or may not mimic structures in the pre-Karoo bedrock. The faulting appears to be post-sedimentation. No evidence was found for growth faults producing abnormal thicknesses of Karoo sediments. It is always possible to correlate the internal stratigraphy, at least at the formational level across the faults. Abnormal thicknesses of the basalts are preserved on the downthrow sides of the major faults. A major dyke swarm coeval with the extrusive basalts trends east-southeast right across north-central Botswana to cut across older structural trends.Over 200 kimberlites are shown on the new map. The kimberlites are distributed throughout Botswana in a number of separate clusters. Most of the kimberlites are of Cretaceous age. Isopachs are shown of the Kalahari Group, which is generally < 180 m in total thickness.  相似文献   

3.
The Bone Mountains, located in Southwest Sulawesi along the SE margin of Sundaland, are composed of Oligocene to possibly lower Miocene marginal basin successions (Bone Group) that are juxtaposed against continental margin assemblages of Eocene–Miocene age (Salokalupang Group). Three distinct units make up the latter: (i) Middle–Upper Eocene volcaniclastic sediments with volcanic and limestone intercalations in the upper part (Matajang Formation), reflecting a period of arc volcanism and carbonate development along the Sundaland margin; (ii) a well-bedded series of Oligocene calc-arenites (Karopa Formation), deposited in a passive margin environment following cessation of volcanic activity, and (iii) a series of Lower–Middle Miocene sedimentary rocks, in part turbiditic, which interfinger in the upper part with volcaniclastic and volcanic rocks of potassic affinity (Baco Formation), formed in an extensional regime without subduction.The Bone Group consists of MORB-like volcanics, showing weak to moderate subduction signatures (Kalamiseng Formation), and a series of interbedded hemipelagic mudstones and volcanics (Deko Formation). The Deko volcanics are in part subduction-related and in part formed from melting of a basaltic precursor in the overriding crust. We postulate that the Bone Group rocks formed in a transtensional marginal basin bordered by a transform passive margin to the west (Sundaland) and by a newly initiated westerly-dipping subduction zone on its eastern side.Around 14–13 Ma an extensional tectonic event began in SW Sulawesi, characterized by widespread block-faulting and the onset of potassic volcanism. It reached its peak about 1 Ma year later with the juxtaposition of the Bone Group against the Salokalupang Group along a major strike-slip fault (Walanae Fault Zone). The latter group was sliced up in variously-sized fragments, tilted and locally folded. Potassic volcanism continued up to the end of the Pliocene, and locally into the Quaternary.  相似文献   

4.

Devonian and Carboniferous (Yarrol terrane) rocks, Early Permian strata, and Permian‐(?)Triassic plutons outcrop in the Stanage Bay region of the northern New England Fold Belt. The Early‐(?)Middle Devonian Mt Holly Formation consists mainly of coarse volcaniclastic rocks of intermediate‐silicic provenance, and mafic, intermediate and silicic volcanics. Limestone is abundant in the Duke Island, along with a significant component of quartz sandstone on Hunter Island. Most Carboniferous rocks can be placed in two units, the late Tournaisian‐Namurian Campwyn Volcanics, composed of coarse volcaniclastic sedimentary rocks, silicic ash flow tuff and widespread oolitic limestone, and the conformably overlying Neerkol Formation dominated by volcaniclastic sandstone and siltstone with uncommon pebble conglomerate and scattered silicic ash fall tuff. Strata of uncertain stratigraphic affinity are mapped as ‘undifferentiated Carboniferous’. The Early Permian Youlambie Conglomerate unconformably overlies Carboniferous rocks. It consists of mudstone, sandstone and conglomerate, the last containing clasts of Carboniferous sedimentary rocks, diverse volcanics and rare granitic rocks. Intrusive bodies include the altered and variably strained Tynemouth Diorite of possible Devonian age, and a quartz monzonite mass of likely Late Permian or Triassic age.

The rocks of the Yarrol terrane accumulated in shallow (Mt Holly, Campwyn) and deeper (Neerkol) marine conditions proximal to an active magmatic arc which was probably of continental margin type. The Youlambie Conglomerate was deposited unconformably above the Yarrol terrane in a rift basin. Late Permian regional deformation, which involved east‐west horizontal shortening achieved by folding, cleavage formation and east‐over‐west thrusting, increases in intensity towards the east.  相似文献   

5.
赞比亚东北部姆波洛科索盆地古元古代姆波洛科索群是研究早前寒武纪河流相、浅海相沉积序列和基底组分的重要地层单元。本文通过对该地区岩石地层组成、沉积时代与沉积环境方面进行研究及系统总结,并结合对该地区姆巴拉组实测剖面及其碎屑岩岩石学和地球化学分析数据,获得以下认识:姆波洛科索群可能形成于1860 Ma之后,其上覆卡萨马群可能形成于1434 Ma之后;姆波洛科索盆地沉积环境主要包括:辫状河、冲积扇、湖泊以及浅海等;姆波洛科索群底部姆巴拉组碎屑岩以班委乌卢地块基底花岗岩为主要物源,形成于被动大陆边缘构造背景之下;姆波洛科索盆地可能属于被动大陆边缘型盆地;化探分析数据显示盆地东部与北部地区分别具有金、铀找矿潜力。  相似文献   

6.
The southern part of the Korean Peninsula preserves important records of the Paleozoic evolutionary history of East Asia. Here we present SHRIMP U–Pb ages of detrital zircon grains from Paleozoic metasedimentary successions (Okcheon and Joseon Supergroups, Yeoncheon Group, Taean Formation, and Pyeongan Supergroup) that are incorporated into the major Phanerozoic mountain belts (Okcheon and Hongseong-Imjingang Belts) in South Korea, providing new insights for provenances and paleotectonic evolution of the South Korean Peninsula during Paleozoic time. The zircon ages from our samples display two distinct spectra patterns in their presence/absence of Neoproterozoic and/or Paleozoic populations. Our results, together with the available data from the Korean Peninsula, suggest that: (1) the Early to Middle Paleozoic successions in the Okcheon Belt were deposited in continental margin setting(s) formed by Neoproterozoic intracratonic rifting, (2) the Middle Paleozoic metasedimentary rocks in the Imjingang belt can be interpreted as molasse and flysch sediments along an active continental margin, (3) the Late Paleozoic to Early Triassic Taean Formation along the western Gyeonggi Massif represents a syn- to post-collision deltaic complex of a remnant oceanic basin, and (4) the Late Paleozoic to possibly Early Triassic Pyeongan Supergroup in the Okcheon Belt might represent a wedge-top and/or foreland basin. The spatial and temporal discrepancy between the South Korean Peninsula and the Central China Orogenic Belt during Paleozoic might reflect lateral variations in crustal evolution history along the East Asian continental margin during the Paleo-Tethyan Ocean closure.  相似文献   

7.
The North Qilian orogenic belt is the key to figure out the evolution and assembly of Asia. The Upper Silurian Hanxia Formation which is deposited in the north area of North Qilian Orogenic Belt is of utmost important to reveal the architecture and orogenic process of the North Qilian belt. So provenance analysis of the Hanxia Formation is of significance to reveal not only that the tectonic evolution of the central orogenic belt China, but also that Paleozoic Asia plate reconstruction. The ratios of elements and some discrimination diagrams based on geochemistry indicate that felsic rocks constitute their main source rocks. The chemical index of alteration is less than 80, indicating that the source rocks are relatively fresh and of low maturity. On the Th/Sc versus Zr/Sc scatter plot, samples from Hanxia Formation occur along the magmatic compositional variation trend of rocks, indicating that the rocks did not undergo obvious sedimentary sorting and recycling. The major and trace elements discrimination diagrams imply that Hanxia Formation rocks were derived from continental island arc. Recent studies show that the North China plate subducted southwards and produced subduction-related arc magmatism along the southern margin of the North Qilian Terrane during the Silurian. Therefore, we infer that in the late Silurian period the subduction-related arc became accreted to the Central Qilian terrane to the south, forming a composite continental arc, and the North Qilian belt accumulated in a fore-arc basin.  相似文献   

8.
The 1900–1700 Ma Waterberg Group in the main Waterberg fault-bounded basin consists of dominantly coarse siliciclastic red beds with minor volcanic rocks. The sedimentary rocks were deposited mainly by alluvial fans, fluvial braidplains and transgressive shallow marine environments, with lesser lacustrine and aeolian settings. Uplifted, largely granitic source areas were located along the Thabazimbi-Murchison lineament (TML) fault system in the south, and along the Palala shear zone in the northeast. Palaeoplacer titanomagnetite-ilmenite-zircon heavy mineral deposits, best developed in the Cleremont Formation in the centre of the basin, reflect initial fluvial reworking and subsequent littoral marine concentration. Coarse alluvial cassiterite placer deposits are found in the Gatkop area in the southwest of the basin, and appear to have been derived from stanniferous Bushveld Complex lithologies south of the TML. Hydrothermal zinc and U-Cu mineralisation in the Alma lithologies in the same area appears to be related to the TML fault system. Small manganese deposits and anomalous tungsten values occur in the south of the basin, where they are again closely spatially associated with the TML. Copper-barium mineralisation is found associated with dolerite dykes, and in stratigraphically controlled, inferred syngenetic settings. The most interesting of these apparently syngenetic occurrences is found within green coloured reduced mudrocks and inferred volcanic rocks, at an unconformity developed within the overall red bed sequence of the Waterberg Group, adjacent to the TML in the southwest of the basin. The most important potential mineralisation in the main Waterberg basin thus encompasses shoreline placer Ti and the possibility of substantial sediment-hosted copper deposits. Received: 31 May 1996 / Accepted: 17 February 1997  相似文献   

9.
新疆西准噶尔南部地区出露多条蛇绿岩,其中玛依勒蛇绿岩是该地区比较重要的蛇绿岩之一,其所代表的古洋盆的开启、闭合时限一直是地学界争论的焦点。详细的野外调查发现:玛依勒蛇绿混杂岩呈构造岩块的形式就位于中-上志留统玛依拉山岩群复理石基质中或与寒武纪杂岩体在空间上密切共生,表明玛依勒蛇绿岩所代表的古洋盆至少在寒武纪时期就已经开启,一直持续到中-晚志留世;中泥盆统库鲁木迪组分别角度不整合于中-上志留统玛依拉山岩群和寒武纪杂岩体之上,从而限定了玛依勒洋盆闭合时限的上限为中泥盆世之前。地层剖面分析发现库鲁木迪组与玛依拉山岩群之间在岩性特征、地层序列、沉积环境等方面均存在显著差异,表明晚古生代早期是西准噶尔地区构造演化发展的重要转换时期,库鲁木迪组下部的陆相沉积序列是对玛依勒早古生代洋盆闭合过程的沉积学响应。这将对进一步研究西准噶尔的构造演化和古生代中亚地区的构造格局提供了重要的制约。  相似文献   

10.
山西吕梁地区是华北克拉通保存古元古界变质表壳岩良好地区, 其中的岚河群在吕梁山北部岚县南北两侧大量出露, 由碎屑岩、碳酸盐岩夹少量基性火山岩等多个沉积旋回的沉积组合构成, 经历绿片岩相浅变质作用改造, 保留了大量原始沉积构造, 是探讨该群沉积 特征、形成时代及与其它表壳岩群关系的理想对象。 对岚河群 3 件样品的碎屑锆石 LA-ICP-MS U-Pb 定年, 获得底部含砾砂岩最年轻碎屑锆石 2.2 Ga 的峰值年龄, 该群经历了 1.87 Ga 的 区域变质作用, 因而限定岚河群沉积于 2.2～1.87 Ga 之间。 碎屑锆石年龄谱显示了～2.2 Ga 的 主峰期和～2.3 Ga 及太古代中晚期等较小峰期年龄, 指示主要源自古元古代陆壳物质源区, 它们的主峰期年龄锆石与吕梁地区同期岛弧花岗岩锆石 Hf 同位素特征一致, 且其沉积组合反映了物源区活动性较强, 证明岚河群形成于活动陆缘岛弧相关的沉积盆地。 野鸡山群下部的 青杨树湾组和白龙山组沉积组合与岚河群沉积地层序列类似, 它们均形成于 2.2 Ga 左右, 说明野鸡山下部沉积与岚河群相同, 也形成于活动陆缘岛弧环境的沉积盆地, 分别代表了盆地同时异相的沉积产物。 野鸡山群上部程道沟组与黑茶山群沉积序列类似, 具有造山过程相关盆地的磨拉石建造组合特征, 它们均形成于 1.85 Ga 之后, 代表与碰撞造山过程相关前陆盆地快速堆积。 因此, 3 个岩群表壳岩的沉积演化揭示了华北克拉通中部～2.2 Ga 俯冲汇聚相关的活动陆缘岛弧环境, 在～1.85 Ga 转为陆-陆碰撞造山演化过程。  相似文献   

11.
The Palaeoproterozoic Magondi Supergroup lies unconformably on the Archaean granitoid-greenstone terrain of the Zimbabwe Craton and experienced deformation and metamorphism at 2.06–1.96 Ga to form the Magondi Mobile Belt. The Magondi Supergroup comprises three lithostratigraphic units. Volcano-sedimentary rift deposits (Deweras Group) are unconformably overlain by passive margin, back-arc, and foreland basin sedimentary successions, including shallow-marine sedimentary rocks (Lomagundi Group) in the east, and deeper-water shelf to continental slope deposits in the west (Piriwiri Group). Based on the upward-coarsening trend and presence of volcanic rocks at the top of the Piriwiri and Lomagundi groups, the Piriwiri Group is considered to be a distal, deeper-water time-equivalent of the Lomagundi Group. The Magondi Supergroup experienced low-grade metamorphism in the southeastern zone, but the grade increases to upper greenschist and amphibolite facies grade to the north along strike and, more dramatically, across strike to the west, reaching upper amphibolite to granulite facies in the Piriwiri Group.  相似文献   

12.
荆山岩群是胶北地体最重要的古元古代变沉积岩系之一,经历了高角闪岩相?麻粒岩相变质与韧性变形,准确限定其沉积时代与物质来源对探究胶?辽?吉带古元古代构造演化过程具有重要意义.本文利用LA-ICP-MS（激光剥蚀电感耦合等离子质谱仪）对旌旗山地区荆山岩群禄格庄岩组中长石石英岩进行了锆石U-Pb测年和稀土元素分析.根据碎屑锆石内部结构和年龄结果,认为在最年轻一组碎屑锆石中谐和的207Pb/206Pb加权平均年龄2 120 Ma,可以大致限定其原岩的最大沉积时代,两件样品获得的变质年龄分别为1 886±12 Ma与1 969±23 Ma,结合区内禄格庄岩组被2 103~2 085 Ma二长花岗质片麻岩侵入的地质关系,初步限定旌旗山地区禄格庄岩组的沉积时代约为2 100 Ma.长石石英岩中有效碎屑锆石年龄谱图呈现2 105 Ma主峰值年龄和2 185 Ma次峰值年龄,指示旌旗山地区禄格庄岩组的主要物源为古元古代（2 200~ 2 100 Ma）中?酸性岩浆岩或再循环的产物,同时接受了少量太古宙的碎屑物质.综合胶?辽?吉带已发表的其他相关数据,认为以荆山岩群禄格庄岩组为代表的胶?辽?吉带南侧底部变沉积岩沉积时可能位于弧后盆地靠近岛弧一侧,以粉子山岩群小宋岩组为代表的胶?辽?吉带北侧底部变沉积岩则可能位于弧后盆地靠近太古宙大陆一侧.   相似文献   

13.
新疆南天山奥图拉托格拉克一带前震旦系基底地质特征   总被引：5，自引：1，他引：4  
1994年在新疆南天山地区奥图拉托格拉克一带 ,首次发现了晚太古代、元古宙结晶基底。晚太古代变质岩主要由变质深成岩组成 ,表壳岩组合为沙窝大沟岩组 ,岩性为一套变质火山—沉积岩。阜平期变侵入岩为巴什托格拉克片麻杂岩 ,为一套无序的 TTG岩系。五台期变侵入岩为沙窝布拉克片麻岩套。为一套基本有序的变侵入岩系列 ,包括 TTG和二长花岗岩两个岩系。三者组成太古宙古陆核。下元古界奥图拉托格拉克岩群为一套无序变质火山—沉积岩系 ,具有古老沟弧盆体系特征 ,阿牙克托格拉克岩组原岩为古蛇绿岩组合 ,具洋脊玄武岩特征 ;克孜拉格岩组原岩为杂砂岩 ,属盆地沉积 ;卡拉格兹岩组原岩为岛弧火山岩。长城系乱滩布拉克组由一套变火山岩、火山碎屑岩组成 ,属岛弧或活动陆缘沉积 ;卫东庄组为一变质碎屑岩建造 ,具弧盆碎屑岩沉积特征。长城纪末侵入了多岛滩超单元花岗岩  相似文献   

14.
位于大别山东南麓的安庆-潜山地区中新生代碎屑岩比较发育,主元素分析表明,砂岩主要为杂砂岩,其次是岩屑砂岩和长石砂岩。根据主元素、微量元素和稀土元素特征值分析结果,中、上三叠统和下、中侏罗统的源岩来源广泛,属于大陆岛弧、活动大陆边缘和被动大陆边缘构造背景,可能反映了前陆盆地物源的二元特征。古近系源岩主要为活动大陆边缘和大陆岛弧构造环境,说明物源仅来自大别山造山带。稀土元素比值及相关系数分析揭示,中晚三叠世黄马青群的源岩主要为宿松群的长英质片岩、浅粒岩以及大别杂岩,侏罗纪磨山组大致类似于大别群的花岗片麻岩,罗岭组与大别群比较类似。显示大别山造山带在中晚三叠世已经隆升并遭受剥露。  相似文献   

15.
The Late Archaean-Early Proterozoic Transvaal Sequence is preserved within the Transvaal, Kanye and Griqualand West basins, with the 2050 Ma Bushveld Complex intrusive into the upper portion of the succession within the Transvaal basin. Both Transvaal and Bushveld rocks are extensively mineralized, the former containing large deposits of iron, manganese, asbestos, andalusite, gold, fluorine, lead, zinc and tin ores, and the latter some of the World's major occurrences of PGE, chromium and vanadium ores. Transvaal sedimentation began with thin, predominantly clastic sedimentary rocks (Black Reef-Vryburg Formations) which grade up into a thick package of carbonate rocks and BIF (Chuniespoort-Ghaap-Taupone Groups). These lithologies reflect a carbonate-BIF platform sequence which covered much of the Kaapvaal craton, in reaction to thermal subsidence above Ventersdorp-aged rift-related fault systems. An erosional hiatus was followed by deposition of the clastic sedimentary rocks and volcanics of the Pretoria-Postmasburg-Segwagwa Groups within the three basins, under largely closed-basin conditions. An uppermost predominantly volcanic succession (Rooiberg Group-Loskop Formation) is restricted to the Transvaal basin. A common continental rift setting is thought to have controlled Pretoria Group sedimentation, Rooiberg volcanism and the intrusion of the mafic rocks of the Rustenburg Layered Suite of the Bushveld Complex. The dipping sheets of the Rustenburg magmas cut across the upper Pretoria Group stratigraphy and lifted up the Rooiberg lithologies to form the roof to the complex. Subsequent granitic rocks of the Lebowa and Rashoop Suites of the Bushveld Complex intruded both upper Rustenburg rocks and the Rooiberg felsites.  相似文献   

16.
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17.
本文研究了北秦岭及华北地台南缘火山岩约500件岩石化学、120件微量元素和135件稀土元素样品数据。熊耳群、大红口组火山岩属B类的地壳混染型,为大陆裂谷环境;宽坪群、秦岭群变拉斑玄武岩建造属A类的幔源型,为海槽环境;二郎坪群、丹凤群细碧角斑岩建造属C+A、C类的壳幔混合型,为海盆环境。  相似文献   

18.
In the Eastern Lachlan Orogen, the mineralised Molong and Junee‐Narromine Volcanic Belts are two structural belts that once formed part of the Ordovician Macquarie Arc, but are now separated by younger Silurian‐Devonian strata as well as by Ordovician quartz‐rich turbidites. Interpretation of deep seismic reflection and refraction data across and along these belts provides answers to some of the key questions in understanding the evolution of the Eastern Lachlan Orogen—the relationship between coeval Ordovician volcanics and quartz‐rich turbidites, and the relationship between separate belts of Ordovician volcanics and the intervening strata. In particular, the data provide evidence for major thrust juxtaposition of the arc rocks and Ordovician quartz‐rich turbidites, with Wagga Belt rocks thrust eastward over the arc rocks of the Junee‐Narromine Volcanic Belt, and the Adaminaby Group thrust north over arc rocks in the southern part of the Molong Volcanic Belt. The seismic data also provide evidence for regional contraction, especially for crustal‐scale deformation in the western part of the Junee‐Narromine Volcanic Belt. The data further suggest that this belt and the Ordovician quartz‐rich turbidites to the east (Kirribilli Formation) were together thrust over ?Cambrian‐Ordovician rocks of the Jindalee Group and associated rocks along west‐dipping inferred faults that belong to a set that characterises the middle crust of the Eastern Lachlan Orogen. The Macquarie Arc was subsequently rifted apart in the Silurian‐Devonian, with Ordovician volcanics preserved under the younger troughs and shelves (e.g. Hill End Trough). The Molong Volcanic Belt, in particular, was reworked by major down‐to‐the‐east normal faults that were thrust‐reactivated with younger‐on‐older geometries in the late Early ‐ Middle Devonian and again in the Carboniferous.  相似文献   

19.
虎林盆地北部坳陷地层包括下白垩统裴德组、下云山组、上云山组、珠山组，渐新统虎林组和中新统富锦组。北部坳陷砂岩-泥岩由常量、微量和稀土元素组成，揭示早白垩世砂岩-泥岩源区构造背景为活动大陆边缘，渐新统斗新统砂岩-泥岩多呈现出从活动大陆边缘向大陆岛弧转换的地球化学特征。结合沉积相特征和岩屑所反映的源区岩性特点，认为早白垩世时期物源主要来自于坳陷北部完达山造山带和南部古隆起；渐新统物源则主要来自盆地东北部的完达山造山带，并且碎屑岩的原始物质均来自上地壳。  相似文献   

20.
The northern part of the Tasman Fold Belt System in Queensland comprises three segments, the Thomson, Hodgkinson- Broken River, and New England Fold Belts. The evolution of each fold belt can be traced through pre-cratonic (orogenic), transitional, and cratonic stages. The different timing of these stages within each fold belt indicates differing tectonic histories, although connecting links can be recognised between them from Late Devonian time onward. In general, orogenesis became younger from west to east towards the present continental margin. The most recent folding, confined to the New England Fold Belt, was of Early to mid-Cretaceous age. It is considered that this eastward migration of orogenic activity may reflect progressive continental accretion, although the total amount of accretion since the inception of the Tasman Fold Belt System in Cambrian time is uncertain.The Thomson Fold Belt is largely concealed beneath late Palaeozoic and Mesozoic intracratonic basin sediments. In addition, the age of the more highly deformed and metamorphosed rocks exposed in the northeast is unknown, being either Precambrian or early Palaeozoic. Therefore, the tectonic evolution of this fold belt must remain very speculative. In its early stages (Precambrian or early Palaeozoic), the Thomson Fold Belt was probably a rifted continental margin adjacent to the Early to Middle Proterozoic craton to the west and north. The presence of calc-alkaline volcanics of Late Cambrian Early Ordovician and Early-Middle Devonian age suggests that the fold belt evolved to a convergent Pacific-type continental margin. The tectonic setting of the pre-cratonic (orogenic) stage of the Hodgkinson—Broken River Fold Belt is also uncertain. Most of this fold belt consists of strongly deformed, flysch-type sediments of Silurian-Devonian age. Forearc, back-arc and rifted margin settings have all been proposed for these deposits. The transitional stage of the Hodgkinson—Broken River Fold Belt was characterised by eruption of extensive silicic continental volcanics, mainly ignimbrites, and intrusion of comagmatic granitoids in Late Carboniferous Early Permian time. An Andean-type continental margin model, with calc-alkaline volcanics erupted above a west-dipping subduction zone, has been suggested for this period. The tectonic history of the New England Fold Belt is believed to be relatively well understood. It was the site of extensive and repeated eruption of calc-alkaline volcanics from Late Silurian to Early Cretaceous time. The oldest rocks may have formed in a volcanic island arc. From the Late Devonian, the fold belt was a convergent continental margin above a west-dipping subduction zone. For Late Devonian- Early Carboniferous time, parallel belts representing continental margin volcanic arc, forearc basin, and subduction complex can be recognised.A great variety of mineral deposits, ranging in age from Late Cambrian-Early Ordovician and possibly even Precambrian to Early Cretaceous, is present in the exposed rocks of the Tasman Fold Belt System in Queensland. Volcanogenic massive sulphides and slate belt-type gold-bearing quartz veins are the most important deposits formed in the pre-cratonic (orogenic) stage of all three fold belts. The voicanogenic massive sulphides include classic Kuroko-type orebodies associated with silicic volcanics, such as those at Thalanga (Late Cambrian-Early Ordovician. Thomson Fold Belt) and at Mount Chalmers (Early Permian New England Fold Belt), and Kieslager or Besshi-type deposits related to submarine mafic volcanics, such as Peak Downs (Precambrian or early Palaeozoic, Thomson Fold Belt) and Dianne. OK and Mount Molloy (Silurian—Devonian, Hodgkinson Broken River Fold Belt). The major gold—copper orebody at Mount Morgan (Middle Devonian, New England Fold Belt), is considered to be of volcanic or subvolcanic origin, but is not a typical volcanogenic massive sulphide.The most numerous ore deposits are associated with calc-alkaline volcanics and granitoid intrusives of the transitional tectonic stage of the three fold belts, particularly the Late Carboniferous Early Perman of the Hodgkinson—Broken River Fold Belt and the Late Permian—Middle Triassic of the southeast Queensland part of the New England Fold Belt. In general, these deposits are small but rich. They include tin, tungsten, molybdenum and bismuth in granites and adjacent metasediments, base metals in contact meta somatic skarns, gold in volcanic breccia pipes, gold-bearing quartz veins within granitoid intrusives and in volcanic contact rocks, and low-grade disseminated porphyry-type copper and molybdenum deposits. The porphyry-type deposits occur in distinct belts related to intrusives of different ages: Devonian (Thomson Fold Belt), Late Carboniferous—Early Permian (Hodgkinson—Broken River Fold Belt). Late Permian Middle Triassic (southeast Queensland part of the New England Fold Belt), and Early Cretaceous (northern New England Fold Belt). All are too low grade to be of economic importance at present.Tertiary deep weathering events were responsible for the formation of lateritic nickel deposits on ultramafics and surficial manganese concentrations from disseminated mineralisation in cherts and jaspers.  相似文献   

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