Principle stages of granite and pegmatite formation in the southeastern part of the Main Sayan Fault

We performed U-Pb dating by the SHRIMP II method of zircon from granites and pegmatites in the southeastern part of the Main Sayan Fault (northern part of Khamar-Daban and southeastern part of the Belya-Kitoi Terrains in the Central Asian fold belt). According to the results obtained, along with the Late Ordovician granitoid magmatism, the Khamar-Daban and Belya-Kitoi Terrains were characterized by a less massive Carboniferous period at their boundary with the Siberian Craton accompanied by granite and pegmatite formation and reflecting tectonomagmatic activation of the Main Sayan Fault. Three stages of magmatic activation were noted. The earliest stage (about 350 million years ago) implies the formation of pegmatoid quartz-albite-microcline (amazonite) granite veins with Nb-Y mineralization in the fault zone. Oligoclase-microcline pegmatite veins with graphite were crystallized in the fault zone at the second stage (about 330 million years ago). The final stage of endogenetic activity (about 310 million years ago) was characterized by migmatization of the Khangarul Group of the Khamar-Daban Terrain and formation of potassium granites (Fig. 3; Table 1).     

Paleoproterozoic (2.0–1.97 Ga) subduction-related magmatism on the north–central margin of the Yeongnam Massif,Korean Peninsula,and its tectonic implications for reconstruction of the Columbia supercontinent

The Muju area, located on the north–central margin of the Yeongnam Massif, mainly consists of Precambrian orthogneisses (granitic, leucogranitic, augen and dioritic gneisses) with minor migmatite. Zircon U–Pb dating indicates that the protoliths of the orthogneisses intruded at ca. 2.00–1.97 Ga and were metamorphosed at ca. 1.87–1.86 Ga. Magmatic zircon grains within the orthogneisses have positive to negative εHf(t) values (−7.63 to +3.3) and a Neoarchean two-stage model age (T_DM2 = 2.78 Ga), indicating that the protoliths of most of the orthogneisses may have been derived from Archean crustal material. The results of geochemical analysis indicate that the protoliths of the orthogneisses formed by partial melting of metagraywacke and mafic igneous rocks in an arc-related tectonic setting. The intrusion ages and geochemical data of the Paleoproterozoic orthogneisses in the study area match well with those of Paleoproterozoic (ca. 2.00–1.97 Ga) orthogneisses in the northeastern Yeongnam Massif, indicating the presence of regional Paleoproterozoic subduction zones along the northern margin of the Yeongnam Massif at ca. 2.00–1.97 Ga. Meanwhile, ca. 2.00–1.97 Ga subduction-related magmatism has not been reported from the northern Gyeonggi and Nangrim Massifs in the Korean Peninsula or the Jiao–Liao–Ji belt in the eastern North China Craton, indicating that the Yeongnam Massif may not be correlatable with the northern Gyeonggi and Nangrim Massifs or the Jiao–Liao–Ji belt. The Yeongnam Massif may be correlated with the Cathaysia Block in the South China Craton and may have been located near Laurentia and the Siberian Craton within the Columbia supercontinent.     

Detrital zircon provenance of early Palaeozoic sediments at the southwestern margin of the Siberian Craton: Insights from U–Pb geochronology

Detrital zircons from the Ordovician and Devonian sedimentary cover of the Siberian Craton were analyzed for U/Pb geochronology to understand their sediment provenances. Five main age-peaks were identified in the zircon U/Pb age-spectra: (1) Neoarchaean – early Palaeoproterozoic (2.7–2.4 Ga); (2) late Palaeoproterozoic (2.0–1.65 Ga); (3) minor early Neoproterozoic (1.0–0.75 Ga); (4) Ediacaran (0.65–0.60 Ga) and (5) Cambrian – Early Ordovician (0.54–0.47 Ga), reflecting the main magmatic events in the sediment source regions. The oldest zircons (groups 1 and 2) are derived from the Siberian Craton which amalgamated during the Neoarchean – Palaeoproterozoic. The Neoproterozoic zircons (groups 3 and 4) likely sourced from southwestern basement uplifts and Neoproterozoic belts of the Siberian margin such as the Yenisey Ridge and Baikal-Muya region. The provenance of the youngest zircons (group 5) can be traced to the Altai–Sayan fold-belt, where peri-Gondwanan microcontinents and island-arcs accreted to Siberia during late Neoproterozoic – early Palaeozoic progressive consumption of the Palaeo-Asian Ocean.     

Age,Composition, and Geodynamic Environments for the Formation of Granites and Lithium-rich Rare-Element Pegmatite of Khusuingol Field (Sangilen Highlands)

The composition, age, and genetic relationships of spodumene pegmatites of the Khusuingol field (South Sangilen pegmatite belt, SW Sayan), encompassing the large Tastyg lithium deposit, with granitoids of the neighboring polygenic Dzos-Khusuingol batholith have been studied. SHRIMP-II U–Pb zircon analyses yielded an Early Paleozoic age of the granites and pegmatites. The tectonic settings of the formation of these rocks are discussed.     

Precambrian sedimentation in the Urik-Iya Graben,southern Siberian Craton: Main stages and tectonic settings

The Paleoproterozoic sedimentary and volcanic-sedimentary sequences of the Urik-Iya Graben at southern flank of the Siberian Craton have been studied. Based on the isotopic U-Pb LA-ICP-MS dating of detrital zircons contained in the clastic fraction of the studied rocks, three main extension stages accompanied by sedimentation are recognized; each stage is characterized by certain types of sediments and conditions of their accumulation. The oldest rocks (Ingashi Formation) mark early extension events (～1.91?1.87 Ga), which were caused by collapse of the orogen that arose due to collision of the Biryusa and Sharyzhalgai blocks. The basin formed as a result of extension is regarded as an aulacogen. Granitoids of the Sayan Complex were emplaced in the cratonic lithosphere at the final stage of the first extension stage. The second stage of extension started ～1.75 Ga ago as a response to the effect of the inferred mantle plume on the lithosphere of the Siberian Craton. It was accompanied by deposition of the Daldarma Formation. Stress inversion took place at the final stage (～1.70 Ga), and an intracratonic fold zone arose at the place of the paleoaulacogen. The third extension stage (1.65?1.60 Ga) corresponds to the time of molasse accumulation in pull-apart basins (Yermosokha Formation). The final stage of rifting was marked by emplacement of granitoids (Chernaya Zima Complex, 1.53 Ga), which completed the active tectonic events in the region. Afterward, the Urik-Iya Graben transformed into a stable intracratonic domain. The available data allow us to revise the tectonic history of the Urik-Iya Graben. In light of new evidence, this structural unit may be interpreted as a long-evolving paleoaulacogen. The series of revealed sedimentation settings reflects the formation of a consolidated continental lithosphere at the southern flank of the Siberian Craton.     

Geochronological Constraints on Evolution of Singhbhum Mobile Belt and Associated Basic Volcanics of Eastern Indian Shield

The Singhbhum Mobile Belt (SMB) of the eastern Indian shield represents a roughly east-west-trending arcuate belt of folded supracrustals overlying the granite-greenstone basement of the Singhbhum-Orissa Craton along its northern, eastern and western margins and is bounded by the Chotanagpur Gneissic Complex to further north. The radiometric ages of the basement Singhbhum and equivalent granites and the intrusive anorogenic Mayurbhanj granite pluton constrain the time of evolution of this mobile belt between 3.12 and 3.09 Ga. Hence, the SMB supracrustals also known as Singhbhum Group, is late Mesoarchaean in age and not Proterozoic as thought earlier. The evolution of the SMB was followed by emplacement of some major basic igneous rocks within or adjacent to the supracrustals. These include Simlipal volcanics at >3.09 Ga on the SMB, Mayurbhanj gabbro along with Mayurbhanj granite at 3.09 Ga along the marginal part of the craton near the SMB, and the Dalma volcanics on the SMB along with the Dhanjori volcanics adjacent to SMB at 2.80 Ga. The 2.80 Ga old basic volcanics is also associated with emplacement of some small granite plutons occurring along the marginal part of the craton, one of them, the Tamperkola granite intrudes the SMB. The >3.09 Ga onward igneous activities along the marginal part of Singhbhum-Orissa Craton took place essentially under anorogenic tectonic setting before being affected by a major metamorphism at 2.50 Ga, which is recorded on the Dalma volcanics and on some small granite pluton occurs along the marginal part of the craton. The Jagannathpur and stratigraphically equivalent Malangtoli volcanics, occurring within the Singhbhum-Orissa Craton at the west, were erupted at 2.25 Ga. The boundary between the SMB supracrustals and the Singhbhum-Orissa Craton is demarked by a prominent shear zone known as the Singhbhum Shear Zone, which shows multiple reactivation, the oldest being at 3.09 Ga, followed by subsequent reactivation during Palaeo- and Mesoproterozoic periods at 2.2, 1.8, 1.6-1.5, 1.4 and 1.0 Ga respectively. The Singhbhum Group and the adjacent Chotanagpur Gneissic Complex appear to have evolved from a near shore syn-rift and a distal post-rift stable shelf sedimentary assemblages respectively, which were deposited without any stratigraphic break in a marine basin existed in the present north of the Singhbhum-Orissa Craton. Both of these assemblages were deformed and metamorphosed together during Proterozoic at 2.5 to >2.3 Ga, 1.6 Ga and 1.0 Ga.     

Accretionary Tectonics of Rock Complexes in the Western Margin of the Siberian Craton

The geological, geochemical, and isotope-geochronological evidence of the events at the final stage of the Neoproterozoic history of the Yenisei Range is considered (beginning from the formation of fragments of the oceanic crust in the region and their accretion to the Siberian Craton until the postaccretionary stage of crustal tension and onset of the Caledonian orogeny). Based on an analysis of new data on the petrogeochemical composition, age, and geodynamic nature of the formation of contrasting rocks in the composition of tectonic mélange of the Near-Yenisei (Prieniseiskaya) regional shear zone, we have found the chronological sequence of events that marks the early stages of the Paleoasian Ocean evolution in the zone of its junction with the Siberian Craton. These events are documented by the continental marginal, ophiolitic, and island-arc geological complexes, each of which has different geochemical features. The most ancient structures are represented by fragments of oceanic crust and island arcs from the Isakovka terrane (700–620 Ma). The age of glaucophane-schist metamorphic units that formed in the paleosubduction zone corresponds to the time interval of 640–620 Ma. The formation of high-pressure tectonites in the suture zone, about 600 Ma in age, marks the finishing stage of accretion of the Isakovka block to the western margin of the Siberian Craton. The final events in the early history of the Asian Paleoocean were related to the formation of Late Vendian riftogenic amygdaloidal basalts (572 ± 6.5 Ma) and intrusion of postcollisional leucogranites of the Osinovka massif (550–540 Ma), which intruded earlier fragments of the oceanic crust in the Isakovka terrane. These data allow us to refine the Late Precambrian stratigraphic scheme in the northwestern Trans-Angarian part of the Yenisei Range and the evolutionary features of the Sayan–Yenisei accretionary belt. The revealed Late Neoproterozoic landmarks of the evolution of the Isakovka terrane are attributed to the terminal phase of the breakup of Rodinia, separation of the Siberian Craton, and opening of the Paleoasian Ocean.     

First data on late vendian granitoid magmatism of the Northwestern Sayan–Yenisei accretionary belt

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 (T_Nd(DM)-2st = 1490–1650 Ma and ε_Nd(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.     

Formation and evolution of the Archean continental crust of China: A review

The mainland of China is composed of the North China Craton, the South China Craton, the Tarim Craton and other young orogenic belts. Amongst the three cratons, the North China Craton has been studied most and noted for its widely-distributed Archean basement rocks. In this paper, we assess and compare the geology, rock types, formation age and geochemical composition features of the Archean basements of the three cratons. They have some common characteristics, including the fact that the crustal rocks prior to the Paleoarchean and the supracrustal rocks of the Neoarchean were preserved, and Tonalite-Trondhjemtite-Granodiorite (TTG) magmatism and tectono-magmatism occurred at about 2.7 Ga and about 2.5 Ga respectively. The Tarim Craton and the North China Craton show more similarities in their early Precambrian crustal evolution. Significant findings on the Archean basement of the North China Craton are concluded to be: (1) the tectonic regime in the early stage (>3.1 Ga) is distinct from modern plate tectonics; (2) the continental crust accretion occurred mostly from the late Mesoarchean to the early Neoarchean period; (3) a huge linear tectonic belt already existed in the late Neoarchean period, suggesting the beginning of plate tectonics; and (4) the preliminary cratonization had already been completed by about 2.5 Ga. Hadean detrital zircons were found at a total of nine locations within China. Most of them show clear oscillatory zoning, sharing similar textures with magmatic zircons from intermediate-felsic magmatic rocks. This indicates that a fair quantity of continental material had already developed on Earth at that time.     

华北克拉通中部在古元古代时是一个造山带吗？

文中报道了笔者对华北古元古代花岗岩研究的初步结果,指出在2.0Ga前,华北东西两块地壳厚度明显不同,大体以太原为界,东部地壳很薄,中部很厚,西部较厚;至1.9~1.8Ga,在华北北部可能存在一个地壳加厚的区域,大体是东西向(或NEE向)展布的;至1.8Ga以后,华北克拉通整体垮塌了。笔者分析了现有资料,认为华北晚太古代和古元古代期间存在洋壳的依据不足,华北中部带为一造山带和碰撞带的见解也是值得进一步商榷的。     

Interaction of crustal and mantle materials,sources of trace elements during the formation and evolution of Early Paleozoic Li-rich granite-pegmatite systems in southeastern Tuva

We present new data on the age, composition, and environments of formation of granites of the Kystarys complex and the associated Li-rich rare-element pegmatites of the South Sangilen pegmatite belt including the large Tastyg lithium deposit. It has been established that they formed during the Early Paleozoic collisional orogeny in the Tuva-Mongolian massif at the Cambrian-Ordovician boundary. The granites of the Kystarys complex are moderately alkaline high-K rocks and are enriched in Zr, Nb, Y, and REE; therefore, they are classified as postcollisional, transitional to within-plate (A-type). The spodumene pegmatites of the South Sangilen pegmatite belt are similar to the above granites in age and isotopic and geochemical parameters, which suggests a paragenetic relationship between these rocks. Pegmatites form several pegmatite fields within the belt, which differ in trace-element signatures. In addition to predominant Li, Cs, and Ta, specific to all spodumene pegmatites (LCT family), pegmatites of two fields have high contents of Nb, Y, REE, and Zr, which are indicator elements of NYF family pegmatites. It has been established that the formation of spodumene pegmatites with combined LCT-NYF geochemical signatures was preceded by the intrusion of dikes of monzogabbro with the geochemical characteristics of OIB and of alkali aegirine granites and by the formation of associated metasomatites enriched in Zr, Nb, Y, and REE. Based on the geological, mineralogical, and geochemical data, we substantiate the hypothesis of the formation of Li-bearing granite-pegmatite melts from a mixed source resulted from the influence of fluids of an alkaline igneous complex of mantle genesis on the crustal protolith.     

Age, composition of rocks, and geological setting of the Snezhnoe beryllium deposit: Substantiation of the Late Paleozoic East Sayan rare-metal zone, Russia

The Snezhnoe phenakite-beryl deposit is one of the highest-grade deposits in the Altai-Sayan beryllium province. This deposit is spatially associated with the alkali granite of the Ognit Complex and localized in the apical part of the granitic pluton. The trace element composition of granite, as well as of Be and Ta-Nb ores was studied. The Rb-Sr age of Be mineralization estimated at 305 Ma is consistent with the time of formation of numerous rare-metal alkali granitic plutons in the Eastern Sayan and the eastern Tuva. The region of these granitic plutons is outlined as the Late Paleozoic East Sayan rare-metal metallogenic zone specialized for Nb, Ta, Be, Li, Zr, Th, and REE mineralization. The East Sayan zone is localized in the marginal part of the Barguzin igneous province and is similar to the marginal zone of this province in composition of igneous associations and metallogenic specialization. The formation of the Barguzin igneous province and the East Sayan metallogenic zone is related to the evolution of the Late Carboniferous-Early Permian mantle plume.     

Layered intrusions and volcanic sequences in Central Brazil: Geological and geochronological constraints for Mesoproterozoic (1.25 Ga) and Neoproterozoic (0.79 Ga) igneous associations

A 350-km long belt of layered complexes and associated volcano-sedimentary sequences forms a continental-scale feature exposed along the internal portion of the Neoproterozoic Brasília Belt in central Brazil. This study provides new geochronological results and a critical review of the available data of these igneous associations of central Brazil. Precise age dating combined with geological and petrological studies indicate that this belt consists of two distinct igneous rock associations. The 1.25 and 0.79 Ga igneous episodes are constrained by reliable U–Pb zircon ages (SHRIMP and ID-TIMS) obtained in different regions and lithotypes of this belt. Both igneous associations were affected by high-grade metamorphism and tectonism at ca. 0.76 Ga, which partially disrupted the original igneous stratigraphy of the layered complexes and volcano-sedimentary sequences. The present configuration of this belt results from later events, probably caused by final ocean closure and continental collision between the São Francisco and Amazonian continents at ca. 0.63 Ga.     

华北和圣弗朗西斯科克拉通前寒武纪地质对比

一些学者提出华北克拉通在新元古代早期之前与圣弗朗西斯科克拉通（圣弗朗西斯科-刚果克拉通）相邻,但缺少证据;本文总结两个古陆地质记录,为评价这一古构造格局模型提供线索。两个古陆陆壳生长的峰期均为～2.7 Ga前;不同之处是,华北古陆经历了显著的～2.5 Ga前的陆壳生长和改造,而圣弗朗西斯科克拉通则似乎没有。华北古陆2.4～2.2 Ga期间发育少量变质火山-沉积岩系和花岗岩,～2.1 Ga前后广泛发育裂谷火山-沉积建造及侵入岩,2.0～1.9 Ga发育超高温变质作用和类似弧岩浆活动,导致两个克拉通（东、西华北克拉通）拼合形成统一的华北古陆;同一时期,圣弗朗西斯科克拉通南、北缘发育2.4～2.0 Ga岩浆作用,指示长期处于大陆边缘弧或者岛弧背景,～2.0 Ga还发育超高温变质作用。两个古陆都发育～2.0 Ga前类似大陆边缘弧特点的岩浆活动,只是圣弗朗西斯科克拉通时代稍早。1.8 Ga以来,两个古陆均发育多期岩墙群,部分基本同期,如～1.78 Ga岩墙群、～1.7 Ga岩墙群和～0.92 Ga岩墙群等;不同的是,华北古陆发育约1.3～1.2 Ga岩床/墙群,而圣弗朗西斯克拉通发育～1.5 Ga岩墙群。1.8～0.8 Ga,两个古陆上都断续发育（火山）-沉积建造：1.8～1.6 Ga以及1.4～1.2 Ga,两者的沉积建造同样以石英砂岩等碎屑岩为主,碳酸盐岩较少;1.2～1.0 Ga前,两者的记录均较少,或暂不能确定;1.0～0.8 Ga,两者均发育碎屑岩和碳酸盐岩;1.6～1.4 Ga,华北古陆发育碳酸盐岩建造,而圣弗朗西斯科克拉通则发育碎屑岩建造。华北古陆新元古界地层中碎屑锆石常显示～1.5 Ga的峰值,该期岩浆岩鲜少报道于华北古陆,但却见于圣弗朗西斯科克拉通。两个陆块都发育太古宙-古元古代条带状铁建造铁矿、古元古代石墨矿、中新元古代沉积-喷流型铅锌矿等。不过,华北古陆发育的古元古代硼矿、菱镁矿,中元古代碳酸岩型稀土矿等在圣弗朗西斯科不发育;而后者发育的绿岩带型相关金矿、镍矿、祖母绿宝石矿等,华北似乎不发育。另外,0.7～0.5 Ga,圣弗朗西斯科克拉通周边广泛发育泛非期造山带,而华北古陆并没有这一事件的明确记录;显生宙,圣弗朗西斯科克拉通相对稳定,中生代与刚果克拉通分离;但华北古陆内部经历强烈的构造-岩浆活动（峰期在中生代）。华北与圣弗朗西斯科克拉通前寒武纪是否相邻还需进一步地质对比和古地磁工作,尤其应关注约2.0～1.9 Ga岩浆-变质（造山）事件、约1.8～1.7 Ga岩浆-沉积（裂谷）事件以及约0.9 Ga岩浆-沉积（裂谷）事件。从地质记录的相似性角度来看,华北东南缘与圣弗朗西斯科南缘的地质记录相似性最大,可延续性最强,最可能相邻。     

Provenance of Paleozoic–Mesozoic sedimentary rocks in the Inner Zone of Southwest Japan: An evaluation based on Nd model ages

Nd model ages using depleted mantle (TDM) values for the sedimentary rocks in the Inner Zone of the SW Japan and western area of Tanakura Tectonic Line in the NE Japan allow classification into five categories: 2.6–2.45, 2.3–2.05, 1.9–1.55, 1.45–1.25, and 1.2–0.85 Ga. The provenance of each terrane/belt/district is interpreted on the basis of the TDMs, ¹⁴⁷Sm / ¹⁴⁴Nd vs. ¹⁴³Nd / ¹⁴⁴Nd relation, Nd isotopic evolution of the source rocks in East China and U–Pb zircon ages. The provenance of 2.6–1.8 Ga rocks, which are reported from Hida–Oki and Renge belts and Kamiaso conglomerates, is inferred to be the Sino–Korean Craton (SKC). The 2.3–1.55 Ga rocks, mostly from Ryoke, Mino and Ashio belts, are originally related with the SKC and/or Yangtze Craton (YC). The provenances of the sedimentary rocks with 1.45–0.85 Ga, from the Suo belt, Higo and some districts in the Mino and Ashio belts, are different from the SKC and YC. Especially, the Higo with 1.2–0.85 Ga is considered as a fragment of collision zone in East China. Akiyoshi belt probably belongs to the youngest age category of 1.2–0.85 Ga.Some metasedimentary rocks from the Ryoke belt have extremely high ¹⁴⁷Sm / ¹⁴⁴Nd and ¹⁴³Nd / ¹⁴⁴Nd ratios, whose main components are probably derived from mafic igneous rocks within the Ryoke belt itself and from the adjacent Tamba belt.     

Timing of Proterozoic magmatism in the Sunsas belt,Bolivian Precambrian Shield,SW Amazonian Craton

We present new U-Pb zircon and monazite ages from the Sunsas belt granitic magmatism in Bolivia,SW Amazonian Craton.The geochronological results revealed four major magmatic events recorded along the Sunsas belt domains.The older igneous event formed a granitic basement coeval to the Rio Apa Terrane(1.95-1.85 Ga)in the southern domain.The second magmatic episode is represented by 1.68 Ga granites associated to the Paraguá Terrane(1.69-1.66 Ga)in the northern domain.The 1.37-1.34 Ga granites related to San Ignacio orogeny represent the third and more pervasive magmatic event,recorded throughout the Sunsas belt.Moreover,magmatic ages of～1.42 Ga revealed that the granitogenesis asso-ciated to the Santa Helena orogeny also affected the Sunsas belt,indicating that it was not restricted to the Jauru Terrane.Lastly,the 1.10-1.04 Ga youngest magmatism was developed during the Sunsas oro-geny and represents the final magmatic evolution related to Rodinia assembly.Likewise,the 1.95-1.85 and 1.68 Ga inherited zircon cores obtained in the～1.3 Ga and 1.0 Ga granite samples suggest strong par-tial melting of the Paleoproterozoic sources.The 1079±14 Ma and 1018±6 Ma monazite crystallization ages can be correlated to the collisional tectono-thermal event of the Sunsas orogeny,associated to reac-tions of medium-to high-grade metamorphism.Thus,the Sunsas belt was built by heterogeneous 1.95-1.85 Ga and 1.68 Ga crustal fragments that were reworked at 1.37-1.34 Ga and 1.10-1.04 Ga related to orogenic collages.Furthermore,the 1.01 Ga monazite age suggests that granites previously dated by zir-con can bear evidence of a younger thermal history.Therefore,the geochronological evolution of the Sunsas belt may have been more complex than previously thought.     

Early Carboniferous paleogeography of the northern Verkhoyansk passive margin as derived from U–Pb dating of detrital zircons: role of erosion products of the Central Asian and Taimyr–Severnaya Zemlya fold belts

The first U–Pb dating of detrital zircons from the Lower Carboniferous sandstones in the frontal part of the northern Verkhoyansk fold-and-thrust belt showed that detrital zircon age spectra for the Lower Visean (Krestyakh Formation) and the Upper Visean–Serpukhovian (Tiksi Formation) rocks are quite different. The Early Visean sandstones contain up to 95% detrital zircons of Precambrian age, while those of Late Visean–Serpukhovian age, only 55%. The shape of age distribution plots of Precambrian zircons for both samples is similar, indicating that reworking of terrigenous sediments of the Krestyakh Formation or the same sources dominated in Early Visean time (crystalline basement of the craton, eroded Meso- and Neoproterozoic sedimentary complexes, and igneous rocks of Central Taimyr) contributed significantly to the accumulation of the Late Visean–Serpukhovian deposits. In the rocks of the Tiksi Formation, 45% of detrital zircons are of Paleozoic age, while 24% are Early Paleozoic, with prevailing Cambrian and Ordovician ages. Possible provenance areas with abundant igneous rocks of this age could be the Taimyr–Severnaya Zemlya and Central Asian fold belts extending along the northern, western or southwestern margins of the Siberia. The presence of Middle–Late Devonian zircons is thought to be related to the erosion of granitoids of the Yenisei Ridge and the Altai–Sayan region. Early Carboniferous detrital zircons probably had a provenance in igneous rocks of the Taimyr–Severnaya Zemlya fold belt, on the assumption that collision between the Kara block and the northern margin of the Siberian continent had already occurred by that time. In Early Visean time, sedimentation occurred in small deltaic fans, likely along steep fault scarps that formed as a result of Middle Paleozoic (Devonian–Carboniferous) rifting. The clastic material came from small rivers that eroded the nearby area. Late Visean–Serpukhovian time was marked by a sharp increase in the amount of clastic material and by the appearance of detrital zircons coming from new provenance regions, such as fold belts extending along the northern and southwestern margins of the Siberian continent. A large river system, which was able to transport clastic material over large distances to deposit it in submarine fans on the northern Verkhoyansk passive continental margin, had already existed by that time.     

Source of Pb in orogenic lode-gold mineralisation: Pb isotope constraints from deep crustal rocks from the southwestern Archaean Yilgarn Craton, Australia

Southern Cross was one of the earliest gold mining centres in Western Australia. Over 142 tonnes of gold have been produced from the district, and, on a gold per hectare basis, the Southern Cross greenstone belt in the southwestern Yilgarn Craton is the most productive of Western Australia's Archaean greenstone belts. The SW Yilgarn Craton is characterised by high-grade (amphibolite- to granulite-facies) metamorphism, extensive granitoid magmatism and older greenstone volcanism ages, compared to the well-known greenschist-facies metamorphism and younger (2.7 Ga) eruption ages which dominate in the Eastern Goldfields Province. The Pb-isotope compositions of deep-seated granitoids in the SW Archaean Yilgarn Craton, which were emplaced coeval with a craton-wide major orogenic lode-gold mineralization event at about 2.64–2.63 Ga, have been determined for 96 whole-rock and 24 K-feldspar samples. The Pb isotope data of the granitoids are consistent with a crustal origin for their genesis, probably by reworking (partial melting) of older continental crust. The Pb isotope composition of greenstones, which are the main host rocks for gold mineralisation, and pyrites from the komatiite-hosted syngenetic Ni deposits in the amphibolite-facies Forrestania greenstone belt, have also been determined, with initial Pb-isotope ratios higher than that for the Eastern Goldfields Province. The Pb isotopic character of the orogenic lode-gold deposits in the region is intermediate between coeval granitoid and greenstone Pb, indicating that the ore fluids contained metals from both reservoirs. The Pb in the ore fluid of the most deeply formed deposit, Griffin's Find, overlaps the isotopic composition of coeval granitoids, indicating the deep-seated granitoid magmatism was the primary source for Pb in the ore fluids. Received: 8 October 1998 / Accepted 22 December 1998     

Isotopic geochronological evidence for the Paleoproterozoic age of gold mineralization in Archean greenstone belts of Karelia, the Baltic Shield

The Rb-Sr age of metasomatic rocks from four gold deposits and occurrences localized in Archean granite-greenstone belts of the western, central, and southern Karelian Craton of the Baltic Shield has been determined. At the Pedrolampi deposit in central Karelia, the dated Au-bearing beresite and quartz-carbonate veins are located in the shear zone and replace Mesoarchean (～2.9 Ga) mafic and felsic metavolcanic rocks of the Koikar-Kobozero greenstone belt. At the Taloveis ore occurrence in the Kostomuksha greenstone belt of western Karelia, the dated beresite replaces Neoarchean (～2.7 Ga) granitoids and is conjugated with quartz veins in the shear zone. At the Faddeinkelja occurrence of southern Karelia, Aubearing beresite in the large tectonic zone, which transects Archean granite and Paleoproterozoic mafic dikes, has been studied. At the Hatunoja occurrence in the Jalonvaara greenstone belt of southwestern Karelia, the studied quartz veins and related gold mineralization are localized in Archean granitoids. The Rb-Sr isochrons based on whole-rock samples and minerals from ore-bearing and metasomatic wall rocks and veins yielded ～1.7 Ga for all studied objects. This age is interpreted as the time of development of ore-bearing tectonic zones and ore-forming hydrothermal metasomatic alteration. New isotopic data in combination with the results obtained by our precursors allow us to recognize the Paleoproterozoic stage of gold mineralization in the Karelian Craton. This stage was unrelated to the Archean crust formation in the Karelian Block and is a repercussion of the Paleoproterozoic (2.0–1.7 Ga) crust-forming tectonic cycle, which gave rise to the formation of the Svecofennian and Lapland-Kola foldbelts in the framework of the Karelain Craton. The oreforming capability of Paleoproterozoic tectonics in the Archean complexes of the Karelian Craton was probably not great, and its main role consisted in reworking of the Archean gold mineralization of various genetic types, including the inferred orogenic mesothermal gold concentrations.     

中朝陆台北侧褶皱带构造发展的几个问题

中朝与西伯利亚陆台之间的乌拉尔—蒙古—鄂霍茨克褶皱系是古亚洲洋演化的结果。其发展分为两个大的阶段:早期阶段从中元古代起在北部形成蒙古—鄂霍茨克洋,到寒武纪初封闭,形成兴凯褶皱带;晚期阶段从震旦—寒武纪初起在南部形成乌拉尔—蒙古洋,到泥盆纪大洋封闭,形成早及中古生代褶皱带。这就是中朝与西伯利亚陆台边缘褶皱带发育不对称的原因。 乌拉尔—蒙古洋最后封闭的缝合带在内蒙古中部形成中古生代褶皱带。它包括贺根山蛇绿岩带,二道井—查干诺尔混杂体带和它们之间的锡林浩特花岗岩—变质岩带。后者是造山碰撞的中心,上泥盆统法门阶的磨拉石堆积主要沿此带分布。 石炭—二叠纪时,本区广泛兴起裂谷活动。这些裂谷发育在不同的基底之上,多数发生于不同时期构造带的界线上。它们在新增生的年青陆壳上形成,其特征不同于红海或东非型裂谷;其岩浆活动和变形、变质作用使年青陆壳增厚并更加稳固。