Multistage Deformation in the Northeastern Segment of the Jiangshao Fault (Suture) Belt: Constraints for the Relationship between the Yangtze Plate and the Cathaysia Old Land

Multistage deformation events have occurred in the northeastern Jiangshao Fault （Suture） Belt. The earliest two are ductile deformation events. The first is the ca. 820 Ma top-to-the-northwest ductile thrusting, which directly resulted from the collision between the Cathaysia Old Land and the Chencai Arc （？） during the Late Neoproterozoic, and the Jiangnan Orogenic Belt that formed as the ocean closed between the Yangtze Plate and the jointed Cathaysia Old Land and the Chencai Arc due to continuous compression. The second is the ductile left-lateral strike-slipping that occurred in the latest Early Paleozoic. Since the Jinning period, all deformation events represent the reactivation or inversion of intraplate structures due to the collisions between the North China and Yangtze plates during the Triassic and between the Philippine Sea and Eurasian plates during the Cenozoic. In the Triassic, brittle right-lateral strike-slipping and subsequent top-to-the south thrusting occurred along the whole northeastern Jiangshao Fault Zone because of the collision between the North China and Yangtze plates. In the Late Mesozoic, regional extension took place across southeastern China. In the Cenozoic, the collision between the Philippine Sea and Eurasian plates resulted in brittle thrusts along the whole Jiangnan Old land in the Miocene. The Jiangshao Fault Belt is a weak zone in the crust with long history, and its reactivation is one of important characteristics of the deformation in South China; however, late-stage deformation events did not occur beyond the Jiangnan Old Land and most of them are parallel to the strike of the Old Land, which is similar to the Cenozoic deformation in Central Asia. In addition, the Jiangnan old Land is not a collisional boundary between the Yangtze Plate and Cathaysia Old Land in the Triassic.

The Southward Extension of Cathaysia Block: Evidence from Zircon UPb Dates of Borehole Volcanics in the Northern South China Sea

Five Paleogene volcanics sampled from the northern South China Sea were analyzed via LA-ICP-MS zircon U-Pb dating, including basalt and andesite from Borehole SCSVI and volcanic agglomerate from Borehole SCSV2, respectively. A total of 162 zircon U-Pb dates for them cover an age range from Neoarchean to Eocene, in which the pre-Paleocene data dominate. The Paleogene dates of 62.5±2.2 Ma and 42.1±2.9 Ma are associated with two igneous episodes prior to opening of South China Sea basin. Those pre-Paleocene zircons are inherited zircons mostly with magmatogenic oscillatory zones, and have REE features of crustal zircon. Zircon U-Pb dates of 2518-2481 Ma, 1933- 1724 Ma, and 1094-1040 Ma from the SCSV1 volcanics, and 2810-2718 Ma, 2458-2421 Ma, and 1850-993.4 Ma from the SCSV2 volcanics reveal part of Precambrian evolution of the northern South China Sea, well comparable with age records dated from the Cathaysia block. The data of 927.0±6.9 Ma and 781±38 Ma dated from the SCSV2 coincide with amalgamation between Yangtze and Cathaysia blocks and breakup of the Rodinia, respectively. The age records of Caledonian orogeny from the Cathaysia block are widely found from our volcanic samples with concordant mean ages of 432.0±5.8 Ma from the SCSV1 and of 437±15 Ma from the SCSV2. The part of the northern South China Sea resembling the Cathaysia underwent Indosinian and Yanshannian tectonothermal events. Their age signatures from the SCSV1 cover 266.5±3.5 Ma, 241.1±6.0 Ma, 184.0±4.2 Ma, 160.9±4.2 Ma and 102.8±2.6 Ma, and from the SCSV2 are 244±15 Ma, 158.1±3.5 Ma, 141±13 Ma and 96.3±2.1 Ma. Our pre-Paleogene U-Pb age spectra of zircons from the borehole volcanics indicate that the northern South China Sea underwent an evolution from formation of Precambrian basement, Caledonian orogeny, and Indosinian orogeny to Yanshannian magmatism. This process can be well comparable with the tectonic evolution of South China, largely supporting the areas of the northern South China Sea as part of southward extension of the Cathaysia.

Relation of Isotope Geochemical Steep Zones with Geophysical Fields and Tectonics in the Junction Area of the Cathaysian,Yangtze and Indochina Plates

Through lead isotope geochemical mapping in the Yunnan-Guizhou area geochemical steep zones (GSZ) have been established, which clearly reveal the junction relationship of the Cathaysian, Yangtze and Indo-China plates. GSZ are closey related to gravity Moho gradient zones and lithospheric thickness. The GSZ between the Yangtze and Cathaysian plates is consistent with the Shizong-Mile tectonic belt, where island are basalts are well developed. The Yangtze-Indo-China GSZ is parallel to the Jingdong-Mojiang volcanic belt in rift-island are environments. The evidence of geology, geophysics and geochemistry all indicates that Cathaysia was subducted towards the Yangtze plate and that the Yangtze plate was underthrust beneath the Indo-China, which took place from the Early Carboniferous to the Early Triassic.

An Early Paleozoic Tectonic Mélange at the Western Margin of West Cathaysia: Constraints from Organic-walled Microfossils

The Jiangshan-Shaoxing-Pingxiang Fault(JSP Fault) is traditionally considered as the boundary between the Yangtze and Cathaysia blocks in South China. Whether the previously defined Shenshan and Kuli formations located along the JSP fault and near the Xinyu City, Jiangxi Province, are continuous strata or parts of a tectonic mélange is important for understanding the geological history of South China. A carbonaceous phyllite from the area, previously considered as part of the Neoproterozoic Shenshan and Kuli formations, is analyzed palynologically in this study. The AsteridiumComasphaeridium acritarch assemblage found in the slate can be correlated with the basal Cambrian AsteridiumHeliosphaeridium-Comasphaeridium(AHC) acritarch assemblage in Tarim and the Yangtze Block. The early Cambrian biostratigraphical age assignment for the carbonaceous phyllite indicates the presence of both Neoproterozoic and Cambrian rocks in the sedimentary package, and supports that the package is a part of tectonic mélange rather than a continuous Neoproterozoic strata. The Cambrian slate is the youngest known lithology in the mélange at present.

The Metamorphism and Its Tectonic Implications of Indosinian High Pressure Granulites from the Badu Complex of the Cathaysia Block, Southwestern Zhejiang Province, South China

The Badu Complex is the oldest metamorphic rock in Cathaysia Block which experienced several episodes of metamorphism Especially indosinian metamorphic reworking in the southwestern Zhejiang Province, South China. The degree of indosinian metamorphism reaches granulite facies. However, there is still insufficient understanding of the characteristics of the Indosinian granulite metamorphism in the Cathaysia and many interpretations of its tectonic significance. Therefore, we present detailed petrology, mineral chemistry and LA-ICP-MS zircon U-Pb age in this paper from pelitic granulites of the Badu Complex, which is composed of "sillimanite + garnet + cordierite + spinel + biotite + k-feldspar" assemblage and garnet pyroxenite with garnet amphibolite which is consists of "garnet + clinopyroxene + orthopyroxene + amphibole + plagioclase". By comprehensive study we get following new findings: Pelitic granulites record four stages of metamorphic mineral assemblages, including prograde(M1), pressure peak(M2), Peak(M3) and post-peak decompressional and then cooling(M4) stages. The prograde M1 assemblage consists of garnet1(core) + staurolite + kyanite + biotite + quartz ± rutile ± chlorite;The pressure peak M2 assemblage consists of garnet1(mantle) + sudoite + rutile + kyanite + corundum + biotite + quartz;The peak M3 have garnet2(rim-mantle) + biotite + sillimanite + quartz ± K-feldspar ± plagioclase ± ilmenite assemblag;the M4 stage is consist of garnet + cordierite + biotite + sillimanite + quartz + ilmenite ± spine ± K-feldspar. The garnet pyroxenite and garnet amphibolites have experienced three stages of metamorphic evolution. Peak high-pressure granulite facies stage M2 consists of garnet + sahlite ± ilmenite ± quartz;Post-peak near isothermal decompression medium granulite facies stage M3 is characterized by typical decompression reaction textures and assemblage of orthopyroxene + plagioclase(An=90–92);amphibolites facies retrograde metamorphic stage M4 is characterized by amphibole + plagioclase(An=33–35) + ilmenite ± sahlite ± quartz mineral assemblage. By means of phase equilibrium simulation and traditional thermobarometer, P-T conditions of 785–820 ℃ and 8.9–9.9 kbar for M3 stage, 780–860 ℃ and 5.7–6.2 kbar for decompressional M4 stage, 705–720 ℃ and 4.5–4.7 kbar for cooling M4 stage in pelitic granulites were obtained. And also 11.6–12.5 kbar and 780–840 ℃ for M2 stage, 7.4–8.2 kbar and 800–880 ℃ for M3 stage, 6.6–7.5 kbar and 500–560 ℃ for M4 stage were obtained in garnet pyroxenite and garnet amphibolite. A clockwise P-T path is confirmed in the two type rocks of the Badu Complex which reflected a near-isothermal decompressional metamorphic process. The peak metamorphism can reach highpressure granulite facies. In addition, the mineral assemblage of garnet + rutile + kyanite + corundum in the peak metamorphic stage of pelitic granulite indicates that it may underwent ultra-high-pressure metamorphism, and the acidic plagioclase exsolution of clinopyroxene in garnet pyroxenite also suggests that it may be retrograded eclogites, which indicates that the deeper Cathaysian block may have eclogite metamorphism. Analyses of LA-ICP-MS zircon U-Pb dating indicate that the metamorphic age of pelitic granulite is 233.5 Ma–subduction/collision followed by rapid exhumation and cooling events. The events may relate with the amalgamation of the Indochina BlockSouth China Block North China Block in the paleo-Tethyan domain.

Geochemistry and Petrogenesis of Cretaceous Adakitic Dykes from Eastern Cathaysia Block

An intrusive dyke is linear in regional scale,tectonic stresses play an important role in controlling the orientation of fractures that form for the dyke when magma rises buoyantly into the lithosphere

PALAEOZOIC TECTONIC PALAEOGEOGRAPHY OF THE CATHAYSIA IN EASTERN ZHE JIANG AND NORTHERNFUJIAN, CHINA

Based on the data about sedimentary facies and palaeogeography, this paper proves the existence of the Cathaysia (the part in eastern Zhejiang and northern Fujian, the same hereinafter) and makes a survey about its palaeogeography since Sinian Period. It also discusses the evolution of the tectonic environment of this region during Phanerozoic Eon, according to the features such as the composition of sandstones derived from the old land and alkalinity of volcanic rocks and so on. Continuous uplifting was maintained in Cathaysia during Sinian Period and Paleozoic Era, typically with no significant tectono-magmatic activity being observed. Its northwestern margin belongs to the type of passive continental margin during the middle and late phase of Caledonian Cycle. It showed the characteristics of a steady continent in late Paleozoic era, but was turned quickly into an active continental margin after the middle Jurassic period.

Remnants of the amalgamation of the east and west Cathaysia blocks revealed by a short-period dense nodal array

The Cathaysia block located at the southeast South China block(SCB)is considered formed by the amalgamation of the east and west Cathaysia blocks along the Gaoyao-Huilai and Zhenghe-Dapu deep faults(here referred as GHF and ZDF,respectively).Although the extension of the ZDF to the northeast,which represents the amalgamation of the two sub-blocks has been confirmed,the development of the GHF to the southwest remains to be verified.To better constrain the detailed deep structure beneath the southwest Cathaysia,which hold great significance for revealing the evolution of the SCB,a linear seismic array with 331 nodal geophones was deployed across the Sanshui basin(SSB).Combining with the regional 10 permanent stations(PA),we obtained two profiles with teleseismic P-wave receiver function stacking.The most obvious feature in our results is the ascending Moho towards the coastal area,which is consistent with the passive margin continental and extensional tectonic setting.The stacking profile from the dense nodal array(DNA)shows that the Moho is offset beneath the transition zone of the Nanling orogeny and SSB.We deduce that this offset may be casued by the deep extension of the GHF,which represents the remnants of the amalgamation of the Cathaysia block.From the other evidences,we infer that the widespread and early erupted felsic magmas in the SSB may have resulted from lithospheric materials that were squeezed out to the surface.The relative higher Bouguer gravity and heat flow support the consolidation of magmas and the residual warm state in the shallow crustal scale beneath the SSB.The sporadic basaltic magmas in the middle SSB may have a close relation to deep extension of the GHF,which serves as a channel for upwelling hot materials.

Origin,evolution and extinction of Cathaysia flora

Recent research results showed that the Cathaysia flora originated and developed from the global uniform Lepidodendropsis flora of the Early Carboniferous, which had already become an independent flora in the early Late Carboniferous (Namurian B to C). The center of origin of the Cathaysia flora is restricted to the North China Plate. On the basis of the successional characteristics of the Cathaysia flora in different geological ages, it may be divided into seven evolutionary stages. The evolutionary trend of the Cathaysia flora, as a whole, was characterized by the gradual increase of the typical Cathaysian elements in the sequence from the early Late Carboniferous to the early Late Permian, which began to decline during the late Late Permian. The climatic differentiation, tectonic movement,oceanic circulation, palaeogeographical environment, extraterrestrial event and plant evolution caused the mass extinction of the Cathaysia flora on a large scale by the end of the Permian.

The Cathaysia Flora and the Mixed Late Permian Cathaysian-Angaran Floras in East Asia

The Cathaysla flora, one of the most prominent floras of the Carboniferous and Permian, was mainly distributed In East Asia and was characterized by numerous endemic elements. China Is one of the most Important localities of the Cathaysla flora and It ;s also the center of origin of this flora. This paper reviews and discusses the characteristics of the Cathaysla flora and the blogeographlcally mixed Permian Cathayslan-Angaran floras of East Asia. In addition, the formative mechanism of the mixed Permian floras Is also discussed.

Discovery of a Late Permian Angara-Cathaysia mixed flora from Acheng of Heilongjiang,China,with discussions on the closure of the Paleoasian Ocean

This work documents a new flora from the Upper Permian Hongshan Formation of Acheng County, Heilongjiang Province, Northwest China. The flora consists of 20 species: Paracalamites sp., Pecopteris tangwangheensis Huang, Callipteris obese Huang, Callipteris shenshuensis Huang, C. tangwangheensis Huang, C. heilongjiangensis Huang, C. zeilleri Zalessky, C. sp., Comia yichunensis Huang, C. tenueaxis Huang, Iniopteris sibirica Zalessky, Supaia teiliensis Huang, Compsopteris tchirkovae Zalessky, C. cf. adzvensis Zalessky, Nilssonia sp. 1, Nil. sp. 2, Taeniopteris cf. densissima Halle, T. cf. nystraemii Halle, T. sp. and Noeggerathiopsis derzavinii Neub. It is dominated by Angara species but mixed with some typical Cathaysian elements. The age of the flora is assigned to late of the Late Permian according to the stratigraphic ranges of the known species and the comparisons of it with the similar floras. The new discovery indicates that the final collision between the North China Plate and Siberian Plate occurred in Late Permian along the Xar Moron River-Changchun-Yanji sutured zone, and the Paleoasian Ocean was finally closed at the end of the Permian.

The Pre-Sturtian Negative δ^(13)C Excursion of the Dajiangbian Formation Deposited on the Western Margin of Cathaysia Block in South China

The Dajiangbian Formation in South China is a siliciclastic-dominated sedimentary succession with low-grade metamorphism deposited on the western margin of the Cathaysia Block, and is capped by a glaciogenic diamictite（the Sizhoushan Formation）. The Sizhoushan glaciogenic strata can be attributed to the Jiangkou glacial（Sturtian glacial） episode as they share stratigraphic and lithological similarities with Jiangkou strata in South China. Some carbonate, chert and shale units throughout the upper part of the Dajiangbian Formation were sampled for carbonate carbon isotope（δ^（13）C_（carb）） and organic carbon isotope（δ^（13）C_（org）） analyses. A range of geochemical indices including oxygen isotopes（δ^（18）O） and Mn/Sr（Fe/Sr） ratios suggest that primary carbon isotope values were preserved in the upper Dajiangbian Formation. The upper Dajiangbian Formation shows δ^（13）C_（carb） of-0.1‰, upward decreasing towards to-5.4‰. We suggest that the negative δ^（13）C excursion beneath the Sizhoushan diamictite is correlative with the Pre-Sturtian Islay δ^（13）C_（carb） anomaly and allows correlation with the global Neoproterozoic isotope stratigraphy. We find that carbonate and organic carbon isotope data of the upper Dajiangbian Formation are coupled, consistent with the δ^（13）C_（carb）-δ^（13）C_（org） pattern observed on multiple continents.

华南东部元古代构造格局及其古位置重建

包括扬子、华夏和琼西南诸多块体的华南东部保存了与哥伦比亚和罗迪尼亚超大陆聚散有关的丰富地质记录,是理解东亚前寒武纪动力学演化的关键地区。本文基于琼西南、扬子东部和华夏陆块元古代地层和岩浆记录,分析并综述了华南东部地区元古代构造过程及其在超大陆的古位置。研究表明,琼西南地块在中元古代(~1.45 Ga)时期形成于哥伦比亚超大陆内部的非造山裂谷环境,经历了~1.05 Ga的麻粒岩相高级变质作用。其与扬子西南缘关系紧密,在~1.30~1.05 Ga期间,可能作为中元古代Albany-Fraser造山带的一部分。华夏和扬子东部在新元古代早期显示差异的地质特征,两者因古华南洋而分隔。江山-绍兴缝合带以东的华夏陆块发育εHf(t)值为负的~1.0~0.9 Ga长英质火山岩,与江-绍缝合带之西的扬子陆块同期具正εHf(t)值的双溪坞弧迥然不同,他们很可能是响应于原高止大洋俯冲而作为早新元古代(~1.0~0.9 Ga)原华夏造山作用的地质记录。怀玉和江南地区广泛发育~870~830 Ma的火成岩(集中在850~830 Ma),其碎屑岩含~860~830 Ma碎屑锆石年龄峰值、~980 Ma锆石颗粒较少。相反华夏陆块较少发育同期火成岩,碎屑岩中~980 Ma碎屑锆石丰富而~860~830 Ma碎屑锆石少见。以裂谷环境为其成因性质的~820~750 Ma板溪群、沥口群和马面山群及同期火成岩广泛见于华夏和怀玉地块及江南造山带,并以角度不整合经沧水铺群和骆家门砾岩与冷家溪群及其相当岩系分割,自此使之进入相对稳定的板内沉积演化期。研究认为,新元古代早期(~1.0~0.9 Ga)在华夏内部武夷-云开一线发育了与印度Eastern Ghats造山带走向相接的增生造山带,同时在扬子与华夏陆块之间发育了新元古代古华南洋,该大洋向西持续俯冲形成了长寿命的新元古代(~0.97~0.83 Ga)华南沟-弧系统,相继形成了~0.98~0.88 Ga的双溪坞洋内弧,~0.87~0.83 Ga怀玉大陆弧及~0.87~0.83 Ga的江南陆内弧后盆地,可与罗迪尼亚超大陆外缘印度西北的新元古代德里造山带相对比。该系统内双溪坞洋内弧盆在~0.87 Ga关闭而转入~0.87~0.83 Ga的怀玉-江南安第斯型活动大陆边缘,进而于~830~810 Ma由扬子和华夏陆块沿江南造山带拼合而成古华南陆块,自810 Ma之后由于罗迪尼亚超大陆裂解及大规模后造山裂谷作用,造就了板溪群及其相当岩系和同期双峰式火成作用。

山西太原西山下二叠统太原组鳞木属化石研究

华夏植物群是晚古生代全球四大著名植物群之一,鳞木属(Lepidodendron)广泛分布于四大植物群中。华夏植物区鳞木属因叶痕较大、叶痕下无通气道痕而被视为地域特征显著的东方型鳞木,区别于具有通气道痕的欧美植物区鳞木属。山西太原西山地区是华夏植物群的重要分布地之一,本文对太原西山地区下二叠统太原组的4块东方型鳞木化石进行鉴定和描述。结果表明,它们分属三种鳞木属叶座化石,即Lepidodendron oculus-felis、Lepidodendron cervicisum和Lepidodendron cf.aolungpylukense。根据鳞木属的大化石记录和相似属的研究成果,推测该属可能在晚泥盆世晚期起源于华南板块,跨洋流到达土耳其小亚细亚一带后开始分化,一支向西北到达欧洲西部并扩散至美洲北部,另一支从土耳其一带向北扩散至西伯利亚,最终散布到东欧、中亚地区。

华夏地块造山型金矿床:时空分布规律、地质-地球化学特征、成矿机制与动力学背景

造山型金矿床具有重要的经济价值,其成矿理论研究对金矿勘查和矿床学学科发展具有重要意义。华夏地块是我国重要的钨-锡-银-铅-锌多金属成矿带,近年来在华夏地块的变质地体中发现数十处造山型金矿床和矿化点,为该区的成矿理论研究提供了新的课题。较之区域钨锡等多金属矿床的研究程度,造山型金矿床成矿作用研究较为薄弱,尚未进行系统的成矿作用和成因机制总结。华夏地块内发育的造山型金矿床主要包括东华夏武夷山地区的双旗山和何宝山金矿,西华夏云开地区的河台与海南岛的抱伦金矿等。本文重点对上述四个典型矿床的地质-地球化学特征、成矿时代、成矿流体和成矿物质来源等方面已有数据和文献资料进行系统的归纳总结,以期阐明华夏地块造山型金矿床的时空分布规律、成矿机制和地球动力学背景。研究发现,华夏地块造山型金矿床主要发育浸染状与石英-硫化物型矿化,金矿体主要赋存于前寒武纪变质地体中,受脆-韧性剪切带控制。成矿流体为H_(2)O-CO_(2)-NaCl±CH_(4)±N_(2)体系,主成矿阶段成矿温度集中于220~280℃,成矿流体可能具有变质、地幔或岩浆热液来源;而流体不混溶、热液体系氧逸度升高和铋熔体捕获是金沉淀的重要机制。华夏地块存在加里东期、印支期和燕山期三期造山型金成矿事件,分别对应陆内造山、古太平洋板块俯冲及后撤的地球动力学背景。

Formation history and protolith characteristics of granulite facies metamorphic rock in Central Cathaysia deduced from U-Pb and Lu-Hf isotopic studies of single zircon grains

The petrochemical as well as zircon U-Pb and Lu-Hf isotopic studies of granulite facies metamorphic rock from the Taoxi Group in eastern Nanling Range, Central Cathaysia indicate that its protolith is the sedimentary rock with low maturation index. The clastic materials are mostly from middle Neoproterozoic (~736 Ma) granitoid rocks with minor Neoarchaean and Paleoproterozoic rocks. The timing of this Neoproterozoic magmatism is in agreement with the second period of magmatism widespread surrounding the Yangtze Block. Hf isotopic data indicate that the Neoproterozoic granitoids resulted from the recycled Paleoproterozoic mantle-derived crustal materials. The sedimentary rock was deposited in Late Neoproterozoic Era, and carried into low crust in Early Paleozoic. The partial melting of the meta-sedimentary rock took place at about 480 Ma and subsequently granulite facies metamorphism occurred at ca. 443 Ma. The zircons forming during this time interval (Early Paleozoic) show large Hf isotope variations, and their -Hf(t) values increase from -13.2 to +2.36 with decreasing age, suggesting the injection of mantle-derived materials during partial melting and metamorphism processes in the Early Paleozoic. Calculation results show that this metamorphic rock, if evolved to Mesozoic, has similar isotopic composition to the nearby Mesozoic high Si peraluminous granites, implying that this kind of granulite facies metamorphic rock is probably the source material of some Mesozoic peraluminous granitoids in eastern Nanling Range.

Caledonian reworking of Paleoproterozoic basement in the Cathaysia Block: Constraints from zircon U-Pb dating, Hf isotopes and trace elements

A combined study of zircon U-Pb dating, Hf isotopes and trace elements has been carried out for granodioritic neosomes of migmatites from the Tianjingping area in northwestern Fujian Province. Zircons are characterized by zoning, higher Th/U ratios (mostly ≥0.1), HREE enrichment, and positive Ce and negative Eu anomalies, and show features similar to magmatic or anatectic zircons. Apparent 206Pb/238U ages for the zircons are 447±2 Ma (95% conf., MSWD = 0.88), corresponding to a Caledonian event. εHf(t) values are ?13.3 to ?9.7, indicating a crustal source. Two-stage Hf model ages are 1.7 to 1.9 Ga, suggesting that protolith of the migmates was probably formed in the Paleoproterozoic. The granodioritic neosomes have the characteristics of peraluminous calc-alkaline granite, and their REE patterns and trace elements spidergrams show features of middle to upper crustal rocks. Together with previous studies, we conclude that the protolith of the Cathaysia basement in the Tianjingping area was likely formed in the middle-late Paleoproterozoic and experienced partial melting during the Caledonian period. The recognition of Caledonian reworking of the Paleoproterozoic basement in the Cathaysia Block provides a new insight into the tectonic evolution of the Cathaysia Block in the Caledonian pe- riod and the interaction between the Cathaysia Block and the Yangtze Block.

Grenvillian orogeny in the Southern Cathaysia Block:Constraints from U-Pb ages and Lu-Hf isotopes in zircon from metamorphic basement

Metamorphic basement rocks in the Cathaysia Block are composed mainly of meta-sediments with different ages. New zircon U-Pb geochronological results from the meta-sedimentary rocks exposed in the Zengcheng and Hezi areas, southern Cathaysia Block, show that they consist dominantly of early Neoproterozoic (1.0―0.9 Ga) materials with minor Paleo- to Mesoproterozoic and late Neoproterozoic (0.8―0.6 Ga) components, suggesting that the detritus mostly come from a Grenvillian orogen. The youngest detrital zircon ages place a constraint on the deposition time of these sediments in Late Neoproterozoic. Zircon Hf isotopic compositions indicate that the Grenvillian zircons were derived from the reworking of Mesoproterozoic arc magmatic rocks and Paleoproterozoic continental crust, implying an arc-continent collisional setting. Single-peak age spectra and the presence of abundant euhedral Grenvillian zircons suggest that the sedimentary provenance is not far away from the sample location. Thus, the Grenvillian orogen probably preexisted along the southern margin of the Cathaysia Block, or very close to the south. Similarity in the ages of Grenvillian orogeny and the influence of the assembly of Gondwana in South China with India and East Antarctic are discussed, with suggestion that South China was more likely linked with the India-East Antarctica continents in Early Neoproterozoic rather than between western Laurentia and eastern Australia.

华夏陆块早寒武世沉积地层年代学与地球化学组成:对源区和构造背景的指示

华夏陆块早古生代沉积记录对于了解华南陆块在Gondwana超大陆演化过程中所起的作用具有重要意义。本文对广东省中山市神湾地区下寒武统八村群开展了锆石年代学和元素地球化学研究。结果表明,八村群变泥质粉砂岩的碎屑锆石年龄可分为4034~3122 Ma、2765~2250 Ma、1765~1443 Ma、1126~901 Ma、884~773 Ma以及595~547 Ma六组,其中最年轻的一组碎屑锆石加权平均年龄将该地层的最大沉积时间限定在551±4 Ma。锆石的Hf同位素特征则指示八村群沉积物源可能以古老地壳物质再循环为主,伴少量初生地壳物质。八村群变粉砂岩和变泥岩样品的化学风化指数(CIA)和成分成熟度(ICV)分别为79.8~86.4和0.39~0.87,均表明源区经历了相对强烈的化学风化作用。元素地球化学结果显示,八村群样品强烈富集不相容元素,而亏损Ni、Cr和Co等,指示八村群源区可能以活动大陆边缘构造背景下的长英质岩石为主。综合对比八村群与世界其他陆块同时期沉积地层的碎屑锆石年龄组成,本文认为八村群代表了新元古代晚期至早古生代早期Gondwana超大陆聚合过程中造山作用的沉积响应,支持华夏陆块位于Gondwana超大陆北缘,靠近北印度板块和羌塘地体,是该超大陆的重要组成部分。

华夏地块新元古代沉积记录与超大陆重建

新元古代-早古生代,Rodinia超大陆裂解至Gondwana大陆聚合的过程对华南构造格局与古地理演化具有重要的制约作用,然而在这过程中华夏地块的位置、华夏与扬子之间的关系等问题仍存在争议。本文通过同位素地层年代学、新元古代冰期事件及成矿事件对比了华夏地块武夷南部-南岭地区及华夏西缘新元古代中-晚期地层。在此基础上,对新元古代沉积物进行碎屑锆石物源分析,发现华夏西缘拉伸纪晚期-埃迪卡拉纪曾出现多次物源方向的转换,并在成冰纪晚期同时出现来自华南内部和外部的双向物源。结合浅海陆棚的沉积环境,表明此时扬子与华夏之间并没有宽阔的大洋相隔。华夏地块拉伸纪晚期-埃迪卡拉纪碎屑岩中包含了大量中元古代至新元古代早期的碎屑锆石,与东冈瓦纳北部印度、东南极等地区的沉积记录吻合,指示华夏地块至少自750 Ma时期就接收到来自印度北缘的碎屑物质。在Rodinia超大陆裂解至Gondwana大陆聚合期间,华南一直保持在超大陆边缘的古地理位置,与印度北缘相连。