Lithologic Boundaries in Permian Post-glacial Sediments of the Gondwana-affinity Regions of China:Typical Sections,Age Range and Correlation

In Southwest China, Gondwana-affinity Permo-Carboniferons deposits are known to occur in the Northern Himalayas, the Lhasa Block and the South Qiangtang Block, the Baoshan Block and the Tengchong Bock. The three-fold clastic successions, namely diamictite-pebbly mudstone-dark mudstone and shale are commonly interpreted as representing deposits of glacial-deglacial-postglacial periods in marine environments. Deposits, for example, the Dingjiazhai Formation in the Baoshan Block, the Kongshuhe Formation in the Tengchong Block, the Yongzhu Group and the Poindo Group in the Lhasa Block, are all succeeded by carbonate deposits. This marks a significant change from post-glacial clastic environment to a carbonate environment. Available paleontological data show that the change from post-glacial clastic environment to carbonate environment took place in the Baoshan, Tengchong and Lhasa Block at the beginning of the Artinskian. The carbonate environment in the Baoshan Block was spoiled by the eruption of the Woniusi Basalts, and in the Xainza area of the Lhasa Block was shortly replaced by clastic environment until the Kungurian. In the northern Himalayas limestones began to occur in the Late Permian in a fluctuating manner.

Cambro-Silurian magmatisms at the northern Gondwana margin(Penninic basement of the Ligurian Alps)

The Early Paleozoic evolution of the northern margin of Gondwana is characterized by several episodes of bimodal magmatism intruded or outpoured within thick sedimentary basins. These processes are well recorded in the Variscan blocks incorporated in the Ligurian Alps because they experienced low temperature Alpine metamorphism. During the Paleozoic, these blocks, together with the other Alpine basements, were placed between the Corsica-Sardinia and the Bohemian Massif along the northern margin of Gondwana. In this framework, they host several a variegated lithostratigraphy forming two main complexes(Complexs I and II) that can be distinguished by both the protoliths and their crosscutting relationships, which indicate that the acidic and mafic intrusives of Complex II cut an already folded sequence made of sediments, basalts and granitoids of Complex I. Both complexes were involved in the Variscan orogenic phases as highlighted by the pervasive eclogite-amphibolite facies schistosity(foliation II). However, rare relicts of a metamorphic foliation at amphibolite facies conditions(foliation I)is locally preserved only in the rocks of Complex I. It is debatable if this schistosity was produced during the early folding event e occurred between the emplacement of Complex I and II e rather than during an early stage of the Variscan metamorphic cycle.New SHRIMP and LA ICP-MS Ue Pb zircon dating integrated with literature data, provide emplacement ages of the several volcanic or intrusive bodies of both complexes. The igneous activity of Complex I is dated between 507 ± 15 Ma and 494 ± 5 Ma, while Complex II between 467 ± 12 Ma and 445.5 ± 12 Ma.The folding event recorded only by the Complex I should therefore have occurred between 494 ± 5 Ma and 467 ± 12 Ma. The Variscan eclogite-amphibolite facies metamorphism is instead constrained between ~420 Ma and ~300 Ma. These ages and the geochemical signature of these rocks allow constraining the Early Paleozoic tectono-magmatic evolution of the Ligurian blocks, from a middleeupper Cambrian rifting stage, through the formation of an Early Ordovician volcanic arc during the Rheic Ocean subduction, until a Late Ordovician extension related to the arc collapse and subsequent rifting of the PaleoThetys. Furthermore, the ~420-350 Ma ages from zircon rims testify to thermal perturbations that may be associated with the Silurian rifting-related magmatism, followed by the subduction-collisional phases of the Variscan orogeny.

LA-ICP-MS U-Pb Geochronology of Detrital Zircons in Eastern Liaoning Province： An Early Paleozoic Formation Associated with the Gondwana Supercontinent Event

Objective The Liao-Ji orogenic belt is a famous Paleoproterozoic orogenic belt in the East Block of the North China Craton(NCC),which extend in NE-SW direction.The geological mass in the Paleoproterozoic Liao-Ji belt is mainly composed of the Liaoji granites and metamorphic volcanic-sedimentary rocks of the Liaohe group(and its

Late Cambrian to Early Silurian Granitic Rocks of the Gemuri Area, Central Qiangtang, North Tibet: New Constraints on the Tectonic Evolution of the Northern Margin of Gondwana

The Paleozoic tectonic framework and paleo–plate configuration of the northern margin of Gondwana remain controversial. The South Qiangtang terrane is located along the northern margin of Gondwana and records key processes in the formation and evolution of this supercontinent. Here, we present new field, petrological, zircon U-Pb geochronological, and Lu-Hf isotopic data for granitic rocks of the Gemuri pluton, all of which provide new insights into the evolution of the northern margin of Gondwana. Zircon U-Pb dating of the Gemuri pluton yielded three concordant ages of 488.5 ± 2.1, 479.9 ± 8.9, and 438.5 ± 3.5 Ma. Combining these ages with the results of previous research indicates that the South Qiangtang terrane records two magmatic episodes at 502–471 and 453–439 Ma. These two episodes are associated with enriched zircon Hf isotopic compositions(εHf(t) =-10.1 to-3.9 and-16.6 to-6.5, respectively), suggesting the granites were formed by the partial melting of Paleoproterozoic–Mesoproterozoic metasedimentary rocks(Two–stage Hf model ages(TCDM) = 2094–1704 and 2466–1827 Ma, respectively). Combining these data with the presence of linearly distributed, contemporaneous Paleozoic igneous rocks along the northern margin of Gondwana, we suggest that all of these rocks were formed in an active continental margin setting. This manifests that the two magmatic episodes within the Gemuri area were associated with southward subduction in the Proto-(Paleo-) Tethys Ocean.

High Ba-Sr adakitic charnockite suite from the Nagercoil Block,southern India:Vestiges of Paleoproterozoic arc and implications for Columbia to Gondwana

The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane(SGT)in India and is mainly composed of charnockitic rocks and felsic gneisses(charnockite suite).In this study,we present petrologic,geochemical,zircon U-Pb,REE,and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block.Based on field investigations and petrologic studies,the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene.The charnockites and leucogneiss show transition from adakites to non-adakitic magmatic rocks,with enrichment in LREEs(light rare earth elements)and LILEs(large ion lithophile elements),and depletion in HREEs(heavy rare earth elements)and HFSEs(high field strength elements).Some of the charnockites and the leucogneiss show typical HSA(high silica adakite)characters,(high SiO_(2),Al_(2)O_(3),Ba-Sr,La/Yb,and Sr/Y).The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge.The high Ba-Sr features were possibly inherited from subducted oceanic crust melting under high thermal gradient during Precambrian.The magmas were underplated and subjected to fractional crystallization.Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims.Magmatic zircon grains from the charnockites show ages ranging from 1983±8.8 Ma to 2046±14 Ma,and the metamorphic domains show an age range of 502±14 Ma to 547±8.7 Ma.Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860±20 Ma and 575.6±8.8 Ma.Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma.The REE data of the zircon grains show LREE depletion and HREE enrichment,with the metamorphic grains showing more depletion in HREE.Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yieldedε_(Hf)(t)values from-1.17 to 0.46 with T_(DM)and T_(DM)~C and age peaks at 2392 Ma and 2638 Ma,suggesting Neoarchean to Paleoproterozoic juvenile sources.We suggest that the high Ba-Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent,and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic-Cambrian.Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.

A history of Proterozoic terranes in southern South America:From Rodinia to Gondwana

The role played by Paleoproterozoic cratons in southern South America from the Mesopro- terozoic to the Early Cambrian is reconsidered here. This period involved protracted continental amal- gamation that led to formation of the supercontinent Rodinia, followed by Neoproterozoic continental break-up, with the consequent opening of Clymene and Iapetus oceans, and finally continental re-assembly as Gondwana through complex oblique collisions in the Late Neoproterozoic to Early Cambrian. The evidence for this is based mainly on a combination of precise U-Pb SHRMP dating and radiogenic isotope data for igneous and metamorphic rocks from a large area extending from the Rio de la Plata craton in the east to the Argentine Precordillera in the west and as far north as Arequipa in Peru. Our interpretation of the paleogeographical and geodynamic evolution invokes a hypothetical Paleoproterozoic block （MARA） embracing basement ultimately older than 1.7 Ga in the Western Sierras Pampeanas （Argentina）, the Arequipa block （Peru）, the Rio Apa block （Brazil）, and probably also the Paraguaia block （Bolivia）.

Detrital zircon geochronology of quartzites from the southern Madurai Block,India:Implications for Gondwana reconstruction

Detrital zircons are important proxies for crustal provenance and have been widely used in tracing source characteristics and continental reconstructions.Southern Peninsular India constituted the central segment of the late Neoproterozoic supercontinent Gondwana and is composed of crustal blocks ranging in age from Mesoarchean to late Neoproterozoic-Cambrian.Here we investigate detrital zircon grains from a suite of quartzites accreted along the southern part of the Madura） Block.Our LA-ICPMS U-Pb dating reveals multiple populations of magmatic zircons,among which the oldest group ranges in age from Mesoarchean to Paleoproterozoic（ca.2980-1670 Ma,with peaks at 2900-2800 Ma,2700-2600 Ma,2500-2300 Ma,2100-2000 Ma）.Zircons in two samples show magmatic zircons with dominantly Neoproterozoic（950-550 Ma） ages.The metamorphic zircons from the quartzites define ages in the range of 580-500 Ma,correlating with the timing of metamorphism reported from the adjacent Trivandrum Block as well as from other adjacent crustal fragments within the Gondwana assembly.The zircon trace element data are mostly characterized by LREE depletion and HREE enrichment,positive Ce,Sm anomalies and negative Eu,Pr,Nd anomalies.The Mesoarchean to Neoproterozoic age range and the contrasting petrogenetic features as indicated from zircon chemistry suggest that the detritus were sourced from multiple provenances involving a range of lithologies of varying ages.Since the exposed basement of the southern Madurai Block is largely composed of Neoproterozoic orthogneisses,the data presented in our study indicate derivation of the detritus from distal source regions implying an open ocean environment.Samples carrying exclusive Neoproterozoic detrital zircon population in the absence of older zircons suggest proximal sources in the southern Madurai Block.Our results suggest that a branch of the Mozambique ocean might have separated the southern Madurai Block to the north and the Nagercoil Block to the south,with the metasediments of the khondalite belt in Trivandrum Block marking the zone of ocean closure,part of which were accreted onto the southern Madurai Block during the collisional amalgamation of the Gondwana supercontinent in latest Neoproterozoic-Cambrian.

Provenance Variability during Damuda Sedimentation in the Talchir Gondwana Basin, India – A Statistical Assessment

The Talchir Gondwana basin houses the Talchir Formation at the base, succeeded by the Damuda Group and the Kamthi Formation in upward progression. The present study is an attempt to determine the provenance of the Damuda Group and its variability in terms of location, climate and tectonism through time from the composition of sandstone grains and detritus of the constituent Karharbari, Barakar and Barren Measures formations. The Damuda sandstones are composed of variable amounts of monocrystalline undulatory, nonundulatory and polycrystalline quartz grains, potash and plagioclase feldspars as well as metamorphic and sedimentary rock fragments in addition to heavy accessories. Palaeocurrent studies suggest that the Eastern Ghats Supergroup lying to the south of the basin served as the source area of the Damuda sediments. Plots of sandstone composition in tectonic setting discrimination diagrams suggest derivation of the detritus from craton interior, continental block and recycled orogen provinces. Statistical analyses indicate significant differences in the detrital modes of the sandstones of the Karharbari, Barakar and Barren Measures formations, which may be attributed to temporal and spatial variation of the provenance coupled with climate change in commensurate with Damuda sedimentation.

The Gondwana Orogeny in northern North Patagonian Massif:Evidences from the Caita Có granite, La Se?a and Pangaré mylonites,Argentina

Structural analyses in the northern part of the North Patagonia Massif, in the foliated Caita Co granite and in La Sefia and Pangare mylonites, indicate that the pluton was intruded as a sheet-like body into an opening pull-apart structure during the Gondwana Orogeny. Geochronological studies in the massif indicate a first, lower to middle Permian stage of regional deformation, related to movements during indentation tectonics, with emplacement of foliated granites in the western and central areas of the North Patagonian Massif. Between the upper Permian and lower Triassic, evidence indicates emplacement of undeformed granitic bodies in the central part of the North Patagonian Massif. A second pulse of deformation between the middle and upper Triassic is related to the emplacement of the Caita CO granite, the development of mylonitic belts, and the opening of the Los Menucos Basin. During this pulse of deformation, compression direction was from the eastern quadrant.

Gondwana Terrane Assembly in Northern Mozambique:A Snapshot of Crustal Processes in the Monapo Klippe

The Nampula Subprovince in Northern Mozambique is a Mesoproterozoic gneiss terrane with a Pan-African(523-550 Ma)amphibolite-facies met- amorphic overprint.The province forms a pivotal part of the evolution and final assembly of Gondwana on the eastern seaboard of the African continent.

^(40)Ar/^(39)Ar Geochronology of the Late Paleozoic Woniusi Basalts from the Baoshan Terrane, SW China:Implications for the Rifting of the Northern Margin of Gondwana

Objective Although the occurrence of Late Paleozoic rifting on the northern margin of Gondwana is widely accepted,the precise reason for the rifting is not constrained.The Woniusi basalts in the Baoshan terrane cover an area of～1.2×10~4 km~2 and have been considered to be likely part

Extensional collapse of the Gondwana orogen: Evidence from Cambrian mafic magmatism in the Trivandrum Block, southern India

The assembly of Late Neoproterozoice Cambrian supercontinent Gondwana involved prolonged subduction and accretion generating arc magmatic and accretionary complexes, culminating in collision and formation of high grade metamorphic orogens. Here we report evidence for mafic magmatism associated with post-collisional extension from a suite of gabbroic rocks in the Trivandrum Block of southern Indian Gondwana fragment. Our petrological and geochemical data on these gabbroic suite show that they are analogous to high Fe tholeiitic basalts with evolution of the parental melts dominantly controlled by fractional crystallization. They display enrichment of LILE and LREE and depletion of HFSE with negative anomalies at Zre Hf and Ti corresponding to subduction zone magmatic regime. The tectonic affinity of the gabbros coupled with their geochemical features endorse a heterogeneous mantle source with collective melt contributions from sub-slab asthenospheric mantle upwelling through slab break-off and arc-related metasomatized mantle wedge, with magma emplacement in subduction to post-collisional intraplate settings. The high Nb contents and positive Nbe Ta anomalies of the rocks are attributed to inflow of asthenospheric melts containing ancient recycled subducted slab components and/or fusion of subducted slab materials owing to upwelling of hot asthenosphere. Zircon grains from the gabbros show magmatic crystallization texture with low U and Pb content. The LA-ICPMS analyses show ^(206) Pb/^(238) U mean ages in the range of 507-494 Ma suggesting Cambrian mafic magmatism. The post-collisional mafic magmatism identified in our study provides new insights into mantle dynamics during the waning stage of the birth of a supercontinent.

Stratigraphic Control of Petrography and Chemical Composition of the Lower Gondwana Coals, Ib-Valley Coalfield, Odisha, India

The Ib-valley coalfield of Odisha, India contains five coal seams viz. Ib-seam at the bottom overlain successively by Rampur seam, Lajkura seam, Parkhani seam and Belpahar seam. Twenty one representative samples were collected from three major seams (Ib, Rampur and Lajkura) and their petrography and chemical studies were carried out. Samples were not collected from the Parkhani and Belpahar seams as these are very small seams exposed locally having no regional correlation. The macroscopic study shows the dominance of durain which imparts a dull appearance to these coals. The maceral analysis reveals that vitrinite percentage varies from 4.5% to 80.2%, the exinite from 3.30% to 22.2% and the inertinite from 12.5% to 92.2% in different samples of the Ib valley coalfield. The very high proportion of inertinite suggests a shallower water deposition of plant materials followed by prolonged period of exposure and repeated cycle of weathering. The proximate analysis results show that the top Lajkura seam is comparatively lower in rank than the underlying Ib and the Rampur seam. The ultimate analysis exhibites that the percentage of variation in C is found from 77.88 to 85.79, H from 4, 4 to 5.91 and O from 7.26 to 15.3. H/C and O/C ratio including C.V. in this coalfield showing distinct variations from the bottom to top seam. The analyses results indicate that the petrographic and chemical characters of the ib valley coals are stratigraphically controlled.

Dyke Swarms Florianópolis: Petrologic and Structural Aspects Related to Rifting Supercontinent Gondwana and Formation South Atlantic in the Santa Catarina of Island, Brazil

From a point of magmatic view,the rupturing Gondwana Supercontinent is registered on the South American shelf in continental flood basalts,mafic dyke swarms,basins rift and,to a lesser extent,by intrusions alkaline.Among those

Palynostratigraphy of the Zorritas Formation, Antofagasta region, Chile： Insights on the Devonian]Carboniferous boundary in western Gondwana

The Middle Member of the Zorritas Formation in the Antofagasta region of northern Chile, yielded terrestrial and marine palynomorph assemblages which span the Devonian/Carboniferous boundary. The assemblages show a clear predominance of terrestrial palynomorphs with 70 miospore species, 18 marine phytoplankton species, two non-marine algae and one chitinozoan species, all coming from 15 productive levels. Palynomorphs are poorly preserved and most of them are reworked. Three palyno- logical associations are recognized based on miospores. These are assigned to the Tournaisian-Visean, Tournaisian and probable latest Famennian. Age assignments are discussed in the frame of the spore zonal schemes established for Euramerica and western Gondwana. The stratigraphical distribution of spores allows the identification of the probable position of the Devonian/Carboniferous boundary within the Zorritas Formation. This system boundary is proposed for the first time in Palaeozoic sedimentary rocks of northern Chile. The presence of Gondwanan typical miospore species indicates affinities with this palaeocontinent even though the Tournaisian and Tournaisian-Viseao miospore associations sup- port the cosmopolitanism already suggested for the early Carboniferous flora. The significant number of reworked palynomorphs together with the sedimentological analysis of the studied sections, suggest that these deposits were severely impacted by the climatic change and major sea level fluctuations. Similar conditions were recorded in coeval western Gondwana basins.

Cambrian-early Ordovician volcanism across the South Armorican and Occitan domains of the Variscan Belt in France:Continental break-up and rifting of the northern Gondwana margin

The Cambrian-lower Ordovician volcanic units of the South Armorican and Occitan domains are ana- lysed in a tectonostratigraphic survey of the French Variscan Belt. The South Armorican lavas consist of continental tholeiites in middle Camhrian-Furongian sequences related to continental break-up. A significant volcanic activity occurred in the Tremadocian, dominated by crustal melted rhyolitic lavas and initial rifting tholeiites. The Occitan lavas are distributed into five volcanic phases： （I） basal Cambrian rhyolites, （2） upper lower Cambrian Mg-rich tholeiites close to N-MORBs but crustal contaminated, （3） upper lower-middle Cambrian continental tholeiites, （4） Tremadocian rhyolites, and （5） upper lower Ordovician initial rift tholeiites. A rifting event linked to asthenosphere upwelling took place in the late early Cambrian but did not evolve. It renewed in the Tremadocian with abundant crustal melting due to underplating of mixed asthenospheric and lithospheric magmas. This main tectono-magmatic conti- nental rift is termed the ＂Tremadocian Tectonic Belt＂ underlined by a chain of rhyolitic volcanoes from Occitan and South Armorican domains to Central Iberia. It evolved with the setting of syn-rift coarse siliciclastic deposits overlain by post-rift deep water shales in a suite of sedimentary basins that fore- casted the South Armorican-Medio-European Ocean as a part of the Palaeotethys Ocean.

The Boundary Between Gondwana and Pacifica and the Suturing Ages of Their Allied Terranes in Southwestern China

Two terranes formed since the Late Palaeozoic can be distinguished in southwestern China. One is charac-terized by the Permo-Carboniferous ice-rafted marine gravel-bearing clastic formation and the cold-water faunaof the Gondwana facies, including the Gangmar Co, Lhasa, Sa' gya, Tengchong and Baoshan terranes and theother is marked by the Upper Palaeozoic of the Yangtze type with the Cathaysian flora and the Pacific-typefusulinids, comprising the Changning-Menglian, Shuangjiang-Lancang, Qamdo and Bayan Har terranes. TheLongmu Co-Shuanghu-Dengqen-North Lancang River-Kejie-Mengding suture zone between the two groups ofterranes is the boundary between Gondwana and Pacifica in southwestern China. On the grounds of thesedimentary formation and successive southwestward migration of the Asian nonmarine Jurassic-Cretaceousendemic bivalves, the ages of the suture and some terranes to the southwest of the suture zone are discussed.The Baoshan terrane and the Nyainrong-Sog terrane in the Lhasa composite terrane were firstly pieced togeth-er with the Asian continent in the early Early Jurassic. The northern Tibet-western Yunnan microplate, in-cluding the Gangmar Co, Lhasa and Tengchong terranes, collided with the Asian continent at the end of theEarly Cretaceous Neocomian.

Mineralogical Study of Almandine-Hercynite-Muscovite-Ilmenite Hornblendite Dykes from the Southern Margin of the Gondwana Graben at Richughuta in Palamau District of the Eastern Indian Shield

Introduction The rectangular block of Proterozoic formation lying between north of the Singhbhum Mobile Belt(SMB,2.3-2.4 Ga,Saha 1994),Neogene sediments of the Bengal basin and the Quaternary-Recent alluvium of the Ganga

Early Cambrian high pressure/low temperature metamorphism in the southeastern Tarim craton in response to circum-Gondwana cold subduction

The circum-Gondwana subduction initiated by the early Cambrian has been suggested to reflect the establishment of the modern plate tectonics.The metamorphic rocks with low thermobaric(T/P)ratios indicative of cold subduction in the present tectonic regime have not been well investigated.To better understand the circum-Gondwana subduction and to test its possible link with the emergence of the modern plate tectonics,this study focused on blueschist-facies metamorphic rocks in the Altyn Tagh of the southeastern Tarim craton.Mineral assemblage and chemistry,phase equilibrium modelling,and quartz-in-garnet Raman elastic geobarometry reveal that the zoisite blueschist and glaucophane(Gln)-bearing quartz schist in northern Altyn Tagh were metamorphosed to lawsonite to epidote blueschistfacies at 520–545℃ and 16–19 kbar.It reflects high-pressure(HP)/low temperature(LT)metamorphism with low T/P ratios of<300℃/GPa and thermal gradients of<10℃/km.These blueschist-facies metamorphic rocks underwent rapid decompression starting at P-T conditions of<495℃ and<9.6 kbar during exhumation.Ar-Ar geochronology records paragonite Ar-Ar plateau ages of 520–506 Ma for the zoisite blueschist samples and phengite Ar-Ar plateau ages of 522–516 Ma for the Gln-bearing quartz schist samples,suggesting that the peak HP/LT metamorphism occurred prior to ca.522 Ma.Based on new results and available data from the major Gondwana blocks,cold subduction was suggested to profoundly operate along circum-Gondwana in the early Cambrian after the amalgamation of Gondwana.The extensive circum-Gondwana subduction represents the earliest global cold subduction in Earth’s history associated with the establishment of the modern plate tectonics,as directly recorded by the studied early Cambrian blueschist-facies metamorphic rocks and a dramatic drop in the mean T/P of metamorphism since the early Paleozoic.