Absence of Archean basement in the South Kunlun Block: Nd-Sr-O isotopic evidence from granitoids

Abstract   The West Kunlun mountain range along the northwestern margin of the Tibetan Plateau is crucial in understanding the early tectonic history of the region. It can be divided into the North and South Kunlun Blocks, of which the former is considered to be part of the Tarim Craton, whereas consensus was not reached on the nature and origin of the South Kunlun Block. Samples were collected from the 471 Ma Yirba Pluton, the 405 Ma North Kudi Pluton and the 214 Ma Arkarz Shan Intrusive Complex. These granitoids cover approximately 60% of the Kudi area in the South Kunlun Block. Sr, Nd, and O isotope compositions preclude significant involvement of mantle-derived magma in the genesis of these granitoids; therefore, they can be used to decipher the nature of lower–mid crust in the area. All samples give Mesoproterozoic Nd model ages (1.1–1.5 Ga) similar to those of the exposed metamorphic complex of this block but significantly different from those of the basement of the North Kunlun Block (2.8 Ga). This indicates that the South Kunlun Block does not have an Archean basement, and, thus, does not support the microcontinent model that suggests the South Kunlun Block was a microcontinent once separated from and later collided back with the North Kunlun Block.     

U-Pb dating of zircon from the Central Zone of the East Kunlun Orogen and its implications for tectonic evolution

LA-ICP-MS and SHRIMP U-Pb dating of zircons from orthogneisses and amphibolite from the Central Zone of the Kunlun Orogen is reported in this paper. One orthogneiss sample has metamorphic zircons yielding weighted average 206Pb/238U age of 517.0 5.0/-6.0 Ma, and the other orthogneiss sample con- tains zircons with inherited magmatic cores giving three population 207Pb/206Pb ages of 955 Ma, 895 Ma and 657 Ma for the magmatic protolith, and metamorphic recrystallized rims with peak 206Pb/238U ages of 559 12/?17 Ma and 516 ± 13 Ma. The amphibolite yielded three populations of weighted average 206Pb/238U age of 482.0 10/?8.0 Ma, 516.2 ± 5.8 Ma and 549 ± 10 Ma for the metamorphic zircons. These dating results recorded the tectonothermal events that occurred in the early Paleozoic and the Pre- cambrian time. The records of the Cambrian magmatic-metamorphic event in the Qinling Orogen, the Altyn Tagh belt, north margin of the Qaidam Block and the Kunlun Orogen suggest that continental assembly probably occurred in the early evolutionary history of the Proto-Tethys.     

Mineral inclusions in zircon domains and geological significance of SHRIMP U-Pb dating for coesite-bearing zircons of paragneiss in Sulu terrane,eastern China

Laser Raman spectroscopy and cathodoluminescence (CL) image reveal that zircons separated from paragneisses in the southwestern Sulu terrane (eastern China) preserve multi-stage mineral assemblages in different zircon domains. In the same paragneiss zircon sample, some zircon grains retain inherited (detrital) cores with abundant low-pressure mineral inclusions of Qtz + Phe + Ap + impurities and Qtz + Phe + impurities. The ultrahigh-pressure (UHP) metamorphic overgrowths mantles of these zircons preserve Coe, Coe + Phe and other UHP mineral inclusions, indicating that these inherited (detrital) zircons from protoliths experienced metamorphic recrystallization during the Sulu UHP metamorphic event. However, other zircon grains preserve UHP mineral inclusions of Coe, Coe + Ap and Coe + Phe in the cores and mantles, whereas the outmost rims contain quartz (Qtz) and other low-pressure mineral inclusions. These phenomena prove that the second group zircons were crystallized at UHP metamorphic stage and overpr     

SHRIMP U–Pb zircon ages of the Hida metamorphic and plutonic rocks,Japan: Implications for late Paleozoic to Mesozoic tectonics around the Korean Peninsula

A new U–Pb zircon geochronological study for the Hida metamorphic and plutonic rocks from the Tateyama area in the Hida Mountains of north central Japan is presented. The U–Pb ages of metamorphic zircon grains with inherited/detrital cores in paragneisses suggest that a metamorphic event took place at around 235–250 Ma; the cores yield ages around 275 Ma, 300 Ma, 330 Ma, 1 850 Ma, and 2 650 Ma. New age data, together with geochronological and geological context of the Hida Belt, indicate that a sedimentary protolith of the paragneisses is younger than 275 Ma and was crystallized at around 235–250 Ma. Detrital ages support a model that the Hida Belt was located in the eastern margin of the North China Craton, which provided zircon grains from Paleoproterozoic to Paleozoic rocks and also from Archean and rare Neoproterozoic rocks. Triassic regional metamorphism possibly reflects collision between the North and South China Cratons.     

High-pressure granulite from Western Kunlun,northwestern China: Its metamorphic evolution,zircon SHRIMP U-Pb ages and tectonic implication

High-pressure mafic granulites occurring as lenticular bodies within garnet-amphibolites in Kangxiwar Fault have been first reported in this paper. The P-T conditions of two metamorphic stages were ob-tained using calibrated geothermal barometers and ThermoCalc Program. The peak metamorphic con-dition of these high-pressure granulites is about 760―820℃,1.0―1.2 GPa and the retrograde meta-morphic condition is about 620―720℃,0.7―0.8 GPa. The petrological studies show that they have a near-isobaric cooling P-T...     

Nature of the Precambrian metamorphic blocks in the eastern segment of Central Tianshan: Constraint from geochronology and Nd isotopic geochemistry

The Central Tianshan Tectonic Zone (CTTZ) is anarrow domain between an early Paleozoic southernTianshan passive continental margin and a late Paleo-zoic northern Tianshan arc zone, which is character-ized by the presence of numerous Precambrian meta-morphic basement blocks. Proterozoic granitoidgneisses and metamorphic sedimentary rocks,namely Xingxingxia and Kawabulag and Tianhugroups, are the most important lithological assem-blages in these metamorphic basement blocks, and alittle of …     

SHRIMP zircon U-Pb ages for the Paleoproterozoic metamorphic-magmatic events in the southeast margin of the North China Craton

A garnet-pyroxene bearing amphibolite as a xenolith hosted by the Mesozoic igneous rocks from Xuzhou-Suzhou area was dated by zircon SHRIMP U-Pb method, which yields a metamorphic age of 1918 ± 56 Ma. In addition, the zircons from a garnet amphibolite as a lens interbedded with marble in the Archean metamorphic complex named Wuhe group in the Bengbu uplift give a metamorphic U-Pb age of 1857 ± 19 Ma, and the zircons from Shimenshan deformed granite in the eastern margin of the Bengbu uplift give a magma crystallization U-Pb age of 2054 ± 22 Ma. Both the Xuzhou-Suzhou area and Bengbu uplift are located in the southeastern margin of the North China Craton. Therefore, these ages indicate that there is a Paleoproterozoic tectonic zone in the southeastern margin of the North China Craton, and its metamorphic and magmatic ages are consistent with those of the other three Paleoproterozoic tectonic zones in the North China Craton. In view of the large scale sinistral strike-slip movement occurred at the Mesozoic along the Tan-Lu fault zone, the position of the eastern Shandong area, which is a south section of the Paleoproterozoic Jiao-Liao-Ji Belt, was correlated to Xuzhou-Suzhou-Bengbu area prior to movement of the Tan-Lu fault zone. This suggests that the Xuzhou-Suzhou-Bengbu Paleoproterozoic tectonic zone might be a southwest extension of the Paleoproterozoic Jiao-Liao-Ji Belt. Supported by National Natural Science Foundation of China (Grant No. 40634023)     

Zircon Senstive High Resolution Ion Microprobe (SHRIMP) study of granitoid intrusions in Zhaoye Gold Belt of Shandong Province and its implication

The zircon Sensitive High Resolution Ion Microprobe (SHRIMP) results show that granitoid intrusions in Zhaoye Gold Belt were emplaced at two periods of Mesozoic: Linglong and Luanjiahe types of granitic intrusions were emplaced between 160 Ma and 150 Ma (late Jurassic); Guojialing type of granodioritic intrusions, 130 Ma and 126 Ma (early Cretaceous). All the three types contain at least two major generations of inherited zircons with Precambrian (>650 Ma) and early Mesozoic ages (200–250 Ma), respectively. The former suggests that these plutonic rocks are of crustal origin and that Precambrian basement with component of sialic crust up to 3.4 Ga old (Middle Archean) exists in the region. The presence of abundant inherited zircons with early Mesozoic age indicates that the Precambrian basement was affected by a major tectono-thermal event, that is the collision of the North and South China blocks, at 250 Ma to 200 Ma. SHRIMP results also indicate that the gold mineralization in the region took place between 126 Ma and 120 Ma. Project supported by the Sino-Australian Economic and Technical Fund.     

Metamorphism and metamorphic K–Ar ages of the Mesozoic accretionary complex in Northland, New Zealand

Abstract A southwest dipping Mesozoic accretionary complex, which consists of tectonically imbricated turbiditic mudstone and sandstone, hemipelagic siliceous mudstone, and bedded cherts and basaltic rocks of pelagic origin, is exposed in northern North Island, New Zealand. Interpillow limestone is sometimes contained in the basaltic rocks. The grade of subduction‐related metamorphism increases from northeast to southwest, indicating an inverted metamorphic gradient dip. Three metamorphic facies are recognized largely on the basis of mineral parageneses in sedimentary and basaltic rocks: zeolite, prehnite‐pumpellyite and pumpellyite‐actinolite. From the apparent interplanar spacing d₀₀₂ data for carbonaceous material, which range from 3.642 to 3.564 Å, the highest grade of metamorphism is considered to have attained only the lowermost grade of the pumpellyite‐actinolite facies for which the highest temperature may be approximately 300°C. Metamorphic white mica K–Ar ages are reported for magnetic separates and <2 µm hydraulic elutriation separates from 27 pelitic and semipelitic samples. The age data obtained from elutriation separates are approximately 8 m.y. younger, on average, than those from magnetic separates. The age difference is attributed to the possible admixture of nonequilibrated detrital white mica in the magnetic separates, and the age of the elutriation separates is considered to be the age of metamorphism. If the concept, based on fossil evidence, of the subdivision of the Northland accretionary complex into north and south units is accepted, then the peak age of metamorphism in the north unit is likely to be 180–130 Ma; that is, earliest Middle Jurassic to early Early Cretaceous, whereas that in the south unit is 150–130 Ma; that is, late Late Jurassic to early Early Cretaceous. The age cluster for the north unit correlates with that of the Chrystalls Beach–Taieri Mouth section (uncertain terrane), while the age cluster for the south unit is older than that of the Younger Torlesse Subterrane in the Wellington area, and may be comparable with that of the Nelson and Marlborough areas (Caples and Waipapa terranes).     

Radiometric ages of Alpine metamorphic rocks in the western and central Alps

Abstract The chronological characteristics of Alpine metamorphic rocks are described and Alpine metamorphic events are reinterpreted on the basis of chronological data for the western and central Alps from 1960 to 1992. Metamorphic rocks of the Lepontine, Gran San Bernardo, Piemonte, Internal Crystalline Massifs and Sesia-Lanzo mostly date Alpine metamorphic events, but some (along with granitoids and gneisses from the Helvetic and Southern Alps) result from the Variscan, Caledonian or older events and thus predate the Alpine events. Radiometric age data from the Lepontine area show systematic age relations: U-Pb monazite (23-29 Ma), Rb-Sr muscovite (15–40 Ma) and biotite (15–30 Ma), K-Ar biotite (10-30 Ma), muscovite (15–25 Ma) and hornblende (25-35 Ma), and FT zircon (10-20 Ma) and apatite (5-15 Ma), which can be explained by the different closure temperatures of the isotopic systems. A 121 Ma U-Pb zircon age for a coesite-bearing whiteschist (metaquartzite) from the Dora-Maira represents the peak of ultra-high pressure metamorphism. Coesite-free eclogites and blueschists related to ultra-high pressure rocks in the Penninic crystalline massifs yield an ⁴⁰Ar-³⁹Ar plateau age of about 100 Ma for phengites, interpreted as the cooling age. From about 50 Ma, eclogites and glaucophane schists have also been reported from the Piemonte ophiolites and calcschists, suggesting the existence of a second high P/T metamorphic event. Alpine rocks therefore record three major metamorphic events: (i) ultra-high and related high P/T metamorphism in the early Cretaceous, which is well preserved in continental material such as the Sesia-Lanzo and the Penninic Internal Crystalline Massifs; (ii) a second high P/T metamorphic event in the Eocene, which is recognized in the ophiolites and calcschists of the Mesozoic Tethys; and (iii) medium P/T metamorphism, in which both types of high P/T metamorphic rocks were variably reset by Oligocene thermal events. Due to the mixture of minerals formed in the three metamorphic events, there is a possibility that almost all geochronological data reported from the Alpine metamorphic belt show mixed ages. Early Cretaceous subduction of a Tethyan mid-ocean ridge and Eocene continental collision triggered off the exhumation of the high pressure rocks.     

New paleontological evidence on time determination of the east part of the Eastern Kunlun Mélange and its tectonic significance

New paleontological evidence suggests that the composition of the matrix and slices from the middle and the south of the Eastern Kunlun Melange Belt is very complex, ranging from Proterozoic to Mesozoic in geological time. A Cambrian acritarch assemblage has been discovered from the middle part of the Eastern Kunlun Melange, a Neoproterozoic to the early Paleozoic acritarch assemblage has been discovered from the south of the Eastern Kunlun Melange,and so has been an Early Permian radiolarian from the A'nyemaqen Melange in Buqingshan.In addition, some sporopollen has been obtained from the Mesozoic tectonic slices. The above-mentioned paleontological evidence indicates that the Eastern Kunlun Orogenic Belt experienced two episodes from ocean to continent from the Neoproterozoic to the Early Paleozoic and in the Late Paleozoic respectively. In the process of intracontinent development in Mesozoic, because of heavy thrust-nappe, strike-slip sheer and crust shortening, the Mesozoic formation was intercalated in melange by slices and the Eastern Kunlun Orogenic Belt became more complex.     

Time constraints for Mesoproterozoic upper amphibolite facies metamorphism in NW Namibia: a multi-isotopic approach

This study presents the chronological evolution of the upper amphibolite facies Orue Unit in NW Namibia. Metasedimentary and meta-igneous rocks of the Orue Unit were investigated using the Pb–Pb stepwise leaching technique on garnet and rutile, U–Pb multi-grain analysis on rutile, Sm–Nd–Lu–Hf leaching technique on garnet, SHRIMP analysis on zircon and Ar–Ar dating on amphibole. Each of these techniques pertains to different processes that occurred before, during, or after the metamorphic peak. Our age data can be integrated with petrological constraints to provide a more complete understanding of the metamorphic cycle. Our pre-peak metamorphic zircon ages, peak metamorphic garnet ages and peak to late peak metamorphic amphibole ³⁹Ar–⁴⁰Ar ages bracket the upper amphibolite facies metamorphic event including hydration or dehydration processes into a time span of only ca. 20 Ma. The age data obtained by peak metamorphic mineral analyses cluster around 1340–1320 Ma. Based on age data and field observation, we interpret the upper amphibolite facies metamorphism as a large-scale regional mid-crustal event. Spot analyses of inherited zircon cores obtained by SHRIMP reflect the sedimentary origin of the respective rocks of the Orue Unit and derivation from Palaeoproterozoic protoliths. The metamorphic rocks south of the anorthositic Kunene Intrusive Complex (KIC) have previously been ascribed to the Palaeoproterozoic Epupa Complex at the SW margin of the Congo craton and were thus thought to be older than the Mesoproterozoic KIC. Our data show that the high-grade metamorphic overprint took place 30–50 Ma after emplacement of the KIC. Rutile growth ages of 1248 Ma in one sample reflect fluid activity which seems to be a local phenomenon since there is no other evidence of geological activity throughout the Orue Unit at that time. The rutile ages predate the emplacement of satellite intrusions in that area by 30 Ma and there is no causal relation between these two events.     

华南晋宁期造山运动──地质年代学和地球化学制约

综合了前人和作者最新的地质年代学和地球化学研究成果,对华南晚元古代晋宁期造山运动的演化提供了化学地球动力学制约晚元古代早期（0．97－1．0Ga）的皖南、赣东北和桂北蛇绿岩在元素地球化学上具有相似的岛弧特征,但它们的Nd同位素组成明显不同新获得的高精度结石U－Ph年龄资料表明,桂北地区的本洞、三防和元宝山等三个主要花岗岩岩体均形成于820-825Ma,排除了本区有中元古代晚期花岗岩的存在．扬子南缘中元古代到三叠纪各个时代地层中的泥质沉积岩的TDM在晚元古代早期从约1．8Ga急剧降低至约1．3Ga,反映了这个时期的沉积物源区有大量新生馒源物质的加入．根据研究资料,提出了华南和扬子块体晋宁期陆-弧-陆碰撞模式     

Ar-Ar geochronology of Late Mesozoic volcanic rocks from the Yanji area, NE China and tectonic implications

Ar-Ar dating results of late Mesozoic-Cenozoic volcanic rocks from the Yanji area, NE China provide a new volcano-sedimentary stratigraphic framework. The previously defined “Triassic-Jurassic” volcanic rocks (including those from Sanxianling, Tuntianying, Tianqiaoling and Jingouling Fms.) were erupted during 118―106 Ma, corresponding to Early Cretaceous. The new eruption age span is slightly younger than the main stage (130―120 Ma) of the extensive magmatism in the eastern Central Asian Orogenic Belt and its adjacent regions. Subduction-related adakites occurring in the previously defined Quanshuicun Fm. were extruded at ca. 55 Ma. Based on these new Ar-Ar ages, the late Mesozoic to Palaeocene volcano-sedimentary sequences is rebuilt as: Tuopangou Fm., Sanxianling/Tuntianying Fm. (118―115 Ma), Malugou/Tianqiaoling Fm. (K1), Huoshanyan/Jingouling Fm. (108―106 Ma), Changcai Fm. (K2), Quanshuicun Fm. (~55 Ma) and Dalazi Fm. Our results suggest that subduction of the Pa- laeo-Pacific Ocean beneath the East Asian continental margin occurred during 106 to 55 Ma, consistent with the paleomagnetic observations and magmatic records which indicated that the Izanagi-Farallon ridge subduction beneath the southwestern Japan took place during 95―65 Ma.     

Cretaceous volcanic-intrusive magmatism in western Guangdong and its geological significance

The Nanling Mountains lying in the southern part of South China are an economically important gran-ite-related multi-metallogenic province. The Nanling Mountains granites can be described as: temporally spanning from Caledonian to Yanshanian and spatially distributed as three EW trending zones: the north one in Zhuguangshan-Qingzhangshan, the middle one in Dadongshan-Guidong, and the south one in Fogang-Xinfengjiang with two neighboring zones’ midline having an interval of ca. latitude …     

SHRIMP U-Pb zircon age,geochemistry and Nd isotope of the Guandaoshan pluton in SW Sichuan: Petrogenesis and tectonic significance

SHRIMP U-Pb zircon age, geochemical and Nd isotopic data are reported for the Neo-proterozoic Guandaoshan pluton in the Yanbian region, SW Sichuan. This pluton is of typical I-type granite and emplaced at (857 ± 13) Ma. Geochemical and Nd isotopic characters suggest that the pluton was generated by partial melting of pre-existing, young (late Mesoproterozoic to early Neo-proterozoic) low-K tholeiitic protolith within an intraplate anorogenic setting. The Guandaoshan pluton probably records the earliest magmatism induced by the proposed ca. 860–750 Ma mantle superplume beneath the supercontinent Rodinia.     

SHRIMP zircon U-Pb age and significance of Early Paleozoic volcanic rocks in East Kunlun orogenic belt, Qinghai Province, China

A great deal of practical data in recent years have proved that the East Kunlun orogenic belt and even the China central orogenic belt are complex orogenic belts that underwent polycycle orogenic evolvement[1―7]. Each orogenic cycle has left a compositional print, the multi-period ophiolites[4―6] and various types of tec-tono-magmatic production in the same orogenic belt. There is a suite of shallow metamorphic volcanic rocks in the Nuomuhong area in the east part of the East Kunlun orogen…     

SHRIMP U-Pb zircon age,geochemistry and Nd isotope of the Guandaoshan pluton in SW Sichuan: Petrogenesis and tectonic significance

SHRIMP U-Pb zircon age, geochemical and Nd isotopic data are reported for the Neo-proterozoic Guandaoshan pluton in the Yanbian region, SW Sichuan. This pluton is of typical I-type granite and emplaced at (857 ± 13) Ma. Geochemical and Nd isotopic characters suggest that the pluton was generated by partial melting of pre-existing, young (late Mesoproterozoic to early Neo-proterozoic) low-K tholeiitic protolith within an intraplate anorogenic setting. The Guandaoshan pluton probably records the earliest magmatism induced by the proposed ca. 860–750 Ma mantle superplume beneath the supercontinent Rodinia.

     

Petrogenesis and dating of the Kangding complex,Sichuan Province

The Kangding group, also known as the Kangding complex, includes granulites, amphibolites, felsic gneisses and gneissic granites that are distributed along a belt from Kangding, Mianning to Panzhihua, in Sichuan Province. The complex has long been thought to represent the crystalline basement of the Yangtze block. On the basis of U-Pb and Pb-Pb whole rock ages[1,2] , and of similarities in metamorphic fa-cies and association of metamorphic rocks with typical Archean high grade terrains, t…     

Two episodes of subduction and collision events at the northern foot of Dabie Mountains: Evidence from petrology and structural geology of granitoid rocks

The intrusive bodies studied include Mafan diorites ((462.7±1.5) Ma,⁴⁰Ar/³⁹Ar amphibole plateau age), Duhudian granites ((293±12) Ma, U-Ph zircon age) and Suxianshi granites ((146.2±0.9) Ma) in Beihuaiyang area at the northern foot of Dabie Mountains, central China. Petrological studies indicate that all of them belong to I-type granitoid rocks. Among them, the Mafan and Duhudian stocks were formed by arc magmatism, while the Suxianshi pluton is a post-collisional granitic body. Three intrusive bodies have distinctive characteristics of structural deformation. The Mafan stock has a rather complicated structure pattern resulting from polyphase deformation during the Caledonian and Mesozoic, the Duhudian stock has been pronouncedly deformed during the Hercynian-Yanshanian events, while regional foliation is not pronounced within the Yanshanian Suxianshi stock. Combination of regional stratigraphic, regional structural and geochronological data shows that the Yangtze plate has experienced two episodes of subduction northward beneath the North China plate during the Paleozoic and following collisional events. The first phase of collision at about 400 Ma resulted in the formation of the Beihuaiyang crystalline basement and the Caledonian high-pressure metamorphism in Dabie orogenic zone, and a late phase of continent-continent collision (~230 Ma) is responsible for the Triassic ultrahigh- and high-pressure metamorphism in Dabie Mountains and for orogenic uplift of the Dabie Mountains. It is suggested that the Beihuaiyang tectonic belt at the northern foot of the Dabie Mountains is a multicyclic suture.