An Important Spreading Event of the Neo-Tethys Ocean during the Late Jurassic and Early Cretaceous: Evidence from Zircon U-Pb SHRIMP Dating on Diabase in Nagarze, Southern Tibet

Widely distributed in Gyangzê-Chigu area, southern Tibet, NW- and nearly E-W-trending diabase（gabbro）-gabbro diorite dykes are regarded as the product of the large-scale spreading of the late Neo-Tethys Ocean. In order to constrain the emplacement age of these dykes, zircons of two samples from diabases in Nagarzê were dated by using the U-Pb SHRIMP method. Two nearly the same weighted mean ^206pb/^23SU ages were obtained in this paper, which are 134.9±1.8 Ma （MSWD=0.65） and 135.5 ± 2.1 Ma （MSWD=1.40）, respectively. They not only represent the crystallization age of the diabase, but also documented an important spreading event of the Neo-Tethys Ocean during the late Jurassic and early Cretaceous. This dating result is of great significance to reconstruct the temporal framework of the late Neo-Tethys Ocean in the Qinghai-Tibet Plateau.

SHRIMP zircon U-Pb dating of the mafic and felsic intrusive rocks of the Saza area in the Lupa goldfields, southwestern Tanzania: Implication for gold mineralization

The Lupa Goldfield (LGF) is one of the eight structural terranes in the NW – SE striking Ubendian Belt of SW Tanzania. The LGF is comprised of granitic gneisses with bands of amphibolites which are intruded by mafic intrusions including gabbros, granodiorites, diorites;and various granites as well as metavol-canics. These rocks are cross-cut by narrow mafic dykes and aplites. SHRIMP zircon U-Pb data are presented for the granodiorite and a mafic dyke that cross-cut the granodiorites in the Saza area of the LGF, with the aim of constraining the mafic and felsic magmatism and their implication to gold mineralization. The zircon U-Pb data shows that the Saza granodiorites were emplaced at 1924 ± 13 Ma (MSWD = 2.6) whereas the cross-cutting mafic dyke yielded a zircon U-Pb age of 1758 ± 33 Ma (MSWD = 0.88). The dated granodiorite sample was in sheared contact with an altered mafic intrusive rock, most likely a diorite, along which an auriferous quartz vein occurs. The 1924 ± 13 Ma age of granodiorites is within error of the reported molybdenite Re-Os age of 1937 Ma determined for the gold mineralization event in Lupa Goldfields. Although auriferous quartz veins are younger than the granodiorites, the more or less similar ages between the emplacement of granodiorites and the mineralizing event indicate that the granodiorites might be the heat source (or driver) of hydrothermal fluids responsible for gold mineralization in the Lupa goldfields. This would further suggest that gold mineralization in the LGF is intrusion-related type. The mafic dykes represent the youngest rocks to have been emplaced in the area and hence the 1758 ± 33 Ma age of the mafic dykes conclude the magmatic evolution in the Lupa goldfields during the Palaeoproterozoic.

Zircon SHRIMP U-Pb dating for island arc volcanic rock of Fangniugou area in Yitong region of Jilin Province

Polymetallic iron ore sulphate deposits of marine volcanic rock have been developed in the Fangniugou area,Jilin Province,China,but the division of volcanic ore-bearing strata has not been specifically elucidated and there is disagreement about the division.The sampling and SHRIMP U-Pb zircon dating of volcanic rock for Daheishan in the Fangniugou area and the northeast slope of the Duanjiadian were described.The volcanic rock formation period and recorded the volcanic events in the Daheishan mountains were systematically researched.Two samples of high-precision U-Pb zircon dating were used to represent the volcanic rock fomation period of the Late Silurian.The measured data reflect that multiple volcanic activities occurred during the Middle Silurian,Early Silurian,Middle Ordovician and Silurian,and Late Ordovician,probably matching volcanic events in the Songnan Basin identified from zircon dating.At the same time,it is confirmed that a controversial "conglomerate of Daheishan" did in fact develop in the Late Silurian,and those sections of both the Dazigou and Xinlitun-Taoshan with graptolite had been reversed.

SHRIMP Zircon U-Pb Dating of the Tongshi Magmatic Complex in Western Shandong and Its Geological Implications

The SHRIMP U-Pb zircon dating result of the Tongshi magmatic complex in western Shandong is presented in this paper. The Tongshi magmatic complex comprises fine-grained porphyritic diorite and syenitic porphyry. Eighteen analyses for fine-grained porphyritic diorite gave two concordia ages, in which ten analyses constitute the young age group, giving ^206Pb/^238U ages ranging from 167.9 Ma to 183 Ma with a weighted mean age of 175.7±3.8 Ma, and the other eight yielded ^207Pb/^206Pb ages of 2502 Ma to 2554 Ma with a weighted mean 2518±11 Ma. Two analyses for syenitic porphyry gave ages of 2485 Ma and 2512 Ma, respectively. The age of 175.7±3.8 Ma indicates that the crystallization of the Tongshi magmatic complex occurred in the Middle Jurassic, whereas that of 2518±11 Ma is interpreted as the age of inherited magmatic zircons in the Neoarchean Wutai period.

Formation Age of the Sujiagou Komatiites in Western Shandong: Further Constraints from SHRIMP U-Pb Zircon Dating on Granitic Dykes

Komatiites are presented as direct evidence for higher mantle temperatures during the Archean. In the North China Craton, komatiites with spinifex structure have been identified only at one locality, i.e. the Sujiagou area, western Shandong. They were considered as formed during the early Neoarchean mainly based on their association with supracrustal rocks considered to be that age. This study carried out SHRIMP U-Pb zircon dating on metamorphosed trondhjemitic and monzogranitic dykes intruding the Sujiagou komatiites, and they have magmatic zircon ages of 2592 ± 12 Ma and 2586 ± 13 Ma respectively. This provides direct evidence that the komatiites formed during the early Neoarchean.

Zircon SHRIMP U-Pb dating of the Neogene coral reefs,Xisha Islands,South China Sea:implications for tectonic evolution

The Xisha Block is a minor one in the South China Sea and an important tectonic unit in the northwestern part of the region.Zircon SHRIMP U-Pb ages for three volcanic intrusive core samples from Xike-1,an exploratory well penetrating the bioherms of the Xisha Islands.The core samples are from the Miocene reef carbonate bedrock and are recognized as dark-gray biotite-hornblende gabbro,gray fne-grained biotite diorite,and gray fine-grained granite,respectively.Zircon cathodoluminescence (CL)images and trace Th,U and Pb compositions of the zircons show that these rocks are of volcanic intrusive origin.Zircon SHRIMP U-Pb dating yielded six groups of ages,ranging from 2451-1 857 Ma to early Cretaceous, which indicate that the formation and evolution of the Xisha Block was affected by the evolution and closure of Neotethys Ocean,probably within its eastern extension into South China Sea.Both old,deepsourced material,including fragments from Rodina supercontinent,and recent mantle-derived magma products contributed to the emergence and formation of the Xisha block.The SHRIMP U-Pb results also proved that this process differed from that of the Kontum massif,the Hainan Block,and the South China Block,but is similar to that of the Nansha and Zhongsha blocks.The process was associated with the effects of Yanshanian magmatism induced by subduction mechanisms of the Paleo-Pacific Plate or the reworking of the multiple magmatisms since the Early to mid-Yanshanian,possibly jointly experienced by the Xisha-Zhongsha-Nansha Block.

SHRIMP zircon U-Pb dating of a small tonalite intrusion in metamorphic belt of Chinese Altai orogen and its geological implication

Small granitic intrusions occur in the progressive metamorphic belts of the Chinese Ahai orogen. SHRIMP U-Pb analyses were performed on zircons separated from a tonalite intrusion and yielded a concordant age of 409.6±3.7 Ma （ MSWD = 0.93 ）, restricting the emplacement and crystallization of the tonalite intru- sion to the Early Devonian. Combined with the existing geological data of the contemporary large granitic plutons in the Chinese Altai orogen, the tonalite is considered to be formed together with other granitic rocks in a continental arc setting. The tonalite intrusion has consistent foliation with its country rocks, indicating the strain resuiting in the regional deformation should be very strong during or after the early Devonian.

U-Pb SHRIMP-II Baddeleyite and Zircon Dating of the Early Proterozoic Monchegorsk Layered Mafite-Ultramafite Complex(Kola Peninsula): Evidence of Synchronous Magmatism

The Early Paleoproterozoic Monchegorsk Complex is exposed over an area of 550 km;and comprises two layered mafite–ultramafite intrusions:the Monchepluton of ultramafic and mafic rocks and the predominantly gabbroid

辽东宽甸地区硼酸盐矿床成矿时代的限定：来自SHRIMP锆石U-Pb年代学和硼同位素地球化学的制约

辽宁宽甸地区砖庙硼矿区的硼矿体呈层状或透镜状赋存于古元古代辽河群里尔峪组火山—沉积建造下部的蛇纹石化大理岩之中。本研究对矿区内外的伟晶岩和变粒岩中的电气石进行了LA-MC-ICP-MS硼同位素微区原位测试,分析了矿床成因;同时对栾家沟矿段矿体上盘含电气石变粒岩和斜长角闪岩进行了SHRIMP锆石U-Pb定年,探讨了成矿时代。得到以下数据和认识:1矿区伟晶岩中电气石的δ11 B为10.9‰~12.7‰,变粒岩中电气石的δ11B为5.7‰~7.6‰,矿区外伟晶岩中电气石的δ11B为-9.9‰^-9.2‰,变粒岩中电气石的δ11 B为-8.3‰^-5.9‰。硼同位素组成往外降低的现象说明,围岩及侵位其中的伟晶岩的B同位素组成均受硼矿床影响,硼矿可能是海相蒸发沉积成因;2含电气石变粒岩核部岩浆锆石的207 Pb/206 Pb加权平均年龄为2174±10Ma,代表了辽吉裂谷早期的火山喷发时代,亦大致代表了初始的含硼蒸发岩的沉积时代上限,根据硼同位素研究结果,可将宽甸地区硼矿的初始沉积成矿时代限定在2.17Ga;3斜长角闪岩重结晶锆石207 Pb/206 Pb加权平均年龄为1869±28Ma,代表了吕梁运动所引起的区域构造热事件和混合岩化作用的时间。

Protracted zircon growth in migmatites and In situ melt of Higher Himalayan Crystallines:U-Pb ages from Bhagirathi valley, NW Himalaya,India

The Higher Himalayan Crystallines(HHC), in western Garhwal, Uttarakhand are located in a regionalscale intracontinental ductile shear zone(15-20 km wide) bounded by the Main Central Thrust at the base, and the South Tibetan Detachment System at the top. The migmatite zone in the centre has the highest grade of metamorphism in the NW Himalayas and show evidence of flowage. Zircons extracted from samples of metasediment, migmatite, biotite granite and in situ partial melt(tourmaline-bearing leucogranite) along the Bhagirathi Valley, preserve U-Pb isotopic evidence of magmatic history, magma source and effects of the Himalayan orogeny in the region. Three distinct periods of zircon growth in the leucogranite record the episodic influx of magma between 46 Ma and 20 Ma indicating a time span of more than 25 Ma between the onset of fluid-fluxed partial melting in the mid-crustal intracontinental shear zone and the emplacement of the magma into the upper crust in a post-collisional extensional setting. Metamorphic zircon growth was initiated about 46 Ma, when the partial melts were generated as the migmatite zone was exhumed.

SHRIMP zircon age of the high aeromagnetic anomaly zone in central Tarim Basin and its geological implications

In order to get the correct isotopic age, SHRIMP U-Pb zircon date of Precambrian hornblende granite in Well TD2, located in the central aeromagnetic belt in the eastern of the Tarim basin, was carried out. The result showed a dependable age of 1908.2 ± 8.6 Ma, which demonstrated that the granite pluton is the result of the magmatic activity in early Palaeoproterozoic. It is indicated that the central aeromagnetic belt across Tarim basin, divided it into north and south block, is formed before Neoproterozoic by a large scale tectonothermal events based on the seismic and drilling date. The Tarim continent may have different age and type basements formed the united crystalline basement in Precambrian. This result has yielded new intraplate evidence to constrain the relation between the Tarim plate and the Colombia supercontinent.

SHRIMP zircon U-Pb dating of late Paleoproterozoic kondalites in the Daqing Mountains area on the North China Craton

The Daqing Mountains area comprises a typical occurrence of the Khondalite Belt in the Western Block of the North China Craton (NCC). In this area, both early and late Paleoproterozoic metasedimentary rocks have been identified in what was originally called the Upper Wula Mountains "Subgroup". Six metasedimentary rock samples yielded SHRIMP U-Pb zircon ages of 2.56-2.04 Ga for detrital and 1.96-1.83 Ga for metamorphic zircons. Based on these data and previously published results, the following conclusions can be drawn: 1) The source region for the late Paleoproterozoic detrital sedimentary rocks is mainly 2.55 2.4 and 2.2 2.04 Ga in age, consistent with the early Precambrian geological history identified widely in the basement of the NCC. 2) The majority of sedimentary rocks of the khondalite series were deposited between 2.04 and 1.95 Ga, and then in a protracted period (1.96 and 1.83 Ga) underwent a complex history of amphibolite to granulite-facies metamorphism.

Geochemistry and zircon SHRIMP U-Pb dating of granitoids from the west segment of the North Qaidam

Granitoid intrusives such as Saishitenshan, Tuanyushan, Aolaohe and Sanchagou occur widely in the western segment of North Qaidam. All these bodies trend NW, roughly parallel to the regional structure. Zircon SHRIMP dating for these granites show that they range in age from Ordovician to Permian; 465.4±3.5 Ma for Saishitenshan, 469.7±4.6 Ma and 443.5±3.6 Ma for Tuanyushan, 372.1±2.6 Ma for Aolaohe, and 271.2±1.5 Ma and 259.9±1.2 Ma for Sanchagou. Both the Tuanyshan and Aolaohe plutons record two distinct intrusive events. Geochemically, the early Paleozoic granites have an island arc or active continental margin affinity, and their protolith may have been Mesoproterozoic oceanic crust derived from depleted mantle. The protolith of the late Paleozoic granites may have been Mesoproterozoic lower crust from the root of an island arc with the magmas reflecting a mixture of mantle and crustal material.

SHRIMP zircon U-Pb dating and its geological significance of Chibaisong gabbro in Tonghua area,Jilin Province,China

SHRIMP zircon U-Pb dating for Chibaisong No.1 gabbro in the Tonghua area, Jilin Prov- ince, is discussed in the paper. The cathodoluminescence (CL) images of the zircons indicate that they can be divided into two major types, i.e. euhedral-subhedral one with striped absorption and round one with obvious oscillatory zoning rims. The dating results of the zircons suggest that Chibai- song gabbro in the Tonghua area was formed at 134±7Ma—the Early Cretaceous. The concordia ages of 2497±13Ma, 787±35Ma, 321±10Ma, 217±11Ma of zircons imply that the Tonghua area might geologically be located in the convergent region of the Yangtze Block (YB) and the North China Block (NCB) in the early Mesozoic and the zircons should be caught during magma intrusion. The existence of the Early Cretaceous basic dyke swarm in the Tonghua area shows that an intensive extensional environment occurred in the Early Cretaceous. It is suggested that the magmatism and lithospheric extension in the Tonghua area should be related to the subduction of the Pacific plate.

SHRIMP zircon U-Pb dating of the intrusives in the Tongling metallogenic cluster and its dynamic setting

This paper selected five typical Mesozoic intrusives from the Tongling metallogenic cluster (Xiaotongguanshan, Fenghuangshan, Xinqiao, Dongguashan, and Shatanjiao plutons), and made a systemic SHRIMP zircon U-Pb dating for the five plutons, which produced

Zircon SHRIMP U-Pb dating of granites from Dulan and the chronological framework of the North Qaidam UHP belt, NW China

Zircon SHRIMP dating of granites from Dulan,east segment of North Qaidam UHP belt shows that they are 406.6±3.5 Ma for Yematan-E,407.3±4.3 and 397±6 Ma for Balijiehatan-W,404.5±4.0 and 397.0±3.7 Ma for Shuiwenzhan-N,380.5±5.0 Ma for Shuiwenzhan-S,382.5±3.6 and 372.5±2.8 Ma for Chachagongma.These granites from Dulan represent the products of the third and fourth periods of Paleozoic magmatism in North Qaidam.Geochemically,the granitoids with metalumious to weak peratuminous are quartz diorite,granodiorite,and granite in composition and mainly belong to calc-alkaline series,a few samples to calc or alkali-calc series.The third period of granites is a rock association of granodiorite+granite,with initial 87Sr/86Sr ratios from 0.7082 to 0.7110 and T2DM model ages from 1.41–1.90 Ga;and the fourth period of granites is a rock association of quartz diorite+granodiorite+granite,with initial 87Sr/86Sr ratios from 0.7072 to 0.7091 and T2DM model ages from 1.07–1.38 Ga.Therefore,the third period of granites has higher initial 87Sr/86Sr ratios and T2DM model ages.On the contrary,the fourth period of granites has Nd(t)values from 0.6 to-3.0,higher than that of the third granite with Nd(t)values-3.2 to-9.3.Thus,the data comparison indicates that the third granites may derive from Paleo-proterzoic continental crust with mantle material whereas the fourth granites may derive from the Meso-proterzoic basalt crust with continental material.Combined with regional geology,we thought that the third granites were formed relative to plate exhumation and the fourth granites to delamination of the lithospheric mantle.

Zoned Zircon from Eclogite Lenses in Marbles from the Dabie-Sulu UHP Terrane,China: A Clear Record of Ultra-deep Subduction and Fast Exhumation

Eclogite lenses in marbles from the Dabie-Sulu ultrahigh-pressure （UHP） terrane are deeply subducted meta-sedimentary rocks. Zircons in these rocks have been used to constrain the ages of prograde and UHP metamorphism during subduction, and later retrograde metamorphism during exhumation. Inherited （detrital） and metamorphic zircons were distinguished on the basis of transmitted light microscopy, cathodoluminescence （CL） imaging, trace element contents and mineral inclusions. The distribution of mineral inclusions combined with CL imaging of the metamorphic zircon make it possible to relate zircon zones （domains） to different metamorphic stages. Domain 1 consists of rounded, oblong and spindly cores with dark-luminescent images, and contains quartz eclogite facies mineral inclusion assemblages, indicating formation under high-pressure （HP） metamorphic conditions of T = 571-668℃ and P =1.7-2.02 GPa. Domain 2 always surrounds domain 1 or occurs as rounded and spindly cores with white-luminescent images. It contains coesite eclogite facies mineral inclusion assemblages, indicating formation under UHP metamorphic conditions of T = 782-849℃ and P 〉 5.5 GPa. Domain 3, with gray-luminescent images, always surrounds domain 2 and occurs as the outermost zircon rim. It is characterized by low-pressure mineral inclusion assemblages, which are related to regional amphibolite facies retrograde metamorphism of T = 600- 710℃ and P = 0.7-1.2 GPa. The three metamorphic zircon domains have distinct ages; sample H1 from the Dabie terrane yielded SHRIMP ages of 245 ± 4 Ma for domain 1, 235 ± 3 Ma for domain 2 and 215± 6 Ma for domain 3, whereas sample H2 from the Sulu terrane yielded similar ages of 244 ± 4 Ma, 233 ± 4 Ma and 214 ± 5 Ma for Domains 1, 2 and 3, respectively. The mean ages of these zones suggest that subduction to UHP depths took place over 10-11 Ma and exhumation of the rocks occurred over a period of 19-20 Ma. Thus, subduction from - 55 km to 〉 160 km deep mantle depth took place at rates of approximately 9.5-10.5 km/Ma and exhumation from depths 〉160 km to the base of the crust at -30 km occurred at approximately 6.5 km/Ma. We propose a model for these rocks involving deep subduction of continental margin lithosphere followed by ultrafast exhumation driven by buoyancy forces after break-off of the UHP slab deep within the mantle.

The Dabie Orogen as the early Jurassic sedimentary provenance: Constraints from the detrital zircon SHRIMP U-Pb dating

The SHRIMP U-Pb ages of detrital zircon from the oldest Mesozoic strata, the Fanghushan Fomation, in the Hefei Basin range from 200 Ma to ca. 2500 Ma, which indicates that the Dabie Orogen as the early Jurassic sedimentary provenance was complex. The composition of the Dabie Orogen includes: the Triassic high pressure-ultrahigh pressure metamorphic rocks, of which the detrital zircon ages are from 234 Ma to 200 Ma; the rocks possibly related to the Qinling and Erlangping Groups representing the southern margin of the Sino-Korean craton in the Qinling and Dabie area, of which the detrital zircon has an age of 481-378 Ma; the Neoproterozoic rocks originated from the Yangtze croton, of which the detrital zircon ages are 799-721 Ma old; and the rocks with the detrital zircon ages of ca. 2000 Ma and ca. 2500 Ma, which could be the old basement of the Yangtze craton.

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 overprinted by the late retrogressive metamorphism related to the Sulu terrane exhumation. SHRIMP U-Pb dating reveals that zircons separated from the paragneisses recorded complicated geochronological traces. Some zircons retain inherited cores with the 206Pb/238U ages of 284-754 Ma, indicating the complexity of the detrital zircons in protoliths. Coesite-bearing zircon domains recorded 238-266 Ma (with the average age of 245(14 Ma) for the UHP metamorphic event. The retrogressive rims of zircons recorded 213-223 Ma (with the average age of 217(15 Ma) for the late-stage amphibolite facies metamorphic event, indicating that the rapid exhumation time for the Sulu UHP terrane is about 220 Ma.

SHRIMP zircon U-Pb geochronology of early Mesozoic felsic igneous rocks from the southern Lancangjiang and its tectonic implications

The SHRIMP zircon U-Pb geochronology of three typical samples, including two monzo nitic granites from the Lincang batholith and a rhyolite from the Manghuai Formation are presented in the southern Lancangjiang, western Yunnan Province. The analyses of zircons for the biotite monzonitic granites from the northern (02DX-137) and southern (20JH-10) Lincang batholith show the single and tight clusters on the concordia, and yield the weighted mean 206Pb/238U ages of 229.4 ± 3.0 Ma and 230.4 ± 3.6 Ma, respectively, representing the crystallized ages of these granites. The zircons for the rhyolitic sample (02DX-95) from the Manghuai Formation give a weighted mean 206Pb/238U age of 231.0 ± 5.0 Ma. These data suggest that the igneous rocks from the Lincang granitic batholith and Manghuai Formation have a similar crystallized age. In combination with other data, it is inferred that both were generated at a narrow age span (~230 Ma) and were originated from the postcollisional tectonic regime. An early Proterozoic 206Pb/238U apparent age of 1977±44 Ma is additionally obtained from one zircon from the biotite monzonitic granite (southern Lincang batholith), indicative of devel- opment of the early Proterozoic Yangtze basement in the region. These precisely geochronological data provide important constraints on better understanding the Paleozoic tectonic evolution of the Tethys, western Yunnan Province.