U-Pb Age and Hf Isotope Study of Detrital Zircons from the Wanzi Supracrustals:Constraints on the Tectonic Setting and Evolution of the Fuping Complex,Trans-North China Orogen

Located in the middle segment of the Trans-North China Orogen, the Fuping Complex is considered as a critical area in understanding the evolution history of the North China Craton （NCC）. The complex is composed of various high-grade and multiply deformed rocks, including gray gneiss, basic granulite, amphibolite, fine-grained gneiss and marble, metamorphosed to upper amphibolite or granulite facies. It can be divided into four rock units： the Fuping TTG gneisses, Longquanguan augen gneisses, Wanzi supracrustals, and Nanying granitic gneisses. U-Pb age and Hf isotope compositions of about 200 detrital zircons from the Wanzi supracrustals of the Fuping Complex have been analyzed. The data on metamorphic zircon rims give ages of 1.82-1.84 Ga, corresponding to the final amalgamation event of the NCC, whereas the data for igneous zircon cores yield two age populations at -2.10 and -2.51 Ga, with some inherited ages scattering between 2.5 and 2.9 Ga. These results suggest that the Wanzi supracrustals were derived from the Fuping TTG gneisses （-2.5 Ga） and the Nanying granitic gneisses （2.0-2.1 Ga） and deposited between 2.10 and 1.84 Ga. All zircons with -2.51 Ga age have positive initial εHf values from ＋1.4 to ＋10.9, suggesting an important crustal growth event at -2.5 Ga through the addition of juvenile materials from the mantle. The Hf isotope data for the detrital zircons further imply that the 2.8 Ga rocks are important components in the lower crust, which is consistent with a suggestion from Nd isotope data for the Eastern Block. The zircons of 2.10 Ga population have initial εHf values of-4.9 to ＋6.1, interpreted as mixing of crustal re-melt with minor juvenile material contribution at 2.1 Ga. These results are distinct from that for the Western Block, supporting that the Fuping Complex was emplaced in a tectonic active environment at the western margin of the Eastern Block.

Ages and Hf isotopes of detrital zircons from the Permian strata in the engbatu area(Inner Mongolia) and tectonic implications

The Central Asian Orogenic Belt(CAOB) was built up through protracted accretion and collision of a variety of terranes/micro-continents during Neoproterozoice Mesozoic time. To understand potential links among Paleozoic subduction and accretionary processes that were operative during the development of the southeastern CAOB, we conducted a combined U-Pb and Hf-isotope analysis of detrital zircons from previously defined Devonian, Carboniferous and Early Permian strata in the Bengbatu area,Inner Mongolia. Detrital zircons from(meta-) sandstones in these strata commonly yield major Paleozoic age populations at ca. 300-261 Ma, 351-300 Ma and 517-419 Ma, and also give several Precambrian ages that range from 2687 Ma to 544 Ma. The youngest ages redefine the deposition of all these strata to be in the Middle Permian(Wordiane Capitanian) or later, much younger than previously considered.These ages, coupled with regional magmatic records, support an interpretation of most surrounding areas as possible detritus sources, including the Mongolian arcs to the north, the Northern Accretionary Orogen to the south, and the intervening Erenhote Hegenshan Ophiolite Belt. Zircons with magmatic ages of ca. 500-350 Ma and ca. 300-261 Ma display a large range of εHf(t) values(-13.97 to +15.31),whereas ca. 350-300 Ma zircons are dominated by positive εHf(t) values(+0.14 to +16.00). These results support the occurrence of two significant shifts of the zircon εHf(t) values, which has tectonic implications for the understanding of the Carboniferouse Permian evolution of the southeastern CAOB. A marked shift from mixed to positive zircon εHf(t) values at 350 -330 Ma likely manifests the incipient opening of the Hegenshan Ocean, due to the slab rollback of the subducting Paleo-Asian Oceanic lithosphere. Another shift from positive to mixed zircon εHf(t) values at ca. 300 Ma likely corresponds to a tectonic switch from syn-orogenic subduction-related to post-orogenic extensional setting, genetically related to the tectonic collapse of a formerly overthickened crust.

The U-Pb Geochronology and Lu-Hf Isotope Compositions of Detrital Zircons from the Nanhua Group of the Longsheng Region,South China and their Implications for Pan-African Events

It is unclear whether the South China blocks have an affinity with continental Gondwana due to a lack of direct Pan-African magmatic and metamorphic features.In this study,we conducted U-Pb geochronological and Lu-Hf isotopic analyses for detrital zircons from a sandstone of the Chang'an Formation of the Nanhua Group in the Longsheng region of northern Guangxi,with the aim of constraining the timing of sedimentation and information as to its source,as well as seeking evidence for Pan-African events in the South China blocks.The results show that the ages of detrital zircons peaked at 654.7±6.2 Ma,773.2±4.1 Ma and 821.9±6.5 Ma,with some at 920–870 Ma;the youngest age indicates the existence of the Pan-African thermal event.The ε_(Hf)(t)and T_(DM2) values demonstrate that the study area has experienced three stages of crustal growth at 3.0–2.4 Ga,2.1–1.5 Ga and 1.3–0.9 Ga.With intensively distributed Neoproterozoic mafic-ultramafic and granitic plutons emplaced at 830–810 Ma along the southwestern section of the Jiangnan Orogenic Belt and positiveεHf(t)values from a large group of zircon grains,it is proposed that the sediments of the Chang'an Formation(of Nanhua Group)were largely sourced from the southeastern margin of the Yangtze block.Comparison with the zircon age spectra of the Cathaysian block shows that about 79%of the Pan-African aged detrital zircon grains that have TDM2=1352–1031 Ma andεHf(t)=3.68–8.79,were sourced from the recycled Grenvillian crust of the Cathaysian block,suggesting that the Cathaysian block had a close connection with Gondwana.

Sao Francisco-Congo Craton break-up delimited by U-Pb-Hf isotopes and trace-elements of zircon from metasediments of the Aracuaí Belt

Detrital zircon U-Pb geochronology combined with Hf isotopic and trace element data from metasedimentary rocks of the Aracuai Belt in southeastern Brazil provide evidence for break-up of the Congo-Sao Francisco Craton. The U-Pb age spectra of detrital zircons from metasediments of the Rio Doce Group(RDG) range from 900-650 Ma and define a maximum depositional age of ca. 650 Ma. Zircon trace element and whole rock data constrain an oceanic island arc as source for the deposition setting of the protoliths to the metasediments. Zircon ε_(Hf)(t) values from these rocks are positive between +1 and +15, supporting previous evidence of a Neoproterozoic extensional phase and oceanic crust formation in a precursor basin to the Aracuai Belt. Recrystallization of detrital zircon at ca. 630 Ma is compatible with a regional metamorphic event associated with terrane accretion to the Paleoproterozoic basement after transition from an extensional to a convergent regime. The juvenile nature, age spectra and trace element composition recorded in detrital zircons of metasediments from the Aracuai Belt correspond with zircons from metasedimentary rocks and oceanic crust remnants of other orogenic belts to its south. This suggests that rifting and oceanic crust formation of the entire orogenic system, the so-called Mantiqueira Province, was contemporaneous, most likely related to the opening of a large ocean. It further indicates that the cratonic blocks involved in the orogenic evolution of the Mantiqueira Province were spatially connected as early as 900 Ma.

Zircon U-Pb-Hf isotopes and mineral chemistry of Early Cretaceous granodiorite in the Lunggar iron deposit in central Lhasa, Tibet Y, China

The Lunggar iron deposit belongs to the Bangong-Nujiang metallogenic belt and is located in central Lhasa on the Tibetan Plateau.In the Lunggar deposit,iron mineralization formed in the skarnization contact zone between the Early Cretaceous granodiorite and the late Permian Xiala Formation limestone.In this study,we achieved detailed zircon U-Pb-Hf isotopes and mineral chemistry for the Early Cretaceous granodiorite.Zircon U-Pb dating results indicate that the Early Cretaceous granodiorite emplaced at ca.119 Ma.Based on the trace elements in zircons and the mineral chemical composition of amphibole and biotite,the Early Cretaceous granodiorite was believed to form under condition of high temperature(>700°C),low pressure(100400 MPa),and relatively high oxygen fugacity(lgfO2)(13.6 to 13.9)and H2O content(4%8%).Zircon trace elements,Hf isotope and biotite chemistry collectively reveal that significant juvenile mantle-derived magmas contributed to the source of the granodiorite.The relatively high logfO2 and shallow magma chamber are beneficial for skarn iron mineralization,implying remarkable potential for further prospecting in the Lunggar iron deposit.

Geochemistry and detrital zircon records of the Ruyang-Luoyu groups,southern North China Craton:Provenance,crustal evolution and Paleo-Mesoproterozoic tectonic implications

Paleo-to Mesoproterozoic sedimentary rocks in the southern margin of the North China Craton(NCC)are represented by the Ruyang and Luoyu groups.We studied the sedimentary rocks from the Yunmengshan and Beidajian formations of the Ruyang Group and the Cuizhuang and Sanjiaotang formations of the Luoyu Group.Detrital zircon grains from these formations have U–Pb age populations of 3.64–3.31 Ga,2.96–2.86 Ga,2.72–2.59 Ga,2.56–2.47 Ga,2.45–2.0 Ga,1.99–1.85 Ga and 1.84–1.65 Ga.The geochemical features of the sedimentary rocks suggest that some of the sediments were sourced from intermediate to felsic magmatic rocks.The age groups of the detrital zircon are roughly consistent with the tectono-thermal events in the southern margin of the NCC.The Hf isotopic compositions of detrital zircon from the sedimentary rocks in Ruyang and Luoyu groups suggest that significant crustal growth and reworking of the NCC took place during the Neoarchean and early-to mid-Paleoproterozoic,while crustal reworking at the Paleoarchean and late-Paleoproterozoic,and crustal growth at the Mesoarchean.We suggest the depositional times of the Ruyang Group and Luoyu Group are constrained to no older than 1.75–1.7 Ga and 1.7–1.65 Ga,respectively.Formation of late-Paleoproterozoic basins related to the strike slip and extrusion tectonics that cross-cut the NCC during the late Paleoproterozoic(<1.75 Ga),and the late Paleoproterozoic sedimentation once isochronous developed in the southern margin of the NCC through the Taihang region of the interior NCC and linked the Yanshan–Liaoxi regions of the northern NCC.

Neoproterozoic tectonic geography of the south-east Congo Craton in Zambia as deduced from the age and composition of detrital zircons

The Southern Irumide Belt(SIB)is an orogenic belt consisting of a number of lithologically varied Mesoproterozoic and Neoproterozoic terranes that were thrust upon each other.The belt lies along the southwest margin of the Archaean to Proterozoic Congo Craton,and bears a Neoproterozoic tectonothermal overprint relating to the Neoproterozoic-Cambrian collision between the Congo and Kalahari cratons.It preserves a record of about 500 million years of plate interaction along this part of the Congo margin.Detrital zircon samples from the SIB were analysed for U-Pb and Lu-Hf isotopes,as well as trace element compositions.These data are used to constrain sediment-source relationships between SIB terranes and other Gondwanan terranes such as the local Congo Craton and Irumide belt and wider afield to Madagascar(Azania)and India.These correlations are then used to interpret the Mesoproterozoic to Neoproterozoic affinity of the rocks and evolution of the region.Detrital zircon samples from the Chewore-Rufunsa and Kacholola(previously referred to as Luangwa-Nyimba)terranes of the SIB yield zircon U-Pb age populations and evolvedε(Hf)(t)values that are similar to the Muva Supergroup found throughout eastern Zambia,primarily correlating with Ubendian-Usagaran(ca.2.05-1.80 Ga)phase magmatism and a cryptic basement terrane that has been suggested to underlie the Bangweulu Block and Irumide Belt.These data suggest that the SIB was depositionally connected to the Congo Craton throughout the Mesoproterozoic.The more eastern Nyimba-Sinda terrane of the SIB(previously referred to as Petauke-Sinda terrane)records detrital zircon ages andε(Hf)(t)values that correlate with ca.1.1-1.0 Ga magmatism exposed elsewhere in the SIB and Irumide Belt.We ascribe this difference in age populations to the polyphase development of the province,where the sedimentary and volcanic rocks of the Nyimba-Sinda terrane accumulated in extensional basins that developed in the Neoproterozoic.Such deposition would have occurred following late-Mesoproterozoic magmatism that is widespread throughout both the Irumide and Southern Irumide Belts,presently considered to have occurred in response to collision between a possible microcontinental mass and the Irumide Belt.This interpretation implies a multi-staged evolution of the ocean south of the Congo Craton during the mid-Mesoproterozoic to late-Neoproterozoic,which ultimately closed during collision between the Congo and Kalahari cratons.

Detrital Zircon Records of the Banxi Group in the Western Jiangnan Orogen:Implications for Crustal Evolution of the South China Craton

The Neoproterozoic evolution of the Jiangnan Orogen is important for understanding the tectonic history of South China.As a volcanic-sedimentary sequence developed in the Nanhua rift,the Banxi Group preserves the records of important magmatic and tectonic events linked to the assembly and breakup of the Rodinia supercontinent.In this study,we report the results from whole-rock major-and trace-element concentrations,with zircon LA-(MC)-ICP-MS U-Pb ages,trace elements and Lu-Hf isotopic compositions of sandstones from the Banxi Group.The rocks are characterized by high SiO_(2)(65.88%–82.76%,with an average of 75.50%)contents,moderate(Fe_(2)O_(3)^(T)+MgO)(1.81%–7.78%,mean:3.79%)and TiO_(2)(0.39%–0.54%,mean:0.48%),low K_(2)O/Na_(2)O(0.03–0.40,mean:0.10)ratios and low Al_2O_(3)/SiO_(2)(0.11–0.24,mean:0.15)ratios.The sandstones have highΣREE contents(mean:179.1 ppm),with chondrite-normalized REE patterns similar to the upper crust and PAAS,showing enriched LREE((La/Yb)_N mean:14.85),sub-horizontal HREE curves and mild Eu(Eu/Eu^(*):0.75–0.89,mean:0.81)negative anomalies.Their geochemical characteristics resemble those of passive continental margin sandstones.Most of the zircons are magmatic in origin and yield a U-Pb age distribution with three peaks:a major age peak at 805 Ma and two subordinate age peaks at 1990 Ma and 2470 Ma,implying three major magmatic sources.The Neoproterozoic zircons haveε_(Hf)(t)values ranging from-47.4 to 12.4(mostly-20 to 0),suggesting a mixture of some juvenile arc-derived material and middle Paleoproterozoic heterogeneous crustal sources.The Hf model ages of middle Paleoproterozoic zircons(~1990 Ma)with negativeε_(Hf)(t)values(-12.65 to-6.21,Ave.=-9.8)concentrated around the Meso-Paleoarchean(mean T_(DM)^(C)=3.3–3.1 Ga).For late Neoarchean detrital zircons(~2470 Ma),ε_(Hf)(t)values are divided into two groups,one with negative values(-9.16 to-0.6)with model ages of 3.5–2.9 Ga,the other featuring positive values(1.0 to 3.9)with model ages of 2.9–2.7 Ga,recording a crustal growth event at~2.5 Ga.Neoproterozoic zircons show volcanic arc affinities with partly intraplate magmatic features.We propose that the Banxi Group formed in a rift basin within a passive continental margin setting,which derived detritus from felsic to intermediate rocks from the Yangtze Block and a small amount of arc volcanic rocks.The middle Paleoproterozoic detrital zircon data suggest Columbia-aged basement lies beneath the western Jiangnan orogen.

Detrital zircon geochronology and provenance of sediments within the Mesozoic basins:New insights into tectonic evolution of the Qinling Orogen

Mesozoic sedimentary units within the Nanzhao and Mashiping basins record the paleogeographic and tectonic evolution of the Qinling Orogen(QO).This study uses new detrital zircon U-Pb ages and Hf isotopic data to constrain the timing of deposition and provenance of the Taishanmiao,Taizishan,Nanzhao,and Mashiping formations of the North Qinling Orogen(NQO).The detrital zircons can be split by age peaks into five major groups,including Early Cretaceous,Late Triassic,Early Paleozoic,Neoproterozoic and Paleoproterozoic age peaks.On the basis of the youngest zircon ages and age-diagnostic fossils,we conclude that the Taishanmiao(youngest age of 234 Ma)and Taizishan(216 Ma)formations were deposited during the Late Triassic,whereas the Nanzhao Formation(110 Ma)was deposited during the Early Cretaceous rather than the Late Jurassic as previously thought.The Mashiping Formation(110 Ma)was also deposited during the Early Cretaceous.Combined with zircon Hf isotopic compositions,zircons from Late Triassic units were generally derived from the NQO,South Qinling Orogen(SQO),and North China Craton(NCC),with minor amounts derived from the Xing-Meng Orogenic Belt.The sediments within the Nanzhao Formation were mainly derived from the QO,with a minor contribution from the NCC.The Early Cretaceous conglomerates of the Mashiping Formation were generally derived from recycled earlier detritus.This implies that Late Triassic deposition was related to the final closure of the Mianlue Ocean,whereas Early Cretaceous deposition was correlated to the continued intercontinental subduction of the Yangtze Craton beneath the QO.The change in provenance within these Mesozoic sediments suggests the QO underwent two periods of significant uplift,which was a process generated sediments that were deposited in a series of basins of this area.

Paleozoic tectonic evolution of the proto-Korean Peninsula along the East Asian continental margin from detrital zircon U-Pb geochronology and Hf isotope geochemistry

Detrital zircon geochronology and Hf isotope analysis can be used for inferring provenance characteristics,and to evaluate the tectonic evolution of sedimentary basins and their link with regional orogenesis.The Paleozoic sequences of the Okcheon Belt consist of the Lower Paleozoic Joseon and the Upper Paleozoic Pyeongan supergroups with Middle Paleozoic hiatus locally on top of the Neoproterozoic bimodal volcanic rocks,reflecting an intracontinental rift setting between the two basements(viz.Gyeonggi and Yeongnam massifs)at southern part of the Korean Peninsula.Our detrital zircon U-Pb ages and Lu-Hf isotope results show that all these Paleozoic strata commonly have Paleoproterozoic and Paleozoic zircon ages with rare Meso-to Neoproterozoic ages.The individual zircon populations display following features,allowing estimation of their sedimentary provenances:(i)The Paleoproterozoic zircons(ca.1.85 Ga and 2.50 Ga)with similar ranges ofεHf(t)values are most common in the basement rocks of the Korean Peninsula,and were sourced from both the Gyeonggi and Yeongnam massifs.(ii)The Meso-to Neoproterozoic zircons,preserved only in the Middle to Late Cambrian clastic sedimentary rocks within the carbonate sequences probably reflect proximal provenance.(iii)The youngest Paleozoic zircons of each formation,almost coincident with their deposition ages,suggest presence of syndepositional magmatism,indicating proximal magmatic sources during their deposition.(iv)The Cambrian-Ordovician zircons,from the Lower Paleozoic sequences,but rare in the successive Upper Paleozoic sequences,suggest a provenance change after the hiatus between the two sedimentary successions.(v)The Permian zircons showing differentεHf(t)values indicate that detrital sources were varied at that time.The integrated results in our study suggest provenance variability linked to diverse tectonic environments,reflecting prolonged subduction-related crustal evolution of the proto-Korean Peninsula during the Paleozoic.

The complexity of sediment recycling as revealed by common Pb isotopes in K-feldspar

Detrital zircon U-Pb geochronology has become the gold standard in evaluating source to sink relationships in sedimentary basins. However, the physical and chemical robustness of zircon, which make it such a useful mineral for provenance studies, is also a hindrance as zircon can be recycled through numerous sedimentary basins, thus obscuring the first cycle source to sink relationship. An elegant approach to addressing this potential issue is to compare the Pb isotope composition of detrital K-feldspar, a mineral which is unlikely to survive more than one erosion-transport-deposition cycle, with that of magmatic K-feldspar from potential basement source terranes. Here we present new in situ Pb isotope data on detrital K-feldspar from two Proterozoic arkosic sandstones from Western Australia, and magmatic K-feldspar grains from potential igneous source rocks, as inferred by the age and Hf isotope composition of detrital zircon grains. The data indicate that the detrital zircon and K-feldspar grains could not have been liberated from the same source rocks, and that the zircon has most likely been recycled through older sedimentary basins. These results provide a more complete understanding of apparently simple source to sink relationships in this part of Proterozoic Western Australia.

赞皇杂岩翁城地区长城系常州沟组砂岩碎屑锆石U-Pb-Hf同位素研究

常州沟组是华北克拉通太古宙-古元古代变质基底上最早的沉积盖层之一,其碎屑锆石U-Pb年代学与Hf同位素特征分析对探讨长城系形成时代、源区特征以及基底演化均具有重要的研究意义。本文对华北克拉通中部赞皇杂岩瓮城地区长城系常州沟组底部砂岩样品进行了LA-ICP-MS碎屑锆石U-Pb定年和LA-MC-ICP-MS碎屑锆石Lu-Hf同位素分析。砂岩样品中碎屑锆石主要年龄峰值约为2 500 Ma,推断其碎屑物质主要来自于华北克拉通新太古代晚期变质基底,而最年轻的碎屑锆石年龄为1 822 Ma,结合赞皇杂岩变质基底普遍经历了1 850~1 800 Ma变质作用以及区域上上覆大红峪组火山岩中1 635 Ma结晶锆石年龄,限定瓮城地区长城系常州沟组沉积时代为1 800~1 635 Ma。砂岩样品中碎屑锆石的εHf(t)值变化于-6.8~+5.2之间,相应的两阶段模式年龄峰值约为2 820 Ma,结合赞皇杂岩已发表的2 900~2 700 Ma岩浆锆石和碎屑锆石Hf同位素结果,进一步表明2 900~2 700 Ma为赞皇杂岩地壳生长最主要的时期。综合太行山中南部地区已发表的长城系常州沟组的沉积学与新的年代学数据,推测赞皇杂岩瓮城地区长城系常州沟组沉积于陆内裂谷盆地。

A Deep Mantle Source for the Late Neoarchean Metamorphosed Basalts in Eastern Hebei,North China Craton:Insights from Whole-Rock Geochemistry and Sm-Nd Isotopes,and Zircon U-Pb-Hf Isotopes

The basalts within the greenstone belt worldwide serve as an ideal target to decipher the nature of Archean mantle sources and further to extend the understanding of the early stages of Earth's evolution.To provide important insights into the issues,we carried out a detailed investigation of whole-rock geochemistry and Sm-Nd isotopes,and zircon U-Pb-Hf isotopes for the Late Neoarchean metamorphosed basalts in eastern Hebei,North China Craton.U-Pb isotopic dating using the LA-ICPMS on zircons reveals that the basalts in eastern Hebei erupted at ca.2.48-2.51 Ga and subsequently experienced multiple regional metamorphic events at 2477 and 1798 Ma,respectively.The metamorphosed basalts are featured by low SiO_(2),MgO,K_(2)O+Na_(2)O,and high Fe O contents,endowed with the subalkaline and high-Fe tholeiitic affinities.The radiogenic initial Nd and Hf isotope values and correlations among V,Ni and Cr contents strongly imply that the basalts experienced significant clinopyroxene and olivine fractionation and minor crustal contamination during magma evolution.They are also characterized by the relatively low total REE contents and exhibit significant depletions to moderate enrichments in the LREE contents,indicating the derivation from a deep mantle source in an Archean proto-mantle plume setting.

吉林敦化地区万宝岩组碎屑锆石U-Pb-Hf同位素组成:对区域构造演化的制约

为制约古亚洲洋在吉林东部地区的最终闭合时间,本文选取吉林省敦化地区万宝岩组变质粉砂岩为研究对象,开展系统的碎屑锆石微量元素组成和U-Pb-Hf同位素研究,确定了万宝岩组的沉积时限和物源区特征,并通过碎屑锆石微量元素获得晚古生代地壳厚度的变化规律,探讨了华北板块北缘东段晚古生代的构造演化历史。万宝岩组由互层的大理岩、变质粉砂岩和变质细砂岩组成,碎屑锆石定年结果显示,万宝岩组最年轻峰值年龄约为316 Ma,此外还存在355、398、1 842和2 360 Ma的峰值年龄。其中,古生代碎屑锆石(409~312 Ma)以具有负的εHf(t)值(-15.32~-1.60)及新太古代—古元古代的TDM2年龄(2 293~1 480 Ma)为特征,侵入万宝岩组闪长岩体的时期为276 Ma。综合研究认为,敦化地区万宝岩组沉积时限为312~276 Ma,即早二叠世时期,其沉积时限和岩石组合特征可与延边地区的庙岭组相对比。万宝岩组中的古生代碎屑锆石来自华北板块太古宙—古元古代结晶基底物质的部分熔融。结合其中古元古代碎屑锆石(62.9%)的大量出现,暗示敦化地区或/和附近地区存在华北板块前寒武纪的结晶基底。通过地壳厚度计算表明,敦化地区和内蒙古地区晚古生代的地壳厚度变化趋势一致,说明二者晚古生代的演化历史趋于同步。约245 Ma地壳厚度达到最大(80 km),暗示了古亚洲洋的最终闭合。

U–Pb ages and Hf isotopes for detrital zircons from quartzite in the Paleoproterozoic Songshan Group on the southwestern margin of the North China Craton

In situ U-Pb dating and Lu-Hf isotopic analysis were carried out for detrital zircons from quartzite in the Paleoproterozoic Songshan Group on the southern margin of the North China Craton (NCC). The re- sults provide further constraints on the crustal formation and evolution history of NCC. Four 207Pb/206Pb age populations were obtained from 99 analyses, with clusters at ~3.40 Ga, 2.77―2.80 Ga, ~2.50 Ga and 2.34 Ga, respectively. The 3.40 Ga old zircons have similar Hf isotopic compositions to those from Ar- chean rocks in the Jidong and Anshan areas of NCC. However, crustal remnants older than 3.6 Ga have been identified in the southern margin of NCC, the South China Craton, the northwestern part of the Qinling Orogen and its adjacent area. Thus, it is not easy to trace the source rock from which the 3.40 Ga detrital zircons were derived. It can be inferred that the crustal remnants older than 3.40 Ga might have been widely distributed in the North China Craton. The 2.77―2.80 Ga zircons make up a relatively small proportion and have the highest εHf (t) values (up to 6.1±1.6), consistent with the Hf isotopic composition of the depleted mantle at 2.83 Ga. Their single-stage Hf model age of 2.83 Ga is close to their crystallized age, suggesting that their source rocks were extracted from the contemporaneous depleted mantle. The ~2.50 Ga zircon grains constitute about 85% of the total grain population and their Hf isotopic compositions indicate major growth of juvenile crust at ~2.50 Ga but minor reworking of ancient crust. The youngest zircon dated in this study gave an U-Pb age of 2337±23 Ma, which can be considered the maximum depositional age of the formation of the Songshan Group.

Provenance of Late Mesozoic Strata and Tectonic Implications for the Southwestern Ordos Basin,North China:Evidence from Detrital Zircon U-Pb Geochronology and Hf Isotopes

In order to determine the provenance and variation characteristics of sandstone-type uranium deposits located in the southwest Ordos Basin,U-Pb geochronology and Hf isotope analyses were conducted on detrital zircons from the Late Mesozoic strata of the SD01 well in the Zhenyuan area.The detrital zircon U-Pb ages of four samples exhibited four main peaks at 250–330,420–500,1720–2000,and 2340–2580 Ma,with a small number of zircons dated at 770–1100 Ma.The detrital zircon age spectrum and further restriction provided by the in-situ Hf isotopic data suggest that the provenance of each stratum was mainly derived from the crystalline basement rock series(Khondalites,intermediate-acidic intrusive rocks,and metamorphic rocks)of the Alxa Block to the northwest and the Yinshan Block to the north,with minor amounts of Caledonian magmatic rocks and Jingning Period rocks from the western part of the northern Qilian orogenic belt to the west and the northern Qinling orogenic belt to the south.The provenance of the sandbody has not changed significantly and is of the Middle Jurassic–Early Cretaceous.The clear variations in the zircon ages of the samples from the Zhiluo and Anding formations were likely influenced by climate change during the Middle–Late Jurassic.The Triassic zircon age(<250 Ma)first appeared in Early Cretaceous strata,suggesting that tectonic activity was relatively strong in the northern Qinling orogenic belt during the Late Jurassic and produced extensive outcrops of Indo-Chinese granite,which were a source of basin sediments.

Exploring the tectonostratigraphy of the Pakistan Himalaya with new detrital zircon geochronology and neodymium isotope data from the Kaghan Valley

In the central Himalaya,the Greater and Lesser Himalayan tectonostratigraphic zones can be distinguished from each other by combining detrital zircon U-Pb ages and whole-rock Nd isotopic data.In the Hazara-Kashmir syntaxis of northern Pakistan,rock units in the Kaghan valley have been variously assigned to the Tethyan,Greater,and Lesser Himalayan zones.To determine which tectonostratigraphic zones are represented,we sampled across the Batal thrust in the northern Kaghan valley because this structure is identified in some research as the Main Central thrust.Samples from the footwall yield Paleo-to Mesoproterozoic maximum depositional ages(-1.8-1.1 Ga)and an averageεNd(0)value of-14.3.Samples from the hanging wall yield Neoproterozoic maximum depositional ages(~1000-600 Ma)andεNd(0)values of-17.3.The contrasting detrital zircon ages show that the Batal thrust in the Kaghan valley is a major structural division.However,these data lack the characteristic detrital zircon age spectra andεNd(0)values of Greater and Lesser Himalayan rocks north and south of the Main Central thrust in the central Himalaya,respectively.Therefore,either the Batal thrust is not the Main Central thrust,or the Main Central thrust in the Kaghan valley cuts a different structural level and carries rock units not seen outside the Hazara-Kashmir syntaxis.

胶莱盆地早白垩世瓦屋夼组砂岩中碎屑锆石U-Pb-Hf同位素组成及其构造意义

本文报道了胶莱盆地莱阳群最底部瓦屋夼组长石石英砂岩中碎屑锆石的LA-ICP-MS U-Pb年代学和原位Hf同位素分析结果，进而约束了瓦屋夼组砂岩的沉积时代和物源及其构造意义。碎屑锆石多数呈自形–半自形晶，发育岩浆生长环带，暗示它们为岩浆成因；少数晚三叠世锆石呈均匀无结构的阴极发光特点，缺乏岩浆环带，暗示它们为变质锆石。82个谐和年龄的峰值分别为129 Ma、158 Ma、224 Ma、253 Ma、461 Ma、724 Ma、1851 Ma和2456 Ma。上述定年结果结合原位Hf同位素分析表明：（1）瓦屋夼组的沉积时代为早白垩世（129~106 Ma）；（2）1851 Ma、2456 Ma年龄的锆石主要来源于华北克拉通前寒武纪基底岩石；新元古代（729~721 Ma）岩浆锆石和晚三叠世（226~216 Ma）变质锆石来源于苏鲁造山带；晚古生代锆石记录了华北克拉通北缘同时代的岩浆事件；晚三叠世（231~223 Ma）岩浆锆石和158~129 Ma锆石则与胶北、胶东同时期的岩浆事件相对应；（3）胶莱盆地与合肥盆地具有不同的沉积时代和物源属性；（4）瓦屋夼组中苏鲁造山带物源的存在，暗示苏鲁高压–超高压变质岩石至少在早白垩世时期已经出露地表。

滇西保山地块早古生代碎屑锆石U-Pb-Hf同位素研究及其对冈瓦纳大陆重建的制约

滇西地区出露的古生界公养河群和孟定街群分别位于保山地块的西部和东部,其沉积时代、构造归属、碎屑物质来源及在早古生代冈瓦纳大陆重建中的古地理位置具有重要研究意义。本文对公养河群2个砂岩样品和孟定街群的4个变质砂岩样品的碎屑锆石进行U-Pb定年和Lu-Hf同位素分析。其中,公养河群的碎屑锆石年龄谱范围是3862~533Ma,εHf(t)值的范围是-37.8^+11.0,最小年龄峰期为549~533Ma,表明该群的最大沉积年龄为早寒武世早期,该群可能为寒武系地层。孟定街群的碎屑锆石年龄谱范围是3097~542Ma,εHf(t)值的范围是-39.5^+10.5,其最小年龄峰期(576~458Ma)将该群的沉积下限时代限制在晚奥陶世。结合保山地块的其他古生代地层的碎屑锆石研究,我们认为保山地块在早古生代位于冈瓦纳大陆北缘,物源主要来自印度大陆,但~1.17Ga年龄峰的出现说明其东部可能接受了一定比例来自西澳大利亚的沉积物质。这一结果表明保山地块在冈瓦纳大陆北缘重建中的位置应该靠近印度大陆,而其东缘接近澳大利亚大陆。

Detrital Zircon U-Pb Geochronology and Lu-Hf Isotopic Compositions of the Wuliangshan Metasediment Rocks in SW Yunnan(China)and Its Provenance Implications

The Wuliangshan Group occurs to the east of the Lancang giant igneous zone in SW Yunnan, and is mainly composed of low-grade metamorphosed sedimentary rocks. The group has been considered as the syn-orogenic product of the Baoshan with Simao-Indochina blocks. However, its depositional time and provenance remain to be poorly constrained. This paper presents zircon U-Pb dating and Lu-Hf-isotopic data for five representative sandstone samples from the Wuliangshan Group. The detrital grains yield a major age-peak at ~259 Ma, and four subordinary age-peaks at ~1 859, ~941, ~788, and ~447 Ma, respectively. Our results suggest that the Wuliangshan metasedimentary sequence was deposited after Middle Triassic rather than previously-thought Cambrian. The detrital zircon age spectrum, along with in-situ Lu-Hf isotopic data suggest that the Wuliangshan Group might be a syncollisional sedimentary product related to the collision of Baoshan with Simao-Indochina blocks. It is inferred that the provenance of the Wuliangshan Group is mainly from the Simao/Yangtze blocks to the east rather than the Baoshan Block or Lancang igneous zone to the west.