Jurassic detrital zircon U–Pb and Hf isotopic geochronology of Luxi Uplift,eastern North China,and its provenance implications for tectonic–paleogeographic reconstruction

Relatively successive sequences of Late Mesozoic are preserved and exposed in Luxi Uplift (LU), eastern North China block (NCB), which is an important region to study the late Mesozoic tectonic evolution of the eastern NCB. In this study, in situ U–Pb ages and Hf isotopic analyses on detrital zircons from the sandstones of Jurassic Fangzi and Santai Formations in LU combining the analysis of sandstone detrital modes were performed, with an aim to trace the Jurassic sediment provenances and the tectonic–paleogeographic configuration of eastern NCB. Three sandstone samples (one from Fangzi Formation and two from Santai Formation) have very similar U–Pb age spectrums which can be divided into three major groups: Phanerozoic (I), Paleoproterozoic (II), and Neoarchean (III). Detrital zircons of Group II and Group III broadly match the age spectra of the basement of NCC which exposed extensively in the northern part. No middle Neoproterozoic magmatic zircons or Triassic metamorphic zircons were found in this study, ruling out the clastic provenance transported from the Sulu orogen to LU. Dominant zircon populations of Group Iare Late Paleozoic (250–393 Ma) recording the corresponding magmatic activities which are not found both in LU and its peripheral tectonic terranes, but can be well compared with that of the northern NCB (NNCB) and the Xing-Meng Orogenic Belt (XMOB). Furthermore, Hf isotope compositions of the Phanerozoic detrital zircons can be distinctly divided into two clusters with ε_Hf(t) values ranging from −1.0 to +12.7 and −21.9 to −3.0, respectively resemble those from the XMOB and NCB (mainly from NNCB). Sandstone detrital modes analysis indicates the provenance came from the areas that have been eroded deeply to expose the basement rocks which accords with the tectonic setting of the NNCB. This research proposes that an evident mountain or provenance region once increasingly developed along NNCB during Early to Late Jurassic (182–155 Ma) due to the continuous collision of the Siberia and North China–Mongolian plates, easily shed mass clastic materials southward into the inner NCB and became the major provenance of Jurassic sediments in LU.     

Diagenesis of the Triassic Yanchang Formation Tight Sandstone Reservoir in the Xifeng–Ansai Area of Ordos Basin and its Porosity Evolution

This work aims to reveal the evolution of the porosity in the Triassic Yanchang Formation tight sandstone reservoir of the Xifeng–Ansai area of Ordos Basin. Based on destructive diagenesis(compaction and cementation) and constructive diagenesis(dissolution) of sandstone reservoirs, this study analyzed the diagenesis characteristics of the tight sandstone reservoirs in this area, and discussed the relationship between sandstone diagenesis and porosity evolution in combination with present porosity profile characteristics of sandstone reservoir. The effect simulation principle was employed for the mathematical derivation and simulation of the evolution of porosity in the Yanchang Formation tight sandstone reservoirs. The result shows that compaction always occurs in tight sandstone reservoirs in the Yanchang Formation, and cementation occurs when the burial depth increases to a certain value and remains ever since. Dissolution occurs only at a certain stage of the evolution with window features. In the corresponding present porosity profile, diagenesis is characterized by segmentation. From the shallow to the deep, compaction, compaction, cementation and dissolution, compaction and cementation occur successively. Therefore, the evolution of sandstone porosity can be divided into normal compaction section, acidification and incremental porosity section, and normal compaction section after dissolution. The results show that the evolution of sandstone porosity can be decomposed into porosity reduction model and porosity increase model. The superposition of the two models at the same depth in the three stages or in the same geological time can constitute the evolution simulation of the total porosity in sandstone reservoirs. By simulating the evolution of sandstone reservoir porosity of the eighth member in Xifeng area and the sixth member in Ansai area, it shows that they are similar in the evolution process and trend. The difference is caused by the regional uplift or subsidence and burial depth.     

Detrital zircon U–Pb ages of Late Triassic–Late Jurassic deposits in the western and northern Sichuan Basin margin: constraints on the foreland basin provenance and tectonic implications

Upper Triassic to Upper Jurassic strata in the western and northern Sichuan Basin were deposited in a synorogenic foreland basin. Ion–microprobe U–Pb analysis of 364 detrital zircon grains from five Late Triassic to Late Jurassic sandstone samples in the northern Sichuan Basin and several published Middle Triassic to Middle Jurassic samples in the eastern Songpan–Ganzi Complex and western and inner Sichuan Basin provide an initial framework for understanding the Late Triassic to Late Jurassic provenance of western and northern Sichuan Basin. For further understanding, the paleogeographic setting of these areas and neighboring hinterlands was constructed. Combined with analysis of depocenter migration, thermochronology and detrital zircon provenance, the western and northern Sichuan Basin is displayed as a transferred foreland basin from Late Triassic to Late Jurassic. The Upper Triassic Xujiahe depocenter was located at the front of the Longmen Shan belt, and sediments in the western Sichuan Basin shared the same provenances with the Middle–Upper Triassic in the Songpan–Ganzi Complex, whereas the South Qinling fed the northern Sichuan Basin. The synorogenic depocenter transferred to the front of Micang Shan during the early Middle Jurassic and at the front of the Daba Shan during the middle–late Middle Jurassic. Zircons of the Middle Jurassic were sourced from the North Qinling, South Qinling and northern Yangtze Craton. The depocenter returned to the front of the Micang Shan again during the Late Jurassic, and the South Qinling and northern Yangtze Craton was the main provenance. The detrital zircon U–Pb ages imply that the South and North China collision was probably not finished at the Late Jurassic.     

Geochemistry and zircon U–Pb geochronology of the Pulang complex,Yunnan province,China

The Pulang complex is located tectonically at the southern margin of the Yidun–Zhongdian island arc belt in Yunnan province, China, and is closely related to formation of the Pulang copper deposit, which is the largest copper deposit in Asia. The Pulang complex can be divided into three intrusion stages based on contact relationships and petrological characteristics: (1) a first stage of quartz dioritic porphyry; (2) a second stage of quartz monzonitic porphyry; and (3) a third stage of granodioritic porphyry. The crystallization ages of these intrusion stages were determined by single-zircon U–Pb dating, yielding ages of 221.0 ± 1.0, 211.8 ± 0.5, and 206.3 ± 0.7 Ma for the first, second, and third stages, respectively. These dates, integrated with previous geochronological data and field investigations, indicate that the second-stage quartz monzonitic porphyry has a close spatial and temporal relationship with the large Pulang porphyry copper deposit. These age data, geochemical and Sr–Nd isotopic results suggest that the Pulang complex formed in the Indo-Chinese epoch (257 ～ 205 Ma) by multiphase intrusion of a mixture of mantle- and crust-derived magmas.     

Study on oil–source correlation by analyzing organic geochemistry characteristics: a case study of the Upper Triassic Yanchang Formation in the south of Ordos Basin,China

In the south of the Ordos Basin, the oil source of the Upper Triassic Yanchang Formation is confused all the time, which affects further exploration. In this study, oil sources from the oil layers of Ch6, Ch8 and Ch9 are all analyzed and confirmed. Through their carbon isotope value and biomarkers, characteristics of crude oils from the Yanchang Formation are analyzed. Then, the oil–source relation is discussed, with the source rocks’ features. Finally, the oil–source relation is calculated through cluster analysis. It is believed that the oils from the Yanchang Formation deposit in a similar redox environment, with weak oxidation–weak reduction, and have all entered maturity stage. Ch9 crude oil is more mature than crude oils from Ch6 and Ch8, and has more advanced plants and fewer algae. Gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS) analysis show that crude oils from Ch6 and Ch8 may come from Ch7, and Ch9 crude oil may not. Cluster analysis displays that crude oils from Ch6 and Ch8 have closer squared Euclidean distance with Ch7 source rocks than Ch9 crude oil does, indicating crude oils from Ch6 and Ch8 stem from Ch7 source rocks. And Ch9 crude oil has rather close squared Euclidean distance with Ch9 source rocks, illustrating Ch9 crude oil may be from Ch9 source rocks. This research may provide the theoretical basis for the next exploration deploy in the south of Ordos Basin.     

Late Paleocene–early Eocene granitoids in the Jiamusi Massif,NE China: Zircon U–Pb ages,geochemistry, and tectonic implications

Northeast (NE) China is characterized by large areas of Mesozoic and Paleozoic granitoids, whereas Cenozoic granitoids are scarce. This paper reports LA-ICP-MS zircon U–Pb ages and whole-rock geochemical data for late Paleocene–early Eocene granitoids from the Jiamusi Massif, NE China, in order to determine their petrogenesis and tectonic implications. Geochronological data indicate that the granodiorite and dioritic porphyry from the Wudingshan pluton formed at 51.5 ± 0.3 Ma and 56.3 ± 0.8 Ma, respectively. The biotite–quartz diorite, biotite granodiorite, and dioritic porphyry have high SiO₂ (68.38–70.06 wt.%), Al₂O₃ (15.34–15.79 wt.%), and Na₂O (3.96–4.49 wt.%) contents, low MgO contents (1.10–1.26 wt.%), A/CNK ratios of 0.99–1.11, and are classified as medium- to high-K calc-alkaline and weakly peraluminous I-type granitoids. They are enriched in LREEs and LILEs, and depleted in HFSEs, with Nb/Ta ratios of 10.4–15.0. Moreover, they have negative Nb–Ta–Ti anomalies, indicating that they were derived from continental crust. Combining with the previously published isotopic data and regional geological results, we suggest that the late Paleocene–early Eocene granitoids (56–52 Ma) were probably derived from partial melting of juvenile lower crust, and formed in an active continental margin setting, possibly related to subduction slab rollback of the Paleo-Pacific Plate.     

The Palaeocene-early Oligocene Zacatecas conglomerate,Mexico: sedimentology,detrital zircon U–Pb ages,and sandstone provenance

ABSTRACT

This article presents detailed mapping results and the first U–Pb zircon dating and sedimentological characterization of the Zacatecas Conglomerate, which belongs to the Palaeogene red beds of central Mexico, deposited in fault-bounded basins during the Late Cretaceous to Eocene Laramide orogeny. The conglomerate was divided into five depositional facies associations according to their clast-type abundances and interlayered volcanic rocks. The lowermost member has a maximum depositional age based on young zircon grain ages varying from ca. 63 to 81 Ma. It is unconformably overlain by a continuous sequence characterized by a conglomerate rich in granite clasts at the bottom, with an interlayered tuff dated at 37.64 ± 0.36 Ma. Near the top, another tuff was dated at 30.84 ± 0.47 Ma, and a sandstone has a maximum depositional age of ca. 31.5 Ma. Normal grading, massive textures, channels, channel-form sandstone bodies, and upward-finning successions suggest that the Zacatecas Conglomerate is of fluvial origin. Late Jurassic to Early Cretaceous ages from zircons in plutonic rocks and sandstones bracket possible source regions for the Zacatecas Conglomerate. One possible source is Late Jurassic-Early Cretaceous granite derived from the Alisitos-Guerrero arc of western Mexico. Another possible source is the Tuna Manza Diorite, now exposed 250 km southeast of the study area. The lack of pre-Jurassic grains implies that possible sources such as the Nazas arc or the Potosí fan were not cropping out at that time, or at least that these areas were not affected by the fluvial system feeding the Zacatecas Conglomerate. It is possible that during the Palaeocene-early Oligocene the fluvial systems drained from west to east and from southeast to north, according to the above-mentioned constraints.     

Detrital zircon U–Pb geochronology of Permian strata in the Galilee Basin,Queensland, Australia

The late Carboniferous to Triassic tectonic history of eastern Australia includes important periods of regional-scale crustal extension and contraction. Evidence for these periods of tectonism is recorded by the extensive Pennsylvanian (late Carboniferous) to Triassic basin system of eastern Australia. In this study, we investigate the use of U–Pb dating of detrital zircons in reconstructing the tectonic development of one of these basins, the eastern Galilee Basin of Queensland. U–Pb detrital zircon ages were obtained from samples of stratigraphically well-constrained Cisuralian and Lopingian (early and late Permian, respectively) sandstone in the Galilee Basin. Detrital zircons in these sandstones are dominated by a population with ages in the range of 300–250 Ma, and ages from the youngest detrital zircons closely approximate depositional ages. We attribute these two fundamental findings to (1) appreciable derivation of detrital zircons in the Galilee Basin from the New England Orogen of easternmost Australia and (2) syndepositional magmatism. Furthermore, Cisuralian sandstone of the Galilee Basin contains significantly more >300 Ma detrital zircons than Lopingian sandstone. The transition in detrital zircon population, which is bracketed between 296 and 252 Ma based on previous high-precision U–Pb zircon ages from Permian ash beds in the Galilee Basin, corresponds with the Hunter–Bowen Orogeny and reflects a change in the Galilee Basin from an earlier extensional setting to a later foreland basin environment. During the Lopingian foreland basin phase, the individual depocentres of the Galilee and Bowen basins were linked to form a single and enormous foreland basin that covered >300 000 km² in central and eastern Queensland.     

Petrology,zircon U–Pb geochronology and tectonic implications of the A1-type intrusions: Keban region,eastern Turkey

The Southeast Anatolian Orogenic Belt (SAOB), the most extensive segment of the Alpine-Himalayan Orogenic Belt, resulted from the northward subduction of the southern branch of the Neotethys oceanic crust beneath the Anatolian micro-plate. We present new whole-rock geochemistry, zircon U–Pb ages, and Lu–Hf isotope data from the stocks and dykes with a length of up to tens of meters belonging to the Keban magmatic rocks, eastern Turkey. These rocks are represented by syenite and quartz monzonite intruded into the Keban metamorphic complex. The geochemistry data indicates that the samples bear mostly metaluminous, variably high alkalines (K₂O + Na₂O), Ga/Al ratios and zircon saturation temperature, and typically the A-type granite characters. According to the Y/Nb vs Yb/Ta diagram, the Keban magmatic rocks show A₁-type geochemical signatures modified by crustal melts. Syenite and quartz monzonite samples from Keban magmatic rocks give zircon U–Pb ages of 77.4 ± 0.34 Ma, 76.3 ± 0.3 Ma and 76.36 ± 0.34 Ma, respectively. On the primitive mantle-normalised trace element patterns, the Keban magmatic rocks show enrichment in large-ion lithophile elements (LILEs) relative to high field strength elements (HFSEs). They are coupled with slightly negative Nb–Ta anomalies. Chondrite-normalised rare earth-element patterns show strong enrichment in LREEs relative to HREEs, a typical A-type granites feature. The zircons have negative εHf_(t) values that vary from ?2.68 to ?0.41, and Hf model ages (T_DM2) range from 1171.54 to 1329.26 Ma, indicating the enriched lithospheric mantle sources and crustal contribution. The sources and evolution of the alkaline magmas might be related to the post-collisional tectonic setting.     

Crustal stabilization:Evidence from the geochemistry and U–Pb detrital zircon geochronology of quartzites from Simlipal Complex,Singhbhum Craton,India

Cratonic stabilization was a critical crustal process during the Hadean to Archean for the formation of cratons.The understanding of how and where this process took place is significant to evaluate the architecture of continents.The Singhbhum Craton of eastern India has well preserved Precambrian volcanosedimentary sequences.The Simlipal volcano-sedimentary complex of Singhbhum Craton consists of circular bands of mafic volcanic rocks interlayered with quartzites/shales/phyllites.In the present study,we report petrographic and geochemical characteristics of quartzites from Simlipal Complex coupled with U–Pb ages of detrital zircons and zircon geochemistry to understand the provenance and depositional conditions and its connection with the crustal stabilization in the Singhbhum Craton.The quartzites are texturally mature with sub-angular to sub-rounded quartz grains followed by feldspars embedded in a silty matrix.Based on modal compositions and major element ratios,these quartzites are categorized as quartz arenite and sub-lithic arenites.Trace element abundances normalized to Archean Upper Continental Crust(AUCC)display positive anomalies at U,Zr,Hf and negative anomalies at Nb.REE patterns are characterized by negative Eu anomalies(Eu/Eu^*=0.47–0.97)and flat HREE suggesting felsic provenance.These quartzites show depletion of LILE,enrichment of HFSE and transition metals relative to AUCC.High weathering indices such as CIA,PIA,and ICV are suggestive of moderate to intense chemical weathering.Low trace element ratios such as Th/Cr,Th/Sc,La/Sc,La/Co and Th/Co indicate a predominantly felsic source for these rocks.The overall geochemical signatures indicate passive margin deposition for these quartzites.Detrital zircons from the Simlipal quartzites yield U–Pb ages 3156±31 Ma suggesting Mesoarchean crustal heritage.The trace element geochemistry of detrital zircons suggests that the zircons are magmatic in origin and possibly derived from the 3.1 Ga anorogenic granite/granitoid provenance of Singhbhum Craton.These observations collectively indicate the Mayurbhanj Granite and Singhbhum Granite(SBG-III)provenance for these quartzites,thereby tracking the stabilization of the eastern Indian Shield/Singhbhum Craton back to Mesoarchean.     

Late Mesozoic magmatism from the Daye region,eastern China: U–Pb ages,petrogenesis, and geodynamic implications

Late Mesozoic dioritic and quartz dioritic plutons are widespread in the Daye region, eastern Yangtze craton, eastern China. Detailed geochronological, geochemical, and Sr–Nd isotopic studies have been undertaken for most of these plutons, in an attempt to provide a comprehensive understanding in the age, genesis and geodynamical control of the extensive magmatism. SHRIMP and LA-ICP-MS zircon U–Pb dating indicate that the plutons were emplaced in the range of latest Jurassic (ca. 152 Ma) to early Cretaceous (ca. 132 Ma), which was followed by dyke emplacement between 127 and 121 Ma and volcanism during the 130–113 Ma interval. Both diorites and quartz diorites are sodic, metaluminous, high-K calc-alkaline, and characterized by strongly fractionated, sub-parallel REE patterns without obvious Eu anomalies. The rocks are enriched in highly incompatible elements and large ion lithophile elements, but depleted in high field strength elements. Samples of diorite and quartz diorite have similar Sr–Nd isotopic compositions that are consistent with the early Cretaceous basalts and mafic intrusions throughout the eastern Yangtze craton. The geochemical and isotopic data, together with results of geochemical modeling, indicate an enriched mantle source for the plutonic rocks. The quartz diorites have geochemical signatures resembling adakites, such as high Al₂O₃ (15–19 wt.%), Sr (630–2,080 ppm), Na₂O (>3.5 wt.%), negative Nb–Ta anomalies, low Y (7–19 ppm), Yb (0.5–1.8 ppm), Sc (5–15 ppm), and resultant high Sr/Y (45–200) and La/Yb (31–63) ratios. Genesis of the adakitic quartz diorites is best explained in terms of low-pressure intracrustal fractional crystallization of cumulates consisting of hornblende, plagioclase, K-feldspar, magnetite, and apatite from mantle-derived dioritic magmas. Mantle-derived magmatism broadly coeval with that of the Daye region also is widespread in other regions of the eastern Yangtze craton, reflecting large-scale melting of the lithospheric mantle during the Late Mesozoic. The large-scale magmatism was most likely driven by lithospheric extension associated with thinning of lithospheric mantle beneath the eastern China continent.     

Contrasting provenance of Late Archean metasedimentary rocks from the Wutai Complex, North China Craton: detrital zircon U–Pb, whole-rock Sm–Nd isotopic, and geochemical data

Detrital zircon U–Pb ages, whole-rock Nd isotopic, and geochemical data of metasedimentary rocks from the Wutai Complex in the Central Zone, North China Craton, have been determined. Compositionally, these rocks are characterized by a narrow variation in SiO₂/Al₂O₃ (2.78–3.96, except sample 2007-1), variable Eu anomalies, spanning a range from significantly negative Eu anomalies to slightly positive anomalies (Eu/Eu* = 0.58–1.12), and positive ε _Nd (t) values (0.1–1.97). The 18 detrital zircons of one sample yielded age populations of 2.53 Ga, 2.60 Ga, and 2.70–2.85 Ga. Geochemical data reveal intermediate source weathering, varying degrees of K-metasomatism in the majority of these metasedimentary rocks, whereas other secondary disturbances seem to be negligible. Detailed analysis in detrital zircon U–Pb geochronology, whole-rock Nd isotope, and geochemistry shows that these metasedimentary rocks are derived from a mixed provenance. The predominant derivation is from the late Archean granitoids and metamorphic volcanics in the Wutai Complex, and there is also input of older continental remnants, except TTG gneisses, from the Hengshan and Fuping Complexes. The sediments were probably deposited in fore-arc or/and intra-arc basins within an arc system.     

U–Pb dating of detrital zircon grains in the Paleocene Stumpata Formation,Tethyan Himalaya,Zanskar, India

The sediments deposited on the northern margin of Greater India during the Paleocene allow the timing of collision with the Spontang Ophiolite, the oceanic Kohistan–Dras Arc and Eurasia to be constrained. U–Pb dating of detrital zircon grains from the Danian (61–65 Ma) Stumpata Formation shows a provenance that is typical of the Tethyan Himalaya, but with a significant population of grains from 129 ± 7 Ma also accounting for ∼15% of the total, similar to the synchronous Jidula Formation of south central Tibet. Derivation of these grains from north of the Indus Suture can be ruled out, precluding India’s collision with either Eurasia or the Kohistan–Dras before 61 Ma. Despite the immediate superposition of the Spontang Ophiolite, there are no grains in the Stumpata Formation consistent with erosion from this unit. Either Spontang obduction is younger than previously proposed, or the ophiolite remained submerged and/or uneroded until into the Eocene. The Mesozoic grains correlate well with the timing of ∼130 Ma volcanism in central Tibet, suggesting that this phase of activity is linked to extension across the whole margin of northern India linked to the separation of India from Australia and Antarctica at that time. Mesozoic zircons in younger sedimentary rocks in Tibet suggest a rapid change in provenance, with strong erosion from within or north of the suture zone starting in the Early Eocene following collision. We find no evidence for strongly diachronous collision from central Tibet to the western Himalaya.     

SIMS zircon U–Pb dating of the Late Cretaceous dinosaur egg-bearing red deposits in the Tiantai Basin,southeastern China

Dinosaur eggs or fragments are abundant and extensively distributed in China. They can be very informative in biostratigraphic division and correlation of continental strata where other fossils are relatively lacking. Despite remarkable discoveries of vertebrate fossils, particularly dinosaur eggs and skeletons from the middle and Late Cretaceous of both northern and southern China, there is hardly any direct evidence for the ages of the vertebrate-bearing terrestrial deposits. To constrain their depositional ages, here we have obtained SIMS U–Pb zircon ages from the tuffs interbedded with dinosaur egg-bearing sediments from the Laijia and Chichengshan formations of the terrestrial red deposits of the Late Cretaceous in the Tiantai Basin, Zhejiang Province, southeastern China. The SIMS zircon U–Pb ages from the Laijia and Chichengshan formations are about 96–99 Ma (Cenomanian) and 91–94 Ma (Turonian), respectively, providing direct time constraints on the vertebrate and dinosaur egg evolution in the Late Cretaceous as well as a basis for correlation with terrestrial Cretaceous deposits in other regions of southern and northern China.     

Sedimentological characteristics and new detrital zircon SHRIMP U–Pb ages of the Babulu Formation in the Fohorem area,Timor-Leste

Sedimentological characteristics and zircon provenance dating of the Babulu Formation in the Fohorem area, Timor-Leste, provide new insights into depositional process, detailed sedimentary environment and the distribution of source rocks in the provenance. Detrital zircon sensitive high-resolution ion microprobe (SHRIMP) U–Pb ages range from Neoarchean to Triassic, with the main age pulses being Paleozoic to Triassic. In addition, the maximum deposition ages based on the youngest major age peak (ca 256–238 Ma) of zircon grains indicate that the basal sedimentation of the Babulu Formation occurred after the early Upper Triassic. The formation consists predominantly of mudstone with minor sandstone, limestone and conglomerate that were deposited in a deep marine environment. These deposits are composed of six lithofacies that can be grouped into three facies associations (FAs) based on the constituent lithofacies and bedding features: basin plain deposits (FA I), distal fringe lobe deposits (FA II) and medial to distal lobe deposits (FA III). The predominance of mudstone (FA I) together with intervening thin-bedded sandstones (FA II) suggest that the paleodepositional environment was a low energy setting with slightly basin-ward input of the distal part of the depositional lobes. Discrete and abrupt occurrences of thick-bedded sandstone (FA III) within the FA I mudstone suggests that sandstone originated from a collapse of upslope sediments rather than a progressive progradation of deltaic turbidites. This combined petrological and geochronological study demonstrates that the Babulu Formation in the Fohorem area of the Timor-Leste was initiated as a submarine lobe system in a relatively deep marine environment during the Upper Triassic and represents the extension of the Gondwana Sequence at the Australian margin.     

The formation and rejuvenation of continental crust in the central North China Craton: Evidence from zircon U–Pb geochronology and Hf isotope

The Trans-North China Orogen (TNCO) along the central part of the North China Craton (NCC) is considered as a Paleoproterozoic suture along which the Eastern and Western Blocks of the NCC were amalgamated. Here we investigate the Precambrian crustal evolution history in the Fuping segment of the TNCO and the subsequent reactivation associated with extensive craton destruction during Mesozoic. We present zircon LA-ICP-MS U–Pb and Lu–Hf data on TTG (tonalite–trondhjemite–granodiorite) gneiss, felsic orthogneiss, amphibolite and granite from the Paleoproterozoic suite which show magmatic ages in the range of 2450–1900 Ma suggesting a long-lived convergent margin. The ε_Hf(t) values of these zircons range from −11.9 to 12 and their model ages suggest magma derivation from both juvenile components and reworked Archean crust. The Mesozoic magmatic units in the Fuping area includes granite, diorite and mafic microgranular enclaves, the zircons from which define a tight range of 120–130 Ma ages suggesting a prominent Early Cretaceous magmatic event. However, the ε_Hf(t) values of these zircons show wide a range from −30.3 to 0.2, indicating that the magmatic activity involved extensive rejuvenation of the older continental crust.     

The U–Pb ages and Hf isotopes of detrital zircons from Hainan Island,South China: implications for sediment provenance and the crustal evolution

In situ U–Pb dating and Hf isotopic of detrital zircons from beach sediments of Yalong Bay were analyzed to trace sedimentary provenance and reveal the crustal evolution of Hainan Island in South China. The grain size distribution of the sediments displays a clear single-peak feature, indicating the sediments were formed under the same condition of hydrodynamic force. The detrital zircons had Th/U ratios of greater than 0.1, and REE pattern displayed a positive Ce anomaly and a negative Eu anomaly, indicating that these zircons are predominantly of magmatic origin. The U–Pb spectrum of detrital zircons mainly peaked at the Yanshanian (96–185 Ma), Hercynian–Indosinian (222–345 Ma) and Caledonian (421–477 Ma). A portion of the detrital zircons were of Neoproterozoic origin (728–1,003 Ma), which revealed that the basement in the eastern region of Hainan Island was mainly of Neoproterozoic, with rare Archean materials. The positive ε _Hf(t) values (0 to +10.1) of the Neoproterozoic detrital zircons indicated that the juvenile crust grew in the southeastern Hainan Island mainly during the Neoproterozoic period. The Neoproterozoic orogeny in the southeastern part of the island (0.7–1.0 Ga) occurred later than in the northwestern region of the island (1.0–1.4 Ga). Importantly, the Grenvillian orogeny in the southeastern area of Hainan Island shared the same timing with that of the western Cathaysia Block; i.e., both areas concurrently underwent this orogenic event, thereby forming a part of the Rodinia supercontinent. Afterwards, the crust experienced remelting and reworking during the Caledonian Hercynian–Indosinianand Yanshanian accompanied by the growth of a small amount of juvenile crust.     

Petrogenesis of the Wudaogou intermediate–mafic complex,NW China: zircon U–Pb dating,whole-rock and isotope geochemistry,and geological implications

The Wudaogou plutonic complex is located in the eastern Yanbian area of Jilin Province and consists of hornblende gabbros, gabbroic diorites, and quartz diorites that contain abundant dioritic microgranular xenoliths. Zircon U–Pb dating of gabbroic and quartz diorites yielded weighted mean ²⁰⁶Pb/²³⁸Pb ages of 263.5 ± 5.1 Ma (N = 12, mean squared weighted deviation (MSWD) = 0.78, probability = 0.66) and 262.0 ± 5.6 Ma (N = 10, MSWD = 0.50, probability = 0.87), respectively. These units are characterized by high Na₂O/K₂O (0.33–0.77) ratios and Al₂O₃ (15.05–18.91 wt%) concentrations and are large ion lithophile element (LILE) (light rare earth element (LREE), Rb, Ba, K, etc.) enriched and high field strength element (HFSE) (Nb, Ta, P, Ti) depleted. They also have initial ⁸⁷Sr/⁸⁶Sr values of 0.70192–0.70420 and ?_Nd(t) values of +1.9 to +4.7 with two-stage model ages (T_DM2) of 653–878 Ma. These characteristics indicate that these rocks formed from calc–alkaline magmas derived from partial melting of a mixture of juvenile crust formed attending the Neoproterozoic subduction of the Palaeo-Asian oceanic crust and lower crustal material. The dioritic xenoliths have whole-rock compositions that are similar to their host rocks, but with negative ?_Nd(t) values (?1.6 to ?4.3) and older T_DM2 ages (1166–1382 Ma), further indicating that this magmatic event involved older crustal material. Combining these data with existing knowledge of the crustal evolution of this area, we conclude that this complex formed in a post-collisional extensional setting during closure of the Palaeo-Asian Ocean.