Crustal Accretion and Reworking within the Khanka Massif: Evidence from Zircon Hf Isotopes of Phanerozoic Granitoids

The Central Asian Orogenic Belt(CAOB)is one of the largest Phanerozoic accretionary orogen.(Windley et al.,1990,2007;Jahn et al.,2000a,b,c;Yakubchuk,2002,2004;Xiao et al.,2003,2004).It is the optimal study area for revealing the accretion and reworking processes of the continental crust.The Khanka Massif is located in the most eastern part of the CAOB,and mainly crops out in the territory of Russia,with a small segment in NE China.In addition,a large number of multi-stage granitic rocks are formed in geological evolution in this area,recording amounts of information about crustal accretion and reworking processes(De Paolo et al.,1991;Rudnick,1995;Wu et al.,2011).In view of this,this paper uses the spatial-temporal variations of trace elements and zircon Hf isotopic compositions of phanerozoic granitoids within the Khanka Massif as a case to reveal the crustal accretion and reworking processes of micro continental massifs from the orogenic belt,further to understand the formation and evolution processes and mechanisms of the global continental crust.According to the statistics of zircon U-Pb ages of granitoids in the Khanka Massif,indicate that the granitic magmatisms in the Khanka Massif have eleven peaks:492 Ma,460 Ma,445Ma,430Ma,425Ma,302Ma,287Ma,258Ma,249 Ma,216Ma and 213Ma,it can be divided into eight main stages:Late Cambrian,Middle-Late Ordovician,Middle Silurian,Late Carboniferous,EarlyPermian,Middle-Late Permian—Early Triassic,Late Triassic-Early Jurassic,Early Cretaceous.The Phanerozoic granitoids in Khanka massif are selectedinthispaperasasuiteof granodiorite-monzogranite-syenogranite.TheSi O2contents of the Phanerozoic granitoids exceed 65%,and has high Al2O3,low Mg#,TFe2O3,Cr,Co and Ni contents.This suggests that mixture with mantle-derived magma did not occur,and it should be a typical crustal source(Lu and Xu,2011).Combined with evident characteristics of light rare-earth elements(LREEs)and large ion lithophile elements(LILEs)enrichment,and heavy rare-earth elements(HREEs)and high field-strength elements(HFSEs)loss,we suggest that the primary magma was derived by partial melting of lower crustal material(Xu et al.,2009),and geochemical properties of the Phanerozoic granitoids essentially reflect the nature of the magmatic source region.According to the temporal variation of zircon Hf isotopic data of Phanerozoic granitioids,zircon Hf isotopic compositions of Phanerozoic granitoids have a obvious correlation with age.With the decrease of formation time ofthePhanerozoicgranitoids(Late Cambrian~Middle-LateOrdovician~Middle Silurian~EarlyPermian~Middle-LatePermian–Early Triassic~Late Triassic-Early Jurassic),εHf(t)values of zircons gradually increase,whereas their TDM2 ages gradually decrease(Paleoproterozoic–Neoproterozoic),suggesting that the generation of granitic magmas from the Khanka Massif could have experienced the change from the melting of the ancient crust to the juvenile crust during Paleozoic to Mesozoic.According to the sample location,it can be found thatεHf(t)values of Phanerozoic granitoids have the tendency to decrease with latitude increase,showing that components of the ancient continental crust gradually increase from south to north.However,at the same latitude range,theεHf(t)values of Phanerozoic granitoids also inconsistent.Taken together,these differences reveal the horizontal and vertical heterogeneity of the lower continental crust within the Khanka Massif.According to the relative probability of two-stage model(TDM2)ages of zircon Hf isotope from Phanerozoic granitoids within the Khanka massif,it could be divided into three stages:(1)Late Paleoproterozoic(2)Mesoproterozoic(3)Neoproterozoic.It reveals that the main part of the continental crust within the Khanka MassifwereformedinLate Paleoproterozoic–Neoproterozoic.The Phanerozoic granitoids in the Khanka Massif reworked from the source rockswithdifferent ages(Paleoproterozoic–Mesoproterozoic–Neoproterozoic).     

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.     

Permian Tectonic Evolution in Southwestern Khanka Massif: Evidence from Zircon U‐Pb Chronology,Hf isotope and Geochemistry of Gabbro and Diorite

Laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating and geochemical data for the Permian gabbros and diorites in the Hunchun area are presented to constrain the regional tectonic evolution in the study area. Zircons from gabbro and diorite are euhedral-subhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios (0.26–1.22), implying their magmatic origin. The dating results indicate that the gabbro and diorite formed in the Early Permian (282±2 Ma) and in the Late Permian (255±3 Ma), respectively. In addition, the captured zircons with the weighted mean age of 279±4 Ma are also found in the diorite, consistent with the formation age of the gabbro within uncertainty. The gabbros belong chemically to low-K tholeiitic series, and are characterized by low rare earth element (REE) abundances, flat REE pattern, weak positive Eu anomalies (δEu), and depletion in high field strength elements (HFSEs, Nb, Ta, and Ti), similar to the high-aluminum basalts from island arc setting. Initial Hf isotopic ratios of zircons from the gabbro range from +7.63 to +14.6, suggesting that its primary magma could be mainly derived from partial melting of a depleted lithospheric mantle. The diorites belong to middle K calc-alkaline series. Compared with the gabbros, the diorites have higher REE abundance, weak negative Eu anomalies, and more depletion in HFSEs (Nb, Ta, and Ti), similar chemically to the volcanic rocks from an active continental margin setting. Initial Hf isotopic ratios and Hf two-stage model ages of zircons from the diorite range from +11.22 to +14.17 and from 424 to 692 Ma, respectively, suggesting that its primary magma could be mainly derived from partial melting of the Early Paleozoic and/or Neoproterozoic accretted lower crust. Taken together, it is suggested that geochemical variations from the Early Permian gabbros to the Late Permian diorites reveal that the subduction of the Paleo-Asian oceanic plate beneath the Khanka Massif and collision between the arc and continent (Khanka Massif) happened in the late stage of the Late Paleozoic.     

Hydrothermal Zircon Geochronology in the Shangxu Gold Deposit and its Implication for the Early Cretaceous Orogenic Gold Mineralization in the Middle Bangonghu–Nujiang Suture Zone

As a typical orogenic gold deposit in Tibet, Shangxu gold deposit is located at the Bangong Lake–Nujiang River Metallogenic Belt in the south of Qinghai–Tibet Plateau. In this paper, zircon U-Pb dating, trace elements and Hf isotopic analysis were performed on Au-bearing quartz veins in the Shangxu gold deposit. Zircons from Au-bearing quartz veins can be divided into three types: detrital, magmatic, and hydrothermal zircons. There are two age peaks in detrital zircons: ca. 1700 Ma and ca. 2400 Ma. There are two groups of concordant ages including 157 ± 4 Ma(MSWD = 0.69) and 120 ± 1 Ma(MSWD = 0.19) in magmatic zircons, in which εH f(t) value of ca. 120 Ma from the magmatic zircons range from +8.24 to +12.9. An age of 119 ± 2 Ma(MSWD = 0.42) was yielded from hydrothermal zircons, and their εH f(t) values vary between +15.7 and +16.4. According to sericite Ar-Ar age, this paper suggests that an age of 119 ± 2 Ma from hydrothermal zircons represent the formation age of the Shangxu gold Deposit, and its mineralization should be related to the collision between Lhasa Block and Qiangtang Block. The metallogenic age is basically the same as the diagenetic age of Mugagangri granite, and εH f(t) value of hydrothermal zircon is significantly higher than that of the contemporaneous magmatic zircon, which indicates that there is a genetic relationship between the gold mineralization and the deep crust-mantle magmatism.     

Neoproterozoic Crustal Reworking and Growth in the Zhangbaling Uplift, Tan–Lu Fault Zone: Evidence from the Feidong Complex and Zhangbaling Group

Intensive mid-Neoproterozoic magmatism is the salient feature of the Yangtze Block, preserving abundant information about crustal reworking and growth. Zircon U–Pb–Lu–Hf isotope analysis was performed on material from the Feidong Complex (FDC) and Zhangbaling Group (ZBLG) of the Zhangbaling Uplift, in order to determine the age and magmatic source of the Neoproterozoic igneous rocks as well as the detrital provenance for the sedimentary rocks, to further provide important data for understanding the mid-Neoproterozoic crustal evolution of the Northeast Yangtze Block. The amphibolite and gneissic granites in the Feidong Complex (FDC) gave similar protolith ages of 782–776 Ma. The synmagmatic zircons exhibited variable negative εHf(t) values of ?26.9 to ?8.3. Early (ca. 2.4 Ga) to late Paleoproterozoic (ca. 2.0–1.9 Ga) inherited zircons were found in the gneissic monzogranite, with negative εHf(t) values of ?11.2 to ?7.2, indicating strong reworking of the ancient crustal materials of the Northeast Yangtze Block. Whereas the amphibolites represent minor crustal growth through emplacement of continental rifting-related mafic magmas. The quartz–keratophyres in the Xileng Formation of the ZBLG in contrast systematically yield young protolith crystallization ages of 754–727 Ma with high εHf(t) values of ?2.0 to +5.6, indicating their derivation from the reworking of juvenile crustal materials. The detrital zircons from the metasiltstone in the Beijiangjun Formation yield variable 206Pb/238U ages (871–644 Ma) with a peak age at 741 ± 11 Ma and εHf(t) values of ?4.3 to +5.3, which is consistent with those of the Xileng Formation, but distinct from the FDC, indicating that the provenance of the metasiltstone is primarily the underlying Xileng Formation. The mid-Neoproterozoic igneous and sedimentary rocks of the Zhangbaling Uplift were products from continental rifting zones along the northern margin of the Yangtze Block, situated in different positions from the Susong Complex and the Haizhou Group. The transition from ancient to juvenile crustal sources for felsic magmatic rocks is attributed to gradually increased crustal extension during continental rifting.     

Age and Origin of Paleogene Granitoids from Western Yunnan Province, China: Geochemistry, SHRIMP Zircon Ages, and Hf-in-Zircon Isotopic Compositions

We report geochemical data, SHRIMP zircon ages and Hf-in-zircon isotopic compositions for Cenozoic granitoids from major fault systems in the Tethyan belt in western Yunnan Province, southwestern China.Four magmatic pulses occurred in the Paleogene, namely at ca.57 Ma, ca.50 Ma, 45–40 Ma, and 38–34 Ma.Early magmatism of this episode(57–50 Ma) produced S-type granites whose zircons yielded εHf(t) values of-5.0 to-0.3.In contrast, late magmatism of this episode reflects heterogeneous sources.Zircons from a granite porphyry along the Ailaoshan-Red River fault system have slightly positive εHf(t) values suggesting derivation from relatively young crust and/or a juvenile source.However, zircons from a granite along the Gaoligong fault system have strongly negative εHf(t) values and suggest derivation from a Paleoproterozoic crustal source.The composition of the granitoids varies with age(from ca.57 Ma to ca.34 Ma) from peraluminous to metaluminous and also suggests a change from syn-collisional to late-orogenic tectonic setting.A new tectonic model, impacting lithospheric wedge(ILW) is shown for the origin of Paleogene granitoids in this paper.     

Geochemical and Nd-Hf Isotopic Constraints on the Petrogenesis of an Archean Granitoid in the Erguna Massif,NE China

Crystalline basement and Precambrian crustal growth of the continental massifs within the Central Asian Orogenic Belt (CAOB) are still pending problems. Our geological and geochemical investigations identified an Archean (2606 Ma) granitic pluton in the Biliya area of the Erguna Massif. The Neoarchean granitoids show high and positive in-situ zircon εHf(t) (+0.3 to +10.0), whole-rock εNd(t) (+4.8) and whole-rock εHf(t) values (+2.1). They are characterized by high Y + Ce + Zr + Nb (> 220 ppm) and Zr contents and could be classified as A-type granites. These granitoids are characterized by high Zr saturation temperatures (TZr) (796–836°C). They were derived from partial re-melting of juvenile mafic lower crust in an intracontinental back-arc extensional environment. This newly identified Neoarchean granitic pluton may represent the crystalline basement of the several continent massifs within the CAOB, and their high ?Hf(t)–?Nd(t) values may also indicate the occurrence of lateral crustal growth events in these massifs during the Neoarchean.     

Early Neoarchean Magmatic and Paleoproterozoic Metamorphic Events in the Northern North China Craton: SHRIMP Zircon Dating and Hf Isotopes of Archean Rocks from the Miyun Area, Beijing

The Miyun area of Beijing is located in the northern part of the North China Craton(NCC)and includes a variety of Archean granitoids and metamorphic rocks.Magmatic domains in zircon from a tonalite reveal Early Neoarchean(2752±7 Ma) ages show a small range in ε_(Hf)(t) from 3.1 to 7.4and t_(DM1)(Hf) from 2742 to 2823 Ma,similar to their U-Pb ages,indicating derivation from a depleted mantle source only a short time prior to crystallization.SHRIMP zircon ages of granite,gneiss,amphibolite and hornblendite in the Miyun area reveal restricted emplacement ages from 2594 to2496 Ma.They also record metamorphic events at ca.2.50 Ga,2.44 Ga and 1.82 Ga,showing a similar evolutionary history to the widely distributed Late Neoarchean rocks in the NCC.Positive ε_(Hf)(t) values of 1.5 to 5.9,with model ages younger than 3.0 Ga for magmatic zircon domains from these Late Neoarchean intrusive rocks indicate that they are predominantly derived from juvenile crustal sources and suggest that significant crustal growth occurred in the northern NCC during the Neoarchean.Late Paleoproterozoic metamorphism developed widely in the NCC,not only in the Trans-North China Orogen,but also in areas of Eastern and Western Blocks,which suggest that the late Paleoproterozoic was the assembly of different micro-continents,which resulted in the final consolidation to form the NCC,and related to the development of the Paleo-Mesoproterozoic Columbia or Nuna supercontinent.     

Oldest Basement (ca. 462 Ma) in Indonesian Borneo and its Implication for Early Paleozoic Tectonic Evolution of SE Asia

The lack of preserved basement results in uncertain placements of many terranes in Southeast Asia. Here, we flag the first evidence of the oldest basement in Indonesian Borneo, which can help locate terranes in Borneo on the northern margin of Gondwana in the early Paleozoic and explain the regional tectonic setting of the island. Two schist samples from the Embuoi Complex in the Semitau Block, Northwest Kalimantan yielded zircon U-Pb dates of 453.3 ± 1.9 Ma and 462.4 ± 2.6 Ma, respectively, representing the formation time of the protolith. Petrographic, internal structural and high Th/U ratios of zircons indicate that the protolith of schists is of magmatic origin. The zircons have εHf(t) values of ?4.1 to +1.1 and Hf model ages of 1.37–1.69 Ga, indicating they were derived from a mixed source of juvenile crust with old components. By comparison of zircon age distribution, two-stage Hf model ages and εHf(t) variations of the early Paleozoic igneous rocks from Semitau with those of South China, Tengchong–Baoshan, and Indochina, the Semitau Block was most likely a part of or placed next to the Indochina Block of northern Gondwana during the early Paleozoic. Such a similar tectono-magmatic pattern on northern Gondwana formed a prolonged early Paleozoic arc-related belt associated with subduction of the Proto-Tethyan Ocean.     

Ages,Sources and Tectonic Settings of the Triassic Igneous Rocks in the Easternmost Segment of the East Kunlun Orogen,Central China

U–Pb analysis of zircons from igneous rocks in the Elashan Mountain, easternmost segment of the East Kunlun Orogen yielded 252–232 Ma. Geochemically, these rocks are mainly high in SiO_2, K_2O and K_2O+Na_2O contents, low in P_2O_5 and TiO_2 contents, depleted in Ba, Sr, P, Ti and enriched in U, Hf, Zr, showing features of I–type granite. The zircon εHf(t) values of the Early Triassic Jiamuge'er rhyolite porphyry(252±3 Ma) are positive(+1.6 to +12.1), suggesting a juvenile crustal source mixing with little old crustal component, and the zircon εHf(t) values of the Middle Triassic Manzhang'gang granodiorite(244±3 Ma) and Dehailong diorite(237±3 Ma) are predominately negative(-8.4 to +1.0), indicating an older crustal source. In comparison, the zircon εHf(t) values of the Late Triassic syenogranites from Suigen'ergang(234±2Ma), Ge'ermugang(233±2 Ma) and Yue'ergen(232±3 Ma) plutons vary from-3.8 to +5.0, suggesting a crust-mantle mixing source. From Early–Middle Triassic(252–237 Ma) to Late Triassic(234–232 Ma), the geochemical characteristics of these rocks show the change from a subduction–collision setting to a post-collision or within-plate setting. By comparing of these new age data with 77 zircon U–Pb ages of igneous rocks of the eastern part of East Kunlun orogen from published literatures, we conclude that the igneous rocks of Elashan Mountain and these of the eastern part of East Kunlun Orogen belong to one magmatic belt. All these data indicate that the Triassic magmatic events of the eastern part of East Kunlun Orogen can be divided into three stages: 252–238 Ma, 238–226 Ma and 226–212 Ma. Statistically, the average εHf(t) values of the threestage igneous rocks show a tendency, from the old to young, from-0.75±0.25 to lower-2.65±0.52 and then to-1.22±0.25, respectively, which reveal the change of their sources. These characteristics can be explained as a crust-mantle mixing source generated in a subductional stage, mainly crust source in a syn–collisional stage and a crust-mantle mixing source(lower crust with mantle-derived underplating magma) in a post-collisional stage. The identification of these three magmatic events in the Elashan Mountain, including all the eastern part of East Kunlun Orogen, provides new evidence for better understanding of the tectonic evolution of the northward subduction and closure of the Paleo-Tethyan(252–238 Ma), the collision of the Songpan–Ganzi block with the southern margin of Qaidam block(238–226 Ma), and the post–collisional setting(226–212 Ma) during the Early Mesozoic period.     

S?o Francisco-Congo Craton break-up delimited by U-Pb-Hf isotopes and trace-elements of zircon from metasediments of the Ara?uaí 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.     

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 εHf(t) and TDM2 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 positive εHf(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 and εHf(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.     

Geochronology and geochemistry of early Paleozoic intrusive rocks from the Khanka Massif of the Russian Far East

The Russian Far East and Northeast(NE)China are located in the eastern part of the Central Asian Orogenic Belt(CAOB),which consists of a series of micro-continental massifs including the Erguna,Xing’an,Songnen–Zhangguangcai Range,Bureya,Jiamusi,and Khanka massifs.The Khanka Massif is located in the easternmost part of the CAOB,mainly cropping out in the territory of Russia,with a small segment in NE China.To the north and west of the Khanka Massif are the Jiamusi and Songnen–Zhangguangcai Range massifs,respectively.The boundary between these massifs is marked by the Dunhua–Mishan Fault.To the south lies the North China Craton,and to the east is the Sikhote–Alin Orogenic Belt separated by the Arsenyev Fault.However,the early Paleozoic evolution and tectonic attributes of the Khanka Massif are debated.These conflicting ideas result from the lack of systematic research on early Paleozoic igneous rocks from the Russian part of the Khanka Massif.It is generally accepted that the CAOB represents the largest known Phanerozoic accretionary orogenic belt.However,questions remain concerning the nature of the deep crust beneath the Khanka Massif,and whether Precambrian crust exists within the massif itself. In this paper,we report new zircon U–Pb ages,Hf isotopic data,and major-and trace-element compositions of the early Paleozoic intrusive rocks from the Khanka Massif of the Russian Far East,with the aim of elucidating the early Paleozoic evolution and the tectonic attributes of the Khanka Massif,as well as the nature of the underlying deep crust. New U–Pb zircon data indicate that early Paleozoic magmatism within the Khanka Massif can be subdivided into at least four stages:~502 Ma,~492 Ma,462–445 Ma,and~430 Ma. The~502 Ma pyroxene diorites show negative Eu anomalies,and the~492 Ma syenogranites,intruding the~502 Ma diorites,show positive Eu anomalies.These observations indicate that the primary parental magmas of these rocks were derived from different origins. The 462–445 Ma magmatism is made up of syenogranites and tonalites.The~445 Ma Na-rich tonalites contain low REE concentrations,and are enriched in Eu and Sr.These observations,together with the positiveεHf(t)values,indicate that they were derived from magmas generated by partial melting of cumulate gabbros. The~430 Ma I-type granodiorites and monzogranites from the northern Khanka Massif,and the A-type monzogranites from the central Khanka Massif display zirconεHf(t)values ranging from–5.4 to+5.8.This suggests that they formed from magmas generated by partial melting of heterogeneous lower crustal material. Zircon Hf isotopic data reveal the existence of Precambrian crustal material within the Khanka Massif.The geochemistry of the Middle Cambrian intrusive rocks is indicative of formation in an extensional setting,while Late Cambrian–middle Silurian magmatism was generated in an active continental margin setting associated with the subduction of a paleo-oceanic plate beneath the Khanka Massif.Regional comparisons of the magmatic events indicate that the Khanka Massif has a tectonic affinity to the Songnen–Zhangguangcai Range Massif rather than the Jiamusi Massif.     

Paleoproterozoic juvenile magmatism within the northeastern sector of the São Francisco paleocontinent: Insights from the shoshonitic high Ba–Sr Montezuma granitoids

New,integrated petrographic,mineral chemistry,whole rock geochemical,zircon and titanite UPb geochronology,and zircon Hf isotopic data from the Montezuma granitoids,as well as new geochemical results for its host rocks represented by the Corrego Tingui Complex,provides new insights into the late-to post-collisional evolution of the northeastern Sao Francisco paleocontinent.U-Pb zircon dates from the Montezuma granitoids spread along the Concordia between ca.2.2 Ga to 1.8 Ga and comprise distinct groups.Group I have crystallization ages between ca.2.15 Ga and 2.05 Ga and are interpreted as inherited grains.Group II zircon dates vary from 2.04 Ga to1.9 Ga and corresponds to the crystallization of the Montezuma granitoids,which were constrained at ca.2.03 Ga by the titanite U-Pb age.Inverse age zoning is common within the ca.1.8 Ga Group III zircon ages,being related to fluid isotopic re-setting during the Espinhaco rifiting event.Zircon ε_(Hf)(t) analysis show dominantly positive values for both Group I(-4 to+9) and Ⅱ(-3 to+8) zircons and T_(DM2) model ages of 2.7-2.1 Ga and 2.5-1.95 Ga,respectively.Geochemically,the Montezuma granitoids are weakly peraluminous to metaluminous magnesian granitoids,enriched in LILES and LREE,with high to moderate Mg#and depleted in some of the HFSE.Their lithochemical signature,added to the juvenile signature of both inherited and crystallized zircons,allowed its classification as a shoshonitic high Ba-Sr granitoid related to a late-to post-collisional lithosphere delamination followed by asthenospheric upwelling.In this scenario,the partial melting of the lithospheric mantle interacted with the roots of an accreted juvenile intra-oceanic arc,being these hybrid magma interpreted as the source of the Montezuma granitoids.The Corrego Tingui Complex host rocks are akin to a syn-to late-collisional volcanic arc granitoids originated from the partial melting of ancient crustal rocks.The results presented in this study have revealed the occurrence of juvenile rocks,probably related to an island arc environment,that are exotic in relation to the Paleo-to Neoarchean crust from the Sao Francisco paleocontinent's core.     

Zircon Geochronology and Trace Element Geochemistry from the Xiaozhen Copper Deposit, North Daba Mountain: Constraints on Albitites Petrogenesis

Albitite often accompanies with various metal and gem mineral deposits and a large number of occurrences have been reported globally, including the South Qinling orogen, China. The Xiaozhen copper deposit is a typical deposit in the North Daba Mountain area of the South Qinling orogen whose distribution is controlled by albitite veins and fractures. As there are few studies on the petrogenesis of albitite in Xiaozhen copper deposit, this paper focuses on the petrogenesis of albitite and its mineralization age. Detailed fieldwork and mineral microscopic observations initially suggest that albitite from the Xiaozhen copper deposit is igneous in origin. Further zircon trace element geochemistry studies indicate that these zircons have high Th/U ratios(0.5), low La content, high(Sm/La)N and Ce/Ce*values, and a strong negative Eu anomaly, which are commonly seen in magmatic zircons. The chondrite–normalized rare earth element(REE) patterns are consistent with magmatic zircons from throughout the world, and they fall within or near the field of magmatic zircons on discriminant diagrams. The calculated average apparent Ti–in–zircon temperature for young zircons is 780°C, consistent with magmatic zircon crystallization temperatures. Therefore, zircon geochemistry indicates that the albitite origin is magmatic. SIMS U–Pb dating on nine magmatic zircons yielded a concordia age of 154.8±2.2 Ma, which represents the formation of albitite and the metallogenic age. More importantly, it is consistent with the ages of Yanshanian magmatism and metallogenesis in the South Qinling orogen, so formation of the Xiaozhen copper deposit may be a closely related geological event.     

Geochemistry, Geochronology and Lu-Hf Isotopes of Peraluminous Granitic Porphyry from the Walegen Au Deposit, West Qinling Terrane

Walegen Au deposit is closely correlated with granitic intrusions of Triassic age, which are composed of granite and quartz porphyries. Both granite porphyry and quartz porphyry consist of quartz, feldspar and muscovite as primary minerals. Weakly peraluminous granite porphyry(A/CNK=1.10–1.15) is enriched in LREE, depleted in HREE with Nb-Ta-Ti anomalies, and displays subduction-related geochemistry. Quartz porphyry is strongly peraluminous(A/CNK=1.64–2.81) with highly evolved components, characterized by lower TiO_2, REE contents, Mg~#, K/Rb, Nb/Ta, Zr/Hf ratios and higher Rb/Sr ratios than the granite porphyry. REE patterns of quartz porphyry exhibit lanthanide tetrad effect, resulting from mineral fractionation or participation of fluids with enriched F and Cl. LAICP-MS zircon U-Pb dating indicates quartz porphyry formed at 233±3 Ma. The ages of relict zircons from Triassic magmatic rocks match well with the detrital zircons from regional area. In addition, ε_(Hf)(t) values of Triassic magmatic zircons from the granite and quartz porphyries are -14.2 to -9.1(with an exception of +4.1) and -10.8 to -8.6 respectively, indicating a crustal-dominant source. Regionally, numerous Middle Triassic granitoids were previously reported to be formed under the consumption of Paleotethyan Ocean. These facts indicate that the granitic porphyries from Walegen Au deposit may have been formed in the processes of the closing of Paleotethyan Ocean, which could correlate with the arc-related magmatism in the Kunlun orogen to the west and the Qinling orogen to the east.     

Emplacement Ages and Petrogenesis of the Molybdenum–bearing Granites in the Jinduicheng Area of East Qinling, China: Constraints from Zircon U–Pb Ages and Hf Isotopes

The Mesozoic porphyry assemblage in the Jinduicheng area is a special molybdenum area in China, the Mo deposits, including the Jinduicheng, Balipo, Shijiawan, Huanglongpu, are distributed. The emplacement age and geochemical features of the granites in the Jinduicheng area can provide essential information for the exploration and development of the porphyry molybdenum deposit. In this study, we report LA–ICP–MS zircon U–Pb age and zircon Hf isotopic compositions of granite porphyries from the Jinduicheng area, and provide insights on the petrogensis and source characteristics of the granites. The results show that the zircon U–Pb ages of the Jinduicheng granite porphyry (143±1 Ma) and the Balipo granite (154±1 Ma), agree well with the Re–Os ages of molybdenite in the Jinduicheng molybdenum polymetallic deposit (139±3 Ma) and the Balipo molybdenum polymetallic deposit (156±2 Ma), indicating that the emplacement of granite porphyries occurred between Late Jurassic and Early Cretaceous. Zircons granite from the Jinduicheng area give the εHf(t) values mainly ranging from ?10 to ?16, and ?20 to ?24, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.86–2.0 Ga, and 2.2–2.6 Ga, respectively) of zircons of the granite from the Jinduicheng values. The ore–forming materials are mainly derived from crust, with minor mantle substances. Zircons of the granite from the Balipo area give εHf(t) values ranging from ?18 to ?20, ?28 to ?38, and ?42 to ?44, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.88–3.0 Ga, and 3.2–3.90 Ga, respectively). the εHf(t) values of the Jinduicheng porphyry more than that of the Balipo porphyry, and two–stage model ages (tDM2) less than that of the Balipo porphyry, shows that he source of the porphyries originated from ancient lower crustal materials in the Jinduicheng area, and mixed younger components, more younger components contributed for the source of the Jinduicheng porphyry.     

Integration of zircon and apatite U–Pb geochronology and geochemical mapping of the Wude basalts(Emeishan large igneous province):A tool for a better understanding of the tectonothermal and geodynamic evolution of the Emeishan LIP

Radiogenic isotopic dating and Lu–Hf isotopic composition using laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS)of the Wude basalt in Yunnan province from the Emeishan large igneous province(ELIP)yielded timing of formation and post-eruption tectonothermal event.Holistic lithogeochemistry and elements mapping of basaltic rocks were further reevaluated to provide insights into crustal contamination and formation of the ELIP.A zircon U–Pb age of 251.3±2.0 Ma of the Wude basalt recorded the youngest volcanic eruption event and was consistent with the age span of 251-263 Ma for the emplacement of the ELIP.Such zircons hadε_Hf(t)values ranging from7.3 to+2.2,identical to those of magmatic zircons from the intrusive rocks of the ELIP,suggesting that crust-mantle interaction occurred during magmatic emplacement,or crust-mantle mixing existed in the deep source region prior to deep melting.The apatite U–Pb age at 53.6±3.4 Ma recorded an early Eocene magmatic superimposition of a regional tectonothermal event,corresponding to the Indian–Eurasian plate collision.Negative Nb,Ta,Ti and P anomalies of the Emeishan basalt may reflect crustal contamination.The uneven Nb/La and Th/Ta values distribution throughout the ELIP supported a mantle plume model origin.Therefore,the ELIP was formed as a result of a mantle plume which was later superimposed by a regional tectonothermal event attributed to the Indian–Eurasian plate collision during early Eocene.     

Provenance of Conglomerate and Sandstone from Early Permian Shoushangou Formation in Xi Ujimqin, Inner Mongolia: Implications for Understanding Paleo-Asian Ocean Subduction

During the Late Carboniferous to Early Permian, a rift was formed by post-collisional extension after ocean closure or an island arc-related basin formed by Paleo-Asian Ocean (PAO) subduction in the Xi Ujimqin area. Nevertheless, the closure time of the PAO is still under debate. Thus, to identify the origin of the PAO, the geochemistry and U-Pb age of zircons were analyzed for the extra-large deep marine, polymict clastic boulders and sandstones in the Shoushangou Formation within the basin. The analyses revealed magmatic activity and tectonic evolution. The conglomerates include megaclasts of granite (298.8 ± 9.1?Ma) and granodiorite porphyry (297.1 ± 3.1?Ma), which were deposited by muddy debris flow. Results of this study demonstrated that the boulders of granitoids have the geochemistry of typical I-type granite, characterized by low Zr + Nb + Ce + Y and low Ga/Al values. The granitoid boulders were formed in island arc setting, indicating the presence of arc magmatism in the area that is composed of the Late Carboniferous to Early Permian subduction-related granitoid in southern Xi Ujimqin. Multiple diagrams for determining sedimentary provenance using major and trace elements indicate that Shoushangou sediments originated from continental island arc-related felsic rocks. Detrital zircon U-Pb age cluster of 330–280?Ma was obtained, indicating input from granite, ophiolite, Xilin Gol complex, and Carboniferous sources to the south. The basin was geographically developed behind the arc during the Early Permian period because the outcropped intrusive rocks in the Late Carboniferous to Early Permian form a volcanic arc. The comprehensive analyses of source areas suggest that Shoushangou sediments developed in a backarc basin in response to the northward subduction of the PAO. The backarc basin and intrusive rocks, in addition to previously published Late Carboniferous to Early Permian magmatic rocks of arc unit in Xilin Gol, confirm the presence of an Early Permian trench-arc-basin system in the region, represented by the Baolidao arc and Xi Ujimqin backarc basin. This study highlights the importance and potential of combined geochemical and geochronological studies of conglomerates and sandstone for reconstructing the geodynamic setting of a basin.     

Paleozoic post-collisional magmatism and high-temperature granulite-facies metamorphism coupling with lithospheric delamination of the East Kunlun Orogenic Belt,NW China

Lithosphere extension and upwelling of asthenosphere at post-collisional stage of an orogenic cycle generally induce diverse magmatism and/or associated high-temperature metamorphism. Nevertheless, the intimate coexistence of post-collisional magmatic activity and high-temperature metamorphism is rare.In this contribution, a lithological assemblage composing of diverse magmatic rocks deriving from distinct magma sources and coeval high-temperature metamorphism was identified in eastern Kunlun.Petrography, ages, mineral chemistry and whole-rock geochemistry demonstrated that those intimately coexistent diverse rocks were genetically related to post-collisional extension. The garnet-bearing mafic granulites in Jinshuikou area interior of the East Kunlun Orogenic Belt are mainly composed of garnet,orthopyroxene, and plagioclase, with peak metamorphic P–T conditions of ~ 701–756 ℃and 5.6–7.0 kbar,representing a granulite-facies metamorphism at 409.7 ± 1.7 Ma. The diverse contemporaneous magmatic rocks including hornblendites, gabbros and granites yield zircon U–Pb ages of 408.6 ± 2.5 Ma,413.4 ± 4.6 Ma, and 387–407 Ma, respectively. The hornblendites show N-MORB-like REE patterns with(La/Sm)Nvalues of 0.85–0.94. They have positive zircon εHf(t) values of 0.1–4.9 and whole-rock εNd(t) values of 3.9–4.7 but relatively high(⁸⁷Sr/⁸⁶Sr)_ivalues of 0.7081 to 0.7088. These features demonstrate that the hornblendites derived from a depleted asthenospheric mantle source with minor continental crustal materials in source. As for the gabbros, they exhibit arc-like elemental signatures, low zircon εHf(t) values(-4.3 to 2.5) and variable whole-rock εNd(t) values(-4.9 to 1.2) as well as high(⁸⁷Sr/86 Sr)ivalues(0.7068 to 0.7126), arguing for that they were originated from partial melting of heterogeneous lithospheric mantle anteriorly metasomatized by subducted-sediment released melts. Geochemistry of the granites defines their strongly peraluminous S-type signatures. Zircons from the granites yield a large range of εHf(t) values ranging from -30.8 to -5.1, while the whole-rock samples yield consistent(⁸⁷Sr/86 Sr)ivalues(0.7301 to 0.7342) and negative εNd(t) values(-10.1 to -12.4). These features indicate that the S-type granites could be generated by reworking of an ancient crust. Taken together, the penecontemporaneous magmatism and metamorphic event, demonstrated the early-middle Devonian transition from crustal thickening to extensional collapse. The post-collisional mantle-derived magmas serve as an essential driving force for the high-temperature granulite-facies metamorphism and anataxis of the crust associated with formation of S-type granite. This study not only constructs a more detail Proto-Tethys evolution process of the eastern Kunlun, but also sheds new light on better understanding the intimate relationship between magmatism and metamorphism during post-collisional extensional collapse.