Constructing the latest Neoproterozoic to Early Paleozoic multiple crust-mantle interactions in western Bainaimiao arc terrane,southeastern Central Asian Orogenic Belt

Identifying the crust-mantle interactions in association with the evolution of the Precambrian microcontinents provides critical constraints on the accretionary evolution in the Central Asian Orogenic Belt(CAOB).The Bainaimiao arc terrane(BAT)is one of the most important Precambrian microcontinents in southeastern CAOB,however,few studies have paid attention to the types and the evolving processes of the crust-mantle interactions that occurred before its final accretion onto the northern North China Craton.This study presents an integrated study of geochronology,zircon Hf isotope and whole-rock geochemistry on the latest Neoproterozoic diabases and the Early Paleozoic arc intrusions in the western BAT.The latest Neoproterozoic(ca.546 Ma)diabases display low SiO2(46.52-49.24 wt.%)with high MgO(8.23-14.41 wt.%),Cr(66-542 ppm)and Ni(50-129 ppm),consisting with mantle origin.Their highly negative zirconεHf(t)(-12.0 to-24.7)and high Fe/Mn ratios(62.1-81.7)further indicate a significantly enriched mantle source.Considering that the BAT maybe initially separated from the Tarim Craton with a thickened crustal root,we propose that these diabases were generated through partial melting of an enriched lithospheric mantle source that had been hybridized by lower-crustal eclogites during foundering of the BAT lower crust.The Early Paleozoic(ca.475-417 Ma)arc intrusions in western BAT can be divided into PeriodsⅠandⅡat approximately 450 Ma.The PeriodⅠ(>450 Ma)intrusions contain abundant mafic minerals like hornblende and pyroxene,and show positive zirconεHf(t)(+1.5 to+10.9).They are predominantly medium-K calc-alkaline with broad correlations of SiO2 versus various major and trace elements,which correlate well with the experimental melts produced by the fractional crystallization of primitive hydrous arc magmas at 7 kbar.We assume they were formed through mid-crustal differentiation of the mantle wedge-derived hydrous basaltic melts.By contrast,the PeriodⅡ(≤450 Ma)intrusions are characterized by variable zircon eHf(t)(-15.0 to+11.5)with irregular variations in most major and trace elements,which are more akin to the arc magmas generated in an open system.The general occurrence of elder inherited zircons,along with the relatively high Mg#(>45)of some samples,call upon a derivation from the reworking of the previously subduction-modified BAT lower crust with the input of mantle-derived mafic components.In combination with the Early Paleozoic tectonic melanges flanking western BAT,we infer that the compositional transition from PeriodⅠtoⅡcan be attributed to the tectonic transition from south-dipping subduction of Solonker ocean to north-dipping subduction of South Bainaimiao ocean in southeastern CAOB.The above results shed light not only on the latest Neoproterozoic to Early Paleozoic multiple crust-mantle interactions in western BAT,but also on the associated crustal construction processes before the final arc-continent accretion.

Petrogenesis of the Late Triassic shoshonitic Shadegai pluton from the northern North China Craton: Implications for crust-mantle interaction and post-collisional extension

Latest Permian to Triassic plutons are widespread in the northern North China Craton(NCC); most of them show calc-alkaline, high-K calc-alkaline, or alkaline geochemical features. The Shadegai pluton in the Wulashan area has shoshonitic affinity and I-type character, and is composed of syenogranites containing abundant mafic microgranular enclaves(MMEs). LA-MC-ICP-MS U-Pb data yield weighted mean 206 Pb/238 U ages of 222 ± 1 Ma and 221 ± 1 Ma for the syenogranites and MMEs, respectively, suggesting their coeval formation during the Late Triassic. The syenogranites have high SiO_2(70.42-72.30 wt%),K_2O(4.58-5.22 wt.%) and Na_2O(4.19-4.43 wt.%) contents but lower concentrations of P_2O_5(0.073-0.096 wt.%) and TiO_2(0.27-0.37 wt.%), and are categorized as I-type granites, rather than A-type granites, as previously thought. These syenogranites exhibit lower(^(87)Sr/^(86)Sr)i ratios(0.70532-0.70547) and strongly negative whole-rock εNd(t) values(-12.54 to-11.86) and zircon εHf(t) values(-17.81 to-10.77),as well as old Nd(1962-2017 Ma) and Hf(2023-2092 Ma) model ages, indicating that they were derived from the lower crust.Field and petrological observations reveal that the MMEs within the pluton probably represent magmatic globules commingled with their host magmas. Geochemically, these MMEs have low SiO_2(53.46-55.91 wt.%)but high FeOt(7.27-8.79 wt.%) contents. They are enriched in light rare earth elements(LREEs) and large ion lithophile elements(LILEs), and are depleted in heavy rare earth elements(HREEs) and high field strength elements(HFSEs). They have whole-rock(^(87)Sr/^(86)Sr)i ratios varying from 0.70551 to 0.70564, εNd(t) values of -10.63 to -9.82, and zircon εHf(t) values of -9.89 to 0.19. Their geochemical and isotopic features indicate that they were derived from the subcontinental lithospheric mantle mainly metasomatized by slab-derived fluids, with minor involvement of melts generated from the ascending asthenospheric mantle. Petrology integrated with elemental and isotopic geochemistry suggest that the Shadegai pluton was produced by crust-mantle interactions, i.e., partial melting of the lower continental crust induced by underplating of mantle-derived mafic magmas(including the subcontinental lithospheric mantle and asthenospheric mantle), and subsequent mixing of the mantle-and crust-derived magmas. In combination with existing geological data, it is inferred that the Shadegai pluton formed in a post-collisional extensional regime related to lithospheric delamination following the collision between the NCC and Mongolia arc terranes.

Study of crust-mantle transitional zone along the northeast margin of Qinghai-Xizang plateau

This study deals with complexity, frequency spectrum and velocity model of the crust-mantle transitional zone in different tectonic units along the northeast margin of Qinghai-Xizang plateau, based on PmP waveform data from two deep seismic sounding profiles passing through the area. It reveals that Moho has stable tectonic features in Ordos and Lingzhong basins, where crust and mantle are coupled as first-order discontinuity. Moho shows obvious signs of activity in Haiyuan seismic region and in the contact zone between Bayanhar block and Qaidam block.Crust and mantle in these two areas are coupled as complicated crust-mantle transitional zone consisting of multiple laminae with alternate high and low velocities, totaling 20 km in thickness. The difference between Moho of different tectonic units reflects heterogeneity of the coupled crust-mantle zone; the difference between fine structures of Haiyuan seismic region and Maqin fault zone reflects different deep material composition of the two continent-continent collision zones and the interaction between blocks.

Upper crustal anisotropy from local shear-wave splitting and crust-mantle coupling of Yunnan,SE margin of Tibetan Plateau

The upper crustal anisotropy of Yunnan area, SE margin of Tibetan Plateau, is investigated by measuring the shear wave splitting of local earthquakes. The mean value of the measured delay times is 0.054 s and far less than that from Pms splitting analysis, indicating that the crustal anisotropy is contributed mostly from mid-lower crust. The fast polarization directions are mostly sub-parallel to the maximum horizontal compression directions while the stations near fault zones show fault-parallel fast polarization directions, suggesting both stress and geological structure contribute to the upper crust anisotropy.Comparing fast polarization directions from shear wave splitting of local earthquakes and Pms, large angle differences are shown at most stations, implying different anisotropy properties between upper and mid-lower crust. However, in southwestern Yunnan, the fast polarization directions of Pms and Swave splitting are nearly parallel, and the stress and surface strain rate directions show strong correlation, which may indicate that the surface and deep crust deformations can be explained by the same mechanism and the surface deformation can represent the deformation of the whole crust. Therefore,the high correlation between surface strain and mantle deformation in this area suggests the mechanical coupling between crust and mantle in southwestern Yunnan. In the rest region of Yunnan, the crustmantle coupling mechanisms are supported by the lack of significant crustal anisotropy with Ne S fast polarization directions from Pms splitting. Therefore, we conclude that the crust and upper mantle are coupled in Yunnan, SE margin of Tibetan Plateau.

A model of crust-mantle differentiation for the early Earth

The Archean continents,primarily composed of the felsic tonalite-trondhjemite-granodiorite(TTG)suite,were formed or conserved since~3.8 Ga,with significant growth of the continental crust since~2.7 Ga.The difficulty in direct differentiation of the felsic crustal components from Earth’s mantle peridotite leads to a requirement for the presence of a large amount of hydrated mafic precursor of TTG in Earth’s proto-crust,the origin of which,however,remains elusive.The mafic proto-crust may have formed as early as~4.4 Ga ago as reflected by the Hf and Nd isotopic signals from Earth’s oldest geological records.Such a significant time lag between the formation of the mafic proto-crust and the occurrence of felsic continental crust is not reconciled with a single-stage scenario of Earth’s early differentiation.Here,inspired by the volcanism-dominated heat-pipe tectonics witnessed on Jupiter’s moon Io and the resemblances of the intensive internal heating and active magmatism between the early Earth and the present-day Io,we present a conceptual model of Earth’s early crust-mantle differentiation,which involves an Io-like scenario of efficient extraction of a mafic proto-crust from the early mantle,followed by an intrusion-dominating regime that could account for the subsequent formation of the felsic continents as Earth cools.The model thus allows an early formation of the preTTG proto-crust and the generation of TTG in the continent by providing the favorable conditions for its subsequent melting.This model is consistent with the observed early fractionation of the Earth and the late but rapid formation and/or accumulation of the felsic components in the Archean continents,thus sheds new light on the early Earth’s differentiation and tectonic evolution.

Crust-mantle structure under South Pole and Ross Sea Beach in Antarctica

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Seismic anisotropy of upper mantle in eastern Tibetan Plateau and related crust-mantle coupling pattern

By using the polarization analysis of teleseismic SKS waveform data recorded at 116 seismic stations which respectively involved in China National Digital Seismograph Network, and Yunnan, Sichuan, Gansu and Qinghai regional digital networks, and portable broadband seismic networks deployed in Sichuan, Yunnan and Tibet, we obtained the SKS fast-wave direction and the delay time between fast and slow waves of each station by use of the stacking analysis method, and finally acquired the fine image of upper mantle anisotropy in the eastern Tibetan Plateau and its adjacent regions. We analyzed the crust-mantle coupling deformation on the basis of combining the GPS observation results and the upper mantle anisotropy distribution in the study area. The Yunnan region out of the plateau has dif-ferent features of crust-mantle deformation from the inside plateau. There exists a lateral transitional zone of crust-mantle coupling in the eastern edge of the Tibetan Plateau, which is located in the region between 26° and 27°N in the west of Sichuan and Yunnan. To the south of transitional zone, the fast-wave direction is gradually turned from S60°―70°E in southwestern Yunnan to near EW in south-eastern Yunnan. To the north of transitional zone in northwestern Yunnan and the south of western Sichuan, the fast-wave direction is nearly NS. From crust to upper mantle, the geophysical parameters (e.g. the crustal thickness, the Bouguer gravity anomaly, and tectonic stress direction) show the feature of lateral variation in the transitional zone, although the fault trend on the ground surface is inconsis-tent with the fast-wave direction. This transitional zone is close by the eastern Himalayan syntaxis, and it may play an important role in the plate boundary dynamics.

Late Mesozoic crust-mantle interaction in southeastern Fujian——Isotopic evidence from the Pingtan igneous complex

UNDERPLATING Of mantle-derived basaltic magma and interacting with the lower crust materials are believed to be an important mechanism for the growth and transformation of the crust.

Subduction-zone peridotites and their records of crust-mantle interaction

Subduction is the core process of plate tectonics. The mantle wedge in subduction-zone systems represents a key tectonic unit, playing a significant role in material cycling and energy exchange between Earth's layers. This study summarizes research progresses in terms of subduction-related peridotite massifs, including supra-subduction zone(SSZ) ophiolites and mantle-wedge-type(MWT) orogenic peridotites. We also provide the relevant key scientific questions that need be solved in the future. The mantle sections of SSZ ophiolites and MWT orogenic peridotites represent the mantle fragments from oceanic and continental lithosphere in subduction zones, respectively. They are essential targets to study the crust-mantle interaction in subduction zones. The nature of this interaction is the complex chemical exchanges between the subducting slab and the mantle wedge under the major control of physical processes. The SSZ ophiolites can record melt/fluid-rock interaction, metamorphism,deformation, concentration of metallogenic elements and material exchange between crust and mantle, during the stages from the generation of oceanic lithosphere at spreading centers to the initiation, development, maturation and ending of oceanic subduction at continental margins. The MWT orogenic peridotites reveal the history of strong metamorphism and deformation during subduction, the multiple melt/fluid metasomatism(including silicatic melts, carbonatitic melts and silicate-bearing C-HO fluids/supercritical fluids), and the complex cycling of crust-mantle materials, during the subduction/collision and exhumation of continental plates. In order to further reveal the crust-mantle interaction using subduction-zone peridotites, it is necessary to utilize high-spatial-resolution and high-precision techniques to constrain the complex chemical metasomatism, metamorphism,deformation at micro scales, and to reveal their connections with spatial-temporal evolution in macro-scale tectonics.

U-Pb isotopic geochemistry of the post-collisional mafic-ultramafic rocks from the Dabie Mountains——Crust-mantle interaction and LOMU component

The U-Pb isotope geochemical study of the pyroxenite-gabbro intrusion in the Dabie Mountains shows that the post-collisional mafic-ultramafic rocks of the Dabie Mountains are char-acterized by relative high Pb contents, low U contents and low U/Pb ratios. These characters may be results of interaction between lithosphere or depleted asthenospheric mantle (DMM) and lower crust, but have nothing to do with mantle plume and subducted continental crust. It was first ob-served that some samples with lower 206Pb/204Pb and higher 207Pb/204Pb ratios show typical char-acters of the LOMU component. The Pb, Sr, and Nd isotopic tracing shows that three components are needed in the source of the Zhujiapu pyroxenite-gabbro intrusion. They could be old enriched sub-continental lithospheric mantle (LOMU component), lower crust and depleted asthenospheric mantle. The crust-mantle interaction process producing primitive magma of post-collisional ma-fic-ultramafic rocks in the Dabie Mountains could be described by a lithospheric delamination and magma underplating model. After continent-continent collision, delamination of the thickened lithosphere induced the upwelling of depleted asthenospheric mantle, which caused partial melting of asthenospheric mantle and residual sub-continental lithospheric mantle. The basaltic magma produced in this process underplated in the boundary between the crust and mantle and interacted with lower crust resulting in the geochemical characters of both enriched lithospheric mantle and lower crust.

Golmud-Ejin heat flow profile and straightforward calculation of crust-mantle temperature

The Golmud-Ejin heat flow profile consists of 18 observed heat flow values. They arelimited in data number, distributed unevenly and vary from 55 mW·m-2 to 79 mW·m-2

Mechanism of Structure Variations at Rifted Margins in the Central Segment of South Atlantic:Insights from Numerical Modeling

Rifted margins in the central South Atlantic portray spatial variability in terms of preserved width and thickness,which relates to complex rift-related fault activities.However,there is still a lack of systematic and quantitative explanations for the causes of the variations that are observed along the paired rifts.To elucidate this issue,2D viscous-plastic thermomechanical numerical models are applied to capture the behavior of deformation,in which we investigate the effects of extensional rate,crustal strength and thickness on crust-mantle coupling,and timing of transition from rifting to breakup.Our numerical experiments demonstrate that crust-mantle decoupling accounts for crustal hyperextension,and that incorporating moderate-intensity rheology into lower crust may yield insights into the hyper-extended crust and asymmetric architecture observed in the central South Atlantic.The results also suggest that undulations in lithospheric basement cause asymmetric mantle upwelling.The lower crust of fold belts takes priority to be thermally weakened over craton and induces rift migration simultaneously.A new mechanism for the formation of failed rift is described,where the mechanical decoupling derived from thermally weakened lower crust gives access to dual rift migration.These results reinforce the interpretation on how crustal rheology shapes margins architectures and highlight the first-order effects of crust-mantle coupling.

Geology and mineralization of the Daheishan supergiant porphyry molybdenum deposit(1.65 Bt),Jilin,China:A review

The Daheishan supergiant porphyry molybdenum deposit(also referred to as the Daheishan deposit)is the second largest molybdenum deposit in Asia and ranks fifth among the top seven molybdenum deposits globally with total molybdenum reserves of 1.65 billion tons,an average molybdenum ore grade of 0.081%,and molybdenum resources of 1.09 million tons.The main ore body is housed in the granodiorite porphyry plutons and their surrounding inequigranular granodiorite plutons,with high-grade ores largely located in the ore-bearing granodiorite porphyries in the middle-upper part of the porphyry plutons.Specifically,it appears as an ore pipe with a large upper part and a small lower part,measuring about 1700 m in length and width,extending for about 500 m vertically,and covering an area of 2.3 km^(2).Mineralogically,the main ore body consists of molybdenite,chalcopyrite,and sphalerite horizontally from its center outward and exhibits molybdenite,azurite,and pyrite vertically from top to bottom.The primary ore minerals include pyrite and molybdenite,and the secondary ore minerals include sphalerite,chalcopyrite,tetrahedrite,and scheelite,with average grades of molybdenum,copper,sulfur,gallium,and rhenium being 0.081%,0.033%,1.67%,0.001%,and 0.0012%,respectively.The ore-forming fluids of the Daheishan deposit originated as the CO_(2)-H_(2)O-NaCl multiphase magmatic fluid system,rich in CO_(2)and bearing minor amounts of CH4,N2,and H2S,and later mixed with meteoric precipitation.In various mineralization stages,the ore-forming fluids had homogenization temperatures of>420℃‒400℃,360℃‒350℃,340℃‒230℃,220℃‒210℃,and 180℃‒160℃and salinities of>41.05%‒9.8%NaCleqv,38.16%‒4.48%NaCleqv,35.78%‒4.49%NaCleqv,7.43%NaCleqv,and 7.8%‒9.5%NaCleqv,respectively.The mineralization of the Daheishan deposit occurred at 186‒167 Ma.The granites closely related to the mineralization include granodiorites(granodiorite porphyries)and monzogranites(monzogranite porphyries),which were mineralized after magmatic evolution(189‒167 Ma).Moreover,these mineralization-related granites exhibit low initial strontium content and high initial neodymium content,indicating that these granites underwent crust-mantle mixing.The Daheishan deposit formed during the Early-Middle Jurassic,during which basaltic magma underplating induced the lower-crust melting,leading to the formation of magma chambers.After the fractional crystallization of magmas,ore-bearing fluids formed.As the temperature and pressure decreased,the ore-bearing fluids boiled drops while ascending,leading to massive unloading of metal elements.Consequently,brecciated and veinlet-disseminated ore bodies formed.

Helium,Argon,and Xenon Isotopic Compositions of Ore-forming Fluids in Jinding-Baiyangping Polymetallic Deposits,Yunnan,Southwest China

The Jinding superlarge lead and zinc deposit has attracted the attention of geologists of the world and itsmetal logenesis has long been in dispute. This paper takes the Jinding deposit and the Baiyangping Cu-Ag-Co deposit which was recently found at about 30 km north of Jinding as one ore belt, and, based on researches on the helium, argon, and xenon isotopic compositions of primary inclusions in ore-forming solutions of the main stage, the authors have found that the 3He/4He ratio of the ore-forming fluid is 2.7×10-6 (varying from 0.19 to 1.97 Ra), the 4He/40Ar ratio (0.24-3.12) is close to the mantle characteristic ratio, and the xenon isotopic composition and evolution show characters of the mantle xenon. The above results reveal the characteristics of mantle source and crust-mantle fluid mixing (mantle helium reaching 32%) and the metallogenic contributions of the deep processes in the Jinding-Baiyangping ore belt.

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(^(87)Sr/^(86)Sr)_(i)values 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(^(87)Sr/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(^(87)Sr/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.

Generation of andesite through partial melting of basaltic metasomatites in the mantle wedge:Insight from quantitative study of Andean andesites

Continental crust in average exhibits a similar composition in both major and trace elements to andesites along active continental margins.For this reason,andesitic magmatism above oceanic subduction zones is considered to have played a key role in the generation of continental crust along convergent plate boundaries.With respect to the origin of andesites themselves,however,there is still a hot debate on how they have acquired their geochemcial compositions.The debate is mainly centralized on the relative contributions of crustal contamination,magma differentiation and source mixing,which reaches an impasse in the past decades.The essential reason for this kind of debates is that these three mechanisms only can account for some of the geochemical observations for andesites,leading to insufficient discrimination among them.Nevertheless,the geochemical features of andesites are primarily controled from early to late by the composition of their source rocks in addition to partial melting and magma differentiation processes.If source mixing and partial melting processes in the early stage of andesite magmatism can account for the first-order geochemical features of andesites,there is no need to invoke the late processes of magma differentiation and crustal contamination for andesite petrogenesis.This is illustrated by quantitative forward modeling of the geochemical data for Quaternary andesites from the Andean arc in South America based on an integrated interpretation of these data.The modeling has run with four steps from early to late:(1)dehydration of the subducting oceanic crust at forearc depths;(2)partial melting of the subducting terrigenous sediment and altered oceanic basalt at subarc depths to produce hydrous felsic melts;(3)the generation of basaltic metasomatites(e.g.,Si-excess pyroxenite)in the mantle wedge through reaction of the mantle wedge peridotite with large amounts of the hydrous felsic melts;(4)the production of andesitic melts by partial melting of the basaltic metasomatites.The results not only testify the hypothesis that the trace element and radiogenic isotope compositions of andesites can be directly produced by the source mixing and mantle melting but also demonstrate that partial melting of the basaltic metasomatites can reproduce the lithochemical composition of andesites.The compositional variations of Andean andesites within a single volcanic zone and among different volcanic zones can be explained by incorporating different amounts of heterogeneous hydrous felsic melts into their mantle sources,followed by different degree of partial melting under different pressures and temperatures.Therefore,the source mixing and partial melting processes at subarc depths can account for the first-order geochemical features of Andean andesites.In this regard,it may be not necessary for andesite petrogenesis to invoke the significant contributions from the processes of magma differentiation and crustal contamination.

Early Paleozoic adakite in the Liuyuan area from the Beishan orogenic belt,NW Gansu Province:Petrogenesis and implication for tectonic setting

The Liuyuan area,which is located on the southern margin of the Beishan orogenic belt,develops abundant Early Paleozic granitoids.SHRIMP zircon U-Pb dating yielded a weighted mean 206Pb/238U age of 421±8 Ma for the Liuyuan granodiorite(Zhao Zehui et al.,2007),implying its Late Silurian intrusion.Geochemical compositions showed that the Liuyuan granodiorite is characterized by high SiO2(65.01%-67.31%),A12O3(17.17%-18.05%) and Na2O(Na2O/K2O=1.67-1.87) but low Mg# contents calculated as 100×Mg2+/(Mg2++∑Fe2+) from 28.77 to 31.15,as well as being enriched in Sr(472×10-6-517×10-6) but depleted in Yb(1.2×10-6-1.42×10-6) and Y(12.8×10-6-14×10-6).The REEs are characterized by right-inclined patterns with LREE enrichment,HREE depletion and slightly negative Eu anomalies(Eu/Eu*=0.91-0.97).Major and trace elements indicate that the granodiorite is an adakite.The Nb/Ta values of the granodiorite vary from 10.80 to 18.01 and Nb/U from 6.32 to 10.09,both lying between the values of the crust and the mantle.The rock has low εNd(t) values(-2.5--0.8) and high ISr(0.706321-0.706495).Geochemical and Sr-Nd isotopic compositions indicate that the Liuyuan granodiorite is possibly derived from partial melting of thickening lower crust,related to mantle underplating.The Yb-Ta and Y+Nb-Rb discriminant diagrams imply the Liuyuan granodiorite intruded in a local extensional tectonic setting during late collision.Combined with previous studies on geochronology,geochemistry and tectonic setting of granitoids,we interprete that the constraint of this adakite in the Liuyuan area indicates that the tectonic setting may have transformed from collision to extension during the Early Devonian.

Timing of formation of the Hongdonggou Pb-Zn polymetallic ore deposit,Henan Province,China:Evidence from Rb-Sr isotopic dating of sphalerites

The Hongdonggou Pb-Zn polymetallic ore deposit,located in the southwestern part of the Luanchuan Mo-W-Pb-Zn-Ag polymetallic ore mineralization in Henan Province,China,is an important part of the East Qinling metallogenic belt.The orebodies in the deposit,which are vein,bedded and lenticular,are mainly hosted in the syenite porphyry,and formed within the carbonate and clastic rocks of the Yuku and Qiumugou formations partially.The genesis of the deposit has previously been argued to be of hydrothermal-vein type or of skarn-hydrothermal type.In this study,we report the results of Rb-Sr isotopic dating based on sphalerites from the main orebody of the Hongdonggou Pb-Zn polymetallic ore deposit,which yield an isochron age of 135.7 ± 3.2 Ma,constraining the timing of mineralization as early Cretaceous.The age is close to those reported for the Pb-Zn deposits in the Luanchuan ore belt.The(^(87)Sr/^(86)Sr),values of the sphalerites(0.71127 + 0.00010) are lower than that of terrigenous silicates(0.720) and higher than the mantle(0.707),suggesting that the metallogenic components were mainly derived through crust-mantle mixing.Combining the results from this study with those from previous work,we propose that the Hongdonggou Pb-Zn polymetallic ore deposit is a hydrothermal-vein deposit associated with the early Cretaceous tectonothermal event,and the mineralization is controlled by NWand near EW-trending faults in the Luanchuan Mo-W-Pb-Zn-Ag polymetallic ore concentration belt.

Geology and mineralization of the Pulang supergiant porphyry copper deposit(5.11 Mt)in Shangri-la,Yunnan Province,China:A review

The porphyry copper belt in the Geza island arc in southwestern China is the only Indosinian porphyry copper metallogenic belt that has been discovered and evaluated so far.The Pulang porphyry copper deposit(also referred to as the Pulang deposit)in this area has proven copper reserves of 5.11×106 t.This deposit has been exploited on a large scale using advanced mining methods,exhibiting substantial economic benefit.Based on many research results of previous researchers and the authors’team,this study proposed the following key insights.(1)The Geza island arc was once regarded as an immature island arc with only andesites and quartz diorite porphyrites occurring.This understanding was overturned in this study.Acidic endmember components such as quartz monzonite porphyries and quartz monzonite porphyries have been identified in the Geza island arc,and the mineralization is mainly related to the magmatism of quartz monzonite porphyries.(2)Complete porphyry orebodies and large vein orebodies have developed in the Pulang deposit.Main orebody KT1 occurs in the transition area between the potassium silicate alteration zone of quartz monzonite porphyries and the sericite-quartz alteration zone.Most of them have developed in the potassium silicate alteration zone.The main orebody occurs as large lenses at the top of the hanging wall of rock bodies,with an engineering-controlled length of 1920 m and thickness of 32.5‒630.29 m(average:187.07 m).It has a copper grade of 0.21%-1.56%(average:0.42%)and proven copper resources of 5.11×10^(6) t,which are associated with 113 t of gold,1459 t of silver,and 170×10^(3) t of molybdenum.(3)Many studies on diagenetic and metallogenic chronology,isotopes,and fluid inclusions have been carried out for the Pulang deposit,including K-Ar/Ar-Ar dating of monominerals(e.g.,potassium feldspars,biotites,and amphiboles),zircon U-Pb dating,and molybdenite Re-Os dating.The results show that the porphyries in the Pulang deposit are composite plutons and can be classified into pre-mineralization quartz diorite porphyrites,quartz monzonite porphyries formed during the mineralization,and post-mineralization granite porphyries,which were formed at 223±3.7 Ma,218±4 Ma,and 207±3.9 Ma,respectively.The metallogenic age of the Pulang deposit is 213‒216 Ma.(4)The petrogeochemical characteristics show that the Pulang deposit has the characteristics of volcanic arc granites.The calculation results of trace element contents in zircons show that quartz monzonite porphyries and granite porphyries have higher oxygen fugacity.The isotopic tracing results show that the diagenetic and metallogenic materials were derived from mixed crust-and mantle-derived magmas.

Extension Model of Crustal Uplifting in Western Shandong

Block faults, as the -dominant tectonic framwork of western Shandong, were formed by the linked extensional fault system through two extensional movements during the Meso-Cenozoic. Both of the extensional movements experienced the same evloutional process: first, the upper crust was pulled apart to form faults; then the Tai-Lu-Yi (Taishan-Lushan-Yishan) fault block occurring in the footwall of the extensional fault was uplifted, which induced the shallow-level detachment movement along the early Precambrian and Palaeozoic unconformity; the " branching" fault in the upper part of the deep-level detachment layer propagated. As the shallow detachment moved towards the north and the deep one towards the south, the Tai-Lu-Yi fault block acted as the common footwall of both the southern and northern detachment systems. The Tai-Lu-Yi fault block rebounded and uplifted as the overlying material was pulled apart to cause an unloading. Sialic material of the mid-crust below the deep detachment flowed to and