Whether a Neoarchean basement existing in the Songnen massif is currently debated.Identification of Archean magmatism from the Songnen Massif is helpful to resolve this issue.Here,we report newly discovered Neoarchean...Whether a Neoarchean basement existing in the Songnen massif is currently debated.Identification of Archean magmatism from the Songnen Massif is helpful to resolve this issue.Here,we report newly discovered Neoarchean Shanquan pluton in the Western Songnen Massif.These Neoarchean Shanquan pluton are mainly composed of granites that are exposed near the town of Shanquan in Heilongjiang Province.LA-ICP-MS zircon U-Pb dating reveals that the sample 2015TW1 has an upper intercept age of 2801±69 Ma and a weighted mean age of 2708±18 Ma,while samples LJ27QY1 and LJ27QY2 have upper intercept ages of 2677±57 Ma and 2653±18 Ma,and weighted mean ages of 2649±10 Ma and 2653±15 Ma,respectively.This indicates that these granites were formed at~2.7 Ga.Most of the~2.7 Ga zircons have older TDM2 ages of 2762–3326 Ma with positiveεHf(t)values ranging from 0 to 6.4,while a few of the zircons have negativeεHf(t)values ranging from-8.1 to-11.5 and older TDM2 ages varying from 3158 to 3264 Ma.The zircon Hf isotopes indicate that Paleo-Mesoarchean crusts might once existed in the Songnen Massif,and the studied Neoarchean magmas were principally derived from partial melting of these Paleo-Mesoarchean ancient crust.Based on the geochronological spectrum of magmatic and detrital zircons,the Songnen,Erguna,Jiamusi,Bureya massifs may have a common basement prior to the Neoproterozoic and may even be linked with the Triam Craton.展开更多
Tectonic processes involving amalgamations of microblocks along zones of ocean closure represented by granite-greenstone belts(GGB) were fundamental in building the Earth's early continents. The crustal growth and...Tectonic processes involving amalgamations of microblocks along zones of ocean closure represented by granite-greenstone belts(GGB) were fundamental in building the Earth's early continents. The crustal growth and cratonization of the North China Craton(NCC) are correlated to the amalgamation of microblocks welded by 2.75-2.6 Ga and ~2.5 Ga GGBs. The lithological assemblages in the GGBs are broadly represented by volcano-sedimentary sequences, subduction-collision related granitoids and bimodal volcanic rocks(basalt and dacite) interlayered with minor komatiites and calc-alkalic volcanic rocks(basalt, andesite and felsic rock). The geochemical features of meta-basalts in the major GGBs of the NCC display affinity with N-MORB, E-MORB, OIB and calc-alkaline basalt, suggesting that the microblocks were separated by oceanic realm. The granitoid rocks display arc signature with enrichment of LILE(K,Rb, Sr, Ba) and LREE, and depletion of HFSE(Nb, Ta, Th, U, Ti) and HREE, and fall in the VAG field. The major mineralization includes Neoarchean BIF-type iron and VMS-type Cu-Zb deposits and these,together with the associated supracrustal rocks possibly formed in back-arc basins or arc-related oceanic slab subduction setting with or without input from mantle plumes. The 2.75-2.60 Ga TTG rocks,komatiites, meta-basalts and metasedimentary rocks in the Yanlingguan GGB are correlated to the upwelling mantle plume with eruption close to the continental margin within an ocean basin. The volcanosedimentary rocks and granitoid rocks in the late Neoarchean GGBs display formation ages of 2.60-2.48 Ga, followed by metamorphism at 2.52-2.47 Ga, corresponding to a typical modern-style subduction-collision system operating at the dawn of Proterozoic. The late Neoarchean komatiite(Dongwufenzi GGB), sanukitoid(Dongwufenzi GGB and Western Shandong GGB), BIF(Zunhua GGB) and VMS deposit(Hongtoushan-Qingyuan-Helong GGB) have closer connection to a combined process of oceanic slab subduction and mantle plume. The Neoarchean cratonization of the NCC appears to have involved two stages of tectonic process along the 2.75-2.6 Ga GGB and ~2.5 Ga GGBs, the former involve plume-arc interaction process, and the latter involving oceanic lithospheric subduction, with or without arcplume interaction.展开更多
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 Neoarc...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.展开更多
The late Neoarchean metamorphosed volcanic rocks in the southern Liaoning Terrane(SLT) of the eastern North China Craton(NCC) are mainly composed of amphibolites and felsic gneisses and can be chemically classified as...The late Neoarchean metamorphosed volcanic rocks in the southern Liaoning Terrane(SLT) of the eastern North China Craton(NCC) are mainly composed of amphibolites and felsic gneisses and can be chemically classified as basalt(Group#1),basaltic andesite(Group#2),dacite(Group#3) and rhyodacite(Group#4).LA-ICP-MS zircon U-Th-Pb dating reveals that they formed at ~2.53-2.51 Ga.Group#1 samples are characterized by approximately flat chondrite-normalized rare earth element(REE) patterns with low(La/Yb)_N ratios and a narrow range of(Hf/Sm)N ratios,and their magmatic precursors were generated by partial melting of a depleted mantle wedge weakly metasomatized by subducted slab fluids.Compared to Group#1 samples,Group#2 samples display strongly fractionated REE patterns with higher(La/Yb)_N ratios and more scattered(Hf/Sm)N ratios,indicative of a depleted mantle wedge that had been intensely metasomatized by slab-derived melts and fluids.Group#3 samples are characterized by high MgO and transition trace element concentrations and fractionated REE patterns,which resemble typical high-Si adakites,and the magmatic precursors were derived from partial melting of a subducted oceanic slab.Group#4 samples have the highest SiO_2 and the lowest MgO and transition trace element contents,and were derived from partial melting of basaltic rocks at lower crust levels.Integrating these tholeiitic to calcalkaline volcanic rocks with the mass of contemporaneous dioritic-tonalitic-trondhjemitic-granodioritic gneisses,the late Neoarchean volcanic rocks in the SLT were most likely produced in an active continental margin.Furthermore,the affinities in lithological assemblages,metamorphism and tectonic regime among SLT,eastern Hebei to western Liaoning Terrane(EH-WLT),northern Liaoning to southern Jilin Terrane(NL-SJT),AnshanBenxi continental nucleus(ABN) and Yishui complex(YSC) collectively indicate that an integral and much larger continental block had been formed in the late Neoarchean and the craton-scale lateral accretion was a dominantly geodynamic mechanism in the eastern NCC.展开更多
The Neoarchean Bundelkhand greenstone sequences at Mauranipur and Babina areas within the Bundelkhand Gneissic Complex preserve a variety of magmatic rocks such as komatiitic basalts, basalts,felsic volcanic rocks and...The Neoarchean Bundelkhand greenstone sequences at Mauranipur and Babina areas within the Bundelkhand Gneissic Complex preserve a variety of magmatic rocks such as komatiitic basalts, basalts,felsic volcanic rocks and high-Mg andesites belonging to the Baragaon, Raspahari and Koti Formations.The intrusive and extrusive komatiitic basalts are characterized by low SiO_2(39-53 wt.%), high MgO(18-25 wt.%).moderately high Fe_2O_3(7.1-11.6 wt.%), Al_2O_3(4.5-12.0 wt.%), and TiO_2(0.4-1.23 wt.%)with super to subchondritic(Gd/Yb)N ratios indicating garnet control on the melts. The intrusive komatiitic suite of Ti-enriched and Al-depleted type possesses predominant negative Eu and positive Nb, Ti and Y anomalies. The chemical composition of basalts classifies them into three types with varying SiO_2, TiO_2, MgO, Fe_2O_3, Al_2O_3 and CaO. At similar SiO_2 content of type Ⅰ and Ⅲ basalts, the type II basalts show slightly high Al_2O_3 and Fe_2O_3 contents. Significant negative anomalies of Nb, Zr, Hf and Ti, slightly enriched LREE with relatively flat HREE and low ∑REE contents are observed in type Ⅰ and Ⅱ basalts. TypeⅢ basalts show high Zr/Nb ratios(9.8-10.4), TiO_2(1.97-2.04 wt.%), but possess strikingly flat Zr, Hf, Y and Yb and are uncontaminated. Andesites from Agar and Koti have high SiO_2(55-64 wt.%), moderate TiO_2(0.4-0.7 wt.%), slightly low Al_2O_3(7-11.9 wt.%), medium to high MgO(3-8 wt.%) and CaO contents(10-17 wt.%). Anomalously high Cr, Co and Ni contents are observed in the Koti rhyolites. Tholeiitic to calc alkaline affinity of mafic-felsic volcanic rocks and basalt-andesite dacite-rhyolite differentiation indicate a mature arc and thickened crust during the advanced stage of the evolution of Neoarchean Bundelkhand greenstone belt in a convergent tectonic setting where the melts were derived from partial melting of thick basaltic crust metamorphosed to amphibolite-eclogite facies. The trace element systematics suggest the presence of arc-back arc association with varying magnitudes of crust-mantle interaction. La/Sm, La/Ta,Nb/Th, high MgO contents(>20 wt.%), CaO/Al_2O_3 and(Gd/Yb)_N > 1 along with the positive Nb anomalies of the komatiite basalts reflect a mantle plume source for their origin contaminated by subductionmetasomatized mantle lithosphere. The overall geochemical signatures of the ultramafic-mafic and felsic volcanic rocks endorse the Neoarchean plume-arc accretion tectonics in the Bundelkhand greenstone belt.展开更多
The Neoarchean charnockites of North margain of North China Craton(NCC) has become a hot topic into understanding the Early Precambrian basement. Although there is a broad consensus that charnockite is usually related...The Neoarchean charnockites of North margain of North China Craton(NCC) has become a hot topic into understanding the Early Precambrian basement. Although there is a broad consensus that charnockite is usually related to granulite facies metamorphism, whether its petrogenesis and tectonics characteristics remains controversial. Inclusions within hypersthene and garnet in charnockite are used to identify the peak granulite facies mineral assemblage, with the formation of Magnesian-charnockite attributed to anatexis of the protolith associated with this granulite facies metamorphism. The distribution of major and trace elements in charnockite is very uneven, significant depleted in LILEs(eg. Cs, U, Th) and HFSEs(eg. Nb, Ta, P and Ti), riched in Sr. Raising to the coexistence of Eu-enrichment and Eu-depletion type of REE patterns that influenced by the content of plagioclase and the remnants minerals of zircon and apatite. Comparative the petrography, geochemistry and geochronology data of Magnesian-charnockite indicate that the ratios of mafic pellites and basalts involved in anatectic melting are different by the upwelling of mantle magma, also resulting in the Eu anormals characteristics. The formation of the Magnesian-charnockite is closely connected with the subduction of the NCC oceanic crust(About ~2.5 Ga). However, Ferroan-charnockite may be the formed by the crystallization differentiation of the upwelling of mantle-derived shoshonitic magma(About ~2.45 Ga), with the lower crust material addition.展开更多
The first data on P-T metamorphic conditions coupled with U-Pb monazite and zircon age obtained for the Neoarchean Kitoy granulite-gneiss terrane(SW Siberian Craton).Alumina gneisses of the Kitoy terrane indicate two-...The first data on P-T metamorphic conditions coupled with U-Pb monazite and zircon age obtained for the Neoarchean Kitoy granulite-gneiss terrane(SW Siberian Craton).Alumina gneisses of the Kitoy terrane indicate two-staged metamorphic evolution.The first stage of regional metamorphism(M1)occurred at high-amphibolite facies conditions at T=780-800℃ and P=8-9 kbar.The second stage(M2)belongs to MT-HT/LP type of metamorphism with the wide temperature interval 600-750℃ and pressure 2-4 kbar.Two age peaks were established on the basis of U-Pb monazite and zircon dating in garnet-anthophyllite gneisses.Both of them correspond to the Neoarchean age:the age of M1 falls into the interval of ca.2489-2496 Ma,the age of M2-ca.2446-2456 Ma.The high-temperature metamorphism of the Kitoy block and nearly coeval granitoid magmatism can be an evidence for the Neoarchean collision in SW Siberian craton.展开更多
The late Archean(~3.0-2.5 Ga)was a key period of continental growth globally,which is widely considered to reflect the onset of vigorous plate tectonic activity,although related continental growth modes remain content...The late Archean(~3.0-2.5 Ga)was a key period of continental growth globally,which is widely considered to reflect the onset of vigorous plate tectonic activity,although related continental growth modes remain contentious.Here we investigate a suite of late Neoarchean metavolcanic rocks from the southwest Qixia area of the Jiaobei terrane in the North China Craton.The rocks in this suite include amphibolites,clinopyroxene amphibolites,and hornblende plagioclase gneisses.We present zircon U-Pb isotopic data which indicate that the protoliths of these rocks formed during~2549-2511 Ma.The(clinopyroxene)amphibolites correspond to meta-basaltic rocks,with some containing high modal content of titanite.These rocks show moderate to high FeO_(T)(8.96-13.62 wt.%)and TiO_(2)(0.59-1.59 wt.%),flat to less fractionated REE patterns,and mildly negative Th,Nb,and Ta anomalies,resembling those of Fe-tholeiites.In addition,they display positive zirconε_(Hf)(t)values(+2.6 to+8.7),and are devoid of crustal contamination or fractional crystallization.Combined with the low Nb/Yb(mostly<1.60)and(Hf/Sm)_N(mostly<0.95),low to moderate Th/Yb(0.08-0.54),and low V/Sc(5.53-9.19)ratios,these basaltic rocks are interpreted to have been derived from a relatively reduced and depleted mantle source that was mildly metasomatized by hydrous fluids.The hornblende plagioclase gneisses are meta-andesitic rocks,and occur interlayered with the basaltic rocks.They are transitional between tholeiitic and calc-alkaline rock series,and show fractionated REE patterns with evidently negative Th,Nb,and Ta anomalies.The depleted zirconε_(Hf)(t)values(+2.4 to+8.4)and quantitative chemical modeling suggest that the andesitic rocks were most likely generated by injection and mixing of juvenile felsic magmas with the tholeiitic basaltic magmas.In general,the chemical features and genesis of late Neoarchean meta-basaltic rocks in our study area resemble those of Mariana back-arc basin basalts.Combined with regional geological data,it is proposed that the Jiaobei terrane witnessed late Neoarchean crustal growth under a paired continental arc-back arc setting.On a regional context,we propose two distinct geodynamic mode of late Neoarchean continental growth across North China Craton(particularly the Eastern Block),i.e.,(1)arc-continent accretion along northwestern part of the Eastern Block;and(2)paired continental arc-back arc system surrounding the~3.8-2.7 Ga continental nuclei to the southeast.展开更多
The Archean North China Craton is composed of the Western Block,Eastern Block and the intervening Central Orogenic Belt.A 4-10 km wide and 85 km long tectonic mélange belt informally called the Zanhuang
This study presents zircon LA-ICP-MS U-Pb geochronology,trace elements characteristics,whole rock geochemistry composition and zircon Hf isotopic data of Shuimowan tonalites in Dengfeng City.The results show that zirc...This study presents zircon LA-ICP-MS U-Pb geochronology,trace elements characteristics,whole rock geochemistry composition and zircon Hf isotopic data of Shuimowan tonalites in Dengfeng City.The results show that zircons from Shuimowan tonalites have oscillatory growth zoning,relatively high Th/U ratios(0.8--1.7)and upturned zircon rare earth elements(REE),indicating that they are magmatic origin.Shuimowan tonalites yield a weighted mean 207 Pb/206 Pb age of 2522±9 Ma,indicating they were formed in the latest Neoarchean.The tonalites are characterized by relatively low SiO 2 contents,high MgO and Na 2O contents,high REE(∑REE=322×10-6-354×10-6),obvious fractionation of REE,enrichment in LREE and feeble negative Eu anomaly(Eu/Eu*=0.97--0.99).The samples are also enriched in large ion lithophile elements and depleted in high field strength elements,with negative Nb,Ta,P and Ti anomalies.TheεHf(t)values of zircon grains from Shuimowan tonalites range between 3.5 and 5.3.Combined with regional tectonic evolution,it is suggested that Shuimowan tonalites were derived from partial melting of mantle peridotite metasomatized by the slab-derived felsic melt and formed in the arc magma tectonic setting related to plate subduction.Research on the Neoarchean Shuimowan tonalites provides a constraint for the study of the Pre-Cambrian tectonic evolution in the southern margin of North China Craton.展开更多
The crustal growth of the North China Craton(NCC) during the Neoarchean time(2.5—2.8 Ga) is a hotly controversial topic,with some proposing thai the main crustal growth occurred in the late Neoarchean (2.5—2.6 Ga),i...The crustal growth of the North China Craton(NCC) during the Neoarchean time(2.5—2.8 Ga) is a hotly controversial topic,with some proposing thai the main crustal growth occurred in the late Neoarchean (2.5—2.6 Ga),in agreement with the time of the magmatism,whereas others suggest that the main crustal accretion took place during early Neoarchean time(2.7—2.8 Ga),consistent with the time of crustalformation of other cratons in the world.Zircon U-Pb ages and Hf isotope compositions can provide rigorous constraints on the time of crustal growth and the evolution and tectonic division of the NCC.In this contribution, we make a comprehensive review of zircon Hf isotope data in combination with zircon U-Pb geochronology and some geochemistry data from various divisions of the NCC with an aim to constrain the Neoarchean crustal growth of the NCC.The results suggest that both 2.7—2.8 Ga and 2.5—2.6 Ga crustal growth are distributed over the NCC and the former is much wider than previously suggested.The Eastern block is characterized by the main 2.7—2.8 Ga crustal growth with local new crustal-formation at 2.5—2.6 Ga,and the Yinshan block is characterized by～2.7 Ga crustal accretion as revealed by Hf-isotope data of detrital zircons from the Zhaertai Group.Detrital zircon data of the Khondalite Belt indicate that the main crustal growth period of the Western block is Paleoproterozoic involving some～2.6 Ga and minor Early- to Middle-Archean crustal components,and the crustal accretion in the Trans-North China Orogen(TNCO) has a wide age range from 2.5 Ga to 2.9 Ga with a notable regional discrepancy.Zircon Hf isotope compositions,coupled with zircon ages and other geochemical data suggest that the southern margin may not be an extension of the TNCO,and the evolution and tectonic division of the NCC is more complex than previously proposed,probably involving multi-stage crustal growth and subduction processes.However, there is no doubt that 2.7—2.8 Ga magmatism and crustal-formation are more widely distributed than previously considered,which is further supported by the data of zircons from Precambrian lower crustal rocks, overlying sedimentary cover,modern river sediments and Late Neoarchean syenogranites.展开更多
The basalts within the greenstone belt worldwide serve as an ideal target to decipher the nature of Archean mantle sources and further to extend the understanding of the early stages of Earth's evolution.To provid...The basalts within the greenstone belt worldwide serve as an ideal target to decipher the nature of Archean mantle sources and further to extend the understanding of the early stages of Earth's evolution.To provide important insights into the issues,we carried out a detailed investigation of whole-rock geochemistry and Sm-Nd isotopes,and zircon U-Pb-Hf isotopes for the Late Neoarchean metamorphosed basalts in eastern Hebei,North China Craton.U-Pb isotopic dating using the LA-ICPMS on zircons reveals that the basalts in eastern Hebei erupted at ca.2.48-2.51 Ga and subsequently experienced multiple regional metamorphic events at 2477 and 1798 Ma,respectively.The metamorphosed basalts are featured by low SiO_(2),MgO,K_(2)O+Na_(2)O,and high Fe O contents,endowed with the subalkaline and high-Fe tholeiitic affinities.The radiogenic initial Nd and Hf isotope values and correlations among V,Ni and Cr contents strongly imply that the basalts experienced significant clinopyroxene and olivine fractionation and minor crustal contamination during magma evolution.They are also characterized by the relatively low total REE contents and exhibit significant depletions to moderate enrichments in the LREE contents,indicating the derivation from a deep mantle source in an Archean proto-mantle plume setting.展开更多
Within the high-grade metamorphic basement, the central portion of North China Craton (NCC), a group of Neoarchean khondalites (KS) is identified. They are characterized by large ion lithophile elements (LILE) enrichm...Within the high-grade metamorphic basement, the central portion of North China Craton (NCC), a group of Neoarchean khondalites (KS) is identified. They are characterized by large ion lithophile elements (LILE) enrichment, lower abundances of Zr, Hf and Sr. Their rare earth element (REE) distribution has significant LREE enrichment and negative Eu anomalies. The protoliths of KS are interpreted as feldspathic quartzite, shale or petite and carbonite, deposited in a shallow sea upon cratonic shelf distant from the land. KS’s source region might be dominated by granitic rocks, with a minor amount of TTG, underwent comparatively severe chemical weathering. Considering relevent tectonic constraints, we suggest that khondalites from central portion of NCC, an important metamophosed sedimentary cover, are the most significant exogenetic marker of Neoarchean continental cratonization for NCC.展开更多
An ancient unconformity event is identified within the granulite-facies province of North China, which is marked by the boundary between the overlying khondalite series (KS) and the basement grey gneiss complex (BGGC)...An ancient unconformity event is identified within the granulite-facies province of North China, which is marked by the boundary between the overlying khondalite series (KS) and the basement grey gneiss complex (BGGC). REE patterns of KS suggest that their protoliths aM mature sediments. As documented by isotopic ages and metamorphic P-T-t paths, KS is originally deposited after the basement complex formed. Furthermore, the BGGC was overprinted by the metamorphic event associated with the KS. The binary structure of KS-BGGC is well preserved in the western part of North China craton (NCC), and it is structurally truncated and overlain by the Palaeoproterozoic Wntai rift, which suggests that the unconformity occurred in the Neoarchean, and represents the major tectono-thermal episodes of the Neoarchean continental cratonization of NCC.展开更多
This study presents a comprehensive account of the petrogenetic and geodynamic evolution of the Bellara Trap volcanic rocks from the Ingaldhal Formation, Chitradurga Group, western Dharwar Craton(WDC). Geochemical att...This study presents a comprehensive account of the petrogenetic and geodynamic evolution of the Bellara Trap volcanic rocks from the Ingaldhal Formation, Chitradurga Group, western Dharwar Craton(WDC). Geochemical attributes of these rocks are consistent with two groups with distinct evolutionary trends: one comprising tholeiitic, MORB(mid-ocean ridge basalt) type basalts(BTB) and the other corresponding to calc-alkaline andesites(BTA). Basalts are essentially composed of clinopyroxene and plagioclase whereas the andesites are porphyritic with phenocrysts of plagioclase, clinopyroxene and polycrystalline quartz embedded in a groundmass of K-feldspar, quartz and opaques. Primary igneous mineralogy is overprinted by greenschist facies metamorphism resulting in chlorite-actinolite-plagioclase assemblage. The BTB samples reflect nearly flat REE patterns with weak LREE enrichment in contrast to pronounced LREE enhancement over HREE discernible for BTA. Tectonically, the BTB samples correspond to an active mid-oceanic ridge-rift setting with a MORB composition, whereas a back-arc basin(BAB) regime is corroborated for the BTA samples fractionating from back-arc basin basalts. Geochemical imprints of subduction input are more pronounced in BTA compared to BTB as mirrored by their elevated abundances of incompatible fluid mobile elements like Ba, Th, U and LREE. The BTB is endowed with an N-to E-MORB signature attributable to minor contributions from subduction-related components at the inception of a back-arc basin in the vicinity of an active subduction system. The BTA derived through differentiation of a basaltic magma with BABB(back-arc basin basalt) affinity compositionally akin to a heterogeneous source mantle carrying depleted MORB-type and enriched arc-type components inducted with progressive subduction. The BABB-type andesites and MORB-type basalts from Bellara Traps record a compositional heterogeneity of mantle in an intraoceanic arc-back arc system. Mantle processes invoke a BABB-MORB spectrum with a MORB-like endmember and an arc-like endmember associated with a juvenile back-arc basin. This study infers a Neoarchean analogue of Mariana-type back-arc rift setting proximal to the arc with a gradual transition from anhydrous to hydrous melting processes synchronized with MORB-mantle and arc-mantle interaction during initiation of a nascent back arc adjacent to the arc. The MORB-BABB compositional spectrum for the Bellara Traps conforms to a Neoarchean back-arc basin that evolved under an extensional tectonic regime associated with incipient stages of back-arc rifting and incorporation of subduction-derived components in the mantle output. This study complies with Neoarchean intraoceanic accretionary cycle plate tectonics in WDC.展开更多
Archean rock exposures in the Yangtze Craton of South China are scarce and have been only studied in small-scale outcrops for understanding its early crustal evolution.Geological investigations have been carried out f...Archean rock exposures in the Yangtze Craton of South China are scarce and have been only studied in small-scale outcrops for understanding its early crustal evolution.Geological investigations have been carried out for three Neoarchean gneissic granitic plutons from the Dabie orogen in the northeastern margin of the Yangtze Craton.Zircon U-Pb geochronology constrains the emplacement of high-K monzogranite at 2645±30 Ma,high-K syenogranite at 2630±37 Ma and Na-rich granodiorite at 2497±29 Ma.These findings provide direct evidence for the existence of∼2.7-2.5 Ga rocks in the Dabie orogen,which significantly contribute to the distribution and evolution of Neoarchean basement rocks in the Yangtze Craton.Zircon crystals from the three granite samples giveεHf(t)values of−0.9 to 3.7,−4.2 to−0.4 and−4.7 to 0.1,respectively,corresponding to T_(DM2) ages of 3186-2909,3372-3141 and 3297-3005 Ma.The magmatic zircons have δ^(18)O values of 5.06±0.27‰to 5.79±0.30‰(average 5.59‰),6.14±0.24 to 7.35±0.26‰(average 6.87‰)and 5.95±0.17‰to 7.09±0.17‰(average 6.55‰),respectively.Considering the possible decrease of δ^(18)O value due to the lead loss during post-crystallization alteration,the primary δ^(18)O values might be substantially higher than those of the normal mantle zircon value(δ^(18)O=5.3±0.6‰).These isotopic data indicate that the Jiamiao Neoarchean granites were largely generated through reworking of Paleo-Mesoarchean basement rocks with a minor contribution of supracrustal material.Integrating our findings with previous results,we infer that the Archean-Paleoproterozoic complexes/terranes of the Yangtze Craton have distinct petrogenesis and the timings of the transition from Na-rich to high-K granites,crustal growth,and tectonothermal evolution before∼2.0 Ga.However,all of them underwent metamorphism at about 2.0 Ga.These observations also reveal that the Yangtze Craton might comprise several microcontinents that evolved individually and collided to form a unified craton at∼2.0 Ga,synchronous with the assembly of the Columbia supercontinent.However,the lack of relevant data from the southeastern Yangtze Craton may have a critical influence on this conclusion and should be solved in the future.展开更多
基金co-supported by the National Key R&D Program of China(Grant No.42130305)China Geological Survey(Grant Nos.DD20221687,DD20230047,DD20160047)the NSFC project(Grant Nos.41802238,42102271)。
文摘Whether a Neoarchean basement existing in the Songnen massif is currently debated.Identification of Archean magmatism from the Songnen Massif is helpful to resolve this issue.Here,we report newly discovered Neoarchean Shanquan pluton in the Western Songnen Massif.These Neoarchean Shanquan pluton are mainly composed of granites that are exposed near the town of Shanquan in Heilongjiang Province.LA-ICP-MS zircon U-Pb dating reveals that the sample 2015TW1 has an upper intercept age of 2801±69 Ma and a weighted mean age of 2708±18 Ma,while samples LJ27QY1 and LJ27QY2 have upper intercept ages of 2677±57 Ma and 2653±18 Ma,and weighted mean ages of 2649±10 Ma and 2653±15 Ma,respectively.This indicates that these granites were formed at~2.7 Ga.Most of the~2.7 Ga zircons have older TDM2 ages of 2762–3326 Ma with positiveεHf(t)values ranging from 0 to 6.4,while a few of the zircons have negativeεHf(t)values ranging from-8.1 to-11.5 and older TDM2 ages varying from 3158 to 3264 Ma.The zircon Hf isotopes indicate that Paleo-Mesoarchean crusts might once existed in the Songnen Massif,and the studied Neoarchean magmas were principally derived from partial melting of these Paleo-Mesoarchean ancient crust.Based on the geochronological spectrum of magmatic and detrital zircons,the Songnen,Erguna,Jiamusi,Bureya massifs may have a common basement prior to the Neoproterozoic and may even be linked with the Triam Craton.
基金jointly supported through the Foreign Expert grant from China University of Geosciences(Beijing)the Professorial position at the University of Adelaide, Australia to M.Santosh
文摘Tectonic processes involving amalgamations of microblocks along zones of ocean closure represented by granite-greenstone belts(GGB) were fundamental in building the Earth's early continents. The crustal growth and cratonization of the North China Craton(NCC) are correlated to the amalgamation of microblocks welded by 2.75-2.6 Ga and ~2.5 Ga GGBs. The lithological assemblages in the GGBs are broadly represented by volcano-sedimentary sequences, subduction-collision related granitoids and bimodal volcanic rocks(basalt and dacite) interlayered with minor komatiites and calc-alkalic volcanic rocks(basalt, andesite and felsic rock). The geochemical features of meta-basalts in the major GGBs of the NCC display affinity with N-MORB, E-MORB, OIB and calc-alkaline basalt, suggesting that the microblocks were separated by oceanic realm. The granitoid rocks display arc signature with enrichment of LILE(K,Rb, Sr, Ba) and LREE, and depletion of HFSE(Nb, Ta, Th, U, Ti) and HREE, and fall in the VAG field. The major mineralization includes Neoarchean BIF-type iron and VMS-type Cu-Zb deposits and these,together with the associated supracrustal rocks possibly formed in back-arc basins or arc-related oceanic slab subduction setting with or without input from mantle plumes. The 2.75-2.60 Ga TTG rocks,komatiites, meta-basalts and metasedimentary rocks in the Yanlingguan GGB are correlated to the upwelling mantle plume with eruption close to the continental margin within an ocean basin. The volcanosedimentary rocks and granitoid rocks in the late Neoarchean GGBs display formation ages of 2.60-2.48 Ga, followed by metamorphism at 2.52-2.47 Ga, corresponding to a typical modern-style subduction-collision system operating at the dawn of Proterozoic. The late Neoarchean komatiite(Dongwufenzi GGB), sanukitoid(Dongwufenzi GGB and Western Shandong GGB), BIF(Zunhua GGB) and VMS deposit(Hongtoushan-Qingyuan-Helong GGB) have closer connection to a combined process of oceanic slab subduction and mantle plume. The Neoarchean cratonization of the NCC appears to have involved two stages of tectonic process along the 2.75-2.6 Ga GGB and ~2.5 Ga GGBs, the former involve plume-arc interaction process, and the latter involving oceanic lithospheric subduction, with or without arcplume interaction.
基金financially supported by the National Natural Science Foundation of China(grants No.41173065 and 40703012)the China Geological Survey(grants No.1212011121075, 12120114020901,12120113094000 and 1212011120332)the Basic Outlay of Scientific Research Work from the Ministry of Science and Technology of the People's Republic of China(grant No.J1403)
文摘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.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.41530207 and 41772188)。
文摘The late Neoarchean metamorphosed volcanic rocks in the southern Liaoning Terrane(SLT) of the eastern North China Craton(NCC) are mainly composed of amphibolites and felsic gneisses and can be chemically classified as basalt(Group#1),basaltic andesite(Group#2),dacite(Group#3) and rhyodacite(Group#4).LA-ICP-MS zircon U-Th-Pb dating reveals that they formed at ~2.53-2.51 Ga.Group#1 samples are characterized by approximately flat chondrite-normalized rare earth element(REE) patterns with low(La/Yb)_N ratios and a narrow range of(Hf/Sm)N ratios,and their magmatic precursors were generated by partial melting of a depleted mantle wedge weakly metasomatized by subducted slab fluids.Compared to Group#1 samples,Group#2 samples display strongly fractionated REE patterns with higher(La/Yb)_N ratios and more scattered(Hf/Sm)N ratios,indicative of a depleted mantle wedge that had been intensely metasomatized by slab-derived melts and fluids.Group#3 samples are characterized by high MgO and transition trace element concentrations and fractionated REE patterns,which resemble typical high-Si adakites,and the magmatic precursors were derived from partial melting of a subducted oceanic slab.Group#4 samples have the highest SiO_2 and the lowest MgO and transition trace element contents,and were derived from partial melting of basaltic rocks at lower crust levels.Integrating these tholeiitic to calcalkaline volcanic rocks with the mass of contemporaneous dioritic-tonalitic-trondhjemitic-granodioritic gneisses,the late Neoarchean volcanic rocks in the SLT were most likely produced in an active continental margin.Furthermore,the affinities in lithological assemblages,metamorphism and tectonic regime among SLT,eastern Hebei to western Liaoning Terrane(EH-WLT),northern Liaoning to southern Jilin Terrane(NL-SJT),AnshanBenxi continental nucleus(ABN) and Yishui complex(YSC) collectively indicate that an integral and much larger continental block had been formed in the late Neoarchean and the craton-scale lateral accretion was a dominantly geodynamic mechanism in the eastern NCC.
基金the funds from Council of Scientific and Industrial Research (CSIR)Ministry of Earth Sciences, Government of India for the financial support(MoES/P.O.(Geosci)/4/2013)
文摘The Neoarchean Bundelkhand greenstone sequences at Mauranipur and Babina areas within the Bundelkhand Gneissic Complex preserve a variety of magmatic rocks such as komatiitic basalts, basalts,felsic volcanic rocks and high-Mg andesites belonging to the Baragaon, Raspahari and Koti Formations.The intrusive and extrusive komatiitic basalts are characterized by low SiO_2(39-53 wt.%), high MgO(18-25 wt.%).moderately high Fe_2O_3(7.1-11.6 wt.%), Al_2O_3(4.5-12.0 wt.%), and TiO_2(0.4-1.23 wt.%)with super to subchondritic(Gd/Yb)N ratios indicating garnet control on the melts. The intrusive komatiitic suite of Ti-enriched and Al-depleted type possesses predominant negative Eu and positive Nb, Ti and Y anomalies. The chemical composition of basalts classifies them into three types with varying SiO_2, TiO_2, MgO, Fe_2O_3, Al_2O_3 and CaO. At similar SiO_2 content of type Ⅰ and Ⅲ basalts, the type II basalts show slightly high Al_2O_3 and Fe_2O_3 contents. Significant negative anomalies of Nb, Zr, Hf and Ti, slightly enriched LREE with relatively flat HREE and low ∑REE contents are observed in type Ⅰ and Ⅱ basalts. TypeⅢ basalts show high Zr/Nb ratios(9.8-10.4), TiO_2(1.97-2.04 wt.%), but possess strikingly flat Zr, Hf, Y and Yb and are uncontaminated. Andesites from Agar and Koti have high SiO_2(55-64 wt.%), moderate TiO_2(0.4-0.7 wt.%), slightly low Al_2O_3(7-11.9 wt.%), medium to high MgO(3-8 wt.%) and CaO contents(10-17 wt.%). Anomalously high Cr, Co and Ni contents are observed in the Koti rhyolites. Tholeiitic to calc alkaline affinity of mafic-felsic volcanic rocks and basalt-andesite dacite-rhyolite differentiation indicate a mature arc and thickened crust during the advanced stage of the evolution of Neoarchean Bundelkhand greenstone belt in a convergent tectonic setting where the melts were derived from partial melting of thick basaltic crust metamorphosed to amphibolite-eclogite facies. The trace element systematics suggest the presence of arc-back arc association with varying magnitudes of crust-mantle interaction. La/Sm, La/Ta,Nb/Th, high MgO contents(>20 wt.%), CaO/Al_2O_3 and(Gd/Yb)_N > 1 along with the positive Nb anomalies of the komatiite basalts reflect a mantle plume source for their origin contaminated by subductionmetasomatized mantle lithosphere. The overall geochemical signatures of the ultramafic-mafic and felsic volcanic rocks endorse the Neoarchean plume-arc accretion tectonics in the Bundelkhand greenstone belt.
基金financially supported by the National Natural Science Foundation of China (41872194, 41872203)
文摘The Neoarchean charnockites of North margain of North China Craton(NCC) has become a hot topic into understanding the Early Precambrian basement. Although there is a broad consensus that charnockite is usually related to granulite facies metamorphism, whether its petrogenesis and tectonics characteristics remains controversial. Inclusions within hypersthene and garnet in charnockite are used to identify the peak granulite facies mineral assemblage, with the formation of Magnesian-charnockite attributed to anatexis of the protolith associated with this granulite facies metamorphism. The distribution of major and trace elements in charnockite is very uneven, significant depleted in LILEs(eg. Cs, U, Th) and HFSEs(eg. Nb, Ta, P and Ti), riched in Sr. Raising to the coexistence of Eu-enrichment and Eu-depletion type of REE patterns that influenced by the content of plagioclase and the remnants minerals of zircon and apatite. Comparative the petrography, geochemistry and geochronology data of Magnesian-charnockite indicate that the ratios of mafic pellites and basalts involved in anatectic melting are different by the upwelling of mantle magma, also resulting in the Eu anormals characteristics. The formation of the Magnesian-charnockite is closely connected with the subduction of the NCC oceanic crust(About ~2.5 Ga). However, Ferroan-charnockite may be the formed by the crystallization differentiation of the upwelling of mantle-derived shoshonitic magma(About ~2.45 Ga), with the lower crust material addition.
基金financial support of the Ministry of Science and Higher Education of the Russian Federationthe International Partnership Program of Chinese Academy of Sciences,Grant No.132744KYSB20190039。
文摘The first data on P-T metamorphic conditions coupled with U-Pb monazite and zircon age obtained for the Neoarchean Kitoy granulite-gneiss terrane(SW Siberian Craton).Alumina gneisses of the Kitoy terrane indicate two-staged metamorphic evolution.The first stage of regional metamorphism(M1)occurred at high-amphibolite facies conditions at T=780-800℃ and P=8-9 kbar.The second stage(M2)belongs to MT-HT/LP type of metamorphism with the wide temperature interval 600-750℃ and pressure 2-4 kbar.Two age peaks were established on the basis of U-Pb monazite and zircon dating in garnet-anthophyllite gneisses.Both of them correspond to the Neoarchean age:the age of M1 falls into the interval of ca.2489-2496 Ma,the age of M2-ca.2446-2456 Ma.The high-temperature metamorphism of the Kitoy block and nearly coeval granitoid magmatism can be an evidence for the Neoarchean collision in SW Siberian craton.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.41530207 and 41872196)Central University Basic Scientific Research Business Expenses of China University of Geosciences(Beijing)(Grant Nos.2-9-2019-055 and 2-9-2016-006)support by the undergraduate innovation and entrepreneurship program(X201911415003)。
文摘The late Archean(~3.0-2.5 Ga)was a key period of continental growth globally,which is widely considered to reflect the onset of vigorous plate tectonic activity,although related continental growth modes remain contentious.Here we investigate a suite of late Neoarchean metavolcanic rocks from the southwest Qixia area of the Jiaobei terrane in the North China Craton.The rocks in this suite include amphibolites,clinopyroxene amphibolites,and hornblende plagioclase gneisses.We present zircon U-Pb isotopic data which indicate that the protoliths of these rocks formed during~2549-2511 Ma.The(clinopyroxene)amphibolites correspond to meta-basaltic rocks,with some containing high modal content of titanite.These rocks show moderate to high FeO_(T)(8.96-13.62 wt.%)and TiO_(2)(0.59-1.59 wt.%),flat to less fractionated REE patterns,and mildly negative Th,Nb,and Ta anomalies,resembling those of Fe-tholeiites.In addition,they display positive zirconε_(Hf)(t)values(+2.6 to+8.7),and are devoid of crustal contamination or fractional crystallization.Combined with the low Nb/Yb(mostly<1.60)and(Hf/Sm)_N(mostly<0.95),low to moderate Th/Yb(0.08-0.54),and low V/Sc(5.53-9.19)ratios,these basaltic rocks are interpreted to have been derived from a relatively reduced and depleted mantle source that was mildly metasomatized by hydrous fluids.The hornblende plagioclase gneisses are meta-andesitic rocks,and occur interlayered with the basaltic rocks.They are transitional between tholeiitic and calc-alkaline rock series,and show fractionated REE patterns with evidently negative Th,Nb,and Ta anomalies.The depleted zirconε_(Hf)(t)values(+2.4 to+8.4)and quantitative chemical modeling suggest that the andesitic rocks were most likely generated by injection and mixing of juvenile felsic magmas with the tholeiitic basaltic magmas.In general,the chemical features and genesis of late Neoarchean meta-basaltic rocks in our study area resemble those of Mariana back-arc basin basalts.Combined with regional geological data,it is proposed that the Jiaobei terrane witnessed late Neoarchean crustal growth under a paired continental arc-back arc setting.On a regional context,we propose two distinct geodynamic mode of late Neoarchean continental growth across North China Craton(particularly the Eastern Block),i.e.,(1)arc-continent accretion along northwestern part of the Eastern Block;and(2)paired continental arc-back arc system surrounding the~3.8-2.7 Ga continental nuclei to the southeast.
文摘The Archean North China Craton is composed of the Western Block,Eastern Block and the intervening Central Orogenic Belt.A 4-10 km wide and 85 km long tectonic mélange belt informally called the Zanhuang
基金projects of the Natural Science Foundation of China(41722204)Basic Scientific Research Foundation of Central Universities of China(Jilin University).
文摘This study presents zircon LA-ICP-MS U-Pb geochronology,trace elements characteristics,whole rock geochemistry composition and zircon Hf isotopic data of Shuimowan tonalites in Dengfeng City.The results show that zircons from Shuimowan tonalites have oscillatory growth zoning,relatively high Th/U ratios(0.8--1.7)and upturned zircon rare earth elements(REE),indicating that they are magmatic origin.Shuimowan tonalites yield a weighted mean 207 Pb/206 Pb age of 2522±9 Ma,indicating they were formed in the latest Neoarchean.The tonalites are characterized by relatively low SiO 2 contents,high MgO and Na 2O contents,high REE(∑REE=322×10-6-354×10-6),obvious fractionation of REE,enrichment in LREE and feeble negative Eu anomaly(Eu/Eu*=0.97--0.99).The samples are also enriched in large ion lithophile elements and depleted in high field strength elements,with negative Nb,Ta,P and Ti anomalies.TheεHf(t)values of zircon grains from Shuimowan tonalites range between 3.5 and 5.3.Combined with regional tectonic evolution,it is suggested that Shuimowan tonalites were derived from partial melting of mantle peridotite metasomatized by the slab-derived felsic melt and formed in the arc magma tectonic setting related to plate subduction.Research on the Neoarchean Shuimowan tonalites provides a constraint for the study of the Pre-Cambrian tectonic evolution in the southern margin of North China Craton.
基金supposed bv the National Natural Science Foundation of China(Grant Nos.90814008,40634023 and 40973043)the National Basic Research Program of China(Grant No. 2009CB825002)+1 种基金Critical reviews and many useful suggestions by Prof.M.Santosh,Prof.Guochun Zhao(University of Hong Kong)an anonymous reviewer have greatly improved the final version of the manuscript
文摘The crustal growth of the North China Craton(NCC) during the Neoarchean time(2.5—2.8 Ga) is a hotly controversial topic,with some proposing thai the main crustal growth occurred in the late Neoarchean (2.5—2.6 Ga),in agreement with the time of the magmatism,whereas others suggest that the main crustal accretion took place during early Neoarchean time(2.7—2.8 Ga),consistent with the time of crustalformation of other cratons in the world.Zircon U-Pb ages and Hf isotope compositions can provide rigorous constraints on the time of crustal growth and the evolution and tectonic division of the NCC.In this contribution, we make a comprehensive review of zircon Hf isotope data in combination with zircon U-Pb geochronology and some geochemistry data from various divisions of the NCC with an aim to constrain the Neoarchean crustal growth of the NCC.The results suggest that both 2.7—2.8 Ga and 2.5—2.6 Ga crustal growth are distributed over the NCC and the former is much wider than previously suggested.The Eastern block is characterized by the main 2.7—2.8 Ga crustal growth with local new crustal-formation at 2.5—2.6 Ga,and the Yinshan block is characterized by～2.7 Ga crustal accretion as revealed by Hf-isotope data of detrital zircons from the Zhaertai Group.Detrital zircon data of the Khondalite Belt indicate that the main crustal growth period of the Western block is Paleoproterozoic involving some～2.6 Ga and minor Early- to Middle-Archean crustal components,and the crustal accretion in the Trans-North China Orogen(TNCO) has a wide age range from 2.5 Ga to 2.9 Ga with a notable regional discrepancy.Zircon Hf isotope compositions,coupled with zircon ages and other geochemical data suggest that the southern margin may not be an extension of the TNCO,and the evolution and tectonic division of the NCC is more complex than previously proposed,probably involving multi-stage crustal growth and subduction processes.However, there is no doubt that 2.7—2.8 Ga magmatism and crustal-formation are more widely distributed than previously considered,which is further supported by the data of zircons from Precambrian lower crustal rocks, overlying sedimentary cover,modern river sediments and Late Neoarchean syenogranites.
基金supported financially by the National Natural Science Foundation of China(Nos.42002238 and 41872057)。
文摘The basalts within the greenstone belt worldwide serve as an ideal target to decipher the nature of Archean mantle sources and further to extend the understanding of the early stages of Earth's evolution.To provide important insights into the issues,we carried out a detailed investigation of whole-rock geochemistry and Sm-Nd isotopes,and zircon U-Pb-Hf isotopes for the Late Neoarchean metamorphosed basalts in eastern Hebei,North China Craton.U-Pb isotopic dating using the LA-ICPMS on zircons reveals that the basalts in eastern Hebei erupted at ca.2.48-2.51 Ga and subsequently experienced multiple regional metamorphic events at 2477 and 1798 Ma,respectively.The metamorphosed basalts are featured by low SiO_(2),MgO,K_(2)O+Na_(2)O,and high Fe O contents,endowed with the subalkaline and high-Fe tholeiitic affinities.The radiogenic initial Nd and Hf isotope values and correlations among V,Ni and Cr contents strongly imply that the basalts experienced significant clinopyroxene and olivine fractionation and minor crustal contamination during magma evolution.They are also characterized by the relatively low total REE contents and exhibit significant depletions to moderate enrichments in the LREE contents,indicating the derivation from a deep mantle source in an Archean proto-mantle plume setting.
文摘Within the high-grade metamorphic basement, the central portion of North China Craton (NCC), a group of Neoarchean khondalites (KS) is identified. They are characterized by large ion lithophile elements (LILE) enrichment, lower abundances of Zr, Hf and Sr. Their rare earth element (REE) distribution has significant LREE enrichment and negative Eu anomalies. The protoliths of KS are interpreted as feldspathic quartzite, shale or petite and carbonite, deposited in a shallow sea upon cratonic shelf distant from the land. KS’s source region might be dominated by granitic rocks, with a minor amount of TTG, underwent comparatively severe chemical weathering. Considering relevent tectonic constraints, we suggest that khondalites from central portion of NCC, an important metamophosed sedimentary cover, are the most significant exogenetic marker of Neoarchean continental cratonization for NCC.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 49132070, 49302035, 49572140).
文摘An ancient unconformity event is identified within the granulite-facies province of North China, which is marked by the boundary between the overlying khondalite series (KS) and the basement grey gneiss complex (BGGC). REE patterns of KS suggest that their protoliths aM mature sediments. As documented by isotopic ages and metamorphic P-T-t paths, KS is originally deposited after the basement complex formed. Furthermore, the BGGC was overprinted by the metamorphic event associated with the KS. The binary structure of KS-BGGC is well preserved in the western part of North China craton (NCC), and it is structurally truncated and overlain by the Palaeoproterozoic Wntai rift, which suggests that the unconformity occurred in the Neoarchean, and represents the major tectono-thermal episodes of the Neoarchean continental cratonization of NCC.
基金supported by the projects of the CSIR-Emeritus ScientistINDEX Project from the Council of Scientific and Industrial Research (CSIR) to the National Geophysical Research Institute to Chakravadhanula Manikyamba+1 种基金the SERB-Research Scientist Project (No. SB/SRS/2019-20/27/EA) to Sohini Gangulythe DST INSPIRE fellowship for pursuing the Ph.D. programm at NGRI to Arijit Pahari。
文摘This study presents a comprehensive account of the petrogenetic and geodynamic evolution of the Bellara Trap volcanic rocks from the Ingaldhal Formation, Chitradurga Group, western Dharwar Craton(WDC). Geochemical attributes of these rocks are consistent with two groups with distinct evolutionary trends: one comprising tholeiitic, MORB(mid-ocean ridge basalt) type basalts(BTB) and the other corresponding to calc-alkaline andesites(BTA). Basalts are essentially composed of clinopyroxene and plagioclase whereas the andesites are porphyritic with phenocrysts of plagioclase, clinopyroxene and polycrystalline quartz embedded in a groundmass of K-feldspar, quartz and opaques. Primary igneous mineralogy is overprinted by greenschist facies metamorphism resulting in chlorite-actinolite-plagioclase assemblage. The BTB samples reflect nearly flat REE patterns with weak LREE enrichment in contrast to pronounced LREE enhancement over HREE discernible for BTA. Tectonically, the BTB samples correspond to an active mid-oceanic ridge-rift setting with a MORB composition, whereas a back-arc basin(BAB) regime is corroborated for the BTA samples fractionating from back-arc basin basalts. Geochemical imprints of subduction input are more pronounced in BTA compared to BTB as mirrored by their elevated abundances of incompatible fluid mobile elements like Ba, Th, U and LREE. The BTB is endowed with an N-to E-MORB signature attributable to minor contributions from subduction-related components at the inception of a back-arc basin in the vicinity of an active subduction system. The BTA derived through differentiation of a basaltic magma with BABB(back-arc basin basalt) affinity compositionally akin to a heterogeneous source mantle carrying depleted MORB-type and enriched arc-type components inducted with progressive subduction. The BABB-type andesites and MORB-type basalts from Bellara Traps record a compositional heterogeneity of mantle in an intraoceanic arc-back arc system. Mantle processes invoke a BABB-MORB spectrum with a MORB-like endmember and an arc-like endmember associated with a juvenile back-arc basin. This study infers a Neoarchean analogue of Mariana-type back-arc rift setting proximal to the arc with a gradual transition from anhydrous to hydrous melting processes synchronized with MORB-mantle and arc-mantle interaction during initiation of a nascent back arc adjacent to the arc. The MORB-BABB compositional spectrum for the Bellara Traps conforms to a Neoarchean back-arc basin that evolved under an extensional tectonic regime associated with incipient stages of back-arc rifting and incorporation of subduction-derived components in the mantle output. This study complies with Neoarchean intraoceanic accretionary cycle plate tectonics in WDC.
基金supported by the National Natural Science Foundation of China(Grant No.41972242)the Regional Geological Survey Project of China Geological Survey(Grant Nos.DD20190050&DD20221634)the Open Fund of the Research Center for Petrogenesis and Mineralization of Granitoid Rocks(Grant Nos.PMGR202002&PMGR202112)。
文摘Archean rock exposures in the Yangtze Craton of South China are scarce and have been only studied in small-scale outcrops for understanding its early crustal evolution.Geological investigations have been carried out for three Neoarchean gneissic granitic plutons from the Dabie orogen in the northeastern margin of the Yangtze Craton.Zircon U-Pb geochronology constrains the emplacement of high-K monzogranite at 2645±30 Ma,high-K syenogranite at 2630±37 Ma and Na-rich granodiorite at 2497±29 Ma.These findings provide direct evidence for the existence of∼2.7-2.5 Ga rocks in the Dabie orogen,which significantly contribute to the distribution and evolution of Neoarchean basement rocks in the Yangtze Craton.Zircon crystals from the three granite samples giveεHf(t)values of−0.9 to 3.7,−4.2 to−0.4 and−4.7 to 0.1,respectively,corresponding to T_(DM2) ages of 3186-2909,3372-3141 and 3297-3005 Ma.The magmatic zircons have δ^(18)O values of 5.06±0.27‰to 5.79±0.30‰(average 5.59‰),6.14±0.24 to 7.35±0.26‰(average 6.87‰)and 5.95±0.17‰to 7.09±0.17‰(average 6.55‰),respectively.Considering the possible decrease of δ^(18)O value due to the lead loss during post-crystallization alteration,the primary δ^(18)O values might be substantially higher than those of the normal mantle zircon value(δ^(18)O=5.3±0.6‰).These isotopic data indicate that the Jiamiao Neoarchean granites were largely generated through reworking of Paleo-Mesoarchean basement rocks with a minor contribution of supracrustal material.Integrating our findings with previous results,we infer that the Archean-Paleoproterozoic complexes/terranes of the Yangtze Craton have distinct petrogenesis and the timings of the transition from Na-rich to high-K granites,crustal growth,and tectonothermal evolution before∼2.0 Ga.However,all of them underwent metamorphism at about 2.0 Ga.These observations also reveal that the Yangtze Craton might comprise several microcontinents that evolved individually and collided to form a unified craton at∼2.0 Ga,synchronous with the assembly of the Columbia supercontinent.However,the lack of relevant data from the southeastern Yangtze Craton may have a critical influence on this conclusion and should be solved in the future.
