Abstract:Based on previous researches, this paper chiefly summarized some progresses made in the study of continental lower crust granulite xenoliths in North China Craton (Sino-Korean Craton) and South China region as well as their geological significance. Eight aspects are dealt with in this paper: ① general situation; ② current researches conducted both in China and abroad; ③ modes of occurrence of granulite xenoliths; ④ rock types, associated mantle rocks, mineral assemblages and p-t conditions of granulite xenoliths; ⑤ dating of original rock age and metamorphic age; ⑥ petrochemistry and geochemistry of granulite xenoliths; ⑦ lower crust position in North China Craton and South China region represented by granulite xenoliths; ⑧ geological significance of isotope ages and genesis of granulite xenoliths. Four scientific problems and some suggestions concerning further studies are also put forward in this paper.

Abstract:The Zanhuang metamorphic complex is significant for understanding the Precambrian tectonics and evolution of the North China Craton. Metabasic rocks composed of amphibolite and amphibole-bearing plagioclase gneiss as thin layers or lenses are widely distributed within felsic gneisses and biotite-plagioclase gneisses. These metabasic rocks together with country rocks underwent high-amphibolite facies metamorphism, and abundant metamorphic zircons were formed during this thermal event. SIMS U-Pb chronological analysis indicates that metamorphic zircons record peak high-amphibolite facies metamorphism at 1 868～1 842 Ma. These Paleoproterozoic metamorphic ages are largely in accordance with metamorphic ages of ～1 850 Ma produced from high-pressure granulites in the northern segment of the Trans-North China Orogen, indicating that a significant subduction-collision event did occur in the Trans-North China Orogen between the eastern block and the western block during Paleoproterozoic (～1 850 Ma).

Abstract:The Longshoushan Group is a part of Precambrian metamorphic basement of the Alxa block. Its origin is particularly important for constraining the western boundary of the North China Craton(NCC)and understanding the evolutionary history of China's cratons. In this study, LA-ICP-MS U-Pb dating technique was used to determine the ages of different rocks from Longshoushan Group and Dunzigou Group. The analytical results of detrital zircon grains from the metasedimentary rock in the Longshoushan Group gave two age populations: ～2.01 Ga and～2.15 Ga. The magmatic zircons and metamorphic zircons from the granitic gneiss yield age spans of 2.04～2.17 Ga and 1.89～1.93 Ga, respectively. These ages indicate that the Longshoushan Group was formed in Paleoproterozoic. The metamorphic zircons from amphibolite in the Longshoushan Group yielded a metamorphic age of ca.1.85 Ga, indicating that the Longshoushan Group underwent an amphibolite-facies metamorphism during late Paleoproterozoic. Detrital zircon ages of the metasedimentary rock from the overlying Dunzigou Group vary from 2.03 to 2.05 Ga, suggesting a single Paleoproterozoic provenance. These data imply that the southern Alxa block had an affinity with the NCC during early Precambrian period.

Abstract:The Huangjinshan pyroxene diorite intruded Paleoproterozoic Hutuo Group, and was cut and penetrated by late Paleoproterozoic dolerite in Wutai Mountains area. SHRIMP zircon dating of pyroxene diorite yielded a ²⁰⁷Pb/²⁰⁶Pb age of 1 755±12 Ma, which is similar to ages of the widely distributed Paleoproterozoic mafic dyke swarms in the North China Craton. The pyroxene diorite sample contains high TiO₂, Fe₂O₃, P₂O₅, K₂O and Na₂O, and low MgO (Mg^#, 36～39). The sample has high concentration of REE (365.75×10^-6～411.97×10^-6), with strong LREE fractionation and slight fractionation of HREE, and slightly negative Eu anomaly. The rock samples are enriched in Rb, Ba, Sr, Zr and Hf, and are depleted in Cr and Ni. The variation of (⁸⁷Sr/⁸⁶Sr)_i and (¹⁴³Nd/¹⁴⁴Nd)_i ratios is small, and εNd(t=1.76 Ga)values vary from -6.08 to -4.81. Based on a comprehensive analysis of all evidence, the authors hold that Huangjinshan pyroxene diorite was partially melted from enriched upper lithosphere mantle related to the mantle plume and was fractionally crystallized with the same magmatic source of mafic dyke swarms widely distributed in North China Craton, thus representing a different stage of the same magmatic cycle. Zircons in pyroxene diorite samples show the same characteristics as basic-intermediate rocks, but their Th/U ratios are very low, similar to features of the metamorphic zircon. Generally speaking, Th/U ratios are high in pyroxene diorite whereas the partition coefficients of Th and U are very low in plagioclase, clinopyroxene and hornblende. It is thus inferred that the Th/U ratios in zircon are independent of the source magma and major diagenetic minerals, and are probably related to crystallization of Th-rich accessory minerals. The zircons with very low Th/U ratios in pyroxene diorite indicate that we should be very careful in explanation of the genesis of zircon by Th/U ratios.

Abstract:Al-rich paragneisses in Jingshan Group are extensively distributed in the early Precambrian metamorphic basement of Shandong peninsula, southeast part of the North China Craton. Zircons separated from Al-rich paragneisses are divided into three main types based on cathodoluminescence (CL) and in situ U-Pb dating, i.e., inherited (magmatic or detrital) zircon, HP metamorphic zircon and retrogressive zircon. The inherited zircon records two group ²⁰⁷Pb/²⁰⁶Pb ages of ～2 650 Ma and ～2 100 Ma, indicating two magmatic-thermal events occurring in Neoarchean and Paleoproterozoic epochs and the existence of Paleoproterozoic protoliths of Al-rich paragneisses. In contrast, the homogeneous HP metamorphic zircon records younger ²⁰⁷Pb/²⁰⁶Pb ages ranging from 1 900 Ma to 1 850 Ma, which represent peak HP granulite-facies metamorphic times of Al-rich paragneisses in Jingshan Group . The retrogressive zircon records the youngest ²⁰⁷Pb/²⁰⁶Pb ages of 1 840～1 820 Ma, which represent late medium-and low-granulites-facies retrograde metamorphic times of Al-rich paragneisses in Jingshan Group. These results indicate that the Paleoproterozoic protoliths of Al-rich paragneisses, together with their TTG rocks and mafic rocks, were subducted to coeval Paleoproterozoic HP metamorphism (1 900～1 850 Ma), followed by late medium-and low-granulites-facies retrogression (1 840～1 820 Ma). This new result has very important significance for deep discussion of the genetic mechanism and geodynamic model of the HP granulites distributed in the southeast part of the North China Craton.

Abstract:Abundant and complex metamorphic rocks are widespread in Sanjiang region, southeastern Tibetan plateau. Amphibole-bearing metamorphic rocks, comprising amphibolite and amphibole-bearing plagioclase gneiss, occur as lenses or thin layers within metamorphic supracrustal rocks. Amphibolite could be subdivided into two types: one is a retrogressive product of garnet-pyroxenolite, and the other is a product of mafic protolith which experienced amphibolite- to granulite-facies metamorphism. The amphibolite has an average SiO₂ content of ～50.0%, with high-Al, low-Ti, Zr and Zr/Y ratio. The chondrite-normalized REE patterns show enrichment of LREE with slightly negative or no Eu anomalies. These geochemical characteristics are very similar to those of the island-arc basalt, indicating that the protolith of the amphibolites was formed in the subduction-collision tectonic setting. In contrast, the amphibole-bearing plagioclase gneiss has a higher average SiO₂ content of ～63.64% with low MgO and TiO₂ content, characterized by the enrichment of large ionic lithophile elements (LILE) such as K, Rb, Ba and Th, and the depletion of high field strength elements (HFSE) such as Ti, Zr, Hf, Nb and Ta. The REE patterns are characterized by relatively high fractionations of LREE and HREE with pronounced negative Eu anomalies. These geochemical features are inherited from those of andesitic or andesitic/basaltic rocks, indicating that the protolith of the amphibole-bearing plagioclase gneiss appeared in a plate convergence tectonic setting.

Abstract:Ultramafic rocks occur mainly as inclusions or xenoliths in Yishui magmatic and metamorphic complexes, without typical spinifex texture. Their chemical compositions are characterized by high MgO (22.23%～27.49%,>20%) and low SiO₂ (38.60%～49.40%), TiO₂ (0.11%～0.39%,<0.5%) and K₂O (0.02%～0.39%,<0.5%) content. As for other oxide compositions, total iron (FeO^T) values are in the range of 7.68%～11.14%, CaO content ranges 5.15%～12.86%, and Al₂O₃ content varies remarkably in the range of 1.56%～8.94%. The CaO/Al₂O₃ ratios of most samples are 0.61～1.36(≈1), with the exception of three samples, whose CaO/Al₂O₃ ratios are 7.70～8.20 (>1) and MgO/FeO^T ratios are 2.00～3.33. MnO(0.13%～0.20%) and Na₂O(0.12%～1.03%) content is low. The rocks can be roughly divided into two types, i.e., olivine-pyroxenite and spinel-hornblende-pyroxenite. The former containing olivine shows strong serpentinization, with a mineral assemblage of calcic clinopyroxene+olivine+minor orthopyroxene, followed by the altered mineral assemblage of serpentine±chromite+magnetite±hornblende±spinel. The latter containing no olivine has features of local talcization, and its mineral assemblage consists of (bronze) pyroxene + clinopyroxene (diopside)+spinel, followed by hornblende+magnetite±talc±serpentine. In general, the ultramafic rocks have fairly low REE content (∑REE) =11.45×10^-6～22.63×10^-6) with LREE/HREE ratios in the range of 1.64～4.40. The chondrite-normalized REE patterns of all samples show negative anomalies of Ce and Eu. Most samples show indistinct fractionation of LREE, LREE-HREE and HREE, with the exception of three olivine-containing samples showing relatively high LREE/HREE ratios (3.35～4.40). The trace elements in the ultramafic rocks show significantly different anomalies of incompatible elements Rb, Ba, U, Nb, Sr and Zr. Ba and Nb assume negative anomalies, and Rb and U as well as part of Sr display positive anomalies; in addition, negative Zr and Ti anomalies appear in olivine-pyroxenite, and there exist no Zr and Ti anomalies. SHRIMP zircon U-Pb dating of the ultramafic rock (YS0631) shows that the metamorphic zircon U-Pb ages are 2 560～2 605 Ma, with a crystal zircon age of 2 719 Ma. Hf isotopic composition of the sample has Hf(t) value of 8.2, indicating the depleted mantle model age of 2 680 Ma. In summary, the ultramafic rocks originated from the mantle, formed in the early Neoarchean, and were then subjected to anatexis and magmatic effects, thus experiencing metamorphic transformation.

Abstract:Carbon and oxygen isotopes of carbonate strata in Liaohe Group, Zhongtiao Group and Wanzi Group were studied in this paper. The δ¹³C_PDB values of banded marble in Wangjiagou Formation of Liaohe Group vary from-1.02‰ to 3.14‰, mostly in the range of 0.16‰～1.79‰. The average δ¹³C_PDB is 1.07‰, which is higher than the average δ¹³C_PDB of marine carbonate. The δ¹⁸O_PDB values of Wangjiagou banded marble vary from -17.2‰ to -10.1‰, mostly in the range of -13.4‰～-10.1‰. The average δ¹⁸O_PDB is -11.9‰. The δ¹³C_PDB values of Yujiashan marble in Zhongtiao Group vary from -0.2‰ to 0.8‰, mostly in the range of 0～0.3‰. The average δ¹³C_PDB of fourteen samples along one section is 0.34‰, slightly lower than the average δ¹³C_PDB of marine carbonate. The average δ¹³C_PDB of the next sixteen samples along another section is 0.54‰, basically consistent with the average δ¹³C_PDB of marine carbonate. The δ¹⁸O_PDB values of Yujiashan marble vary from -7.9‰ to -6.1‰. The average δ¹⁸O_PDB of the first fourteen samples and the second sixteen samples are -6.80‰ and -6.88‰ respectively, with no obvious difference. The δ¹³C_PDB values of Songjiakou marble in Wanzi Group vary from 1.0‰ to 3.8‰, 2.65‰ on average, which is higher than the average δ¹³C_PDB of marine carbonate evidently. The δ¹⁸O_PDB values of Songjiakou marble vary from -8.8‰ to -5.7‰, -6.97‰ on average. The results show that all the studied marbles were formed in a comparatively stable but fluctuating environment. There existed seasonal variations of sea level and climate but no sudden drastic event during the marble sedimentary period. As to the Jatulian event, marbles in Songjiakou Formation showed response but marbles in Yujiashan formation had no response to it. The effect on Wangjiagou Formation is uncertain. This study has also proved that the Jatulian event was a global event that had extensive influence in space but could serve as an eruptive event in time scale.

Abstract:The formation of the Columbian supercontinent at 1.9～1.8 Ga has been a topic of wide interest in recent years. The assemblage of the supercontinent has been recorded in the Siberian craton by the 1.9～1.8 Ga high grade metamorphic belt. The U-Pb zircon geochronological study has gained a new insight into the geological evolution of the southeastern margin of the Siberian craton. Zircons from migmatitic biotite plagioclase gneiss show core-rim textures in cathodoluminescence (CL) image. Core features indicate detrital deposits of magmatic origin zircons. Structureless overgrowths are metamorphic in origin. The four age groups of detrital cores are ≥2.57, ～2.39, ～2.33 and ～2.20 Ga. The age of migmatitic overgrowths is 1.84 Ga. It is therefore suggested that the sediments were deposited at～2.20 Ga and derived from Archean and Paleoproterozoic source rocks. These data indicate that the metamorphic rocks were formed in Paleoproterozoic instead of Archaean as conventionally thought. Hafnium analysis shows that the cores of zircons from migmatitic felsic gneiss have negative or positive as well as variable εHf(t) values (-16.2 to+2.7) and Archean (3.7 to 2.8 Ga) depleted-mantle model ages, the overgrowths of zircon have negative variable εHf (t) values (-18.6 to -7.5) and Archean (3.6 to 2.9 Ga) depleted-mantle model ages. The εHf(t) values of most zircon cores are negative, indicative of a recycled continental crust. The source region of these magmas might have been related to Archean material of the Aldan Craton, suggesting derivation from an isotopically heterogeneous old crust source. U-Pb in situ zircon dating shows a 1.84 Ga overgrowth of zircons in migmatitic gneiss, implying Paleoproterozoic migmatization. The 1.84 Ga age of the migmatization event is correlated with the 1.9～1.8 Ga high grade metamorphism recorded in other regions of the world such as North America craton, Greenland, Baltica, and North China Craton, and was probably related to the formation of the Columbia.

Abstract:This paper has reported zircon U-Pb dating, Hf isotopes, major and trace elements, and Sr-Nd isotope data of the volcanic rocks from the Laotudingzi Formation in the eastern margin of the Jiamusi Massif and the upper segment of the Baoquan Formation in the Xiao Hinggan Mountains, with the aim of constraining the regional tectonic evolution in eastern Heilongjiang Province. The former is composed mainly of rhyolite and subordinately of alkaline basalt, whereas the latter consists chiefly of rhyolite. Zircons from these volcanic rocks display striped absorption or fine-scale oscillatory growth zoning as well as high Th/U ratios(0.28～1.64), implying a magmatic origin. The dating results show that they were probably all formed in middle Devonian(a weighted mean ²⁰⁶Pb/²³⁸U age of 386 Ma). The mafic rocks from the Laotudingzi Formation in the eastern margin of the Jiamusi Massif have the data SiO₂=50.40%～55.66%, Mg^#=0.39～0.50, Na₂O/K₂O=2.88～4.99, Al₂O₃=15.66%～18.06%,(⁸⁷Sr/⁸⁶Sr)_i=0.705 99, εNd(t)=+2.04, and show the enrichment of light rare earth elements (LREEs) and Cr, Co, Ni and Zr, and depletion of Nb, Ta, Ti, with high Zr/Y, Nb/U, Ta/U and Ce/Pb ratios, whereas the felsic rocks have the data SiO₂=77.59%～78.75%, Na₂O/K₂O=0.32～0.36, Al₂O₃=11.62%～11.76%,(⁸⁷Sr/⁸⁶Sr)_i=0.703 78～0.707 36, εNd(t)=-2.20～-4.15, εHf(t)=+1.8～+8.6, t_DM1= 671～998 Ma, and display enrichment of Rb, Th, U, K and depletion of Nb, Ta, U, P, Ti. These data are typical of bimodal volcanism and indicate that the former might have been derived from the lithosphere mantle, contaminated by crustal material, whereas the latter probably originated from partial melting of the newly accreted crust. The rhyolite from the upper Baoquan Formation in the Xiao Hinggan Mountains is characterized by high SiO₂(74.64%～76.09%), enrichment of K₂O(Na₂O/K₂O=0.42～0.81), low Al₂O₃(12.56%～12.63%), enrichment of high field strength elements(such as Zr and Hf)and large ion lithophile elements(LILEs)such as Th, U and K, and strong depletion of Sr, Eu, P and Ti. These data are similar to features of A-type rhyolites. Besides, these volcanic rocks have εHf(t)=+2.5～+6.4, t_DM1= 837～983 Ma, consistent with the data of Phanerozoic granitoids in the CAOB, suggesting that they might have originated from partial melting of the newly accreted crust. Combined with the regional geological data, it is inferred that there might have existed a passive continental-margin setting in the eastern margin of the Jiamusi Massif in middle Devonian, where the bimodal volcanic rocks were probably formed. Furthermore, the coeval A-type rhyolite of the upper Baoquan Formation in the Xiao Hinggan Mountains was probably formed in an intra-continental extensional environment.

Abstract:Petrogenesis and tectonic setting of Mesozoic granites in central Da Hinggan Mountains constitute the key to investigating the tectonic and magmatic evolution of Northeast China. Systematical studies of petrology, geochemistry and Sr-Nd and Lu-Hf isotopes of the granites in Wulanhaote-Suolun region indicate that the Middle-Late Triassic Chagan granite is of A₂ type. The Early-Middle Jurassic Jingyang granite is an I-type granite and the Dashizhai granite is a very special kind of granite which shows tetrad REE patterns. On the basis of the Sr values, the Early Cretaceous granites can be divided into two types, i.e., the high-Sr type and the low-Sr type. The two types of granites possess the same or similar magmatic sources but originated in different depths. The high-Sr type granite is similar to C-type adakitic granite which originated from the higher pressure of the lower crust, while the low-Sr type and Yonghetun granite are highly fractionated I-type granites derived from the middle crust of lower pressure. Considering Sr-Nd-Hf isotopic data of granites in the Wulanhaote-Suolun region and the results of previous studies, the authors suggest that crustal growth of the study area occurred in the Phanerozoic. As indicated by the high positive zircon εHf(t) and εNd(t) values and the new young two-stage model age of each of the five intrusions, their magmatic sources must have mainly consisted of new crustal materials during the accretion in Phanerozoic, with the addition of some old crust components. And along with the variation of the emplacement time of the granites gradually towards newness,the εHf(t) values of the zircon change to lowness. The authors consider that magmatic underplating and exhumation of the old crust caused by the mantle upwelling were responsible for the complicatedness of the compositions of the lower crustal source rock.

Abstract:The Chuzhou basin, one of the several late Mesozoic volcanic basins developed in the middle and lower reaches of the Yangtze River, is the only basin directly superimposed upon the Dabie orogenic belt, with relatively old basement composed of Neoproterozoic-lower Paleozoic strata. The volcanic rocks in the Chuzhou basin are mainly intermediate-acidic trachyandesite and trachydacite, which belong to high-K cal-alkaline series and greatly differ from most late Mesozoic volcanic basins in the middle and lower reaches of the Yangtze River such as Ningwu basin, Luzong basin, Lishui basin and Huaining basin which belong to the shoshonitic series in geochemistry. In this study, the authors used zircon SHRIMP U-Pb technique to perform accurate dating of a trachyandesitic sample from the Huangshiba Formation in the Chuzhou basin, which yielded an emplacement age of 128±1 Ma. This age is similar to the emplacement ages of volcanic/sub-volcanic rocks in other late Mesozoic volcanic basins, suggesting that the whole volcanism in the middle and lower reaches of the Yangtze River were developed in a very short period of time. The volcanic rocks in the Chuzhou basin have remarkably lower εNd(t) values than those in other volcanic basins but are similar to those of the late Mesozoic granitoid intrusive bodies in the Dabie orogen, indicating that their parent magma might have been mainly derived from partial melting of "old" lower crust.

Abstract:The Tianzhushan intrusive body is one of the representative plutons in the Dabie orogen, where late Mesozoic granitoid intrusive bodies are widely distributed, locates near the Wuhe-Shuihou fault which separates the UHP metamorphic complex of South Dabie from the block of North Dabie. This intrusive body is a composite intrusion consisting of three generations of intrusions: diorite, quartz syenite/granodiorite, and alkali-feldspar granite respectively from early to late. All the complexes belong to high-K calc-alkaline series, but the geochemical characteristics of the alkali-feldspar granite are remarkably different from other types of rocks and similar to things of A-type granite to a considerable degree. The alkali-feldspar granite has abundant enclaves and lower Zr saturation temperature,showing great difference from typical A-type granite and probably belonging to a highly evolved I-type granite. The geochemical characteristics of the Tianzhushan intrusive body are similar to those of other late Mesozoic granitoid intrusive bodies in the Dabie orogen, derived from partial melting of "old" lower crust under the tectonic backdrop of all eastern China lithospheric thinning in late Mesozoic. The granodiorite and alkali-feldspar granite are similar to each other in the emplacement age, and their zircon LA-ICP-MS U-Pb ages are 127.8 ±0.7 Ma and 127.7±1.0 Ma respectively, corresponding to the lithofacies features. It is thus held that the granodiorite had not been entirety concreted during the intrusion of the alkali-feldspar granitic magma.

Abstract:The mafic-ultramafic rocks of Dongdougou are located in the orogenic belt between the Tarim plate and the Yili-central Tianshan plate, southwestern Tianshan. Harzburgite is the main type of peridotite, generally metasomatized by hydrous melt or fluid. It includes different types of spinels, being red-brown, brown, dark green, and light green in color. Cr₂O₃ and FeO decrease gradually whereas Al₂O₃ and MgO increase with the metasomatism. Studies indicate that red-brown and brown picotiles constitute the primary type, while green magnesium spinels possess the second place. The compositions of the primary picotiles are variable with Cr^# and Mg^# in the range of 0.41～0.87 and 0.21～0.61 respectively, which may indicate polyphase origin of melting. Secondary spinels have different shapes, and their compositions vary tremendously, exhibiting two stages of metasomatism or metamorphism. The primary picotiles have characteristics of peridotite in a subducting upper plate mantle wedge zone, which implies the host rocks might have been the fragments of peridotite from a SSZ volcanic arc environment.

Abstract:The existence of the special apatite-orthopyroxene association in the felsic gneiss of the Larsemann Hills, east Antarctica, suggests the granulite facies metamorphism of the gneiss. The concomitant fluid-absent partial melting in the felsic gneiss was responsible for the melt segregation and residues which were favorable for the formation of Ap-Opx. The residual minerals like apatite and ilmenite are enriched in REE and have strongly affected the REE patterns of the rocks. The presence of the Ap-Opx assemblage implies the existence of appropriate but insufficient effective CaO component in the system. The crystallization of minerals in order of apatite, magnetite-ilmenite, garnet and orthopyroxene has demonstrated the changing mobile-residual components and progressive dehydration in the high-grade metamorphism. The metamorphic felsic rock rich in Ap-Opx is the unique rock derived in metamorphism, with no corresponding protolith.