Fluid/melt inclusions in Cenozoic mantle xenoliths from Linqu,Shandong Province,eastern China: Implications for asthenosphere-lithosphere interactions

Fluid and melt inclusions in mantle xenoliths are thought as direct samples to study mantle liquids. Here we apply Raman mi- crospectroscopy and microthermometry to fluid/melt inclusions in lherzolite xenoliths in Qiaoshan basalts, a Miocene volcano in Linqu, Shandong Province, eastern China. These inclusions include (1) early CO2 fluid inclusions, (2) early carbonate melt inclu-sions, (3) late CO2 fluid inclusions, and (4) late silicate melt inclusions. Among the early CO2 fluid inclusions, most consist of...     

Hf isotopes of the 3.8 Ga zircons in eastern Hebei Province, China： Implications for early crustal evolution of the North China Craton

Zircon U-Pb dating indicates that the fuchsite quartzite in eastern Hebei Province was derived from weathering and erosion of the 3.6-3.8 Ga granitic rocks. In-situ zircon Hf analyses show that the Lu-Hf isotopic system remained closed during later thermal disturbances. Zircons with concordant ages have Hf isotopic model ages of about 3.8 Ga, suggesting a recycling of this ancient crust. The -3.8 Ga zircons have similar Hf isotopic compositions to those of chondrite, indicating that their source rocks （granitic rocks） were derived from partial melting of the juvenile crust which originated from a mantle without significant crust-mantle differentiation. Therefore, it is proposed that there was no large-scale crustal growth before -3.8 Ga in eastern Hebei Province. Considering zircon Hf isotopic data from other areas, it is concluded that the most ancient crust in the North China Craton probably formed at about 4.0 Ga, and the possibility to find crust older than 4.0 Ga is very limited.     

Carbon isotopic composition of mantle xenoliths in alkali basalt from Damaping, Hebei

The carbon isotopic composition of CO-2, CO and CH-4 extracted by pyrolysis from spinel lherzolite and black pyroxenolite xenoliths in alkali basalt from Damaping has been measured with GC_MS. The results show that, at heating temperatures from 400 to 1 140℃, the δ 13C of CO-2 and CO is -22‰--27‰, and that of CH-4 -30‰--50‰. The data imply that the magma which was generated in the upper mantle by partial melting in the area has experienced the multistage degassing process, and the δ 13C values represent the carbon isotopic composition of CO-2, CO and CH-4 remaining in it, respectively.     

Repeated modification of lithospheric mantle in the eastern North China Craton: Constraints from SHRIMP zircon U-Pb dating of dunite xenoliths in western Shandong

Four dunite xenoliths from the Tietonggou intrusion of western Shandong,China,were subjected to SHRIMP zircon U-Pb dating to constrain timing of the North China Craton(NCC) destruction,a topic of much controversy.Cathodoluminescence images revealed that 15 of the 18 zircon grains from the xenoliths display striped absorption.The rest showed oscillatory growth zoniation.All the zircons had variable contents of Th(49-3569 ppm;average,885 ppm) and U(184-5398 ppm;average,1277 ppm),and variable Th/U ratios(0.15-2.04).These zircon characteristics indicate a magmatic origin.The zircon age data can be divided into five groups:131-145,151-164,261-280,434-452,and 500-516 Ma.Group I(131-145 Ma) is consistent with timing of formation of the Tietonggou high-Mg diorites.Group II(151-164 Ma) is similar in age to Middle-Late Jurassic magmatism in the eastern NCC,which included both mantle-derived and intensive crust-derived magmatism.Group III(261-280 Ma) is similar in age to the Emeishan large igneous province,and Group IV(434-452 Ma) is similar in age to Paleozoic high-silica magmatism in the eastern NCC.Group V(500-516 Ma) may correspond to the global Pan-African event.Results indicate repeated modification of lithospheric mantle in the eastern NCC,and suggest that the most intensive modification occurred in the late Mesozoic(131-164 Ma).     

Evidence of Nd isotope for unhomogeneity and origin of upper mantle of North China platform

Based on isptopic age of Sm-Nd and its initial composition and its evolution obtained during the recent years of archean metamorphic magnesio-ferro the vocanics of upper mantle of the North China platform, it is concluded that the isotopic composition of Archean upper mantle of the North China platform is not homogeneous, and values of I_ND don not change regularly through the whole Archean; in contrast, they present obvious differences in different regions. All this demands that the unhomogeneity of Archean upper mantle of the North China platform inherits initial unhomogeneity of origin, and the origin of the North China platform should contribute to uneven accumulation of planetesimals.     

Uppermost mantle structure of the North China Craton: Constraints from interstation Pn travel time difference tomography

The uppermost mantle is the key area for exchange of heat flux and material convection between the crust and lithospheric mantle. Spatial variations of lithospheric thinning and dynamic processes in the North China Craton could inevitably induce the velocity heterogeneity in the uppermost mantle. In this study, we used Pn arrivals from permanent seismic stations in North China and surrounding regions to construct a tomographic image of the North China Craton. The tomographic method with Pn travel time difference data were used to study the velocity variations in the uppermost mantle. Pn velocities in the uppermost mantle varied significantly in the Eastern, Central and Western blocks of the North China Craton. This suggests that the lithosphere beneath different blocks of the North China Craton have experienced distinct tectonic evolutions and dynamic processes since the Paleozoic. The current uppermost mantle has been imprinted by these tectonic and dynamic processes. Fast Pn velocities are prominent beneath the Bohai Bay Basin in the Eastern Block of the North China Craton, suggesting residuals of the Archean lithospheric mantle. Beneath the Tanlu Fault Zone and Bohai Sea, slow Pn velocities are present in the uppermost mantle, which can be attributed to significant lithospheric thinning and asthenospheric upwelling. The newly formed lithospheric mantle beneath Yanshan Mountain may be the dominant reason for the existence of slow Pn velocities in this region. Conversely, the ancient lower crust and lithospheric mantle already have been delaminated. In the Central Block, significant slow Pn velocities are present in Taihangshan Mountain, which also extends northward to the Yinchuan-Hetao Rift on the northern margin of the Ordos Block and Yinshan Orogen. This characteristic probably is a result of hot asthenospheric upwelling along the active tectonic boundary on the margin of the Western Block. The protracted thermal erosion and underplating of hot asthenospheric upwelling may induce lithospheric thinning and significant slow velocities in the uppermost mantle. Fast velocities beneath the Western Block suggest that the thick, cold and refractory Archean lithospheric keel of craton still is retained without apparent destruction.     

冀北退变榴辉岩的Pb同位素特征

冀北退变榴辉岩的全岩Pb同位素比值(206Pb/204Pb)i,(207Pb/204Pb)i和(208Pb/204Pb)i分别为17.324～17.460,15.412～15.464和37.216～37.380;△(207Pb/204Pb)i和△(208Pb/204Pb)i相应为4.026～8.034和61.285～69.928,表明岩浆源区为具DUPAL异常的富集地幔,可能为亏损的软流圈地幔(DMM)与第一类富集地幔端元(EMI)相混合的异常地幔,指示该区早先存在有一次板块消减事件.这对正确认识华北古陆块北缘的大地构造格局和演化具有十分重要的意义.     

Thermodynamic evolution of lithosphere of the North China craton： Records from lower crust and upper mantle xenoliths from Hannuoba

Lithospheric thinning in East China attracts much attention of geologists. In many cases where a lithospheric thinning is inferred, the trigger for instability is a preced-ing episode of crustal thickening by the continental colli-sion[1]. Lithospheric processes (e.g. lithospheric thinning) could be recorded by the thermal history of the lower crustal and upper mantle xenoliths. Xu et al.[2] suggested that the cooling (from >1200 to 850℃) recorded by spinel harzburgite from Northeast China …     

U-Pb ages and Hf isotopes for detrital zircons from quartzite in the Paleoproterozoic Songshan Group on the southwestern margin of the North China Craton

In situ U-Pb dating and Lu-Hf isotopic analysis were carried out for detrital zircons from quartzite in the Paleoproterozoic Songshan Group on the southern margin of the North China Craton （NCC）. The results provide further constraints on the crustal formation and evolution history of NCC. Four ^207Pb/^206Pb age populations were obtained from 99 analyses, with clusters at -3.40 Ga, 2.77-2.80 Ga, -2.50 Ga and 2.34 Ga, respectively. The 3.40 Ga old zircons have similar Hf isotopic compositions to those from Archean rocks in the Jidong and Anshan areas of NCC. However, crustal remnants older than 3.6 Ga have been identified in the southern margin of NCC, the South China Craton, the northwestern part of the Qinling Orogen and its adjacent area. Thus, it is not easy to trace the source rock from which the 3.40 Ge detrital zircons were derived. It can be inferred that the crustal remnants older than 3.40 Ga might have been widely distributed in the North China Craton. The 2.77-2.80 Ga zircons make up a relatively small proportion and have the highest εHf（t） values （up to 6.1±1.6）, consistent with the Hf isotopic composition of the depleted mantle at 2.83 Ga. Their single-stage Hf model age of 2.83 Ga is close to their crystallized age, suggesting that their source rocks were extracted from the contemporaneous depleted mantle. The -2.50 Ga zircon grains constitute about 85% of the total grain population and their Hf isotopic compositions indicate major growth of juvenile crust at -2.50 Ga but minor reworking of ancient crust. The youngest zircon dated in this study gave an U-Pb age of 2337±2.3 Ma, which can be considered the maximum depositional age of the formation of the Songshan Group.     

Mantle olivine xenocrysts entrained in Mesozoic basalts from the North China craton：Implication for replacement process of lithospheric mantle

Mesozoic (125 Ma) Fangcheng basalts fromShandong Province contain clearly zoned olivines that arerare in terrestrial samples and provide first evidence for thereplacement of lithospheric mantle from high-Mg peridotitesto Iow-Mg peridotites through peridotite-melt reaction.Zoned olivines have compositions in the core (Mg# = 87.2--90.7) similar to those olivines from the mantle peridotiticxenoliths entrained in Cenozoic basalts from the NorthChina craton and in the rim (Mg# = 76.8--83.9) close to oli-vine phenocrysts of the host basalts (75.7--79.0). Thesecompositional features as well as rounded crystal shapes andsmaller grain sizes (300—800 μm) demonstrate that thesezoned olivines are mantle xenocrysts, i.e. disaggregates ofmantle peridotites. Their core compositions can representthose of olivines of mantle peridotites. The zoned texture ofolivines was formed through rapid reaction between the oli-vine xenocryst and the host basalt. This olivine-basaltic meltreaction could have been ubiquitous in the Mesozoic litho-spheric mantle beneath the North China craton, i.e. an im-portant type of the replacement of lithospheric mantle. Thereaction resulted in the transformation of the Paleozoic re-fractory (high-Mg) peridotites to the late Mesozoic fertile(Iow-Mg) and radiogenic isotope-enriched peridotites, lead-ing to the loss of old lithospheric mantle.     

In situ Re-Os isotope ages of sulfides in Hannuoba peridotitic xenoliths： Significance for the frequently-occurring mantle events beneath the North China Block

In situ Re-Os isotopes of sulfides in peridotitic xenoliths from Cenozoic Hannuoba basalts were analyzed by LAM-MC-ICPMS. The suifides developed two types of occurrences including silicate-enclosed and interstitial. In the enclosed sulfides, 187Os/188Os vary from 0.1124 to 0.1362 and 187Re/188Os from 0.0026 to 1.8027. In the interstitial ones, 187Os/188Os have a range from 0.1174 to 0.1354 and 187Re/188Os from 0.0365 to 1.4469. The oldest age, calculated by TRD for the enclosed sulfides, is 2.1 Ga. An isochron age of 2.3±1.2 Ga is obtained by five grains of enclosed sulfides and primitive mantle. The sulfides used have lower Re-Os isotopic ratio than primitive mantle. Meanwhile, an isochron age of 645±225 Ma is given by all in- terstitial sulfides and the enclosed sulfides with higher Re-Os isotopic ratio due to Re addition after man- tle formation. In addition, the model age of 1.3 Ga recorded by one interstitial sulfide, having similar TDM and TRD, should be meaningful to deep thermal event. The coexistence of different ages, revealed by in situ Re-Os isotope, indicates frequently-occurring mantle events beneath Hannuoba area.     

河北省藓类植物新记录及其地理分布

首次报道9种河北省藓类植物新记录：（1）深色红叶藓（Bryoerythrophyllumatrorubens）,（2）纽藓（Tortellahumilis）,（3）树生墙藓（Tortulalaevipila）,（4）短尖叶墙藓（Tortulaschmidii）,（5）拟阔叶小石藓（Weisiaplatyphylloides）,（6）齿边缩叶藓（Ptychomitriumdentatum）,（7）狭叶缩叶藓（Ptychomitriumlinearifolium）,（8）卷叶紫萼藓（Grimmiaincurva）,（9）厚边紫萼藓（Grimmiaunicolor）,并对它们的认别特征做了简要讨论．     

Geochemical characteristics and petrogenesis of Mesozoic basalts from the North China Craton： A case study in Fuxin, Liaoning Province

Occurrence of Cretaceous basalts in Fuxin County, Liaoning Province provides us an opportunity to understand Mesozoic mantle processes beneath the northern margin of the North China Craton (NNCC). Fuxin Jianguo basalts occur as volcanic channel phases with well-developed columnar jointings and contain few spinel lherzolite and pyroxenite xenoliths. They are poor in silica and rich in alkalis, Ti and Al, belonging to alkaline basalts. In trace element compositions, Jianguo basalts are moderately enriched in LREE and LILE, but not depleted in HFSE. They have low Sr and high Nd and Pb isotopic ratios. These geochemical characteristics suggest that Jianguo basalts originated from the depleted asthenosphere, representing an undifferentiated and uncontaminated primitive magma. Presence of these basalts indicates that the lithosphere beneath the region had thickness less than 65 km at the time of basalt eruption and was mainly composed of fertile pargasite-bearing spinel Iherzolite and plagioclase pyroxenite. The voluminous basaltic-andesitic magmatism during the early Jurassic-late Cretaceous time indicates that the commencement and accomplishment of lithosphere thinning in the NNCC was much earlier than that in the southern margin, since the mafic-intermediate volcanism only occurred at the Cretaceous time in the southern margin and the basalts with an asthenosphere isotopic signature at the Tertiary. This shows that highly spatial and temporal heterogeneity existed in the Mesozoic lithosphere evolution.     

河北省蜘蛛新记录及其地理分布

首次报道１１种河北省蜘蛛新记录：（１）镜斑后鳞蛛（Ｍｅｔａｌｅｕｃａｕｇｅｙｕｎｏｈａｍｅｎｓｉｓ）,（２）松林园蛛（Ａｒａｎｅｕｓｐｉｎｅｕｓ）,（３）板隅希蛛（Ａｃｈａｅａｒａｎｅａｔａｂｕｌａｔａ）,（４）波斑盖蛛（Ｎｅｒｉｅｎｅｃｌａｔｈｒａｔａ）,（５）拟白斑猎蛛（Ｅｖａｒｃｈａｐａｒａｌｂａｒｉａ）,（６）莱塞舞蛛（Ａｌｏｐｅｃｏｓａｌｅｓｅｒｔｉａｎａ）,（７）伪楔舞蛛（Ａｌｏｐｅｃｏｓａｐｓｅｕｄｏｃｕｎｅａ ｔａ）,（８）埃氏花蟹蛛（Ｘｙｓｔｉｃｕｓｅｍｅｒｔｏｎｉ）,（９）钝叉花蟹蛛（Ｘｙｓｔｉｃｕｓｏｂｔｕｓｆｕｒｃｕｓ）,（１０）乳花蟹蛛（Ｘｙｓｔｉｃｕｓｌａｔｉｃｅｐｓ）,（１１）甘肃平腹蛛（Ｇｎａｐｈｏｓａｋａｎｓｕｅｎｓｉｓ）,并记述了它们的地理分布。     

Discovery of Late Paleozoic retrograded eclogites from the middle part of the northern margin of North China Craton

The northern margin of the North China Craton (NCC), located between the Paleo-Asian Ocean tectonic region on the north and the NCC on the south, is a key region for studying the tectonic evolution of NCC. A Pre-cambrian retrograded eclogite (2500 Ma or 1800 Ma) was reported in Baimashi near Hengshan Mountain in the NCC, which is characterized by the vermicular symplec-tite of diopside and plagioclase with absence of ompha-cite[1,2]. In Hongqiyingzi Group from the middle part of the …     

Chondritic osmium isotopic composition of late Archean convecting upper mantle：Evidence from Zunhua podiform chromitites,Hebei, North China

The Os isotopic composition and evolution of con-vecting upper mantle (CUM) are an important and diffi-cult scientific issue related to the distributions of PGEs inearth’s interior and the accretion history of the earth. De-termination of 187Os/188Os of modern CUM has been at-tempted via analyses of abyssal peridotites, mid-oceanridge basalts (MORB), MORB glasses and sulfides. Abyssal peridotites, which are mantle samples re-covered from the ocean ridges, represent the upperm…     

Sr, Nd and Pb isotopic characteristics of granulite and pyroxenite xenoliths from Hannuoba Basalts in five-dimensional space and their geological implications

Sr, Nd and Pb isotopic characteristics of granulite and pyroxenite xenoliths from Han-nuoba Basalts in five-dimensional space are studied. Combined with the distribution of xenoliths, it is suggested that the isotopic relationship between various xenoliths can be well explained by the processes of delamination.     

LA-(MC)-ICPMS U-Pb zircon geochronology and Lu-Hf isotope compositions of the Taihua complex on the southern margin of the North China Craton

Widely distributed on the southern margin of the North China Craton, the Taihua complex extends roughly in an east-west direction and the relatively complete successions are found in Lushan County, Henan Province. Like many other Archean terranes, the Taihua Complex can be divided into two major lithological units along the Dangze River, namely gneisses series and supracrustal rocks. The former is located on the north side of the river and chiefly composed of TTG gneisses and amphibolites; the latter on the south side of the river is mainly supracrustal rock. Coupled with the previous studies, the results obtained by this study show that the Taihua complex was formed in a large time span from Neoarchean to Palaeoproterozoic. The TTG gneisses and amphibolites are dated at Neoarchean (2794–2752 Ma). The 2.9 Ga and 3.1 Ga zircons in amphibolites could be xenocrysts. In the North China Craton, the 2.8–2.7 Ga old rocks crop out in several areas e.g. western Shandong Province, Jiaodong Peninsula and Lushan area of Henan Province. In addition, 2.8–2.7 Ga detrital zircons or xenocryst zircons have been recognized in Huai’an, Fuping, Wutai areas of North China Craton and also reported in the Early Paleozoic diamondiferous kimberlites in Mengyin and Fuxian. All these age results indicate that the 2.8–2.7 Ga rocks may have been developed much broader region than today’s outcrops. Zircon Hf and whole rock Nd isotopes show that the 2.8–2.7 Ga tectono-thermal event represents an important period of crustal growth with minor ancient crust reworked in the North China Craton. However the formation of supracrustal rocks is limited to 2.2–2.0 Ga in the Palaeoproterozoic time, not the Archaean, as previously believed. Combined with the chronological data of aluminium-rich metamorphic rocks (Khondalite series) on the southern margin of the North China Craton and adjacent areas, it is suggested that the above areas have widely developed Paleoproterozoic passive continental margin environment.     

Precipitation of rutile needles in garnet from sillimanite-bearing pelitic granulite from the Khondalite Belt,North China Craton

Pelitic granulite from the Khondalite Belt, North China Craton, is composed of garnet, sillimanite, perthite, biotite and quartz. Oriented rutile needles in gar- net are reported for the first time from the granulite. The rutile needles have been identified by optical microscopy and confirmed by in situ Raman spectroscopy, where they show the characteristic bands at 446-448 and 610 cm-1. Because of their very strong shape preferred orientation in 3-4 easily observable directions, these futile needles are interpreted to have formed by precipitation during exhu- mation and cooling following peak metamorphism. The ternary feldspar geothermometer gives a peak metamorphic temperature of ,- 980 ℃ at 10 kbar. The presence of oriented rutile needles in garnet is suggested to be a valuable indicator of ultrahigh-temperature （UHT） metamorphism in the Khondalite Belt and therefore likely in other UHT terrains.