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 …     

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.     

华北克拉通北缘典型高锶花岗岩区域锶型矿泉水分布特征及成因

华北克拉通北缘存在大量高锶花岗岩体,但其周边区域锶型矿泉水的赋存情况鲜有研究.首次以都山岩体作为典型高锶花岗岩,通过水文地质调查、水样采集、化验分析等方法,对其周边区域锶型矿泉水的分布和形成机理进行了分析.同时对寿王坟岩体、碾子峪岩体、小寺沟岩体、杨杖子岩体等四处高锶花岗岩体周边区域水体进行调查取样分析,以验证锶型矿泉...     

Activation of northern margin of the North China Craton in Late Paleozoic: Evidence from U-Pb dating and Hf isotopes of detrital zircons from the Upper Carboniferous Taiyuan Formation in the Ningwu-Jingle basin

LA-MC-ICPMS U-Pb dating has been performed on detrital zircons from the Upper Carboniferous Tai-yuan Formation (N-8) in the Ningwu-Jingle Basin, west of the North China Craton (NCC). The ages of 72 detrital zircon grains are divided into three groups: 303―320 Ma (6 grains), 1631―2194 Ma (37 grains, peaked at 1850 Ma), 2318―2646 Ma (29 grains, peaked at 2500 Ma). Detrital zircons of Group 2 and Group 3 were likely derived from the basement of the NCC. Group 1 zircons exhibit 176Hf/177Hf ratios ranging from 0...     

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.     

Carbothermic reduction behaviors of Ti-Nb-bearing Fe concentrate from Bayan Obo ore in China

To support the development of technology to utilize low-grade Ti-Nb-bearing Fe concentrate, the reduction of the concentrate by coal was systematically investigated in the present paper. A liquid phase formed when the Ti-Nb-bearing Fe concentrate/coal composite pellet was reduced at temperatures greater than 1100℃. The addition of CaCO₃ improved the reduction rate when the slag basicity was less than 1.0 and inhibited the formation of the liquid phase. Mechanical milling obviously increased the metallization degree compared with that of the standard pellet when reduced under the same conditions. Evolution of the mineral phase composition and microstructure of the reduced Ti-Nb-bearing Fe concentrate/coal composite pellet at 1100℃ were analyzed by X-ray diffraction and scanning electron microscopy-energy-dispersive spectroscopy. The volume shrinkage value of the reduced Ti-Nb-bearing Fe concentrate/coal composite pellet with a basicity of 1.0 was approximately 35.2% when the pellet was reduced at 1100℃ for 20 min, which enhanced the external heat transfer to the lower layers when reduced in a practical rotary hearth furnace. The present work provides key parameters and mechanism understanding for the development of carbothermic reduction technology of a Ti-Nb-bearing Fe concentrate incorporated in a pyrometallurgical utilization flow sheet.     

Palaeoproterozoic Khondalite Belt in the western North China Craton： New evidence from SHRIMP datin8 and Hf isotope composition of zircons from metamorphic rocks in the Bayan Ui-Helan Mountains area

Zircom U-Pb age and Hf isotope analyses were made on gneissic granite and garnet-mica two-feldspar gneiss from the Helanshan Group in the Bayan Ul-Helan Mountains area, the western block of the North China Craton (NCC). Zircons from the gneissic granite commonly show core-mantle-rim structures, with magmatic core, metamorphic mantle and rim having ages of 2323±20 Ma, 1923±28 Ma and 1856±12 Ma, respectively. The core, mantle and rim show similar Hf isotope compositions, with single-stage depleted mantle model ages (TDM1) of 2455 to 2655 Ma (19 analyses). Most of the detrital zircons from the garnet-mica two-feldspar paragneiss have a concentrated U-Pb age distribution, with a weighted mean 207Pb/206Pb age of 1978±17 Ma. A few detrital zircons are older (2871 to 2469 Ma). The age for metamorphic overgrown rim was not determined because of strong Pb loss due to their high U content. The zircons show large variation in Hf isotope composition, with TDM1 ages of 1999 to 3047 Ma. In com- bination with previous studies, the main conclusions are as follows: (1) protolith of the khondalite se- ries in the Helanshan Group formed during Palaeoproterozoic rather than the Archaean as previously considered; (2) The results lend support to the contention that there is a huge Palaeoproterozoic Khondalite (metasedimentary) Belt between the Yinshan Mountains Block and the Ordos Block in the Western Block of NCC; (3) The widely-distributed bodies of early Palaeoproterozoic orthogneisses in the Khondalite Belt might be one of the important sources for detritus material in the khondalite series; (4) Collision between the Yinshan Block, the Ordos Block and the Eastern Block occurred in the same tectonothermal event of late Palaeoproterozoic, resulting in the final assembly of the NCC.     

New occurrence of Ba-REE fluorcarbonate minerals at Bayan Obo, Inner Mongolia, North China, and their mineralogical features

Ba-REE fluorcarbonate minerals from a carbonatite dyke at Bayan Obo, Inner Mongolia, North China, are first reported in this contribution, in which chemical composition, rare earth element (REE) patterns, and intergrowth relationships for these minerals have been investigated. Syntactic intergrowth or syntaxy between cebaite and cordylite, as well as cordylite and huanghoite were observed. This syntactic texture resulted from the variation of chemical composition of crystallizing agents for those minerals that crystallized directly from carbonatite magmas. It is worth noting that REE patterns of the Ba-REE fluorcarbonate minerals in the dyke are similar to those of the corresponding minerals from the ore hosted dolomite marble of the Bayan Obo giant REE-Nb-Fe mineral deposit, which implies their relation in origin.     

Delamination and destruction of the North China Craton

This article presents an overview on recent developments in studies of chemical and physical processes of lithospheric delamination with respect to destruction of the North China Craton. It is emphasized that the pyroxenite source resulting from interaction between eclogite-derived melt and peridotite is a direct consequence of delamination. The pyroxenite source thus formed has unique mineralogical and geochemical features, which characterize Mesozoic basalts of the North China Craton. Melt-peridotite interaction played an important role in refertilization of cratonic lithospheric mantle, leading to density increase, weakening and final destabilization of the North China Craton. The nature of the melt is the key to distinguish mechanisms of destructing this craton.     

First SHRIMP zircon U-Pb ages for Hutuo Group in Wutaishan： Further evidence for Palaeoproterozoic amalgamation of North China Craton

A felsic tuffaceous rock, obtained from a metamorphosed sequence of volcanics and sediments of the Hutuo Group, 8 km south of Taihuai in Wutaishan, contains two zircon populations. These record SHRIMP 207Pb/206Pb weighted mean ages of 2180±5 Ma and 2087±9 Ma, respectively. The older date is within error of the age of the Dawaliang Granite in Wutaishan and is considered to be     

Water content in the early Cretaceous lithospheric mantle beneath the south-central Taihang Mountains: implications for the destruction of the North China Craton

Based on studies of the water content of the early Cretaceous Feixian high-magnesium basalts in the eastern part of the North China Craton （NCC）, it has been suggested that the early Cretaceous lithospheric mantle of the eastern NCC was highly hydrous （〉1,000 ppm, HeO wt.） and that this high water content had significantly reduced the vis- cosity of the lithospheric mantle and provided a prerequisite for the destruction of the NCC. The eastern part of the NCC had undergone multistage subduction of oceanic plates from the south, north, and east sides since the early Paleozoic, and these events may have caused the strong hydration of the NCC lithospheric mantle. To determine which subduction had contributed most to this hydration, we measured the water contents of the peridotite xenoliths hosted by the early Cretaceous high-magnesium diorites of Fushan in the south- central part of the Taihang Mountains. Our results demon- strate that the water content of the early Cretaceous litho- spheric mantle beneath the south part of the Taihang Mountains was ~ 40 ppm and significantly lower than that of the contemporary lithospheric mantle beneath the eastern part of the NCC. Thus, the hydration of the early Cretaceous lithospheric mantle of the eastern part of the NCC can be ascribed to the subduction of the Pacific plate from the west side. Thus, the main dynamic factor in the destruction of the NCC was likely the subduction of the Pacific plate.     

华北克拉通北缘中段中新元古代热构造事件及其演化

近年华北地块北缘陆续发现和厘定出许多中新元古代变质火山-沉积地层,各种类型的深成侵入岩体以及各种样式的构造形迹,但对其性质及构造属性认识不统一。作者在详细研究前人成果基础上,认为华北地块北缘中段中新元古代经历了中元古代早期的伸展裂解、中元古代晚期的挤压汇聚、新元古代-早古生代的伸展裂解及早古生代晚期的挤压汇聚演化过程,伴随挤压汇聚有火山深成侵入岩浆活动和构造变质热事件的年代记录。中元古代晚期挤压汇聚事件表明华北地块北缘发育一条中元古代晚期大陆边缘碰撞造山带,这一碰撞造山事件为华北地块在 Rodinia 超大陆拼合模式提供了最基本的制约条件。     

Comparison of mantle-derived matierals from different spatiotemporal settings: Implications for destructive and accretional processes of the North China Craton

Cratonic destruction or lithospheric thinning beneath North China makes it as one of the most ideal areas for the studying on the formation and evolution of continent. However, the mechanism, time, range and dynamic setting of the destruction, even the lithospheric status before the destruction, are contentious. The comparison among mantle xenoliths in the volcanic rocks from different captured times （e.g. Paleozoic, Mesozoic and Cenozoic） and locations （e.g. intra-plate or its rim, the translithospheric Tanlu fault or the North-South Gravity Line）, and peridotitic massifs within the Sulu-Dabie ultrahigh-pressure metamorphism belt along the southern margin of the North China Craton, indicates that （1） the cratonic lithosphere is heterogeneous in structure and composition, and contains mantle weak zones; and （2） the Mesozoic-Cenozoic lithospheric thinning process is complex, including lateral spreading of lithosphere, interaction between melt and peridotite, non-even asthenospheric erosion （huge lithospheric thinning）, and the limited lithospheric accretion and thus thickening, which resulted in the final replacement of the refractory cratonic lithosphere by juvenile fertile mantle. In early Mesozoic, the integrity of the North China Craton was interrupted, even destroyed by subduction and collision of the Yangtze block. The mantle wedge of the North China Craton was also metasomatized and modified by melt/fluids revealed from the subducted Yangtze continent. Lithospheric mantle extension and tectonic intrusion of the North China Craton also occurred, accompanied by the asthenospheric upwelling that due to the detachement of the subducted Yangtze continent （orogenic root）. During early Cretaceous-early Tertiary, the huge thinning of lithosphere was triggered by the upwelling asthenosphere due to the subduction of the Pacific plate. Since late Tertiary, the cooling of the upwelling asthenosphere resulted in the replacement of the mantle in existence by the newly accreted lithosphere, accompanied with a little thickness in lithosphere and thus finally achieved the lithospheric thinning as a whole. The translithospheric faults, such as the Tanlu fault, play excellent channels for asthenospheric upwelling. Meanwhile, the channels in lithosphere are usually irregular, which resulted in different eruption times of magma. Peridotite xenolith in the basalts erupted at 100 Ma is mainly fertile, indicating such a fact, that is, the mantle replacement occurred before the eruption （e.g. 125--100 Ma） beneath the eastern part of the North China Craton.     

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.     

On the timing and duration of the destruction of the North China Craton

The timing and duration of the destruction of the North China Craton, which is pivotal to understanding the destruction mechanism and its geodynamic controlling factors, still remain controversial. On the basis of the principles of magma genesis and evolution, first we outline magmatic expressions that can be related to cratonic destruction, then use magmatic and basin evolution trends to constrain the timescale of the lithospheric thinning in North China. The main conclusions include： （1） the thinning of the lithosphere beneath the North China Craton might have started, at least locally, since late Carboniferous-late Triassic, attained its climax during the late Jurassic-early Cretaceous, and continued till the end of late Cretaceous-early Cenozoic. The destruction of the North China Craton was a relatively slow, rather than a dramatic process. （2） The weakened lithospheric zones along the margins and interiors of the craton played an important role in cratonic destruction, partly accounting for the heterogeneous pattern of cratonic destruction. （3） The tectonic factors that controlled the destruction of the North China Craton may be multiple. The late Carboniferous southward subduction of the Paleo-Asian plate and the late Triassic collision between North China and South China may have re-activated the craton by influencing the thermal and integral structure of the craton. The Pacific subduction underneath the eastern Asian continent played a determinant role in the cratonic destruction, governing the distribution patterns of post-Mesozoic basins and major tectonic configuration, temporal change of magmatism and formation of the North-South gravity lineament.     

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.