A ca. 2.2Ga Acidic Magmatic Event at the Northern Margin of the Yangtze Craton: Evidence from U-Pb Dating and Hf Isotope Analysis of Zircons from the Kongling Complex

Objective The Yangtze craton collisional orogeny at ca. extensional events at ca. 1 experienced Paleoproterozoic 1.95-2.0 Ga and post-orogenic 85 Ga related to amalgamation of the Columbia （Nuna） supercontinent （Zhao and Cawood, 2012）. A ca. 2.15 Ga suprasubduction zone ophiolitic melange was recongized in the Archean- Paleoproterozoic Kongling Complex of the northern Yangtze craton （Han et al., 2017）. However, the tectonic evolution in early Paleoproterozoic from 2.4 Ga to 2.2 Ga remains unclear. We report here the presence of a suite of Paleoproterozoic （2.2 Ga） granites in the Huangling dome, northern Yangtze craton, which may provide important insights into crustal growth processes in the craton prior to the assembly of Columbia.

Desertification Direction of the Northern Margin of Hobq Desert

The Hobq Desert, located in the northern Ordos Plateau is a typical in-situ desertification desert, which is quite different in characteristics and genesis from the Tengger Desert to the west and Muus Desert to the south. The northern margin of Hobq Desert is strictly constrained to the south bank of the Yellow River. This relationship between deserts and rivers indicates that desertification may cause passive migration of river channels（Fig, la）.

^(40)Ar/^(39)Ar Geochronology of the Late Paleozoic Woniusi Basalts from the Baoshan Terrane, SW China:Implications for the Rifting of the Northern Margin of Gondwana

Objective Although the occurrence of Late Paleozoic rifting on the northern margin of Gondwana is widely accepted,the precise reason for the rifting is not constrained.The Woniusi basalts in the Baoshan terrane cover an area of～1.2×10~4 km~2 and have been considered to be likely part

A New Fauna——Qinghezhen Fauna——from the Northern Margin of the North China Platform

In the Inner Mongolia axis and Jiaoliao anteclise along the northern margin of the North China Platform.it has been found that the strata formerly considered as Archaean and Proterozoic are in fact an ophiolite suitesimilar to the Early Palaeozoic Ondor Sum Group in the Northern Geosyncline region of China. The stratahave been named in northern Liaoning as the Qinghezhen Group. The emphasis of this paper is on the discus-sion of the simall shelly fossils found in the siliceous rocks in the upper part of the Qinghezhen Group. Thisophiolite suite stretches in an E-W direction for about 1000 km along the northern margin of the North ChinaPlatform. in which 15 fossil localities with stable stratigraphic horizons have been discovered. In this paper. 4types. 7 genera (including 5 new ones) and 10 species (including 8 new ones and 1 new subspecies) aredescribed, which are collectively referred to as the Qinghezhen Fauna. The characteristics of these fossils are:shell form simple. the maximum length not exceeding 4 mm. with obvious shell wall and wall ornaments. TheQinghezhen Fauna is comparable in shell structure of some genera and species with the Meishucun Fauna inSouth China, but differs from the latter in having only monotonous fossil groups developed in a distinctly va-ried ecological environment. The two faunas may belong to the same evolutionary stage of the Early Cambrianbut have developed parallelly in different regions. The existence of the Qinghezhen Fauna represents an impor-tant biological event in the Early Cambrian in the Northern Geosyncline region of China. The discovery of theQinghezhen Fauna will bring new knowledge and profound influence to a series of problems on basic geologyand mineral deposit prospecting such as the Cambrian faunas. biogeographical povincialism in China and thegeotectonic features of the northern margin of the North China Platform.

Neoproterozoic Magmatism in the Northern Margin of the Tarim Craton: Implications for Rodinia Reconstruction

The geodynamic processes for the Neoproterozoic mafic-ultramafic intrusions and dykes in the Kuluketage region,Tarim Craton has also been debated for some time.Some researchers suggested that the Neoproterozoic

Geodynamic characteristics of tectonic extension in the northern margin of South China Sea

Based on the geothermal and gravitation methods, this paper investigated the rheological and thermal structure of the lithosphere under the northern margin of South China Sea. The result shows that the temperature of the upper crust is 150–300°C lower than that of the lower crust, and the viscous coefficient of the upper crust is 2–3 orders of magnitude larger than that of the lower crust. It reveals that the upper crust is characterized by brittle deformation while the lower crust by ductile deformation. A channel of lower-viscosity should be formed between the upper and lower crust when the lithosphere is scattered and spreads out toward ocean from northwest to southeast along the northern margin of South China Sea. And, a brittle deformation takes place in the upper part of the lithosphere while a ductile deformation takes place in the lower part of the lithosphere due to different viscous coefficients and temperature. The layered deformation leads the faulted blocks to rotate along the faulting and the marginal grabens to appear in the northern margin of South China Sea in Cenozoic tectonic expansion.

Middle and Late Tertiary Palaeogeography and Palaeoenvironment on the Northern Continental Margin of the South China Sea

Based essentially on research results of calcareous nannofossils, combined with some other microfossil da-ta and several secondary depositional breaks, this paper discusses the criteria of division and comparison of themiddle and late Tertiary marine sediments, palaeogeographical and palaeoenvironmental evolution andpalaeoclimates on the northern continental margin of the South China Sea, comprising the Tainan basin, PearlRiver Mouth basin. Southeast Hainan basin and Beibu Gulf basin. Study shows that the upper Oligocene toPliocene strata in the whole area consist essentially of marine sediments except in the Beibu Gulf basin. Theyinclude littoral. neritic and deltaic sediments as well as carbonate rock-bioherm limestone. The sea advancedfrom southeast to northwest. During the transgression there appeared three culminations coinciding to thestages of deposition of nannofossil zones NN4-5, NN11 and 13-15.

Geochronology,Petrology and Geochemistry of Xingdi No.3 Mafic-Ultramafic Intrusions in the Northeastern Tarim Craton,NW China

The Xingdi mafic-ultramafic intrusions occur in the northeastern margin of the Tarim craton. The Xingdi No. 3 intrusion is the smallest of four intrusions, with an exposed area of 1.7 km2, and the zircon U-Pb age of the intrusion is 752±4 Ma. The intrusion consists of gabbros, pyroxenites and peridotites, and exhibits a crystallization sequence of the main rock-forming minerals as olivine, orthopyroxene, clinopyroxene and plagioclase. Mineralization occurred at or near the boundaries of the intrusion between pyroxenites and peridotites, and appears as a layered or lenticular shape about 500 m long and 4–15 m wide. The primary sulfides have a relatively simple mineralogy dominated by pyrrhotite-pentlandite-chalcopyrite assemblages, which occur as droplet, star-like and graphic texture and locally sideronitic structures. Geochronological and geochemistry investigations suggest that the Xingdi mafic-ultramafic intrusions and coeval volcanic rock in the Kuluktag area of the Tarim craton formed in an intracontinental breakup environment. Based on the composition of the dominant rockforming minerals and covariant relationships of other oxides versus Mg O, the parental magma of the Xingdi No.3 intrusion belongs to high-Mg tholeiitic basaltic magmas with Mg O of 10.78 wt%. The Xingdi No.3 intrusive rocks are characterized by light REE enrichment relative to heavy REE, negative Nb-Ta anomalies, low 143Nd/144Nd ratios（from 0.511183 to 0.511793） and high initial 87Sr/86Sr ratios（from 0.7051 to 0.7113）. The magma was derived from the enriched-lithospheric mantle and was contaminated during emplacement. According to rock assemblages, mineralization, olivine characteristics, geochemical characteristics and mass balance, there are better copper-nickel ore prospects in the Xingdi No.3 intrusion than in the other three intrusions in the area.

In situ LA-ICP-MS zircon U-Pb age of ultrahigh-pressure eclogites in the Yukahe area,northern Qaidam Basin

Zircon grains were selected from two types of ultrahigh-pressure(UHP)eclogites,coarse-grained phengite eclogite and fine-grained massive eclogite,in the Yukahe area,the western part of the North Qaidam UHP metamorphic belt.Most zircon grains show typical metamorphic origin with residual cores in some irregular grains and sector,planar or misty internal textures on the cathodoluminescence(CL)images.The contents of REE and HREE of the core parts of grains range from 173 to 1680μg/g and 170 to 1634μg/g,respectively,in phengite eclogite,and from 37 to 2640(g/g and 25.7 to 1824μg/g,respectively,in massive eclogite.The core parts exhibit HREE-enriched patterns,representing the residual zircons of protolith of the Yukahe eclogite.The contents of REE and HREE of the rim parts and the grains free of residual cores are much lower than those for the core parts.They vary from 13.1 to 89.5(g/g and 12.5 to 85.7μg/g,respectively,in phengite eclogite,and from 9.92 to 45.8μg/g and 9.18 to 43.8(g/g,respectively,in massive eclogite.Negative Eu anomalies and Th/U ratios decrease from core to rim.Positive Eu anomalies are shown in some grains.These indicate that the presence of garnet and the absence of plagioclase in the peak metamorphic mineral assemblage,and the zircons formed under eclogite facies conditions.LA-ICP-MS zircon U-Pb age data indicate that phengite eclogite and massive eclogite have similar metamorphic age of 436±3Ma and 431±4Ma in the early Paleozoic and magmatic protolith age of 783―793 Ma and 748―759 Ma in the Neo-proterozoic.The weighted mean age of the metamorphic ages(434±2 Ma)may represent the UHP metamorphic age of the Yukahe eclogites.The metamorphic age is well consistent with their direct country rocks of gneisses(431(3 Ma and 432±19 Ma)and coesite-bearing pelitic schist in the Yematan UHP eclogite section(423―440 Ma).These age data together with field observation and lithology,allow us to conclude that the Yukahe eclogites were Neo-proterozoic igneous rocks and may have experienced subduction and UHP metamorphism with continental crust at deep mantle during the early Paleozoic,therefore the metamorphic age of 434±2 Ma of the Yukahe eclogites probably represents the continental deep subduction time in this area.