Sanzhong Li

Mesozoic, Not Paleoproterozoic SHRIMP U-Pb Zircon Ages of Two Liaoji Granites, Eastern Block, North China Craton

The Paleoproterozoic Jiao-Liao-Ji orogen in the North China craton is composed mainly of the Liaohe Group (and its equivalents) and the Liaoji Granites. The latter have long been considered to be Paleoproterozoic in age, but have not been precisely constrained by reliable isotopic ages. CL and BSE images reveal the existence of both magmatic and xenocrystal/inherited zircons in one rock sample each from the Dandong and Gaoliduntai granites, two major Liaoji Granite intrusions. The magmatic zircons occur as either single grains or rims surrounding or truncating xenocrystal/inherited zircon cores, and are characterized by euhedral, prismatic grains with well-developed oscillatory zoning, whereas the xenocrystal/inherited zircons occur either as cores surrounded by the igneous zircon rims, or as single grains exhibiting weakly zoned bands. The magmatic zircons yielded ages of 157.4 ± 5.7 Ma and 156.3 ± 4.8 Ma for the Dandong and Gaoliduntai granites, respectively, indicating that these two plutons were emplaced in the Mesozoic, not in the Paleoproterozoic as previously considered. The xenocrystal/inherited zircons in these samples yield ages ranging from 2343 to 1971 Ma, much older than that of the magmatic zircons. Although the precise ages of other Liaoji Granite bodies remain unknown, SHRIMP U-Pb zircon data for one sample of each of the Dandong and Gaoliduntai granites require a re-evaluation of previous tectonic models for evolution of the Paleoproterozoic Jiao-Liao-Ji orogen.

Tectonics of South China continent and its implications

This paper aims at exploring the tectonic characteristics of the South China Continent (SCC) and extracting the universal tectonic rules from these characteristics, to help enrich the plate tectonic theory and better understand the continental dynamic system. For this purpose, here we conduct a multi-disciplinary investigation and combine it with the previous studies to reassess the tectonics and evolution of SCC and propose that the tectonic framework of the continent comprises two blocks, three types of tectonic units, four deformation systems, and four evolutionary stages with distinctive mechanism and tectonic characteristics since the Neoproterozoic. The four evolutionary stages are: (1) The amalgamation and break-up of the Neoproterozoic plates, typically the intracontinental rifting. (2) The early Paleozoic and Mesozoic intracontinental orogeny confined by plate tectonics, forming two composite tectonic domains. (3) The parallel operation of the Yangtze cratonization and intracontinental orogeny, and multi-phase reactivation of the Yangtze craton. (4) The association and differentiation evolution of plate tectonics and intracontinental tectonics, and the dynamic characteristics under the Meso-Cenozoic modern global plate tectonic regime.

Seismic attenuation tomography of the Northeast Japan arc: Insight into the 2011 Tohoku earthquake (Mw 9.0) and subduction dynamics

Detailed three-dimensional (3-D) P and S wave attenuation (Qp and Qs) models of the crust and upper mantle under the entire Northeast Japan (Tohoku) arc from the Japan Trench to the Japan Sea coast are determined, for the first time, using a large number of high-quality t* data measured precisely from P and S wave spectra of local earthquakes. The suboceanic earthquakes used in this work are relocated precisely using sP depth phases. Our results reveal a prominent landward dipping high-Q zone representing the subducting Pacific slab, a landward dipping intermediate- to high-Q zone in the mantle wedge between the Pacific coast and the volcanic front, and significant low-Q anomalies in the crust and mantle wedge between the volcanic front and the Japan Sea coast. Prominent high-Q patches surrounded by low-Q anomalies are revealed in the interplate megathrust zone under the Tohoku fore arc where the great 2011 Tohoku-oki earthquake (Mw 9.0) occurred. The high-Q patches in the megathrust zone generally exhibit large coseismic slips of megathrust earthquakes and large slip deficit on the plate interface. We think that these high-Q patches represent asperities in the megathrust zone, whereas the low-Q anomalies reflect weakly coupled areas. We also find that the hypocenters of the 2011 Tohoku-oki interplate earthquakes (Mw > 7.0) are located in areas where Qp, Qs, and Qp/Qs change abruptly. These results suggest that structural heterogeneities in the megathrust zone control the interplate seismic coupling and the nucleation of megathrust earthquakes.

LA-ICP-MS U-Pb Zircon Geochronology of the Yushulazi Group in the Eastern Block, North China Craton

The Paleoproterozoic Jiao-Liao-Ji belt in the North China craton is composed mainly of the Liaohe Group (and its equivalents) and the Liaoji Granites. They are uncomformably overlain by the sedimentary Yushulazi Group, which itself is overlain by the Neoproterozoic (0.9-0.8 Ga) Yongning Group. The Yushulazi Group has long been considered as a Proterozoic assemblage, but its depositional age has never been precisely constrained in terms of modern geochronology. Cathodoluminescence images reveal that most detrital zircon grains from this formation are characterized by concentric-oscillatory zoning, with comparatively low luminescence and high Th/U ratios, suggesting an igneous origin, whereas minor grains have structureless overgrowth or recrystallization rims that are characterized by low Th/U ratios, indicating a metamorphic origin. The results of LA-ICP-MS U-Pb zircon analyses show that the detrital zircon grains have concordant U-Pb ages of two populations—i.e., 1.05-1.37 Ga and 1.87-2.51 Ga—with an inherited zircon core giving a concordant age of 3.35 Ga. The U-Pb age range of 1.87-2.51 Ga is in good accordance with that of the Paleoproterozoic Liaohe Group and other basement rocks in the Eastern Block of the North China craton. Zircon ages of 1.05-1.31 Ga are, for the first time, reported for the Precambrian basement. The recognition of these Mesoproterozoic (1.05-1.31 Ga) igneous zircons from the Yushulazi Group indicate the existence of Grenvillian-aged magmatism in the Eastern Block of the North China craton. The Yushulazi Group must have deposited at some time between 1.05 Ga and 0.9 Ga, prior to sedimentation of the 0.9-0.8 Ga Yongning Group and it is not the upper part of the Paleoproterozoic Liaohe Group, as previously suggested.

Metamorphism of the Lüliang amphibolite: Implications for the Tectonic Evolution of the North China Craton

The Lüliang Complex is located in the southern sector of the Trans-North China Orogen, a continent-continent collisional belt along which the discrete Archean Eastern and Western blocks amalgamated to form the basement of the North China Craton. The complex consists of Paleoproterozoic supracrustal rocks and granitoid plutons of which the former include amphibolites and pelitic schists/gneisses. Petrological evidence from the Lüliang amphibolites indicates three distinct metamorphic mineral assemblages. The early inclusion assemblage (M1) is composed of hornblende + plagioclase + quartz + ilmenite, preserved as mineral inclusions within garnet porphyroblasts. The THERMOCALC program yielded maximum P-T conditions of 7.1 to 6.1 kbar and 668 to 655 °C for the M1 assemblage, based on the core compositions of garnet porphyroblasts and inclusion-type hornblende and plagioclase. The peak porphyroblast-matrix assemblage (M2) is garnet + hornblende + plagioclase + clinopyroxene ± quartz ± rutile, representing the growth of garnet porphyroblasts and matrix minerals. The P-T conditions of the M2 assemblage were estimated at 9.2 to 8.3 kbar and 753 to 748 °C, based on the rim compositions of garnet porphyroblasts and matrix plagioclase, hornblende and clinopyroxene. The post-peak symplectite assemblage (M3) is represented by cummingtonite + plagioclase symplectite surrounding embayed garnet grains, with the maximum P-T conditions of 5.1 to 4.1 kbar and 737 to 697 °C, based on the rim compositions of garnet and symplectic cummingtonite and plagioclase. A combination of petrographic textures, reaction relations, mineral compositions and P-T data define a clockwise P-T path involving near-isothermal decompression for the Lüliang amphibolites. This suggests that like those metamorphic complexes in the northern part of the Trans-North China Orogen, the Lüliang Complex in the central part of the orogen also underwent initial crustal thickening (M1 and M2), followed by erosional and/or extensional exhumation (M3), which is in accordance with collision between the Eastern and Western Blocks to form the coherent basement of the North China Craton at ∼1.85 Ga.

Mesozoic tectonics in the Eastern Block of the North China Craton: implications for subduction of the Pacific plate beneath the Eurasian plate

Abstract The Jiao-Liao massif is located in the hanging wall of the north-dipping Dabie–Sulu suture zone and is an important part of the Eastern Block of the North China Craton. Several important tectonic models for the tectonic evolution of Eastern Asia rely on critical information from the Jiao-Liao massif. This paper combines new sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon ages of the Dandong Granite in the southern Liaoning Province, China, with extensive field data for the eastern North China Craton, including the Bohai Bay Basin. Combined with other recent SHRIMP dating, we use this information to summarize the Mesozoic tectonic reactivation and evolutionary processes of the Jiao-Liao massif of the Eastern Block of the North China Craton. In this study we identify a c. 160 Ma episode of partial melting of Palaeoproterozoic plutons in the Jiao-Liao massif. Cathode luminescence and backscatter electron imagery reveal c. 167–157 Ma magmatic euhedral single zircons and magmatic zircon rims surrounding c. 2100 Ma cores in the Dandong Granites near the Liaonan Neoarchaean terrane. This partial melting is probably related to in situ remelting of ancient lower continental material, mostly the North China Craton. The Dandong plutons are aligned in a NE–SW direction and are extensively deformed by subhorizontal ductile thrust-related shearing and subsequent NNE–SSW trending folds. Here, we show that for the Dandong area the first deformation occurred between 195 and 193 Ma, based on K–Ar and 40Ar/39Ar ages of muscovites from east–west-trending shear zones on the Liaodong Peninsula. Based on the field relationships between the plutons and structural fabrics, a range from 153 to 145 Ma is defined as the duration of the second deformation in the Dandong Granites. The third deformation is marked by the formation of NNE–SSW strike-slip faults between 135 and 95 Ma. This deduced age range is similar to an 40Ar/39Ar age range of 128–132 Ma of initial sinistral strike-slip faulting of the Tan-Lu fault in Anhui Province and to a biotite cooling age of 100±2.3 Ma of the Yilan–Yitong segment of the Tan-Lu fault in the Jilin Province. These faults are transtensive and controlled the formation of pull-apart basins. However, during the third deformation, some metamorphic core complexes in Eastern China formed in the overlapping area between the large-scale sinistral faults. Our SHRIMP data also indicate that the Liaodong basement and its Early Mesozoic magmatism are similar to the Jiaodong basement and its Mesozoic magmatism. Therefore, the Early Mesozoic evolution of the Liaodong area, similar to that of the Jiaodong area, was also closely related to the Sulu orogen in the Early Mesozoic and to the Pacific subduction throughout the Mesozoic.

Tectonic evolution of the Tongbai-Hong’an orogen in central China: From oceanic subduction/accretion to continent-continent collision

The Tongbai-Hong’an orogen is located in a key tectonic position linking the Qinling orogen to the west and the Dabie-Sulu orogen to the east. Because the orogen preserves a Paleozoic accretionary orogenic system in the north and a latest Paleozoic-Mesozoic collisional orogenic system in the south, it may serve as an ideal place to study the tectonic evolution between the North and South China Blocks. The available literature data in the past 20 years indicate that the tectonic processes of the Tongbai-Hong’an orogen involved four stages during the Phanerozoic: (1) Early Paleozoic (490–420 Ma) oceanic subduction, arc magmatism and arc-continent collision created a new Andean-type active continental margin on the North China Block; (2) Late Paleozoic (340–310 Ma) oceanic subduction and accretion generated separated paired metamorphic belts: a medium P/T Wuguan-Guishan complex belt in the south of the Shandan-Songpa fault and a high P/T Xiongdian eclogite belt in the northern edge of the Mesozoic HP metamorphic terrane; (3) Latest Paleozoic-Early Mesozoic (255–200 Ma) continental subduction and collision formed the Tongbai HP terrane in the west and the Hong’an HP/UHP terrane in the east as a consequence of deep subduction towards the east and syn-subduction detachment/exhumation of the down-going slab; (4) Late Mesozoic (140–120 Ma) extension, voluminous magma intrusion and tectonic extrusion led to the final exhumation of the Tongbai-Hong’an-Dabie HP/UHP terrane and the wedge-shaped architecture of the terrane narrowing towards the west. However, many open questions still remain about the details of each evolutionary stage and earlier history of the orogen. Besides an extensive study directly on the Tongbai-Hong’an orogen in the future, integrated investigation on the “soft-collisional” Qinling orogen in the west and the “hard-collisional” Dabie-Sulu orogen in the east is required to establish a general tectonic model for the whole Qinling-Tongbai-Hong’an-Dabie-Sulu orogenic belt.

Isolation, polymorphism and expression study of two distinct major histocompatibility complex class II B genes from half-smooth tongue sole (Cynoglossus semilaevis)

Major histocompatibility complex (MHC) class II antigens are important in vertebrate immune system, which present peptides to CD4+ T cells. In the present study, cDNAs encoding MHC class II B gene were isolated from the cDNA library of half‐smooth tongue sole (Cynoglossus semilaevis), and the full length cDNA sequences were got by rapid amplification of cDNA ends polymerase chain reaction. The polymorphism of its open reading frame, 3′ untranslated region and intron 1 was studied. Nineteen class II B alleles were identified from nine individuals and clustered into two groups, designated as Cyse‐DAB and Cyse‐DBB. The deduced amino acid sequences among Cyse‐DAB and Cyse‐DBB alleles shared identities from 94.0% to 99.6% and 92.4% to 99.6%, respectively, while the identities between Cyse‐DAB and Cyse‐DBB genes varied from 85.1% to 92.0%. Three Cyse‐DAB alleles and one Cyse‐DBB allele were observed in each of two individuals, and three Cyse‐DBB alleles and one Cyse‐DAB allele in another individual, which indicated at least two loci existed in each gene. Two different 3′ UTR sequences were identified and one belonged to Cyse‐DAB, the other belonged to Cyse‐DBB. Both five Cyse‐DAB and five Cyse‐DBB intron 1 sequences were identified from genomic sequences, among which two sequences of each gene were identified in a single individual, which suggested the existence of at least two Cyse‐DAB and two Cyse‐DBB loci. Both the two genes’‐specific tissue and developmental stage expression were studied by reverse‐transcription polymerase chain reaction, which showed that the two genes had similar expression patterns in tissue study with high expression in spleen and kidney, low expression in liver, gill and ovary, moderate expression in brain, heart, intestine and testis. While in developmental analysis, Cyse‐DBB had higher expression than Cyse‐DAB in early developmental stages, which indicated that the two genes might have different functions in those stages. Therefore, in half‐smooth tongue sole, two different MHC class II B genes exist and could differentiate from each other whether by sequence analysis or by developmental stage expression study.

Structural Geology and Tectonics in Marine Science: Perspectives in the Research of Deep Sea and Deep Interior

The fields of structural geology and tectonics have witnessed great progress over the last decade and are poised for further expansion in the future. One of the significant breakthroughs is the establishment of the ‘Beyond Plate Tectonics Theory’ where a combination of conceptual models and numerical modeling on plume tectonics and plate tectonics has enabled new insights into the structural and tectonic architecture and processes in the deep interior and deep sea. This paper synthesizes developments of structural geology and tectonics from a macroscopic perspective in deep interior and deep sea. Four key techniques are also reviewed: satellite altimetry for surface structures in deep-sea multi-beam sea-floor mapping; tomography for tectonics of the deep interior; diverse modeling approaches and software for unfolding dynamic evolution; and techniques for HT/HP experiments on material rheology and in situ component measurements.

Late Cretaceous basalts and rhyolites from Shimaoshan Group in eastern Fujian Province, SE China: age, petrogenesis, and tectonic implications

ABSTRACT Southeastern China is characterized by an extensive Late Mesozoic (Yanshanian) tectono-magmatic-metallogenic event. Although Late Cretaceous volcanism gradually weakened during the epilogue of the Yanshanian event, its petrogenesis and geodynamic processes remain unclear. In this study, we present new zircon U–Pb–Hf isotopic, whole-rock elemental, and Sr–Nd isotopic compositions data, for volcanic rocks from the Zhaixia Formation of the Shimaoshan Group in Fujian Province. The lower member of the Zhaixia Formation consists of basalts and rhyolites, and the upper member is only rhyolites. These volcanic rocks erupted in the early stage of Late Cretaceous, with basalts erupting earlier (ca. 99–98 Ma) than rhyolites (ca. 98–94 Ma). These basalts record high-K calc-alkaline to shoshonitic, light rare earth element (LREE)- and LILE-enrichment, high field strength element (HFSE)depletion with negligible Eu anomalies, and uniform whole-rock εNd(t) (–3 to –6) and zircon εHf(t) (–3.3 to –14.1) values. The overlying rhyolites record peraluminous and high-K calc-alkaline characteristics, LREE- and LILE-enrichment with negative Eu anomalies, and Nb–Ta depletion. The whole-rock εNd(t) and zircon εHf(t) values of these rhyolites both increase from the lower member (εNd(t), –1.5 to –4.7; εHf(t), –5.1 to –16.1) to the upper member (εNd(t), –0.5 to 0.1; εHf(t), –0.3 to –4.3). The features imply that these basalts were derived from the partial melting of the enriched lithospheric mantle and the overlying rhyolites from the melting of the crustal components, respectively. Data from the rhyolites in the upper member indicate that more juvenile, Nd–Hf isotopically depleted materials were injected into their source. During the Late Cretaceous, the new, fast rollback of the subducting slab triggered lithospheric extension and asthenospheric upwelling beneath the coastal regions, which induced the melting of lithospheric mantle and crustal components. As continued, the new round of basaltic underplating provided necessary heat to cause partial melting of the deep crust, including the younger, juvenile, and isotopically depleted crustal components.