The Sino-Korean Craton and supercontinent history: Problems and perspectives

The Sino-Korean Craton (SKC) is an enigmatic block in the history of supercontinents older than Pangea. Its accretion to Eurasia and the effect of the broad region of Mesozoic–Cenozoic extension in northern Eurasia that crosses the eastern part of the SKC are among several problems that need to be resolved in understanding the configuration of SKC and the overprinting of earlier histories in this block. We present a synopsis of these problems and perspectives for future research.     

A Quartz-Carbonate Gold Deposit in North Margin of Sino-Korean Archean Craton

1. IntroductionThe gold deposits in Archean greenstone belts are the most important gold resources in the world, and their wall rocks are low-grade metamorphic greenstones (greenschist facies or sub-greenschist facies metamorphism). The ore bodies always appear very large in scale. The Sino-Korean Archean craton was not so stable as in Canada, South Africa, Australia and Russia, and its Archean greenstone belts are much smaller and with high grade metamorphism, where the gold deposits are …     

汉诺坝玄武岩中麻粒岩类捕掳体的岩石学特征

根据矿物组合特征,汉诺坝玄武岩中的麻粒岩捕掳体可划分为四种类型：长英质麻粒岩、苏长质麻粒岩、二辉二长麻粒岩和二辉麻粒岩,其中以二辉麻粒岩最为常见。麻粒岩捕掳体均具变质重结晶结构以及块状或条带状构造。不同种类的麻粒岩捕掳体在矿物组成和矿物成分上存在明显差别,但各主要矿物之间存在一定的成分相关性。应用Ｗｏｏｄ和Ｂａｎｎｏ二辉石温度计的计算结果表明,含二辉石麻粒岩捕掳体的平衡温度分布于８００°～９５０℃之间,主要集中于９００°±５０℃范围内,具Ｏｐｘ＋Ｃｐｘ＋Ｐｌ矿物组合的二辉麻粒岩捕掳体的形成压力范围约为０．６～１．１ＧＰａ。二辉二长麻粒岩落在相似的温压范围内。麻粒岩捕掳体在９５０℃处的突然消失指示了第三纪时汉诺坝地区岩石学壳幔边界的温度。     

Late Ordovician volcanism in Korea constrains the timing for breakup of Sino-Korean Craton from Gondwana

In the early Paleozoic the Sino-Korean Craton (SKC) and South China Craton (SCC) were situated along the margin of east Gondwana. The SKC was connected to core Gondwana by an epeiric sea which was the site for deposition of lower Paleozoic sequences of SKC. The SKC and SCC may have drifted away from core Gondwana sometime during the mid-Paleozoic and would have been outboard microcontinents in the late Paleozoic, until they collided to form the East Asian continent in the Triassic. The breakup of SCC from Gondwana was suggested to have taken place at ∼380 Ma, while no reliable suggestions have hitherto been made for breakup of SKC from Gondwana. This study presents a convincing evidence for breakup of SKC from Gondwana, based on the recognition of Late Ordovician volcanism in Korea. New SHRIMP U–Pb zircon ages, 445.0 ± 3.7 Ma and 452.5 ± 3.2 Ma, are obtained from trachytic rocks of the Ongnyeobong Formation of Taebaeksan Basin in Korea which occupied the marginal part of the SKC in the early Paleozoic. This Late Ordovician volcanism along with previous records of Ordovician volcanic activities along the western margin of the SKC is interpreted indicating the development of an incipient oceanic ridge. The oceanic ridge uplifted the SKC including the epeiric sea, which subsequently resulted in terminating the early Paleozoic sedimentation of the epeiric sea. The paucity of lower Paleozoic volcanic rocks across much of the SKC however suggests that the oceanic ridge did not extend into the epeiric sea. Instead, spreading of oceanic ridge entailed dextral movement of associated transform faults, which may have played a major role in breakup of SKC from mainland Gondwana by the end of Ordovician.     

Thermal and petrological structure of the lithosphere beneath Hannuoba, Sino-Korean Craton, China: evidence from xenoliths

Deep-seated xenoliths entrained in the Hannuoba basalts of the northern Sino-Korean Craton include mafic and felsic granulites, mantle wall-rock from spinel– and garnet–spinel peridotite facies, and basaltic crystallisation products from the spinel-pyroxenite and garnet-pyroxenite stability fields. The mineral compositions of the xenoliths have been used to estimate temperatures and, where possible, pressures of equilibration, and to construct a geothermal framework to interpret the upper mantle and lower crustal rock-type sequences for the region. The xenolith-derived paleogeotherm is constrained in the depth interval of 45–65 km and like others from areas of young basalt magmatism, is elevated and strongly convex toward the temperature axis. Two-pyroxene granulites give the lowest temperatures and garnet pyroxenites the highest, while the spinel lherzolites fall between these two groups. The present-day Moho beneath the Hannuoba area is defined at 42 km by seismic data, and coincides with the deepest occurrence of granulite. Above this boundary, there is a lower crust–upper mantle transition zone about 10-km thick, in which spinel lherzolites and mafic granulites (with variable plagioclase contents) are intermixed. It is inferred that this underplating has resulted in a lowering of the original pre-Cenozoic Moho (then coinciding with the crust–mantle boundary, CMB) from about 30 km to its present-day position and was due to intrusions of basaltic magmas that displaced peridotite mantle wall-rock and equilibrated to mafic granulites. Trace element patterns of the diopsides (analysed by laser ablation-ICPMS) from the Cr-diopside series spinel lherzolites and associated layered xenoliths (spinel lherzolites and pyroxenites) indicate a fertile uppermost mantle with moderate depletion by low degrees of partial melting and little evidence of metasomatic activity. The similarity in major and trace element compositions of the minerals in both rock types suggests that the layered ultramafic xenoliths formed by mantle deformation processes (metamorphic segregation), rather than by melt veining or metasomatism.     

Nature and Evolution of Cenozoic Lithospheric Mantle beneath Shandong Peninsula,Sino-Korean Craton,Eastern China

The Shanwang and Qixia basalts lie within the North China block and were erupted in Miocene to Pliocene time (18.1 to 4.3 Ma) and Pliocene time (6.4 to 5.9 Ma), respectively. The Shanwang area lies astride the Tancheng-Lujiang (Tanlu) fault zone, a major lithospheric fault, whereas the Qixia area lies east of the fault zone. The basaltic rocks (alkali olivine basalts, basanites, nephelinites) carry abundant deep-seated xenoliths including spinel lherzolite (dominant), dunite, and pyroxenite, and a megacryst suite including augite, anorthoclase, phlogopite, ilmenite, and garnet. Xenoliths with coarse-grained microstructures are common in the Qixia xenolith suite, but are absent in Shanwang. Reconstructed bulk compositions of the lherzolites range from relatively depleted (<3% modal diopside) to fertile (>12% modal diopside). Equilibration temperatures of 850° to 1020°C indicate entrainment of these lherzolites from depths ≤45 km, within the lithosphere; the geotherm may have been higher beneath Shanwang. The Shanwang suite contains less-depleted lherzolites, and more pyroxenites, than the Qixia suite. The chondrite-normalized REE patterns in clinopyroxenes of the Shandong xenoliths vary from LREE depleted, through concave shaped, to LREE enriched; spidergrams for the clinopyroxenes can be divided into depleted, fertile, and metasomatic types. Progressive depletion in Na and Al is accompanied by depletion in moderately incompatible elements such as Y, Yb, and Zr, and an increase in Mg#. Ti and Zr in clinopyroxenes have not been affected by the metasomatic process, and MREE have been little disturbed, whereas the light rare-earth elements, Nb, and Sr have been strongly enriched during metasomatism; this suggests that carbonate-rich fluids/melts were the metasomatic agent. The mantle beneath the Shandong Peninsula sampled by these basalts is dominantly Phanerozoic in character rather than Archean or Proterozoic lithospheric mantle. This mantle probably represents a mixture of older lithospheric mantle and newly accreted material that replaced the Archean lithospheric keel through extension, thermal erosion, and fluid/melt metasomatism. The differences in micro-structures, chemistry, temperature, and fluid/melt activity between Shanwang and Qixia are ascribed to their spatial relationships to the Tanlu fault, which is a major translithospheric suture that hasplayed an important role in the Cenozoic replacement of the pre-existing Archean lithospheric mantle.     

桂北构造蚀变岩型金矿的发现及成矿规律研究

桂北地区金矿划分为石英脉型、石英细脉薄脉型和构造蚀变岩型金矿.不同级别剪切带构造控制着矿化集中区、矿床、矿体的分布,以及与矿脉形态、产状和矿化类型有着空间上的密切联系.具有上部石英脉型、中部石英细脉薄脉型、下部构造蚀变岩型金矿的矿化分带模式.桂北地区成矿条件好,与国内外许多大型超大型剪切带型金矿有类似成矿地质背景.研究认为,在桂北地区找矿应转变找矿思路,在老矿山深部及周边地区,具有大型构造蚀变岩型金矿找矿前景.     

Gold metallogeny associated with craton destruction: A geophysical perspective from the North China Craton

Currently ranking as the largest producer of gold in the world, China's gold reserves are spread over 200 major gold deposits and several minor deposits. A large part of these belong to the late Mesozoic gold deposits in the North China Craton (NCC) that occur along craton margins, as well as within the cratonic interior in reactivated paleo sutures, and show a close spatio-temporal relationship with zones of lithospheric thinning and craton destruction. Here we integrate and evaluate geophysical information from the NCC through an analysis of receiver function and tomography that suggest mantle upwelling accompanied by lower crustal or lithospheric delamination. Our results identify that the major gold belts in the NCC are largely located above zones of mantle upwelling and craton destruction. The faults and paleo sutures provided the pathways for migration of ore-bearing fluids, with the granitoids offering favorable conditions for gold deposition.     

Ulkan-Dzhugdzhur ore-bearing anorthosite-rapakivi granite-peralkaline granite association,Siberian Craton: Age,tectonic setting,sources, and metallogeny

The paper systematizes and integrates the results of geological, isotopic geochronological, and geochemical studies of the igneous rocks that make up the Ulkan-Dzhugdzhur anorthosite-rapakivi granite-peralkaline granite association and related mineralization. This association is a typical example of anorogenic igneous rocks that formed in the within-plate geodynamic setting most likely under effect of the mantle superplume, which was active in the territory of the Siberian Craton 1.75–1.70 Ga ago. The igneous rock association formed in a discrete regime that reflected the pulsatory evolution of a sublithospheric mantle source. The prerift (1736–1727 Ma) and rift proper (1722–1705 Ma) stages and a number of substages are distinguished. All igneous rocks pertaining to this association have mixed mantle-crustal origin. Basic rocks crystallized from the OIB-type basaltic magma, which underwent crustal contamination at various depths. Felsic rocks are products of mantle and crustal magma mixing. The contribution of mantle component progressively increased in a time-dependent sequence: moderately alkaline subsolvus granite → moderately alkaline and alkaline hypersolvus granites → peralkaline hypersolvus granite. All endogenic deposits in the studied district are related to a single source represented by the mantle plume and its derivatives. The Fe-Ti-apatite deposits hosted in anorthosite formed as a result of intense lower crustal contamination of basaltic magma near the Moho discontinuity and two stages of fractional crystallization at lower and upper crustal depth levels. The rare-metal deposits are genetically related to peralkaline granite. Formation of uranium deposits was most likely caused by Middle Riphean rejuvenation of the region, which also involved rocks of the Ulkan-Dzhugdzhur association.     

Cambrian trace fossils of the Cruziana ichnofacies from the Bikaner-Nagaur Basin,north western Indian Craton

The Marwar Supergroup of the Bikaner-Nagaur Basin is composed of sediments deposited from the late Neoproterozoic (Ediacaran) to Upper Cambrian. The Nagaur Sandstone Formation of the Nagaur Group (uppermost division of the Marwar Supergroup) preserves trace fossils significant for establishing Early Cambrian biostratigraphic zones and depositional facies. Fifteen ichnospecies (and eight ichnogenera) identified in the Nagaur Sandstone Formation include “Treptichnus” pedum, Cruziana cf. tenella, Cruziana isp., Diplichnites ispp. A, B, and C, Gyrophyllites isp., Lockeia isp., Merostomichnites isp., Monomorphichnus gregarius isp. nov., Monomorphichnus isp., Planolites isp., Psammichnites isp., Rusophycus bikanerus isp. nov., Rusophycus cf. carbonarius, Rusophycus isp. and radial trace fossils.These trace fossils belong to ethological categories pascichnia, repichnia, cubichnia, and fodinichnia and represent arthropod and worm-like burrowing biota. The assemblage and a regional comparison with contemporaneous trace fossils in the eastern Gondwanan realm suggest that the sequence in the study area belongs to the Cruziana tenella Ichnozone and to Stage 2 (upper part of Terreneuvian), however the Middle Cambrian is not excluded. The trace fossil assemblage belongs to the archetypal Cruziana ichnofacies. Cross bedded sandstone, mud cracks and rainprints in the ichniferous strata of the Nagaur Sandstone Formation indicate deposition in an intertidal sand flat with channels that was exposed episodically.     

华北板块北缘早白垩世的底侵作用：来自麻粒岩包体的证据

内蒙古四子王旗地处华北板块北缘中段,近年来在该区的早白垩世碱性玄武岩中发现了下地壳麻粒岩包体。本文研究的麻粒岩包体多数为中酸性的苏长麻粒岩,只有个别属于基性的二辉麻粒岩。麻粒岩包体的主量元素特征为SiO₂含量在49.9%到69.24%之间,MgO含量在0.92%~3.56%之间,Mg^#为43.0~62.9,Al₂O₃在13.91%~22.79%之间;稀土元素总量变化较大（∑REE在33.76×10^-6~184.13×10^-6之间）,分配模式也不尽相同,反映这些包体来自于不同源区或经历了不同的演化过程,但总体特征是LREE相对HREE富集,大多数样品的Eu呈现明显的正异常;由于包体的来源不同或经历了不同的演化阶段,它们的微量元素特征也有很大的差异。本区研究的麻粒岩包体的地球化学特征与华北地台的麻粒岩包体和麻粒岩地体都有很大的不同,反映了地壳组成横向上的不均一性。计算得出二辉麻粒岩的平衡温压条件分别为940~947℃和1.2±0.1GPa;苏长麻粒岩的平衡温度范围为927~715℃。通过对麻粒岩包体的岩相学、平衡温压条件估算、锆石形态特征分析和锆石的LA-ICP-MS年代学研究,得到本区早白垩世时的下地壳组成和之前的演化过程：本区下地壳在约40km深处可分为上下两部分,上部主要由苏长麻粒岩组成,厚度至少为9km,下部可能由二辉麻粒岩组成;下地壳上部的苏长麻粒岩是晚太古代（2509±35Ma）的岩浆岩经历了早白垩世（约122Ma）的玄武质岩浆底侵,发生了麻粒岩相变质和部分熔融形成的。推测本区岩石圈减薄事件的起始时间为122Ma。     

华北克拉通北缘显生宙四次底侵作用及其构造-岩浆活动与深部背景

通过对华北克拉通北缘显生宙四次(P₁,T₃,J₁,K₁)底侵作用的研究,将华北克拉通的活化与岩石圈深部地幔物质的底辟体上涌联系起来。不同阶段底侵作用在岩浆来源深度、与构造格局关系、对地壳垂向增生的贡献、幔源物质脉动式上涌等方面的差异与变化,显示它们是一个分阶段连续热演化的深部过程,其动力学机制是深部的高热流和地幔物质的向上运移。对应于地幔物质上涌,必然存在同期的地幔底辟体隆起的岩石圈结构变化。通过对华北中生代盆山系形成机制的讨论,认为该区高分辨率面波层析成像所显示的地幔底辟体上涌的特征可以反映中生代岩石圈底侵作用的深部背景。     

Early cretaceous igneous activities in the north flank of the North China Craton: the Shouwangfen complex example

ABSTRACT

The Early Cretaceous igneous complexes in the north flank of the North China Craton (NCC) provide a window to investigate the Mesozoic magmatism in the NCC. Here we report the precise timing of Early Cretaceous magmatism and magma petrogenesis of the different rock types in the north flank of the NCC based on petrology, mineral chemistry, geochemistry, zircon geochronology and Sr-Nd isotopes. Zircon U-Pb dating reveals that the Shouwangfen complex was crystallized at 130–128 Ma. The rocks display enrichment in large ion lithophile elements (LILE) and LREE, and depletion in high field strength elements (HFSE) and HREE, with relatively high Sr/Y and La/Yb values, typical of subduction-related magmatic rocks. The mafic microgranular enclaves show typical igneous textures, acicular apatites, sieve-texture of plagioclase phenocrysts and overgrowth of amphibole around the pyroxene, corresponding to magma mixing and mingling and thermal exchange. The quartz monzonites display normal zoning of the plagioclase, low and homogeneous εNd(t) values and linear co-variations in two-component diagrams. The quartz monzodiorites are characterized by high and homogeneous εNd(t) values. Petrologic feature and geochemical data suggest that the quartz monzonites represent lower crustal magma with minor contribution of enriched melt of the sub-continental lithospheric mantle (SCLM), followed by fractional crystallization. The mafic microgranular enclaves were sourced from enriched SCLM, followed by mixing and mingling with the host quartz monzonitic magma. The quartz monzodiorites are mainly SCLM-derived and subsequently mixed with lower crust melts. The high water contents (≥3%) of these Early Cretaceous igneous complexes suggests a hydrous SCLM beneath the NCC. The Early Cretaceous igneous complexes formed within an extensional tectonic setting which were related to the retreat and dehydration of the paleo-Pacific slab. The hydration of the lithosphere induced extensive crust-mantle interaction and large-scale water-rich magmatism, leading to lithospheric thinning in the NCC during the Mesozoic.     

中朝与扬子板块的鉴别特征

本文强调了要从地质演化历史过程中,综合运用地质、地球化学、地球物理的资料来对比及鉴别不同板块的特征。综合运用结晶基底的形成时间,某些元素的含量、某些元素的比值,铅同位素比值的变化,地幔包体中稀土元素配分曲线的特征,中元古界是变质的还是沉积的,晋宁事件的存在与否,震旦纪冰碛层的特征,早寒武纪含磷岩系与黑色页岩系的存在与否,400Ma前后的沉积间断,晚古生代煤系地层的发育特征,板块运移距离的大小,岩石圈的厚度,平均P波速度与剪切波速度的差异、壳内低阻层的存在与否等特征就可鉴别中朝与扬子板块。认识这些特征,将有助于弄清东亚地区其他小地块(如朝鲜半岛南部地块,Hida地块,柴达木地块和塔里木地块等)的归属问题。     

Sedimentation in a closed trough north of the Iberia Abyssal Plain in the northeast Atlantic†

Mirrol Trough of the northeast Atlantic contains five NNE-SSW trending, en echelon, turbidite-filled basins deeper than 5500 m, each ranging from 4 to 10 km in width and 19 to 65 km in length. Trough deposition has consisted mainly of turbidites from adjacent hills and ridges as indicated by the physiography of the region, sediment isopach map, the nature of the sediments in the trough, and benthic foraminiferal depth indicator species. The sedimentation rate on abyssal hills and ridges, as deduced from palaeomagnetic evidence, is 1.36 cm/10³ years. Using this sedimentation rate, it is estimated that Mirrol Trough subsided relative to the surrounding area and began receiving sediments between 8.3 and 11.5 m.y. ago; and the deposition of the most recent turbidite has occurred sometime between 29,000 and 44,000 years b.p. Tilting of the base of the most recent turbidite with respect to the basin floor is observed, and this is attributed to relative sinking of the eastern margin of the trough after the deposition of the most recent turbidite.     

Mesoproterozoic Earthquake Events and Breakup of the Sino-Korean Plate

In the Mesoproterozoic time, the northern part of the Sino-Korean Plate experienced a period of intensive tectonic extension and breakup. 1. An abundance of sedimentary earthquake records is preserved in the Chuanlinggou, Tuanshanzi and Gaoyuzhuang formations in the Mesoproterozoic Changcheng System （1800-1400 Ma） and in the Mesoproterozoic Wumishan Formation of the Jixian System （1400-1000 Ma）. These earthquake records are characterized by various liquefied sand-veins, carbonate microspar and coarser spar veins, limestone dikes, liquefied breccia and various forms of liquefied contorted bedding. This deformation is always associated with synsedimentary faults and igneous activity. 2. Three liquefaction models for soft carbonate sediments are recognized, including liquefaction in laminated carbonate rocks, liquefaction in thin-bedded carbonates and large-scale liquefaction along huge carbonate dikes. 3. Based on the record of earthquake and volcanic activities, the Sino-Korean Plate experienced at least twice intraplate breakups. One occurred between 1800-1400 Ma, and the other occurred at about 1200 Ma. The last breakup resulted in formation of the Yan-Liao aulacogen, a tectonic zone characterized by deeper material vibrancy, active faults, major igneous activity and frequent earthquakes.     

上扬子克拉通北部晚古生代-中三叠世大陆边缘盆地的形成与演化

上扬子克拉通北部晚古生代-中三叠世的沉积盆地是在勉-略洋盆南侧发展起来的被动大陆边缘盆地, 在泥盆纪-中二叠世以稳定沉降为主, 向北以碳酸盐岩缓坡与台地向勉略洋盆过渡; 中二叠世末期受峨眉地裂运动影响形成隆坳相间的格局; 早-中三叠世构造体制由伸展变为挤压, 沉积建造由开阔海碳酸盐岩台地逐渐向半局限台地、半封闭海湾膏盐湖相以及陆相碎屑岩含煤岩系过渡.该陆缘盆地经历了晚三叠世上扬子北缘前陆盆地、中侏罗世-早白垩世川西、川北前陆盆地, 以及晚白垩世至今构造残留盆地的改造.其中, 晚三叠世须三-须六期上扬子北缘前陆盆地的前缘隆起大致沿汶川、剑阁和万源一线分布.热年代学分析结果表明, 汶川、剑阁和万源一线以南的上二叠统烃源岩在早中生代始终处于埋藏增温状态, 只是自晚白垩世才进入抬升降温阶段, 呈"同代"烃源岩的特征; 而汶川、剑阁和万源一线以北的龙门山、米仓山和大巴山山前冲断地区, 上二叠统烃源岩则围绕生烃窗经历了多次增温和降温过程, 热演化历史复杂, 呈"隔代"烃源岩的特征.因此, 对于上扬子克拉通北部晚古生代-中三叠世陆缘盆地的勘探, 汶川、剑阁和万源一线以南比其北侧更有利.