Abstract The North China Craton contains one of the longest, most complex records of magmatism, sedimentation, and deformation on Earth, with deformation spanning the interval from the Early Archaean (3.8 Ga) to the present. The Early to Middle Archaean record preserves remnants of generally gneissic meta-igneous and metasedimentary rock terranes bounded by anastomosing shear zones. The Late Archaean record is marked by a collision between a passive margin sequence developed on an amalgamated Eastern Block, and an oceanic arc–ophiolitic assemblage preserved in the 1600 km long Central Orogenic Belt, an Archaean–Palaeoproterozoic orogen that preserves remnants of oceanic basin(s) that closed between the Eastern and Western Blocks. Foreland basin sediments related to this collision are overlain by 2.4 Ga flood basalts and shallow marine–continental sediments, all strongly deformed and metamorphosed in a 1.85 Ga Himalayan-style collision along the northern margin of the craton. The North China Craton saw relative quiescence until 700 Ma when subduction under the present southern margin formed the Qingling–Dabie Shan–Sulu orogen (700–250 Ma), the northern margin experienced orogenesis during closure of the Solonker Ocean (500–250 Ma), and subduction beneath the palaeo-Pacific margin affected easternmost China (200–100 Ma). Vast amounts of subduction beneath the North China Craton may have hydrated and weakened the subcontinental lithospheric mantle, which detached in the Mesozoic, probably triggered by collisions in the Dabie Shan and along the Solonker suture. This loss of the lithospheric mantle brought young asthenosphere close to the surface beneath the eastern half of the craton, which has been experiencing deformation and magmatism since, and is no longer a craton in the original sense of the word. Six of the 10 deadliest earthquakes in recorded history have occurred in the Eastern Block of the North China Craton, highlighting the importance of understanding decratonization and the orogen–craton–orogen cycle in Earth history.
The Paleoproterozoic Xiong'er Group in the North China craton is composed of mafic to felsic volcanic rocks and minor sedimentary rocks (4.3%), and crops out over an area of 60,000 km2. The volcanic and sedimentary strata, which vary from 3 km to 7 km in thickness, unconformably overlie an Archean and Paleoproterozoic crystalline basement, and are unconformably overlain by Meso-Neoproterozoic terrigenous clastic rocks and carbonates. Xiong'er volcanic rocks include basaltic andesite + andesite and dacite + rhyolite dated at 1760 Ma. The andesitic rocks contain clinopyroxene and plagioclase with minor olivine and orthopyroxene, but lack amphibole and biotite, suggesting crystallization from an anhydrous magma. All analyzed volcanic rocks are enriched in large-ionlithophile elements (LILE; e.g., K, Rb, Ba) and light rare-earth elements (LREE), and are depleted in high-field-strength elements (HFSE; e.g., Nb, Ta, and Ti). They have high LILE/HFSE ratios and low Ti/Zr (40 to 8) and Sr/Y (16 to 2) ratios and 147Sm/144Nd (0.09792 to 0.1332), 143Nd/144Nd (0.511082 to 0.511480), εNd(t = 1.76 Ga) (-3.8 to -9), and TDM (2.45 to 3.07 Ga). The geochemical and isotopic compositions indicate derivation from an enriched subcontinental lithospheric mantle previously contaminated by a subducted slab. The magmas exhibit the effects of low-pressure assimilation and fractional crystallization. The Xiong'er Group is contemporaneous with 1760 Ma mafic dike swarms, massif-type anorthosites, and rapakivi granites in the northern part of the North China craton. It formed in a continental-rift environment, marking the initiation of the breakup of the surpercontinent, Columbia.
Abstract The Jiaodong Peninsula or eastern Shandong Province, the most important gold producing in region China, is located in the southeastern margin of the North China Craton. The gold deposits in the Jiaodong Peninsula are divided into three gold belts, from west to east, the Zhaoyuan–Laizhou, Penglai–Qixia and Muping–Rushan belts. The deposits occur as gold-bearing quartz veins and disseminated- and stockwork-style ores adjacent to fault zones. Most of the gold deposits can be classified in four stages: stage I, quartz–(minor) pyrite; stage II, pyrite–quartz–gold; stage III, quartz–base metal sulphide minerals; stage IV, quartz–carbonate. Ar–Ar ages, Rb–Sr isochrons, and hydrothermal zircon sensitive high-resolution ion microprobe U–Pb ages obtained from these deposits suggest a gold mineralization time of 120±10 Ma. The Sr–Nd isotopic compositions of pyrites and the associated rocks suggest that the ore-forming materials were probably derived from a mixed source. Fluid inclusion studies show that ore-forming fluids of gold deposits are consistent throughout the Jiaodong Peninsula, with similar mineralizing temperature and pressure conditions. Ore-forming fluids are characterized by H 2 O–CO 2 –NaCl±CH 4 . The optimal mineralizing temperature and pressure ranges are 170–335 °C and 0.7–2.5 kbar. Oxygen and hydrogen isotope data show that ore fluids are of magmatic origin. Gold deposits in the Jiaodong Peninsula formed in the same mineralizing–geodynamic conditions, and are related to the Mesozoic tectonic transition in the eastern North China Craton. Gold metallogeny is only one expression of the Mesozoic tectonic transition.
The North China craton is the only known place where an Archaean craton with a thick tectospheric root lost half of that root in younger tectonism by processes such as delamination, convection, hydration-weakening, compositional change or some other mechanism. In this volume, authors provide data constraining the geometry and timing of root loss, aimed at understanding why and how continental roots are lost in general. Modelling how often this process may have occurred in the geological past, and how much lithospheric material has been recycled to the convecting mantle through this mechanism, could drastically change our current understanding of crustal growth rates and processes. Possible triggering mechanisms for root loss include collision of the South China (Yangtze) and North China cratons in the Triassic, the India–Asia collision, closure of the Solonker and Monhgol–Okhotsk oceans, Mesozoic subduction of the Pacific Plate beneath eastern China, impingement of mantle plumes, mantle hydration from long-term subduction and several rifting events. In this volume, we link studies of crustal tectonics with investigations aimed at determining the nature of and timing of the formation and loss of the root, in order to better-understand mechanisms of continental root formation, evolution and recycling/removal.
The Wulashan gold deposit, situated along the northwestern margin of the North China craton (NCC), is hosted by ductile-brittle faults within Archean metamorphic volcano-sedimentary rocks of the Wulashan Group. This deposit is characterized by gold-bearing quartz-K feldspar and quartz veins. Both granitoid batholiths and pegmatite dikes intruded the metamorphic basement rocks, and are spatially associated with gold mineralization. Contrasting genetic models have been proposed for the deposit due to lack of reliable age data. Our new SHRIMP U-Pb zircon ages for these intrusions now reveal important constraints on the mineralization time and tectonic evolution of this region. These intrusions contain inherited zircons of about 2.55 Ga, probably from the Wulashan basement that was intruded by pegmatite dikes at about 1.84 Ga; the latter probably are related to the major tectonic event leading to the final amalgamation of the NCC. The basement subsequently underwent at least three tectono-thermal events during Phanerozoic time (at 353 ± 7, 169 ± 7, and 132 ± 2 Ma). Combined with previous Ar-Ar and K-Ar ages, we suggest two gold mineralization episodes for the Wulashan gold deposit. The first episode occurred at about 350 Ma, indicated by ages of a goldrelated fuchsite and the Dahuabei granitoid batholith. This supports a previously proposed model that relates gold mineralization to the Dahuabei granite that formed during collision of the Paleo-Mongolian block with the NCC. The second one occurred in the late Yanshanian period, as indicated by the mineralized K-feldspar-rich vein of 132 ± 2 Ma. This episode is simultaneous with those in the eastern NCC, indicative of a widespread late Yanshanian metallogenic event that was a response either to the subduction of the Izanagi-Pacific plate beneath eastern China or to the removal of the Early Cretaceous lithosphere in the eastern NCC.
Abstract The North China Craton (NCC) is the only place currently recognized where an Archaean craton developed a continental root in the Archaean, and subsequently lost half of that root in younger tectonism. In this volume, various authors have advanced different models of root loss, and provided geological, geophysical and geochemical data that help constrain the geometry and timing of root loss. Understanding why and how roots are lost may help us understand how often this process may have occurred in the geological past, and how much lithospheric material has been recycled to the convecting mantle through this mechanism, potentially drastically changing our current understanding of crustal growth rates and processes. With current data, there are several equally plausible possibilities that require further data collection for testing. There are several possible tectonic triggers that may have caused half the root to be lost, acting either separately or together. These include collisional, extensional, plume-related, fluid-weakening, spontaneous, and more complex hybrid mechanisms. We also do not know why only the eastern half of the root was lost, and not the root from beneath the whole craton. One tantalizing idea is that the root grew independently, by tectonic underplating of subducted buoyant oceanic lithosphere, beneath the previously separate eastern and western halves of the craton by 2.5 Ga, with modification at 1.8 Ga. If so, perhaps only the eastern half of the root was lost in younger tectonism because there was some physical or geometric difference between the two halves. Alternatively, collisional or subduction-related tectonic processes acting only on the Eastern Block may have caused the disruption of the tectosphere there in the Mesozoic. The timing of and mechanism for loss of the root is not uniquely resolvable with current data, but a solution to the problem is in reach. Possible triggering mechanisms include, but are not limited to, collision of the South China (Yangtze) and North China Cratons in the Triassic, the India–Asia collision, closure of the Solonker and Mongol–Okhotsk oceans, Mesozoic subduction of the Pacific plate beneath Eastern China, impingement of mantle plumes, mantle hydration from long-term subduction, and several rifting events. In this concluding review, we link studies of crustal tectonics with investigations aimed at determining the nature and timing of the formation and loss of the root, to better understand mechanisms of continental root formation, evolution and recycling–removal.
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