冀东陆壳结构的岩石学模型

冀东地区的古老变质岩系是一个出露的大陆地壳断面。根据变质岩系的变质相、亚相的研究和地质温压计计算的结果推定的深度,并结合地球物理测深资料,以及笔者测定和前人的岩石高压下波速实验资料提出了本区大陆地壳结构的岩石学模型。下地壳由麻粒岩相岩石组成,上部为角闪石麻粒岩亚相的中性成分的麻粒岩,下部为辉石麻粒岩亚相的基性成分的麻粒岩构成,底部夹有透镜状蛇纹石化橄榄岩以及紫苏花岗岩。中地壳主要由高角闪岩相的中性-中酸性成分的片麻岩、片岩构成,顶部为低角闪岩相的片麻岩、片岩,广泛发育英云闪长岩和花岗闪长岩岩体,含隙间高温流体相(fluid phase),形成高导-低速层。上地壳主要为绿片岩相(部分低角闪岩相)的板岩、千枚岩、片岩、变粒岩以及花岗岩组成,顶部为沉积盖层     

A model for lower continental crust

This proposed model is based on geological, geophysical and geochemical data. Previous models suggested for the lower continental crust consisted of basalt, gabbro, or charnockitic rocks; however, experimental and field petrological data indicate that the bulk of crustal rocks are metamorphic. A lower crust of heterogeneous metamorphic rocks also agrees with seismic reflection results which show numerous reflections from “layering”. Geothermal conditions favor a “dry” charnockitic or gabbroic lower crust rather than an amphibolitic lower crust because heat production data imply that wet amphibolitic rocks would have a higher heat production than their dry metamorphic equivalents. Relatively high velocities from field and laboratory measurements in such low-density rocks as granite, syenite, anorthosite and granulitic rocks in general imply that the composition of the lower crust is more felsic than gabbro. Variation in seismic velocity and depths from crustal refraction studies and numerous seismic reflections all indicate a highly heterogeneous lower crust. The lower crust, which has traditionally been described as gabbroic or mafic, may consist of such diverse rocks as granite gneiss, syenite gneiss, anorthosite, pyroxene granulite, and amphibolite, interlayered on a small scale, deformed, and intruded by granite and gabbro. Interlayering of these rocks explains the presence and character of seismic reflections. Abrupt changes in dip, tight folding, disruption of layers, intrusion, and changes in layer thickness explain the characteristic discontinuity of deep reflections. Igneous intrusions may be floored by metamorphic rocks. The lower crust consists of a complex series of igneous and metamorphic rock of approximate intermediate composition.     

Tectonic evolution of lower crustal rocks in an exposed magmatic arc section in the Hidaka metamorphic belt, Hokkaido, northern Japan

Abstract : The Hidaka metamorphic belt consists of an island-arc assembly of lower to upper crustal rocks formed during early to middle Paleogene time and exhumed during middle Paleogene to Miocene time. The tectonic evolution of the belt is divided into four stages, D₀rs, D₁, D₂rs, and D₃, based on their characteristic deformation, metamorphism, and igneous activity. The premetamorphic and igneous stage (D₀) involves tectonic thickening of an uppermost Cretaceous and earliest Tertiary accretionary complex, including oceanic materials in the lower part of the complex. D₁ is the stage of prograde metamorphism with increasing temperatures at a constant pressure during an early phase, and with a slight decrease of pressure at the peak metamorphic phase, accompanying flattening of metamorphic rocks and intrusions of mafic to intermediate igneous rocks. At the peak, incipient partial melting of pelitic and psammitic gneisses took place in the amphibolite–granulite facies transition zone, the melt and residuals cutting the foliations formed by flattening. In the deep crust, large amounts of S-type tonalite magma formed by crustal anatexis, intruded into the granulite facies gneiss zone and also into the upper levels of the metamorphic sequence during the subsequent stage. During D₁ stage, mafic and intermediate magmas supplied and transported heat to form the arc-type crust and at the same time, the magmatic underplating caused extensional doming of the crust, giving rise to flattening and vertical uplifting of the crustal rocks. D₂ stage is characterized by subhorizontal top-to-the-south displacement and thrusting of lower to upper crustal rocks, forming a basal detachment surface (décollement) and duplex structures associated with intrusions of S-type tonalite. Deformation structures and textures of high-temperature mylonites formed along the décollement, as well as the duplex structures, show that the D₂ stage movement occurred under a N-S trending compressional tectonic regime. The depth of intra-crustal décollement in the Hidaka belt was defined by the effect of multiplication of two factors, the fraction of partial melt which increases downward, and the fluid flux which decreases downward. The crustal décollement, however, might have extended to the crust-mantle boundary and/or to the lithosphere and asthenosphere boundary. The subhorizontal movement was transitional to a dextral-reverse-slip (dextral transpression) movement accompanied by low-temperature mylonitization with retrograde metamorphism, the stage defined as D₃. The crustal rocks from the basal décollement to the upper were tilted eastward on the N–S axis and exhumed during the D₃ stage. During D₂ and D₃ stages, the intrusion of crustal acidic magmas enhanced the crustal deformation and exhumation in the compressional and subsequent transpressional tectonic regime.     

三河-平谷8.0级地震区地壳结构和活动断裂研究——利用单次覆盖深反射和浅层地震剖面

跨1679年三河-平谷8.0级地震区完成的单次覆盖深地震反射剖面和浅层地震反射剖面,揭示了三河-平谷地震区的地壳结构和断裂的深、浅构造特征.结果表明,该区地壳以TWT6～7 s左右的强反射带为界分为上地壳和下地壳,上地壳厚约18～21 km,下地壳厚约13～15 km.剖面揭示的地壳深断裂和浅部活动断裂具有上下一致的对...     

地壳主要岩石流变参数及华北地壳流变性质研究

岩石流变参数和变形机制是根据断层摩擦和岩石幂次流动本构关系建立岩石圈强度剖面的基础。近 30年来 ,高温高压实验取得了很大进展 ,获得了大量地壳矿物和岩石流变资料。本文系统总结了这些流变实验资料 ,并应用流变数据结合地震震源深度分布 ,对华北地壳流变性质进行了研究。结果表明 ,以花岗岩和低级变质岩为代表的上地壳为脆性破裂 ,其强度受断层摩擦约束 ,以长英质片麻岩为主的中地壳和以中性麻粒岩为主的下地壳上层处于塑性流变状态 ,由干的基性麻粒岩组成的下地壳下层处于脆性向塑性流变的过渡状态。华北地壳的这种物质组成和流变为地壳不同层次的解耦和强震孕育提供了力学条件 ,也构成了不同尺度块体的底边界     

Tectono-magmatic evolution of the 1.9-Ga great bear magmatic zone, Wopmay orogen, northwestern Canada

The 1875-1840-Ma Great Bear magmatic zone is a 100-km wide by at least 900-km-long belt of predominantly subgreenschist facies volcanic and plutonic rocks that unconformably overlie and intrude an older sialic basement complex. The basement complex comprises older arc and back-arc rocks metamorphosed and deformed during the Calderian orogeny, 5–15 Ma before the onset of Great Bear magmatism. The Great Bear magmatic zone contains the products of two magmatic episodes, separated temporally by an oblique folding event caused by dextral transpression of the zone: (1) a 1875-1860-Ma pre-folding suite of mainly calc-alkaline rocks ranging continuously in composition from basalt to rhyolite, cut by allied biotite-hornblende-bearing epizonal plutons; and (2) a 1.85-1.84-Ga post-folding suite of discordant, epizonal, biotite syenogranitic plutons, associated dikes, and hornblende-diorites, quartz diorites, and monzodiorites. The pre-folding suite of volcanic and plutonic rocks is interpreted as a continental magmatic arc generated by eastward subduction of oceanic lithosphere. Cessation of arc magmatism and subsequent dextral transpression may have resulted from ridge subduction and resultant change in relative plate motion. Increased heat flux due to ridge subduction coupled with crustal thickening during transpression may have caused crustal melting as evidenced by the late syenogranite suite. Final closure of the western ocean by collision with a substantial continental fragment, now forming the neoautochthonous basement of the northern Canadian Cordillera, is manifested by a major swarm of transcurrent faults found throughout the Great Bear zone and the Wopmay orogen.Although there is probably no single evolutionary template for magmatism at convergent plate margins, the main Andean phase of magmatism, exemplified by the pre-folding Great Bear magmatic suite, evolves as larger quantities of subduction-related mafic magma rise into and heat the crust. This results in magmas that are more homogeneous, siliceous, and explosive with time, ultimately leading to overturn and fractionation of the continental crust.     

Developing plate tectonics theory from oceanic subduction zones to collisional orogens

Crustal subduction and continental collision is the core of plate tectonics theory. Understanding the formation and evolution of continental collision orogens is a key to develop the theory of plate tectonics. Different types of subduction zones have been categorized based on the nature of subducted crust. Two types of collisional orogens, i.e. arc-continent and continent-continent collisional orogens, have been recognized based on the nature of collisional blocks and the composition of derivative rocks. Arc-continent collisional orogens contain both ancient and juvenile crustal rocks, and reworking of those rocks at the post-collisional stage generates magmatic rocks with different geochemical compositions. If an orogen is built by collision between two relatively old continental blocks, post-collisional magmatic rocks are only derived from reworking of the old crustal rocks. Collisional orogens undergo reactivation and reworking at action of lithosphere extension, with inheritance not only in the tectonic regime but also in the geochemical compositions of reworked products(i.e., magmatic rocks). In order to unravel basic principles for the evolution of continental tectonics at the post-collisional stages, it is necessary to investigate the reworking of orogenic belts in the post-collisional regime, to recognize physicochemical differences in deep continental collision zones, and to understand petrogenetic links between the nature of subducted crust and post-collisional magmatic rocks. Afterwards we are in a position to build the systematics of continental tectonics and thus to develop the plate tectonics theory.     

Complex Archean lower crustal structure revealed by COCORP crustal reflection profiling in the Wind River Range,Wyoming

A COCORP deep crustal reflection profile across the Wind River uplift crosses exposed Archean rocks and resolves an unusual complex deep crustal structure at a depth of 24–31 km in an area where depth relations in Precambrian rocks can be inferred. The different levels of exposure across the beveled plunge of the Wind River uplift reveal supracrustal rocks at shallower levels with migmatites and pyroxene granulites at deeper levels. For the first time, deep crustal structure from reflection profiling may be interpreted in terms of exposed basement geology. A folded, multilayered deep structure shown by relfection data resembles multiply folded pyroxene granulite interlayered with granitic gneiss exposed in the central Wind River uplift; isoclinal folding is suggested in the folded layered seismic structure. Earlier seismic reflection studies suggested a simpler lower crust. These data indicate that lower crustal structure may have a complexity similar to deeply eroded Precambrian granulite-facies rocks. If this seismic feature represents folded metamorphic rocks, it seems unlikely that this Archean crust could have been thickened by underplating after 2.7 b.y. B.P. and the crust would have to be at least 30 km thich when this structure was formed.     

A continental crustal model and its geothermal implications

The following crustal model based on realistic estimates of metamorphic rock volumes and H₂O content is proposed as a basis for geothermal calculations: (1) a surface zone of intermediate metamorphic rocks containing granitic intrusions and grading downward into (2) a more felsic migmatite zone, (3) a lower crustal zone of approximately andesitic composition crystallized in granulite or possibly amphibolite facies. Heat production values and thickness for the three zones are 3 HGU, 5 HGU, 0.5–1.5 HGU and 8, 8, and 18 km respectively. If the surface heat flow is 1.2 HFU, the model predicts a temperature of only 407°C at the Moho and an upper mantle heat flow of 0.3–0.5 HFU. The low temperatures resulting from this model rule out a seismic low-velocity zone in the crust produced by thermal effects.     

Nature and growth rate of the Northern Izu–Bonin (Ogasawara) arc crust and their implications for continental crust formation

The bulk composition of the continental crust throughout geological history is thought by most previous workers to be andesitic. This assumption of an andesitic bulk composition led to an early hypothesis by 72 ) that the continental crust was created by arc magmatism. This hypothesis for the origin of continental crust was challenged by several authors because: (i) the mean rate of arc crust addition obtained by 50 ) is too small to account for some certain phases of rapid crustal growth; and (ii) the bulk composition of ocean island arcs, the main contributor to the Archean and early Proterozoic crust, is basaltic rather than andesitic ( 4 ; 49 ). New data from the Northern Izu–Bonin arc are presented here which support the 72 ) hypothesis for the origin of the continental crust by andesitic arc magma. A geological interpretation of P wave crustal structure obtained from the Northern Izu–Bonin arc by 66 ) indicates that the arc crust has four distinctive lithologic layers: from top to bottom: (i) a 0.5–2-km-thick layer of basic to intermediate volcaniclastic, lava and hemipelagite (layer A); (ii) a 2–5-km-thick basic to intermediate volcaniclastics, lavas and intrusive layer (layer B); (iii) a 2–7-km-thick layer of felsic (tonalitic) rocks (layer C); and (iv) a 4–7-km-thick layer of mafic igneous rocks (layer D). The chemical composition of the upper and middle part of the northern Izu–Bonin arc is estimated to be similar to the average continental crust by 73 ). The rate of igneous addition of the Northern Izu–Bonin arc since its initial 45-Ma magmatism was calculated as 80 km³/km per million years. This rate of addition is considered to be a reasonable estimate for all arcs in the western Pacific. Using this rate, the global rate of crustal growth is estimated to be 2.96 km³/year which exceeds the average rate of crustal growth since the formation of the Earth (1.76 km³/year). Based on this estimate of continental growth and the previously documented sediment subduction and tectonic erosion rate (1.8 km³/year, 24 ), several examples of growth curves of the continental crust are presented here. These growth curves suggest that at least 50% of the present volume of the continental crust can be explained by arc magmatism. This conclusion indicates that arc magmatism is the most important contributor to the formation of continental crust, especially at the upper crustal level.     

早前寒武纪地壳增生、再造作用与基底变质建造分析──以华北为例

早前寒武纪地壳演化的具体表现可以从增生作用和陆壳再造作用这两个方面进行描述按照增生表壳岩系类型可以将早前寒武纪大陆地壳划分为绿岩型和沉积型陆壳增生区;按陆壳再造作用的类型可以将早期大陆地壳划分为变质改造型和重熔分异型陆壳再造区对区域上绿岩型表壳岩系、沉积型表壳岩系;TTG岩系、钾质花岗岩系等与地壳演化进程的关系作了概括．不同类型陆壳区反映了地壳增生进程是不一样的,增生地壳受再造作用的程度以及遭受的陆壳再造作用类型也可以是不同的,而一个完整的地壳演化旋回应包含活动增生、陆壳再造与克拉通化作用,一个地壳区地壳演化往往是这些作用交替发展并形成与邻区地壳演化进程的差异．进而提出了早前寒武纪克拉通基底建造分析的思路、原则和模式     

The deep and shallow structure,composition and its relation to earthquakes in Chaoyang — Yixian seismic region

This paper describes synthetically the seismic activity, deep and shallow structures and rock dynamic features in and near Chaoyang—Yixian region. It is supposed that there is a low velocity layer in middle crust and the three-layered crustal velocities are all lower than that in both sides of the region. There exists uplifts of upper mantle and asthenosphere-low resistance layer. It is also studied the composition of matter of three-layered crust, low velocity layer, upper mantle and asthenosphere. In the end the direct relations between the deep and shallow structure, composition and the seismic activity and new activities of faults in this region are discussed.     

The influence of crustal structure on compositions of subduction-related magmas

A survey of Sr isotopic ratios and other compositional features of subduction-related magma suites reveals significant correlations between these averaged parameters and characteristics of the underlying crust (i.e., thickness, composition, and age). These observations lead to the conclusion that crust and(or) mantle rocks in the hanging walls of subduction zones are involved in modification of primary mafic magmas (typically basalt or basaltic andesite). It is proposed that mafic magmas will stagnate within the crust or uppermost mantle where they may differentiate and react with wall rocks. The extent to which such processes manifest themselves will depend upon details of the local crustal structure. In particular, the composition and age of the crust will strongly influence such parameters as Sr, Nd and Pb isotopic compositions. Such data strongly indicate the involvement of crustal rocks in locales underlain by old sialic crust (e.g., central Andes). Depending upon the level of magma stagnation and evolution within the crust, different trends in isotopic composition may result. These isotopic trends may be enhanced by partial melting of the wall rocks to produce relatively silicic anatectic magmas, and locally they may reflect subduction of continental sediments. Interpretation of the isotopic data may be more ambiguous in locales underlain by younger and more mafic continental crust (Cascades, E Eleutians) and those underlain by oceanic crust owing to the similarity in isotopic composition of primary magmas and the latter crustal materials. Yet some degree of crustal involvement in magmatic evolution seems highly probable even in these more primitive terranes. Consequently, most island arc magmas, and especially those more evolved than basalt, are probably not primary in the sense that they do not represent direct melts of the upper mantle. Studies of arc volcanic rocks may yield misleading conclusions concerning processes of magma generation related to subduction unless evolutionary processes are defined and their effects considered. It appears that modern volcanic arcs provide a poor analog for models of early crustal development because the modern mantle-derived magmatic components are more mafic in composition than average continental crust.     

Metamorphism, partial preservation, and exhumation of ultrahigh-pressure belts

The Dabie-Sulu belt of east-central China, the Kokchetav Complex of northern Kazakhstan, the Maksyutov Complex of the South Urals, the Dora Maira Massif of the Western Alps, and the Western Gneiss Region of southwestern Norway lie astride intracontinental suture zones. All represent collisional mountain belts. Adjoining Eurasian regions exhibit little or no evidence of a coeval calc-alkaline arc. Each metamorphic complex contains mineralogic and textural relics of the presence or former existence of coesite ± diamond. Other ultrahigh-P, moderate-T metamorphic phases, including K-rich clinopyroxene, Mg-rich garnet, ellenbergerite, lawsonite, Al-rutile, glaucophane, high-Si phengite, and associations such as coesite + dolomite, magnesite + diopside, and talc + kyanite, diopside, jadeite, or phengite also testify to pressures approaching or exceeding 2.8 GPa. Each of the five well-studied Eurasian ultrahigh-pressure complexes consists chiefly of old, cool continental crust. Deep-seated recrystallization took place during the Phanerozoic. Subduction zones constitute the only known plate-tectonic environment where such high-P, low-T conditions exist. A model involving underflow of a salient of continental crust imbedded in oceanic crust-capped lithosphere explains the ultrahigh- pressure metamorphism. Partly exhumed ultrahigh-pressure terranes consist of relatively thin sheets 7 ± 5 km thick. During early stages of plate descent, hydration of relatively anhydrous units occurs, and volatiles are expelled from hydrous rocks. If present, aqueous fluids markedly catalyze reactions. Experimental studies on MORB bulk compositions demonstrate that, for common subduction-zone P–T trajectories, amphibole (the major hydrous phase in metabasaltic rocks) dehydrates at less than ~ 2.0 GPa; accordingly, mafic blueschists and amphibolites expel H₂O at great depth and, except for some coarse-grained, dry metagabbros, tend to recrystallize to eclogite. Serpentinized mantle beneath the oceanic crust devolatilizes at comparable pressures. In contrast, phengite and biotite remain stable to pressures exceeding 3.5 GPa in associated quartzofeldspathic rocks. So, under ultrahigh-pressure conditions, the micaceous lithologies that dominate the continental crust fail to evolve significant H₂O, and may transform incompletely to eclogitic assemblages. Although hydrous rocks expel volatiles during compaction and shallow burial, very deep underflow of partly hydrated oceanic crust + mantle generates most of the volatile flux along and above a subduction zone prior to continental collision. As large masses of sialic crust enter the convergent plate junction, fluid evolution at deep levels severely diminishes, and both convergence and dehydration terminate. After cessation of ultrahigh-pressure recrystallization, tectonic slices of sialic massifs return to shallow depths along the subduction channel, propelled by buoyancy; collisional sheets that retain ultrahigh-pressure effects lose heat efficiently across both upper (extensional, normal fault) and lower (subduction, reverse fault) tectonic contacts. These sheets ascend to midcrustal levels rapidly at average exhumation rates of 2–12 mm/year. Surviving ultrahigh-pressure relics occur as micro-inclusions encased in dense, strong, impermeable, unreactive mineralogic hosts, and are shielded during return towards conditions characteristic of midcrustal levels. Rehydration attending decompression is incomplete; its limited extent reflects the coarse grain size and relative impermeability of the rocks undergoing retrogression, as well as declining temperature and lack of aqueous fluids.     

Deep crustal reflection survey in central Israel

The results of the first deep crustal reflection survey in Israel are described. The line crosses central Israel in a SE-NW direction from near the Dead Sea rift to the Mediterranean sea. The data reveals a correlation between the reflectivity and type of crust as previously determined on the basis of magnetic and crustal refraction data. To the southeast, in an area which is thought to be underlain by continental crust, the upper crust is mostly transparent while the lower crust shows distinct reflections. Near the Mediterranean sea, where the crystalline crust was previously shown to be thinner with higher magnetization and of possible oceanic origin, the upper crust is reflective while in general the lower crust is significantly less reflective. The lateral boundary between these two patterns of crustal reflectivity coincides with the magnetic boundary which was previously used to differentiate between the two types of crusts. Detailed analysis of crustal reflections does not seem to be justified with the present data except in special cases. One such case is the determination that the uppermost basement in the coastal plain is highly reflective, possibly due to metamorphic layering. Comparison of the deep reflection data with MT and seismic refraction data indicates possible correlation in the southeastern part of the line of high conductivity with lower crust reflections and of refraction Moho with the termination of lower crustal reflections. This correlation does not extend into the northwestern part of the section in which the crust is, most probably, no longer continental.     

Differential exhumation of tectonic units and ultrahigh-pressure metamorphic rocks in the Dabie Mountains, China

A model involving buoyancy, wedging and thermal doming is postulated to explain the differential exhumation of ultrahigh-pressure (UHP) metamorphic rocks in the Dabie Mountains, China, with an emphasis on the exhumation of the UHP rocks from the base of the crust to the upper crust by opposite wedging of the North China Block (NCB). The Yangtze Block was subducted northward under the NCB and Northern Dabie microblock, forming UHP metamorphic rocks in the Triassic (240–220 Ma). After delamination of the subduction wedge, the UHP rocks were exhumed rapidly to the base of the crust by buoyancy (220–200 Ma). Subsequently, when the left-lateral Tan–Lu transform fault began to be activated, continuous north–south compression and uplifting of the orogen forced the NCB to be subducted southward under the Dabie Orogen (`opposite subduction'). Opposite subduction and wedging of the North China continental crust is responsible for the rapid exhumation of the UHP and South Dabie Block units during the Early Jurassic, at ca 200–180 Ma at a rate of ∼ 3.0 mm/year. The UHP eclogite suffered retrograde metamorphism to greenschist facies. Rapid exhumation of the North Dabie Block (NDB) occurred during 135–120 Ma because of thermal doming and granitoid formation during extension of continental margin of the Eurasia. Amphibolite facies rocks from NDB suffered retrograde metamorphism to greenschist facies. Different unit(s) and terrane(s) were welded together by granites and the wedging ceased. Since 120–110 Ma, slow uplift of the entire Dabie terrane is caused by gravitational equilibrium.     

Inherent gravitational instability of thickened continental crust with regionally developed low- to medium-pressure granulite facies metamorphism

Petrological arguments show that regionally developed low- to medium-pressure, high-temperature granulite facies metamorphism may critically enhance the lowering of crustal density with depth. This leads to gravitational instability of homogeneously thickened continental crust, mainly due to changes in mineral assemblages and the thermal expansion of minerals in conjunction with the exponential lowering of the effective viscosity of rocks with increasing temperature. It is argued that crustal processes of gravitational redistribution (crustal diapirism) contributing to the exhumation of granulite facies rocks may be activated in this way.     

Large-scale Basement-involved Landslides, California Continental Borderland

— Large seafloor relief, shallow metamorphic basement, and seismic activity in the California Continental Borderland combine to produce major submarine slides capable of generating local tsunamis. The Catalina Schist basement complex of the Borderland contains melange units, faults between metamorphic facies, and foliation derived from a history of deep subduction underthrusting and subsequent tectonic exhumation along regional low-angle fault systems. Neogene volcanic and sedimentary rocks covered the exhumed metamorphic basement forming an interface with a strong contrast in material properties. Neogene transtensional block-faulting formed steep escarpments that cut through and elevated the low-angle detachment surface, providing slip surfaces with free faces susceptible to failure along the rheological boundary. Two basement-involved slope failure examples west of San Diego are described, including large block-glides and progressive rotational slumps along the steep northeast-facing Thirtymile Bank escarpment and along the southwest flank of Fortymile Bank.     

Provenance of sandstones from the Wakino Subgroup of the Lower Cretaceous Kanmon Group, northern Kyushu, Japan

Abstract The Wakino Subgroup is a lower stratigraphic unit of the Lower Cretaceous Kanmon Group. Previous studies on provenance of Wakino sediments have mainly concentrated on either petrography of major framework grains or bulk rock geochemistry of shales. This study addresses the provenance of the Wakino sandstones by integrating the petrographic, bulk rock geochemistry, and mineral chemistry approaches. The proportions of framework grains of the Wakino sandstones suggest derivation from either a single geologically heterogeneous source terrane or multiple source areas. Major source lithologies are granitic rocks and high‐grade metamorphic rocks but notable amounts of detritus were also derived from felsic, intermediate and mafic volcanic rocks, older sedimentary rocks, and ophiolitic rocks. The heavy mineral assemblage include, in order of decreasing abundance: opaque minerals (ilmenite and magnetite with minor rutile), zircon, garnet, chromian spinel, aluminum silicate mineral (probably andalusite), rutile, epidote, tourmaline and pyroxene. Zircon morphology suggests its derivation from granitic rocks. Chemistry of chromian spinel indicates that the chromian spinel grains were derived from the ultramafic cumulate member of an ophiolite suite. Garnet and ilmenite chemistry suggests their derivation from metamorphic rocks of the epidote‐amphibolite to upper amphibolite facies though other source rocks cannot be discounted entirely. Major and trace element data for the Wakino sediments suggest their derivation from igneous and/or metamorphic rocks of felsic composition. The major element compositions suggest that the type of tectonic environment was of an active continental margin. The trace element data indicate that the sediments were derived from crustal rocks with a minor contribution from mantle‐derived rocks. The trace element data further suggest that recycled sedimentary rocks are not major contributors of detritus. It appears that the granitic and metamorphic rocks of the Precambrian Ryongnam Massif in South Korea were the major contributors of detritus to the Wakino basin. A minor but significant amount of detritus was derived from the basement rocks of the Akiyoshi and Sangun Terrane. The chromian spinel appears to have been derived from a missing terrane though the ultramafic rocks in the Ogcheon Belt cannot be discounted.     

Constraints on the age of basement and crustal growth in Tianshan Orogen by Nd isotopic composition

Based on study of Nd isotopic composition for 101 rocks of various types from Tianshan Orogen, the age and character of basement and continental crustal evolution of the Tianshan Orogen were proposed. It is deduced that the continental crustal basement of the Tianshan Orogen was formed 1. 8 Ga ago. The protolith of its metamorphic rocks was derived from long-term depleted mantle source in the ancient are tectonic setting probably. The Tianshan Orogen is obviously different from the North Tarim Block in age of basement and post-evolution history. It was also shown that Paleozoic continental crustal growth happened extensively in the Tianshan Orogen, which is distinguished from Yangtse Block and Cathaysia Block in eastern China. Project supported by the National Natural Science Foundation of China (Grant No. 49633250). It belongs to the National “305” Project in Xinjiang, which is one of the National Key Projects in the Ninth Five-Year Plan (96-915-07-05A).