Subduction and Collision of the Jinsha River Paleo-Tethys: Constraints from Zircon U-Pb Dating and Geochemistry of the Ludian Batholith in the Jiangda–Deqen–Weixi Continental Margin Arc

The Jiangda–Deqen–Weixi continental margin arc(DWCA) developed along the base of the Changdu–Simao Block and was formed as a result of the subduction of the Jinsha River Ocean Slab and the subsequent collision. The Ludian batholith is located in the southern part of the DWCA and is the largest batholith in northwest Yunnan. Granite samples from the Ludian batholith yield an early Middle Permian age of 271.0 ± 2.8 Ma. The geochemical data of the early Middle Permian granitoids show high Si2 O, low P2 O5 and MgO contents that belong to calc-alkaline series and peraluminous I-type rocks. Their εHf(t) values range from-5.01 to +0.58, indicating that they were formed by hybrid magmas related to the subduction of the Jinsha River Tethys Ocean. The monzonite and monzogranite samples yield Late Permian ages of 250.6 ± 1.8 Ma and 252.1 ± 1.3 Ma, respectively. The Late Permian granitoids are high-K calc alkaline and shoshonite series metaluminous I-type rocks. Their εHf(t) values range from-4.12 to-1.68 and from-7.88 to-6.64, respectively. The mixing of crustal and mantle melts formed the parental magma of the Late Permian granitoids. This study, combined with previous work, demonstrates the process from subduction to collision of the Jinsha River Paleo-Tethys Ocean.     

Lithostratigraphy, Sedimentology, and Provenance of the Balfour Formation (Beaufort Group) in the Fort Beaufort–Alice Area, Eastern Cape Province, South Africa

Abstract: The Balfour Formation has a pronounced lithological variation that is characterized by alternating sandstone- and mudstone-dominated members. The sandstone-dominated Oudeberg and Barberskrans Members are composed of lithofacies that range from intraformational conglomerates to fine-grained sediments, whereas the mudstone-dominated members (Daggaboersnek, Elandsberg, and Palingkloof) are dominated by the facies Fm and Fl. Petrography, geochemistry, and a paleocurrent analysis indicated that the source rock of the Balfour Formation was to south east and the rocks had a transitional/dissected magmatic arc signature. The sandstones-rich members were deposited by seasonal and ephemeral high-energy, low-sinuous streams, and the fine-grained-rich members were formed by ephemeral meandering streams. The paleoclimates have been equated to present temperate climates; they were semiarid becoming arid towards the top of the Balfour Formation. This has been determined by reconstructing the paleolatitude of the Karoo Basin, geochemistry, paleontology, sedimentary structures, and other rock properties, like color.     

Zircon U–Pb Geochronology and Geochemistry of the Early Cretaceous Volcanic Rocks from the Manitu Formation in the Hongol Area,Northeastern Inner Mongolia

We undertook zircon U-Pb dating and geochemical analyses of volcanic rocks from the Manitu Formation in the Hongol area,northeastern Inner Mongolia,to determine their age,petrogenesis and sources,which are important for understanding the Late Mesozoic tectonic evolution of the Great Xing'an Range.The volcanic rocks of the Manitu Formation from the Hongol area consist primarily of trachyandesite,based on their chemical compositions.The zircons from two of these trachyandesites are euhedral-subhedral in shape,display clear oscillatory growth zoning and have high Th/U ratios(0.31-1.15),indicating a magmatic origin.The results of LA-ICP-MS zircon U-Pb dating indicate that the volcanic rocks from the Manitu Formation in the Hongol area formed during the early Early Cretaceous with ages of 138.9-140.5 Ma.The volcanic rocks are high in alkali(Na_2O + K_2O = 6.22-8.26 wt%),potassium(K_2O = 2.49-4.58 wt%) and aluminium(Al_2O_3 = 14.27-15.88 wt%),whereas they are low in iron(total Fe_2O_3 = 3.76-6.53 wt%) and titanium(TiO_2 = 1.02-1.61 wt%).These volcanic rocks are obviously enriched in large ion lithophile elements,such as Rb,Ba,Th and U,and light rare earth elements,and are depleted in high field strength elements,such as Nb,Ta and Ti with pronounced negative anomalies.Their Sr-Nd-Pb isotopic compositions show positive ε_(Nd)(t)(+0.16‰ to+1.64‰) and low T_(DM)(t)(694-767 Ma).The geochemical characteristics of these volcanic rocks suggest that they belong to a shoshonitic series and were likely generated from the partial melting of an enriched lithospheric mantle that was metasomatised by fluids released from a subducted slab during the closure of the MongolOkhotsk Ocean.Elemental and isotopic features reveal that fractional crystallization with the removal of ferromagnesian minerals,plagioclase,ilmenite,magnetite and apatite played an important role during the evolution of the magma.These shoshonitic rocks were produced by the partial melting of the enriched lithospheric mantle in an extensional regime,which resulted from the gravitational collapse following the final closure of the Mongol-Okhotsk Ocean in the Middle-Late Jurassic.     

Early Permian–Late Triassic Magmatism in the Tuotuohe Region of the Qinghai–Tibet Plateau: Constraints on the Tectonic evolution of the Western Segment of the Jinshajiang Suture

In this paper we present new zircon U–Pb ages, whole-rock major and trace element analyses, and zircon Hf isotopic data for magmatic rocks in the Tuotuohe region of the western segment of the Jinshajiang suture. Our aim is to constrain the Early Permian–Late Triassic tectonic evolution of the region. Zircons from the magmatic rocks of the Tuotuohe region are euhedral–subhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios(0.4–4.6), indicating a magmatic origin. The zircon U–Pb ages obtained using LA–ICP–MS are 281 ± 1 Ma, 258 ± 1 Ma, 244 ± 1 Ma, and 216 ± 1 Ma, which indicate magmatism in the Early Permian–Late Triassic. A diorite from Bashihubei(BSHN) has SiO2 = 57.18–59.97 wt%, Al2O3 = 15.70–16.53 wt%, and total alkalis(Na2O + K2O) = 4.46–6.34 wt%, typical of calc-alkaline and metaluminous series. A gabbro from Bashibadaoban(BSBDB) belongs to the alkaline series, and is poor in SiO2(45.46–54.03 wt%) but rich in Al2O3(16.19–17.39 wt%) and total alkalis(Na2O + K2O = 5.48–6.26 wt%). The BSHN diorite and the BSBDB gabbro both display an enrichment of LREEs and LILEs and depletion of HFSEs, and they have no obvious Eu anomaly; they have relatively low MgO contents(2.54–4.93 wt%), Mg# values of 43 to 52, and low Cr and Ni contents(8.07–33.6 ppm and 4.41–14.2 ppm, respectively), indicating they differentiated from primitive mantle magmas. They have low Nb/U, Ta/U, and Ce/Pb ratios(1.3–9.6, 0.2–0.8, and 0.1–18.1, respectively), and their initial Hf isotopic ratios range from +9.6 to +16.9(BSHN diorite) and +6.5 to +12.6(BSBDB gabbro), suggesting their primary magmas were derived mainly from the partial melting of a mantle wedge that had been metasomatized by subduction fluids. Taking all the new data together, we conclude that the western and eastern segment of the Jinshajiang suture regions underwent identical processes of evolution in the Early Permian–Late Triassic: oceanic crust subduction before the Early Permian, continental collision during the Early–Middle Triassic, and post-collisional extension from the Late Triassic.     

Geochemistry and Zircon U–Pb–Hf Isotopic Systematics of the Sanchahe Quartz Monzonite Intrusion in the North Qinling Tectonic Zone, Central China: Implications for its Petrogenesis and Tectonic Setting

The Sanchahe quartz monzonite intrusion is situated in the middle segment of the North Qinling tectonic belt, Central China mainland, and consists chiefly of sanukitoid–like and granodioritic-monzogranitic rocks. The sanukitoid–like rocks are characterized by quartz monzonites, which display higher Mg#(55.0–59.0), and enrichments in Na2 O+K2 O(7.28–8.94 %), Ni(21-2312 ppm), Cr(56-4167 ppm), Sr(553-923 ppm), Ba(912-1355 ppm) and LREE((La/Yb)N =9.47–15.3), from negative to slightly positive Eu anomalies(δEu=+0.61 to +1.10), but also depletion in Nb, Ta and Ti. The granodioritic-monzogranitic rocks diaplay various Mg#of 6.00-53.0, high Na2 O+K2 O(7.20– 8.30%), Sr(455–1081 ppm) and(La/Yb)N(27.6–47.8), with positive Eu anomalies(δEu=1.03–1.57) and depleted Nb, Ta and Ti. Laser ablation inductively coupled plasma mass spectrometry(LA-ICPMS) zircon U-Pb isotopic dating reveals that the sanukitoid-like rocks were emplaced at two episodes of magmatism at 457±3 Ma and 431±2 Ma, respectively. The monzogranites were emplaced at 445±7Ma. Sanukitoid–like rocks have their εHf(t) values ranging from +0.3 to +15.1 with Hf–depleted mantle model ages of 445 to 1056 Ma, and the monzogranite shows its εHf(t) values ranging from 21.6 to +10.8 with Hf–depleted mantle model ages of 635 to 3183 Ma. Petrological, geochemical and zircon Lu –Hf isotopic features indicate that the magmatic precursor of sanukitoid–like rocks was derived from partial melting of the depleted mantle wedge materials that were metasomatized by fluids and melts related to subduction of oceanic slab, subsequently the sanukitoid magma ascended to crust level. This emplaced mantle magma caused partial melting of crustally metamorphosed sedimentary rocks, and mixing with the crustal magma, and suffered fractional crystallization, which lead to formations of quartz monzonites. However, the magmatic precursor of the granodioritic-monzogranitic rocks were derived from partial melting of subducted oceanic slab basalts. Integrated previous investigation for the adackitic rocks in the south of the intrusion, the Sanchahe intrusion signed that the North Qinling tectonic zone was developed in an early Paleozoic transitionally tectonic background from an island arc to back–arc.     

Sedimentary Conditions of Evaporites in the Late Jurassic Xiali Formation, Qiangtang Basin: Evidence from Geochemistry Records

The Qiangtang Basin (QB), located in the central Tibetan Plateau, is a Jurassic marine basin and one of the most important prospective salt resource belts in China. In recent decades, many outcrops of gypsiferous?bed have been found in the Jurassic marine strata in the basin. Salt springs with abnormally high sodium (Na+) contents had been identified in the Late Jurassic Xiali Formation (Fm.) in the basin in the last years. However, to date, no potash or halite deposits have been identified in the QB. Gypsum outcrops and salt springs are very important?signs in the investigation of halite and potash deposits. Therefore, the Xiali Fm. is?a potentially valuable layer to evaluate for the possible presence of halite and potash deposits in the basin. However,?few studies?have explored the formation?conditions of evaporites in the unit. Here, we present detailed geochemical records from the Yanshiping section related to the study of the formation?conditions of evaporites in the Xiali Fm. of the QB. Climate proxies based on the obviously increased anion concentrations of SO42? and Cl? and the significant correlation?coefficients of Ca2+-SO42? (R = 0.985) and Na+-Cl? (R = 0.8974) reveal that the upper member of the Xiali Fm. (the upper Xiali Fm.) formed under an arid climate and evolved into the sulfate phase or early chloride phase. Provenance proxies based on the obviously increased K+ and Na+ ion concentrations and the significant correlation?coefficient of Na+-Cl? (R = 0.8974) suggest that the upper Xiali Fm. featured optimal provenance conditions for the possible formation of halite deposits. The regression and the semi-closed tidal?flat environment in the upper Xiali Fm. were favorable for the formation of potash and halite deposits. The low Mg2+ /Ca2+ values (mean value = 1.82) and significant Na+-Cl? correlation?coefficient (R = 0.8974) also suggest that the upper Xiali Fm. is the layer most likely to contain potential halite deposits. In addition, the macroscopic correlations of tectonism, provenance, paleoclimate, saliferous strata and sedimentary?environment between the QB and the adjoining Amu Darya Basin in Central Asia reveal that the two basins shared similar geologic settings that were favorable for the formation of evaporites during the Late Jurassic. Therefore, the upper Xiali Fm. is a valuable layer to explore for halite deposit and may be potentially valuable in the future exploration for potash deposits in the QB.     

Facies Analysis and Sequence Stratigraphy of the Qal’eh Dokhtar Formation (Middle–Upper Jurassic) in the West of Boshrouyeh, East Central Iran

The study area is located in the east Tabas Block in Central Iran. Facies analysis of the Qal’eh Dokhtar Formation (middle Callovian to late Oxfordian) was carried out on two stratigraphic sections and applied to depositional environment and sequence stratigraphy interpretation. This formation conformably overlies and underlies the marly-silty Baghamshah and the calcareous Esfandiar formations, respectively. Lateral and vertical facies changes documents low- to high energy environments, including tidal-flat, beach to intertidal, lagoon, barrier, and open-marine. According to these facies associations and absence of resedimentation deposits a depositional model of a mixed carbonate–siliciclastic ramp was proposed for the Qal’eh Dokhtar Formation. Seven third-order depositional sequences were identified in each two measured stratigraphic sections. Transgressive systems tracts (TSTs) show deepening upward trends, i.e. shallow water beach to intertidal and lagoonal facies, while highstand systems tracts (HST) show shallowing upward trends in which deep water facies are overlain by shallow water facies. All sequence boundaries (except at the base of the stratigraphic column) are of the no erosional (SB2) types. We conclude eustatic rather than tectonic factors played a dominant role in controlling carbonate depositional environments in the study area.     

Diagenesis of the Triassic Yanchang Formation Tight Sandstone Reservoir in the Xifeng–Ansai Area of Ordos Basin and its Porosity Evolution

This work aims to reveal the evolution of the porosity in the Triassic Yanchang Formation tight sandstone reservoir of the Xifeng–Ansai area of Ordos Basin. Based on destructive diagenesis(compaction and cementation) and constructive diagenesis(dissolution) of sandstone reservoirs, this study analyzed the diagenesis characteristics of the tight sandstone reservoirs in this area, and discussed the relationship between sandstone diagenesis and porosity evolution in combination with present porosity profile characteristics of sandstone reservoir. The effect simulation principle was employed for the mathematical derivation and simulation of the evolution of porosity in the Yanchang Formation tight sandstone reservoirs. The result shows that compaction always occurs in tight sandstone reservoirs in the Yanchang Formation, and cementation occurs when the burial depth increases to a certain value and remains ever since. Dissolution occurs only at a certain stage of the evolution with window features. In the corresponding present porosity profile, diagenesis is characterized by segmentation. From the shallow to the deep, compaction, compaction, cementation and dissolution, compaction and cementation occur successively. Therefore, the evolution of sandstone porosity can be divided into normal compaction section, acidification and incremental porosity section, and normal compaction section after dissolution. The results show that the evolution of sandstone porosity can be decomposed into porosity reduction model and porosity increase model. The superposition of the two models at the same depth in the three stages or in the same geological time can constitute the evolution simulation of the total porosity in sandstone reservoirs. By simulating the evolution of sandstone reservoir porosity of the eighth member in Xifeng area and the sixth member in Ansai area, it shows that they are similar in the evolution process and trend. The difference is caused by the regional uplift or subsidence and burial depth.     

Geochronology, Geochemistry and Sr-Nd-Hf Isotopes of Early–Middle Triassic Adakitic Plutons in Central-eastern Jilin Province, NE China: Constraints on the Non-synchronous Closure of Paleo-Asian Ocean

The Changchun–Yanji suture zone (CYSZ) in NE China is considered as the suture between the North China Craton (NCC) and Central Asian Orogenic Belt (CAOB). The geochronology, geochemistry and Sr-Nd-Hf isotopes of Early–Middle Triassic adakitic plutions from the CYSZ, are presented in this paper to discuss their petrogenesis and tectonic setting, as well as to constrain the timing and style of the Paleo-Asian Ocean''s final closure. In Early Triassic, the Dayushan pluton (ca. 250 Ma) from western CYSZ has negative εNd(t) values, bidirectional provenances (NCC and CAOB) of εHf(t), which are formed in a collision tectonic setting. In contrast, in eastern CYSZ, the early Triassic samples in Liangshan (ca. 242 Ma) were high Mg# values, positive εNd(t), single provenances (CAOB) of εHf(t) resulting from a subduction setting. In the Middle Triassic, the A-type granites in western CYSZ are found in previous studies representing a post-collisional extensional environment, whereas syn-collisional Lianyanfeng granites (ca. 237 Ma) in eastern CYSZ with low ISr and large scale εNd(t) and εHf(t) values from bidirectional provenances (NCC and CAOB), represent a collisional setting. The Paleo-Asian Ocean''s occurred in a scissor-like fashion along the CYSZ during the Triassic period.     

Neoproterozoic–Early Paleozoic Tectonic Evolution of the South China Craton: New Insights from the Polyphase Deformation in the Southwestern Jiangnan Orogen

A >1500–km–long northeast–southwest trending Neoproterozoic metamorphic belt in the South China Craton (SCC) consists of subduction mélange and extensional basin deposits. This belt is present under an unconformity of Devonian–Carboniferous sediments. Tectonic evolution of the Neoproterozoic rocks is crucial to determining the geology of the SCC and further influences the reconstruction of the Rodinia supercontinent. A subduction mélange unit enclosed ca.1000–850–Ma mafic blocks, which defined a Neoproterozoic ocean that existed within the SCC, is exposed at the bottom of the Jiangnan Orogen (JO) and experienced at least two phases deformation. Combined with new (detrital) zircon U–Pb ages from metasandstones, as well as igneous rocks within the metamorphic belt, we restrict the strongly deformed subduction mélange as younger than the minimum detrital age ca. 835 Ma and older than the ca. 815 Ma intruded granite. Unconformably overlying the subduction mélange and the intruded granite, an intra–continental rift basin developed <800 Ma that involved abundant mantle inputs, such as mafic dikes. This stratum only experienced one main phase deformation. According to our white mica 40Ar/30Ar data and previously documented thermochronology, both the Neoproterozoic mélange and younger strata were exhumed by a 490–400–Ma crustal–scale positive flower structure. This orogenic event probably induced the thick–skinned structures and was accompanied by crustal thickening, metamorphism and magmatism and led to the closure of the pre–existing rift basin. Integrating previously published data and our new results, we agree that the SCC was located on the periphery of the Rodinia supercontinent from the Neoproterozic until the Ordovician. Furthermore, we prefer that the convergence and dispersal of the SCC were primarily controlled by oceanic subduction forces that occurred within or periphery of the SCC.     

新疆库鲁克塔格早志留世地层沉积学、物源分析新认识

库鲁克塔格地区早志留世地层主要由灰绿色砂岩和粉砂岩组成,为浊流成因,沉积环境为海底扇。运用LA-ICP-MS U-Pb方法,对早志留世2件砂岩碎屑锆石进行U-Pb年龄测定,共获得了89组U-Pb有效年龄,获得了地层的物源、研究区区域对比和早古生代的构造演化资料。碎屑锆石的谐和年龄表明,689~836Ma为早志留世地层的主要物源区,866~986Ma、1055~1463Ma和1708~2490Ma为次要物源区,部分为二次搬运。志留纪碎屑锆石的年龄概率图指出,早志留世可能为岩浆活动的安静期,早志留世之后,库鲁克塔格地区中—晚奥陶世岩石大规模隆升。碎屑锆石年龄和CL图像揭示,新元古代时期发育大量岩浆活动,可能与南天山洋向塔里木板块俯冲相关。区域变质作用同样在碎屑锆石中有所反映。     

库鲁克塔格下古生界土什布拉克组形成时代及源区：碎屑锆石U-Pb年代学证据

库鲁克塔格地区是土什布拉克组的命名地和典型剖面分布区,主要由灰绿色砂岩及粉砂岩组成。运用LA-ICP-MS U-Pb方法,对土什布拉克组3件砂岩碎屑锆石进行U-Pb年龄测定,共获得了183组U-Pb有效年龄,既限定了地层的最早形成时代,同时又获取研究区早古生代的演化资料。获得14个较年轻锆石年龄表明,土什布拉克组形成于中—晚志留世。碎屑锆石的谐和年龄表明,物源主要集中在422～537 Ma、559～999 Ma、1018～1574Ma和1604～2498Ma。碎屑锆石年龄394～537Ma和CL图像揭示,在早古生代时期发育大量岩浆岩,但目前地表仅有少量的岩浆岩记录。研究区新元古代的岩浆锆石年龄值,可能与罗迪尼亚超大陆的聚合-裂解有关。碎屑锆石也表明研究区发育区域变质作用,部分与哥伦比亚超大陆有关。     

Neoproterozoic Volcanic Rocks in the Southern Quruqtagh of Northwest China:Geochemistry,Zircon Geochronology and Tectonic Implications

The Early Neoproterozoic Beiyixi Formation volcanic rocks of the southern Quruqtagh comprise mainly of a suite of tholeiitic basalts,alkaline andesites,and calc-alkaline rhyolites.The rhyolites are characterized by variably fractionated enrichment in light rare earth elements（LREE） and flat in heavy rare earth elements（HREE）,and strongly negative Eu anomalies.Compared to the rhyolites,the andesites also exhibit enrichment in LREE and flat HREE（chondrite-normalized values of La/Yb,and La/Sm are 13.30-41.09,3.18-6.89 respectively）.Their rare earth element patterns display minor negative Eu anomalies.Both of them exhibit coherent patterns with strongly to moderately negative anomalies of Nb,Zr,Ti,and Hf on spider diagrams.Two rhyolite and one andesite magmatic zircons with defined oscillatory zoning yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 743±7 Ma,741±2 Ma,and 727±4 Ma.These ages are interpreted to represent the timing of volcanic eruptions. According to geochemistry and rock type,these volcanic rocks formed within a continental island-arc environment following subduction of the oceanic crust during the Early Neoproterozoic period.     

库鲁克塔格地区新元古代贝义西组的构造环境:来自碎屑岩地球化学的证据

库鲁克塔格位于南天山和塔里木盆地接合部,保留相对较完整的地层记录.其中新元古代贝义西组为一套火山-沉积组合序列,长期以来被认为是Rodinia裂解产物.本文通过对该套组合中的沉积岩(主要是细碎屑岩)地球化学分析,并对该套组合的物源区特征和形成构造环境进行研究,结果并不支持这一结论.研究结果表明,贝义西组砂岩主要为成熟度...     

松辽盆地开鲁坳陷钱家店地区姚家组砂岩地球化学特征及物源和构造背景分析

为了开展钱家店铀矿床砂岩型铀矿的进一步找矿工作,对采集到的上白垩统姚家组19件砂岩样品进行了主、微量和稀土元素分析,并结合前人成果,对姚家组的沉积物源及源岩构造背景进行了探讨。结果表明,姚家组砂岩主要为长石砂岩,矿物成分主要为石英、钾长石和斜长石等;其轻重稀土比为6.96~14.66,均值为10.17;LaN/YbN为7.58~20.95,均值为11.74,说明轻稀土元素相对重稀土元素明显富集,分馏明显。稀土元素配分模式曲线高度一致,也表明姚家组砂岩具有同源性;其ICV值为0.86~2.78,平均值1.34,大部分大于1,表现为未成熟的性质,为初次旋回的沉积物;修正后的CIA均值62.5,暗示源岩经历中等化学风化作用;砂岩碎屑为近源的第一次旋回沉积物,受沉积分选和再循环作用影响不大;姚家组源岩以火山弧物质和大陆上地壳长英质物质为主,源岩主要形成于大陆边缘和大陆岛弧环境;开鲁坳陷形成于早白垩世随着古太平洋板块向欧亚板块俯冲速度的减小而在东北地区出现的北西-南东向拉张构造环境中,并接受盆地西部大兴安岭南段海西期和燕山期岩浆岩、火山岩沉积。     

Provenance, Tectonic Setting and Geochemistry of Ahwaz Sandstone Member (Asmari Formation, Oligo-Miocene), Marun Oilfield, Zagros Basin, SW Iran

The Asmari Formation deposited in the Zagros foreland basin during the OligoceneMiocene. Lithologically, the Asmari Formation consists of limestone, dolomitic limestone, dolomite, argillaceous limestone, some anhydrite(Kalhur Member) and sandstones(Ahwaz Member). This study is based on the analysis of core samples from four subsurface sections(wells Mn-68, Mn-281, Mn-292 and Mn-312) in the Marun Oilfield in the Dezful embayment subzone in order to infer their provenance and tectonic setting of the Ahwaz Sandstone Member. Petrographical data reveal that the Ahwaz Sandstone comprises 97.5% quartz, 1.6% feldspar, and 0.9% rock fragments and all samples are classified as quartz arenites. The provenance and tectonic setting of the Ahwaz Sandstone have been assessed using integrated petrographic and geochemical studies. Petrographic analysis reveals that mono- and poly-crystalline quartz grains from metamorphic and igneous rocks of a craton interior setting were the dominant sources. Chemically, major and trace element concentrations in the rocks of the Ahwaz Sandstone indicate deposition in a passive continental margin setting. As indicated by the CIW′ index(chemical index of weathering) of the Ahwaz Sandstone(average value of 82) their source area underwent "intense" recycling but "moderate to high" degree of chemical weathering. The petrography and geochemistry results are consistent with a tropical, humid climate and low-relief highlands.     

鸡西盆地早白垩世城子河组和穆棱组物源分析

充分利用研究区的野外露头,特别是露头所显示的砾石排列方向和各种层理构造、地震资料、岩芯重矿物资料,系统分析了能够指示物源方向的4种参数-古水流方向,地震反射特征、重矿物稳定系数及组合分异特征、鸡西盆地早白垩世沉积特征,结果表明,这4种参数的匹配情况良好,总体显示城子河组时期盆地大致存在西部和东南部两个方向的物源,其中西部物源为主要物源区,分别从西北、西部以及西南3个方向供给盆地沉积物,东南部物源区为次要物源区,影响范围较小;穆棱组时期基本继承了城子河组时期的物源体系,只是源区相对后退,反映出从城子河组到穆棱组为水进和湖盆范围变大的过程,东南部物源的影响范围较城子河组时期变大。利用重矿物组合特征进行源区对比,认为盆地西部物源区为小兴安岭-张广才岭造山带,盆地东南部物源来自延吉褶皱带。     

东昆仑花石峡北部上二叠统格曲组源区特征:来自碎屑组成和岩石地球化学的证据

东昆仑南缘上二叠统（乐平统）格曲组为一套由砾岩、砂岩和钙质泥岩构成的扇三角洲-浅海碳酸盐台地相沉积组合,记录了东昆仑造山带海西-印支过渡期构造演化过程,是解析该构造演化过程的理想对象。通过分析花石峡北坦地克借地区格曲组碎屑岩的碎屑组成与主量、微量和稀土元素特征,探讨了其物源区属性。结果显示,砂岩类型为长石砂岩和岩屑长石砂岩,石英、长石和岩屑平均含量分别为50.9%、36.8%、12.4%,长石以钾长石为主,岩屑和砾石成分复杂。砂岩的SiO₂、Al₂O₃、TiO₂、TFe₂O₃、MgO、K₂O和Na₂O平均百分含量分别为62.06%、13.26%、0.44%、4.53%、3.02%、2.42%和3.18%;微量元素比值Th/Sc和Th/U较高,平均为1.06和7.71;稀土元素总量∑REE平均120.43×10-6,LREE/HREE和（La/Yb）_N均值分别为9.34和12,轻稀土相对富集,δEu平均为0.96,Eu异常不明显,REE特征与大陆岛弧背景区杂砂岩相似,与东昆仑地体加里东期俯冲-碰撞型火山弧花岗岩具有亲缘性。碎屑组分和主量、微量元素特征与判别图解揭示,格曲组砂岩物源区为海西旋回早期从东昆仑地体裂离的东昆南微地块,源岩以花岗岩为主,变质岩、沉积岩和酸性-基性火山岩较少,其中花岗岩形成构造背景为加里东期的大陆岛弧。结合区域地质和前人研究成果,认为格曲组为前陆盆地系统的隆后盆地沉积。     

Geochemistry of Carboniferous Sandstones (Sardar Formation), East‐Central Iran: Implication for Provenance and Tectonic Setting

Geochemical analysis of sandstones from the Sardar Formation (from two stratigraphic successions) in east-central Iran were used for identification of geochemical characterization of sandstones, provenance and tectonic setting. Sandstones in the two lithostratigraphic successions have similar chemical compositions suggesting a common provenance. Bulk-rock geochemistry analysis of Carboniferous sandstones from Sardar Formation indicates that they are mainly quartz dominated and are classified as quartzarenites, sublitharenites and subarkoses, derived from acid igneous to intermediate igneous rocks. Discrimination function analysis indicates that the sandstones of Sardar Formation were derived from quartzose sedimentary provenance in a recycled orogenic setting. Also, major and trace elements in sandstones of Sardar Formation (e.g., K2O/Na2O vs. SiO2) indicate deposition in a stable passive continental margin (PM). Chemical index of alteration (CIA) for these rocks (> 65%) suggests a moderate to relatively high degree of weathering in the source area.     

鄂尔多斯盆地东胜地区直罗组砂岩的地球化学特征与物源分析

沉积岩物源分析对揭示盆地砂体展布、物质组成、储集层性质及砂岩型铀矿床铀源等科学问题具有重要的意义。对取自鄂尔多斯盆地东北部8个钻井中的中侏罗统直罗组砂岩进行了详细的岩石学和地球化学研究,试图鉴别岩石的源区和形成的构造环境。研究表明,砂岩以中粗粒杂砂岩为主,其w(SiO₂)值及w(Al₂O₃)/w(SiO₂)值中等到较高,w(K₂O)值相对较高,Fe₂O₃、MgO、TiO₂含量较低,暗示碎屑物质的富长英质、贫镁铁质特征。Nb、Ta、Ti、P等不活动元素的强烈亏损和K、Rb、Sr、Ba等LILE的富集,共同指示源区具有明显的俯冲带的特征;而w(TFe₂O₃+MgO)-w(TiO₂)、w(TFe₂O₃+MgO)-w(Al₂O₃)/w(SiO₂)、w(Th)-w(Sc)-w(Zr)/10、w(Th)-w(Co)-w(Zr)/10等判别特征则表明砂岩源区岩石可能形成于大陆弧-活动大陆边缘环境。而且,在球粒陨石标准化分配模式中,LREE强烈富集,HREE无明显分异、有着较平坦的曲线,Eu无异常或表现为弱的正、负异常;在PAAS标准化曲线中,轻重稀土均无明显分异,仅Eu表现为明显正异常。本区直罗组砂岩与华北北缘显生宙闪长岩-花岗闪长岩有着很强的亲缘性。