Geochemistry of Permian Mafic Igneous Rocks from the Napo-Qinzhou Tectonic Belt in Southwest Guangxi, Southwest China: Implications for Arc-Back Arc Basin Magmatic Evolution

The Napo-Qinzhou Tectonic Belt （NQTB） lies at the junction of the Yangtze, Cathaysia and Indochina （North Vietnam） Blocks, which is composed of five major lithotectonic subunits： the Qinzhou-Fangcheng Suture Zone （QFSZ）, the Shiwandashan Basin （SB）, the Pingxiang-Nanning Suture Zone （PNSZ）, the Damingshan Block （DB） and the Babu-Lingma Suture Zone （BLSZ）. On the basis of geochemical compositions, the Permian mafic igneous rocks can be divided into three distinct groups： （1） mafic igneous rocks （Group 1） from the Longjing region in the PNSZ and Hurun region in the BLSZ, which are characterized by intermediate Ti, P and Zr with low Ni and Cr contents; （2） mafic igneous rocks （Group 2） from the Naxiao and Chongzuo region in the DB, characterized by low-intermediate Ti, P and Zr with high Ni and Cr concentrations; and （3） mafic igneous rocks （Group 3） from the Siming region in the Jingxi carbonate platform of the northwestern margin of the NQTB, with intermediate-high Ti, P and Zr and low Ni and Cr contents. The Group 1 rocks yield a weighted mean 206 Pb/ 238 U age of 250.5±2.8 Ma and are geochemically similar to basalts occurring in back-arc basin settings. The Group 2 rocks exhibit geochemical features to those basalts in island arcs, whereas the Group 3 rocks show geochemical similarity to that of ocean island basalts. All three groups are characterized by relatively low ε Nd （t） values （-2.61 to ＋1.10） and high initial 87 Sr/ 86 Sr isotopic ratios （0.705309-0.707434）, indicating that they were derived from a subduction-modified lithospheric mantle and experienced assimilation, fractional crystallization, and crustal contamination or mixing during magmatic evolution. Accordingly, we propose the existence of an arc-back arc basin system that developed along the NQTB at the border of SW Guangxi Province （SW China） and northern Vietnam, and it was formed by continued northwestward subduction of the Cathaysian （or Yunkai） Block under the Yangtze Block, and northeastward subduction of the Indochina Block beneath the Yangtze Block during Permian time.

Geochemistry and Geochronology of OIB-type Early Jurassic Magmatism in the Zhangguangcai Range, NE China, as a Result of Continental Back-arc Extension

The Zhangguangcai Range in the Xing’an(Hinggan) Mongolian Orogenic Belt, NE China, contains Early Jurassic(c. 188 Ma) Dabaizigou(DBZG) porphyritic dolerite. Compared with other island-arc mafic rocks, the DBZG dolerite is characterized by high trace-element contents, relatively weak Nb and Ta enrichments, and no Zr, Hf or Ti depletions, similar to OIB-type rocks. Analysed rocks have(87Sr/86Sr)i ratios of 0.7033–0.7044, relatively uniform positive εNd(t) values of 2.3–3.2 and positive εHf(t) values of 8.5–17.1. Trace-element and isotopic modelling indicates that the DBZG mafic rocks were generated by partial melting of asthenospheric mantle under garnet-to spinel-facies conditions. The occurrence of OIB-like mafic intrusion suggests significant upwelling of the asthenosphere in response to lithospheric attenuation caused by continental rifting. These processes occurred in an incipient continental back-arc environment in the upper plate of a palaeo-Pacific slab subducting W–NW beneath East Asia.

Intra-continental back-arc basin inversion and Late Carboniferous magmatism in Eastern Tianshan,NW China:Constraints from the Shaquanzi magmatic suite

The Yamansu belt,an important tectonic component of Eastern Tianshan Mountains,of the Central Asian Orogenic Belt,NW China hosts many Fe-(Cu)deposit.In this study,we present new zircon U-Pb geochronology and geochemical data of the volcanic rocks of Shaquanzi Formation and diorite intrusions in the Yamansu belt.The Shaquanzi Formation comprises mainly basalt,andesite/andesitic tuff,rhyolite and sub-volcanic diabase with local diorite intrusions.The volcanic rocks and diorites contain ca.315-305 Ma and ca.298 Ma zircons respectively.These rocks show calc-alkaline affinity with enrichment in large-ion lithophile elements(LILEs),light rare-earth elements(LREEs),and depletion in high field strength elements(HFSEs)in primitive mantle normalized multi-element diagrams,which resemble typical back-arc basin rocks.They show depleted mantle signature with ε_(Nd)(t)ranging from+3.1 to +5.6 for basalt;+2.1 to+4.7 for andesite;-0.2 to+1.5 for rhyolite and the ε_(Hf)(t)ranges from-0.1 to +13.0 for andesites;+5.8 to +10.7 for andesitic tuffs.We suggest that the Shaquanzi Formation basalt might have originated from a depleted,metasomatized lithospheric mantle source mixed with minor(3-5%)subduction-derived materials,whereas the andesite and rhyolite could be fractional crystallization products of the basaltic magma.The Shaquanzi Formation volcanic rocks could have formed in an intracontinental back-arc basin setting,probably via the southward subduction of the Kangguer Ocean beneath the Middle Tianshan Massif.The Yamansu mineralization belt might have undergone a continental arc to back-arc basin transition during the Late Carboniferous and the intra-continental back-arc basin might have closed in the Early Permian,marked by the emplacement of dioritic magma in the Shaquanzi belt.

Carbonate Sequence Stratigraphy of a Back-Arc Basin: A Case Study of the Qom Formation in the Kashan Area, Central Iran

The Qom Formation comprises Oligo-Miocene deposits from a marine succession distributed in the Central Basin of Iran. It is composed of five members designated as A-F. Little previous work exists on the sequence stratigraphy. Based on an integrated study of sequence stratigraphy with outcrop data, wells and regional seismic profiles, the Qom Formation is interpreted as a carbonate succession deposited in a mid.Tertiary back-arc basin. There are two second-order sequences （designated as SS1 and SS2） and five third-order sequences （designated as S1-S5）. Five distinct systems tracts including transgressive, highstand, forced regressive, slope margin and Iowstand have been recognized. The relationship between the sequences and lithologic sub-units has been collated and defined （S1 to S5 individually corresponding to A-C1, C2--C4, D-E, the lower and upper portions of F）; a relative sea level change curve and the sequence stratigraphic framework have been established and described in detail. The coincidence of relative sea level change between that of the determined back-arc basin and the world indicates that the sedimentary cycles of the Qom Formation are mainly controlled by eustatic cycles. The variable combination of the systems tracts and special tectonic-depositional setting causally underpin multiple sequence stratigraphic framework styles seen in the carbonates of the back-arc basin revealing： （1） a continental margin basin that developed some form of barrier, characterized by the development of multiple cycles of carbonate-evaporites; （2） a flat carbonate ramp, which occurred on the southern shelf formed by the lack of clastic supply from nearby magmatic islands plus mixed siliciclastics and carbonates that occurred on the northern shelf due to a sufficient clastics supply from the land; and （3） a forced regressive stratigraphic stacking pattern that occured on the southern shelf and in basin lows due to the uplifting of the southern shelf. Thick and widespread aggradational framework limestone usually occurs in the initial sequences （S1 and S3） of the supersequence, which led to preferential oil reservoir deposition but a lack of source and cap rocks, whereas the retrogradational and progradational framework limestone usually occurs in the later sequences （S2 and S4-S5） of the supersequence, which results in two perfect sets of source, reservoir and cap rock assemblies, so that the limestone in sub-member C2-C4 and the F-Member can be predicted as important objects for oil exploration.

Bottom Simulating Reflector and Gas Seepage in Okinawa Trough:Evidence of Gas Hydrate in an Active Back-Arc Basin

To look for gas hydrate, 22 multi-channel and 3 single-channel seismic lines on the East China Sea （ECS） shelf slope and at the bottom of the Okinawa Trough were examined. It was found that there was indeed bottom simulating reflector （BSR） occurrence, but it is very rare. Besides several BSRs, a gas seepage was also found. As shown by the data, both the BSR and gas seepage are all related with local geological structures, such as mud diapir, anticline, and fault-controlled graben-like structure. However, similar structural ＂anomalies＂ are quite common in the tectonically very active Okinawa Trough region, but very few of them have developed BSR or gas seepage. The article points out that the main reason is probably the low concentration of organic carbon of the sediment in this area. It was speculated that the rare occurrence of gas hydrates in this region is governed by structure-controlled fluid flow. Numerous faults and fractures form a network of high-permeability channels in the sediment and highly fractured igneous basement to allow fluid circulation and ventilation. Fluid flow in this tectonic environment is driven primarily by thermal buoyancy and takes place on a wide range of spatial scales. The fluid flow may play two roles to facilitate hydrate formation： to help gather enough methane into a small area and to modulate the thermal regime.

Generation of Back-Arc Basins as Side Effect of Shortening Processes: Examples from the Central Mediterranean

The evolution of the Mediterranean area since the Oligocene-Lower Miocene has been driven by the convergence of the surrounding plates. This implies that the observed deformation pattern in that region must be the most convenient shortening pattern, i.e. the one controlled by the minimum action principle. To understand why the fulfilment of such condition has required a complex spatio-temporal distribution of major tectonic events, such as uplift, lateral displacement and bending of orogenic belts, consumption of large lithospheric domains and formation of back arc basins, it may be very useful to take into account a basic tectonic concept, which helps to identify the process that can minimize the resistance of tectonic forces. Such concept starts from the fact that the most convenient consumption process is the one that involves low buoyancy oceanic lithosphere (Tethyan domains). However, such process is highly favoured where the oceanic lithosphere is stressed by vertical forces, a situation that develops when orogenic wedges are forced to over thrust and load the oceanic domain to be consumed. This interpretation can provide plausible and coherent explanations for the complex pattern of the observed deformations. In this view, the generation of back arc basins is taken as a side effect of an extrusion process, as suggested by numerical and mechanical experiments.

Deep geodynamics of far field interconti- nental back-arc extension: Formation of Cenozoic volcanoes in northeastern China

There are three cases of variation of trench location possible to occur during subduction: trench fixed, trench ad- vancing, and trench retreating. Retreat of trench may lead to back-arc extension. The Pacific plate subducts at low angle beneath the Eurasia plate, tomographic results indicate that the subducted Pacific slab does not penetrate the 670 km discontinuity, instead, it is lying flat above the interface. The flattening occurred about 28 Ma ago. Geo- dynamic computation suggests: when the frontier of the subducted slab reaches the phase boundary of lower and upper mantle, it may be hindered and turn flat lying above the boundary, facilitates the retreat of trench and back-arc extension. Volcanism in northeastern China is likely a product of such retreat of subduction, far field back-arc extension, and melting due to reduce of pressure while mantle upwelling.

TRIASSIC SEQUENCE STRATIGRAPHY AND CORRELATION FROM POLY-ARC AND BACK-ARC SYSTEM IN EASTERN TIBET

It is dominantly characterized that arc and back\|arc basin occur mutually in arc\|basin systems, Jomda arc and Sinda back\|arc basin located in Qamdo area are typical(Fig.1). Jomda arc covered by Triassic with thickness about 10000m.Marine sediments predominate, and are Characterized by the largely thick turbidity rocks and arc volcanic rocks of calc\|alkali suite which frequent volcanic events raised. Sinda back\|arc basin with a land\|crust basement is filled by the Upper Triassic sedimentary strata of more than 5000m. The active marginal sediments are composed of terrigenous,basinal and volcanic turbidity deposits of bathyal to deep\|sea facies,Characteristic extensive alkali basalts and submarine spout hot water deposits. Based on investigation of the cutcrop pro\|file, isotime grillwork for Triassic sequence stratigraphy has been established. for example Jomda arc basin, including 6 type 1 and 4 type 2 boundaries.10 three\|order sequences are divided, including 6 type 1 and 4 type 2 sequences. These sequences evolves during 37Ma,the estimated average time of a sequences is 3～7Ma,with being generally 1～2Ma,the longest being about 10Ma. type 1 and type 2 sequence boundaries are identified, in Upper Triassic Sinda back\|arc basin two type 1 and one type 2 sequences are divided. Relations have been first concluded among mainly controlled factors of sequence stratigraphies in arc and back\|arc basin systems. First, more sequences product and three\|units of its structures are complete in arc systems of complicated tectonic\|volcanic topographies, for example Jomda arc area of island\|sea framework, because lots of deposits are supplied and accumulations are allowed. Secondly, tectonic control is very clear, type 1 boundaries of SQ1 and SQ7 are clearly unconformity interfaces stressed by tectonism.Thirdly,volcanic rocks is greatly related with sequences, and there are various volcanic rocks in mang sequences,for example Jomda sequence stratigraphies,volcanic rocks of calc alkaline suite occurs in LST which thickness occupying in LST is middle; both tholeiite and calc\|alkaline,alkaline suite (Sinda back\|arc area) in TST, thickness smallest; calc\|alkaline suite in HST, Thickness biggest. It proves that intra\|genetic association between volcanic and relative sea\|level changes, which is gained by the concordance of thick curves of volcanic rock and sea\|level in different systematic traces. When thickness of volcanic rocks growing or progressing, relative sea\|level falls; otherwise, when reducing, it rises. There are larger differences in quantities, structures and types of sequences by comparing sequence stratigraphies of arc, back\|arc with craton area. Those varieties are responses for interactions among tectonic\|volcano, sediment and eustacy. It is pointed out that tectonic and arc volcanic processes are crucial.

Origin of Cu in the PACMANUS hydrothermal field from the eastern Manus back-arc basin: evidence from mass balance modeling

Hydrothermal precipitates associated with active vents in the eastern Manus Basin, an actively opening back-arc basin in the Bismarck Sea, Papua New Guinea, are among the most Cu-rich on the modern seafloor. The volcanic rocks associated with this mineralization may be insufficiently enriched in Cu to account for the Cu content of the sulfides by simple leaching. The PACMANUS hydrothermal field lies in the eastern portion of the eastern Manus Basin. Mass balance modeling of the PACMANUS hydrothermal system indicates that simple leaching of a stationary reaction zone (0.144 km^3) by hydrothermal fluids cannot yield the Cu found in associated sulfide deposits because unacceptably high leaching, transportation and precipitation efficiencies are required to derive the Cu in sulfides by leaching processes. With 100% leaching, transport and precipitating efficiency, 0.166 km^3 of volcanic rocks would need to be leached to account for the Cu budget of hydrothermal sulfide deposits. The key requirement for forming metal-rich magmatic fluids is a large amount of metals available to enter the exsolved vapor phase. Magmas generated in the eastern Manus Basin inherently have high fO2 because of metasomatism of the mantle source by oxidized materials from the subducted slab, leading to copper enrichment in the magma chamber. Moreover, the presence of Cu in gas-rich melt inclusi on bubbles in Pual Ridge andesite is evidence that degassing and partitioning of Cu into the magmatic volatile phase has occurred in the eastern Manus Basin. Numerical mass balance modeling indicates that approximately 0.236 Mt Cu was potentially transferred to the hydrothermal system per cubic kilometer magma. Magmatic degassing seems to play a more significant role than leaching.

Optimization of back bead geometry in the PMAG-TIG twin arc hybrid root welding process using grey based Taguchi method

This study investigated multi-response optimization of the pulse metal active gas-tungsten inert gas( PMAG-TIG) twin arc hybrid root welding process for an optimal parametric combination to yield favorable back bead geometry of welded joints using grey relational analysis and Taguchi method.Eighteen experimental runs based on an orthogonal array following the Taguchi method were performed to derive objective functions to be optimized within the experimental domain.The objective functions were selected in relation to parameters of PMAG-TIG twin arc root welding back bead geometry: back bead width to root reinforcement ratio and deposited metal height.The Taguchi approach was followed by grey relational analysis to solve the multi-response optimization problem.The significance of factors on overall quality characteristics of the weld joint was also evaluated quantitatively using analysis of variance.Optimal results were verified through additional experiments,and showed to feasibility of applying grey relation analysis in combination with Taguchi technique for continuous improvement of product quality in the manufacturing industry.

北山地区芨芨台子蛇绿岩地球化学特征及形成环境

甘肃北山地区芨芨台子蛇绿岩是芨芨台子–小黄山蛇绿岩带重要组成部分,位于公婆泉单元和明水–旱山微陆块之间的北山造山带中部,主要由超基性岩、辉长岩和玄武岩组成。为揭示芨芨台子蛇绿岩带的形成环境,开展辉长岩、玄武岩岩石学及地球化学研究。辉长岩、玄武岩MgO为6.04%~6.73%、6.21%~9.66%,Mg^(#)为32.33~37.03、27.58~46.27,SI固结指数27.66~31.55、24.96~42.20,Al_(2)O_(3)为15.82%~16.79%、13.38%~15.38%,Na_(2)O高于K_(2)O含量(Na_(2)O/K_(2)O=9.75~17.15、1.95~23.26),Na_(2)O+K_(2)O分别为4.48%~4.90%和3.37%~4.68%,P_(2)O_(5)分别为0.07%~0.09%和0.16%~0.27%,均具富集LREE和LILE,亏损HREE和HFSE,Eu无明显异常(δEu=0.98~1.09、0.88~1.06);(^(87)Sr/^(86)Sr)i为0.703700~0.704768,(^(143)Nd/^(144)Nd)i为0.512234~0.512361,ε_(Nd)(t)为+4.18~+6.66。这些特征指示芨芨台子蛇绿岩带属于SSZ型蛇绿岩带,玄武岩与辉长岩来源于亏损地幔部分熔融,并经历了一定程度的结晶分异及地壳混染作用。结合区域地质背景,芨芨台子蛇绿岩形成于弧后盆地,为红柳河–牛圈子–洗肠井洋盆北向俯冲引起弧后扩张所致。

后弧（reararc）岩浆作用的特征及其意义

后弧岩浆作用（rear arc magmatism）是一个新的术语，国内文献大多认为与弧后（back arc）相当，也译为弧后。实际上rear arc 不同于back arc，前者仍然属于弧的范围，而后者已不属于弧结构。目前，对后弧岩浆作用的研究还十分有限， 原因一是 rear arc 出露较少，二是 rear arc 的鉴别标志不清楚。本文尝试对后弧玄武岩（rear arc basalt， RAB）作一个简单的介绍， 并采用对大量数据进行分析比较的方法与典型的岛弧玄武岩（IAB）和弧后盆地玄武岩（BAB）作一个对比。研究表明，后弧玄武岩主要由中-高 K 钙碱性和钾玄岩系列组成， 与典型的 IAB 和 BAB 相比， RAB 富集 Na2O、K2O、P2O5 ，贫CaO。后弧岩浆作用的微量元素具有典型的弧岩浆岩的特点，但LILE 及HFSE 比典型的岛弧岩浆的含量更富集，LREE 明显高于岛弧岩浆岩。 与岛弧岩浆相似，后弧岩浆同样具有明显的Nb-Ta 负异常。研究表明，上述3 类玄武岩很难区分开。但是，BAB 和RAB之间还是有一些不同的，如Sc/Nb-Ba/Y、Cu/P2O5-Y/Zr、Sc/Nb-Sr/Y 以及F2O3 /Zr-Y/Zr 等判别图。本文作者指出，后弧岩浆作用的提出完善了弧结构：一个完整的弧，从海沟向弧的方向，随着板块的俯冲作用，岩浆源区深度增加，地壳混染程度增加，依次出现前弧、弧和后弧岩浆作用， 至弧的后部，洋壳拉张，出现弧后盆地。前弧以玻安岩为代表，弧主要是IAB，后弧为碱性玄武岩，弧后则为MORB（＋IAB 的印记）。显然，后弧岩浆作用的提出，对古造山带岛弧结构的恢复、古俯冲方向的确定是有积极意义的。

准噶尔盆地西北缘晚泥盆世的岩浆作用及构造意义:来自红山梁组玄武岩的岩石地球化学证据

红山梁组是准噶尔盆地西北缘包古图构造带新发现的一套最老地层单位,时代为晚泥盆世,以红色硅质岩、凝灰质硅质粉砂岩、玄武岩、安山玄武岩为主。前人有关区内火山岩的岩石地球化学特征及构造演化研究仅限于石炭纪—二叠纪,而红山梁组玄武岩则提供了前石炭纪的重要信息。本组玄武岩可细分为拉斑玄武岩和碱性玄武岩两类。拉斑玄武岩普遍具有较低的TiO_(2)(0.30%~1.16%)、Al_(2)O_(3)(12.80%~18.46%)、较高的TFe_(2)O_(3)(8.97%~13.57%)含量以及Mg^(#)值(42.23~64.37),显示右倾的稀土模式,亏损Nb、Ta、Ti,具有N-MORB和IAT特征,是弧后盆地环境下经俯冲流体交代的尖晶石二辉橄榄岩,在亏损地幔源区发生5%~10%的部分熔融而成;碱性玄武岩普遍具有高TiO_(2)(1.74%~1.88%)、Al_(2)O_(3)(15.92%~18.07%),低TFe_(2)O_(3)(6.39%~7.62%)和Mg^(#)值(41.84~47.13)特征,无明显的Nb、Ta负异常,与OIB极为相似,是石榴子石+尖晶石二辉橄榄岩发生5%~10%部分熔融的产物,可能源自海山/洋岛环境。结合前人研究成果,本文认为准噶尔盆地西北缘在泥盆纪同时发育弧后盆地和海山/洋岛环境两类岩浆活动。

EWM coldArc“冷弧焊”——一种低能量的熔化极气体保护焊技术及其应用

介绍了EWM coldArc"冷弧焊"技术,该焊接电弧是在熔化极气体保护电弧焊中短路过渡电弧基础上的一种创新。通过对焊接过程中电弧电压和电流进行精确的控制和调节,使电弧稳定,同时又能显著地降低电弧能量。焊接中工件的受热少,变形小,在薄板焊接,电弧钎焊,异种材料焊接和厚板打底焊等应用中提高了MIG/MAG的焊接质量,扩展了MIG/MAG的应用范围。

A NEURAL NETWORK FOR WELD PENETRATION CONTROL IN GAS TUNGSTEN ARC WELDING

Realizing of weld penetration control in gas tungsten arc welding requires establishment of a model describing the relationship between the front-side geometrical parameters of weld pool and the back-side weld width with sufficient accuracy. A neural network model is developed to attain this aim. Welding experiments are conducted to obtain the training data set （including 973 groups of geometrical parameters of the weld pool and back-side weld width） and the verifying data set （108 groups）. Two data sets are used for training and verifying the neural network, respectively. The testing results show that the model has sufficient accuracy and can meet the requirements of weld penetration control.

中甸三叠纪弧后前陆盆地中的碎屑锆石:亲扬子地块群的原特提斯岩浆记录

作为东特提斯造山系的主体,我国的青藏高原及其周缘地区保留了最为完整的特提斯演化相关地质记录,但原特提斯阶段的构造演化历史尚未取得共识。三江造山带位于巨型阿尔卑斯-喜马拉雅造山系的东段。晚古生代-早中生代古特提斯构造运动、中-晚中生代新特提斯构造运动和新生代以来的陆-陆碰撞构造运动的多次叠加和改造致使造山带内部分地块的原特提斯演化历史难以恢复,阻碍了古地理、古构造格局的合理重建。针对东羌塘地块和中咱地块新元古代至古生代时期的构造演化研究程度较低,相关数据报道较少,本文通过对横穿中咱地块剖面的综合研究,认为中甸东侧发育早三叠世小型弧后前陆盆地。该弧后前陆盆地充填物主要为下三叠统碎屑岩,长石岩屑砂岩的碎屑锆石中岩浆锆石的表面年龄峰值区间主要为1900~1800Ma、970~940Ma、510~410Ma、390~320Ma和301~240Ma。中咱地块古生界两个年龄峰值(390~320Ma和301~240Ma)与扬子地块古生界碎屑锆石年龄谱高度相似,表明中咱地块的前寒武纪基底与扬子地块相连。东羌塘、中咱、兰坪(印支)地块与扬子地块一起组成大扬子地块,其西南缘、东南缘发育早古生代岩浆岩带。在印度-欧亚大陆碰撞之前,这一岩浆岩带呈近东西向位于大扬子地块南缘,为其内部古生界的沉积物源区。

玉树北部二叠纪镁铁质岩的成因及其对大陆弧后盆地形成的指示

系统地调查与研究弧后盆地岩浆作用能为探究汇聚板块边缘的壳幔相互作用、板块俯冲动力学和弧后盆地形成-演化机制等提供重要信息。本文以最近在青海玉树北部地区发现的二叠纪镁铁质岩类为研究对象,开展了岩相学、锆石U-Pb年代学、岩石地球化学与同位素地质学等研究,以期为深入认识大陆弧后盆地形成机制及有关镁铁质岩浆的起源提供关键线索。锆石LA-ICP-MS U-Pb年代学测定结果表明,玉树北部辉长岩的结晶年龄为260±1 Ma。玄武岩样品具有相对低的TiO2和Nb/Y值以及相对高的Ce/Nb值,其相对于原始地幔要显著富集轻稀土和Th等元素,亏损Nb、Ta、Ti和P等元素,可与世界上典型弧后盆地玄武岩(例如Okinawa Trough BABBs)成分特征类比。而辉长岩样品具有相对高的TiO2和Nb/Y值以及相对低的Ce/Nb值,其相对于原始地幔要显著富集轻稀土和Th等元素,轻微亏损Nb、Ta和Ti,总体上具有与OIB类似的成分特征。玄武岩样品具有变化较大的ISr(0.706~0.709)和εNd(t)值(-1.8~+1.3),而辉长岩样品则具有相对均一的ISr(0.709)和εNd(t)值(-1.8~-1.5)。综合本次研究成果可以确定,玄武岩应该起源于一个受俯冲组分改造的岩石圈地幔,而辉长岩应该来自于一个与地幔柱相关的源区。结合区域最新研究资料可以进一步判断研究区镁铁质岩应该形成于大陆弧后盆地扩张的背景中,并且该弧后盆地的产生很可能与洋壳深俯冲导致的板块回撤、峨眉山地幔柱活动密切相关。

滇东地区裂谷盆地内火山-侵入岩序列与金属成矿

碱性岩浆对金属成矿和金属矿集区有独特控制作用,因火山—侵入岩序列与金属成矿和岩浆叠加侵入构造系统识别难度大,长期制约了深部勘探和找矿预测。本文以云南东川铁铜金矿集区(元古宙陆缘裂谷盆地)和个旧锡铜钨铯铷多金属矿集区(三叠纪弧后裂谷盆地)为主,采用大比例尺构造岩相学填图新方法,解析研究了碱性岩浆活动有关的火山—侵入岩侵入序列与岩石组合、裂谷盆地演化和岩浆叠加侵入构造系统,揭示了它们与滇东地区铁氧化物铜金型(IOCG)、铜钴-金红石-稀土和锡铜钨铯铷多金属矿叠加成矿内在关系。研究认为:①云南东川铁铜金矿集区内,新太古代末期碱性岩类以方解石钠长岩(2520±14 Ma)和碱性铁质苦橄岩(2529±77 Ma)为主。新太古界—古元古界小溜口岩组(>2.50Ga)顶部古岩溶风化壳,受中元古代火山喷发—岩浆侵入构造叠加再造形成了特殊单元(独立填图单元,2.50~1.80Ga),它们是铜钴-金红石-稀土矿床的新找矿层位。②在中元古界因民组一段内,铁钠质碱性基性岩、铁钾质粗面岩和铁质碱性辉绿辉长岩等岩石组合形成于因民期火山断陷成盆期。因民组二段和三段是稀矿山式铁铜矿床储矿层位,铁铜矿层下盘铁钾质粗面岩为独居石型稀土成矿层位。在格林威尔造山期碱性钛铁质辉长岩(1097~1047 Ma)-碱性钛铁质闪长岩-碱性二长斑岩等碱性钛铁质侵入岩体,形成了白锡腊深部IOCG矿床和金红石富集成矿。③在个旧三叠纪弧后裂谷盆地内,三叠纪碱性苦橄岩和碱玄岩中形成了Sn-Cu-Zn-Li-Rb-Cs初始富集;在晚白垩世浅色花岗岩叠加成矿作用下,形成了金云母矽卡岩型锡铜钨铯铷矿床。④裂谷盆地内早期碱性岩中初始富集金属与后期富含成矿金属的碱性侵入岩叠加成矿可能是金属超常富集机理。在东川地区岩浆叠加侵入构造内,岩浆热液角砾岩筒对铜钴-金红石-稀土元素叠加富集成矿控制显著;在个旧地区,浅色花岗岩侵入于碱性苦橄岩-碱玄岩中,对金云母矽卡岩型锡铜钨钴铯铷矿床的叠加富集成矿控制显著。

管式电弧加热器电极背侧冷却强化数值模拟

基于COMSOL共轭传热对10MW级管式电弧加热器电极的背侧冷却进行了固体传热、流体传热和湍流流动的耦合计算,得到了背侧矩形直肋结构不同肋化系数β、换热表面粗糙度Ra条件下电极的温度和冷却通道流动阻力系数,对计算数据进行了回归分析,得到了β、Ra对弧根处电极温度和冷却通道阻力系数的综合影响的近似表达式。研究结果发现:随着电极背侧肋化系数β从1到2.2不断增加,电极内壁温度单调降低,降幅为12~14%,冷却通道阻力系数则增加了26.3~46.9%,并且在粗糙度较高时,β的变化对阻力系数的影响程度更大。背侧换热表面Ra由3.2um增加到80.6um时,弧根处电极壁面温度随之降低,降幅为6.5%~11%,但随着Ra的提高,增加Ra对降低电极温度的作用逐渐减弱,阻力系数则单调增加了近2倍。利用回归分析得到的表达式可对不同β和Ra条件下的弧根处内壁温度和流动阻力系数进行工程估算。

胶-辽-吉造山带辽河群含钴层位里尔峪组变火成岩成因机制及其对复杂构造演化过程的制约

辽河群里尔峪组变基性岩与变长英质粒状岩石记录了胶-辽-吉古元古代造山带复杂演化过程的重要信息。该组不仅是辽东钴富集成矿的关键层位,也是深入探讨胶-辽-吉造山带古元古代起始构造背景及其演化过程的关键研究对象。本文通过野外地质调查、岩相学、全岩地球化学、锆石年代学以及Lu-Hf同位素的综合研究,对里尔峪组中变基性岩与变长英质粒状岩石的原岩属性、成因机制、年代格架及构造背景进行了深入研究,结合胶-辽-吉带古元古代的构造演化过程及其与Co元素的初始来源的内在成因关系进行了初步讨论。里尔峪组变基性岩岩石主要由斜长角闪岩与变角闪石岩组成,变长英质粒状岩石包括浅粒岩和变粒岩。野外观察发现大量变基性岩侵入到变长英质粒状岩石中。锆石U-Pb定年结果表明,变基性岩的原岩形成时代为2160~2130Ma,变长英质粒状岩石原岩的形成时代为2200~2160Ma,两者共同经历了1950~1850Ma古元古代变质事件的改造。根据地球化学特征,变基性岩可分为三种类型:第一类斜长角闪岩属于拉斑玄武岩系列,轻微富集LREE,类似E-MORB特征,Nb、Ta、Ti、Zr和Hf轻微亏损,暗示有限的流体交代和地壳混染,变质锆石ε_(Hf)(t)值为-2.3~5.9,t DM1集中在2200~2100Ma,表明其原岩来源于亏损的软流圈地幔,指示古元古代新生地壳生长事件;第二类斜长角闪岩属于钙碱性系列,具有右倾的稀土元素配分曲线,Nb、Ta和Ti元素明显亏损,Zr、Hf正异常,表明其原始岩浆在离开源区后可能经历了地壳混染;第三类变角闪石岩属于超基性岩,REE总量相对偏高,LREE相对富集,Nb、Ta、Ti、Zr和Hf明显亏损,显示出有限的地壳混染和大量流体交代,岩浆锆石ε_(Hf)(t)值为-2.3~6.7,t DM1集中在2500~2200Ma;变质锆石ε_(Hf)(t)值为-5.9~-0.4,t DM1集中在2500~2300Ma,其原岩应来源于富集的岩石圈地幔。在变长英质粒状岩石中,变粒岩的SiO 2含量低于浅粒岩的,二者原岩均属于钙碱性系列并具有相似地球化学属性,暗示原岩来源于相同的岩浆源区。变长英质岩LREE富集而HREE相对亏损;Zr、Hf正异常,而Nb、Ta和Ti元素明显亏损,与弧源陆壳岩石特征相似;岩浆锆石的ε_(Hf)(t)值集中在-2~4,变质锆石ε_(Hf)(t)值则集中在-7~-1,两者t DM2集中在2900~2600Ma之间,表明其原岩为大陆下地壳太古宙TTG的部分熔融的产物。变长英质粒状岩石与变基性岩均指示其原岩形成于弧后盆地的构造环境,并经历了弧后盆地持续张裂至碰撞造山的演变过程,该过程可以划分为三个阶段:(1)2200~2160Ma期间,狼林陆块与北澳大利亚克拉通之间的大洋板块由西南向东北俯冲,随着俯冲的大洋岩石圈板块后撤,岩石圈开始伸展导致弧后盆地初始张裂;这一伸展作用导致软流圈地幔上涌,加热上覆太古宙大陆地壳;而由于持续的加热,大陆地壳开始部分熔融,形成了大量酸性火山岩(里尔峪组)及酸性侵入岩(条痕状花岗岩)。(2)2160~2130Ma期间,随着俯冲的大洋岩石圈板块后撤,导致上覆岩石圈进一步伸展减薄,弧后盆地继续拉张,软流圈地幔进一步上涌,减压熔融形成2160~2130Ma的基性岩浆;与此同时,软流圈上涌加热上覆岩石圈地幔,部分熔融形成少量富集型基性岩浆。(3)1950~1850Ma期间,狼林陆块与龙岗陆块发生陆-陆碰撞造山作用,并发生区域内角闪岩相-麻粒岩相变质作用;更为重要的是,里尔峪组钴的来源可能与基性岩浆作用密切相关,火山喷发过程中沿裂隙的流体从基性岩中萃取了Co元素,进而在里尔峪组沉淀形成富钴层位,并经历了古元古代变质-变形事件的改造。