北秦岭松树沟榴辉岩的确定及其地质意义

松树沟石榴石角闪岩(榴闪岩)呈透镜状产于松树沟超镁铁岩旁侧的斜长角闪岩中,一直以来被认为是形成于接触交代变质或麻粒岩相变质过程。详细岩相学及矿物元素分析,在榴闪岩的基质矿物、石榴石幔部及锆石包体中发现残留的绿辉石,而且石榴石也保存了明显的进变质主、微量元素成分环带,表明松树沟榴闪岩为榴辉岩退变质的产物,至少经历了从角闪岩相到榴辉岩相再到角闪岩相的三阶段顺时针PT演化过程。锆石定年结果得到榴辉岩的变质年龄为500±8Ma,原岩结晶时代为796±16Ma,与秦岭岩群北侧官坡超高压榴辉岩的变质年龄和原岩年龄完全一致,也与北秦岭区域高压-超高压变质时代和原岩的结晶时代一致。表明松树沟榴辉岩与北秦岭造山带已发现的高压-超高压变质岩石一起都应是古生代大陆深俯冲作用的结果,而松树沟超镁铁岩可能是俯冲的大陆板片在折返过程中携带的俯冲隧道中的交代地幔岩。     

北秦岭松树沟及其邻区高压-超高压榴辉岩的确定及其构造地质意义

详细的岩相学观察和激光拉曼矿物包裹体研究,在松树沟及其邻区秦岭群片麻岩中的榴闪岩和斜长角闪岩透镜体中发现了石榴石+绿辉石的典型榴辉岩相矿物组合,以及指示超高压变质的微粒柯石英包裹体,表明北秦岭松树沟及其邻区是超高压变质作用的产物。北秦岭松树沟超镁铁质岩体旁侧的榴闪岩一直以来都存在着接触交代变质(黄月华等,1984)、麻粒岩相变质(钱加慧等,2013)和退变榴辉岩(刘良等,2013;Zhang et al.,1999)等多种成因观点。本次研究在该榴闪岩的基质矿物角闪石的核部、石榴石变斑晶的幔部包裹体及锆石包体中都发现了残留绿辉石,而且发现石榴石变斑晶保存了很好的进变质矿物包裹体和主、微量元素成分环带,表明松树沟榴闪岩为榴辉岩相退变质的产物,至少经历了从角闪岩相到榴辉岩相再到角闪岩相的三阶段顺时针p-T演化。另外,采用激光拉曼光谱分析方法,对丹凤地区秦岭群片麻岩的多个榴闪岩和斜长角闪岩透镜体进行了详细的锆石包裹体矿物学分析,在其中的一个斜长角闪岩的锆石中发现了超高压矿物柯石英,表明该斜长角闪岩为超高压榴辉岩退变质的产物。LA-ICP-MS锆石U-Pb年代学研究,得到松树沟榴辉岩的峰期变质年龄为(500±8)Ma,原岩结晶时代为(796±16)Ma;得到丹凤地区斜长角闪岩的峰期变质时代为(498±3)Ma,同时得到~450 Ma和~420 Ma两期退变质事件年龄;得到斜长角闪岩的围岩片麻岩的变质年龄为(502±4)Ma。其中榴辉岩和斜长角闪岩的~500 Ma的变质年龄分别来自锆石的石榴石+绿辉石以及柯石英包体的微区,应代表本区高压-超高压榴辉岩相变质的年龄。该年龄与秦岭岩群中已发现的官坡含金刚石榴辉岩(~500 Ma,杨经绥等,2002;陈丹玲等,2011)、清油河含金刚石斜长角闪岩(490±5.8 Ma;Wang et al.,2014)的峰期变质年龄一致,也与秦岭岩群区域片麻岩的~500 Ma的变质时代在误差范围内完全一致(刘良等,2013;Diwu et al.,2014),表明松树沟及其邻区榴辉岩与北秦岭造山带已发现的高压-超高压变质岩石一起都应是古生代大陆深俯冲作用的结果。     

北秦岭造山带西段早古生代榴辉岩相变质岩石的发现及其地质意义SCIEI北大核心CSCD

西秦岭地处中国中央造山系东西转换衔接部位,随着东秦岭以及祁连、柴北缘和东昆仑早古生代高压-超高压变质岩石的陆续发现和深入研究,西秦岭造山带变质作用研究吸引了大家的普遍关注。本文在大范围野外地质调查基础上,在北秦岭造山带西段天水南部的秦岭岩群长英质片麻岩中发现了一套石榴子石斜长角闪岩(榴闪岩),并开展了详细的锆石形貌和内部结构、微区微量元素和U-Th-Pb同位素研究。CL图像显示榴闪岩锆石普遍具有核-幔-边或核-边结构,部分存在原岩残留锆石。定年结果得到榴闪岩原岩残留锆石年龄为710±52Ma,同时得到497±3Ma、452±3Ma和423±7Ma三期变质年龄。其中497±3Ma变质年龄来自锆石核部并显示出轻稀土亏损、重稀土平坦且没有明显负Eu异常的稀土配分曲线特征,表明该时期的矿物组合中有石榴子石但没有斜长石,与榴辉岩相变质锆石特征一致;452±3Ma变质年龄来自锆石幔部或边部,对应测点重稀土元素的分异加大,并出现弱的负Eu异常,说明此时石榴子石被消耗且出现少量斜长石;423±7Ma变质年龄来自锆石的最边部,对应稀土配分曲线表现出更明显的负Eu异常和更大的重稀土元素分异特征,指示此时岩石中石榴子石含量更少,斜长石含量更多。上述结果表明该榴闪岩可能经历了~500Ma的榴辉岩相变质作用,并在~450Ma和~420Ma叠加了两期退变质改造。天水地区榴闪岩无论是其野外产状,还是变质锆石的形貌和内部结构、稀土配分曲线特征及其所记录的原岩和三期变质年龄都与北秦岭造山带东段大陆俯冲型高压-超高压变质榴辉岩近乎一致,指示早古生代时期,北秦岭造山带西段与东段经历了相似的大陆(深)俯冲和折返过程,它们共同构成一条统一的早古生代高压-超高压变质岩带。     

北秦岭高压-超高压岩石的多期变质时代及其地质意义

在岩相学观察和锆石CL图像研究的基础上,利用LA-ICP-MS原位微区定年分析方法,本文确定北秦岭清油河退变榴辉岩的峰期变质时代为490±6Ma,退变质时代为453±9Ma,原岩形成时代为655±9Ma;松树沟超高压长英质片麻岩的峰期变质时代为497±8Ma,两期退变质时代分别为448±4Ma和421±2Ma,原岩形成时代上限832±25Ma;寨根石榴石辉石岩的峰期变质时代为498±2Ma,中压麻粒岩相退变质时代为450±3Ma,角闪岩相退变质时代为426±1Ma,原岩形成时代为573±40Ma;西峡北榴闪岩的角闪岩相变质时代为423±3Ma,原岩形成时代为843±7Ma。新确定的这些岩石的峰期变质时代与前人已报导的区内高压-超高压岩石的峰期变质时代在误差范围内基本一致,结合区内高压-超高压岩石不仅分布在秦岭岩群北缘的官坡-双槐树一带,而且断续出露在秦岭岩群中部或偏南侧的清油河北-松树沟-寨根北甚至西峡北东西一线,进一步表明它们应是同一期构造地质事件的产物。北秦岭已发现的全部正变质的高压-超高压岩石均呈透镜体状分布在围岩片麻岩中,松树沟超高压长英质片麻岩的原岩为典型的陆壳沉积物,因此,这些高压-超高压岩石的形成可能都是陆壳俯冲-深俯冲作用的产物。结合岩相学观察、锆石CL图像和锆石U-Pb定年表明,这些高压-超高压岩石在～500Ma经历了峰期变质作用后,又分别在～450Ma和～420Ma遭受了中压麻粒岩相和或角闪岩相退变质作用的叠加,充分说明这些高压-超高压岩石经历了一个完整的由陆壳俯冲-深俯冲、之后连续两次抬升的构造演化过程。另外,本次研究新获得的这些岩石的原岩形成时代介于843±7Ma～573±40Ma之间,结合官坡榴辉岩的原岩形成时代为791～814Ma以及松树沟榴闪岩原岩时代为787±16Ma的研究,共同表明北秦岭高压-超高压岩石的原岩形成时代均为新元古代,因此,限定俯冲-深俯冲的陆壳物质应来自形成时代为新元古代的大陆地壳或地质体。结合区域地质背景和前人研究成果综合分析,本文初步认为,北秦岭高压-超高压变质岩带的形成是商丹洋向北俯冲拖曳南秦岭新元古代陆壳物质在～500Ma发生陆壳俯冲-深俯冲作用的产物,之后在～450Ma与～420Ma经历了两期抬升。     

江山—绍兴结合带榴闪岩的发现及岩石学、年代学特征

江山—绍兴结合带内浙江溪口一带发现了以岩块、透镜状产出的榴闪岩。榴闪岩主要由角闪石、石榴子石、单斜辉石、斜长石和石英组成,以石榴子石为中心"白眼圈"结构明显,镜下可见石榴子石周围斜长石冠状体,单斜辉石内部及周围由斜长石和角闪石构成的后成合晶与冠状体结构。通过锆石LA-ICP-MS U-Pb测年在白石山头榴闪岩中获得主要变质年龄(451+8/-18)Ma。江山—绍兴结合带榴闪岩的发现为研究华夏地块与扬子陆块之间碰撞拼贴历史提供了新证据。     

北秦岭西部榴闪岩的发现与变质作用过程:锆石年代学和Hf-O同位素制约

秦岭造山带是由多期俯冲-碰撞造山和随后多阶段隆升成山形成的复合型造山带。近年来一个突破性进展是在北秦岭东部即陕西-河南交界地区以及桐柏地区的秦岭群高级变质岩中发现存在大量退变榴辉岩和高压麻粒岩,其中部分退变榴辉岩锆石包裹体中出现柯石英。这些发现证明北秦岭东部和桐柏地区的确在480~500Ma发生过深俯冲作用,随后造山带抬升形成退变榴辉岩。那么,北秦岭西部是否存在类似的(深)俯冲作用?本文首次在北秦岭西部宝鸡眉县地区发现了榴闪岩。该榴闪岩主要由石榴石和角闪石组成,含少量石英、透辉石和绿帘石。石榴石变斑晶都具有明显由退变质扩散作用形成的环带结构,绿帘石变斑晶具有与榴辉岩中绿帘石大致相同的XFe、CaO和Al2O3含量。同时,石榴石变斑晶核部还含有Amp+Cpx+Qtz包裹体,该包裹体矿物组合暗示其退变前可能是榴辉岩,而榴闪岩是在流体活动过程中退变质作用形成的。榴闪岩中锆石的离子探针SIMS定年获得很好的U-Pb谐和年龄(443.9±1.1Ma)和206Pb/238U的加权平均年龄(443.2±2.5Ma)。锆石的低Th和U含量和非常高Th/U比值(0.47~1.66)说明其并非是在"干"体系下形成的进变质锆石,应该是在流体强烈活动下形成的或是进变质锆石被退变质过程完全重置。因此,443Ma应该是榴闪岩的形成年龄即记录退变质作用发生的时间。这些锆石具有亏损的Hf同位素和类似地幔的氧同位素组成。因遭受退变质作用的强烈影响,其εHf(t)值和δ18O值有较宽的分布范围(εHf(t)=2.4~14.7;δ18O=4.25‰~6.39‰),其亏损地幔模式年龄为0.48~0.95Ga。所以,锆石的Hf-O同位素特征指示榴闪岩的原岩主要来自新元古代时期的亏损地幔来源的玄武质岩石。结合北秦岭东部地区榴辉岩发生退变质作用时代间隔可以大致判断北秦岭西部的榴闪岩的峰期变质时代可能为470~480Ma。由此发现,北秦岭东西部早古生代俯冲-碰撞事件时限上存在差异,即北秦岭早古生代俯冲-碰撞作用沿商南-宝鸡一线可能是自东向西发生的。     

秦岭杂岩清油河斜长角闪岩多期变质的证据——来自锆石微量元素和包裹体的启示

北秦岭清油河地区广泛发育以透镜状、条带状或岩墙状赋存于秦岭杂岩石英二长片麻岩中的斜长角闪岩,矿物组合为角闪石、斜长石以及少量的石榴子石、单斜辉石等。锆石阴极发光图像、不同微区矿物包裹体和稀土元素分析,以及不同性质锆石LA-ICP-MS U-Pb定年和微量元素分析等综合研究结果表明,该斜长角闪岩锆石成因十分复杂,可进一步划分为三种类型。第一类锆石呈半自形-他形晶,阴极发光显示条带状分带,锆石稀土总量较高,球粒陨石标准化稀土配分模式中重稀土富集,Eu负异常明显,记录的206Pb/238U加权平均值为774±13Ma,代表了该岩石原岩形成时代;第二类锆石呈他形晶,为典型的变质锆石,阴极发光图像为扇状或面状分带,锆石稀土总量较低,球粒陨石标准化稀土配分模式中重稀土相对平坦,没有Eu的负异常,表明该类锆石结晶时岩石中含有石榴子石,而没有长石,该类锆石矿物包裹体主要为Grt+Cpx+Q,可能代表榴辉岩相(榴辉岩或者石榴子石辉石岩)变质矿物组合,记录的~(206)Pb/~(238)U加权平均值为493±5Ma;第三类锆石呈他形晶或构成第二类锆石的薄边,亦为典型变质锆石,阴极发光为面状分带,锆石稀土总量较低,球粒陨石标准化稀土配分模式中重稀土平坦,具有Eu的异常,锆石包裹体矿物组合为Grt+Cpx+Pl+Amp+Q,应代表退变质矿物组合,记录的206Pb/238U加权平均值为448±4Ma。该斜长角闪岩的原岩年龄(774±13Ma)、峰期变质年龄(493±5Ma)和后期退变质年龄(448±4Ma)与北秦岭已厘定的高压-超高压岩石的原岩年龄、峰期变质和退变质年龄非常吻合,说明该岩石可能是北秦岭高压-超高压变质岩带的一部分。据此,并结合清油河斜长角闪岩中发现残存金刚石的研究成果,可以推测现今秦岭杂岩中出露的一些低级变质相岩石峰期也可能经历了高压-超高压变质,只是由于后期强烈的退变质作用的改造而难于识别和辨认,北秦岭高压-超高压岩石的分布可能远比目前观察到的丰富。此外,本次研究还显示清油河斜长角闪岩原岩具有大陆拉斑玄武岩特征,是陆壳岩石的一部分。这些资料为进一步论证北秦岭早古生代高压-超高压岩石(包括榴辉岩、长英质片麻岩、石榴子石辉岩、榴闪岩和部分斜长角闪岩等)是陆壳俯冲-深俯冲作用的产物提供了新的证据。     

北大别混合岩类型及其成因

大别造山带北大别超高压变质构造单元中广泛发育混合岩。基于对罗田和岳西穹隆中混合岩的野外观察、岩相学、矿物化学和锆石LA-ICP-MS U-Pb定年系统工作,发现北大别混合岩主要分为中等深熔混合岩和高度深熔混合岩两种类型。中等深熔混合岩为叠层状混合岩和膨胀结构混合岩;高度深熔混合岩为眼球状混合岩和析离体状混合岩。锆石U-Pb同位素定年结果表明,混合岩中新生锆石年龄范围为125 Ma~138 Ma,加权平均年龄为130.7 Ma±1.8 Ma;两个继承锆石的年龄分别为602.8 Ma±16.8 Ma和667.3 Ma±17.6 Ma;混合岩叠层状暗色体中锆石年龄连续且分布集中,加权平均年龄为703 Ma±10 Ma,代表原岩的形成年龄。北大别混合岩的原岩为新元古代的岩石,其混合岩化作用发生在140 Ma至125 Ma期间。不同浅色体中斜长石的含量和牌号差异显著,反映了浅色体形成于不同演化程度的熔体结晶。斜长石-角闪石温压计估算结果显示,混合岩形成的温压条件为723℃~768℃和370 MPa~520 MPa,对应于中上地壳环境。混合岩的成因机制以长英质片麻岩水饱和条件下的富水熔融为主。其反应为:黑云母+石英+斜长石+水=角闪石+斜长石(残留)+花岗质熔体。少数混合岩的成因机制为角闪片麻岩中角闪石的脱水熔融。其反应为:角闪石+斜长石+石英=单斜辉石+富水熔体。     

天水地区李子园高压麻粒岩的发现:西秦岭晚泥盆纪造山的证据

西秦岭造山带北缘的天水李子园地区发现一套高压石榴石单辉麻粒岩,在变质的早古生代岛弧火山-沉积岩系中呈透镜状岩块产出。其峰期矿物组合为石榴石+单斜辉石+角闪石+斜长石+钛铁矿/榍石。利用地质温压计得到的温压条件为T=757~792℃、P=1.3~1.5GPa,达到中压相系的高压麻粒岩相变质条件。LA-ICPMS锆石U-Pb定年显示,锆石变质增生边的谐和年龄为384±1.6Ma,表明高压麻粒岩相变质作用的时代为中-晚泥盆世。结合区域地质资料,这一期变质作用要晚于北秦岭造山带中普遍记录的中低压麻粒岩-角闪岩相变质作用,可能与商丹洋闭合之后碰撞造山阶段的地壳加厚过程有关。岩浆锆石核部的谐和年龄为796±2.2Ma,代表石榴石单辉麻粒岩的原岩形成年代。其锆石核部的Hf同位素组成变化较大,对应的εHf(t)值为-7.3~+13.2,显示出不同源区岩浆混合的特征或者陆壳混染。高压麻粒岩全岩地球化学特征同样显示其经历壳幔岩浆混合作用。结合原岩的形成时代、区域上与裂解相关的岩浆作用和构造背景,我们认为原岩可能是造山带垮塌伸展阶段的壳-幔岩浆混合作用的产物,可能与新元古代Rodinia超大陆裂解事件有关。     

柴北缘铁石观榴辉岩锆石U-Pb定年及其地质意义

为查明柴北缘超高压变质带铁石观地区榴辉岩变质时间及流体活动,利用LA-ICP-MS对该区榴辉岩进行了锆石U-Pb定年分析,同时对锆石中包裹体进行了研究。结果表明,榴辉岩中变质锆石~(206)Pb/~(238)U加权平均年龄为426.1±4.9 Ma(MSWD=1.18),与区域上鱼卡、锡铁山、都兰等地榴辉岩变质峰期年龄一致。激光拉曼分析结果显示,包裹体核部矿物为金红石、绿辉石,边部为磷灰石、斜长石,可能为榴辉岩变质峰期捕获的产物。锆石~(176)Hf/~(177)Hf=0.282691~0.282795,~(176)Lu/~(177)Hf=0.000002~0.000228,Hf同位素两阶段亏损地幔模式年龄为769.7~1002.8 Ma,与区域上测得榴辉岩原岩年龄一致。通过搜集区域变质岩年龄数据分析,柴北缘地区超高压变质带年龄可分3期:第1期(470~440 Ma)与洋壳俯冲事件相关,第2期(440~420 Ma)与陆陆俯冲碰撞事件相关,第3期(420~400 Ma)为岩石退变化时期。     

Wavelength-dispersive X-ray fluorescence spectrometric determination of Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites

Komatiites are mantle-derived ultramafic volcanic rocks. Komatiites have been discovered in several States of India, notably in Karnataka. Studies on the distribution of trace-elements in the komatiites of India are very few. This paper proposes a simple, accurate, precise, rapid, and non-destructive wavelength-dispersive x-ray fluorescence (WDXRF) spectrometric technique for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites, and discusses the accuracy, precision, limits of detection, x-ray spectral-line interferences, inter-element effects, speed, advantages, and limitations of the technique. The accuracy of the technique is excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Ba, Pb, and Th and very good (within 4%) for Y. The precision is also excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th. The limits of detection are: 1 ppm for Sc and V; 2 ppm for Cr, Co, and Ni; 3 ppm for Cu, Zn, Rb, and Sr; 4 ppm for Y and Zr; 6 ppm for Nb; 10 ppm for Ba; 13 ppm for Pb; and 14 ppm for Th. The time taken for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in a batch of 24 samples of komatiites, for a replication of four analyses per sample, by one operator, using a manual WDXRF spectrometer, is only 60 hours.     

Isotopic systematics of He,Ar, S,Cu, Ni,Re, Os,Pb, U,Sm, Nd,Rb, Sr,Lu, and Hf in the rocks and ores of the Norilsk deposits

This paper reports the first results of a study of 11 isotope systems (³He/⁴He, ⁴⁰Ar/³⁶Ar, ³⁴S/³²S, ⁶⁵Cu/⁶³Cu, ⁶²Ni/⁶⁰Ni, ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ^206–208Pb/²⁰⁴Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others.     

硅酸盐类样品中硅、铁、铝、钛、锰、钙、镁、钾、钠和磷的x射线荧光光谱测定

本文拟定了一种以熔融法制备样片,用X射线荧光光谱测定硅酸盐类样品中Si、Fe、Al、Tj、Mn、Ca、Mg、K、Na、P等元素的分析方法。在对不同靶材X光管和分光晶体实验对比的基础上,选择了最佳的测量条件。该法具有快速、准确,测量范围广,检测限低,价格便宜等优点。经过近百个各种类型标样或管理样品的分析对比表明,本法不仅适用于硅酸盐类岩石样品的分析,还适用于铁矿、铝土矿、碳酸盐类岩矿样品以及水泥、耐火材料等样品的分析。     

高压微波消解法测定醋酸纤维过滤器采集的微尘粒子中的砷镉钴铬铜铁锰镍铅钒锌

最新的流行病学研究表明,空气中较高浓度的悬浮细颗粒可能对人类的健康有不利的影响。根据该项研究显示,由于心脏病、慢性呼吸问题和肺功能指标恶化而导致死亡率的升高与细尘粒子有关。这些研究结果已经促使欧盟于1999年4月出台了限制空气中二氧化硫、二氧化氮、氧化氮、铅和颗粒物含量的法案(1999/30/EC),对各项指标包括对可吸入PM10颗粒的浓度提出了新的限制性指标。PM10颗粒是指可以通过预分级器分离采集的气体动力学直径小于10μm的细颗粒。目前研究的兴趣重点逐步偏向PM2.5这些更细微颗粒物,PM2.5这种颗粒物对健康有明显的不利影响。在欧盟指令2008/50/EC中,对PM10和PM2.5都提     

硅酸盐中铁、锰、钛、钙、钾、磷、硅、铝、镁、钠、锶、铷、钡的X-射线荧光光谱定量测定

本文介绍样品经四硼酸锂熔融制成玻璃小饼。采用Lachance模式和理论a系数来校正元素间的效应,由3080E型X-射线荧光谱仪和DF-350B数据处理系统完成硅酸盐中十三个项目的测定。     

Viscous, cohesive, non-Newtonian, depositing, radial slurry flow

Mining induced subsidence can significantly affect mining costs where major surface facilities and natural environment need to be protected. Overburden grout injection is a technology used to control coal mine subsidence by injecting the mine waste material extracted from the coal back into the inter-burden rock during longwall mining. The flowing slurry is here categorised as a nonlinear viscous cohesive (Bingham plastic) fluid. During longwall mining the grout slurry is pumped into the separated beds of the rock mass through a central vertical borehole, which is drilled deep into the inter-burden rock strata above the coal seam. However, a blockage can occur in the injection system when the slurry velocity falls below a certain critical threshold velocity, indicating a material phase change from cohesive-viscous to cohesive-frictional. In situ field injection tests through boreholes have been simulated at a smaller scale at the CSIRO laboratory in Brisbane by pumping the slurry through a radial disk (gap = 4 mm) from its centre. Laboratory experiments indicate a general, nonlinear, cohesive, viscous, frictional model for shear behaviour of the slurry, in which the material shear parameters are functions of the disk radial distance. Complete dimensional and dimensionless analytical solutions have been developed based on an approach related to Bingham–Herschel–Bulkley fluid mechanics. The derived formulae include relations for minimum pump pressure, local pressure and pressure gradient, wall shear stress, volume rate, velocity and velocity gradient. The theoretical results match the experimental measurements. The experiments covered slurries with maximum particle sizes of 0.5 to 2 mm with about 50% being larger than 100 µm. The viscosities at the various solids concentrations were measured with a standard torsion viscometer. This study differs from the previous research in several distinct aspects, namely, consideration of the variable shear parameters rather than fixed values, inclusion of total nonlinear behaviour, and implementation of a friction function to mimic behaviour of the deposited and consolidating stiff slurry, which can cause a significant pressure rise as a result of the increased shear resistance.     

Bellechester,Minnesota, USA,lagoon collapses

Bellechester, Minnesota, is a small community of approximately 155 residents located on the county line between Goodhue and Wabasha counties in southeast Minnesota's karst region. Bellechester is served by a 21-year-old wastewater treatment facility (WWTF) consisting of three waste-stabilization ponds. On 28 April 1992 six sinkholes were discovered to have drained cell 2 of the WWTF resulting in the loss of approximately 8.7×10⁶ 1 of partially treated effluent and about 600 m³ of soil into previously undetected subsurface voids of unknown dimensions. In the week following the collapse, approximately 200 water wells located within a 5-km radius of the WWTF were sampled in an after-the-fact, emergency sampling program. Twelve samples with elevated fecal coliform levels, 18 samples with nitrate-nitrogen greater than the 10 mg/1 standard, and no samples with elevated chlorides were found. However, the elevated levels could not be unambiguously attributed to the WWTF collapse. This is the third WWTF to fail by sinkhole collapse in southeast Minnesota since 1974. All three collapsed lagoons have been located in similar geomorphic and stratigraphic settings. However, at least two lagoons have collapsed in the adjacent area in northeast Iowa, and these lagoons are located at different stratigraphic positions. Twenty-two WWTFs constructed in southeast Minnesota's karst region in the last 25 years have been identified as subject to potential sinkhole collapse. An unknown but significant number of manure storage lagoons, flood control structures, etc., have also been constructed in the karst region and are at risk. Public agencies are beginning to develop plans to deal with the risk associated with existing and future waste lagoons in this environment. The critical hydrogeologic parameters that can be used to prioritize the risk of collapse at existing facilities include: (1) the lithology of the first bedrock beneath each lagoon, (2) the thickness of surficial materials between the lagoon and the bedrock surface, (3) the presence and construction of liners (seepage rate), and (4) the proximity to existing sinkholes.     

岩石密度和超高压岩石折返速率

在常温常压条件下对中国大陆科学钻CCSD主孔100-3000米岩心样品进行了密度测量,建立了密度连续剖面,并界定了不同超高压岩石的密度值。通过对比高温高压物性实验资料,岩石密度随着退变程度增强而降低,榴辉岩密度变化序列为3.52g/cm3→3.49g/cm3→3.07g/cm3→2.93g/cm3。超高压长英质岩石密度变化序列为3.00g/cm→2.80g/cm3→2.65g/cm3。上述实验资料是讨论不同折返阶段岩石所受浮力的基础,为研究折返速率大小提供了基本参数。本文通过折返板块运动平衡时,上浮力与粘滞力平衡这一关系式,定量研究了大陆俯冲板块的折返速率,认为密度差产生上浮力从而引起折返,温度对板块折返速率的影响最为显著;密度差大小、折返角度、折返板块大小对折返速率也有直接的影响。定量模拟分析表明,在温度高于850℃时,板块的折返速率可以超过100mm/a;当温度降至700℃时,折返速率则低于1.5mm/a。作者认为在折返早期,温度较高,板块快速折返至60-70km榴辉岩相深度;随着传导散热,温度降低,板块以较慢的速率折返至中下地壳。折返速率的估算表明,浮力是板块折返第一阶段(从>100km深部折返至<40km的中下地壳)的主要驱动力。     

Mercury,arsenic, antimony,and selenium contents of sediment from the Kuskokwim River,Bethel, Alaska,USA

The Kuskokwim River at Bethel, Alaska, drains a major mercury-antimony metallogenic province in its upper reaches and tributaries. Bethel (population 4000) is situated on the Kuskokwim floodplain and also draws its water supply from wells located in river-deposited sediment. A boring through overbank and floodplain sediment has provided material to establish a baseline datum for sediment-hosted heavy metals. Mercury (total), arsenic, antimony, and selenium contents were determined; aluminum was also determined and used as normalizing factor. The contents of the heavy metals were relatively constant with depth and do not reflect any potential enrichment from upstream contaminant sources.