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1.
华北古陆块北缘退变榴辉岩的矿物化学与退变质作用   总被引:1,自引:0,他引:1  
华北古陆块北缘退变榴辉岩呈透镜状产于角闪岩相变质的早元古宙红旗营子群黑云斜长片麻岩中,岩相学研究显示它经历了峰期榴辉岩相、减压过程中的高压麻粒岩相和角闪岩相变质作用。峰期榴辉岩相的矿物组合为石榴子石、绿辉石、金红石和石英等,变质条件为680~730℃和大于1.40~1.50GPa。在退变质早期,绿辉石分解形成钠质透辉石和斜长石(An=20.4~30.7)的蠕虫状后生合晶,榴辉岩转变成高压麻粒岩;晚期的退变质作用表现为高压麻粒岩相矿物组合转变成由钙质角闪石和斜长石(An=31.6~54.8)组成的角闪岩相矿物平衡共生组合。在结构上,主要表现为石榴子石颗粒边部的次变边、保留石榴子石假象的粒状后生合晶和保留辉石假象的蠕虫状后生合晶等,其变质温压条件为530~610℃和0.67~0.81GPa。  相似文献   

2.
大别山北部镁铁-超镁铁质岩带中的榴辉岩主要有两种产状,一是产于变形较强(面理化)的橄榄岩中,另一种是产于片麻岩中。其中,绿辉石中硬玉端元组分大多为Jd=20mol%~52mol%。产于橄榄岩和片麻岩中榴辉岩的石榴子石成分分别相当于Coleman的B型和C型榴辉岩。石榴子石成分特征及钠质单斜辉石中石英针状出溶体的出现表明,本区榴辉岩早期可能经历过超高压变质作用,且至少经历了3个变质阶段,即:①榴辉岩相峰期变质阶段,主要矿物共生组合为石榴子石+绿辉石+金红石±蓝晶石+石英(或柯石英假象?),p≥2.5GPa、t=595~874℃;②高压麻粒岩相变质阶段,主要矿物共生组合为石榴子石+透辉石+紫苏辉石+钛铁矿+尖晶石+斜长石等,p=1.1~1.37GPa、t=817~909℃;③角闪岩相变质阶段,主要矿物共生组合为角闪石+斜长石+磁铁矿等,p=0.5~0.6GPa、t=500~600℃。该区榴辉岩独特的麻粒岩相退变质阶段,表明榴辉岩在折返初期并未能上升到中上地壳,而处于下地壳,它与南部超高压变质岩有不同的p-t演化史,即在榴辉岩相峰期变质之后经历了近等温减压(或稍升温减压)和降温减压变质过程。  相似文献   

3.
在一些典型碰撞造山带中,高压麻粒岩与榴辉岩在空间和时间上密切相关,它们之间的关系对揭示碰撞造山带的造山过程和造山机制具有重要意义.本文以中国西部的南阿尔金、柴北缘及中部的北秦岭造山带为例,详细陈述了这3个地区榴辉岩和相关的高压麻粒岩的野外关系、变质演化和形成时代,目的是要建立大陆碰撞造山带中榴辉岩和相关高压麻粒岩形成的地球动力学背景模式.南阿尔金榴辉岩呈近东西向分布在江尕勒萨依,玉石矿沟一带,与含夕线石副片麻岩、花岗质片麻岩和少量大理岩构成榴辉岩一片麻岩单元,榴辉岩中含有柯石英假象,其峰期变质条件为P=2.8~3.0GPa,T=730~850℃,并在抬升过程中经历了角闪岩-麻粒岩相的叠加;大量年代学研究显示其峰期变质时代为485~500Ma.南阿尔金高压麻粒岩分布在巴什瓦克地区,包括高压基性麻粒岩和高压长英质麻粒岩,它们与超基性岩构成了一个大约5km宽的构造岩石单元,与周围角闪岩相的片麻岩为韧性剪切带接触.长英质麻粒岩和基性麻粒岩的峰期组合均具有蓝晶石和三元长石(已变成条纹长石),形成的温压条件为T=930~1020℃,P=1.8~2.5GPa,并在退变质过程中经历了中压麻粒岩相变质作用叠加.锆石SHRIMP测定显示巴什瓦克高压麻粒岩的峰期变质时代为493~497Ma.都兰地区的榴辉岩分布柴北缘HP-UHP变质带的东端,在榴辉岩和围岩副片麻岩中均发现有柯石英保存,形成的峰期温压条件为T=670~730℃和P=2.7~3.25GPa,退变质阶段经过了角闪岩相的叠加;榴辉岩相变质时代为420~450Mao都兰地区的高压麻粒岩分布在阿尔茨托山西部,高压麻粒岩包括基性麻粒岩长英质麻粒岩,基性麻粒岩的峰期矿物组合为Grt+Cpx+Pl±Ky±Zo+Rt±Qtz,长英质麻粒岩的峰期矿物组合为:Grt+Kf+Ky+Pl+Qtz.峰期变质条件为T=800~925℃,P=1.4~1.85GPa,退变质阶段经历了角闪岩-绿片岩的改造,高压麻粒岩的变质时代为420~450Ma.北秦岭榴辉岩分布在官坡-双槐树一带,榴辉岩的峰期变质组合为Grt+Omp±Phe+Qtz+Rt,所计算的峰期温压条件为T=680~770℃和P=2.25~2.65GPa,年代学数据显示榴辉岩的变质时代为500Ma左右.北秦岭高压麻粒岩分布在含榴辉岩单元的南侧松树沟一带,包括高压基性麻粒岩和高压长英质麻粒岩,与超基性岩在空间上密切伴生,高压麻粒岩的峰期温压条件为T=850~925℃,P=1.45~1.80GPa,锆石U-Pb年代学研究显示其峰期变质时代为485~507Ma.以上三个实例显示,出现在同一造山带、在空间上伴生的高压麻粒岩和榴辉岩有各自不同的变质演化历史,但榴辉岩中的榴辉岩相变质时代和相邻的高压麻粒岩中的高压麻粒岩相变质作用时代相同或相近,这种成对出现的榴辉岩和高压麻粒岩代表了它们同时形成在造山带中不同的构造环境中,即榴辉岩的形成于大陆俯冲带中,而高压麻粒岩可能形成在俯冲带之上增厚的大陆地壳根部.  相似文献   

4.
南秦岭造山带分布于商丹和勉略两条缝合线之间,其东段变质地层以志留系和泥盆系为主,包括少量的震旦系和上古生界。主要岩性包括变质泥质岩、石英岩、大理岩和少量的变质基性岩及片麻岩等。根据野外分布和显微组构特征发现这些岩石至少遭受了两期变质作用:早期为递增变质作用,它以佛坪地区的高角闪岩相—麻粒岩相为中心,向外依次变为低角闪岩相(十字石—蓝晶石带)、绿帘角闪岩相(石榴石带)和绿片岩相(绿泥石和黑云母带),变质时代约为220~260 Ma。麻粒岩相以出现二辉石为特征,包括基性和中酸世麻粒岩等,野外只见于佛坪县城附近。高角闪岩相在泥质岩石中的矿物组合为夕线石-石榴石-黑云母-斜长石-钾长石-石英,其变质条件为t=688~693℃,P=0.5~0.6 GPa;低角闪岩相在泥质岩石中的矿物组合为蓝晶石(十字石)-石榴石-黑云母-白云母-斜长石-石英,其变质条件为t=570~598℃,P-0.7~1.0 CPa;绿帘角闪岩相在泥质岩石中的矿物组合为石榴石-黑云母-白云母-斜长石-绿泥石-石英,变质条件为t=518~545℃,P=0.5~0.8GPa;绿片岩相的矿物组合为白云母-绿泥石-石英-斜长石-(黑云母),其变质压力为0.6~0.65 GPa,温度可能为400~450℃。采用Spear提出的吉布斯方法,以石榴石变斑晶的环带变化得到高角闪岩相、低角闪岩相  相似文献   

5.
南阿尔金吐拉地区基性麻粒岩呈透镜体分布于泥质片麻岩中。基性麻粒岩主要矿物组成为石榴子石、斜方辉石、单斜辉石、角闪石、黑云母和斜长石,显示"巴罗式"变质作用(中压麻粒岩相变质作用)特征。目前南阿尔金吐拉地区发育的"巴罗式"变质岩研究相对薄弱,对岩石学特征、变质演化轨迹及"巴罗式"变质作用成因机制亦不明确。传统矿物温压计指示基性麻粒岩的峰期变质温压条件为T=820℃~870℃,P=8.0~8.5 kPa,退变质阶段温压T=700℃~750℃,P=6~7.5 k Pa,为一个降温降压顺时针型的P-T演化轨迹。锆石U-Pb定年加权平均年龄为~450Ma,结合岩相学研究和锆石特征,认为其代表了峰期麻粒岩相变质时代。基性麻粒岩与区域上深熔作用和花岗质岩浆作用变质年龄相似,较南阿尔金UHP榴辉岩和HP麻粒岩的峰期变质时代晚40~50 Ma,与榴辉岩折返过程中麻粒岩相叠加变质作用时代较相似。说明吐拉地区"巴罗式"变质作用及同时代花岗质岩浆作用和混合岩化作用可能是由于俯冲陆壳发生断离并开始折返上升,在伸展环境下由幔源岩浆上涌加热中地壳形成的。  相似文献   

6.
柴北缘都兰高压麻粒岩的变质演化及形成的动力学背景   总被引:7,自引:5,他引:2  
于胜尧  张建新  李金平 《岩石学报》2009,25(9):2224-2234
在柴北缘-阿尔金HP/UHP变质带东端,新识别出一个高压麻粒岩单元.高压基性麻粒岩是高压麻粒岩单元的主体,还包括少量高压中酸性麻粒岩.高压基性麻粒岩主要由平衡共生的石榴子石、单斜辉石、斜长石组成,还含有不等量的蓝晶石、角闪石、石英、金红石、黝帘石/斜黝帘石、钛铁矿、方柱石等矿物.高压长英质麻粒岩主要包括石榴子石、蓝晶石、钾长石、斜长石、石英等矿物,并具有少量的单斜辉石和角闪石.岩石学和矿物学数据显示高压麻粒岩经历了多阶段的变质演化,温压计算获得峰期高压麻粒岩相的变质条件为1.40~1.85GPa和800~925℃.退变质高角闪岩相的变质条件为P=0.80~1.05GPa和T=580~695℃:进一步的退变质作用发生在低角闪岩相/绿片岩相条件下(<0.8GPa和<550℃).岩石学、矿物学及年代学资料研究表明都兰地区的高压麻粒岩具有与相邻榴辉岩不同的变质演化历史,而不是榴辉岩在抬升过程中热松弛作用所致.高压麻粒岩可能形成于与陆壳俯冲相关的造山带增厚的陆壳根部环境,形成的深度为50~70km.  相似文献   

7.
郭晶  李云帅  于胜尧  张建新 《地质学报》2021,95(12):3691-3704
高压/超高压变质带中的榴辉岩对于揭示造山带的热演化历史及造山过程具有重要的研究意义.本文通过对南阿尔金巴什瓦克地区榴辉岩的详细岩相学研究,认为该榴辉岩经历了榴辉岩相的峰期变质阶段(M1,946~1026℃和2.9~3.2 GPa)、峰后退变质阶段(M2,硬玉+石英=钠长石反应线附近)以及晚期麻粒岩相-角闪岩相的变质阶段(M3,~0.8 GPa,789~841℃).此外,锆石U-Pb年代学结果表明该榴辉岩的变质时代为492.8±2.8 Ma (MSWD=0.77),结合锆石中的石榴子石、绿辉石、金红石和石英包裹体及前人所获得的年代学数据,认为该变质时代记录了早古生代榴辉岩相的变质事件,进而恢复了南阿尔金榴辉岩所记录的顺时针P-T-t轨迹.本研究为南阿尔金巴什瓦克地区超高压变质作用提供了有效的矿物学与岩石学证据,同时为探讨南阿尔金动力学演化过程提供了重要的约束条件.  相似文献   

8.
柴北缘鱼卡河榴辉岩的典型矿物组合为石榴石-绿辉石-多硅白云母-金红石。其中粗粒石榴石变斑晶普遍保存进变质生长环带,从核部到边部石榴石的化学成分、包体矿物的种类和粒度皆呈现出规律的分带性。岩相学和矿物化学研究进一步表明,该榴辉岩经历了前榴辉岩相、榴辉岩相及后榴辉岩相三个主要变质演化阶段。前榴辉岩相以石榴石核部成分及核部包体矿物组合石榴石(GrtⅠ) 角闪石(AmpⅠ) 斜长石(PⅡ) 石英(Qtz)为特征,P-T 估算结果为450~500℃和0.6~0.7GPa。榴辉岩相变质阶段又可细分为早期、峰期榴辉岩和退变角闪榴辉岩三个亚相。早期榴辉岩亚相以石榴石幔部成分和幔部包体矿物组合石榴石(GrtⅡA) 绿辉石(OmpⅡA) 多硅白云母(PheⅡA)±黝帘石(Zoi) 金红石(Ru)为代表,估算的温压条件为580~640℃和2.4~2.5GPa;峰期榴辉岩相以石榴石的边部(GrtⅡB)及基质中绿辉石(OmpⅡB)和多硅白云母(PheⅡB)的核部为代表,矿物组合为 GrtⅡB OmpⅡB PheⅡB Ru,估算的 P-T 条件为620~680℃和3.0~3.4GPa;退变角闪榴辉岩相以共生的石榴石的最边部(GrtⅡC)、基质绿辉石(OmpⅡC)和多硅白云母(PheⅡC)的边部及镁红闪石(AmpⅡ)组合为代表,矿物组合为 GrtⅡC OmpⅡC AmpⅡ PheⅡC,估算的 P-T 条件为700~720℃和2.3~2.4GPa。后榴辉岩阶段主要为麻粒岩-高角闪岩相,以绿辉石分解形成透辉石 钠长石冠状体以及进一步分解形成韭闪石 斜长石,铁红闪石分解形成浅闪石 斜长石为代表,P-T 估算结果为550~600℃和0.6~1GPa。温压估算结果表明,鱼卡河榴辉岩经历了升温升压—升温降压—降温降压的一个顺时针 P-T 演化轨迹,它记录了从俯冲-超高压变质-抬升的连续的演化过程。峰期变质条件为630~680℃和3.0~3.4GPa,已达超高压变质范畴。榴辉岩中进变质矿物组合和生长环带的保存说明榴辉岩的形成经历了相对快速的俯冲和折返的动力学过程。  相似文献   

9.
柴北缘都兰高压麻粒岩的锆石U-Pb定年及其地质意义   总被引:3,自引:0,他引:3  
在柴北缘高压-超高压变质带的东端都兰地区,高压麻粒岩以透镜体的形式存在于石榴白云母片岩、花岗质片麻岩以及斜长角闪岩中。高压麻粒岩的主体为基性麻粒岩,并含少量中酸性麻粒岩。基性麻粒岩主要由石榴子石、单斜辉石、斜长石和石英等组成,而中酸性麻粒岩峰期矿物组合为:石榴子石+斜长石+钾长石+蓝晶石+石英±单斜辉石。根据显微构造和反应结构特征,主要识别出3期变质作用:①峰期高压麻粒岩相阶段(M1);②退变质高角闪岩相阶段(M2);③绿片岩相/低角闪岩相阶段(M3)。选取典型的中酸性麻粒岩样品进行了锆石LA-ICP-MSU-Pb原位定年分析,获得加权平均年龄为446.9±6.5Ma,且CL图像显示锆石内部发育石榴子石、单斜辉石、斜长石等矿物包体,反映锆石可能形成在峰期高压麻粒岩相变质条件下。岩石学和年代学结果显示都兰高压麻粒岩和邻近的榴辉岩同时形成于同一俯冲带的不同热构造环境,高压麻粒岩并非榴辉岩热松弛作用形成的,两者具有各自独立的变质演化历史。  相似文献   

10.
刘凤麟  张立飞 《岩石学报》2014,30(10):2808-2820
喜马拉雅东构造结出露了一套基性高压麻粒岩,其峰期矿物组合为石榴石+单斜辉石+石英+金红石+斜长石,利用相平衡计算其峰期温压条件为904℃、1.37GPa,利用锆石U-Pb定年方法确定其变质年龄为20.7±2.3Ma。角闪斜方辉石麻粒岩为其第一阶段退变产物,其变质矿物组合为斜方辉石+角闪石+斜长石+石英+钛铁矿+磁铁矿,温压条件为压力小于0.6GPa,温度为720~760℃。角闪岩相退变矿物组合为角闪石+斜长石+石英+钛铁矿+磁铁矿,温度小于745℃,压力小于0.6GPa。在角闪斜方辉石麻粒岩中变质锆石获得的定年结果为9.38±0.22M,根据锆石中角闪石+斜长石+石英的矿物包体特征,确定该年龄代表角闪岩相退变质年龄。据此,确定了喜马拉雅东构造结基性高压麻粒岩的PTt轨迹为顺时针2阶段折返过程,即第一阶段发生在20Ma左右的由高压麻粒岩相到角闪岩相退变阶段,第二阶段发生在9Ma左右的从角闪岩相深度折返到地表的阶段,计算得到其折返速率分别为2.4mm/y和2.3mm/y,这2个阶段的折返与目前通常认为的青藏高原2个主要抬升阶段是基本一致的。  相似文献   

11.
Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50–100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N2 in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area.  相似文献   

12.
在野外地质调查的基础上,选取滹沱群豆村亚群底部四集庄组玄武岩、顶部青石村组玄武岩和东冶亚群中下部河边村组玄武岩,进行岩石学和地球化学研究。分析结果表明:玄武岩主量元素高TiO2、TFeO,低MgO,具有演化的基性岩浆的特征。稀土元素含量相对较高,具有弱—中等程度的轻稀土元素富集,中等程度的轻重稀土元素分异,轻微的Eu异常;玄武岩中Cr、Ni含量变化较大,但与Mg#具有很好的正相关性。微量元素配分图解中具有明显的Sr负异常,部分样品具有Nb、Ta和Ti负异常,无Zr、Hf负异常,与岛弧火山岩不同;同时Nb、Ta无分异,Zr/Hf值较高,具有板内玄武岩浆的特征。综合分析认为,滹沱群玄武岩可能形成于板内裂谷环境。在岩浆上升过程中发生橄榄石与尖晶石的分离结晶作用,同时不同程度地受到地壳的混染。  相似文献   

13.
岑巩县羊桥乡罗家塘杷榔组仅出露中-上部地层,岩性单一,均为青灰、灰绿色粉砂质泥、页岩.在其上部层位发现了俞氏贵州始海百合(Guizhoueocrinus yui Zhao,Parsley et Peng,2007),计有棘皮动物始海百合、腕足动物、软体动物-软舌螺、节肢动物-三叶虫等8属9种,包括了2个未定名的新种和1...  相似文献   

14.
填海工程使滨海地区的地下水物理化学条件改变,导致该区域地下水中重金属浓度升高。本文以深港西部通道填海区为例,采用实验室模拟填海条件的办法,初步探讨了影响填海区地下水重金属迁移的关键因素。模拟实验结果表明,填海区地下水中钨元素含量升高与地下水淡化、淤泥氧化过程以及填料风化有关;铜元素含量升高则与淤泥氧化过程以及填料风化有关;钒元素含量升高与地下水淡化和淤泥氧化过程有关,而其他元素含量升高则主要与填料风化释放有关。  相似文献   

15.
马元铅锌矿床是近年扬子陆块北缘铅锌找矿的新突破。矿体呈层状、似层状产于碑坝隆起翼部震旦系灯影组角砾状白云岩层间构造带中,围岩蚀变很弱。矿石中硫化物以闪锌矿、方铅矿为主,中粗粒晶质结构,充填于白云岩角砾间。闪锌矿富集Cd、Ge、Ag,贫In、Tl、Se,Ga/In为6~132,Ge/In多1000,成矿温度以中-低温为主。金属硫化物ε~(34)S值相对集中,为12.9‰~19.4‰,平均为17.4‰,来自于海相硫酸盐的还原。铅同位素组成稳定,~(206)Pb/~(204)Pb为17.858~17.918:~(207)Pb/~(204)Pb为15.603~15.694;~(208)Pb/~(204)Pb为37.756~38.046,具有造山带和上地壳铅的特征,震旦系可能提供了金属成矿物质。闪锌矿中流体包裹体的~3He/~4He为0.03Ra~1.05Ra,~(40)Ar/~(36)Ar为326.1~765.1,~(38)Ar/~(36)Ar为0.183~0.204,表明成矿流体主要为地壳流体和饱和大气水(大气降水或海水)的混合。闪锌矿内流体包裹体挥发分δ~(13)C_(CH_4)值为-36.01‰~-28.80‰,δ~(13)C_(C_2H_6)值为-27.72‰~-22.44‰,δ~(13)C_(CO_2)值为-23.24‰~-9.68‰,表明有机流体参与了成矿作用。石英、方解石的H-O同位素结果表明具有海水和有机水混合的特征。可见,成矿流体具有两种流体混合的特征,一为蒸发海水与围岩反应所形成的盆地卤水,二为有机流体。推测矿区可能存在一个古油气藏,由于TSR生成一高硫气藏,为区内还原性有机流体的主要来源。当富含Pb、Zn等成矿物质的成矿流体运移至富含CH_4和H_2S的还原性流体的矿区角砾岩带时,两种流体混合,Pb、Zn等遇到H_2S发生反应而沉淀成矿,并伴生热液白云石等,形成了马元铅锌矿床。综上所述,我们认为马元矿床属MVT型铅锌矿床。  相似文献   

16.
The geology and mineralogy of host metamorphic rocks, the mineralogy of sulfide ores, and the distribution of PGE mineralization were studied in detail for the Kvinum-1 and Kvinum-2 copper-nickel occurrences of the Kvinum ore field, which are the most promising targets for the copper-nickel-PGE mineralization of the Sredinny Range of Kamchatka. It was established that stringer-disseminated and massive copper-nickel ores are localized in amphibole peridotites, cortlandites, and form ore bodies varying from tens of centimeters to 5–20 m thick among the layered cortlandite-gabbroid massifs. The massive sulfide ores were found only at the bottom of cortlandite bodies and upsection grade into stringer-disseminated and disseminated ores. Pyrrhotite, chalcopyrite, and pentlandite are the major ore minerals with a sharply subordinate amount of pyrite, sphalerite, galena, arsenopyrite, and löllingite. Besides pentlandite, the Ni-bearing minerals include sulforasenides (gersdorffite), arsenides (nickeline), and tellurides (melonite) of nickel. It was found that PGE mineralization represented by antimonides (sudburyite) and tellurobismuthides (michenerite) of Pd with sharply subordinate platinum arsenide (sperrylite) is confined to the apical parts of massive sulfide zones and the transition zone to the stringer-disseminated ores. Ore intervals enriched in arsenides and tellurides of Ni, Pd, and Bi contain high-purity gold. In the central parts of the orebodies, the contents of PGE and native gold are insignificant. It is suggested that the contents of major sulfide minerals and the productivity of PGE mineralization in the cortlandites are defined by combined differentiation and sulfurization of ultramafic derivatives under the effect of fluids, which are accumulated at the crystallization front and cause layering of parental magmas with different sulfur contents. The fluid-assisted layering of mafic-ultramafic massifs resulted in the contrasting distribution of PGM in response to uneven distribution of sulfur (as well as As, Te, and Bi) during liquid immiscibility. The productivity of PGE mineralization significantly increases with increasing contents of S, As, Te, and Bi (elements to which Pt and, especially, Pd have high affinity) in fluids.  相似文献   

17.
 A geophysical survey was conducted to determine the depth of the base of the water-table aquifer in the southern part of Jackson Hole, Wyoming, USA. Audio-magnetotellurics (AMT) measurements at 77 sites in the study area yielded electrical-resistivity logs of the subsurface, and these were used to infer lithologic changes with depth. A 100–600 ohm-m geoelectric layer, designated the Jackson aquifer, was used to represent surficial saturated, unconsolidated deposits of Quaternary age. The median depth of the base of the Jackson aquifer is estimated to be 200 ft (61 m), based on 62 sites that had sufficient resistivity data. AMT-measured values were kriged to predict the depth to the base of the aquifer throughout the southern part of Jackson Hole. Contour maps of the kriging predictions indicate that the depth of the base of the Jackson aquifer is shallow in the central part of the study area near the East and West Gros Ventre Buttes, deeper in the west near the Teton fault system, and shallow at the southern edge of Jackson Hole. Predicted, contoured depths range from 100 ft (30 m) in the south, near the confluences of Spring Creek and Flat Creek with the Snake River, to 700 ft (210 m) in the west, near the town of Wilson, Wyoming. Received, May 1997 · Revised, February 1998 · Accepted, April 1998  相似文献   

18.
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.  相似文献   

19.
20.
李涛  王宗秀 《地质通报》2008,27(4):469-476
对巴颜喀拉山年宝玉则花岗岩岩体样品的锆石、磷灰石进行了裂变径迹(FT)分析。结果显示该区的隆升可以分为三大阶段:①从低绿片岩相到锆石时钟启动:从200MaBP到105.57MaBP,去顶量约为2km,样品埋深上升到距地表约6km深度。去顶速率约为0.02mm/a;②从锆石时钟启动到磷灰石时钟启动:由于磷灰石在此时已抬升到距地表约6km的深度。由此到达时钟启动需距地表约3km时,去顶量应为3km,此阶段的持续时间为101.53MaBP,去顶速率约为0.03mm/a:③从磷灰石时钟启动至达到地表(至今):由于磷灰石在前一阶段也已抬升到距地表约3km的深度。即去顶量为3km。此阶段的持续时间为4.04MaBP,去顶速率约为0.74mm/a。  相似文献   

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