⁴⁰Ar/³⁹Ar and oxygen isotope studies of polymetamorphism from Tinos Island, Cycladic blueschist belt, Greece     

M. BRÖCKER  H. KREUZER  A. MATTHEWS  M. OKRUSCH 《Journal of Metamorphic Geology》1993,11(2):223-240

Abstract Petrological, oxygen isotope and ⁴⁰Ar/³⁹Ar studies were used to constrain the Tertiary metamorphic evolution of the lower tectonic unit of the Cyclades on Tinos. Polyphase high-pressure metamorphism reached pressures in excess of 15 kbar, based on measurements of the Si content in potassic white mica. Temperatures of 450–500° C at the thermal peak of high-pressure metamorphism were estimated from critical metamorphic assemblages, the validity of which is confirmed by a quartz–magnetite oxygen isotope temperature of 470° C. Some ⁴⁰Ar/³⁹Ar spectra of white mica give plateau ages of 44–40 Ma that are considered to represent dynamic recrystallization under peak or slightly post-peak high-pressure metamorphic conditions. Early stages in the prograde high-pressure evolution may be documented by older apparent ages in the high-temperature steps of some spectra. Eclogite to epidote blueschist facies mineralogies were partially or totally replaced by retrograde greenschist facies assemblages during exhumation. Oxygen isotope thermometry of four quartz–magnetite pairs from greenschist samples gives temperatures of 440–470° C which cannot be distinguished from those deduced for the high-pressure event. The exhumation and overprint is documented by decreasing ages of 32–28 Ma in some greenschists and late-stage blueschist rocks, and ages of 30–20 Ma in the lower temperature steps of the Ar release patterns of blueschist micas. Almost flat parts of Ar–Ar release spectra of some greenschist micas gave ages of 23–21 Ma which are assumed to represent incomplete resetting caused by a renewed prograde phase of greenschist metamorphism. Oxygen isotope compositions of blueschist and greenschist facies minerals show no evidence for the infiltration of a δ¹⁸O-enriched fluid. Rather, the compositions indicate that fluid to rock ratios were very low, the isotopic compositions being primarily controlled by those of the protolith rocks. We assume that the fundamental control catalysing the transformation of blueschists into greenschists and the associated resetting of their isotopic systems was the selective infiltration of metamorphic fluid. A quartz–magnetite sample from a contact metamorphic skarn, taken near the Miocene monzogranite of Tinos, gave an oxygen isotope temperature of 555° C and calculated water composition of 9.1%. The value of δ¹⁸O obtained from this water is consistent with a primary magmatic fluid, but is lower than that of fluids associated with the greenschist overprint, which indicates that the latter event cannot be directly related to the monozogranite intrusion.  相似文献   

Detailed <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar dating of geologic events associated with the Mantos Blancos copper deposit,northern Chile     

Verónica Oliveros  Gilbert Féraud  Luis Aguirre  Luis Ramírez  Michel Fornari  Carlos Palacios  Miguel Parada 《Mineralium Deposita》2008,43(3):281-293

The ⁴⁰Ar/³⁹Ar geochronological method was applied to date magmatic and hydrothermal alteration events in the Mantos Blancos mining district in the Coastal Cordillera of northern Chile, allowing the distinction of two separate mineralization events. The Late Jurassic Mantos Blancos orebody, hosted in Jurassic volcanic rocks, is a magmatic-hydrothermal breccia-style Cu deposit. Two superimposed mineralization events have been recently proposed. The first event is accompanied by a phyllic hydrothermal alteration affecting a rhyolitic dome. The second mineralization event is related to the intrusion of bimodal stocks and sills inside the deposit. Because of the superposition of several magmatic and hydrothermal events, the obtained ⁴⁰Ar/³⁹Ar age data are complex; however, with a careful interpretation of the age spectra, it is possible to detect complex histories of successive emplacement, alteration, mineralization, and thermal resetting. The extrusion of Jurassic basic to intermediate volcanic rocks of the La Negra Formation is dated at 156.3 ± 1.4 Ma (2σ) using plagioclase from an andesitic lava flow. The first mineralization event and associated phyllic alteration affecting the rhyolitic dome occurred around 155–156 Ma. A younger bimodal intrusive event, supposed to be equivalent to the bimodal stock and sill system inside the deposit, is probably responsible for the second mineralization event dated at ca. 142 Ma. Other low-temperature alteration events have been dated on sericitized plagioclase at ca. 145–146, 125, and 101 Ma. This is the first time that two distinct mineralization events have been documented from radiometric data for a copper deposit in the metallogenic belt of the Coastal Cordillera of northern Chile. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

赣南崇义—大余—上犹矿集区不同类型含矿石英中白云母40Ar/39Ar年龄及其地质意义   总被引：14，自引：0，他引：14  

刘善宝  王登红  陈毓川  李建康  应立娟  许建祥  曾载淋 《地质学报》2008,82(7):932-2008-01-30

崇义—大余—上犹矿集区是世界著名的黑钨矿床集中区,本文选择钨锡多金属硫化物石英脉型（柯树岭和漂塘矿床）和锡钨石英脉型（仙鹅塘矿床）3个矿床石英中的白云母开展40Ar/39Ar年代学研究,测得坪年龄分别是：钨锡多金属硫化物石英脉型是 158.9 ± 1.4 Ma（漂塘）、158.8 ± 1.2 Ma（柯树岭）;钨锡石英脉型的是231.4 ± 2.4 Ma（仙鹅塘）,在反等时线图上,其对应的截距年龄分别是158.8 ± 1.6 Ma、158.7 ± 1.9Ma和232.5 ± 2.4 Ma。由此表明,在崇余犹矿集区内存在两个不同成矿时期,即以黑钨矿为主的多金属硫化物石英脉型矿床形成于中侏罗世,集中于160~150Ma之间,与南岭地区钨锡矿床的主成矿期是一致的;而以锡石为主的,并含有大量白钨矿的石英脉型矿床可形成于印支期  相似文献   

赣南淘锡坑钨多金属矿床花岗岩和云英岩岩石特征及云英岩中白云母40Ar/39Ar定年     

guochunli 《地质学报》2008,82(1):1274-1284

赣南崇义县淘锡坑钨矿位于南岭东西向构造带东段,属于以黑钨矿石英脉型为主的钨多金属矿床。矿床形成与燕山期中酸性岩浆作用有密切关系,石英矿脉受一组北西向断裂控制,穿切新元古界。本文在淘锡坑钨矿区3个揭露到花岗岩体顶部的中段（206、106、56中段）采集到岩体顶部云英岩样品,利用40Ar/39Ar同位素定年测得云英岩中的白云母的坪年龄分别为152.7 ± 1.5 Ma（206中段）,153.4 ± 1.3 Ma（106中段）,155.0 ± 1.4 Ma（56中段）。与前人用其他方法测定的花岗岩成岩和成矿年龄几乎一致。花岗岩和云英岩全岩稀土元素均具有M型四分组效应和强烈的Eu亏损特征,反映出花岗质岩浆经历了高度分异演化及其岩体结晶晚期流体/熔体相互作用。综合前人在南岭地区同类矿床的研究资料,可知南岭地区160～150Ma成岩成矿作用主要分布于南岭中-东段,可能为大陆边缘弧后岩石圈伸展的构造动力学背景的产物。  相似文献   

东喜马拉雅构造结岩体冷却的⁴⁰Ar/³⁹Ar年代学研究   总被引：2，自引：1，他引：1  

龚俊峰  季建清  陈建军  桑海清  李宝龙  刘一多  韩宝福 《岩石学报》2008,24(10):2255-2272

  相似文献   

广州在沿海开放城市的旅游形象定位研究     

徐君亮 《海岸工程》1999,18(2):18-22

根据国际形象设计发展趋势,提出城市旅游形象设计应有３个层次：一是城市旅游整体形象;二是城市旅游吸引物的特色形象;三是旅游企业形象。根据Ｊｅｎｓｅｎ－Ｖｅｒｂｅｋｅ都市旅游产品界定模式,结合广州实际,分析了广州的旅游吸引物,将广州旅游形象定位为（１）商都旅游,包括购物,美食、商务旅游和现代化城市景观的游览;（２）近现代史迹旅游,包括古代史迹和建筑艺术的观赏,其形象口号为“两个中心”,即商贸中心和近现  相似文献   

胶州湾营养盐的现状和变化   总被引：28，自引：3，他引：28  

沈志良 《海洋科学》1997,21(1):60-64

报道了１９９１年５月至１９９４年２月１２个航次胶州湾ＮＯ３－Ｎ，ＮＯ２－Ｎ，ＮＨ４－Ｎ，ＰＯ４－Ｐ和ＳｉＯ３－Ｓｉ的时空分布基本特征，６０年代于至９０年代的变化表明，胶州湾营养盐的浓度和分布已发生显变化。尤其从６０年代至８０年代，３０年来，胶州湾中东部水城ＰＯ４－Ｐ，ＮＯ３－Ｎ和ＮＨ４－Ｎ浓度分别增加２．２，７．３和７．１倍，ＴＯＮ浓度也增加了３．５倍，ＴＩＮ／ＰＯ４－Ｐ从１０增加至２４．２；Ｔ  相似文献   

<Superscript>40</Superscript>Ar-<Superscript>39</Superscript>Ar dating of lamprophyre dykes in the Baimazhai nickel deposit,Yunnan Province,China, and its geological significance     

Bo Li  Zhilong Huang  Tao Guan  Wei Ding 《中国地球化学学报》2008,27(4):351-355

The Baimazhai nickel deposit, Yunnan Province, China, is located in the southern part of the Sanjiang （Tri-river） alkali-rich intrusive rock belt （Sanjiang ARIR）. In this paper was conducted ^40Ar-^39Ar dating of two phlogopites in lamprophyres which are, as dikes, widely distributed in the orefield, and two plateau ages were acquired, i.e., 32.46±0.62 Ma and 32.01±0.60 Ma, respectively （averaging 32.23±0.60 Ma）. The ages are obviously younger than those of the ore-hosted complex and mineralization of the Baimazhai nickel deposit. In combination with the characteristics, it is indicated that lamprophyres in the orefield and those in the Sanjiang ARIR are similar in tectonic setting, mineral assemblage and geochemistry. It is considered that lamprophyres in the orefield are the important component of the Sanjiang ARIR, and the lamprophyres and ore-hosted complex in the orefield represent the products of two times of different magmatic activity from different mantle sources. On the other hand, the age of lamprophyres in the orefield is older than that of the strike-slip shearing of the Ailaoshan-Honghe fault belt, suggesting that the strike-slip shearing of the Ailaoshan-Honghe fault belt is not the factor leading to magmatic activity of lamprophyres in the orefield, while it is more possible that magmatic activity of the Sanjiang ARIR promoted strike-slip shearing of the fault belt.  相似文献   

郯庐断裂带张八岭隆起北段的左旋走滑挤压变形及其~(40)Ar/~(39)Ar定年   总被引：4，自引：0，他引：4  

张青  朱光  刘国生  C.Teyssier  W.J.Dunlap 《地学前缘》2008,15(3):234-249

郯庐断裂带张八岭隆起北段,自西向东分别出露北北东向的韧性滑脱变形带、脆-韧性过渡带和脆性的前陆褶断带。韧性滑脱变形带内的张八岭群片岩,广泛发生了低绿片相背景下的糜棱岩化。其中呈现为平缓的糜棱面理和近南北向的矿物拉伸线理。显微构造及石英C轴组构分析显示,该韧性滑脱带一致为上盘向南的运动。该带以东依次变为上盘向南南东→南东的逆冲活动,总体上为左旋走滑挤压变形带。张八岭群所在的韧性变形带为深部陡立走滑构造与浅部脆性构造之间的滑脱变形带,其间的差异走滑变形,造成了该滑脱层在总体向北运动中出现上盘向南的剪切变形。对6处张八岭群片岩中15个不同粒级白云母的40Ar/39Ar定年指示,变形发生在(236.2±0.5)~(238.0±0.4)Ma的中三叠世晚期。这表明郯庐断裂带的左行平移发生在华北与华南板块碰撞的深俯冲阶段,起源于陆内转换断层。  相似文献   

石笋流体包裹体中的惰性气体及其在重建长江中游古温度变化中的作用   总被引：2，自引：0，他引：2  

方念乔  胡超涌 《地学前缘》2008,15(4):132-137

文中讨论了一种评估古气温变化的新方法。我们成功地利用石笋流体包裹体所捕获的Xe/Ar比值,重建了末次冰盛期以来盛行东亚季风的长江中游地区的气候演化。一种表达成ln(CXe/CAr)的对数式被证明与冷暖周期变化具有密切的关系。从研究的石笋中所提出的δ13C与Mg/Ca曲线一般随区域古气温波动而变化,但不能排除其中有另类气候信号的叠加。我们的工作则明确地指出,流体包裹体所记录的Xe/Ar在各种反映温度变化的替代指标中可能是最好的一种。整体而言,ln(CXe/CAr)曲线与那些基本随暖期和冷期振荡的曲线保持一致。将稀有气体曲线与δ13C和Mg/Ca信号整合对比之后,我们在研究区划分出末次冰盛期以来8组暖/冷旋回。整合后的气温变化模式合理地解释了过去20000年里的区域环境变化。  相似文献