Mantle derived crystal-poor rhyolitic ignimbrites: Eruptive mechanism from geochemical and geochronological data of the Piedra Parada caldera,Southern Argentina     

Eugenio Aragon  Antonio Castro  Juan Diaz-Alvarado  Lucio Pinotti  Fernando D'eramo  Manuel Demartis  Jorge Coniglio  Irene Hernando  Carmen Rodriguez 《地学前缘(英文版)》2018,9(5):1529-1553

Trace elements, isotopic modeling and U-Th-Pb SHRIMP zircon age constraints are used to reconstruct the eruption history and magmatic processes of the Piedra Parada Caldera. In the early Eocene, the crystal-poor Barda Colorada ignimbrite(BCI), having 15% micro-porphyritic crystals with respect to magmatic components, erupted a volume estimated in more than 300 km~3. The Piedra Parada caldera is located in the Patagonian Andes foreland, at the southern end of the calderas field of the Pilcaniyeu Volcanic Belt(PVB). This belt is related to an extensional tectonic setting as a result of the collision of the Farallon-Aluk ridge with South America, which enabled the development of a transform ocean/continental plate margin followed by the detachment of the Aluk plate and the opening of a slab window. The BCI extra-caldera Plateau is a 100 m thick deposit, having a lower unit with high silica(Si O_2 76 wt.%),potassium poor rhyolitic composition(trondhjemitic like magma), and an upper unit with normal to high potassium rhyolitic composition(granitic like magma). A trace elements modeling of the BCI units shows that the BCI lower and upper units did not evolve from fractionation or immiscibility in the shallow magma reservoir. The BCI also have a primitive isotopic signature(initial87 Sr/86 Sr =0.7031-0.7049 and ε_(Nd)= +3.4 to +3.65). Thus, tectonic, compositional and isotopic constraints suggest the fast ascent of high silica magmas to a shallow reservoir, and point to an upper mantle origin for these rhyolitic magmas in a transitional(Orogenic-Anorogenic) tectono-magmatic setting. U-Th-Pb SHRIMP zircon crystallization ages of the Syn-caldera stage BCI units(56 -51.5 Ma) show a protracted life of 5 Ma for this caldera reservoir. The age of 52.9 ± 0.3 Ma is considered the best fit for the possible maximum age for the caldera collapse. The Late-caldera magmatism has trachyandesitic and rhyolitic compositions.The trace element modeling suggests that these rhyolites evolve from the trachyandesites and do not evolve from the BCI residual magma. The trachyandesites have U-Th-Pb SHRIMP zircon crystallization ages of 52 ± 1 Ma, suggesting that the caldera eruption was triggered by the arrival of the trachyandesitic magma.  相似文献   

Volcanism of the southern part of the Sredinny Range of Kamchatka in the Neogene-Quaternary     

A.O. Volynets  M.M. Pevzner  M.L. Tolstykh  A.D. Babansky 《Russian Geology and Geophysics》2018,59(12):1577-1591

Based on the geochemical characteristics of the Miocene-Quaternary volcanic rocks of the Sredinny Range of Kamchatka, we divide it into northern and southern provinces; the latter comprises the “eastern”, “western”, and “central” flanks. We present new data on the composition of Neogene-Quaternary volcanic rocks in the southern part of the Sredinny Range of Kamchatka: Khangar and Icha volcanic massifs and Mt. Yurtinaya on the “western” flank, Bystrinsky and Kozyrevsky Ridges on the “eastern” flank, and Anaunsky Dol and Uksichan massif located in between. We show systematic differences in the composition of rocks from the “western” and “eastern” flanks. During the Neogene, a typical island-arc volcanism took place within the “eastern” flank. Quaternary volcanic rocks of this area have both island-arc and within-plate geochemical features. We propose to call rocks of this type hybrid rocks. Within the “western” flank, hybrid volcanism has been manifested since the Neogene, while typical island-arc rocks are not found. Magma generation processes on the “western” flank of the Sredinny Ridge are influenced by an enriched mantle source; the effect of fluid is less pronounced here as compared to the rocks of the “eastern” flank, where it is clearly traced.  相似文献   

新疆准噶尔古生代洋盆闭合时限——来自卡拉麦里地区石炭纪碎屑锆石U-Pb年代学的约束   总被引：4，自引：0，他引：4  

白建科  陈隽璐  唐卓  张越 《地质通报》2018,37(1):26-38

新疆准噶尔古生代洋盆闭合时限对中亚造山带古生代构造格局及演化研究具有重要意义。东准噶尔卡拉麦里断裂带南缘广泛出露石炭纪陆相粗碎屑岩系,沉积相分析表明其形成于扇三角洲沉积环境。依据区域地层对比、岩石组合特征及地层接触关系,将其重新厘定为山梁砾石组。选择西段滴水泉和东段双井子2个地区的山梁砾石组剖面进行地层对比,并在2个剖面底部采集粗砂岩样品进行LA-ICP-MS锆石U-Pb年龄测定,获得最年轻的碎屑锆石年龄分别为349±4Ma和355±3Ma,代表山梁砾石组沉积时代晚于349Ma,应为早石炭世早期。碎屑锆石年龄分布特征及砾石成分表明,其物源主要来自断裂带北侧的泥盆纪火山岩。在分析前人资料的基础上,认为山梁砾石组碎屑岩系是卡拉麦里造山带强烈隆升造山过程的沉积学响应,形成于前陆盆地,限定了准噶尔古生代洋盆闭合时限在早石炭世早期之前。  相似文献   

山西新生代汉诺坝玄武岩成因探讨     

张玉生 《中国地质调查》2018,5(6):58-67

根据区域地质调查资料,对山西新生代汉诺坝玄武岩的4个火山洼地、7条剖面进行研究。各个火山旋回底部先出现拉斑玄武岩,向上变为碱性玄武岩,岩石均富集大离子亲石元素和轻稀土元素。由东向西,火山喷发时间由早到晚,岩浆活动由弱到强,拉斑玄武岩减少,碱性玄武岩增多,亚碱性玄武岩的稀土元素和微量元素丰度降低,碱性玄武岩的稀土元素和微量元素丰度升高。在原始地幔标准化微量元素蛛网图上,亚碱性玄武岩具Nb、Ta负异常(槽)或呈双峰式,为岛弧玄武岩; 碱性玄武岩呈“隆起”状,类似于洋岛玄武岩(OIB)。山西汉诺坝玄武岩是板块俯冲与地幔柱联合作用的结果,以地幔柱成因为主,板块俯冲成因为辅。亚碱性玄武岩向碱性玄武岩转变,可能代表玄武岩以板块俯冲成因为主转为以地幔柱成因为主; 碱性玄武岩由钾质向钠质变化、亚碱性玄武岩向富铁镁演化,可能分别代表地幔柱向浅、板块俯冲向深的演化过程。  相似文献   

Neotectonics and seismicity in southern Patagonia     

Laura Perucca  Patricia Alvarado  Mauro Saez 《Geological Journal》2016,51(4):545-559

Research for evaluation of geologic hazards involving earthquakes and volcanic eruptions in southern Argentina seems to have historically received little attention. Nevertheless, the relatively small work done indicates a Neogene tectonic architecture in the area with capability of generating potential hazardous earthquakes in a growing population region. Seismicity and some morphotectonic evidences of Quaternary activity of the Magallanes–Fagnano left‐lateral fault system in the transform boundary between South America and Scotia plates, are analysed in this paper. This fault system is considered to be an important seismogenic source, responsible for large earthquakes that have occurred in southern Argentina. Some examples from the South and Austral Andean Volcanic Zones are also examined in order to show recent volcanic activity which also generated crustal seismicity. Preliminary hazard estimation clearly shows the presence of both potentially active volcanic centres in southern Patagonia that may also trigger seismicity and the high probability for large crustal earthquake generation. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

东昆仑南缘哥日卓托地区马尔争组砂岩碎屑组成、地球化学特征与物源构造环境分析   总被引：2，自引：0，他引：2  

裴先治  胡楠  刘成军  李瑞保  李佐臣  陈有炘  裴磊  刘战庆  陈国超  杨杰 《地质论评》2015,61(2):307-323

出露于东昆仑南缘布青山构造混杂岩带内的马尔争组沉积地层,其主体为一套沉积于被动大陆边缘构造环境的大陆斜坡相深海-半深海浊积岩。利用砂岩碎屑组分统计分析及岩石地球化学特征研究,探讨物源区源岩类型及其构造环境。砂岩骨架成分统计表明马尔争组砂岩主要类型为长石岩屑砂岩且成熟度较低,砂岩碎屑骨架成分为石英、长石、岩屑,含量平均值分别为44%、21%、35%,Dickinson三角图解显示其物源类型为再旋回造山带物源区和岩浆弧物源区的混合物源。砂岩岩石地球化学特征结果显示,马尔争组砂岩样品SiO,=58.12%~72.98%,均值67.77%,REE配分曲线总体表现为右倾,∑LREE/∑HREE=6.5~12.1,δEu=0.63~0.75,Eu具弱负异常,CIA值为56说明源岩遭受初级强度风化作用,具近源沉积特征。研究结果指示马尔争组砂岩物源区构造环境为大陆岛弧,源岩性质为长英质火山岩和花岗岩类源岩且主要来源于北侧东昆仑造山带加里东期岩浆弧与变质基底,沉积盆地类型为深海半深海盆地。它是古特提斯洋北支布青山阿尼玛卿洋演化历史过程中一次重要的沉积响应。  相似文献   

北京市潜在风道的数值模拟与综合识别     

杨土士  王伟文  常鸣  王雪梅 《地球信息科学学报》2020,22(10):1996-2009

过去从局地尺度和微尺度优化规划和建筑设计的角度,城市规划与建筑学科的研究者提出了构建城市区域通风廊道的思想。但对目前的特大城市和城市群而言,无论城市热岛还是污染物输送都可能涉及更大尺度范围的区域影响。结合自然地理资源条件,对城市外围待发展区域的风道识别和规划,可能更具有现实意义。本文基于空气动力学粗糙长度计算通风指数,从动力学角度初步识别出北京不同区域的通风潜力：① 利用数值模拟输出的1月和7月平均水平风场发现,在背景风较强的冬季,水平风速的分布与下垫面的粗糙度保持高度一致,在北京城区东北方向存在一条明显的风道,在通过城区时受城市下垫面的拖曳影响出现显著的风速下降,在城市下风方向风速又有所回升;② 与热力分析对比发现,夏季城市外的低温区域与盛行风向相悖,偏南方向上的补偿空间面积比冬季小且与作用空间的温差也小,流向城市的可利用风资源匮乏;③ 基于近地面温度和粗糙长度加权计算后得到通风指数,冬季为0~0.25,夏季为0~0.60,数值越小通风能力越强,受季节热力差异影响,冬季通风能力显著优于夏季。④ 进一步结合数值模拟的风速分布,将通风评价结果划分为4个等级,从北京市全域尺度分冬、夏两季识别了北京市的潜在风道,冬季贯穿南北的风道全长约200 km,从城市外围引入风资源,可有效提高城市自净能力,而在背景风较弱的夏季,风道贯通性较差,气流疏导能力弱,亟待区域联动优化城市群发展规划。  相似文献   

苏州土地利用及热岛效应的时空变化     

莫新宇  祝善友  张磊 《地理空间信息》2013,11(1):61-63,81,13

选取苏州作为研究区,分别利用1986年和2004年2个时相的Landsat5 TM影像数据对研究区土地利用/覆盖类型进行分类,并采用热红外波段进行地表温度反演,在此基础上分析了下垫面类型与热岛效应的时空变化,深入研究了下垫面类型改变对热岛效应的影响。结果表明,近20a苏州市城区大范围扩张,土地利用变化剧烈,整体表现为水体、植被向不透水下垫面的高强度转化;城市热岛范围由老城区向四周成倍扩大,热岛强度由3.12°增至4.76°,热岛效应变化与土地利用时空变化之间具有明显的对应关系。  相似文献   

Comparing effects of land reclamation techniques on water pollution and fishery loss for a large-scale offshore airport island in Jinzhou Bay,Bohai Sea,China     

《Marine pollution bulletin》2013,72(1-2):29-40

Plans are being made to construct Dalian Offshore Airport in Jinzhou Bay with a reclamation area of 21 km². The large-scale reclamation can be expected to have negative effects on the marine environment, and these effects vary depending on the reclamation techniques used. Water quality mathematical models were developed and biology resource investigations were conducted to compare effects of an underwater explosion sediment removal and rock dumping technique and a silt dredging and rock dumping technique on water pollution and fishery loss. The findings show that creation of the artificial island with the underwater explosion sediment removal technique would greatly impact the marine environment. However, the impact for the silt dredging technique would be less. The conclusions from this study provide an important foundation for the planning of Dalian Offshore Airport and can be used as a reference for similar coastal reclamation and marine environment protection.  相似文献   

泰国清莱地区三叠纪南邦群碎屑锆石LA-ICP-MS U-Pb年龄及其地质意义     

高海龙  冯庆来  聂小妹  CHONGLAKMANI Chongpan  MONJAI Denchok 《地质通报》2014,33(7):995-1007

对于中国滇西和东南亚地区古特提斯缝合带对比一直存在诸多争议。在泰国清莱地区三叠纪南邦群中采集4件碎屑岩样品,进行岩石学、地球化学和锆石U-Pb测年研究。岩石学和地球化学研究表明,该套碎屑岩的源岩主要为基性—中基性岩石,卷入少量长英质岩石,物源区大地构造背景为岛弧带。所测得最古老锆石U-Pb同位素年龄为3269Ma±29Ma,绝大多数年龄集中形成3个峰值：280~250Ma、500~440Ma和1200~1100Ma,指示清莱地区三叠纪南邦群碎屑物源区主要为清莱岛弧火山岩带西部条带和前泥盆纪变质岩系。碎屑锆石年龄图谱的对比结果表明,原特提斯构造阶段之前,南邦地体与西澳大利亚发育类似构造—热事件;在原特提斯构造阶段之后,其构造—热事件特征与扬子构造域相类似,指示古特提斯洋的主洋盆应该在南邦地体以西,支持清迈构造带代表古特提斯主洋盆的观点。  相似文献