Development of a Continental Volcanic Field: Petrogenesis of Pre-caldera Intermediate and Silicic Rocks and Origin of the Bandelier Magmas, Jemez Mountains (New Mexico, USA)     

Rowe  M. C.; Wolff  J. A.; Gardner  J. N.; Ramos  F. C.; Teasdale  R.; Heikoop  C. E. 《Journal of Petrology》2007,48(11):2063-2091

The Miocene–Quaternary Jemez Mountains volcanic field(JMVF) is the site of the Valles caldera and associated BandelierTuff. Caldera formation was preceded by > 10 Myr of volcanismdominated by intermediate composition rocks (57–70% SiO₂)that contain components derived from the lithospheric mantleand Precambrian crust. Simple mixing between crust-dominatedsilicic melts and mantle-dominated mafic magmas, fractionalcrystallization, and assimilation accompanied by fractionalcrystallization are the principal mechanisms involved in theproduction of these intermediate lavas. A variety of isotopicallydistinct crustal sources were involved in magmatism between13 and 6 Ma, but only one type (or two very similar types) ofcrust between 6 and 2 Ma. This long history constitutes a recordof accommodation of mantle-derived magma in the crust by meltingof country rock. The post-2 Ma Bandelier Tuff and associatedrhyolites were, in contrast, generated by melting of hybridizedcrust in the form of buried, warm intrusive rocks associatedwith pre-6 Ma activity. Major shifts in the location, styleand geochemical character of magmatism in the JMVF occur withina few million years after volcanic maxima and may correspondto pooling of magma at a new location in the crust followingsolidification of earlier magma chambers that acted as trapsfor basaltic replenishment. KEY WORDS: crustal anatexis; fractional crystallization; Jemez Mountain Volcanic Field; Valles Caldera; radiogenic isotopes; trace elements  相似文献   

中条山铜矿峪斑岩铜矿金属硫化物的铼-锇同位素年龄及地质意义   总被引：11，自引：4，他引：7  

陈文明  李树屏 《矿床地质》1998,17(3):224-228

Re- Os同位素测年法是测定金属矿床成矿年龄较直接、有效的方法。作者对中条山铜矿峪斑岩铜矿中的含辉钼矿硫化物采用 ICP- MS同位素稀释法进行 Re- Os同位素年龄测定。首次获得 2个 Re- Os同位素等时线年龄 ,其值分别为 (2 94 7± 2 8)× 10 6a与 (2 10 8± 32 )× 10 6a。这些年龄数据有力地说明铜矿峪斑岩铜矿的形成不是一个单一的成矿过程 ,而是一个多期的复合成矿过程。它为确定铜矿峪斑岩铜矿的成矿年龄及建立该矿床的成矿演化模式奠定了重要基础  相似文献   

Petrogenesis of the Tanzawa plutonic complex, central Japan: Exposed felsic middle crust of the Izu–Bonin – Mariana arc     

SHINICHI  KAWATE & MAKOTO  ARIMA 《Island Arc》1998,7(3):342-358

The Miocene Tanzawa plutonic complex, consisting mainly of tonalite intrusions, is exposed at the northern end of the Izu–Bonin – Mariana (IBM) arc system as a consequence of collision with the Honshu Arc. The Tanzawa plutonic rocks belong to the calc-alkaline series and exhibit a wide range of chemical variation, from 43 to 75 wt% SiO₂. They are characterized by relatively high Ba/Rb and Ce/Nb ratios, and low abundances of K₂O, LIL elements, and rare earth elements (REE). Their petrographic and geochemical features indicate derivation from an intermediate parental magma through crystal fractionation and accumulation processes, involving hornblende, plagioclase, and magnetite. The Tanzawa plutonic complex is interpreted to be the exposed middle crust of the IBM arc, which was uplifted during the collision. The mass balance calculations, combining data from melting experiments of hydrous basaltic compositions at lower-to-middle crustal levels, suggest that parental magma and ultramafic restite were generated by dehydration partial melting (∼ 45% melting) of amphibolite chemically similar to low-K tholeiitic basalt. Partial melting of hydrated mafic lower crust might play an important role in felsic middle-crust formation in the IBM arc.  相似文献   

西昌邛海泸山旅游地质资源特征   总被引：1，自引：0，他引：1  

尤显贤 《四川地质学报》1998,(3)

西昌邛海、泸山山水浑然一体,以其邛池夜月、碧波朝阳、渔村夕照、平湖秋月、三教合一寺庙群落同建于山中一道路上而闻名遐迩。邛海、泸山旅游资源十分丰富,种类齐全,并以四川省第二大天然湖泊优势,独特气候而名满天下。  相似文献   

茅山山脉东麓的砾岩层位和时代   总被引：1，自引：1，他引：0  

徐学思  胡连英 《江苏地质》1998,22(1):19-22

通过对茅山东麓砾岩层的实地研究,以５条剖面的岩性、产状和生物等特征为依据,将砾岩分为三类,并分别论述其层位时代。提出了与前人不同的观点。  相似文献   

中国地貌基本形态划分的探讨   总被引：16，自引：1，他引：15  

李钜章 《地理研究》1987,6(2):32-39

本文从地貌学的性质出发,确定形态分类的指导原则应着眼于反映成因的形态。运用模糊数学方法建立形态基本类型的分类系统。给出进一步划分基本形态类型的两个分类方案,并分析它们的优缺点。  相似文献   

Risk, rescue and emergency services: The changing spatialities of Mountain Rescue Teams in England and Wales     

Richard Yarwood 《Geoforum》2010,41(2):257-270

This paper considers the role of the emergency services in society and, in particular, their role in controlling, mitigating and resolving risk. Using a network approach, Mountain Rescue Teams are studied in order to examine how people, agencies, animals, technology and knowledge are deployed to resolve emergencies. The paper traces the changing nature of risk in rural places and the impact of state regulation on the deployment, spatialities and practices of the emergency services. In doing so, it argues that greater attention should be paid to the emergency services by geographers.  相似文献   

大别山北缘千鹅冲斑岩型钼矿床锆石U-Pb和辉钼矿Re-Os年代学及其地质意义   总被引：10，自引：0，他引：10  

杨梅珍  曾键年  覃永军  李法岭  万守权 《地质科技情报》2010,29(5)

河南省光山县千鹅冲钼矿床是大别山地区近年最新发现的大型斑岩型钼矿床。采用LA-ICP-MS锆石U-Pb和ICP-MS辉钼矿Re-Os同位素精细测年技术,对与成矿相关的宝安寨钾长花岗岩、千鹅冲花岗斑岩2个锆石样品和4个细网脉型钼矿石中的辉钼矿样品进行了同位素年代学测定,分别获得(135.3±1.9),(128.8±2.6),(127.82±0.87)Ma的同位素年龄。结果表明,千鹅冲钼矿床成矿作用时间与千鹅冲花岗斑岩成岩作用时间一致,晚于大别山巨量花岗质岩浆活动近7Ma,它们为统一构造背景同期不同次岩浆作用的产物。与成矿相关岩体的地球化学研究结果显示,岩体具有低Sr(wB400×10-6)、低Yb(wB1.8×10-6)、中等程度Eu负异常[δ(Eu)0.5]、轻重REE强烈分异{[w(La)/w(Yb)]N24}等特征,其Sr-Nd同位素显示较高的[N(87Sr)/N(86Sr)]i(0.70669～0.72422,变化较大)和极低的ε(Nd)(t)(-18.01～-21.37)。综合分析表明成岩成矿作用发生在大别造山带碰撞造山后构造体制由挤压收缩向伸展的转折时期,与成矿有关的酸性侵入岩是加厚陆壳部分熔融作用的产物。千鹅冲斑岩型钼矿床与成矿带内汤家坪、大银尖、天目山、银山、东沟钼矿床在成矿时间及成矿岩体地球化学特征的显著差异,反映它们形成于造山带演化的不同历史时期和不同的构造动力学背景。  相似文献   

太行山北段赤瓦屋岩体锆石SHRIMP U-Pb年龄及其意义   总被引：2，自引：0，他引：2  

刘阳 《地质与勘探》2010,46(3):442-447

太行山北段阜平南部赤瓦屋岩体中心相-过渡相-边缘相岩性分别为斑状花岗闪长岩-花岗闪长岩-石英闪长岩。本文选取赤瓦屋岩体边缘相中的两个样品进行了SHRIMP U-Pb年代学数据测试,所得两组年龄值约为134.0Ma、139.8Ma,与同方法所测得的麻棚岩体年龄125.0±3.4Ma相比略早。结合前人资料,赤瓦屋岩体年龄值的测试结果进一步证实了中国东部及东亚地区中生代岩浆活动存在从南东-北西方向的年轻化趋势,并为太行山中生代岩浆活动与古太平洋板块的俯冲有关提供了证据。  相似文献   

南祁连山前区中生代晚期古构造特征的研究     

肖安成  汪立群杨树锋  马立协沈中延  王亮  吴磊  陈元忠 《地质科学》2010,45(1):146-156

南祁连山前区可以分为露头和盆地区两个不同的大地构造单元,本区晚中生代构造活动强烈,控制了新生代的沉积过程和现今中生界残余层序的分布。本文提出了均匀平板状沉积体后期的构造变形可以利用古地质图以及高精度残余地层厚度的变化规律判断古构造带的分析方法,并且对于研究区中生代晚期的古构造特征进行了分析。露头区主要利用古地质图分析方法,研究区集中在赛什腾山-埃姆尼克山北缘的鱼卡和红山地区。盆地区主要利用中生界残余厚度图的分析方法,研究区集中在赛什腾山-埃姆尼克山南侧的赛什腾南部凹陷和马海凸起地区。通过这4个地区古构造特征的研究,提出南祁连山前区中生代晚期在区域性隆升的背景下,形成了一系列古构造带,古构造活动的特点是形成北西-北北西走向的背斜和向斜构造,这些褶皱的波长为15～20 km,为中尺度规模。同时指出,中国西部多数地区均缺失上白垩统,暗示着当时的中亚地区存在一个广阔的晚白垩世古高原。  相似文献