常用玄武岩构造环境判别图解

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玄武岩PPT课件

玄武岩PPT课件
称之为伊丁玄武岩。 辉石玄武岩——富含Px斑晶 斜长玄武岩——富含Pl斑晶,又称斜斑玄武岩
(三) 喷 出 岩
3.种属划分及主要种属岩性特征 (3)按构造类型及特殊结构划分
气孔状玄武岩 玄武浮岩(气孔>50%,教材中称熔渣) 杏仁状玄武岩 枕状玄武岩 球颗玄武岩 玻基玄武岩(或玻基斑状玄武岩) 隐晶质块状玄武岩
基质结构则有:
间粒结构(粗玄结 构):较自形的长板状斜 长石假晶构成的格架中充 填多个辉石及Mt细小颗 粒。
(三) 喷 出 岩
2.结构、构造
间隐结构:较自形的长条状Pl微晶间隙中充填为玻璃-隐晶 质。
间粒间隐结构:(填间结构、填隙结构或拉斑玄武结构)是 上述两者的过渡类型。自形条状斜长石微晶构成的空隙中既充 填有粒状Py和Mt,也有玻璃物质。
温度的升高
挥发组分的加入
压力的降低
5、玄武质岩浆的形成
• 不同构造部位诱发源岩熔融因素的差异
洋中脊和大陆裂谷——减压熔融 俯冲带——下插板块升温,引起熔融 俯冲带——下插板块脱水,引起上部地幔楔
部分熔融—挥发组分的加入
升温和挥发组分的加入
其中杏仁体成分常见为:绿泥石、方解石、石英、蛋白石、 玉燧、沸石等。
(三) 喷 出 岩
3.种属划分及主要种属岩性特征
(1)据粒度划分(适用于野外) 粒玄岩(粗粒玄武岩)——全晶质,粒度相对较粗,
>1mm,肉眼可辩,具间粒结构。
(也可以称为粗玄岩)
中粒玄武岩——粒度<1mm,肉眼可见矿物颗粒,
但无法辩认矿物成分。
玄武岩——粒度<0.1mm(微晶-隐晶质-半晶质,
镜下基质可具间隐结构)。
玻璃质玄武岩——全部或绝大部分为玻璃质组成。

玄武岩类形成的大地构造环境的图解判别

玄武岩类形成的大地构造环境的图解判别

玄武岩类形成的大地构造环境的Th/Hf-Ta/Hf图解判别汪云亮 张成江 修淑芝WA N G YunL iang,ZHA NG Cheng Jiang and XIU ShuZhi成都理工学院三系,成都 6100593th Depar tment of Che ngd u Univ er sity of T echnology,Cheng du610059,C hina2000-07-14收稿,2001-03-28改回.Wang YL,Zhang CJ and Xiu SZ.2001.Th/Hf-Ta/Hf identification of tectonic setting of basalts.Acta Petrologica Sinica, 17(3):413-421Abstract T h,T a a nd Hf are r efr act or y str ong m agmat ophile elements.Because that the geo chem ical behav ior o f T h,T a and Hf is simila r during m agmat ic actio n,the r atio s of T h,T a and Hf co uld r estor e pro cesses o f mantle par tial,mag matic fr act ional cr ystalliza tio n,mantle fractionatio n and so o n.T he T h/Hf and T a/Hf ratios of ba salts,especially primary o ne, reflect the differ ent iation of T h,T a and Hf o f its sour ce r eg ion.In gener al,there is a clo se relationship bet ween these character istics and t ect onic setting.Based o n t he r atios amo ng T h,T a and Hf o f basalts fo rmed fro m typical tectonic setting of t he w o rld,w e pr opose a new tectonic identificat ion scheme of basalts on the T h/Hf and T a/Hf double lo gar ithmic plot. Key words Basalt,T ecto nic setting,T h/Hf-T a/Hf ident ification diagr am.摘 要 T h,T a,Hf是一组耐熔强亲岩浆元素,由于地球化学性质的相似性,其相互之间的比值关系能将深部作用的地球化学过程较好地恢复出来。

图文并茂,瞬间学会识别岩浆岩,沉积岩,变质岩!一学就会

图文并茂,瞬间学会识别岩浆岩,沉积岩,变质岩!一学就会

图文并茂,瞬间学会识别岩浆岩,沉积岩,变质岩!一学就会岩浆岩,沉积岩,变质岩,这三种岩石是最基本的岩石。

1、(岩浆岩)--顾名思义,就是直接由岩浆形成的岩石,指由地球深处的岩浆侵入地壳内或喷出地表后冷凝而形成的岩石。

又可分为侵入岩和喷出岩(火山岩)。

2、沉积岩,顾名思义,就是由沉积作用形成的岩石,指暴露在地壳表层的岩石在地球发展过程中遭受各种外力的破坏,破坏产物在原地或者经过搬运沉积下来,再经过复杂的成岩作用而形成的岩石。

沉积岩的分类比较复杂,一般可按沉积物质分为母岩风化沉积、火山碎屑沉积和生物遗体沉积。

沉积岩主要包括有石灰岩、砂岩、页岩等。

3、变质岩,顾名思义,就是经历过变质作用形成的岩石,指地壳中原有的岩石受构造运动、岩浆活动或地壳内热流变化等内应力影响,使其矿物成分、结构构造发生不同程度的变化而形成的岩石。

又可分为正变质岩和负变质岩。

......................................................................................................——岩浆岩/火成岩——Igneous Rock代表:花岗岩、安山岩、玄武岩定义:岩浆岩由地幔或地壳的岩石经熔融或部分熔融(partial melting)的物质如岩浆冷却固结形成的。

岩浆可以是由全部为液相的熔融物质组成,称为熔体(melt);也可以含有挥发分及部分固体物质,如晶体及岩石碎块。

01石英安山岩Dacite火山喷出岩的一种,有斑晶的特征,与安山岩的组成成分近似,但含有石英的结晶。

02角闪安山岩Hornblende Andesite属于钙碱性系列中性喷出岩,是暗色矿物主要为角闪石的安山岩。

具斑状结构,斑晶由中长石和角闪石组成,角闪石多为棕色。

03角闪紫苏辉石安山岩大多呈紫红灰色或粉红灰色,里面所含的铁镁矿物以角闪石及紫苏辉石为主。

04紫苏辉石安山岩05辉石安山岩Pyroxene Anderite以辉石为主要铁镁矿物斑晶的安山岩。

玄武岩分类、特征及形成构造背景

玄武岩分类、特征及形成构造背景

玄武岩分类、特征及形成构造背景玄武岩,洋壳主要组成,属基性火山岩。

是地球洋壳和月球月海的最主要组成物质,也是地球陆壳和月球月陆的重要组成物质。

1546年,G.阿格里科拉首次在地质文献中,用basalt这个词描述德国萨克森的黑色岩石。

汉语玄武岩一词,引自日文。

日本在兵库县玄武洞发现黑色橄榄玄武岩,故得名。

玄武岩是一种基性喷出岩,其化学成分与辉长岩或辉绿岩相似,SiO2含量变化于45%~52%之间,K2O+Na2O含量较侵入岩略高,CaO、Fe2O3+FeO、MgO含量较侵入岩略低。

矿物成份主要由基性长石和辉石组成,次要矿物有橄榄石,角闪石及黑云母等,岩石均为暗色,一般为黑色,有时呈灰绿以及暗紫色等。

呈斑状结构。

气孔构造和杏仁构造普遍。

玄武岩体积密度为2.8~3.3g/cm3,致密者压缩强度很大,可高达300MPa,有时更高,存在玻璃质及气孔时则强度有所降低。

玄武岩耐久性甚高,节理多,且节理面多成五边形或六边形,构成柱状节理。

性脆,因而不易采得大块石料,由于气孔和杏仁构造常见,虽玄武岩地表上分布广泛,但可作饰面石材不多。

主要成份玄武岩的主要成份是二氧化硅、三氧化二铝、氧化铁、氧化钙、氧化镁(还有少量的氧化钾、氧化钠),其中二氧化硅含量最多,约占百分之四十五至五十左右。

玄武岩的颜色,常见的多为黑色、黑褐或暗绿色;在腾冲火山群附近的玄武岩多为青灰色,也有暗红色、橙色、黄色的。

因其质地致密,它的比重比一般花岗岩、石灰岩、沙岩、页岩都重。

但也有的玄武岩由于气孔特别多,重量便减轻,甚至在水中可以浮起来。

因此,把这种多孔体轻的玄武岩,叫做"浮石",在云南腾冲马站火山群脚下附近的村寨里,人们把这些多孔体轻的玄武岩叫做“泡石”。

成分玄武岩根据其成分不同可以分为拉斑玄武岩、碱性玄武岩、高铝玄武岩。

结构按其结构不同可分为气孔状玄武岩、杏仁状玄武岩、玄武玻璃。

充填矿物按其充填矿物不同可分为橄榄玄武岩、紫苏辉石玄武岩等。

实验七 综合实验:玄武岩的成分与结构成因分析

实验七 综合实验:玄武岩的成分与结构成因分析

和 地 幔
Cr2O3 0.28 0.03 Al2O3 0.06 0.04
0.00 0.17 0.40 0.41 0.19 8.01 0.05 0.35 0.04 4.73 1.46 5.02 0.16 0.47 1.34 0.00

FeO 10.15 7.82 10.40 7.74 4.73 4.68 10.07 2.88 20.09 14.91
方辉橄榄岩尖晶石二辉橄榄岩斜方辉石岩二辉石岩单斜辉石岩斜方辉石岩斜方辉石岩橄榄斜方辉石岩橄榄石橄榄石单斜辉石单斜辉石斜方辉石斜方辉石二辉橄榄岩二辉橄榄岩二辉石岩单斜辉石岩单斜辉石岩橄榄二辉石岩橄榄岩橄榄岩辉石岩辉石岩90401010橄榄单斜辉石岩超镁铁质岩的分类32典型结构a
实习七 河北汉诺坝玄武岩的成分和结构成因分析
51
55
58
14.9
17.1
18.2

Sm
10.5
10.9
11.4
4.2
4.5
4.6

Eu
3.4
3.57
3.72
1.52
1.61
1.62

Tb
1.18
1.2
1.15
0.66
0.69
0.73
Yb
0.94
0.96
0.88
1.47
1.39
1.29
Lu
0.14
0.14
0.11
0.21
0.2
0.18

岩性

8
Al ka li ne
6
4
2
Su balk ali ne
0 35 40 45 50 55 60 65 70 75 80 85

高考地理中的玄武岩

高考地理中的玄武岩

一、什么是玄武岩?玄武岩是一种基性喷出岩,由火山喷发出的岩浆在地表冷却后凝固而成的一种致密状或泡沫状结构的岩石,属于岩浆岩。

同时也是地球洋壳和月球月海(注:月海是指月面上的低洼平原,月球观测的暗色矿物)的主要组成物质。

1.特点(可进行野外辨别)(1)颜色:暗色,多为黑色、黑褐色、暗绿色(2)化学成分:二氧化硅SiO2、三氧化二铝Al2O3、氧化铁Fe2O3、氧化钙CaO2.矿物成分:基性长石、辉石(隐晶质结构);橄榄石、角闪石、黑云母等3.构造(1)气孔构造:当岩浆达到地表时,压力突然减小,气体泡膨胀并迅速释放。

这导致岩浆中的气体迅速逸出,形成大量气孔。

岩浆在地表冷却并逐渐固化成岩石,其中的气孔被保留下来。

这些气孔通常呈现圆形或椭圆形,大小不一。

(2)杏仁构造:指玄武岩中较大的晶体包围着较小的晶体形成的特殊结构。

它得名于杏仁的形状,因为这种结构在岩石切面上呈现出类似杏仁的形状。

(重点:气孔被其他物质填充)4.柱状节理:岩浆冷却形成的。

随着温度的下降,熔岩的体积开始收缩、开裂,由于外界温度低,岩浆内部温度高,因此开裂是从外向内贯穿岩体,形成六方柱状节理。

柱状节理都是沿着冷却面的垂直方向生长,常见的柱状节理都是垂直于地面。

5.产地区域:主要分布在福建省福鼎市、河南省洛阳市蔡店乡、安徽省明光市、云南腾冲火山等洛阳市蔡店乡、安徽省明光市、云南腾冲火山等地区。

6.主要用途:生产铸石的主要原料;化工、建材、冶金、轻工等工业领域;铁路、公路运输石料中的材料。

二、玄武岩地貌玄武岩地貌,作为大自然鬼斧神工的杰作,以其独特的外形特征和丰富的形态类型吸引着人们的目光。

它是由火山喷发出的岩浆冷却后凝固而成的一种岩石,广泛分布于全球各地,特别是在火山活动频繁的地区。

1.玄武岩地貌类型玄武岩地貌的形态丰富多样,常见的有桌状山(或称方山)、玄武岩(熔岩)高原和玄武岩(熔岩)台地等。

桌状山,顾名思义,山顶平坦如桌,四周则是陡峭的边坡,形成了一种独特的地貌景观。

第05讲玄武岩及其相关岩类

第05讲玄武岩及其相关岩类
(B)爆发相——火山锥(volcanic cone):爆发式喷发 (explosion)为主,高粘度和富挥发份的酸性岩浆,由熔岩 和火山碎屑岩组成,中心为火山口或破火山口。也有爆发-宁 静相间。
(C)侵出相——产状岩钟、岩针、岩穹:侵出(extrusion) 方式喷出,高粘度低挥发份酸性岩浆,产在火山通道上部。
侵入岩相:深成相、中深成、浅成相
火山岩相:陆相(可再分)、海相
出露的岩基
3_17
浅成相
捕虏体 岩基
中成相 深成相
岩床 岩盆 岩盖 整合侵入体
不整合侵入体
深成侵入岩相
岩墙 岩株
侵入岩的产状和侵入岩相示意图
第一节 火山岩的一般特点及分类
火山灰流
盛行风
岩屑崩落
1、火山岩的野外 产状和火山岩相
喷气孔
火山泥流
杏仁状构造
4、 主要种属特征 碱性系列
碱性橄榄玄武岩 (alkali olivine basalt)
橄榄粗安岩(碱性橄榄玄武岩的 变种)
(mugearite)
(无紫苏辉石,含钛较高的 普通辉石和透辉石,斜长石 和钾长石)
(斑晶为更长石常见透长石 反应边、橄榄石、钛辉石); 基质具钾长石
4、 主要种属特征 碱性系列
• 思考题(教材)
3) 熔融机制(1):升温
升温后,地温梯度向固相线平移
“正常”的大洋岩石圈地温梯度
3)熔融机制(2):减压
减压后的地温梯度
“正常”的大洋岩石圈地温梯度
3)熔融机制(3):增加挥发份(尤其是H2O)
H2O饱和的固相线
地温梯度
干体系的固相线
2、玄武岩的原生岩浆问题:
原生岩浆(primary magmas):直接由地幔熔融产生的岩浆。 从地幔源区产生后,没有经过成分的改变,而直接上升到

常用玄武岩构造环境判别图解

常用玄武岩构造环境判别图解
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。境环造 构种四等OHS、BAC、TKL、BFO分区以可则解图3F-2F 。岩武玄的境环造构同不种几等)NOC和BIO 括包(BPW、OHS 、BAC+TKL、BFO分区以可解图2F-1F 能功解图 1
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玄武岩的考题重点大地构造环境汇总

玄武岩的考题重点大地构造环境汇总

关于北京大学硕士研究生岩石学考题中的玄武岩的成因与大地构造环境的内容第一节:玄武岩的基本概念及常用分类:玄武岩(Basalt:是一种基性喷出岩,由火山喷发出的岩浆在地表冷却后凝固而成的一种致密状或泡沫状结构的岩石,属于岩浆岩。

其岩石结构常具气孔状、杏仁状构造和斑状结构,有时带有大的矿物晶体,未风化的玄武岩主要呈黑色和灰色,也有黑褐色、暗紫色和灰绿色的。

玄武岩的结构:玄武岩结晶程度和晶粒的大小,主要取决于岩浆冷却速度。

如果是冷却较慢,比如一天降几度,则形成的是几毫米大小、等大的晶体;如果是快速冷却比如一分钟降上百度,则形成的是细小的针状、板状晶体或非晶质玻璃。

因此在通常的地表条件下,玄武岩主要是呈细粒至隐晶质或玻璃质结构,少数为中粒结构。

常含橄榄石、辉石和斜长石斑晶,构成斑状结构。

斑晶在流动的岩浆中可以聚集,称聚斑结构。

这些斑晶可以在、在玄武岩浆通过地壳上升的过程中形成,也有可能于喷发前巨大的岩浆储源中形成。

基质结构变化大,随岩流的厚薄、降温的快慢和挥发组分的多寡,在全晶质至玻璃质之间存在各种过渡类型,但主要是间粒结构、填间结构、间隐结构,较少次辉绿结构和辉绿结构。

玄武岩构造与其固结环境有关。

陆上形成的玄武岩,常呈绳状构造、块状构造和柱状节理;水下形成的玄武岩,常具枕状构造。

而气孔构造、杏仁构造可能出现在各种玄武岩中。

玄武岩的组成:玄武岩的化学成分与辉长岩相似,主要是二氧化硅、三氧化二铝、氧化铁、氧化钙、氧化镁(还有少量的氧化钾、氧化钠,其中SiO2含量最高,一般含量在45%~52%之间,其中K2O+Na2O含量较侵入岩略高,CaO、Fe2O3+FeO MgO含量较侵入岩略低。

玄武岩的矿物成份主要由基性长石和辉石组成,次要矿物有橄榄石,角闪石及黑云母等。

玄武岩的分类:玄武岩根据组成矿物、结构、形成环境等不同分为许多品种(1按次要矿物的不同,可划分为橄榄玄武岩、紫苏辉石玄武岩等(2按结构构造,可分为气孔状玄武岩、杏仁状玄武岩等(3按化学成分和矿物成分,可分为高铝玄武岩、碱性玄武岩和拉斑玄武岩等(4按碱度划分,可分为碱性玄武岩、过渡玄武岩、拉斑玄武岩、钙碱性玄武岩和钾玄岩;(5按形成环境分,包括形成于陆地拉张环境的大陆溢流玄武岩和形成于海底扩张带的洋底玄武岩。

区分大陆玄武岩和弧玄武岩的地球化学准则(夏林祈老师)

区分大陆玄武岩和弧玄武岩的地球化学准则(夏林祈老师)

Earth-Science eviews
2014, V. 139, p. 195-212
2. 基本地球化学原理—
区分大陆玄武岩和弧玄武岩的理论基础
3. 典型事件的启示
选取南太平洋Tonga‒Kermadec
岛弧系的现代岛弧玄武质岩石和
峨眉山大火成岩省的大陆玄武岩
作为分析、比较的对象
全球0 – 350 Ma B. P. 期间大火成岩省分布图(据Courtillot等, 1999; Wignall, 2001; Bryan和Ernst, 2008)
李奇祥等最近(2010)获得 了天山东段觉罗塔格裂谷中四顶 黑山镁铁质–超镁铁质杂岩中辉 长岩的锆石LA-ICP-MS U-Pb年龄 为351.5 ± 1.9 Ma。该镁铁质 –超镁铁质杂岩与357.7 ± 3.5 Ma的A型花岗岩共生,这些也标 示着古亚洲洋在早石炭世早期已 经闭合。
2013-2014年度,我们对于此项重要 的基本理论问题重新加以梳理,建立了 “区分大陆玄武岩和弧玄武岩的地球化 学准则”,并发表于国际地学核心期刊 “Earth-Science Reviews”(Xia, 2014)。现介绍如后:
岩石矿物学杂志
2007年第26卷第1期
77-89页
已被SCI检索刊 物他引17次; 被CNKI《中国引 文数据库》检索刊 物他引94次。
20
Pt2 1 2 3
Basalts
C1m
0
C1m 4
200 400m
5
Pt2 6
Orogenic Unconformity unconformity by extension 天山中段巴仑台北早石炭世裂谷拉伸盆地剖面
1,6: 中元古代花岗片麻岩; 2: 巨砾岩、砾岩; 3: 砂砾岩夹砂岩; 4: 砂岩、页岩互层; 5: 顶部为玄武岩。

130张野外地质构造实拍图,经典、直观、一眼看懂!

130张野外地质构造实拍图,经典、直观、一眼看懂!

130张野外地质构造实拍图,经典、直观、一眼看懂!2018-05-14 13:54剪节理视域宽度2m,图示岩层发育近乎正交的两组剪节理,将其分割为方形的岩块,沿着节理缝还有方解石岩脉充填。

大型褶皱视域宽度200m,逆冲推覆过程中往往会通过褶皱调节应力。

图示为挤压应力背景下形成的大型不协调褶皱。

不整合视域宽度50m,不整合面上覆二叠纪水平石灰岩,下伏晚元古代的倾斜石灰岩,沉积间断为约300个百万年。

劈理折射视域宽度3m,劈理穿过不同能干性的岩层时,劈理面的角度会发生变化。

在强硬层中,劈理与层理的夹角较大,在软弱层中,劈理与层理的夹角较小。

图示浅色的砂岩属于强硬层,几乎不发生发劈理,暗色的泥岩属于软弱层,劈理高度发育。

断层面的擦痕和阶步视域宽度20cm,岩体发生错断后有明显位移,接触面也会断层滑动中留下粗糙不平的擦痕,沿着断层面会有方解石等矿物沿滑动方向呈纤维状生长,然后被拉断而形成一些微小阶梯断口和微细断口,可以用于指示断层运动方向。

不对称的S型布丁构造视域宽度1m,图示为石英脉形成的不对称S型布丁,与鞘褶皱有关,主体布丁下可见封闭状岩脉环,顶部的剪切方向为从左向右。

布丁的肿缩现象视域宽度40cm,韧性差异相差较小的岩层形成布丁时,相对强硬层(白色)局部收缩而不断离,而相对软弱层(灰色)在布丁的颈部收缩处形成小型褶皱。

古水流的线状构造视域宽度2m,河流动力拖拽河床底部岩石运动,留下顺着水流方向长条状凹槽,后来被沉积物充填,形成了线状构造的印模,可以指示水流方向和沉积方向。

鱼骨状交错层理视域宽度50cm,两套交错层理表现出相反的倾向,这是水流方向反复动荡形成的典型特征,一般是潮汐成因。

上面和下面的平行层理表明了很强的水动力。

10斜层理视域宽度40cm,一系列纹层斜交于层系界面,一般形成于动荡的水或者风动力环境中,可以指示其流动方向。

图示斜层理的下部缓慢沉积,与层系界面相切,上部被侵蚀,与层系界面相交。

玄武岩的成因、构造环境分类

玄武岩的成因、构造环境分类

玄武岩的成因、构造环境分类研究意义:因为玄武质岩浆直接来源于上地幔,并可产于多种构造环境中,所以研究玄武岩对于反演地幔物质成分、分析构造环境和地球的深部动力学均具有重大意义。

1、玄武质岩浆的形成地幔橄榄岩部分熔融导致地幔橄榄岩部分熔融的因素:温度的升高;压力的降低;挥发组分的加入。

不同构造部位诱发源岩熔融因素的差异:洋中脊和大陆裂谷——减压熔融俯冲带——下插板块升温,引起熔融俯冲带——下插板块脱水,引起上部地幔楔部分熔融—挥发组分的加入2、玄武岩成分差异的影响因素1)源区的物质成分—地幔成分的不均一性,如饱满型地幔、交代富集型地幔、亏损型地幔。

2)部分熔融程度—如拉斑玄武岩是地幔橄榄岩20-30%部分熔融的产物;碱性玄武岩是地幔橄榄岩<15%部分熔融的产物。

3)源区流体的成分—如CO2使岩浆中的碱度增加。

4)源区的部分熔融条件—P的影响最大,如低压下形成拉斑玄武岩,高压下形成碱性玄武岩。

3、玄武岩的成因与构造环境1)大洋中脊玄武岩(MORB)形成环境:拉张环境形成条件:低压高温,高度部分熔融(20- 30%)源区:亏损的二辉橄榄岩、方辉橄榄岩主要是拉斑玄武岩。

化学成分特征是低LILE,同位素亏损。

MORB分为两种:正常MORB (N-type): 起源于亏损的软流圈上地幔;地幔柱型MORB (P-type):起源于比较富集的地幔柱或热点。

P-type MORB= N-type MORB + OIB sourceMORB的原始岩浆可能是苦橄岩经过Ol的结晶分异而成拉斑玄武岩。

2)大陆裂谷玄武岩——碱性玄武岩、碧玄岩、拉斑玄武岩形成环境:大陆内部拉张环境形成条件:减压为主,温度增加较小,部分熔融程度一般低于洋中脊源区:饱满型和交代富集型的地幔橄榄岩大陆裂谷岩浆作用:代表稳定的大陆开始发生裂解,是新的洋盆形成的前奏。

大陆裂谷岩浆作用的起因:有两种模式,主动模式和被动模式。

主动模式:地幔柱或热点。

江西吉泰盆地碱性玄武岩的地球化学特征及其构造意义

江西吉泰盆地碱性玄武岩的地球化学特征及其构造意义

摘要 : 吉泰盆地位于赣中地区 , 目前尚无在该盆地中发现玄武岩的报道 。新发现的玄武岩产于吉泰盆地南部泰和附近
的南溪镇 。玄武岩露头新鲜 , 蚀变微弱 , 属碱性玄武岩 , 形成于板内快速拉张环境 ; 锆石 U 2Pb年龄为 ( 139 ±017 ) ~
(143 ±111)M a, 表明岩石形成于早白垩世早期 。玄武岩无明显的 Nb、 Ta负异常 , Rb2Sr、 Sm 2Nd同位素组成分析结果
关键词 : 碱性玄武岩 ; 亏损地幔 ; 板内拉张环境 ; 早白垩世早期 ; 赣江断裂 ; 吴川 —四会断裂 ; 吉泰盆地
中图分类号 : P588114 + 5 文献标识码 : A 文章编号 : 1000 - 8527 (2005) 01 - 0133 - 08
Geochem ica l Fea tures and Tecton ic S ign if icance of the A lka li2Ba sa lts from J i’an2Ta ihe Ba sin, J iangx i Prov ince
第 19卷 第 1期 2005年 3月
现 代 地 质 GEOSC IENCE
Vo l119 No11 Mar. 2005
江西吉泰盆地碱性玄武岩的地球化学特征 及其构造意义
余心起 1 , 舒良树 2, 3 , 邓国辉 3 , 王 彬 2 , 祖辅平 2
(11 中国地质大学 地球科学与资源学院 , 北京 100083; 21南京大学 地球科学系 , 江苏 南京 210093; 31 江西地质调查院 , 江西 南昌 330201)
Abstract: New found basalt crop is located near the Nanxi Town, Taihe County, south of J iπan2Taihe B asin,

常用玄武岩构造环境判别图解-最新版

常用玄武岩构造环境判别图解-最新版

F1-F2和F 2-F3图解
0 -1.2 0.1 0.2 0.3 0.4 0.5
-1.7
-1.6
-1.5
-1.4
-1.3
-1.2
F1
SHO
-2.2
F2
-1.3
-2.3
-1.4
WPB (OIB+CON) CAB+LKT
LKT
-2.4
-1.5
OFB
OFB
-1.6
-2.5
CAB
SHO
-1.7
F2
-2.6
主量元素图解
• 在主量元素图解中最常用的元素有Al2O3、MgO、CaO、 TiO2、SiO2等不活泼元素,在部分图解中也采用FeO*、 Na2O、K2O等相对活泼的元素。 • 与微量元素相比主量元素判别图解具有以下优点: (1)由于主量元素分析方法相对简单廉价,因此数据资料容易 获得。 (2)由于主量元素在岩石中的含量较高,所以分析误差相对较 小,由此产生的判别误差也减小.虽然在很多情况下,主 量元素在玄武岩的蚀变或变质作用过程中发生的活化并不 影响图解的判别功能,但是由于大部分主量元素在玄武岩 的蚀变或变质作用过程中都很活泼,因而限制了主量元素 在玄武岩构造环境判别图解中的使用。
F3
F1-F2和F 2-F3图解是由J. A. Pearce于1976 年创立的,它们主要用于区分六种不同构 造环境下形成的玄武岩。
1 图解功能 F1-F2图解可以区分OFB、LKT+CAB、 SHO、WPB(包括 OIB和CON)等几种不同构造环境的玄武岩。 F2-F3图解则可以区分OFB、LKT、CAB、SHO等四种构 造环境。
3 图解建立过程
3.1 建立图解的样品要求 J. A. Pearce在创立该图解时所用样品必须满足下列要求: 样品必须满足12%<CaO+MgO<20%,因为CaO+MgO是一个 简单的分异标志,含量在这个范围的岩石就是通常所说的 玄武岩。 可以区分样品的形成构造环境。区分洋底玄武岩、大陆玄武 岩、洋岛玄武岩及火山弧玄武岩比较容易,但要把火山弧 玄武岩细分为岛弧拉斑玄武岩、钙碱性玄武岩和橄榄安粗 岩就不容易,用SiO2-K2O变量图解可以将橄榄安粗岩区 分出来。 分析必须包括所有主量元素的氧化物,包括H2O在内。样品 分析的总量必须在99-101%之间,经过重新计算后总量为 100%的样品被剔除。 仅采用新鲜的岩石样品,经蚀变或FeO/Fe2O3<0.5的样品被 弃用,由于细碧岩化而使CaO较低的样品通常被第一个条 件所排除。 每一种类型最多采用75个样品,样品数小于75时就采用所有 的样品。

玄武岩的成因、构造环境分类

玄武岩的成因、构造环境分类

玄武岩的成因、构造环境分类研究意义:因为玄武质岩浆直接来源于上地幔,并可产于多种构造环境中,所以研究玄武岩对于反演地幔物质成分、分析构造环境和地球的深部动力学均具有重大意义。

1、玄武质岩浆的形成地幔橄榄岩部分熔融导致地幔橄榄岩部分熔融的因素:温度的升高;压力的降低;挥发组分的加入。

不同构造部位诱发源岩熔融因素的差异:洋中脊和大陆裂谷——减压熔融俯冲带——下插板块升温,引起熔融俯冲带——下插板块脱水,引起上部地幔楔部分熔融—挥发组分的加入2、玄武岩成分差异的影响因素1)源区的物质成分—地幔成分的不均一性,如饱满型地幔、交代富集型地幔、亏损型地幔。

2)部分熔融程度—如拉斑玄武岩是地幔橄榄岩20-30%部分熔融的产物;碱性玄武岩是地幔橄榄岩<15%部分熔融的产物。

3)源区流体的成分—如CO2使岩浆中的碱度增加。

4)源区的部分熔融条件—P的影响最大,如低压下形成拉斑玄武岩,高压下形成碱性玄武岩。

3、玄武岩的成因与构造环境1)大洋中脊玄武岩(MORB)形成环境:拉张环境形成条件:低压高温,高度部分熔融(20- 30%)源区:亏损的二辉橄榄岩、方辉橄榄岩主要是拉斑玄武岩。

化学成分特征是低LILE,同位素亏损。

MORB分为两种:正常MORB (N-type): 起源于亏损的软流圈上地幔;地幔柱型MORB (P-type):起源于比较富集的地幔柱或热点。

P-type MORB= N-type MORB + OIB sourceMORB的原始岩浆可能是苦橄岩经过Ol的结晶分异而成拉斑玄武岩。

2)大陆裂谷玄武岩——碱性玄武岩、碧玄岩、拉斑玄武岩形成环境:大陆内部拉张环境形成条件:减压为主,温度增加较小,部分熔融程度一般低于洋中脊源区:饱满型和交代富集型的地幔橄榄岩大陆裂谷岩浆作用:代表稳定的大陆开始发生裂解,是新的洋盆形成的前奏。

大陆裂谷岩浆作用的起因:有两种模式,主动模式和被动模式。

主动模式:地幔柱或热点。

岩石学习笔记之二:玄武岩

岩石学习笔记之二:玄武岩

岩石学习笔记之二:玄武岩一直觉得玄武岩的名字很酷炫。

青龙、白虎,朱雀、玄武。

玄武岩(basalt)图片玄武岩是基性火山岩,也是地球洋壳和月球月海的最主要组成物质,也是地球陆壳和月球月陆的重要组成物质。

玄武岩名字的由来1546年,G.阿格里科拉首次在地质文献中,用basalt这个词描述德国萨克森的黑色岩石。

汉语玄武岩一词,引自日文。

日本在兵库县玄武洞发现黑色橄榄玄武岩,故得名。

名称和小编认为的玄武没有关系,有点失望~~玄武岩主要矿物是富钙单斜辉石和基性斜长石;次要矿物有橄榄石、斜方辉石、易变辉石、铁钛氧化物、碱性长石、石英或副长石、沸石、角闪石、云母、磷灰石、锆石、铁尖晶石、硫化物和石墨等。

月球玄武岩月球玄武岩是构成月球的主要岩石之一,由月球外层约200公里深处形成的岩泉,经多次喷发(至少5次)在月表结晶(约1050℃)而成。

是月球上最年轻的岩石,形成于距今33~37亿年间,几乎相当于已知的地球最古老岩石。

月球玄武岩细粒、多孔,主要由辉石、斜长石和钛铁矿组成。

其中辉石含量约50~59%,普通辉石多于易变辉石;斜长石约20~29%,为培长石或钙长石;钛铁矿含量约10~18%。

次要矿物有橄榄石、铬铁矿-钛尖晶石、陨硫铁、铁、方英石、金红石、磷灰石、白磷钙矿、铜、云母、镍黄铁矿及若干尚未鉴定出的矿物。

月球玄武岩的化学成分变化较大,特别是Al2O3和FeO,分别变化于7~25%和5~25%之间,一般以贫硅,富钛、铁为特点。

英国的玄武岩峡谷景观。

柱状节理,是玄武岩的重要特征玄武岩的分类按SiO2饱和程度和碱性强弱,玄武岩被分为两大类:①拉斑玄武岩(即亚碱性玄武岩),是SiO2过饱和或饱和的岩石。

不含橄榄石和霞石,以含斜方辉石、易变辉石为特征。

它的SiO2与全碱的关系是(Na2O+K2O)/(SiO2-39)的值小于0.37。

②碱性玄武岩,SiO2不饱和,富碱。

含橄榄石和副长石(如霞石)、沸石等,后两种矿物有时与碱性长石或钾质中长石、钾质更长石一起,呈填隙物产于基质中;不含斜方辉石、易变辉石,仅含富钙的单斜辉石,即透辉石质普通辉石。

沉积环境的判别标志课件

沉积环境的判别标志课件

安山岩 玄武岩
重矿物 辉石、角闪石
轻矿物
安山岩或玄武岩岩屑、中性和基性斜长 石
橄榄岩 重矿物 尖晶石、铬铁矿、橄榄石、紫苏辉石
辉长岩 轻矿物 基性岩岩屑、基性斜长石、蛇纹石
变质岩
重矿物 蓝晶石、十字石、硅线石、石榴石 轻矿物 具波状消光和镶嵌结构的石英
沉积岩
重矿物
锆石(圆)、金红石、石榴石、电气石(较 圆)
沉积环境的判别标志课件
(3) 古水深标志
一般方法:古生态法和遗迹化石标志 原理:元素的聚集和分散与水深和离岸距 离有一定的关系。
由滨岸向深海,Fe、Mn、P、Co、Ni、 Ca、Zn、Y、Pb、Ba 、Cu增加,其中Mn、Ni、 Co、Cu元素含量升高趋势特别显著。
沉积环境的判别标志课件
2、稳定同位素在分析沉积环境中的应用
沉积环境的判别标志课件
试对比四种胶结类型在颗粒接触关系、颗粒 间连接方式、颗粒支撑性质、填隙物数量及压 实压溶强度的特征。
沉积环境的判别标志课件
碎屑颗粒支撑类型
沉积环境的判别标志课件
试对比颗粒支撑和杂基支撑在流体性质、搬运方式、 沉积特点、水动力条件、沉积环境、颗粒接触关系、 粒间填隙物特征、油气储集性能等方面的差异。
不同成因碎屑沉积的累积曲线
沉积环境的判别标志课件
0.001
mm
概率值累 积曲线
沉积环境的判别标志课件
海滩砂的 粒度概率图
海滩沙丘砂的 粒度概率图
沉积环境的判别标志课件
波浪带浅海砂 的粒度概率图
密西西比河三角洲 河口砂坝及河道砂
的粒度概率图
沉积环境的判别标志课件
现代河道砂 的粒度概率图
浊流沉积的 粒度概率图

矿床地球化学结课作业(原著-可直接交)

矿床地球化学结课作业(原著-可直接交)

矿床地球化学结课作业(原著-可直接交)中国地质⼤学(北京)课程期末考试作业矿床地球化学作业(⼀)根据下列给定的⽕⼭岩岩⽯化学数据计算⽕⼭岩的特征参数,并作出图解,分析⽕⼭岩岩⽯系列和形成环境(参考岩⽯矿床地球化学教材第三章计算⽅法)。

原数据中⽕⼭岩岩性有流纹斑岩、杏仁状流纹斑岩、⾓砾岩和硅化⾓砾岩。

共有样品18个,数据包括样品全分析与部分微量元素。

全析中⼤多样品SiO2含量⼤于63%,样品岩性以流纹岩为主。

根据样品全分析数据计算出的⽕⼭岩的各类特征参数如表1表⽰,先将样品数据进⾏CIPW 标准矿物计算,其中氧化铁调整⽅法为TFeO=FeO+0.8998Fe2O3,所计算出的标准矿物均为重量百分含量,则可得出各矿物分异指数(DI) = Qz + Or + Ab + Ne + Lc + Kp。

其中固结指数为(SI) =MgO×100/(MgO+FeO+F2O3+Na2O +K2O) (Wt%)。

⾥特曼指数算式为σ43=(Na2O+K2O)^2/(SiO2-43),据表⾥特曼指数多位于1.8-3.3显⽰为钙碱性,由于原岩多数SiO2含量较⾼,⾥特曼指数确定出的钙碱度准确度差。

碱度率(AR) =[Al2O3+CaO+(Na2O+K2O)]/[Al2O3+CaO- (Na2O+K2O)] (Wt%),当SiO2>50%, K2O/Na2O⼤于1⽽⼩于 2.5时, Na2O+K2O=2*Na2O,本例以碱度率对样品碱度进⾏判别,由表可知,杏仁状流纹斑岩的碱度率都为1-3,显⽰钙碱性,流纹斑岩为3.3-5显⽰出弱碱性。

图1 样品SiO2-K2O+Na2O 图解Pc-苦橄⽞武岩;B-⽞武岩;O1-⽞武安⼭岩;O2-安⼭岩;O3-英安岩;R-流纹岩;S1-粗⾯⽞武岩;S2-⽞武质粗⾯安⼭岩;S3-粗⾯安⼭岩;T-粗⾯岩、粗⾯英安岩;F-副长⽯岩;U1-碱⽞岩、碧⽞岩;U2-响岩质碱⽞岩;U3-碱⽞质响岩;Ph-响岩;Ir-Irvine 分界线,上⽅为碱性,下⽅为亚碱性。

玄武岩微量元素判别构造背景图解 Chusi Li Lithos

玄武岩微量元素判别构造背景图解 Chusi Li Lithos

Trace element indiscrimination diagramsChusi Li a ,b ,⁎,Nicholas T.Arndt c ,Qingyan Tang d ,Edward M.Ripley baState Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China bDepartment of Geological Sciences,Indiana University,Bloomington,IN 47405,USA cISTerre,UniversitéJoseph Fourier,38400St Martin d'Hères,France dSchool of Earth Sciences and Key Laboratory of Mineral Resources in Western China Guansu Province,Lanzhou University,Lanzhou 730000,Chinaa b s t r a c ta r t i c l e i n f o Article history:Received 12February 2015Accepted 29June 2015Available online 3July 2015Keywords:BasaltsTrace elementsTectonic discriminationPetrological database utilizationWe tested the accuracy of trace element discrimination diagrams for basalts using new datasets from two petro-logical databases,PetDB and GEOROC.Both binary and ternary diagrams using Zr,Ti,V,Y,Th,Hf,Nb,Ta,Sm,and Sc do a poor job of discriminating between basalts generated in various tectonic environments (continental flood basalt,mid-ocean ridge basalt,ocean island basalt,oceanic plateau basalt,back-arc basin basalt,and various types of arc basalt).The overlaps between the different types of basalt are too large for the con fident application of such diagrams when used in the absence of geological and petrological constraints.None of the diagrams we tested can clearly discriminate between back-arc basin basalt and mid-ocean ridge basalt,between continental flood ba-salt and oceanic plateau basalt,and between different types of arc basalt (intra-oceanic,island and continental arcs).Only ocean island basalt and some mid-ocean ridge basalt are generally distinguishable in the diagrams,and even in this case,mantle-normalized trace element patterns offer a better solution for discriminating be-tween the two types of basalt.©2015Elsevier B.V.All rights reserved.Contents1.Introduction ...............................................................762.Data selection and sample classi fication ...................................................783.Evaluation of discrimination diagrams....................................................783.1.Zr –Ti –Y and Zr/Y versus Zr .....................................................783.2.Th –Hf –Ta triplot ..........................................................793.3.V versus Ti.............................................................793.4.Zr –Nb –Y triplot –Y –Nb triplot ..........................................................793.6.Sm –Ti –V and V –Ti –Sc triplots ....................................................793.7.Th/Yb versus Nb/Yb.........................................................804.Discussion ................................................................814.1.Mantle-normalized incompatible trace element patterns ........................................814.2.Why don't the discrimination diagrams work?............................................814.2.1.More tectonic settings ...................................................814.2.2.Normal MORB are not that normal..............................................824.2.3.Subduction-related basalts are geochemically similar to crust-contaminated basalts........................825.Conclusions................................................................82Acknowledgements ..............................................................83References. (83)1.IntroductionTrace element discrimination diagrams were introduced in the 1970s as a means of identifying the tectonic setting of basalts and other volcanic rocks (e.g.,Pearce and Cann,1973).The procedure wasLithos 232(2015)76–83⁎Corresponding author.E-mail address:cli@ (C.Li)./10.1016/j.lithos.2015.06.0220024-4937/©2015Elsevier B.V.All rightsreserved.Contents lists available at ScienceDirectLithosj o ur n a l h o m e p a g e :w ww.e l s e v i e r.c om /l o c a t e /l i t h osto plot data for samples from known tectonic settings (mid-ocean ridge,ocean island,island arc,etc.)in various trace element diagrams and de-fine fields that distinguished one setting from another (e.g.,Pearce and Norry,1979;Wood,1980).Compared to the data that we now have,the first practitioners (Pearce and Cann,1973;Pearce and Norry,1979;Wood,1980)were severely restricted in both the types of elements they could use and the number of samples at their disposition.When Pearce,Cann,Norry and Wood proposed the first discrimination dia-grams in the 1970s,only a limited number of trace elements could be analysed with reasonable accuracy.Elements such as Rb,Ba,Sr,Zr and Y could be measured by X-ray florescence spectrometry (XRF),and some other elements such as Ta,Th and the light REE (rare earth ele-ment)could be measured,mainly by instrumental neutron activation analysis (INAA).Elements such as Rb,Ba and Sr were known to be mo-bile during metamorphism and hydrothermal alteration,and this re-stricted or eliminated their use for altered samples (Hastie et al.,2007;Pearce and Cann,1973).The choice of diagrams was guided by the geochemical behaviour of trace elements during partial melting and their relative concentrations in different mantle reservoirs.It was known that incompatible elements such as Th,Nb and the light REE were enriched in melts derived from enriched mantle or generated by low-degree partial melting,and de-pleted in magmas derived from the convecting upper mantle.Magmas from island arcs and convergent margins had a distinctive “subduction signature ”,de fined by relative enrichment of the fluid-mobile (non-conservative)large-ion lithophile elements relative to the fluid immo-bile (conservative)high-field strength elements (HSFE)and REE (Pearce and Peate,1995).The average trace element compositions of three types of basalt,which can be considered as endmembers,are shown schematically in Fig.1.The mantle-normalized patterns (Fig.1a)depict the features de-scribed above;i.e.high concentrations of incompatible elements in the low-degree partial melts or melts from enriched mantle that erupt to form ocean island basalts (OIB),depletion of these elements in so-called normal mid-ocean ridge basalts (N-MORB),and negative Nb-Ta anomalies in island arc basalts (IAB).The average compositions of these endmembers plot in the correct fields in the published diagrams (Figs.1b,c)proposed by Pearce and Cann (1973)and Pearce and Norry (1979).These diagrams use three elements,Ti,Zr and Y,which can all be measured accurately by XRF.The relative incompatibility of these elements during lherzolite or harzburgite partial melting is Zr N Ti N Y and therefore in Fig.1c,OIB plots closer to the Zr apex (thought to re flect low-degree melting and/or a trace-element-enriched source)and N-MORB closer to the Y apex (because of high-degree melting,a depleted source and/or the presence of spinel instead of garnet at the site of melting).IAB plots away from the Zr apex re flecting the relative de ficit in this element in some subduction-related magmas (rutile/zircon stability in the source and/or amphibole fractionation?).Wood (1980)proposed another diagram using another three elements,Th,Hf and Ta,which could be measured by INAA.Of these Th is strongly incompatible,Hf is the least incompatible and Ta is depleted relative to the other HSFE in subduction-related magmas.As shown in Fig.1d,this diagram discriminates relatively well between N-MORB,OIB and IAB.During the last forty or so years,these diagrams,and others employing other sets of elements,have continued to be used widely,de-spite of repeated warning by some researchers (e.g.,Snow,2006;Wang and Glover,1992).The initial Pearce and Cann (1973)diagram,for ex-ample,has been cited more than 3000times,with a half of them in the last 10years,according to Google Scholar (Table 2).These diagramsMid-ocean ridgebasaltsWithin-pl ate basalts12051050100500Zr (ppm)Z r /YOIBIABN-MORBc basalts Low-K thoeliitesCalc-alkali basaltsWithin-pl ate basaltsZr3YTi /100OIB IABN-MORBE-MORB & Within-plate tholeiitic basaltsIsland arc tholeiitic basaltsIsland arc calc-alkaline basaltsWithin-plate alkaline basaltsN-MORBThT aHf /3OIBIABN-MORBdS a m p l e / P r i m i t i v e m a n t l eIsland arc basalts110100Th Nb Ta La Ce Nd Zr Hf Sm Ti Gd Y Yb LuabOIBIABIAB, Island arc basaltN-MORB, Normal mid-ocean ridge basalt OIB, Ocean island basaltN-MORBOcean floor Fig.1.Incompatible trace element characteristics of three types of basalt:island arc basalt (IAB),normal mid-ocean ridge basalt (N-MORB)and ocean island basalt (OIB).The compositions of primitive mantle and N-MORB are from Sun and McDonough (1989).Other data are from Table 1.77C.Li et al./Lithos 232(2015)76–83have provided a useful starting point for graduate students faced with the dilemma of having to evaluate a large amount of geochemical data that has suddenly arrived on their desk;but do these diagrams work? And are they the best possible diagrams that can be conceived to deter-mine the tectonic settings of geologically old mafic–ultramafic volcanic rocks?There have been three important developments since the1970s. First,mainly because of the development of inductively coupled plasma mass spectrometry(ICP-MS),it is now possible to analyse a vast range of trace elements:we are no longer restricted to the dozen or so ele-ments that were available to Pearce,Wood,Shervais and the other pio-neers of the technique.It is now possible to choose those element ratios that best reflect,for example,the fractionation of incompatible from more compatible elements;i.e.Th/Y or La/Yb rather than Zr/Y;or iden-tify the subduction signature;i.e.Nb/La or Nb/Th rather than ambiguous Nb–Zr–Y ratios.Second,it has become apparent that magmas eruptingin different tectonic settings have a wide range of compositions and that the distinctions that formed the basis of the earlier discrimination diagrams are no longer so obvious.Third,the total number of analyses of basalts has increased by a factor of almost100,from several hundreds available to Pearce and Cann to more than30,000analyses in databases such as GEOROC and PetDB.The aim of this paper is to employ a larger range of trace elements that is now available to test the accuracy of commonly used trace ele-ment discrimination diagrams for basalts generated in different tectonic environments.We test these diagrams using new datasets taken from public petrological databases.2.Data selection and sample classificationTwo most comprehensive global petrological databases at our dispo-sition are PetDB(/petdb)and GEOROC (http://georoc.mpch-mainz.gwdg.de/georoc/).These two databases are constantly updated and online available to users around the world. The tectonic classification for basalts used by the databases are adopted here:continental arc basalts(CAB),island arc basalts(IAB),intra-oceanic arc basalts(IOAB),back arc basin basalts(BABB),continental flood basalts(CFB),mid-ocean ridge basalts(MORB),oceanic plateau basalts(OPB)and ocean island basalts(OIB)(Table1).We use only the samples that were originally classified as basalts and contain N5wt.%MgO(normalized to100%on a volatile-free basis).The samples that were originally classified as altered basalts are rejected.Data pub-lished before1985were excluded from our selection.The other data selection criteria are age and locality of eruption to ensure an uncompromised tectonic setting for the samples.The samples of differ-ent types of basalt,except CFB and OPB,all erupted in the Cenozoic (Table1).The ages of samples of CFB and OPB vary from Permian to Cre-taceous.We excluded several suites of samples:Columbia Riverflood basalts in the western United States because subduction processes may have played a critical role in their genesis(e.g.,Cabato et al., 2015;Liu and Stegman,2012);samples from the Azores,Galápagos and Iceland because a plume may have interacted with the ridge at these locations(e.g.,Shorttle et al.,2010);and samples from the Chile and Mendocino triple junction areas because their compositions may have been affected by ridge subduction(e.g.,Russo et al.,2010; Thorkelson et al.,2011).The selected samples are further divided into two series,alkaline and subalkaline,using the classification of MacDonald and Katsura(1964). This subdivision is required for the Th–Hf–Ta,Zr–Nb–Y and La–Y–Nb diagrams.3.Evaluation of discrimination diagramsThe sources of datasets used to test the trace element discrimination diagrams are given in Table1and bibliographical information is given in Table2.The numbers of analyses used to test individual diagrams are listed in Table3.The results are given below in the order of the publica-tion date of the selected diagrams.In all the diagrams,newfields for in-dividual types of basalt based on the new datasets are drawn using the 90percentile contour of sample distribution in the diagrams.The distri-butions of individual samples in each of these diagrams are provided as supplementary materials(Figs.S1–S12).3.1.Zr–Ti–Y and Zr/Y versus ZrThese,the oldest discrimination diagrams,were introduced in the early1970s by Pearce and Cann(1973)and Pearce and Norry(1979). Even now,four decades after their publication,these diagrams appearTable1Selected datasets for different types of basalt(MgO N5wt.%and published after1985).Tectonic Setting Location Age N ofsamplesDatabaseArcs ContinentalArc(CA)Andean arc Cenozoic738GEOROC Cascades Cenozoic547CentralAmerican volca-nic arcCenozoic420Baja,California Cenozoic201Intra-oceanic Arc(IOA)Izu-Bonin arc Cenozoic652 Kermadec arc Cenozoic155 Mariana arc Cenozoic199 New HebridesarcCenozoic537 Tonga arc Cenozoic14Island Arc (IA)Aleutian arc Cenozoic250 Kurile arc Cenozoic151 Lesser Antilles Cenozoic91 Ryukyu arc Cenozoic117 Sunda arc Cenozoic138Back Arc Basins(BAB)Cenozoic1792PetDBContinental Flood Basalts(CFB)Antarctica(Koroo andFerrar)Jurassic290GEOROCDeccan Cretaceous955Emeishan Permian406Etendeka Cretaceous68Karooprovince-AfricaMesozoic–Cenozoic121Parana Cretaceous190Siberian Traps Permian277Mid-ocean Ridge Basalts(MORB)Cenozoic18,972PetDBOceanic Plateau (OP)KerguelenPlateauCretaceous204GEOROC Manihiki Plateau Cretaceous20Ontong Java Cretaceous511Ocean Island Basalts(OIB)Canary Islands Cenozoic884GEOROCCape VerdeIslandsCenozoic251Hawaii Cenozoic3216Society Islands Cenozoic172St.Helena Chain Cenozoic85Table2Some influential trace element discrimination diagrams for basalts.Diagram Author(s)PublicationdateNumber ofsampleGoogle scholarcitationZr–Ti–Y Pearce&Cann19736003000Zr–Zr/Y Pearce&Norry19793002000Th–Hf–Ta Wood et al.1979300700Wood19801300Ti–V Shervais198********Zr–Nb–Y Meschede198618501300La–Y–Nb Cabanis&Lecolle1989100a350Ta/Yb–Th/Yb Pearce198********Nb/Yb–Th/Yb Pearce2008Not given500Sm–Ti–V Vermeesch200676050V–Ti–Sca Individual samples and average values.78 C.Li et al./Lithos232(2015)76–83frequently in petrological journals worldwide.However,these diagrams do not stand the test of the new global datasets (Figs.2,3).The old and new fields are signi ficantly different not only in shape but also in size.In addition,the overlaps between different types of basalt revealed by the new datasets are much larger than those shown in the original dia-grams.The new datasets show that all types of basalt cluster together in both diagrams,re flecting the fact that the ratios of these elements in the different types of basalts are not very different.The only signi fi-cant difference is between OIB and MORB.3.2.Th –Hf –Ta triplotThis triplot was first introduced by Wood et al.(1979)and slightly modi fied the next year by Wood (1980).Since the modi fied diagram is more widely used than the original one (Table 2),we only tested the modi fied version.As shown in Fig.4a,b,samples from subduction settings plot far from the Ta apex and OIB plot closer to this apex within the field de fined by Wood et al.(1979).However,the overlap between the different types of basalt is much larger than in the original diagram (Fig.4a,b)and discrete fields cannot be de fined.3.3.V versus TiThis binary plot,introduced by Shervais (1982),was based on the dependence of V partition coef ficients on oxygen fugacity and the com-patibility of both elements in magnetite.It was proposed mainly to dis-tinguish magmas generated in relatively oxidized subduction settings from those in oceanic settings (MORB and OIB).More than three de-cades after its introduction,the plot continues to appear in some inter-national journals.A comparison of the original diagram with the results from the new global datasets (Fig.5)shows that its utility is just as poor as those of Pearce and Cann (1973)and Pearce and Norry (1979).OnlyOIB shows a fair separation from the rest and the other types of basalt cluster together (Fig.5).3.4.Zr –Nb –Y triplotThis diagram,from Meschede (1986),differs from the Zr –Ti –Y triplot of Pearce and Cann (1973)by only one element,i.e.,the replace-ment of Ti by Nb.The change expands the fields for different types of ba-salt (Fig.6)but problems persist.Once again OIB plot where they should,close to the Nb apex and in the field de fined by Meschede (1986)but there again is major overlap with data from other tectonic settings and separate fields cannot be de fi –Y –Nb triplotCabanis and Lecolle (1989)introduced this diagram in a paper pub-lished in French.It has not gained the same popularity as the diagrams described above (Table 1),possibly due to the language barrier.This triplot is distinguished from that of Meschede (1986)by only one ele-ment,i.e.,the replacement of Zr by La (Figs.6,7)but this replacement should,in theory prove useful.The La/Y ratio should distinguish magma from low-degree melting or an enriched source (i.e.OIB)from magma from a depleted source (i.e.N-MORB)and Nb/La should identify magmas from subduction settings.In practice,separation between the fields is poor.OIB plot towards the Nb axis and subduction-related magmas away from this apex,but again there is major overlap between the fields.3.6.Sm –Ti –V and V –Ti –Sc triplotsThese discrimination diagrams,introduced by Vermeesch (2006),are not as popular as those we evaluated previously (Table 1)but weTable 3Number of sample used to test the selected trace element discrimination diagrams for basalts.Diagram Zr –Ti –Y Zr –Zr/Y Th –Hf –Ta Th –Hf –Ta Ti –V Zr –Nb –Y Zr –Nb –Y La –Y –Nb La –Y –Nb Sm –Ti –V V –Ti –Sc Nb/Yb –Th/Yb Series All All Alkaline Subalkaline All Alkaline Subalkaline Alkaline Subalkaline All All All OIB 7778943555779773520073898305480597CFB 166216528851114991681480977225631029742OPB 1911632649197473722479878172CAB 134113422782281048474407494384748646600IAB 52252274184546194348194264267324235IOAB 10841084292429776952273615455479400BABB 952952342429747270155522440480393MORB596859681053076508312053031193158338640493546Table 4Average immobile trace element abundances (ppm)in different types of basalt.Series Type n Th Nb Ta La Ce Nd Zr Hf Sm Ti Gd Y Yb Lu AlkalineOIB 248 6.8580.11 4.1864.35129.3861.03336.0 6.5611.5221,92310.1432.01 2.160.35CFB 80 4.0135.99 2.4235.3576.6341.32263.8 6.359.0218,5798.7838.94 3.120.45OPB 22 1.3912.250.8013.1430.1419.04141.4 3.61 4.8911,202 5.5331.14 3.140.46CAB 111 3.5823.86 1.4037.4474.6237.30180.6 4.167.2111,087 6.4325.10 2.050.30IAB 47 4.8219.29 1.2426.3452.9826.98136.2 3.18 5.959417 5.2926.72 2.300.34IOAB 27 3.627.050.3928.5454.6329.04105.4 2.54 6.396562 6.2129.95 2.450.38BABB 33 1.8119.22 1.3915.3832.2818.62134.5 3.09 4.479155 4.8127.24 2.500.43MORB 119 4.4342.38 2.3837.0773.0434.37245.5 5.637.0313,685 6.3629.46 2.510.36SubalkalineOIB 30 2.5440.54 2.4728.8161.4232.81199.9 4.947.0916,382 6.4923.24 1.660.23CFB 410 1.759.790.6115.0633.2119.75139.4 3.52 5.1011,130 5.5028.36 2.510.37OPB 24 1.1811.430.7710.5024.3315.26110.4 2.96 3.999621 4.7427.58 2.980.43CAB 159 1.55 5.860.3512.2025.7915.7490.3 2.35 3.726240 3.8120.88 1.970.30IAB 103 1.74 4.490.329.0820.2912.6479.8 2.04 3.286260 3.6622.88 2.280.35IOAB 3680.70 1.560.12 6.5414.2810.2154.6 1.50 2.905885 3.5023.73 2.290.36BABB 2330.51 4.130.28 5.2112.599.5578.0 1.91 2.887220 3.6425.17 2.460.38MORB31010.495.950.375.5414.5011.32104.62.713.7988014.5933.393.350.50Data are from PetDB and GEOROC.79C.Li et al./Lithos 232(2015)76–83tested them because the author claimed that they are more accurate than the older diagrams.In term of design,Sm or Sc is added to the Ti –V binary plot of Shervais (1982).Contrary to the author's claim,these ternary diagrams (Figs.8a,b)do no better than the Ti –V binary plot (Fig.5).The areas de fined by the new global datasets are dramati-cally different from those in the original diagrams of Vermeesch (2006)(Figs.8a,b).All types of basalt are tightly clustered with large overlaps in both discrimination diagrams except OIB which shows clear separa-tion from IOAB in the former (Sm –Ti –V,Fig.8a)and from MORB,BABB and IOAB in the later (V –Ti –Sc,Fig.8b).3.7.Th/Yb versus Nb/YbPearce (1982)introduced the binary Th/Yb vs.Ta/Yb plot,and subse-quently,Pearce and Peate (1995)and Pearce (2008)replaced Ta by Nb (Fig.9).The authors'main purposes were to show the differences in these ratios between MORB-OIB and arc basalts and to offer their petro-genetic interpretations for such differences.Unfortunately,thesediagrams have been widely used as a simple tectonic discrimination tool by other researchers recently (e.g.,Furnes et al.,2015;Turner et al.,2014).MORBVolcanic arc basaltsWithin-p late basaltsZr3YTi /100OPB CAB BABBCFBIOABOIBMORBIABBABB, Back arc basaltCAB, Continental arc basalt CFB, Continental flood basalt IAB, Island arc basaltIOAB, Intra-oceanic arc basalt MORB, Mid-ocean ridge basalt OIB, Ocean island basalt OPB, Oceanic plateau basaltFig.2.Zr –Ti –Y ternary diagrams comparing the old (in grey,Pearce and Cann,1973)and new (in colour and black,this study)discrimination fields for basalts.The outlines of the new fields are 90%sample density contours.The sources of new datasets are given in Table 1.1015102050100500Zr (ppm)Z r /YIABMORBWithin-plate basaltsOPBCABBABBCFB IOABOIBMORBIABBABB, Back arc basaltCAB, Continental arc basalt CFB, Continental flood basalt IAB, Island arc basaltIOAB, Intra-oceanic arc basalt MORB, Mid-ocean ridge basalt OIB, Ocean island basalt OPB, Oceanic plateau basaltFig.3.Zr/Y versus Zr binary diagrams comparing the old (in grey,Pearce and Norry,1979)and new (in colour and black,this study)discrimination fields for basalts.E-MORB & intraplate tholeiitic basaltsIsland arc tholeiitic basaltsIsland arc calc-alkaline basaltsN -M O R B ThT aHf /3E-MORB & intraplate tholeiitic basaltsIsland arc tholeiitic basaltsIsland arc calc-alkaline basaltsWithin-plate alkaline basaltsWithin-plate alkaline basaltsN-MORBThTaHf /3AlkalineaSubalkalinebB AB BCABCFB IAB I O A BM O R BOPBOIBB A BBC A B C F BIABI OA B M O R BOIBO P B BABB, Back arc basaltCAB, Continental arc basalt CFB, Continental flood basalt IAB, Island arc basaltIOAB, Intra-oceanic arc basalt MORB, Mid-ocean ridge basalt OIB, Ocean island basalt OPB, Oceanic plateau basaltFig.4.Th –Hf –Ta ternary diagrams comparing the old (in grey,Wood,1980)and new (in colour and black,this study)discrimination fields for basalts.200400600102030V (p p m )C F BMORB & BABBI A BTi (ppm) / 1000O PB MO RBCABC F BO IBIOABIABB AB BIOAB, Intra-oceanic arc basalt MORB, Mid-ocean ridge basalt OIB, Ocean island basalt OPB, Oceanic plateau basaltBABB, Back arc basaltCAB, Continental arc basalt CFB, Continental flood basalt IAB, Island arc basalt Fig.5.V versus Ti binary diagrams comparing the old (in grey,Shervais,1982)and new (in colour and black,this study)discrimination fields for basalts.80C.Li et al./Lithos 232(2015)76–83As shown in Fig.9,the MORB-OIB array de fined by Pearce (2008)is slightly larger than the combined area covered by these two types of ba-salt based on the new global datasets.Overall,MORB and OIB tend to have lower Th/Yb than other types of basalt but signi ficant,variable overlaps between the various types of basalt clearly exist.The OPB field is entirely enclosed by the CFB field,which in turn is entirely enclosed by the CAB field.There are large overlaps between three differ-ent types of arc basalt (IOAB,IAB and CAB).BABB is overlapping with both MORB and IOAB.4.Discussion4.1.Mantle-normalized incompatible trace element patternsA shortcoming of binary and ternary trace element discrimination diagrams is that not all of the important diagnostic features for basalts can be captured in a single plot.As a result,even the best discrimination diagram has at best only partial success.This can be improved if the dis-crimination diagram is used in conjunction with the traditional mantle-normalized trace element (spider)diagram (Fig.10).Compared to the binary or ternary diagrams,the mantle-normalized diagrams reveal more diagnostic features.For example,none of the proposed binary or ternary plot captures the dramatically different abundances of Th and light REE,which are an extremely useful discrimination feature of many basalts.Spider diagrams are particularly useful for the samples that plot in overlapping fields in the binary or ternary diagrams.The presence or lack of pronounced negative Nb –Ta anomalies in the spider diagrams (Fig.10)can be used to classify samples that plot in the common areas of MORB and arc basalts in Figs.6and 7;and contrasting abun-dances of Th and light REE can be used to classify the samples that plot in the common areas of OIB and MORB in Figs.4and 9.4.2.Why don't the discrimination diagrams work?When the diagrams of Pearce and Cann,Wood and Shervais were originally introduced,they met with immediate success and were adopted widely by geochemists.Yet our analysis shows that they,and other similar diagrams proposed subsequently,perform dismally when tested against a wide set of modern geochemical data.Why is this?We can identify three main reasons.4.2.1.More tectonic settingsThe original assignment of tectonic setting was made using only a few categories;e.g.within-plate basalt,mid-ocean ridge basalt and is-land arc basalt in the original Pearce and Cann diagram.Important set-tings like back-arc basins and continental and oceanic plateaus were missing.The introduction of these categories complicates the identi fica-tion of tectonic settings using only a very limited number of geochemi-cal parameters.Y 2NbZr /4Within-plate alkaline basaltsWithin-plate tholeiitic basaltsE-MORBN-MORBVolcanic arc basaltsAlkaline aSubalkalinebY2NbZr /4Within-plate alkaline basaltsWithin-plate tholeiitic basaltsE-MORBN-MORBVolcanic arcbasaltsBABBCABCFB IAB IOABM O RB OPBOIB OPBIOABM O R BIAB BABBCAB OIB C F BBABB, Back arc basaltCAB, Continental arc basalt CFB, Continental flood basalt IAB, Island arc basaltIOAB, Intra-oceanic arc basalt MORB, Mid-ocean ridge basalt OIB, Ocean island basalt OPB, Oceanic plateau basaltFig.6.Zr –Nb –Y ternary diagrams comparing the old (in grey,Meschede,1986)and new (in colour and black,this study)discrimination fields for basalts.Y /15Nb /8La/10N-MORBE-MORBContinental backarc tholeiitic basaltsContinental rift alkaline basaltsContinental basaltsVolcanic arc tholeiitic basaltsVolcanic arc calc-alkaline basaltsAlkalineaY /15Nb /8La/10N-MORBE-MORBContinental backarc tholeiitic basaltsContinental rift alkaline basaltsContinental basaltsVolcanic arc tholeiitic basaltsVolcanic arc calc-alkaline basaltsSubalkalineb B A B BCABC F BIAB M O RB OIBO P BI O A BOPB IOABIABB A BBCABM O RB OIBCFB BABB, Back arc basaltCAB, Continental arc basalt CFB, Continental flood basalt IAB, Island arc basaltIOAB, Intra-oceanic arc basalt MORB, Mid-ocean ridge basalt OIB, Ocean island basalt OPB, Oceanic plateau basaltFig.7.Th –Hf –Ta ternary diagrams comparing the old (in grey,Cabanis and Lecolle,1989)and new (in colour and black,this study)discrimination fields for basalts.81C.Li et al./Lithos 232(2015)76–83。

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。用使的中解图别判境环造构岩武玄在 素元量主了制限而因�泼活很都中程过用作质变或变蚀的 岩武玄在素元量主分部大于由是但�能功别判的解图响影 不并化活的生发中程过用作质变或变蚀的岩武玄在素元量 主�下况情多很在然虽�小减也差误别判的生产此由�小 较对相差误析分以所�高较量含的中石岩在素元量主于由)2( 。得获 易容料资据数此因�价廉单简对相法方析分素元量主于由)1( �点优下以有具解图别判素元量主比相素元量微与 • 。素元的泼活对相等O2K、O2aN 、*OeF用采也中解图分部在�素元泼活不等2OiS、2OiT 、OaC、OgM、3O2lA有素元的用常最中解图素元量主在 •
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.061-9 41:)36(7791 ,.lorteP .lareniM .birtnoC .gnittes cinotcet tnereffid morf saval cifam ni noitisopmoc enexoryponilC .G .E tebsiN .09- 97 :)51(4791 ,.lorteP fo .J .tlasab citiieoht a fo noitadarged citilipS .G .T ecnallaV .912-191:)9(8691 ,.lorteP fo .J .msihpromatem lairub gnirud saval cisab emos fo noitaretla eht ni stnemele rojam fo noitubirtsideR .E .R htimS .021-411:)23(6791 ,sretteL e cneicS yratenalP dna htraE .samgam citlasab fo noitacifissalc ni bN dna P ,K ,rS ,Y ,rZ ,iT fo esu eht no tnemmoC .E .R htimS .422- 302 :)52(0791 ,.lorteP .lareniM .birtnoC .eltnam eht morf amgam yramirp elbissop :yaB niffaB fo stlasab yraitreT .B .D ekrolC .751- 241 :)91(8691 ,.lorteP .lareniM .birtnoC .smargaid noitairav fo yroeht eht ot noitubirtnoc A .H .T ecraeP .131-111:)33( 2991 ,sweiveR ecneicS- htraE .snrettap dna smargaid tnanimircsid lacimehcoeg desu ylnommoc tsom eht fo tset scinotcet A .L revolG ,P gnaW .451-931 :)95( 2891,sretteL ecneicS yratenalP dna htraE .seires cinaclov-oelap fo seitiniffa citamgam eht fo noitacifitnedi fo dohtem a sa noitisopmoc enexoryponilC .la te ,P nonohT ,C R yrunaM ,J reirreteL .811- 101:)95(2891 ,sretteL ecneicS yratenalP dna htraE .saval citiloihpo dna nredom fo sisenegortep eht dna stolP V-iT .W .J siavrehS .633- 623 :)54( 9791 ,sretteL ecneicS yratenalP dna htraE .sgnittes cinotcet tnereffid ni detpure seire s amgam neewteb etanimircsid dna yfissalc ot stnemele ecart fo esu eht fo lasiarppa-eR A.liuerT lehciM,noroJ .L .J dooW .A divaD .74 -33:)96(9791,.lort eP .lareniM .birtnoC .skcor cinaclov ni snoitairav bN dna Y ,rZ ,iT fo snoitacilpmi citenegorteP .J .M yrroN dna .A .J ecraeP .812-702 :)65( 6891 ,ygoloeG lacimehC .margaid Y-rZ-bN eht htiw setiieloht latnenitnoc dna stlasab egdir naeco-dim fo sepyt tnereffid neewteb gnitanimircsid fo dohtem A .M edehcseM .742-142 :)51( 2891 ,sohtiL .sesoprup noitacifissalc rof ytilibatius sti dna margaid noitanimircsid Y-iT- rZ eht fo noissucsid A :gnittes cinotcet dna skcor cinaclov cisaB .T kivtserP .003-092:)91( 3791 ,sretteL ecnei cS yratenalP dna htraE .sesylana tnemele ecart gnisu denimreted skcor cinaclov cisab fo gnittes cinotceT .R nnaC ,.A.J ecraeP .013-803:)97(,2891 ,lorteP dna lareniM .bitnoC .margaid rZ-Y-iT eht gnisu setiieloht latnenitnoc fo noitingocer-noN .E .P mloH .692-682:)32(4791 ,sretteL ecneicS yra tenalP dna htraE ,sdnert noitaitne reffid rieht dna stlasab enivilo ilakla fo nosirapmoc ediwdlrow A .W sregoR ,.J.J rezrawhcS .331- 28:)5(4691 ,.lorteP .J ,saval naiiawaH fo noitisopmoc lacimehC .K .T dlanoDcaM .812-112 :)72( ,5791 ,sretteL ecne icS yratenalP dna htraE .stnemele elibommi gnisu noitanimircsid gnittes cinotcet dna epyt amgaM .A .J retsehcniW ,.A .P dyolF .26-35 :)26(3891 ,srettel ecneicS yratenalP dna htraE .sisenegortep rof snoitacilpmi sti dna stnem - norivne cinaeco fo skcor citlasab rof tnanimircsid tnemele ronim a :5O2P/2OiT/OnM .D .E nelluM .231- 121 :)63(7791 ,sretteL ecneicS yratenalP dna htraE .skcor cinaclov etaidemretni dna cisab fo tnemnorivne cinotcet dna yrtsimehc tnemele rojam neewteb pihsnoitaler ehT .C .T ttekriB ,.E .B namroG ,.H .T ecraeP .624-914:)42(5791 .sretteL ecneicS yratenalP dna htraE .stlasab cinaeco-non dna cinaeco neewteb gnitanimircsid fo dohtem A :margaid 5O2P-O2K- 2OiT ehT .C.T ttekriB dna E.B namroG ,.H .T ecraeP .34- 51:)71( 6791,.lorteP fo J.stlasab ni snrettap tnemele rojam fo sisylana lacitsitatS.A J ecraeP
。岩武玄的成形下境环造 构同不种六分区于用要主们它�的立创年 6791于ecraeP .A .J由是解图3F-2 F和2F-1F
3F
6. 2-
2F
7. 1-
OHS
BAC
BFO
5. 2-
BF O
6. 1 -
4. 2-
5. 1 -
TKL+BAC
TK L
3.2 OHS
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