火成岩lect第二章和的分类

1、第二章 火成岩和火成岩的分类火成岩的定义和与其它岩石的区隔火成岩的分类标准火成岩的分类体系火成岩：由岩浆结晶或凝固的岩石类型火成岩、岩浆岩、地幔岩火成岩与混合岩变形的岩浆岩、正变质岩岩石分类标准岩石形成的深度或岩浆结晶的位置 (岩石的结构Textures)岩石的化学组成岩石的矿物组成Plutonic vs. Volcanic4火山岩 vs 侵入岩Volcanic rocks are erupted at the Earths surface and cool very quickly. There is insufficient time to grow large crystals. Thi

2、s leads to formation of glass or very fine-grained rocks, or to phenocrysts (crystals that grew before eruption) in a fine groundmass.Plutonic rocks crystallize at some depth, and therefore lose heat relatively slowly. Crystals have time to grow after nucleation, and the resulting rocks generally ha

3、ve individual crystals large enough to see unaided.Textures are small-scale penetrative featuresFirst StepPhaneritic.(显晶质结构）：The crystals that compose the rock are readily visible with the naked eye.Aphanitic（隐晶质结构）：The crystals, if any, are too small to be seen readily with the naked eye.Fragmental

4、.(角砾或斑状结构）：The rock is composed of pieces of disaggregated igneous material, deposited and later amalgamated. The fragments may include pieces of pre-exsiting rock, crystal fragment, or glass.Phaneritic Plutonic, or intrusive (侵入岩，深成岩）Aphaneritic Volcanic, or extrusive (火山岩，喷出岩）Fast cooling on the s

5、urface results in many small crystals or quenching to a glass. Gives rise to aphanitic texture (crystals cannot be distinguished with the naked eye), or obsidian (volcanic glass). Slow cooling at depth in the earth results in fewer much larger crystals, gives rise to phaneritic texture. Porphyritic

6、texture develops when slow cooling is followed by rapid cooling. Phenocrysts = larger crystals, matrix or groundmass = smaller crystals. Plutonic Igneous Rocks:forms undergroundmagma never reaches the surfacecools slowlyform large crystalsmedium to coarse grained textureGet exposed at the surface on

7、ly when rock is uplifted and exposedVolcanic Igneous Rocks:Forms on the surfaceLava comes out of a volcanocools rapidlyforms small crystalsglassy or fine-grainedCovers the surface as lava flows or pyroclastic debrisUnder water volcanoes form pillow lavaCrystallization:Magma is a mixture of different

8、 substances. They all have different melting points.So as a magma cools, some substances will form crystals be for other substances. They have a head start in growth and tend to be bigger.If the magma already has crystal present in it and then is cooled rapidly then you will see large crystals embed

9、ded in finer-grained material.This is called a porphyritic texture岩石形成的深度或岩浆结晶的位置 (对应岩石的结构Texture）岩石名称结构侵入岩Phaneritic显晶质结构地下次火山岩porphyritic 斑状结构近地表火山岩Aphanitic隐晶质结构地表Figure 2-1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular diagrams. 根据矿物组成分类标准分类图是根据岩石的组成

10、矿物来划分的（如石英多少、长石多少等）这通常用于侵入岩（实际矿物及其含量），而火山岩中组成矿物难以辨认，至少其相对含量难以确定，所以通常采用化学组成分类的方法（modal composition).当然，可以采用标准矿物计算的方法，根据岩石的化学组成来计算的矿物及其相对含量（normative）.The standard norm calculation is called the CIPW norm, after Cross, Iddings, Pirsson, and Washington (1902).15A classification scheme for coarse-graine

11、d igneous rocks that have more than 10% (quartz + feldspar + feldspathoids). The odd names are mostly from the ancient history of natural science.Figure 2-2. A classification of the phaneritic igneous rocks. a. Phaneritic rocks with more than 10% (quartz + feldspar + feldspathoids). After IUGS.The r

12、ock must contain a total ofat least 10% of the minerals below.Renormalize to 100% (a)Quartz-richGranitoid909060602020Alkali Fs.Quartz SyeniteQuartzSyeniteQuartzMonzoniteQuartzMonzodioriteSyeniteMonzoniteMonzodiorite(Foid)-bearingSyenite5103565(Foid)-bearingMonzonite(Foid)-bearingMonzodiorite90Alkali

13、 Fs.Syenite(Foid)-bearingAlkali Fs. Syenite10(Foid)Monzosyenite(Foid) Syenite(Foid)Monzodiorite(Foid) GabbroQtz. Diorite/Qtz. Gabbro510Diorite/Gabbro/Anorthosite(Foid)-bearingDiorite/Gabbro60(Foid)olitesQuartzoliteGraniteGrano-dioriteTonaliteAlkali Feldspar GraniteQAPF60Mineral content (actual or no

14、rmative) of the rock by volume is divided into Quartz (Q), Alkali feldspar (A), Plagioclase (P), Feldspathoids like nepheline and leucite (F), and Mafic minerals like amphibole, biotite, pyroxenes, and olivine (M).For rocks with M 66Acid40FelsicGranite, rhyolite52-66Intermediate40-70IntermediateDior

15、ite, andesite45-52Basic70-90MaficGabbro, basalt90UltramaficDunite, komatiite By alumina saturation (this controls which dark minerals show up):ChemistryDesignationDistinctive MineralsAl2O3Na2O+K2O+CaOPeraluminousMuscovite, biotite, topaz,corundum, garnet, tourmalineNa2O+K2O+CaOAl2O3 Metaluminous Mel

16、ilite, biotite, pyroxene& Al2O3 Na2O+K2Ohornblende, epidoteAl2O3 Na2O+K2OSubaluminousOlivine, pyroxenesAl2O3 Na2O + K2OPeralkalineSodic pyroxenes & amphiboles26Classification based on Mineralogy & ChemistryFelsic rocks: mnemonic based on feldspar and silica. Also applies to rocks containing abundant

17、 feldspathoids, such as nepheline. GRANITEMafic rocks: mnemonic based on magnesium and ferrous/ferric. Synonymous with ferromagnesian, which refers to biotite, amphibole, pyroxene, olivine, and Fe-Ti oxides. BASALTUltramafic rocks: very rich in Mg and Fe. Generally have little feldspar. PERIDOTITESi

18、licic rocks: dominated by quartz and alkali fsp. Sometimes referred to as sialic (Si + Al).Color IndexDefined as the modal proportion of dark-colored minerals in a rock. Should really be based on the proportion of ferromagnesian minerals as feldspars may range in color.Leucocratic: 0-30% maficsMelan

19、ocratic: 60-100% maficsRhyolite Hand SpecimenGranite Hand SpecimenDeeply Eroded IntrusionsGRANITE INTRUSIONSHALE COUNTRY ROCKTorres del Paine, ChileCoarse Grained Intrusive Rock TexturePotassium Feldspar (stained yellow)Photomicrograph - Phaneritic TexturePhoto credit: C.C. PlummerInterlocking grainsAndesite Hand SpecimenPlagioclase FeldsparphenocrystsMatrix or groundm