火成巖lect第二章和的分類

1、第二章 火成巖和火成巖的分類火成巖的定義和與其它巖石的區(qū)隔火成巖的分類標(biāo)準(zhǔn)火成巖的分類體系火成巖：由巖漿結(jié)晶或凝固的巖石類型火成巖、巖漿巖、地幔巖火成巖與混合巖變形的巖漿巖、正變質(zhì)巖巖石分類標(biāo)準(zhǔn)巖石形成的深度或巖漿結(jié)晶的位置 (巖石的結(jié)構(gòu)Textures)巖石的化學(xué)組成巖石的礦物組成Plutonic vs. Volcanic4火山巖 vs 侵入巖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.(顯晶質(zhì)結(jié)構(gòu)）：The crystals that compose the rock are readily visible with the naked eye.Aphanitic（隱晶質(zhì)結(jié)構(gòu)）：The crystals, if any, are too small to be seen readily with the naked eye.Fragmental

4、.(角礫或斑狀結(jié)構(gòu)）：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 (侵入巖，深成巖）Aphaneritic Volcanic, or extrusive (火山巖，噴出巖）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巖石形成的深度或巖漿結(jié)晶的位置 (對應(yīng)巖石的結(jié)構(gòu)Texture）巖石名稱結(jié)構(gòu)侵入巖Phaneritic顯晶質(zhì)結(jié)構(gòu)地下次火山巖porphyritic 斑狀結(jié)構(gòu)近地表火山巖Aphanitic隱晶質(zhì)結(jié)構(gòu)地表Figure 2-1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular diagrams. 根據(jù)礦物組成分類標(biāo)準(zhǔn)分類圖是根據(jù)巖石的組成

10、礦物來劃分的（如石英多少、長石多少等）這通常用于侵入巖（實(shí)際礦物及其含量），而火山巖中組成礦物難以辨認(rèn)，至少其相對含量難以確定，所以通常采用化學(xué)組成分類的方法（modal composition).當(dāng)然，可以采用標(biāo)準(zhǔn)礦物計算的方法，根據(jù)巖石的化學(xué)組成來計算的礦物及其相對含量（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