Geo 101N 1st Edition Lecture 13Outline of Last Lecture I. Libby Montana-AsbestosII. Asbestos MineralsIII. Ca-Na AmphibolesIV. Volcanos and MagmaV.Rocksa. Igneousb. Sedimentaryc. MetamorphicVI. Geothermal GradientVII. Heat MovementOutline of Current Lecture VIII. Magma Formationa. Decompressionb. Volatile additionc. Heat TransferIX. Major Types of MagmaX. Magma Categoriesa. Felsicb. Intermediatec. Maficd. UltramaficXI. Magma MovementXII. Rock MeltingXIII. Magma CharacteristicsCurrent LectureVII. Magma Formation*remember that the earth is very hot insidea. Decompression-melting due to a decrease in pressure-when the pressure affecting hot mantle rock decreases while the temperature remains the same magma forms-convection-the base of the crust is hot enough to melt rockThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-pressure decreases when hot rock is carried up to shallower depths; mantle plumes, beneath rifts and under oceanic riftsb. Addition of volatiles- locations where chemicals called ‘volatiles’ mix w/hot mantle rock-volatile substances include; water, carbon dioxide-they evaporate easily & can exist in gaseous forms @ Earths surface-sometimes called flux melting-adding volatile lowers the melting point-subduction introduces water to the mantle; this lowers the melting point -only at subduction zonesc. Heat Transfer: rising magma transfers heat as it continues to rise; conductionV. Types of Magmaa. All magma contains a compound of silica and oxygen b. “dry magma” contains no volatilesc. “wet magma” contains volatilesVI. Magma Types a. Felsic (or silica) magma- 66-76% silica; relatively high proportion of silica, also called “silicic”b. Intermediate magma- 52-66% silica; melting mantle forms mafic magma partway between Felsic and Maficc. Mafic magma-45-52%; basalt-contains relatively high concentrations of FeO or Fe2O3 (iron oxide) and MgO (magnesium oxide) relative to silica; “Ma” = magnesium and “fic” = irond. Ultramafic magma- 38-45%; melting containing crust forms felsic or intermediateVII. Magma Movementa. Earth loses heat via convection, conduction and radiationb. temperature variation in the mantle (measured by the velocity of seismic waves through magma)c. pressure also increases as depth goes deeper into the Earthd. pushes lower density magma towards the surfacee. pressure in the mantle keeps it from melting (heat must be added)f. core temperatures around 5000ᵒCVIII. Rock Meltinga. Rocks act just like chocolate chips in a chocolate chip cookie; some warm and melt at lower tempsb. Silica rich melts most quickly & crystalizes last; silica poor melts lastc. Rocks rarely melt completelyd. Partial melting yields a silica rich magma = Felsic magma with mafic residueIV. Different Magma Characteristicsa. Rock source composition: not all magmas have the same source rocks so not all have the same compositionb. Partial Melting: due to temperature & pressure systems that occur on Earth only 2-30% of an original rock can meltc. Assimilation: as magma sits in a magma chamber before completely solidifying it may incorporate chemicals dissolved from the wall rockd. Magma mixing: different magmas formed in different locations from different sources may enter a magma chamber, this can allow distinct magmas to mix and create new and different