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The Chemical Composition of the Solar System and the Earth.

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1 The Chemical Composition of the Solar System and the Earth

2 Two suggestions Expertise comes from making all possible mistakes (Niels Bohr) Expertise comes from making all possible mistakes (Niels Bohr) Nothing can be obtained in geochemistry without careful analytical work (C.J. Allegre) Nothing can be obtained in geochemistry without careful analytical work (C.J. Allegre)

3 Further readings W.M. White, Geochemistry. A on-line text book. W.M. White, Geochemistry. A on-line text book. S.R. Taylor and S.M., 1995. The Continental Crust: Its Composition and Evolution. Blackwell, Oxford. S.R. Taylor and S.M., 1995. The Continental Crust: Its Composition and Evolution. Blackwell, Oxford. W.F. McDonough and S.Sun, The Composition of the Earth, Chemical Geology, 120: 223-253. W.F. McDonough and S.Sun, The Composition of the Earth, Chemical Geology, 120: 223-253. Geochemical Earth Reference Model (GERM) Geochemical Earth Reference Model (GERM) www.EarthRef.org www.EarthRef.org

4 Why do we study element abundances? Fundamental for any geochemical studies Fundamental for any geochemical studies

5 Confusing terms Abundance: for a large system, e.g., Cosmos, Sun, Moon, Earth, crust, regional crust Abundance: for a large system, e.g., Cosmos, Sun, Moon, Earth, crust, regional crust Content/concentration: for a smaller system, e.g., rocks, minerals, natural water. Content/concentration: for a smaller system, e.g., rocks, minerals, natural water.

6 Part 1 The Solar/Cosmic system

7 Sources for studies Meteorite Meteorite Sun ’ s Photosphere Sun ’ s Photosphere Cosmic rays Cosmic rays Earth and moon Earth and moon

8 Classification of meteorites according to texture and chemical composition (White, 2001)

9 Relative abundance of major types of meteorite falls

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11 Characteristics of chondrite groups Carbonaceous chondrites are the most volatile-rich and the most primitive.

12 Condensation sequence of a gas with a solar composition

13 Condesation sequence of minerals

14 Goldschmidt ’ s classification of elements

15 Classification of elements (McDonough and Sun, 1995)

16 Classification of elements according to volatility

17 There is much interest in high T component, i.e., the so-called Refractory Inclusions (RI) or Ca-Al inclusions (CAI), because their composition represents that of the first condensates from a high T gas. There is much interest in high T component, i.e., the so-called Refractory Inclusions (RI) or Ca-Al inclusions (CAI), because their composition represents that of the first condensates from a high T gas. Ca-Al inclusion

18 Carton illustrating the process involved in formation of chondrites and their components

19 Abundances of elements in sun ’ s photosphere vs their abundances in CI chondrites (White, 2001)

20 Comparison of element abundances in solar photosphere and CI carbonaceous chondrites (Taylor and McLennan, 1995)

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22 Solar system abundances of elements relative to Si=10 -6

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24 Characteristic of element abundances of the solar system H and He accounts for 98% in mass. H and He accounts for 98% in mass. Exponential decrease in abundance for elements with atomic number<45. Exponential decrease in abundance for elements with atomic number<45. Elements with even mass show significantly higher abundances than the neighboring elements with odd mass. Elements with even mass show significantly higher abundances than the neighboring elements with odd mass. He exhibit an abnomously high abundance compared to the neighboring Li, Be and B. He exhibit an abnomously high abundance compared to the neighboring Li, Be and B. O and Fe show a peak. O and Fe show a peak. Isotopes with atomic weight being factor of 4 have high abundance. 4 He (Z=2, N=2), 16O (Z=8, N=8), Isotopes with atomic weight being factor of 4 have high abundance. 4 He (Z=2, N=2), 16O (Z=8, N=8), 40Ca (Z=20, N=20). 40Ca (Z=20, N=20).

25 Even-odd mass effect 57 58 59 60 62 63 64 65 66 67 68 69 70 71

26 Sequence of decreasing element abundances in the solar system H  He  O  C  N, Ne  Mg, Si  Fe  S 10 10 to 10 9 10 7 10 6 10 5

27 Neocleosynthesis The Big Bang

28 Steller structure at the onset of supernova stage (White, 2001) The E-process (Si burning) The S-process (neutron capture) The r-process (Rapid neutron capture) Principle mechanism for forming heavier isotopes The p-process (Proton capture) Responsible for the lightest isotopes of a given element

29 The r-process path

30 Part 2 The Moon

31 Representative compositions of lunar rocks

32 Comparison of the composition of the Moon and the Earth

33 Highlights of lunar Geochronology

34 Part 3 The Earth

35 Volumes and masses of the Earth ’ s shells

36 The Earth’s Interior Mantle: Peridotite (ultramafic) Upper to 410 km (olivine  spinel) u Low Velocity Layer 60-220 km Transition Zone as velocity increases ~ rapidly  660 spinel  perovskite-type  Si IV  Si VI Lower Mantle has more gradual velocity increase Figure 1-2. Major subdivisions of the Earth. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

37 The Earth’s Interior Core: Fe-Ni metallic alloy Outer Core is liquid u No S-waves Inner Core is solid Figure 1-2. Major subdivisions of the Earth. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

38 Figure 1-3. Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left, rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford.

39 Part 3-1 The mantle

40 Methods of studies Mantle xenoliths entrained by volcanic rocks Mantle xenoliths entrained by volcanic rocks Massif peridotite: Exhumed mantle slab Massif peridotite: Exhumed mantle slab Mantle-derived volcanic rocks Mantle-derived volcanic rocks Experiments at high P-T Experiments at high P-T Seismic and density properties Seismic and density properties

41 Mantle Rock Types

42 Rock Names Peridotite: ultramafic rock composed of olivine, 2 pyroxenes (opx-cpx) and Al-phase (i.e., plagioclase, spinel, garnet, with the specific phase being a function of pressure, 0-10, 10-25, >25 Kb respectively), includes: lherzolite, harzburgite, dunite Peridotite: ultramafic rock composed of olivine, 2 pyroxenes (opx-cpx) and Al-phase (i.e., plagioclase, spinel, garnet, with the specific phase being a function of pressure, 0-10, 10-25, >25 Kb respectively), includes: lherzolite, harzburgite, dunite

43 Eclogite: mafic (i.e., basaltic) rock composed of Na-rich clinopyroxene and garnet Eclogite: mafic (i.e., basaltic) rock composed of Na-rich clinopyroxene and garnet

44 Pyroxenite: mafic to ultramafic rock, dominantly composed of pyroxene, often containing an Al-phase (e.g., plagioclase, spinel, garnet) Pyroxenite: mafic to ultramafic rock, dominantly composed of pyroxene, often containing an Al-phase (e.g., plagioclase, spinel, garnet)

45 Non-Rock Names Primitive Mantle/Silicate Earth: model composition for the crust + mantle. Primitive Mantle/Silicate Earth: model composition for the crust + mantle. Pyrolite: model composition for the primitive mantle, name derived from pyroxene-olivine-ite. Pyrolite: model composition for the primitive mantle, name derived from pyroxene-olivine-ite. Piclogite: model composition for the mantle, name derived from picritic-eclogite (picrite = olivine-rich basalt). Piclogite: model composition for the mantle, name derived from picritic-eclogite (picrite = olivine-rich basalt).

46 Lherzolite: A type of peridotite with Olivine > Opx + Cpx Olivine Clinopyroxene Orthopyroxene Lherzolite Harzburgite Wehrlite Websterite Orthopyroxenite Clinopyroxenite Olivine Websterite Peridotites Pyroxenites 90 40 10 Dunite Figure 2-2 C After IUGS

47 Mantle rock mineral assemblage Simple: 4 or 5 phases Simple: 4 or 5 phases Olivine (Ol) Olivine (Ol) Orthopyroxene (OPX) Orthopyroxene (OPX) Clinopyroxene (CPX) Clinopyroxene (CPX) Plagioclase (Pl) Plagioclase (Pl) Spinel (Sp) Spinel (Sp) Garnet (Gt) Garnet (Gt)

48 Composition of rocks Pyroliteharzburgitelherzoliteeclogite SiO 2 45464450 Al 2 O 3 4.51.22.216 FeO8.07.38.210 MgO3844418 CaO3.60.92.210 *Mg#89.491.589.958.8 *density  3.3853.3463.3763.970 olivine566265-- orthopyx183021-- clinopyx102850 garnet146650

49 Modal and physical property for lithospheric mantle of different ages (After O ’ Reilly et al., 2001)

50 Mantle Phase Diagrams

51 Phase diagram for aluminous 4-phase lherzolite: l Plagioclase F shallow (< 50 km) l Spinel F 50-80 km l Garnet F 80-400 km Si  VI coord. Si  VI coord. F > 400 km Al-phase = Figure 10-2 Phase diagram of aluminous lherzolite with melting interval (gray), sub-solidus reactions, and geothermal gradient. After Wyllie, P. J. (1981). Geol. Rundsch. 70, 128-153.

52 Mantle phase diagram

53 Phase assemblages and 1 atm density

54 Melting of Mantle Melt: Basalt Melt: Basalt Residue: Peridotite Residue: Peridotite

55 15 10 5 0 0.0 0.2 0.40.6 0.8 Wt.% Al 2 O 3 Wt.% TiO 2 Dunite Harzburgite Lherzolite Tholeiitic basalt Partial Melting Residuum Lherzolite is probably fertile unaltered mantle Dunite and harzburgite are refractory residuum after basalt has been extracted by partial melting Figure 10-1 Brown and Mussett, A. E. (1993), The Inaccessible Earth: An Integrated View of Its Structure and Composition. Chapman & Hall/Kluwer.

56 How does the mantle melt?? 1) Increase the temperature Figure 10-3. Melting by raising the temperature.

57 2) Lower the pressure –Adiabatic rise of mantle with no conductive heat loss –Decompression melting could melt at least 30% Figure 10-4. Figure 10-4. Melting by (adiabatic) pressure reduction. Melting begins when the adiabat crosses the solidus and traverses the shaded melting interval. Dashed lines represent approximate % melting.

58 3) Add volatiles (especially H 2 O) Figure 10-4. Figure 10-4. Dry peridotite solidus compared to several experiments on H2O-saturated peridotites.

59 Experiments on melting enriched vs. depleted mantle samples: Tholeiite easily created Tholeiite easily created by 10-30% PM More silica saturated More silica saturated at lower P Grades toward alkalic Grades toward alkalic at higher P 1. Depleted Mantle Figure 10-17a. Results of partial melting experiments on depleted lherzolites. Dashed lines are contours representing percent partial melt produced. Strongly curved lines are contours of the normative olivine content of the melt. “Opx out” and “Cpx out” represent the degree of melting at which these phases are completely consumed in the melt. After Jaques and Green (1980). Contrib. Mineral. Petrol., 73, 287-310.

60 Experiments on melting enriched vs. depleted mantle samples: l Tholeiites extend to higher P than for DM l Alkaline basalt field at higher P yet F And lower % PM 2. Enriched Mantle Figure 10-17b. Results of partial melting experiments on fertile lherzolites. Dashed lines are contours representing percent partial melt produced. Strongly curved lines are contours of the normative olivine content of the melt. “Opx out” and “Cpx out” represent the degree of melting at which these phases are completely consumed in the melt. The shaded area represents the conditions required for the generation of alkaline basaltic magmas. After Jaques and Green (1980). Contrib. Mineral. Petrol., 73, 287-310.

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62 Melting of mantle Mantle melting Melt=basalt Qz tholeiite Tholeiite Olivine tholeiite Picritic tholeiite Residues=peridotite Lherzolite Harzbergite Dunite T,P

63 CaO-Al 2 O 3 plot showing the range of mantle composition of different ages (O ’ Reilly et al., 2001) DEPLETION

64 Lherozlite from Hannuoba, North China Craton

65 Deepest mantle samples from transition zone: Deepest mantle samples from transition zone: Majorite-Bearing Xenoliths from Malaita,Ontong Java Oceanic Plateau- 9.5 GPa (260 km) to 22 GPa (570 km). Collerson et al., 2000, Science, 288:1215-1223

66 Estimating pressure of garnet and majorite

67 Mantle phase diagram

68 Common lherzolite xenoliths come from a depth of 50-80 km: lithosphere

69 Phase diagram for aluminous 4-phase lherzolite: l Plagioclase F shallow (< 50 km) l Spinel F 50-80 km l Garnet F 80-400 km Si  VI coord. Si  VI coord. F > 400 km Al-phase = Figure 10-2 Phase diagram of aluminous lherzolite with melting interval (gray), sub-solidus reactions, and geothermal gradient. After Wyllie, P. J. (1981). Geol. Rundsch. 70, 128-153.

70 Structure of lithosphere Nyblade, 2001

71 Lithosphere evolution in eastern North China craton (After O ’ Reilly et al., 2001)

72 Estimation of Primitive Mantle Composition

73 Mantle model circa 1975 Figure 10-16a After Basaltic Volcanism Study Project (1981). Lunar and Planetary Institute.

74 Newer mantle model F Upper depleted mantle = MORB+ crust sources F Lower undepleted & enriched OIB source Figure 10-16b After Basaltic Volcanism Study Project (1981). Lunar and Planetary Institute.

75 Earth Core Bulk Silicate Earth/Primitive mantle CrustMantle Upper=depleted Transition=primitive Lower=primitive

76 Primitive vs metasomatism Primitive: Flat REE Primitive: Flat REE Metasomatism: LREE enriched Metasomatism: LREE enriched

77 REE distribution of peridotite showing effect of mantle metasomatism Continental Crust MORB Garnet harzburgite Spinel lherzolite Primitive Mantle 10 2 10 1 10 -1 10 0 LaCePrNdSmEuGdTbDyHoErTmYbLu Chondrite normalization

78 Criteria for estimating Primitive Mantle Composition Should have refractory lithophile element ratios that are similar to CI chondrite. Should have refractory lithophile element ratios that are similar to CI chondrite.

79 Variations with MgO in peridotite

80 Constant refractory element ratios in peridotites

81 Elemental ratios in chondritic meteorites (McDonough and Sun, 1995)

82 Variation of refractory lithophile element ratios in peridotites (McDonough and Sun, 1995)

83 Estimating refractory lithophile elements in bulk silicate Earth (McDonough and Sun, 1995)

84 Estimates of Silicate Earth -Major elements

85 Estimates of Silicate Earth -Trace elements

86 Abundances of elements in Primitive mantle compared to CI condrites

87 Part 3-2 The Core and Bulk Earth

88 The Earth’s Interior Core: Fe-Ni metallic alloy Outer Core is liquid u No S-waves Inner Core is solid Figure 1-2. Major subdivisions of the Earth. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

89 Composition of the Core Poorly constrained beyond its major constituents (i.e., an Fe-Ni alloy). Poorly constrained beyond its major constituents (i.e., an Fe-Ni alloy). Presence of 5-15% of light element(s) (S, O, Si). Presence of 5-15% of light element(s) (S, O, Si). The dominant depository of siderophile elements in the Earth. The dominant depository of siderophile elements in the Earth.

90 Limits on the compositions of the core and bulk Earth (McDonough & Sun, 1995)

91 Liquid silicate-liquid metal partition coefficients

92 Comparison of element distributions in the Earth and carbonaceous chondrites The Earth is more strongly depleted in volatile elements

93 Figure 1-5. Relative atomic abundances of the seven most common elements that comprise 97% of the Earth's mass. An Introduction to Igneous and Metamorphic Petrology, by John Winter, Prentice Hall.

94 Part 3-3 The Oceanic crust

95 The Earth ’ s Crust Oceanic crust Thin: 10 km Relatively uniform stratigraphy = ophiolite suite: = ophiolite suite: Sediments Sediments pillow basalt pillow basalt sheeted dikes sheeted dikes more massive gabbro more massive gabbro ultramafic (mantle) ultramafic (mantle) Continental Crust Thicker: 20-90 km average ~35 km Highly variable composition –Average ~ granodiorite

96 Methods of study Ophiolite Ophiolite Ocean drilling Ocean drilling Seismic studies Seismic studies

97 Structure of oceanic crust

98 Plate Tectonics – Igneous Genesis 1. Mid-ocean Ridges 2. Intracontinental Rifts 3. Island Arcs 4. Active Continental Margins 5. Back-arc Basins 6. Ocean Island Basalts 7. Miscellaneous Intra- Continental Activity u kimberlites, carbonatites, anorthosites...

99 Composition of the Oceanic Crust (Taylor and McLennan, 1995)

100 Part 3-4 The Continental crust The continental crust accounts for 41% of the Earth surface. Approximately 31% of continental area is submerged beneath the oceans.

101 Importance of Determining Crustal Composition Basic constraints on evolution of the Earth. Basic constraints on evolution of the Earth. Most accessible part of the Earth and the best known. Most accessible part of the Earth and the best known. Place for formation of most of ore deposits. Place for formation of most of ore deposits. Important depository for highly incompatible elements (U, K, Cs). Important depository for highly incompatible elements (U, K, Cs). Essential for environmental studies and geochemical exploration. Essential for environmental studies and geochemical exploration.

102 Study of the composition of the continental crust can be traced back to earliest stage of geochemical studies F.M.Clarke, 1889 F.M.Clarke, 1889 F.M.Clarke and H.S.Washington, 1924 F.M.Clarke and H.S.Washington, 1924 V.M.Goldschmidt,1933, who is regarded as the father of modern geochemistry. V.M.Goldschmidt,1933, who is regarded as the father of modern geochemistry. S.R.Taylor, 1994 S.R.Taylor, 1994 D.M.Shaw, 1967 D.M.Shaw, 1967 S.R.Taylor and S.M. McLennan, 1985 S.R.Taylor and S.M. McLennan, 1985 K.H.Wedepohl, 1992 K.H.Wedepohl, 1992

103 What is the Continental Crust ? Extends vertically from the surface to the Mohorovicic discontinuity, a jump in compressional wave Vp speeds from ~7 km/s to ~8 km/s that is interpreted to mark the crust-mantle boundary. Extends vertically from the surface to the Mohorovicic discontinuity, a jump in compressional wave Vp speeds from ~7 km/s to ~8 km/s that is interpreted to mark the crust-mantle boundary. Stratification in seismic velocity and thus rock type and chemical composition. Stratification in seismic velocity and thus rock type and chemical composition. Lateral and vertically heterogeneous and great diversity in rock type. Lateral and vertically heterogeneous and great diversity in rock type.

104 Structure and compositional model of the continental crust (Wedepohl, 1995)

105 Metamorphic Facies Fig. 25-2. Temperature-pressure diagram showing the generally accepted limits of the various facies used in this text. Boundaries are approximate and gradational. The “typical” or average continental geotherm is from Brown and Mussett (1993). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Upper crust Middle Crust Lower Crust

106 Part 3-4-1 The Upper Continental Crust : the most accessible part of the Earth

107 Methods of Studies Large-scale regional sampling (e.g., the Canadian Shield) Large-scale regional sampling (e.g., the Canadian Shield) Using fine-grained clastic sediments Using fine-grained clastic sediments

108 Examples: The Canadian Shield and Eastern China. Examples: The Canadian Shield and Eastern China. The most reliable method for upper crustal composition estimation. The most reliable method for upper crustal composition estimation. The only method for major element composition studies. The only method for major element composition studies. Expensive and time-consuming. Expensive and time-consuming. Not pertain to the study of upper crustal composition in the geological history. Not pertain to the study of upper crustal composition in the geological history. Large-scale regional sampling

109 Sampling in Eastern China

110

111 Fine-Grained Clastic Sediments as Natural Sampling of the Exposed Upper Continental Crust Shale, mudstone, siltstone, graywack, tillite, and loess. Shale, mudstone, siltstone, graywack, tillite, and loess. Simple and much less expensive. Simple and much less expensive. The only way for studying upper crustal composition in geological history. The only way for studying upper crustal composition in geological history. Unsuitable to providing the major element composition. Unsuitable to providing the major element composition. Limited to REE, Y, Th, Sc, Co. Limited to REE, Y, Th, Sc, Co.

112 Geological influences on sedimentary rock composition-Solubility Water-upper crust partition coefficient: Water-upper crust partition coefficient: K y =Natural water/Upper crust K y =Natural water/Upper crust Seawater residence time  y : time for replacement of seawater element concentration. Seawater residence time  y : time for replacement of seawater element concentration.  y =M y /F y  y =M y /F y where M y is the mass of element y in the oceans and F y is the annual mean flux of element y through the ocean reservoir. where M y is the mass of element y in the oceans and F y is the annual mean flux of element y through the ocean reservoir.

113 Residence time vs seawater partition coefficients

114 Weathering Ca, Na and Sr are lost Ca, Na and Sr are lost K, Rb, Cs and Ba are retained. K, Rb, Cs and Ba are retained. Al, Ga, HSFE (Ti, Zr, Hf, Ta, Th) and REE, Y, Sc are immobile. Al, Ga, HSFE (Ti, Zr, Hf, Ta, Th) and REE, Y, Sc are immobile.

115 CIA: Chemical Index of Alteration CIA=Al 2 O 3 /(Al 2 O 3 +CaO*+Na 2 O+K 2 O) in molecular proportion Plagioclase is the dominant phase in the continental crust subjected to weathering. Plagioclase is the dominant phase in the continental crust subjected to weathering.

116

117 Erosion and transportation The sand-size effect. The sand-size effect. Quartz and heavy minerals (zircon, rutile, magnetite, chromite) are enriched in sandstone. Quartz and heavy minerals (zircon, rutile, magnetite, chromite) are enriched in sandstone.

118 Diagenesis Sensitive to redox conditions Sensitive to redox conditions Fe and Mn are soluble in anoxic conditions. Fe and Mn are soluble in anoxic conditions. Fe, Cu, Mo, Pb, Zn, V, Ni, S, C are clearly enriched in anoxic sediments due to incorporation in sulphides and/or absorption on organic compounds. Fe, Cu, Mo, Pb, Zn, V, Ni, S, C are clearly enriched in anoxic sediments due to incorporation in sulphides and/or absorption on organic compounds. U is enriched also in anoxic sediments due to reduction of soluble 6+ U to insoluble 4+ U. U is enriched also in anoxic sediments due to reduction of soluble 6+ U to insoluble 4+ U.

119 Metamorphism Poorly understood. Poorly understood. Li and Pb may increase. Li and Pb may increase. Most elements and particularly REE, Y, Th, HFSE, Cr and Sc are immobile. Most elements and particularly REE, Y, Th, HFSE, Cr and Sc are immobile.

120 Sedimentary rocks as crustal samples Insoluble elements (log   4; K sw  -4) are likely to be transferred almost quantitatively into clastic sediments and give the best information regarding the source-exposed upper crust. Insoluble elements (log   4; K sw  -4) are likely to be transferred almost quantitatively into clastic sediments and give the best information regarding the source-exposed upper crust.

121 REE in fine-grained sediments provide quantitative info on the upper crust composition Insoluble elements Ti Group Ti, Zr, Hf, Nb, Ta, Sn, Cr Heavy minerals Al Group Al, Ga Little dispersion in igneous rocks REE Group REE, Y, Th, Sc, Co, Fe Group Fe, Mn Redox sensitive Cu Group Cu, Pb, Zn Sulphides Quantitatively transferred into fine-grained clastic sediments

122 REE comparison of shales and upper crust

123 Constant element ratios in the upper crust

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125

126

127 Estimation of upper crustal composition Major elements: Major elements: large-scale sampling large-scale sampling Trace elements: Trace elements:  large-scale sampling  large-scale sampling  fine-grained clastic sediments   fine-grained clastic sediments  using REE and their ratios to using REE and their ratios to other elements other elements

128 Various upper crustal major element estimates Taylor & McLennanShaw et al.WedepohlCondieGao et al.Rudnick & Gao 198519671995199319982002 SiO26664.93 66.2165.4665.84 TiO20.50.52 0.550.650.60 Al2O315.214.63 14.9613.6514.31 FeOT4.503.97 4.705.134.92 MnO0.070.0680.070.10.10 MgO2.22.24 2.422.522.47 CaO4.24.12 3.63.313.46 Na2O3.93.46 3.512.753.13 K2O3.43.1 2.732.582.66 H2O0.79 2.11 P2O50.20.15 0.120.150.14 Total100.1797.98 98.8098.4199.71

129 Upper crustal compositional estimates (Taylor and McLennan, 1985)

130 Comparison of loess and upper crustal compositions (Taylor and McLennan, 1985)

131 Part 3-4-2 The deep crust

132 Methods of Studies Amphibolite- and granulite-facies xenoliths entrained mostly in basalts. Amphibolite- and granulite-facies xenoliths entrained mostly in basalts. Exposed deep crustal sections Exposed deep crustal sections Correlation of seismic velocities of rocks with lithologies Correlation of seismic velocities of rocks with lithologies Heat flow constraints Heat flow constraints

133 Crustal structure based on deep crusal xenoliths (Mengel et al., 1992)

134 Deep Crustal Xenoliths Mostly granulite-facies Mostly granulite-facies

135 Histogram of SiO 2 in granulite xenoliths (Rudnick, 1992)

136 Exposed Deep Crustal Section

137 Model for exposed deep crustal cross-section (Percival and Fountain, 1992)

138 P-wave and Poisson ’ s ratio structure along the exposed Kapuskasing deep crustal section (Percival and Fountain, 1994) P-wave velocity (km) Poisson ’ s ratio

139 Contrasts between granulite xenoliths and terrain granulites 麻 粒 岩 地 体 麻 粒 岩 地 体 麻 粒 岩 包 体 麻 粒 岩 包 体 时 代 时 代 太古- 元古宙 后太古宙 压 力 压 力 700-1000 MPa1000-1500 MPa 深 度 深 度 25-35 km35-50 km 岩 性 岩 性中性和长英质为主 镁铁质-超镁铁质为主 SiO 2 55-75%40-55%

140 Correlation of seismic velocities with rock types Compressional P-wave velocity (Vp) Compressional P-wave velocity (Vp) Shear S-wave velocity (Vs) Shear S-wave velocity (Vs) Poisson ’ s ratio (  ) Poisson ’ s ratio (  )  =0.5{1 – 1/[(Vp/Vs)2 – 1]}  =0.5{1 – 1/[(Vp/Vs)2 – 1]}

141 Measurement of seismic velocities of rocks

142 Calculation of velocities in depth V(z)=V(0) + [(dV/dP) T P + (dV/dT) P T]dz V(z)=V(0) + [(dV/dP) T P + (dV/dT) P T]dz Where V(0) and V(z) are velcities at a reference state and at depth z. For common rocks, (dV/dP) T =2  10 -4 to 7  10 -4 km s -1 MPa -1 ; (dV/dT) P = -2  10 -4 to -6  10 -4 km s -1  C -1 For common rocks, (dV/dP) T =2  10 -4 to 7  10 -4 km s -1 MPa -1 ; (dV/dT) P = -2  10 -4 to -6  10 -4 km s -1  C -1

143 Effect of heat flow on Vp (Rudnick and Fountain, 1995)

144 150 MPa 下侵入岩 Vp 随成分的变化 (Fountain and Christensen, 1989)

145 Relation between SiO 2 and Vp of granulites (Rudnick and Fountain, 1995)

146 Density vs Vp Peridotite Eclogite Mafic granulite

147 1 、蛇纹岩 2 、石英岩 3 、花岗岩 4 、花岗闪长岩 5 、角闪岩相长英质片麻岩 6 、石英云母片岩 7 、绿片岩相变辉长岩 8 、辉长岩 9 、斜长角闪岩 1 、长英质角闪片麻岩 2 、长英质片麻岩 3 、中性麻粒岩 4 、斜长岩 5 、镁铁质麻粒岩 6 、斜长角闪岩 7 、麻粒岩相变泥质岩 8 、辉石岩 9 、榴辉岩 10 、纯橄榄岩 / 二辉橄榄岩 Holbrook et al. (1992)

148 Crustal structure in various tectonic settings (Rudnick and Fountain, 1995)

149 Normative mineral composition of continental crust (Taylor and McLennan, 1995)

150

151 Comparison of upper, middle and lower crust compositions (Rudnick and Fountain, 1995)

152 Relation between Continental Crust and MORB

153

154 Comparison of various REE and trace element estimates of continental crust (Rudnick and Fountain, 1995)

155 Comparison of continental crust and various basalts (Hoffmann, 1994)

156 Compositional characteristics of continental crust The upper crust is granitic with 66% SiO 2 and with a significant negative Eu anomaly. The upper crust is granitic with 66% SiO 2 and with a significant negative Eu anomaly. The middle crust is tonalitic with 61% SiO 2. The middle crust is tonalitic with 61% SiO 2. The lower crust is mafic in many regions with ~52% SiO2 and may be more evolved for some cratons (e.g., North China Craton) and collision belts. The lower crust is mafic in many regions with ~52% SiO2 and may be more evolved for some cratons (e.g., North China Craton) and collision belts. Relative depletion in Nb and enrichment in Pb characterize the continental crust and continental crustal rocks- “ the arc signature ”. Relative depletion in Nb and enrichment in Pb characterize the continental crust and continental crustal rocks- “ the arc signature ”. The total continental crust has an andesitic/granodioritic bulk composition with 59- 62%. It contains a significant proportion of the bulk silicate Earth ’ s incompatible element budget (33- 35% of Rb, Ba, K, Pb, Th and U). The total continental crust has an andesitic/granodioritic bulk composition with 59- 62%. It contains a significant proportion of the bulk silicate Earth ’ s incompatible element budget (33- 35% of Rb, Ba, K, Pb, Th and U).

157 Schematic model for growth and evolution of the continental crust (Taylor and McLennan, 1995)

158 Continental crust LaCePrNdSmEuGdTbDyHoErTmYbLu 1 10 100 Rock/Chondrite East China (this study; Eu/Eu*=0.80) Wedepohl (1995; Eu/Eu*=0.83) Rudnick & Fountain (1995; Eu/Eu*=0.98) Taylor & McLennan (1995; Eu/Eu*=1.00) Total Continental Crust

159 Relative Vp change with depth under varying surface heat flows

160 Contrasting lower crustal velocities for Archean and Proterozoic provinces (Durrheim and Mooney, 1991)

161 The following slides are not used in the lectures

162 Generation of tholeiitic and alkaline basalts from a chemically uniform mantle Variables (other than X) –Temperature –Pressure Figure 10-2 Phase diagram of aluminous lherzolite with melting interval (gray), sub-solidus reactions, and geothermal gradient. After Wyllie, P. J. (1981). Geol. Rundsch. 70, 128-153.

163 Liquids and residuum of melted pyrolite Figure 10-9 After Green and Ringwood (1967). Earth Planet. Sci. Lett. 2, 151-160.

164 Initial Conclusions: Tholeiites favored by shallower melting Tholeiites favored by shallower melting –25% melting at < 30 km  tholeiite –25% melting at 60 km  olivine basalt Tholeiites favored by greater % partial melting Tholeiites favored by greater % partial melting –20 % melting at 60 km  alkaline basalt incompatibles (alkalis)  initial melts incompatibles (alkalis)  initial melts –30 % melting at 60 km  tholeiite

165 Crystal Fractionation of magmas as they rise Tholeiite  alkaline Tholeiite  alkaline by FX at med to high P l Not at low P F Thermal divide l Al in pyroxenes at Hi P  Low-P FX  hi-Al shallow magmas shallow magmas (“hi-Al” basalt) (“hi-Al” basalt) Figure 10-10 Schematic representation of the fractional crystallization scheme of Green and Ringwood (1967) and Green (1969). After Wyllie (1971). The Dynamic Earth: Textbook in Geosciences. John Wiley & Sons.

166 Primary magmas Formed at depth and not subsequently modified by FX or Assimilation Formed at depth and not subsequently modified by FX or Assimilation Criteria Criteria –Highest Mg# (100Mg/(Mg+Fe)) really  parental magma –Experimental results of lherzolite melts Mg# = 66-75 Mg# = 66-75 Cr > 1000 ppm Cr > 1000 ppm Ni > 400-500 ppm Ni > 400-500 ppm Multiply saturated Multiply saturated

167 Summary A chemically homogeneous mantle can yield a variety of basalt types A chemically homogeneous mantle can yield a variety of basalt types Alkaline basalts are favored over tholeiites by deeper melting and by low % PM Alkaline basalts are favored over tholeiites by deeper melting and by low % PM Fractionation at moderate to high depths can also create alkaline basalts from tholeiites Fractionation at moderate to high depths can also create alkaline basalts from tholeiites At low P there is a thermal divide that separates the two series At low P there is a thermal divide that separates the two series

168 REE data for oceanic basalts Figure 10-13a. REE diagram for a typical alkaline ocean island basalt (OIB) and tholeiitic mid-ocean ridge basalt (MORB). From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Sun and McDonough (1989). increasing incompatibility

169 Spider diagram for oceanic basalts increasing incompatibility Figure 10-13b. Spider diagram for a typical alkaline ocean island basalt (OIB) and tholeiitic mid-ocean ridge basalt (MORB). From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Sun and McDonough (1989).

170 REE data for UM xenolith s Figure 10-14 Chondrite-normalized REE diagrams for spinel (a) and garnet (b) lherzolites. After Basaltic Volcanism Study Project (1981). Lunar and Planetary Institute. LREE enriched LREE depleted or unfractionated LREE depleted or unfractionated LREE enriched

171 Cross-section of a subduction zone

172 俯冲板片的熔融和大陆地壳的形成 Whinter (2001)

173 The Geothermal Gradient Figure 1-9. Estimated ranges of oceanic and continental steady-state geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface. After Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311.

174 Fig. 25-3. Temperature- pressure diagram showing the three major types of metamorphic facies series proposed by Miyashiro (1973, 1994). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

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177 Earth ’ s earliest history (in Ma)

178 Upper mantle phase diagram

179 Craton vs off-craton differences

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184 Heat flow constrains

185 Heat flow structure

186 Incompatible lithophile element distributions caused by removal of basaltic melt from primitive mantle (Carlson, 1994)

187 REE comparison of various shales and upper crustal estimates

188 SiO2 distribution in granulites Rudnick and Fountain (1995)

189 Comparison of present and paleo- position of exposed crustal sections (Fountain et al., 1990)

190 Average Poisson ’ s ratio vs SiO2 for major rock types (Christensen, 1996)

191 UPPER CRUST MIDDLE CRUST UPPER LOWER CRUST LOWERMOST CRUST 14 km 24 km 32 km 37 km 0 km Sedimentary and Volcanic Rocks Granitoids Low-grade Metamorphic Rocks Vp=6.4 km/s SiO2=62% 90% TTGG gneiss 10% Amphibolite Vp=6.7 km/s SiO2=58% 100% intermediate granulite or 75% felsic+25%mafic granulite Vp=7.1 km/s, SiO2=52% Mafic granulite Bulk Lower Crust 53% Mafic granulite 47% Felsic granulite Vp=6.9 km/s SiO2=55-57% (52%, 7.14 km/s; R & F, 1995) Vp=6.0 km/s SiO2=65% Total Crust Vp=6.4 km/s SiO2=62-64% (59%, 6.67 km/s; R & F, 1995)

192 Comparison of Sr-Nd isotopic composition of basalts (Hofmann, 1994)

193 REE mobility in weathering profile

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195 REE distributions of heavy minerals

196 Effect of zircon addition

197 Effect of allanite addition

198 Effect of monazite addition

199 Interpretation of sedimentary Nd model ages in terms of sedimentary recyling

200  Nd vs Th/Sc for various modern sediments

201 Models for origin of plumes (Hofmann, 1994)

202

203 REE patterns for selected modern sediments

204 Effect of zircon enrichment Zircon enrichment

205 REE patterns of modern and Phanerozoic turbidites

206 Moder turbidite muds and Australian shales

207 Early Proterzoic sedimentary rocks from northern New Mexico and southern Corolado

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209 REE pattern of seawater

210 Ce/Ce* variation of seawter and clastic sediments with tectonic setting

211 Chemical variation of sediments from spreading ridge

212 Variation of REE patterns with stratigraphic order

213 Variation of REE from ridge

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216 Tectonic map of China ( 李献华 )

217 (据李献华)

218 扬子克拉通南缘沉积岩  Nd 随 时代的变化(李献华)

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223 Effect of monazite addition

224 Diagenetic chemical fractionation during formation of chert

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228 REE patterns of Eu-enriched turbidite sandstone

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