trace elements l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Trace elements PowerPoint Presentation
Download Presentation
Trace elements

Loading in 2 Seconds...

play fullscreen
1 / 39

Trace elements - PowerPoint PPT Presentation


  • 577 Views
  • Uploaded on

Trace elements. Chapter 2. Why use trace elements?. Note magnitude of major element changes.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Trace elements' - liam


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide2

Why use trace elements?

Note magnitude of major element changes

Figure 8-2.Harker variation diagram for 310 analyzed volcanic rocks from Crater Lake (Mt. Mazama), Oregon Cascades. Data compiled by Rick Conrey (personal communication).From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

slide3

Why use trace elements?

Now note magnitude of trace element changes

Figure 9-1. Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

slide4

Element Distribution

Goldschmidt’s rules (simplistic, but useful)

1.2 ions with the same valence and radius should exchange easily and enter a solid solution in amounts equal to their overall proportions

How does Rb behave? Ni?

slide6

Goldschmidt’s rules

  • 2. If 2 ions have a similar radius and the same valence: the smaller ion is preferentially incorporated into the solid over the liquid

Fig. 6-10. Isobaric T-X phase diagram at atmospheric pressure After Bowen and Shairer (1932), Amer. J. Sci. 5th Ser., 24, 177-213. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

slide7

3. If 2 ions have a similar radius, but different valence: the ion with the higher charge is preferentially incorporated into the solid over the liquid

slide8

CS

CL

  • Partition coefficient:

D =

Where CS = the concentration of some element in the solid phase

slide9

incompatible elements are concentrated in the melt

D « 1

  • compatible elements are concentrated in the solid

D » 1

slide11

Trace elements strongly partitioned into a single mineral

  • Ni - olivine in Table 9-1 = 14

Figure 9-1a. Ni Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

slide12

Incompatible trace elements concentrate  liquid

  • Reflect the proportion of liquid at a given state of crystallization or melting

Figure 9-1b. Zr Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

slide13

If XNi in the system doubles the XNi in all phases will double

Because of this, the ratios of trace elements are often superior to the concentration of a single element in identifying the role of a specific mineral

slide14

K/Rb often used  the importance of amphibole in a source rock

    • K & Rb behave very similarly, so K/Rb should be ~ constant
    • If amphibole, almost all K and Rb reside in it
    • Amphibole has a D of about 1.0 for K and 0.3 for Rb
slide15

Sr and Ba (also incompatible elements)

      • Sr is excluded from most common minerals except plagioclase
      • Ba similarly excluded except in alkali feldspar
slide16

Compatible example:

  • Ni strongly fractionated olivine > pyroxene
  • Cr and Scpyroxenes » olivine
  • Ni/Cr or Ni/Sc can distinguish the effects of olivine and augite in a partial melt or a suite of rocks produced by fractional crystallization
rare earth elements
Rare Earth Elements
  • Lanthanide series
  • Similar behavior
  • All +3 charge
  • Ionic radius shrinks with increasing atomic #
contrasts and similarities in the d values all are incompatible
Contrasts and similarities in the D values: All are incompatible

Also Note:

REE’s are more compatible in felsic, lower-T melts

contrasts and similarities in the d values all are incompatible20
Contrasts and similarities in the D values: All are incompatible

Also Note:

HREE are less incompatible (smaller size)

Especially in garnet

Eu can  2+ which conc. in plagioclase

slide21

REE Diagrams

Plots of concentration as the ordinate (y-axis) against increasing atomic number

  • Degree of compatibility increases from left to right across the diagram

Concentration

La Ce Nd Sm Eu Tb Er Dy Yb Lu

slide22

Eliminate Oddo-Harkins effect and make y-scale more functional by normalizing to a standard

    • estimates of primordial mantle REE
    • chondrite meteorite concentrations
slide23

10.00

8.00

?

6.00

sample/chondrite

4.00

2.00

0.00

56

La Ce Nd Sm Eu Tb Er Yb Lu

58

60

62

64

66

68

70

72

L

What would an REE diagram look like for an analysis of a chondrite meteorite?

slide24

10.00

8.00

6.00

sample/chondrite

4.00

2.00

0.00

56

La Ce Nd Sm Eu Tb Er Yb Lu

58

60

62

64

66

68

70

72

L

Divide each element in analysis by the concentration in a chondrite standard

slide25
Shape of REE plot determines
    • depth of melting
    • Minerals left behind (or melted)
    • % melt
slide26

REE diagrams for melting model of a garnet lherzolite for various values of F (% melt):

Small % melt,

incompatible elements

Screaming out of rock

Figure 9-4. Rare Earth concentrations (normalized to chondrite) for melts produced at various values of F via melting of a hypothetical garnet lherzolite using the batch melting model (equation 9-5). From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

slide27

Europium anomaly when plagioclase is

    • a fractionating phenocryst

or

    • a residual solid in source

Figure 9-5. REE diagram for 10% batch melting of a hypothetical lherzolite with 20% plagioclase, resulting in a pronounced negative Europium anomaly. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

high and low p melting in mantle
High and low P melting in mantle
  • In garnet or plag stability field?
slide31

Spider Diagrams

An extension of the normalized REE technique to a broader spectrum of elements

Chondrite-normalized spider diagrams are commonly organized by (the author’s estimate) of increasing incompatibility L  R

Different estimates  different ordering (poor standardization)

Fig. 9-6. Spider diagram for an alkaline basalt from Gough Island, southern Atlantic. After Sun and MacDonough (1989). In A. D. Saunders and M. J. Norry (eds.), Magmatism in the Ocean Basins. Geol. Soc. London Spec. Publ., 42. pp. 313-345.

slide32

Application of Trace Elements to Igneous Systems

1. Use like major elements on variation diagrams to document FX, assimilation, etc. in a suite of rocks

  • More sensitive  larger variations as process continues

Figure 9-1a. Ni Harker Diagram for Crater Lake. From data compiled by Rick Conrey. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

slide33

2. Identification of the source rock or a particular mineral involved in either partial melting or fractional crystallization processes

slide34

Shallow (< 40 km) partial melting of the mantle will have plagioclase in the resuduum and a Eu anomaly will result

Garnet concentrates the HREE and fractionates among them

Thus if garnet is in equilibrium with the partial melt (a residual phase in the source left behind) expect a steep (-) slope in REE and HREE

slide35

10.00

67% Ol 17% Opx 17% Cpx

8.00

6.00

sample/chondrite

4.00

2.00

0.00

56

La Ce Nd Sm Eu Tb Er Yb Lu

58

60

62

64

66

68

70

72

10.00

10.00

57% Ol 14% Opx 14% Cpx 14% Grt

8.00

60% Ol 15% Opx 15% Cpx 10%Plag

8.00

6.00

6.00

sample/chondrite

sample/chondrite

4.00

4.00

2.00

2.00

0.00

0.00

56

La Ce Nd Sm Eu Tb Er Yb Lu

58

60

62

64

66

68

70

72

La Ce Nd Sm Eu Tb Er Yb Lu

Garnet and Plagioclase effect on HREE

slide36

Figure 9-3. Change in the concentration of Rb and Sr in the melt derived by progressive batch melting of a basaltic rock consisting of plagioclase, augite, and olivine. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

slide37

Table 9-6 A brief summary of some particularly useful trace elements in igneous petrology

Use as a petrogenetic indicator

Element

Ni, Co, Cr

Highly compatible elements. Ni (and Co) are concentrated in olivine, and Cr in spinel and

clinopyroxene. High concentrations indicate a mantle source.

V, Ti

Both show strong fractionation into Fe-Ti oxides (ilmenite or titanomagnetite). If they behave

differently, Ti probably fractionates into an accessory phase, such as sphene or rutile.

Zr, Hf

Very incompatible elements that do not substitute into major silicate phases (although they may

replace Ti in sphene or rutile).

Ba, Rb

Incompatible element that substitutes for K in K-feldspar, micas, or hornblende. Rb substitutes

less readily in hornblende than K-spar and micas, such that the K/Ba ratio may distinguish these

phases.

Sr

Substitutes for Ca in plagioclase (but not in pyroxene), and, to a lesser extent, for K in K-

feldspar. Behaves as a compatible element at low pressure where plagioclase forms early, but

as an incompatible at higher pressure where plagioclase is no longer stable.

REE

Garnet accommodates the HREE more than the LREE, and orthopyroxene and hornblende do

2+

so to a lesser degree. Sphene and plagioclase accommodates more LREE. Eu

is strongly

partitioned into plagioclase.

Y

Commonly incompatible (like HREE). Strongly partitioned into garnet and amphibole. Sphene

and apatite also concentrate Y, so the presence of these as accessories could have a

significant effect.

Table 9-6. After Green (1980). Tectonophys., 63, 367-385. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

slide38

Trace elements as a tool to determine paleotectonic environment

  • Useful for rocks in mobile belts that are no longer recognizably in their original setting
  • Can trace elements be discriminators of igneous environment?
  • Approach is empirical on modern occurrences
  • Concentrate on elements that are immobile during low/medium grade metamorphism
slide39

Figure 9-8.(a) after Pearce and Cann (1973), Earth Planet, Sci. Lett., 19, 290-300. (b) after Pearce (1982) in Thorpe (ed.), Andesites: Orogenic andesites and related rocks. Wiley. Chichester. pp. 525-548, Coish et al. (1986), Amer. J. Sci., 286, 1-28.(c) after Mullen (1983), Earth Planet. Sci. Lett., 62, 53-62.