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        Revision: Plate Tectonic environments; major elements and common trace elements, element compatibility.

        Research over the last 20 years has demonstrated that a variety of Plate Tectonic environments can be characterised by the chemistry of the rocks, both volcanic and sedimentary, found in those environments. This has given rise to the idea of chemical fingerprinting as a technique for identifying plate environments in ancient terrains.

        Plate Tectonic environments can be classified in a simple way as follows:
                                   OCEANIC ENVIRONMENTS

        a) Oceanic plates formed by basaltic volcanism at Mid-Ocean ridges. The volcanic material is known under the acronym 'MORB' or NMORB; e.g. mid-Atlantic ridge. MORB rocks relatively enriched in alkali elements are known as EMORB, and varieties between NMORB and EMORB are called TMORB (Transitional MORB). There is a full spectrum of types between NMORB and EMORB.
        b) 1)Oceanic volcanic rock added to the oceanic crust by the intrusion of basalt related to mantle 'plume' activity, e.g. Hawaiian islands, Iceland, etc. Acronyms: OIB, OIT, WPT, PMORB (=EMORB).
         2) Oceanic small mantle melts of alkalic material related to plume activity. Acronyms:OIA, WPA; e.g. Hawaii.
         3) Archean komatiitic volcanics. Acronyms: PK, BK.

        c) 1) Very primitive 'Boninitic' island arcs; Bonin Islands;Marianas.
         2) Immature oceanic island arcs; low-K tholeiites; pigeonitic series; Acronyms: LKT, IAT; e.g. Tonga.
         3) Mature oceanic island arcs; calcalkaline; hypersthenic series; high-Al series. Acronyms: CAB (basalt), CAD (dacite), CAR (rhyolite); e.g. Japan, Aleutians
         4) Very mature 'Shoshonitic' island arcs, K2O wt% > Na2O wt%; e.g. Fiji.
                        CONTINENTAL ENVIRONMENTS

      a) Continental rifts; bimodal basalt-rhyolite association; high-Ti basalts, peralkaline rhyolite. Acronyms: WPB; WPT; WPA; e.g. Afar Triangle, East African Rift
        b) Volcanic arcs; Acronyms: CA; e.g. the Andes; NewZealand.
        c) Collisional zones. Acronyms: synCOLG; e.g. the Himalayas.

    Common acronyms:
BK Basaltic komatiite
CA Calc-alkaline
CA  Continental arc
CB Calc-alkali basalt
CAB Calc-alkali basalt
CD Calc-alkali dacite
CR Calc-alkali rhyolite
HFT High Fe tholeiite
HMT HIgh Fe tholeiite
IAB Island arc basalt
IAT Island arc tholeiite
LKT Low-K tholeiite
MORB Mid Ocean ridge basalt
OFB Ocean Floor basalt
OIA Oceanic island alkali
OIT Oceanic island tholeiite
ORG Orogenic granite
PK Peridotitic komatiite
TA Tholeiitic andesite
TB Tholeiitic basalt
TD Tholeiitic dacite
TMORB Transitional MORB
TR Tholeiitic rhyolite
TH or Thol Tholeiitic
VAB Volcanic arc basalt
VAG + synCOLG Volcanic arc granite and syn-collisional granite
WPA Within-plate alkali
WPB Within-plate basalt
WPG Within-plate granite
WPT Within-plate tholeiite
(Spreading Centre Island; Orogenic; Ocean Ridge and Floor; Ocean Island; Continental)

        The geochemical fingerprinting is carried out by plotting geochemical data on variation diagrams, and looking for characteristic inter-element relationships that characterise each geotectonic environment.
        Variation diagrams encompass both major elements and trace elements.

    Major elements:

    Remember: in bipolar plots of incompatible elements, the primary ratio is given by the slope of the trend line or the ratio of the elements in the most primitive member of the series.

    Bipolar plots :       1) SiO2 v total alkalies; 2) FeO v MgO;

    Triangular plots :   1) A-F-M; iron enrichment versus increase in FeO/MgO; cumulates versus liquids (use of partition coefficients);

    FeO/MgO plots : 1)  FeO; SiO2; TiO2; Cr

    Cr V TiO2

    Boina volcanics of the Afar Rift zone - elements versus residual melt fraction (Note: how the trend lines indicate which elements are behaving as compatible or incompatible elements, and that only K approaches being totally incompatible for most of the fractionation.)

       Fingerprinting using trace elements

    Crystallization of certain mineral phases is recognisable in the abundance variation of certain elements with which the phases have a compatible relationship. The following elements are particularly valuable in trace element 'fingerprinting'.
    Cr - garnet; Y and Yb - garnet; Ni - olivine; Sc - clinopyroxene; Sr - plagioclase, carbonates (Celestine - SrSO4); Ti, V, and Co - magnetite; Rb - K-feldspar, biotite; Ba - Kfeldspar (Celsian, Hyalophane); REE - apatite, zircon, monazite; Hf - zircon; Ta and Nb - titanite; Zn - spinel, staurolite; Cu - sulphides; Pt, Pd, Ir - sulphides;

             Bipolar plots
    Compatible versus compatible
    Ni v Cr
    Compatible v incompatible
    Ni v Y;

Nickel versus Yttrium.

    Incompatible versus partly incompatible
    Rb v Sr
    Incompatible versus incompatible
    K v Rb; K v Ba; K v LREE; Nb v Y; Ti v Zr

Niobium versus Yttrium.

Titanium versus Zirconium, and Ti-Zr-Sr/2 triangular plot.

    Triangular plots : Ti/100-Zr-3*Y; Ti-Zr-Sr/2;

Titanium/100-Zirconium-3Y triangular plot.

    Isotopes: 87Sr/86Sr v 143Nd/144Nd

143Nd/144Nd versus 87Sr/86Sr.


Allegre, C.J. and Minster, J.F. 1978. Quantitative models of trace element behaviour in magmatic processes. Earth Planetary Sci. letters, 38, 1-25.
Apted, M.J. and Roy, S.D. 1981. Corrections to the trace element fractionation equations of Hertogen and Gijbels (1976). Geochim. Cosmochim.,45, 777-778.
Hanson, G.N. and Langmuir, C. H. 1978. Modelling of major elements in mantle-melt systems using trace element approaches. Geochimica et Cosmochimica Acta, 42, 725-741.
Hertogen, J. and Gijbels, R. 1976. Calculation of trace element fractionation during partial melting. Geochim. Cosmochim. Acta, 40, 313-322.
Hofmann, A.W. and Hart, S.R. 1978. An assessment of local and regional isotopic equilibrium in the mantle. Earth Planetary Sc. Letters, 38, 44-62.

Jahn, B-M, Chi-Yu, S., and Rama Murthy, V., 1974. Trace element geochemistry of Archean volcanic rocks. Geochim. Cosmochim Acta, 38, 611-627.
Jakes, P. and White, A.J.R. 1972. Major and trace element abundances in volcanic rocks of orogenic areas. Bull. Geol. Soc. America 83, 29-40.
Jakes, P. and Gill, J. 1970. Rare earth elements and the island arc tholeiite series. Earth Planetary Sci. Letters, 9, 17-28.
Nisbett, E.G. and Pearce, J.A. 1977. Clinopyroxene composition in mafic lavas from different tectonic settings Contr. Mineral. Petrol. 63, 149-160.
Morrison, M. A., 1978, The use of "immobile" trace elements to distinguish the palaeotectonic affinities of metabasalts: applications to the Palaeocene basalts of Mull and Skye, northwest Scotland, Earth Planet. Sci. Lett., 39, 407-416.
Pearce, J.A. and Cann, J.R. 1973. Tectonic setting of basic volcanic rocks determined using trace element analyses. Earth Planetary Sci. Letters, 19, 290-300.
Pearce, J.A. and Norry, M.J. 1979. Petrogenetic implications of Ti, Zr, Y, and Nb variations in volcanic rocks. Contr. Mineral. Pet., 69, 33-47.
Smith, R.E. and Smith, S.E. 1976. Comments on the use of Ti, Zr, Y, Sr, K, P, and Nb in classification of basaltic magmas. Earth Planetary Sci. Letters, 32, 114- 120.
Taylor, S.R., Capp, A.C., and Graham, A.L., and Blake, D.H. 1969. Trace element abundances in andesites. II. Saipan, Bougainville, and Fiji. Contr. Mineral. and Petrol. 23, 1-26.
Thompson, R.N., Morrison, M. A., Mattey, D.P., Dickin, A.P., and Moorbath, S. 1980. An assessment of the Th-Hf-Ta diagram as a discrimant for tectonomagmatic classification and in the detection of crustal contamination of magmas. Earth Planetary Sci. Letters 50, 1-10.
Winchester, J.A. and Floyd, P.A. 1976. Geochemical magma type discrimination : application to altered and metamorphosed basic igneous rocks. Earth Planetary Sci. Letters 28, 459-469.
Wood, D. A., 1979, A re-appraisal of the use of trace elements to classify and discriminate between magma series erupted in different tectonic settings, Earth Planet. Sci. Letters, 45, 326-336.

Anderson, A.T., Jr., Significance of hornblende in calc-alkaline andesites and basalts. Am. min., 65, 837-851.
Armstrong, R.L. 1971. Isotopic and chemical constraints on models of magma genesis in volcanic arcs. Earth Planetary Sci. Letters 12, 137-142.
Hellman, P.L. and Green, T.H. 1979. The role of sphene as an accessory phase in the high-pressure partial melting of hydrous mafic compositions. Earth Planetary Sci. Letters, 42, 191-201.
Miyashiro, A., 1975. Island arc volcanic rock series : a critical review. Petrologie, 1, 177-187.
Sun, S.S. 1975. Evolution of the mantle : geochemical evidence form alkali basalts. Geology, 3, 297-302. Discussion by Gill, J.B. and reply by Sun and Hanson in Geology 1976, 625-631.


Structural Provinces of North America.

Niobium versus Yttrium.

Nickel versus Yttrium.

Titanium versus Zirconium, and Ti-Zr-Sr/2 triangular plot.

Titanium/100-Zirconium-3Y triangular plot.

143Nd/144Nd versus 87Sr/86Sr.

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