source and settings of grinitic rocks - PowerPoint PPT Presentation

About This Presentation

source and settings of grinitic rocks


Presentation – PowerPoint PPT presentation

Number of Views:12


Transcript and Presenter's Notes

Title: source and settings of grinitic rocks

Presentation on Sources and settings of
granitic rocks
  • Presented
  • By
  • Indrajeet Saket
  • Ph.D Research Scholar Department of Geology
  • Under supervision
  • of
  • Dr. Meraj Alam (Assistant Professor)
  • Department of Geology IGNTU, Amarkantak

  • Granites are defined in the broadest sense as any
    coarse grained igneous rock containing more than
    5 quartz.
  • Source is defined as the mantle or crustal or
    crustal protolith that contributes directly or
    indirectly to the granite magma.
  • Setting is defined as the global tectonic
    environment in which the parent magma is

  • Two end-member sources of granitic magma
  • Mantle and Crust
  • Mantle source
  • Mantle asthenosphere composition upper mantle
    depleted in incompatible trace elements relative
    to primordial mantle "and often known as
    depleted mantle MORBS (DMM).
  • Mantle Lithosphere composition the mantle
    lithosphere can from a same composition the
    mantle lithosphere can also be ultra-depleted
    incompatible trace element.
  • Mantle-melting-the principle variables are the
    nature and degree of melting.

  • Fig. Source setting of the granite rocks. The
    melting process by which sources generate magma
    are also variable and dependent on setting.
  • DMM
  • AFC
  • MASH

Crustal source variables
  • Crustal composition this varies according to
    rock type and depth in the crust.
  • Igneous and sedimentary protolith. Igneous
    protolith are mainly granites and basalts,
    sedimentary protolith are not exclusively
    siliciclastic and pelitic.
  • Partial crustal melting this process involve
    partial melting of the crust but also effective
    separation of of melt from residue.
  • For the major element Si, Al, Ca, Mg, Na, K, Ti,
    Fe, Mn and P(whole rock) geochemistry 
  • and some trace element
  • Trace elements Partitioning between crystalline
    and liquid phases Partition coefficient
  • D ltlt 1, incompatible elements Large Ion
    Lithophile Elements (LILE) K, Rb, Sr, Ba, Zr,
    U, Th, REE, etc.
  • D gt 1, compatible elements Ni, Cr, Co, etc.
  • Volatile fluxing this may be a cause of some
    intra crustal melting and may also transport into
    the melting region.
  • Simple fluids during prograde metamorphism may
    not be effective of granite

Fig. . Normalized abundances of
incompatible elements in volcanic rocks from Site
U1438. (a) and (b) show fluid immobile trace
elements in Unit 1 basalts compared with various
types of MORB (a) and FAB (b). N-MORB are from
Hofmann (1988), Sun and McDonough (1989), Arevalo
and McDonough (2010) and DMORB are from Salters
and Stracke (2004) and Gale et al. (2013). FAB
data are from Reagan et al. (2010) and Ishizuka
et al. (2011a). (c) shows normalized abundances
of both fluid mobile and immobile incompatible
elements in andesites in sedimentary Unit IV
compared with basalts from basement subunit 1c
and the active Mariana Island arc (Elliott et
al., 1997).
Mantle-crust source interaction
  • Mantle-crust interaction this subduction
    component may be aqueous fluid and siliceous melt
    may be derived from one or both of subducted
    oceanic crust and subducted sediment.
  • MASH (magma assimilation, segregation
    homogenisation) the process and injection of
    mantle-derived magma into the hot base of the
    crust to produce a complex mixture of basic
  • AFC the describes process of wall-rock
    assimilation combined with crystallisation in a
    magma chamber (De Paolo, 1981) the key variable
    in addition to the composition of the magma and
    crust is the relative rate of assimilation and

AFC (Assimilation, fractional crystallisation)
Tectonic Settings
  • Ocean ridge granite (ORG) are the typically small
    volume they are dominantly tonalite and oceanic
    plagiogranite metaluminous and alkali calcic to
    calcic with clinopyroxene and amphibole as the
    principle of mafic minerals.
  • Mid ocean ridges mid oceanic ridges to plume
    related ridge to supra subduction zone ridge the
    mantle source is more enriched because of the
    mixing of the plume mantle with the depleted
    upper mantle reservoir.

Volcanic Arc
  • Volcanic arc may be oceanic or continental crust
    they usually from by melting of mantle
    asthenosphere modified by a subduction component.
    The asthenosphere ifs typically similar to more
    depleted than the MORB reservoir although there
    are exceptions. High degree of partial melting
    especially beneath thin lithosphere.
  • Volcanic Arc granite island arc terranes and
    linear composite batholiths at active continental
    margin. they commonly form I type granodiorite
    and tonalite intrusion which are metaluminous
    calc-alkaline with amphibole, pyroxene and
    biotite as common ferromagnesian minerals.
    volcanic Arc granite have a standard subduction
    signature of with enrichment in LIL element and
    relative to HFSE through crustal interaction is
    common. The hydrous phases especially amphibole
    in their crystallisation sequence also mean that
    element in the REE.

  • S type Granitoids
  • I type granitoids

  • A Type Granitoids
  • M type Granitoids ophiolite sequence

Within Plate Settings
  • The plate setting typically comprises small
    volume of intrusion in the continental rift and
    ocean island setting they are typically alkali
    granite with para alkaline composition contain
    sodic pyroxene and amphibole. The strong
    enrichment in both LIL and HFSE characteristic of
    derivation of an enriched mantle source. Magma
    genesis involve melting of plume related
    asthenosphere and enrich lithosphere.

(No Transcript)
(No Transcript)
Tectonic settings Discrimination
  • Discrimination plot diagram Rb-(NbY) and Nb-Y
    (PEARCE et al.1984)

Write a Comment
User Comments (0)