Milovanović D., Tucci P.,

Morbideli P., Popović D.

Milovanović D., Tucci P.,

Morbideli P., Popović D.

Petrology of mafic granulites from Bistrica, southern part of Zlatibor ultramafic massif

(Dinaridic ophiolite belt, Serbia)

Petrology of mafic granulites from Bistrica, southern part of Zlatibor ultramafic massif

(Dinaridic ophiolite belt, Serbia)

A L P S

A P E N I N

E S

T H

K A R P A

O

A

B A L K

N I

D E

S

D I N A R I D E S

General positionGeneral position

TISSIA

VČMTVČMT

SPPT

SPPT

HTHT

KT

KT

RVOT

RVOT

RVOT

RVOT

SMCT

SMCT

VZCT

VZCT

KBT

KBT

KBT

KBT

JBJB

DITDIT

DIT

DIT

VZWT

VZWT

VZWT

VZWT

DOT

DOT

EBDT

EBDT

DHCDHCTT

Concept of terranes by Concept of terranes by Prof Stevan KaramataProf Stevan Karamata

GEOLOGICAL MAP OF SERBIA&MONTENEGRO 1:500 000

GEOLOGICAL MAP OF SERBIA&MONTENEGRO 1:500 000 Pillow lavas

Ultramafites

LimestonesMelanges

Definition of term - mafic granuliteDefinition of term - mafic granulite

(A proposal on behalf of the IUGS Subcommision on the Systematics of Metamorphic Rocks,(Web version of 31.10.2002)

(A proposal on behalf of the IUGS Subcommision on the Systematics of Metamorphic Rocks,(Web version of 31.10.2002)

Granulite is a high-grade metamorphic rock in which Fe-Mg-silikates are dominantly hydroxil- free.... Granulite is a high-grade metamorphic rock in which Fe-Mg-silikates are dominantly hydroxil- free....

The basis of the rocks names is their mineralogy and structure.

The basis of the rocks names is their mineralogy and structure.

The rocks with >30% mafic mineral may be called mafic granulites.The rocks with >30% mafic mineral may be called mafic granulites.

The term should not be applied to calcsilicate rocks, marbl, ironstones and quartzites.The term should not be applied to calcsilicate rocks, marbl, ironstones and quartzites.

Ultramafic rocks

Ultramafic rocks

Mafic granulitesMafic granulites

Grt

Py

Plg

Amph

Grt

Chemistry of minerals

Py Amph

Plagioclase is Anorthite

Degrees of metamorphism

GrtGrt

AmphAmph

PyPy

PlPl

Grt-Py = 900-10000C, 10 kbars Grt-Py = 900-10000C, 10 kbars Grt-Ho = 830-8800C, 8-10 kbars Grt-Ho = 830-8800C, 8-10 kbars

Reactions:

Baz.Pl+PyI+H2O=Grt+PyII±HoII+An

orBaz.Pl+PyI+H2O=Grt+PyII±HoII+An

or

Baz.Pl+ HoI±PyI =Grt+PyII±HoII+An+H2OBaz.Pl+ HoI±PyI =Grt+PyII±HoII+An+H2O

T

P

Opx-free Grt+Cpx+Pl±Qtz assemblages

AmphiboliteAmphibolite

Eclogite

GranuliteGranulite

Opx+Cpx+Pl+Hbl+ Qtz)

Grt+Cpx+Opx+Pl

±(Hbl or Qtz)

Cpx+Grt±Amph±Qtz)

Grt+Cpx+Pl

±(Hbl or Qtz)

Grt+C

px+P

l

+Hb

l+Qtz

Hbl+Pl+Qtz±(Grt or Cpx)

Grt+C

px+P

l

+Hb

l+Qtz

1000 T (0C)8006004000

4

8

12

16P

(kb

ar)

Qtz-absent

Qtz-present

W&N 91S&D 94

Hbl

PlQtz

Grt

Cpx

L

GrtCpx

Qtz

Pl PlOpx

Hbl

QtzL

V

PlOpx

QtzCpx

Hbl

L Hbl+Qtz=Opx+Cpx+Pl+V

P&B 95R 93

C 88

E&T 86

W&W 94

N&C 00bN&C 00a

P 68,J 78 andWW 93

P&B 95B&L 91

CWT 67B 69

S 81

R 91

Experimental constraints

Degrees of metamorphism

There are significant discrepancies between experimental and natural constraints on the P–T conditions of opy-free grt + cpy+ pl ± Q bearing mineral assemblages and therefore on the P–T position of this reaction.

Protolith

No fractionation of Pl

?

Contamination,Partial melting ?

Protolith

Subduction ?

CONCLUSIONS

Major and trace element whole-rock geochemical data indicate that metamorphism was broadly izochemical

Garnet-clinopyroxene-hornblende-plagioclase thermo-barometry indicates peak metamorphic conditions of about 900-1000°C and 830-880°C at pressures 8-10 kbars Difference in temperature most probably represents a succesion of mineral forming in a cooling period under which hornblende was formed.

Absence of thermal relaxation features in mafic granulites require metamorphism with rapid exhumation

Fabrics of ultramafic rocks and mafic granulites suggest that development of the Grt-Cpx-Ho-Pl assemblages is connect with ophiolite emplacement, subduction, rather than having been caused by heat from the ophiolite.

METAMORPHISM

1000 T (0C)8006004000

4

8

12

16

P (

kbar

)

Qtz-absent

Qtz-present

W&N 91S&D 94

HblPl

Qtz

GrtCpxL

GrtCpx

Qtz

Pl PlOpx

Hbl

Qtz L

V

PlOpx

Qtz Cpx

Hbl

L Hbl+Qtz=Opx+Cpx+Pl+V

P&B 95R 93

C 88

E&T 86

W&W 94

N&C 00bN&C 00a

P 68,J 78 andWW 93

P&B 95B&L 91

CWT 67B 69

S 81

R 91

Experimental constraints

Gr+Py

Gr+Ho

Whole rock compositions, with well defined positive Eu anomalies indicate that protoliths of mafic granulites from Bistrica have a cumulus origin.Whole rock compositions, with well defined positive Eu anomalies indicate that protoliths of mafic granulites from Bistrica have a cumulus origin.

PROTOLITHPROTOLITH

Distinguishing oceanic plateau basalts from MORB is more difficult, because all geochemically gradations exist between these basalts. Distinguishing oceanic plateau basalts from MORB is more difficult, because all geochemically gradations exist between these basalts.

The trace element, rare earth element data suggest that Mafic granulites of Bistrica have protolith features resembling mid-ocean ridge basalt (MORB). The trace element, rare earth element data suggest that Mafic granulites of Bistrica have protolith features resembling mid-ocean ridge basalt (MORB).

The low silica content could be due to loss of a silicic melt (or fluid) during subduction, or loss of SiO2 during seafloor alterationThe low silica content could be due to loss of a silicic melt (or fluid) during subduction, or loss of SiO2 during seafloor alteration

Partial melting or dehydration of the subducted oceanic crust causes loss of LREE Partial melting or dehydration of the subducted oceanic crust causes loss of LREE

Mafic granulites could represent deep cumulus portions of subducted oceanic crust (olivine gabbros ?) Mafic granulites could represent deep cumulus portions of subducted oceanic crust (olivine gabbros ?)

Lack of sheeted dyke complexes in investigated area may suggest also an oceanic plateau (ophiolites formed in back arc basins?) Lack of sheeted dyke complexes in investigated area may suggest also an oceanic plateau (ophiolites formed in back arc basins?)

CONCLUSIONS

Metamorphic changes are most probably related with subduction off oceanic crust (basaltic rocks) during formation of Dinaridic ophiolite belt in Jurassic (?) Metamorphic changes are most probably related with subduction off oceanic crust (basaltic rocks) during formation of Dinaridic ophiolite belt in Jurassic (?)

CONCLUSIONS

THANK YOU