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Milovanović D., Tucci P., Morbideli P., Popović D. Petrology of mafic granulites from Bistrica, southern part of Zlatibor ultramafic massif (Dinaridic ophiolite belt, Serbia). K A R. P A. T H. O. B A L K. A. N I. D. E S. General position. A L P S. - PowerPoint PPT Presentation
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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
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