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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.

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Presentation on theme: "Milovanović D., Tucci P., Morbideli P., Popović D. Milovanović D., Tucci P., Morbideli P., Popović D. Petrology of mafic granulites from Bistrica, southern."— Presentation transcript:

1 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)

2 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 position

3 TISSIA VČMT SPPT HT KT RVOT RVOT SMCT VZCT KBT KBT JB DIT DIT VZWT VZWT DOT EBDT DHCT Concept of terranes by Prof Stevan Karamata GEOLOGICAL MAP OF SERBIA&MONTENEGRO 1: GEOLOGICAL MAP OF SERBIA&MONTENEGRO 1: Pillow lavas Ultramafites Limestones Melanges

4 Definition of term - mafic granulite (A proposal on behalf of the IUGS Subcommision on the Systematics of Metamorphic Rocks,(Web version of ) (A proposal on behalf of the IUGS Subcommision on the Systematics of Metamorphic Rocks,(Web version of ) 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.

5 Ultramafic rocks Mafic granulites Grt Py Plg Amph

6 Grt Chemistry of minerals Py Amph Plagioclase is Anorthite

7 Degrees of metamorphism

8 Grt Amph Py Pl Grt-Py = C, 10 kbars Grt-Ho = C, 8-10 kbars Reactions: Baz.Pl+PyI+H 2 O=Grt+PyII±HoII+An or Baz.Pl+PyI+H 2 O=Grt+PyII±HoII+An or Baz.Pl+ HoI±PyI =Grt+PyII±HoII +An+H 2 O Baz.Pl+ HoI±PyI =Grt+PyII±HoII +An+H 2 O T P Opx-free Grt+Cpx+Pl±Qtz assemblages Amphibolite Eclogite Granulite Opx+Cpx+Pl+Hbl+ Qtz) Grt+Cpx+Opx+Pl ±( Hbl or Qtz) Cpx+Grt ±Amph±Qtz) Grt+Cpx+Pl ± ( Hbl or Qtz) Grt+Cpx+Pl +Hbl+Qtz Hbl+Pl+Qtz ±(Grt or Cpx) Grt+Cpx+Pl +Hbl+Qtz 1000 T ( 0 C) P (kbar) Qtz-absent Qtz-present W&N 91 S&D 94 Hbl Pl Qtz Grt Cpx L Grt Cpx Qtz Pl Opx Hbl Qtz L V Pl Opx Qtz Cpx Hbl L Hbl+Qtz= Opx+Cpx+Pl+V P&B 95 R 93 C 88 E&T 86 W&W 94 N&C 00 b N&C 00 a P 68, J 78 and WW 93 P&B 95 B&L 91 CWT 67 B 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.

9 Protolith

10 No fractionation of Pl ? Contamination, Partial melting ? Protolith Subduction ?

11 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 °C and °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 ( 0 C) P (kbar) Qtz-absent Qtz-present W&N 91 S&D 94 Hbl Pl Qtz Grt Cpx L Grt Cpx Qtz Pl Opx Hbl Qtz L V Pl Opx Qtz Cpx Hbl L Hbl+Qtz= Opx+Cpx+Pl+V P&B 95 R 93 C 88 E&T 86 W&W 94 N&C 00 b N&C 00 a P 68, J 78 and WW 93 P&B 95 B&L 91 CWT 67 B 69 S 81 R 91 Experimental constraints Gr+Py Gr+Ho

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

13 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

14 THANK YOU


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