TY - JOUR
T1 - Mineralogy, petrology and geochemistry of amphibolites from the Kalnik Mt. (Sava Unit, North Croatia)
T2 - Implications for the evolution of north-westernmost part of the Dinaric-Vardar branch of Mesozoic Tethys
AU - Šegvić, Branimir
AU - Lugović, Boško
AU - Slovenec, Damir
AU - Meyer, Hans Peter
N1 - Publisher Copyright:
© 2016, Universita degli Studi di Firenze. All rights reserved.
PY - 2016
Y1 - 2016
N2 - This paper brings a first comprehensive set of mineralogical, petrological and geochemical data of amphibolites associated with mantle peridotites in the Upper Jurassic to mid Lower Cretaceous ophiolite mélange of Kalnik Mt. in northern Croatia. This mélange is emplaced in a Paleogene sedimentary succession. Metamorphic evolution of the amphibolites and the nature of their igneous protoliths are discussed in the frame of late history development of northwestern branch of Dinaric-Vardar Tethys. Primary amphibolite assemblages consist of pargasite-magnesio-hornblende and oligoclase-bytownite (common amphibolite) + almandine-grossular-rich garnet (garnet amphibolites) + clinopyroxene (clinopyroxene amphibolites). Minimum equilibration temperature for the amphibole-plagioclase pairs was estimated at 660±40°C, whereas the peak conditions (790±20°C at 0.79 to 1.04 GPa) were recorded in garnet amphibolite. Retrograde parageneses (albite, actinolite, clinozoisite, titanite, chlorite, pumpellyite, and ‘metamorphic vermiculite’) correspond to greenschist to subgreenschist facies conditions. Protolith REE patterns match modern ocean ridge basalts (LaN/LuN = 0.51-0.82) whilst the normalized multi-element diagram shows slight negative HFSE anomalies (NbN/LaN = 0.44-0.90), diagnostic for a subduction-zone geochemical signature. Overall, geochemical data suggest back-arc basin (BAB) tholeiitic mafic extrusives (lack of Eu anomaly) and IAT-like cumulates (Eu positive anomaly) as amphibolite precursors. The Kalnik Mt. amphibolites are proposed to have formed during the incipient intraoceanic subduction following the model of metamorphic sole at the expense of an oceanic crust originated at the ridge of a back-arc marginal basin. The metamorphism must have taken place during Tithonian (?) as inferred from the protolith age. According to the geological evidences the back-arc magmatic regime was active until the final closure of Mesozoic Tethys in Cretaceous by the obduction of Dinaric ophiolites onto the NW margins of Adria microplate, when part of the metamorphic sole must have been exhumed and obducted together with the rest of ophiolite sequence.
AB - This paper brings a first comprehensive set of mineralogical, petrological and geochemical data of amphibolites associated with mantle peridotites in the Upper Jurassic to mid Lower Cretaceous ophiolite mélange of Kalnik Mt. in northern Croatia. This mélange is emplaced in a Paleogene sedimentary succession. Metamorphic evolution of the amphibolites and the nature of their igneous protoliths are discussed in the frame of late history development of northwestern branch of Dinaric-Vardar Tethys. Primary amphibolite assemblages consist of pargasite-magnesio-hornblende and oligoclase-bytownite (common amphibolite) + almandine-grossular-rich garnet (garnet amphibolites) + clinopyroxene (clinopyroxene amphibolites). Minimum equilibration temperature for the amphibole-plagioclase pairs was estimated at 660±40°C, whereas the peak conditions (790±20°C at 0.79 to 1.04 GPa) were recorded in garnet amphibolite. Retrograde parageneses (albite, actinolite, clinozoisite, titanite, chlorite, pumpellyite, and ‘metamorphic vermiculite’) correspond to greenschist to subgreenschist facies conditions. Protolith REE patterns match modern ocean ridge basalts (LaN/LuN = 0.51-0.82) whilst the normalized multi-element diagram shows slight negative HFSE anomalies (NbN/LaN = 0.44-0.90), diagnostic for a subduction-zone geochemical signature. Overall, geochemical data suggest back-arc basin (BAB) tholeiitic mafic extrusives (lack of Eu anomaly) and IAT-like cumulates (Eu positive anomaly) as amphibolite precursors. The Kalnik Mt. amphibolites are proposed to have formed during the incipient intraoceanic subduction following the model of metamorphic sole at the expense of an oceanic crust originated at the ridge of a back-arc marginal basin. The metamorphism must have taken place during Tithonian (?) as inferred from the protolith age. According to the geological evidences the back-arc magmatic regime was active until the final closure of Mesozoic Tethys in Cretaceous by the obduction of Dinaric ophiolites onto the NW margins of Adria microplate, when part of the metamorphic sole must have been exhumed and obducted together with the rest of ophiolite sequence.
KW - Amphibolite
KW - Dinarides
KW - Metamorphic sole
KW - Neotethys. Kalnik Mt
KW - North Croatia
KW - Ophiolites
KW - Sava Unit
UR - http://www.scopus.com/inward/record.url?scp=84976348454&partnerID=8YFLogxK
U2 - 10.4454/ofioliti.v41i1.441
DO - 10.4454/ofioliti.v41i1.441
M3 - Article
AN - SCOPUS:84976348454
SN - 0391-2612
VL - 41
SP - 35
EP - 58
JO - Ofioliti
JF - Ofioliti
IS - 1
ER -