The Moslavačka Gora crystalline massif in Croatia: a Cretaceous heat dome within remnant Ordovician granitoid crust

Abstract

For a long time the Moslavačka Gora Massif in Croatia has been regarded as a major outcrop of Variscan crystalline basement of the South Tisia block. However, new geochronological data indicate that this massif consists of a Cretaceous S-type granite pluton intruding a Cretaceous low-pressure/high-temperature (LP/HT) metamorphic envelope. The age of the LP/HT metamorphism is estimated at *90-100 Ma using the method of electron microprobe based monazite dating. The Central Granite was dated at 82 ± 1 Ma (LA-SF-ICP-MS zircon age). The metamorphic complex comprises mainly felsic anatexites and orthogneisses of granitic composition, some metapelites (paragneisses and mica schists) and amphibolites. Zircons from three different samples of metagranite were dated at 486 ± 6, 483 ± 6, and 491 ± 1 Ma, suggesting that most of the metamorphic complex represents an Early Ordovician granitic series. The Cretaceous regional metamorphism culminated in granulite facies conditions of *750°C and 3-4 kbar. A retrograde metamorphic event at lower amphibolite facies conditions overprinted the metamorphic complex. This event is probably related to the intrusion of the Central Granite. The southeastern sector of the massif was additionally affected by post-granitic, predominantly NE oriented shearing at greenschist facies conditions. As yet there is no clear evidence for Variscan events in the Moslavačka Gora Massif. Mineral relics of a medium-pressure amphibolite facies metamorphism are preserved in amphibolites. They are older than the Cretaceous LP/HT regional metamorphism, but their age is presently unknown. Some indications for a Permian regional metamorphic event are provided by inherited zircons in the Central Granite that have been dated with a Permian age, and by Permian monazite relics in metapelites. The Cretaceous high heat flow regime recorded in the Moslavačka Gora Massif is unique in the subcrop of the Pannonian Basin and may be a local feature triggered by a mafic intrusion in the lower crust.

The tectonic evolution of a critical segment of the Dinarides‐Alps connection: Kinematic and geochronological inferences from the Medvednica Mountains, NE Croatia

“…In a first instance, it appears to suggest that the Sava Ocean was already closed in this segment of the Dinarides, in contrast with previously proposed latest Cretaceous age of collision [ Schmid et al , ; Ustaszewski et al , ]. The late Cretaceous extension of the Medvednica Mountains is in agreement with the ~100–90 Ma event of low‐pressure high‐temperature regional metamorphism followed by decompressional melting and emplacement of a granitic pluton at ~82 Ma during a period of crustal uplift, which is observed immediately eastward in the Moslavačka Gora Mountains [ Balen and Petrinec , ; Balen et al , ; Starijaš et al , ]. However, the earlier closure of the Sava Ocean is contradicted by the observation of late Cretaceous intraoceanic magmatism and the inferred latest Cretaceous age of collision more eastward in the region of Kozara Mountains situated in a central position along the northern Dinaridic border [ Ustaszewski et al , ].…”

“…To the SW of the studied area in Žumberak Mountains (Figure b), the Žumberak nappe thrusts mainly Upper Triassic dolomites, similar in facies to the Carnian‐Norian Hauptdolomit (or Dolomia Principale) of the Southern Alps, over an ophiolitic mélange and Cretaceous‐Paleogene sediments (Figure b) [ Tomljenović , ]. Interestingly, the Upper Triassic shallow‐water facies of the Žumberak nappe contrasts with coeval deep‐water facies documented in the internal part of the Dinarides following the overall deepening of the Adriatic passive continental margin [e.g., Dimitrijević , ; Starijaš et al , ; Toljić et al , ]. Thus, when compared with the facies of typical internal Dinaridic nappes, which include the Medvednica Mountains [see Schmid et al , ], the paleogeographic provenance of the Žumberak nappe is different.…”

The Late Cretaceous Klepa basalts in Macedonia (FYROM)—Constraints on the final stage of Tethys closure in the Balkans

“…Discrete magmatic centres along the Sava zone include Moslovačka Gora (Starijaš, Gerdes, Balen, Tibljas, & Finger, et al. ), Požeška Gora (Pamić & Šparica, ) and Prosara (Ustaszewski et al., ) in Croatia, Kozara (Ustaszewski et al., ) in Bosnia and Tešića Majdan (Prelević, Wehrheim, Božović, Romer, & Boev, ) in Serbia (Figure ). The origin and geodynamic significance of these centres have been considered either enigmatic (Ustaszewski et al., ) or clearly not ophiolitic (Cvetković et al., ).…”

The Alpine-Carpathian-Dinaridic orogenic system: correlation and evolution of tectonic units

“…We mapped its northern contact with the Mecsek nappe system after Csontos & Vörös (2004). However, we excluded the basement that crops out in the Moslavačka Gora inselberg in Croatia, previously considered as the westernmost tip of Tisza, from the Mecsek nappe system, and attributed it to the Sava Zone owing to the occurrence of mid-Cretaceous gabbros (109 ± 8 Ma; Balen et al 2003) and Late Cretaceous-age high-temperature metamorphism and magmatism (Starijaš et al 2006). The southern contact between the Bihor and the Codru nappe system is rather poorly constrained by subsurface data, except for the area south of Debrecen, where S-dipping reflectors indicate a shear zone (Posgay et al 2006, their Fig.…”

“…2c) Unfortunately, near Zagreb there are no exposures of the Sava Zone in the area of the junction of the Mid-Hungarian Fault Zone that includes the ophiolitic "Intra-Pannonian Belt" (Channell et al 1979) and the westernmost parts of the ophiolite-bearing Sava belt of the Dinarides. Furthermore, the tectonic position of the Moslavačka Gora inselberg, characterized by Cretaceous-age gabbros (109 ± 8 Ma, Balen et al 2003) and Late Cretaceous metamorphism and magmatism (Starijaš et al 2006), is not very clear. Although traditionally attributed to the Tisza Mega-Unit, we interpreted the Moslavačka Gora inselberg as part of the Sava Zone, guided by the fact that areas with a strong Mesozoic metamorphic overprint are unknown from the adjacent internal Dinarides and the Tisza Unit.…”