Two types of metamorphic monazite with contrasting La/Nd, Th, and Y signatures in an ultrahigh-pressure metapelite from the Pohorje Mountains, Slovenia: Indications for pressure-dependent REE exchange between apatite and monazite?

Krenn, Erwin; Janák, Marian; Finger, Friedrich; Broska, Igor; Konečný, Petr

doi:10.2138/am.2009.2981

Cited by 37 publications

(34 citation statements)

References 63 publications

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“…Garnet is the paramount Yttrium container in metapelites [ Pyle et al , 2001] which explains the low Yttrium content in the coexisting monazite. The higher Yttrium contents are most likely related to retrograde breakdown of garnet, which has been documented in the monazites from the UHP metapelites of Pohorje Mountains [ Krenn et al , 2009]. This suggests that the low‐Yttrium monazite generation records the timing of UHP metamorphism in our sample.…”

Section: The Nestos Shear Zonementioning

confidence: 54%

The exposed base of a collapsing wedge: The Nestos Shear Zone (Rhodope Metamorphic Province, Greece)

et al. 2011

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[1] The Nestos Shear Zone (NSZ) in the Rhodope Metamorphic Province is a major high-strain zone between two metamorphic terranes. Microdiamond-bearing ultrahigh-pressure (UHP) rocks occur in the NSZ which was therefore interpreted as a suture zone where subduction and exhumation of these rocks and terrain accretion occurred during the Mesozoic. Our petrological study of samples from the lower part of the NSZ, together with monazite dating of a microdiamond-bearing garnet schist, structural observations, already published results from the upper part, and other published timing constraints, results in a fundamentally different picture: the NSZ is the base of an Eocene age southwestward thrust wedge which included not only the structurally higher parts of the Rhodope Metamorphic Province but also the entire Internal Hellenides. The UHP rocks, for the peak pressure of which we derive an age of ∼200 Ma by monazite dating, are unrelated to the tectonic processes in the NSZ and probably represent slivers of a higher tectonic unit captured by thrusting along the NSZ. Pressure decrease in the footwall and regional extension and basin formation in the hanging wall during the activity of the NSZ show that the overlying thrust wedge was collapsing in late Eocene times. We hypothesize that the transition from subduction to continental collision may start with a pronounced accretion event when the first detachment horizon forms in the middle crust of the downgoing plate. Such an event could trigger slab retreat, an extensional collapse of the internal wedge, and subsequent magmatism.

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Section: The Nestos Shear Zonementioning

confidence: 54%

The exposed base of a collapsing wedge: The Nestos Shear Zone (Rhodope Metamorphic Province, Greece)

et al. 2011

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“…Some of the zircon cores record Permian to Triassic events, most probably reflecting HT-LP metamorphism at that time. Chemical Th-U-Pb (EMPA) dating of monazite (Krenn et al 2009) yielded an age of 100± 6 Ma.…”

Section: Metamorphic Rocksmentioning

confidence: 99%

Tectonic evolution of the southeastern part of the Pohorje Mountains (Eastern Alps, Slovenia)

Kirst¹,

Sandmann²,

Nagel³

et al. 2010

Geologica Carpathica

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Field relations and deformation structures in the southeastern part of the Pohorje Mountains constrain the tectonic evolution of the Austroalpine high-pressure/ultrahigh pressure (HP/UHP) terrane. The Slovenska Bistrica Ultramafic Complex (SBUC) forms a large (ca. 8 1 km size) body of serpentinized harzburgite and dunite including minor garnet peridotite and is associated with partly amphibolitized eclogite bodies. The SBUC occurs in the core of an isoclinal, recumbent, northward closing antiform and is mantled by metasedimentary rocks, mostly gneisses and a few marbles, including isolated eclogite/amphibolite lenses. Before this folding, the SBUC formed the deepest part of the exposed terrane. We interpret the SBUC to be derived from near-MOHO, uppermost mantle which was intruded by gabbros in the subsurface of a Permian rift zone. During Cretaceous intracontinental subduction, the SBUC was most likely part of the footwall plate which experienced HP to UHP metamorphism and was folded during exhumation. In the Miocene, the Pohorje Pluton intruded and, subsequently, the metamorphic rocks together with the pluton were deformed probably due to east-west extension and contemporaneous north-south shortening, thus forming an antiformal metamorphic core complex.

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“…Calcite also occurs along the apatite grain boundaries (Figure a) and seals the fractures in apatite. Oriented monazite and pyrrhotite inclusions in apatite have been reported from a variety of rocks from several UHP localities, including the Dabie and Sulu UHP terranes in China (Liang et al, ; Liu, Massonne, Wu, et al, ; Sun et al, ; Zhang & Liou, ; Zhu & Massonne, , ), the Pohorje Mountains in Slovenia (Krenn et al, ), the Rhodope UHP metamorphic province in Greece (Kostopoulos et al, ), and the Tromsø Nappe of the Scandinavian Caledonides in Norway (Broska et al, ). Dolomite inclusions oriented parallel to the c‐axis of apatite have been found in UHP carbonate‐rich rocks in the Tromsø Nappe of the Scandinavian Caledonides in Norway (Broska et al, ), but the oriented calcite inclusions found in apatite of this study, as far as we know, have never been documented for any UHP rock.…”

Section: Discussionmentioning

confidence: 99%

High‐Pressure Fluid‐Rock Interaction and Mass Transfer During Exhumation of Deeply Subducted Rocks: Insights From an Eclogite‐Vein System in the Ultrahigh‐Pressure Terrane of the Dabie Shan, China

Liu

Massonne

Harlov

et al. 2019

Geochem Geophys Geosyst

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A petrological study was performed on an eclogite-vein system from the Dabie ultrahigh-pressure terrane by focusing on high-pressure (HP) fluid-rock interaction and mass transfer during exhumation. The veins comprise mainly garnet and quartz and resulted from a HP leaching process along fractures in the eclogite during exhumation. Relict peak garnet, phengite, and apatite in this rock system were altered by HP fluids forming characteristic compositional zonings. Zoned garnet in the eclogite records an isothermal exhumation from 3.3 GPa and 665-680°C. Partial dissolution of garnet and a back incorporation of Mn-heavy rare earth element (REE)-Y increased the content of these elements in the altered garnet zone in the veins. Altered phengite is characterized by a Ba-rich rim. Fluid-aided alteration reduced the light REE (LREE) contents and produced oriented monazite, calcite, and pyrrhotite inclusions within apatite, reflecting mobilization and redistribution of LREEs, CO 3 2− , Fe, and S between these minerals. The active HP fluid is proposed to have been a Si-Al-Na-Ba-rich aqueous fluid, as indicated by sodic plagioclase rims around various eclogitic minerals and by the altered phengite composition. Mass balance calculations reveal that LREEs, middle REEs, and Zr-Hf-Th-U were added to and Li, large ion lithophile elements, and Ti-Nb were removed from the quartz-garnet veins, requiring a high fluid flux. These findings shed new light on the nature and behavior of HP fluids and highlight their key role in resetting mineral chemistry and mass transfer in subduction zone metamorphic environments. . (2019). High-pressure fluid-rock interaction and mass transfer during exhumation of deeply subducted rocks: insights from an eclogite-vein system in the ultrahigh-pressure terrane of the Dabie The Dabie-Sulu orogenic belt in east-central China is considered to be one of the largest UHP terranes on Earth. This belt resulted from the Triassic continental collision between the North China and South China blocks (Ernst et al., 2007;Li et al., 1993;Zhang et al., 2009). It is separated into the eastern Sulu terrane and the western Dabie terrane by the sinistral Tanlu strike-slip fault. The western part of the Dabie terrane is further truncated by the Shangma fault and known as the Hongan terrane (Figure 1a).Several large-scale EW trending faults divide the Dabie terrane into five major lithotectonic units with different metamorphic histories (Hacker et al., 2000;Zheng et al., 2005). From north to south, these units are (1) the Beihuaiyang greenschist-facies unit made up of low-grade metasedimentary and metaigneous rocks that are overlain by Jurassic-Cretaceous sedimentary and volcanic rocks; (2) the North Dabie high-T granulite-facies unit composed of typical amphibolite-to granulite-facies rocks, migmatitic gneisses, and minor mafic to ultramafic rocks; (3) the Central Dabie medium-T/UHP eclogite-facies unit including abundant orthogneisses and paragneisses that enclose subordinate bodies of coesite-bearing eclogite, pure to imp...

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Two types of metamorphic monazite with contrasting La/Nd, Th, and Y signatures in an ultrahigh-pressure metapelite from the Pohorje Mountains, Slovenia: Indications for pressure-dependent REE exchange between apatite and monazite?

Cited by 37 publications

References 63 publications

The exposed base of a collapsing wedge: The Nestos Shear Zone (Rhodope Metamorphic Province, Greece)

The exposed base of a collapsing wedge: The Nestos Shear Zone (Rhodope Metamorphic Province, Greece)

Tectonic evolution of the southeastern part of the Pohorje Mountains (Eastern Alps, Slovenia)

High‐Pressure Fluid‐Rock Interaction and Mass Transfer During Exhumation of Deeply Subducted Rocks: Insights From an Eclogite‐Vein System in the Ultrahigh‐Pressure Terrane of the Dabie Shan, China

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