Diamond in metasedimentary crustal rocks from Pohorje, Eastern Alps: a window to deep continental subduction

Janák, Marian; Froitzheim, Nikolaus; Yoshida, Kenta; Sasinková, Vlasta; Nosko, Martin; Kobayashi, Tomoyuki; Hirajima, Tsuyoshi; Vrabec, Mirijam

doi:10.1111/jmg.12130

Cited by 63 publications

(67 citation statements)

References 85 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Smith et al ., ; Smith & Godard, ). Graphitic carbon is partly associated with CO 2 and CH 4 , but no diamond has been identified in fluid‐containing inclusions, as reported in the Western Alps (Frezzotti et al ., ), Pohorje (Janák et al ., ) and Rhodope (Petrík et al ., ). It can be argued that diamond is too small to be detected or has been totally graphitized in the presence of fluid (Korsakov et al ., ).…”

Section: Discussionmentioning

confidence: 97%

Microdiamond on Åreskutan confirms regional UHP metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides

Klonowska

Janák

Majka

et al. 2017

Journal Metamorphic Geology

Self Cite

View full text Add to dashboard Cite

Metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust. Here, we present a new occurrence of diamond within the Seve Nappe Complex (SNC) of the Scandinavian Caledonides, on Åreskutan in Jämtland County, Sweden. Microdiamond is found in situ as single and composite (diamond+carbonate) inclusions within garnet, in kyanite‐bearing paragneisses. The rocks preserve the primary peak pressure assemblage of Ca,Mg‐rich garnet+phengite+kyanite+rutile, with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite. Calculated P–T conditions for this stage are 830–840 °C and 4.1–4.2 GPa, in the diamond stability field. The ultrahigh‐pressure (UHP) assemblage has been variably overprinted under granulite facies conditions of 850–860 °C and 1.0–1.1 GPa, leading to formation of Ca,Mg‐poor garnet+biotite+plagioclase+K‐feldspar+sillimanite+ilmenite+quartz. This overprint was the result of nearly isothermal decompression, which is corroborated by Ti‐in‐quartz thermometry. Chemical Th–U–Pb dating of monazite yields ages between 445 and 435 Ma, which are interpreted to record post‐UHP exhumation of the diamond‐bearing rocks. The new discovery of microdiamond on Åreskutan, together with other evidence of ultrahigh‐pressure metamorphism (UHPM) within gneisses, eclogites and peridotites elsewhere in the SNC, provide compelling arguments for regional (at least 200 km along strike of the unit) UHPM of substantial parts of this far‐travelled allochthon. The occurrence of UHPM in both rheologically weak (gneisses) and strong lithologies (eclogites, peridotites) speaks against the presence of large tectonic overpressure during metamorphism.

show abstract

Section: Discussionmentioning

confidence: 97%

Microdiamond on Åreskutan confirms regional UHP metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides

Klonowska

Janák

Majka

et al. 2017

Journal Metamorphic Geology

Self Cite

View full text Add to dashboard Cite

show abstract

“…In some UHP metamorphic regions, occurrences of relict coesite are lacking for diamond‐bearing metamorphic rocks despite the estimated diamond‐stable UHP conditions using phase equilibrium modelling (e.g. Janák et al., , ; Vrabec, Janák, Froitzheim, & De Hoog, ). Searching for indisputable UHP index minerals, conventional metamorphic petrology has mainly focused on inclusions in zircon and garnet, because these minerals have large bulk moduli (Chopin, ) and advantages for petrochronology (Kylander‐Clark, Hacker, & Cottle, ).…”

Section: Discussionmentioning

confidence: 99%

Factors affecting preservation of coesite in ultrahigh‐pressure metamorphic rocks: Insights from TEM observations of dislocations within kyanite

Taguchi

Igami

Miyake

et al. 2019

Journal Metamorphic Geology

View full text Add to dashboard Cite

To understand the preservation of coesite inclusions in ultrahigh-pressure (UHP) metamorphic rocks, an integrated petrological, Raman spectroscopic and focussed ion beam (FIB) system-transmission electron microscope (TEM) study was performed on a UHP kyanite eclogite from the Sulu belt in eastern China. Coesite grains have been observed only as rare inclusions in kyanite from the outer segment of garnet and in the matrix. Raman mapping analysis shows that a coesite inclusion in kyanite from the garnet rim records an anisotropic residual stress and retains a maximum residual pressure of~0.35 GPa. TEM observations show quartz is absent from the coesite inclusion-host kyanite grain boundaries. Numerous dislocations and sub-grain boundaries are present in the kyanite, but dislocations are not confirmed in the coesite. In particular, dislocations concentrate in the kyanite adjacent to the boundary with the coesite inclusion, and they form a dislocation concentration zone with a dislocation density of~10 9 cm −2 . A high-resolution TEM image and a fast Fourier transform-filtered image reveal that a tiny dislocation in the dislocation concentration zone is composed of multiple edge dislocations. The estimated dislocation density in most of the kyanite away from the coesite inclusion-host kyanite grain boundaries is~10 8 cm −2 , being lower than that in kyanite adjacent to the coesite. In the case of a coesite inclusion in a matrix kyanite, using Raman and TEM analyses, we could not identify any quartz at the grain boundaries. Dislocations are not observed in the coesite, but numerous dislocations and stacking faults are developed in the kyanite. The estimated overall dislocation density in the coesite-bearing matrix kyanite is~10 8 cm −2 , but a high dislocation density region of~10 9 cm −2 is also present near the coesite inclusion-host kyanite grain boundaries. Inclusion and matrix kyanite grains with no coesite have dislocation densities of ≤10 8 cm −2 . Dislocation density is generally reduced during an annealing process, but our results show that not all dislocations in the kyanite have recovered uniformly during exhumation of the UHP rocks. Hence, one of the key factors acting as a buffer to inhibit the coesite to quartz transformation is the mechanical interaction between the host and the inclusion that lead to the formation of dislocations in the kyanite. The kyanite acts as an excellent pressure container that can preserve coesite during the decompression of rocks from UHP conditions. The search for and study of inclusions in kyanite may be a more suitable approach for tracing the spatial distribution of UHP metamorphic rocks.

show abstract

“…Moreover, according to work of Janák et al (2015), the Pohorje metamorphic terrane represented a coherent unit during peak ultrahigh-pressure metamorphism in the Late Cretaceous (c.95-92 Ma) and during the subsequent exhumation. Therefore the marble lenses must have been exposed to the same peak pressure and temperature conditions of ≥3.5 GPa and 800-850 °C as the rest of the unit (Janák et al, 2015), but the marbles apparently did not preserve indicators of this peak pressure and temperature conditions.…”

Section: Petrography and Mineralogymentioning

confidence: 99%

“…Pohorje massif was subjected to metamorphism in the Late Cretaceous (ca. 95-92 Ma; Thöni, 2002;Miller et al, 2005;Janák et al, 2009) when these units reached conditions within stability field of diamond (Janák et al, 2004(Janák et al, , 2006(Janák et al, , 2015Vrabec et al, 2012). The major exhumation of the Pohorje nappe, from ultrahigh pressure depth to mid crustal levels most probably occurred already during the Upper Cretaceous, similarly to the Koralpe area, the north-westward extension of the Pohorje nappe, where Upper Cretaceous (75-70 Ma) cooling ages were determined (Schuster et al, 2004).…”

Section: Geological Setting and Sample Locationmentioning

confidence: 99%

Calcite deformation twins in Pohorje marbles

Nastja¹,

Vrabec²

2018

Geologija

View full text Add to dashboard Cite

Marbles in Pohorje occur in lenses and smaller bodies in the southern and southeastern part of the massif. Marbles are very pure, predominantly calcitic and rarely calcitic-dolomitic, containing a maximum of 5 % of non-carbonate mineral phases. The latter comprise pyroxenes (diopside), amphiboles (tremolite), olivines (forsterite) in places replaced by serpentine, quartz, feldspars (potassium feldspars and plagioclases), epidote, zoisite, vesuvianite, scapolite, muscovite, biotite partly replaced by chlorite, phlogopite, rare grains of titanite, rutile, zircone, apatite, and small grains of ferric oxides and sulfides. Calcite exhibits intensive deformational e-twinning whereas dolomite is undeformed and untwined. All four known types of mechanical twins in calcite were recognized: thin Type I twins, straight thick Type II twins, curved, lensoid and tapered thick Type III twins, and thick patchy Type IV twins. Type III twins are the dominant mechanical twins in the Pohorje marbles indicating the temperature of deformation somewhat above 200 °C. Since they lack signs of grain boundary recrystallization, we assume that the twinning was followed by a decrease temperature during exhumation. With increasing temperature the process of recrystallization along calcite grain becomes pronounced. Small individual untwined calcite crystals are progressively replacing bigger calcite grains. In few examples second generation of Type I deformational twins develop in recrystallized calcite grains, which also implies lowering of temperature due to exhumation. IzvlečekPohorski marmor se pojavlja v lečah in manjših telesih v južnem in jugovzhodnem delu pogorja. Marmorji so po sestavi zelo čisti, skoraj izključno kalcitni, izjemoma kalcitno-dolomitni in vključujejo največ do 5 % nekarbonatnih mineralnih faz. Te vključujejo piroksene (diopsid), amfibole (tremolit), olivine (forsterit) mestoma nadomeščen s serpentinom, kremen, glinence (kalijeve glinence in plagioklaze), epidot, zoisit, vezuvianit, skapolit, muskovit, biotit deloma nadomeščen s kloritom, flogopit, redka zrna titanita, rutila, cirkona in apatita ter majhna zrna železovih oksidov in sulfidov. Kalcitni kristali so močno deformirani z mehanskim dvojčenjem, dolomitni kristali pa so nedeformirani in brez dvojčkov. Našli smo vse štiri znane tipe mehanskih dvojčkov v kalcitu: tanke dvojčke tipa I, ravne in debele dvojčke tipa II, zakrivljene, lečaste in zašiljene dvojčke tipa III, ter debele krpaste dvojčke tipa IV. Prevlada dvojčkov tipa III v pohorskem marmorju nakazuje temperaturo deformacije nekoliko nad 200 °C. Ker ti dvojčki ne kažejo znakov rekristalizacije na robovih zrn, sklepamo, da je dvojčenju sledilo znižanje temperature zaradi ekshumacije kamnin. Z višanjem temperature postane bolj izrazit proces rekristalizacije vzdolž robov kalcitnih zrn. Velika kalcitna zrna so pri tem vedno bolj nadomeščena z majhnimi kristali brez mehanskih dvojčkov. V nekaj primerih so v rekristaliziranih kalcitnih zrnih nastali mehanski dvojčki tipa I druge generacije, kar tudi na...

show abstract

Diamond in metasedimentary crustal rocks from Pohorje, Eastern Alps: a window to deep continental subduction

Cited by 63 publications

References 85 publications

Microdiamond on Åreskutan confirms regional UHP metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides

Microdiamond on Åreskutan confirms regional UHP metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides

Factors affecting preservation of coesite in ultrahigh‐pressure metamorphic rocks: Insights from TEM observations of dislocations within kyanite

Calcite deformation twins in Pohorje marbles

Contact Info

Product

Resources

About