Formation and preservation of fresh lawsonite: Geothermobarometry of the North Makran Blueschists, southeast Iran

Hunziker, Daniela; Burg, Jean‐Pierre; Moulas, Evangelos; Reusser, Éric; Omrani, Jafar

doi:10.1111/jmg.12259

Cited by 26 publications

(34 citation statements)

References 72 publications

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“…We simplified the pelitic composition by ignoring the minute amounts of Na, Ca, and Ti and assumed that the system is saturated in H 2 O (water) and SiO 2 (quartz; i.e., K2O‐FeO‐Fe2O3‐MgO‐Al2O3‐SiO2‐H2O system). The calculated misfit between modeled and measured mineral compositions (see Hunziker et al, , their Equation 1) is minimized for temperatures between 400 and 425°C. For an X value of ~0.62, the crossing of the Si‐in‐Phe (atoms per formula unit or apfu; see Table ) and Mg#‐in‐Cld isopleths at these temperatures occurs at P~1.2 and 1.6GPa, respectively.…”

Section: Resultsmentioning

confidence: 99%

Cretaceous‐Paleogene Tectonics of the Pelagonian Zone: Inferences From Skopelos Island (Greece)

et al. 2019

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We have investigated subduction‐exhumation processes in the Pelagonian zone, exposed on the Northern Sporades islands (Aegean Sea) related to successive episodes of ocean continent and continent‐continent convergence through integrating multiscale structural analysis, metamorphic petrology, and white mica 40Ar/39Ar dating. Two major progressive phases of ductile deformation are documented, which are related to distinct episodes of tectonic burial and exhumation of the Pelagonian continental margin, which was facing the Neotethys/Vardar ocean. Review of existing data sets from neighboring regions shows that both deformation phases can be correlated along strike up to the Dinarides. The first phase of tectonic burial and exhumation (D1) is characterized by NW‐SE tectonic transport, greenschist facies metamorphism, and Early Cretaceous (~105‐135Ma) 40Ar/39 Ar white mica single fusion ages. D1 is correlated with the initial closure of the Vardar ocean by top‐to‐the‐W to NW ophiolite obduction and the underthrusting of the Pelagonian margin below the oceanic upper plate. Underthrusting was followed by exhumation and the deposition of Late Cretaceous‐Paleogene sediments. The second phase of burial and exhumation (D2) is characterized by NE‐SW tectonic transport, greenschist to blueschist facies metamorphism, and latest Cretaceous‐Early Eocene 40Ar/39 Ar white mica ages of S2 fabrics. Top‐to‐the‐SW shearing is correlated with the tectonic burial of the Pelagonian zone below the Eurasian continent (Rhodopia), while top‐to‐the‐NE shearing is attributed to subsequent extensional exhumation. D2 fabrics record low‐grade P‐T conditions suggesting that the decoupled cover formations exposed on Skopelos were incorporated in an accretionary wedge that formed above the subducting Pelagonian basement during Paleogene times.

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Section: Resultsmentioning

confidence: 99%

Cretaceous‐Paleogene Tectonics of the Pelagonian Zone: Inferences From Skopelos Island (Greece)

et al. 2019

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“…P ‐ T conditions of ~22–26 kbar and 490–520°C suggest subduction of the Cycladic continental margin to ~70–80 km depth, along a cool geothermal gradient of ~6–7°C/km. Other Tethyan HP‐LT terranes including Corsica, Elba, Western Turkey, Iran, and Oman record comparably cold geotherms (Brovarone et al, 2011; Davis, 2011; Davis & Whitney, 2006; Hunziker et al, 2017; Papeschi et al, 2020; Plunder et al, 2015, 2016; Ravna et al, 2010; Searle et al, 1994, 2004; Wang et al, 2019; Warren & Waters, 2006), suggesting similar processes occurred along strike at slightly different times.…”

Section: Discussionmentioning

confidence: 99%

The Cycladic Blueschist Unit on Tinos, Greece: Cold NE Subduction and SW Directed Extrusion of the Cycladic Continental Margin Under the Tsiknias Ophiolite

et al. 2020

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High pressure-low temperature (HP-LT) metamorphic rocks structurally beneath the Tsiknias Ophiolite make up the interior of Tinos Island, Greece, but their relationship with the overlying ophiolite is poorly understood. Here, new field observations are integrated with petrological modeling of eclogite and blueschists to provide new insight into their tectonothermal evolution. Pseudomorphed lawsonite-, garnet-, and glaucophane-bearing schists exposed at the highest structural levels of Tinos (Kionnia and Pyrgos Subunits) reached~22-26 kbar and 490-520°C under water-saturated conditions, whereas pseudomorphed lawsonite-and aegirine-omphacite bearing eclogite reached~20-23 kbar and 530-570°C. These rocks are separated from rocks at deeper structural levels (Sostis Subunit) by a top-to-SW thrust. The Sostis Subunit records P-T conditions of~18.5 kbar and 480-510°C and is overprinted by pervasive top-toNE shearing that developed during exhumation from (M 1) blueschist to (M 2) greenschist facies conditions of~7.3 ± 0.7 kbar and 536 ± 16°C. These P-T-D relationships suggest that the Cycladic Blueschist Unit represents a discrete series of tectonometamorphic subunits that each experienced different tectonic and thermal histories. These subunits were buried to variable depths and sequentially extruded toward the SW from a NE dipping subduction zone. The difference in age and P-T conditions between the HP-LT rocks and the overlying metamorphic sole of the Tsiknias Ophiolite suggests that this NE dipping subduction zone was active between circa 74 and 46 Ma and cooled at a minimum rate of 1.2-1.5°C/km/Myr prior to continent-continent collision between Eurasia and Adria/Cyclades. Plain Language Summary High pressure-low temperature metamorphic rocks make up the interior of Tinos Island, Greece and underlie an ancient piece of oceanic crust and mantle (Tsiknias Ophiolite). The rocks that make up Tinos were once mudstones and limestones deposited on the NE margin of the Cycladic-Adriatic continent and were deeply buried in a subduction zone. In this work, we investigate the structures and mineralogy of the Tinos high-pressure rocks and find they were buried to variable depths (80-60 km) and reached temperatures of 500-550°C. These packages of rock were then emplaced against each other during their return journey toward the surface after subduction ended. We document evidence for circa 25 Myr (ca. 74 and 46 Ma) of subduction prior to continent-continent collision (between Eurasia and Adria/Cyclades) on Tinos and that this records the closure of an ancient ocean to the NE of the Cyclades.

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“…Underplating was interpreted to be an important factor for wedge growth due to the emergence of a low-grade metamorphic antiformal stack in the very north of the accretionary wedge ( Fig. 10A; Hunziker et al, 2017). Grando and McClay (2007) showed that underplated sediments may form the footwall of large listric normal faults emerging along the coastline.…”

Section: Comparison To Natural Examplesmentioning

confidence: 99%

Numerical modeling of tectonic underplating in accretionary wedge systems

Ruh

2020

Geosphere

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Many fossil and active accretionary wedge systems show signs of tectonic underplating, which denotes accretion of underthrust material to the base of the wedge. Underplating is a viable process for thickening of the rear part of accretionary wedges, for example as a response to horizontal growth perpendicular to strike. Here, numerical experiments with a visco-elasto-plastic rheology are applied to test the importance of backstop geometry, flexural rigidity, décollement strength, and surface erosion on the structural evolution of accretionary wedges undergoing different modes of sediment accretion, where underplating is introduced by the implementation of two, a basal and an intermediate, décollement levels. Results demonstrate that intense erosion and a strong lower plate hamper thickening of a wedge at the rear, enhancing localized underplating, antiformal stacking, and subsequent exhumation to sustain its critical taper. Furthermore, large strength contrasts between basal and intermediate décollements have an important morphological impact on wedge growth due to different resulting critical taper angles. Presented numerical experiments are compared to natural examples of accretionary wedges and are able to recreate first-order structural observations related to underplating.

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Formation and preservation of fresh lawsonite: Geothermobarometry of the North Makran Blueschists, southeast Iran

Cited by 26 publications

References 72 publications

Cretaceous‐Paleogene Tectonics of the Pelagonian Zone: Inferences From Skopelos Island (Greece)

Cretaceous‐Paleogene Tectonics of the Pelagonian Zone: Inferences From Skopelos Island (Greece)

The Cycladic Blueschist Unit on Tinos, Greece: Cold NE Subduction and SW Directed Extrusion of the Cycladic Continental Margin Under the Tsiknias Ophiolite

Numerical modeling of tectonic underplating in accretionary wedge systems

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