Shah Wali Faryad | Charles University, Prague (original) (raw)

Papers by Shah Wali Faryad

Contributions to Mineralogy and Petrology

Journal of geodynamics, Mar 1, 2024

Earth-Science Reviews, Mar 1, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

$Research paper thumbnail of Olivine-bearing symplectites in fractured garnet from eclogite, Moldanubian Zone (Bohemian Massif) - a short-lived, granulite facies event$

Journal of Metamorphic Geology, Jul 6, 2015

Recent petrological studies on high‐pressure (HP)–ultrahigh‐pressure (UHP) metamorphic rocks in t... more Recent petrological studies on high‐pressure (HP)–ultrahigh‐pressure (UHP) metamorphic rocks in the Moldanubian Zone, mainly utilizing compositional zoning and solid phase inclusions in garnet from a variety of lithologies, have established a prograde history involving subduction and subsequent granulite facies metamorphism during the Variscan Orogeny. Two temporally separate metamorphic events are developed rather than a single P–T loop for the HP–UHP metamorphism and amphibolite–granulite facies overprint in the Moldanubian Zone. Here further evidence is presented that the granulite facies metamorphism occurred after the HP–UHP rocks had been exhumed to different levels of the middle or upper crust. A medium‐temperature eclogite that is part of a series of tectonic blocks and lenses within migmatites contains a well‐preserved eclogite facies assemblage with omphacite and prograde zoned garnet. Omphacite is partly replaced by a symplectite of diopside + plagioclase + amphibole. Garnet and omphacite equilibria and pseudosection calculations indicate that the HP metamorphism occurred at relatively low temperature conditions of ~600 °C at 2.0–2.2 GPa. The striking feature of the rocks is the presence of garnet porphyroblasts with veins filled by a granulite facies assemblage of olivine, spinel and Ca‐rich plagioclase. These minerals occur as a symplectite forming symmetric zones, a central zone rich in olivine that is separated from the host garnet by two marginal zones consisting of plagioclase with small amounts of spinel. Mineral textures in the veins show that they were first filled mostly by calcic amphibole, which was later transformed into granulite facies assemblages. The olivine‐spinel equilibria and pseudosection calculations indicate temperatures of ~850–900 °C at pressure below 0.7 GPa. The preservation of eclogite facies assemblages implies that the granulite facies overprint was a short‐lived process. The new results point to a geodynamic model where HP–UHP rocks are exhumed to amphibolite facies conditions with subsequent granulite facies heating by mantle‐derived magma in the middle and upper crust.

Tectonophysics, 2017

Abstract In the Gemeric Unit of the Central West Carpathians, the magnetic fabric was investigate... more Abstract In the Gemeric Unit of the Central West Carpathians, the magnetic fabric was investigated in Early Palaeozoic metasediments and metavolcanics, Permian to Early Triassic granites, and Late Palaeozoic (molasse) metasediments. In addition to Variscan greenschist facies metamorphism in the Early Palaeozoic basement, all rocks underwent Cretaceous (Alpine) low-grade metamorphism, which significantly modified their mineral composition and fabric; original magnetic minerals were destroyed at least partially and new, mostly paramagnetic, minerals were created. In the Early Palaeozoic metasediments, the magnetic fabric is entirely metamorphic/deformational in origin. In metavolcanics, the magnetic foliations are partly parallel to the Alpine metamorphic foliations developed in relatively incompetent lithologies such as tuffs and tuffites and partly to disjunctive foliations developed in competent rhyolites and its subvolcanic members. Their magnetic fabrics probably represent gradual transition from Variscan to Alpine fabrics. In the Permian granites, the magnetic foliations are near the Alpine mesoscopic disjunctive foliations crosscutting metamorphic schistosity in contact aureoles of granite. In the Late Palaeozoic (molasse) metasediments, the magnetic foliations are near the Alpine metamorphic foliations that are mostly parallel to the original bedding. On regional scale, the magnetic fabrics show curved pattern indicating complex interactions between the Gemeric and underlain Veporic units in the final stages of intendation and collision. The magnetic fabric pattern in the Gemeric Unit roughly resembles that in the Veporic Unit. This results from similar tectonic movements operating at least during Cretaceous collision in both the units. This tectonic process occurred subsequent to the closure of the Meliata ocean and was responsible for creation of the final structure of the Central Western Carpathians. Nevertheless, in contrast to the Veporic unit, where dominantly Alpine type of magnetic fabrics is present, in the Gemeric Unit the Alpine overprint had variable degrees of modification of AMS fabrics ranging from relatively weak to totally obliterated.

Journal of Geosciences, Jan 30, 2016

Numerous dykes of lamprophyres and various types of granitoid, syenitoid, dioritoid, and gabbroid... more Numerous dykes of lamprophyres and various types of granitoid, syenitoid, dioritoid, and gabbroid porphyries of Variscan age crop out in the area of the Central Bohemian Plutonic Complex and adjacent high-to low-grade metamorphic units of the Moldanubian Zone and Teplá-Barrandian Unit. Magnetic fabric in fourteen dykes of lamprophyres and related rocks was investigated. Mostly, the magnetic foliation is roughly parallel to the dyke plane and the magnetic lineation is horizontal with the relics of originally steep fabrics. This type of magnetic fabric originated through magma flow in which the larger surfaces of the magnetic minerals were oriented parallel to the dyke plane and their longer dimensions were parallel to the magma flow. In two localities, the so-called inverse fabrics were found in which the maximum and minimum susceptibility directions were swapped. The dykes of lamprophyres and related rocks were emplaced into already juxtaposed and cooled Teplá-Barrandian Zone, Central Bohemian Plutonic Complex and western Moldanubian Zone not later than 339 Ma. Parallel orientation of dykes giving a steep intrusive contacts mainly in W(NW)-E(SE) trend was caused by the regional stress field of ~WNW-ESE convergence (arc-parallel stretching) during the Variscan Orogeny.

Mineralogy and Petrology, Feb 27, 2015

ABSTRACT

Mineralogy and Petrology, 2002

Retrograde eclogites and serpentinites from the Hochgro Èssen massif, Styria, are parts of the Sp... more Retrograde eclogites and serpentinites from the Hochgro Èssen massif, Styria, are parts of the Speik complex in the Austroalpine basement nappes of the Eastern Alps. They are in tectonic contact with pre-Alpine gneisses, amphibolites, and Permo-Triassic quartz phyllites (Rannach Series). The eclogites are derived from ocean-¯oor basalts with af®nities to mid-ocean ridge and back-arc basin basalts. Fresh eclogites are rare and contain omphacite with a maximum of 39 mol% jadeite content, garnet (Py 15±19) and amphibole. Retrograde eclogites consist of amphibole and symplectites of Na-poor clinopyroxene (5±8 mol% Jd) albite AE amphibole. Amphiboles are classi®ed as edenite, pargasite, tschermakite, magnesiohornblende and actinolite. In relatively fresh eclogite, edenite is a common amphibole and texturally coexists with omphacite and garnet. An average temperature of 700 C was obtained for eclogite facies metamorphism using garnet-pyroxene thermometry. A minimum pressure of 1.5 GPa is indicated by the maximum jadeite content in omphacite. Thermobarometric calculations using the TWEEQ program for amphibole in textural equilibrium with omphacite and garnet give pressures of 1.8±2.2 GPa at 700 C. The equilibrium assemblage of Na-poor clinopyroxene, albite, amphibole and zoisite in the symplectites gives a pressure of about 0.6±0.8 GPa at 590±640 C. 40 Ar/ 39 Ar radiometric dating of edenitic amphibole in textural equilibrium with omphacite gave a plateau age of

Gondwana Research, Apr 1, 2013

ABSTRACT This paper presents monomineral and multiphase inclusions in garnet from eclogites and c... more ABSTRACT This paper presents monomineral and multiphase inclusions in garnet from eclogites and clinopyroxenites, which form layers and boudins in garnet peridotites from two areas in the Moldanubian zone of the Bohemian Massif. The garnet peridotites occur in felsic granulites and reached UHP conditions prior to their granulite facies overprint. In addition to complex compositional zoning, garnets from hosting eclogites and clinopyroxenites preserve inclusions of hydrous phases and alkali silicate minerals including: amphiboles, chlorites, micas and feldspars. Amphibole, biotite and apatite inclusions in garnet have a high concentration of halogens; CO2 and sulfur are involved in carbonates and sulfide inclusions, respectively. The inclusion patterns and compositional zoning in garnet in combination with textural relations among minerals, suggest that the ultramafic and mafic bodies are derived from lithospheric mantle above the subduction zone and were transformed into garnet pyroxenites and eclogites in the subduction zone. Based on compositional, mineral and textural relations, all of these rocks along with the surrounding crustal material were overprinted by granulite facies metamorphism during their exhumation.

Journal of Metamorphic Geology, Dec 1, 2009

Exsolution lamellae of garnet in clinopyroxene and orthopyroxene porphyroclasts from garnet pyrox... more Exsolution lamellae of garnet in clinopyroxene and orthopyroxene porphyroclasts from garnet pyroxenites in the Moldanubian zone were studied to elucidate the pressure-temperature conditions of the exsolution process and to reconstruct the burial and exhumation path of ultramafic rocks in the Variscan orogen. The porphyroclasts occur in a fine-grained matrix with metamorphic fabrics, which consists of clinopyroxene and small amounts of garnet, orthopyroxene and amphibole. The clinopyroxene porphyroclasts contain garnet + orthopyroxene lamellae as well as ilmenite rods that have orientation parallel to (100) planes of the porphyroclasts. Orthopyroxene porphyroclasts host garnet and clinopyroxene lamellae, which show the same lattice preferred orientation. In both cases, lamellar orthopyroxene, clinopyroxene and garnet were partially replaced by secondary amphibole. Composition of exsolution phases and that of host pyroxene were reintegrated according to measured modal proportions and demonstrate that the primary pyroxene was enriched in Al and contained 8-11 mol.% Tschermak components. Conventional thermobarometry and thermodynamic modelling on the reintegrated pyroxene indicate that primary clinopyroxene and orthopyroxene megacrysts crystallized at 1300-1400°C and 2.2-2.5 GPa. Unmixing and exsolution of garnet and a second pyroxene phase occurred in response to cooling and pressure increase before the peak pressure of 4.5-5.0 GPa was reached at 1100°C. This scenario is consistent with a burial of hot upper-mantle ultramafics into a cold subcratonic environment and subsequent exhumation through 900°C and 2.2-3.3 GPa, when the pyroxenites would have partially recrystallized during tectonic incorporation into eclogites and felsic granulites.

International Journal of Earth Sciences, Dec 9, 2009

Metamorphic basement rocks, that are exposed beneath the very low-grade to unmetamorphosed Upper ... more Metamorphic basement rocks, that are exposed beneath the very low-grade to unmetamorphosed Upper Jurassic-Eocene formations north of the Torud fault zone within the Great Kavir Block, were investigated to elucidate the origin of their protoliths and the pressure and temperature conditions of metamorphism. The basement, previously assumed as a pre-Cambrian metamorphic complex, is mostly formed by amphibolite-facies orthogneisses (tonalite, granodiorite,

EGU General Assembly Conference Abstracts, Apr 1, 2015

The Kabul Block is an elongate crustal fragment that is situated within a tectonic zone known as ... more The Kabul Block is an elongate crustal fragment that is situated within a tectonic zone known as the Afghan Central Blocks, which form at the triple junction between the Indian, Eurasian, and Arabian plates. Unique amongst the Afghan Central Blocks, the Kabul Block contains quantifiably Precambrian basement rocks. Recent U/Pb SHRIMP analysis of zircons from the lowermost basement formations (the Sherdarwaza and Khair Khana) indicated the presence of a small Neoarchean component (∼2700 Ma), while the majority of zircon cores yielded ages of 2200-2500 Ma. The Sherdarwaza and Khair Khana Formations consist predominantly of migmatites and orthogneisses that reached granulite-facies conditions. Conventional geothermobarometry and phase equilibria modelling on well preserved granulite-facies assemblages indicate that the rocks reached peak conditions in excess of 850 • C and up to 7 kbar. U/Pb SHRIMP dating of zircon rims in addition to Th/U dating of monazite inclusions in garnet suggest that this event occurred in the late Paleoproterozoic (1800-1900 Ma).

Lithos, Oct 1, 2013

The formation and exhumation of Variscan high-to ultrahigh-pressure metamorphic rocks from the Mo... more The formation and exhumation of Variscan high-to ultrahigh-pressure metamorphic rocks from the Moldanubian Zone in the Bohemian Massif are the subject of controversy regarding their unclear relationship to possible subduction zones. In this paper we present the results of a petrological study of eclogites that occur together with serpentinites within amphibolite facies gneisses in the Moldanubian Zone, east of the Teplá-Barrandian Block. More than 100 bodies of retrogressed eclogite and serpentinite follow an approximately 250 km long SW-NE trending zone in the central part of the Bohemian Massif. Together with surrounding gneisses, the eclogites share a medium to low-pressure amphibolite facies metamorphism. P-T conditions estimated for the eclogite facies stage indicate a relatively low-temperature geothermal gradient similar to those observed in the Saxothuringian Zone, which occurs north and northwest of the Teplá-Barrandian Block. The presence and distribution of eclogites and comparison of their P-T and age data with HP-UHPM rocks in other units in the Bohemian Massif allow us to constrain the Variscan suture, which straddles the SE of the Teplá-Barrandian Block. The existence of this suture in relation to available geotectonic models and its possible continuation through other allochthonous units along the European Variscan Belt are discussed.

EGU General Assembly Conference Abstracts, Apr 1, 2018

Lithos, 2009

Serpentinized peridotiteclinopyroxenite, approximately 11 × 5 m in size, enclosed in high-pressu... more Serpentinized peridotiteclinopyroxenite, approximately 11 × 5 m in size, enclosed in high-pressure felsic granulite, occurs in a quarry near the village of Bory (Gföhl Unit of the Moldanubian Zone of Western Moravia, Czech Republic). The anisotropy of magnetic susceptibility (AMS) ...

We performed 2D petrological-thermomechanical numerical modelling of oceanic-continental subducti... more We performed 2D petrological-thermomechanical numerical modelling of oceanic-continental subduction fol-lowed by continental collision associated with closure of a backarc spreading center and accretion of a magmatic arc to the continent. The initial model setup ...

Geotectonic Research, 2008