Late Archean magmatism and the onset of modern-style plate tectonics
The timing of and processes related to the onset of modern-style plate tectonics have long been vigorously debated. We have started multidisciplinary research into Late Archean TTG suites (tonalite–trondhjemite–granodiorite), which may provide the key information on the complex and protracted transition from vertically-dominated plume tectonics that operated on Early Earth to plate tectonics that we see today.
Tectonic setting of granitoid plutons in arcs and collisional orogens
Using a combination of structural analysis and geochronology, whole-rock and isotopic geochemistry, and gravimetry, we examine plutons as temporal and strain markers of regional deformation. Our present work concentrates on general issues of fabric development in plutons in response to regional strain, interactions of magma mingling, flow, and emplacement with regional tectonics, and spatial and temporal changes in plutonism during evolution of orogenic belts.
Paterson SR, Ardill K, Vernon RH, Žák J (2019) A review of mesoscopic magmatic structures and their potential for evaluating the hypersolidus evolution of intrusive complexes Journal of Structural Geology 125: 997–1016
Žák J, Verner K, Tomek F, Johnson K, Schwartz JJ (2017) Magnetic fabrics of arc plutons reveal a significant Late Jurassic to Early Cretaceous change in the relative plate motions of the Pacific Ocean basin and North America
Žák J, Verner K, Tomek F, Holub FV, Johnson K, Schwartz JJ (2015) Simultaneous batholith emplacement, terrane/continent collision, and oroclinal bending in the Blue Mountains Province, North American Cordillera Tectonics 34: 1107–1128
Tomek F, Žák J, Chadima M (2015) Granitic magma emplacement and deformation during early-orogenic syn-convergent transtension: the Staré Sedlo complex, Bohemian Massif Journal of Geodynamics 87: 50–66
Žák J, Verner K, Janoušek V, Holub FV, Kachlík V, Finger F, Hajná J, Tomek F, Vondrovic L, Trubač J (2014) A plate-kinematic model for the assembly of the Bohemian Massif constrained by structural relations around granitoid plutons Geological Society, London, Special Publications 405: 169–196
Magma flow and strain patterns in volcano–plutonic systems
Volcano–plutonic connection and mechanical processes in and above shallow-level magma chambers still remain poorly understood. Our research has recently concentrated on magma flow patterns in subcaldera plutons, mechanisms of growth and strain patterns in andesite domes, magma flow in both ring and radial dikes associated with collapse calderas, and internal fabric and emplacement of ignimbrite sheets.
Tomek F, Žák J, Svojtka M, Finger F, Waitzinger M (2019) Emplacement dynamics of syn-collapse ring dikes: an example from the Altenberg–Teplice caldera, Bohemian Massif Geological Society of America Bulletin 131: 997–1016
Tomek F, Gilmer AK, Petronis MS, Lipman PW, Foucher MS (2019) Protracted multipulse emplacement of a post-resurgent pluton: the case of Platoro caldera complex (Southern Rocky Mountain volcanic field, Colorado) Geochemistry, Geophysics, Geosystems 20: 5225–5250
Tomek F, Žák J, Verner K, Holub FV, Sláma J, Paterson SR, Memeti V (2017) Mineral fabrics in high-level intrusions recording crustal strain and volcano-tectonic interactions: the Shellenbarger pluton, Sierra Nevada, California Journal of the Geological Society, London 174: 193–208
Tomek F, Žák J, Holub FV, Chlupáčová M, Verner K (2016) Growth of intra-caldera lava domes controlled by various modes of caldera collapse, the Štiavnica volcano–plutonic complex, Western Carpathians Journal of Volcanology and Geothermal Research 313: 183–197
Tomek F, Žák J, Chadima M (2014) Magma flow paths and strain patterns in magma chambers growing by floor subsidence: a model based on magnetic fabric study of shallow-level plutons in the Štiavnica volcano–plutonic complex, Western Carpathians Bulletin of Volcanology 76, Article No. 873
Dynamics of Precambrian accretionary wedges
One of the main goals of our research is to better understand how Precambrian accretionary wedges formed and evolved along convergent plate margins. Based on structural analysis, anisotropy of magnetic susceptibility, geochemistry, and geochronology, we examine mechanisms of sediment accretion, internal strains, formation of ophiolitic mélanges, and late-stage extension in ancient accretionary wedges and compare those processes with modern settings.
Hajná J, Žák J, Ackerman L, Svojtka M, Pašava J (2019) A giant late Precambrian chert-bearing olistostrome discovered in the Bohemian Massif: a record of Oceanic Plate Stratigraphy (OPS) disrupted by mass-wasting along an outer trench slope Gondwana Research 74: 173–188
Hajná J, Žák J, Dörr W (2017) Time scales and mechanisms of growth of active margins of Gondwana: a model based on detrital zircon ages from the Neoproterozoic to Cambrian Blovice accretionary complex, Bohemian Massif Gondwana Research 42: 63–83
Hajná J, Žák J, Kachlík V (2014) Growth of accretionary wedges and pulsed ophiolitic mélange formation by successive subduction of trench-parallel volcanic elevations Terra Nova 26: 322–329
Tectonics of sedimentary basins in collisional orogens
Development of orogenic sedimentary basins reflects a complex interaction among brittle faulting, tectonically-controlled uplift, erosion, and deposition. Our ongoing research is targeted on mechanisms of basin inversion in response to shortening of orogenic upper crust, initiation and tectonics of intracontinental basins during orogenic collapse, and relations between paleotopography, exhumation, and basin development.
Nádaskay R, Žák J, Sláma J, Sidorinová T, Valečka J (2019) Deciphering the Late Paleozoic to Mesozoic tectonosedimentary evolution of the northern Bohemian Massif from detrital zircon geochronology and heavy mineral provenance International Journal of Earth Sciences 108: 2653–2681
Tomek F, Vacek F, Žák J, Petronis MS, Verner K, Foucher MS (2019) Polykinematic foreland basins initiated during orthogonal convergence and terminated by orogen-oblique strike-slip faulting: an example from the northeastern Variscan belt Tectonophysics 766: 379–397
Vacek F, Žák J (2019) A lifetime of the Variscan orogenic plateau from uplift to collapse as recorded by the Prague Basin, Bohemian Massif Geological Magazine 156: 485–509
Žák J, Svojtka M, Opluštil S (2018) Topographic inversion and changes in the sediment routing systems in the Variscan orogenic belt as revealed by detrital zircon and monazite U–Pb geochronology in post-collisional continental basins Sedimentary Geology 377: 63–81
Application of rock-magnetic methods in solving tectonic problems
We employ anisotropy of magnetic susceptibility and other rock-magnetic methods to analyze a wide range of geologic processes, including granitic magma emplacement and deformation, magma flow in dikes, growth of volcanic domes, formation and exhumation of metamorphic core complexes, and basin development during regional extension.
Žák J, Verner K, Ježek J, Trubač J (2019) Complex mid-crustal flow within a growing granite– migmatite dome: an example from the Variscan belt illustrated by the anisotropy of magnetic susceptibility and fabric modeling Geological Journal 54: 3681–3699
Žák J, Sláma J, Burjak M (2017) Rapid extensional unroofing of a granite–migmatite dome with relics of high-pressure rocks, the Podolsko complex, Bohemian Massif Geological Magazine 154: 354–380
Trubač J, Žák J, Chlupáčová M, Janoušek V (2014) Magnetic fabric and modeled strain distribution in the head of a nested granite diapir, the Melechov pluton, Bohemian Massif Journal of Structural Geology 66: 271–283
Verner K, Žák J, Šrámek J, Paclíková J, Zavřelová A, Machek M, Finger F, Johnson K (2014) Formation of elongated granite–migmatite domes as isostatic accommodation structures in collisional orogens Journal of Geodynamics 73: 100–117
Application of continuum mechanics in understanding magmatic processes
Our joint research with the group of Prof. Petr Kabele, Department of Mechanics, Czech Technical University in Prague, utilizes high-end computational facilities to integrate numerical models with geologic data and observations. Our ongoing research targets include modeling of mineral fabric development in magmatic rocks in 3D, cooling of magma bodies, granitoid diapirism, and formation of collapse calderas.
Kabele P, Žák J, Somr M (2017) Finite element modeling of magma chamber–host rock interactions prior to caldera collapse Geophysical Journal International 209: 1851–1865
Map of our current field research localities
Modified after Paul D. Lowman Jr. (NASA Goddard Space Flight Center)