The Finnefjeld domain, Maniitsoq structure, West Greenland: Differential rheological features and mechanical homogenisation in response to impacting?
29
Citation
30
Reference
10
Related Paper
Citation Trend
Keywords:
Cataclastic rock
Brittleness
Lineation
Shearing (physics)
Magma chamber
Cite
Citations (214)
Cataclastic rock
Brittleness
Cite
Citations (29)
Cite
Citations (34)
Since the pioneering works of John Ramsay in the 1970's and 1980's, the analysis of exceptional exposures of small-scale shear zones (i.e. 10-3 – 10−1 m thick) in granitoid rocks provided invaluable insights into the processes controlling strain localisation in the middle and lower continental crust. Indeed, recent advancement in field, microstructural and petrological analyses of such small-scale shear zone have shed new light on the metamorphic, tectonic and fluid conditions promoting shear zone nucleation and development in granitoid rocks. In this paper we provide an overview of these new insights, comparing and integrating the results obtained from field, and microstructural and petrological analyses of small-scale shear zones in granitoid plutons and meta-granitoids from the Alps. A review of the deformation temperature shows that the granitoid shear zones development occurs between 350 and 600 °C, with most of them localising in a restricted temperature window between 450 and 500 °C. At these conditions, the magmatic assemblage is metastable and subjected to a series of metamorphic reactions. Furthermore, the development of shear zone does not occur under-closed system conditions. Introducing or expelling fluids and mass (i.e. metasomatism) during deformation has mineralogical consequences that control the rheology and the way shear zone evolves. Among the main mineralogical and microstructural changes, the breakdown of magmatic feldspar(s) into fine-grained aggregates steers both the rheology and fabric evolution of shear zones in granitoid rocks, triggering further mechano-chemical feedback mechanisms. Future research should consider the occurrence of feedback processes between deformation, metamorphic and metasomatic processes to understand and quantify the evolution with time and strain of shear zone geometry and rheology, as well as of the development of larger-scale shear zone networks.
Metasomatism
Cite
Citations (13)
The emplacement of the ca 1590–1575 Ma Hiltaba Suite granites records a large magmatic event throughout the Gawler Craton, South Australia. The Hiltaba Suite granites intrude the highly deformed Archaean‐Palaeoproterozoic rocks throughout the craton nuclei. Geophysical interpretation of the poorly exposed central western Gawler Craton suggests that the region can be divided into several distinct domains that are bounded by major shear zones, exhibiting a sequence of overprinting relationships. The north‐trending Yarlbrinda Shear Zone merges into the east‐trending Yerda Shear Zone that, in turn, merges into the northeast‐trending Coorabie Shear Zone. Several poorly exposed Hiltaba Suite granite plutons occur within a wide zone of crustal shearing that is bounded to the north by the Yerda Shear Zone and to the south by the Oolabinnia Shear Zone. This wide zone of crustal shearing is interpreted as a major zone of synmagmatic dextral strike‐slip movement that facilitated the ascent of Hiltaba Suite granite intrusions to the upper crust. The aeromagnetic and gravity data reveal that the intrusions are ∼15–25 km in diameter. Forward modelling of the geophysical data shows that the intrusions have a tabular geometry and are less than 6 km deep.
Overprinting
Transpression
Lineation
Shearing (physics)
Cite
Citations (62)
Cataclastic rock
Mylonite
Cite
Citations (44)
Abstract Mid‐to‐lower crustal rock exhumation is common in orogenic belts, but the deformation process exposing these rocks remains debated. Distributed deformation in low viscous crust extruding mid‐to‐lower crustal rocks as channel flow and localized deformation along shear zones imbricating rigid blocks are two end‐members that account for crustal thickening and unroofing. At the northwest of the Early Paleozoic orogenic belt in the South China Block, the Jiuling Massif includes orogenic root rocks exhumed from deep crustal level. Their structural pattern and exhumation history can improve our understanding on how continental mid‐to‐lower crust is deformed, thickened, and finally transported to the surface. Structural analysis reveals that two major mid‐crustal ductile shear zones and their splays are developed at temperatures of ∼350°C–550°C. Anisotropy of magnetic susceptibility (AMS) shows that the Southern Jiuling Batholith has a modified AMS pattern by syn‐orogenic compression, suggesting a gradually deformed rigid block. Combining surface geological evidence and deep structures by gravity modeling, we find shear zones rooted in basal décollement incrementally stacked the rigid granitic blocks. Along strike, the major shear zones evolved differently with more splays at their eastern portions. Thus, tectonic imbrication can evolve to pervasive flow‐like deformation as shear zones continue to splay and form an anastomosed shear zone system. The complexed structures by splayed shear zones segmenting and imbricating small rigid blocks may correspond to the geophysically low‐velocity zone in the crust, so shear zone splaying is a linking mechanism between tectonic imbrication and viscous flow deformation of the crust.
Imbrication
Batholith
Cite
Citations (4)
Mylonite
Cataclastic rock
Batholith
Lineation
Cite
Citations (10)