The influence of partial melting and melt migration on the rheology of the continental crust

Cavalcante, Geane Carolina G.; Viegas, Gustavo; Archanjo, Carlos José; Silva, Marcos Egydio da

doi:10.1016/j.jog.2016.06.002

Cited by 29 publications

(39 citation statements)

References 55 publications

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“…Hence, the middle crust of the internal part of the orogen can be considered to have been very weak during peak metamorphic conditions. Under such conditions strain is taken up by the melt and therefore widely distributed in the middle crust, provided that a large portion of the middle crust contains melt (Cavalcante et al, , , ; Vauchez et al, ). The lack of, or very weak, crystal preferred orientation of quartz is diagnostic for deformation of partially molten rocks, even where a strong mesoscopic foliation is defined by biotite and feldspar (Cavalcante et al, ).…”

Section: Differences In Structural Style and Rheologymentioning

confidence: 99%

“…Under such conditions strain is taken up by the melt and therefore widely distributed in the middle crust, provided that a large portion of the middle crust contains melt (Cavalcante et al, , , ; Vauchez et al, ). The lack of, or very weak, crystal preferred orientation of quartz is diagnostic for deformation of partially molten rocks, even where a strong mesoscopic foliation is defined by biotite and feldspar (Cavalcante et al, ). This diagnostic lack of crystallographic fabric contrasts with the well‐defined crystallographic preferred orientations produced during solid‐state deformation in the high‐ to ultrahigh‐pressure subducted Baltican crust (Barth et al, ) and the Caledonian orogenic wedge (e.g., Fossen, ).…”

Section: Differences In Structural Style and Rheologymentioning

confidence: 99%

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Hot Versus Cold Orogenic Behavior: Comparing the Araçuaí‐West Congo and the Caledonian Orogens

2017

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Observations and modeling show that temperature controls crustal rheology and therefore also the orogenic evolution of continent‐continent collision zones and the associated tectonic style. In order to explore the effect of temperature in a natural environment, we compare eroded sections through the unusually cold lower Paleozoic North Atlantic Caledonian (Scandian) collision zone and the very hot Brasiliano/Pan‐African Araçuaí‐West Congo orogen. A cold and stiff subducting Caledonian continental margin was able to subduct as a rather coherent unit to ultrahigh‐pressure conditions, twice as deep as the Pan‐African/Brasiliano crust that was quickly heated and softened and got involved in partial melting. Furthermore, the Caledonian collision developed large coherent thrust sheets that were transported hundreds of kilometers toward the foreland. This was never achieved in the hot Araçuaí‐West Congo orogen, where much of the tectonic stress was absorbed by the partially molten central part of the orogen through magmatic state deformation. Major mylonite zones (thrusts) such as those seen in the Caledonides are therefore less common in the Araçuaí‐West Congo orogen. Further, the deep continental subduction in the Caledonides developed a strongly asymmetric collision zone, with rapid variations in pressure and temperature. In contrast, the Araçuaí‐West Congo orogen soon developed into a more symmetric geometry due to its easily flowing hot crust, with a relatively flat base and a corresponding plateau in its upper part. Deformation of the cold Caledonian crust was controlled by plate‐tectonic stress, while gravitational forces more strongly influenced the hot Brasiliano/Pan‐African example.

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Section: Differences In Structural Style and Rheologymentioning

confidence: 99%

Section: Differences In Structural Style and Rheologymentioning

confidence: 99%

Hot Versus Cold Orogenic Behavior: Comparing the Araçuaí‐West Congo and the Caledonian Orogens

2017

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“…This suggests that partial melts present in buried rocks played a key role in controlling the style of deformation in continental collision zones: rock strength is significantly decreased even with melt fractions as low as ~7%, and melt-bearing systems may facilitate strain localization (e.g. Rosenberg et al, 2005;Cavalcante et al, 2016). In northern Norway, the fertile Nordmannvik rocks are significantly different in composition compared to the dry, strong Baltica basement of the WGR and Lofoten.…”

Section: Discussion: Nappe Stacking In Continental Collision Zonesmentioning

confidence: 99%

An anticlockwise metamorphic P-T path and nappe stacking in the Reisa Nappe Complex in the Scandinavian Caledonides, northern Norway: evidence for weakening of lower continental crust before and during continental collision

Faber¹,

Stünitz²,

Gasser³

et al. 2018

Preprint

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This study investigates the Caledonian metamorphic and tectonic evolution in northern Norway, examining the structure and tectonostratigraphy of the Reisa Nappe Complex (RNC; from bottom to top, Vaddas, Kåfjord and Nordmannvik 15 nappes). Structural data, phase equilibrium modelling, and U-Pb zircon and titanite geochronology are used to constrain the timing and P-T conditions of deformation and metamorphism that formed the nappes and facilitated crustal thickening during continental collision. Five samples taken from different parts of the RNC reveal an anticlockwise P-T path attributed to the effects of early Silurian heating followed by thrusting. An early Caledonian S1 foliation in the Nordmannvik Nappe records kyanite-grade partial melting at ~760 -790 °C and ~9.4 -11 kbar. Leucosomes formed at 439 ± 2 Ma (U-Pb zircon) in fold 20 axial planes in the Nordmannvik Nappe indicate that compressional deformation initiated while the rocks were still partially molten. This stage was followed by pervasive solid-state shearing as the rocks cooled and solidified, forming the S2 foliation at 680 -730 °C and 9.5 -10.9 kbar. Multistage titanite growth in the Nordmannvik Nappe records this extended metamorphism between 444 and 427 Ma. In the underlying Kåfjord Nappe, garnet cores record lower P-T (590 -610 °C and 5.5-6.8 kbar) but a similar geothermal gradient as the S1 migmatitic event in the Nordmannvik Nappe, indicating formation at a higher 25 relative position in the crust. S2 shearing in the Kåfjord Nappe occurred at 580-605 °C and 9.2-10.1 kbar, indicating a considerable pressure increase during nappe stacking. Gabbro intruded in the Vaddas Nappe at 439  1 Ma, synchronously with migmatization in the Nordmannvik Nappe. In the Vaddas Nappe S2 shearing occurred at 630-640 ºC and 11.7-13 kbar.Titanite growth along the lower RNC boundary records S2-shearing at 432 ± 6 Ma. It emerges that early Silurian heating (~440 Ma), probably resulting from large-scale magma underplating, initiated partial melting that weakened the lower crust, which 30 facilitated dismembering of the crust into individual nappe units. This tectonic style contrasts subduction of mechanically strong continental crust to great depths.Solid Earth Discuss., https://doi.Figure 1: (a) Simplified map of the Scandinavian Caledonides and their inferred palaeotectonic origin, modified from Gee et al. (2010). LN = Lyngsfjellet Nappe, WGR = Western Gneiss Region, NNC = Narvik Nappe Complex, KNC = Kalak Nappe Complex, RNC = Reisa Nappe Complex., TNC = Trondheim Nappe Complex. (b) Map showing the extent of the Reisa Nappe Complex in northern Norway, based on Zwaan (1988) and own correlations. The Vaddas, Kåfjord and Nordmannvik nappes are shown in 5colour. The study area is denoted by the black box (Fig. 2).

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“…Heterogeneities of shear zones and faults have also been largely regarded as properties favoring such structures as conduits of fluids, including magma (Rosenberg, 2004), as well as representing loci of magma generation (Leloup et al, 1999) and emplacement (Rosenberg, 2004), hence further increasing the importance of shear zones in the development of orogens and most other tectonic settings. Indeed, the absence of shear zones as magma pathways may favor deep entrapment of melts (Cavalcante et al, 2016) or their presence may function as an obstacle for flow of melts and crustal masses (Leech, 2008). Earlier studies have highlighted how deep strike-slip shear zones can account for the observed aspect of extrusion in collisional orogens (e.g., eastern Tibet and Indochina) by means of very large offsets on a network of splaying faults controlled by upper-crustal strength (Tapponnier et al, 1982).…”

Section: Introductionmentioning

confidence: 99%

Zippered Shear Zone Model for Interacting Shear Zones in the Borborema Province, Brazil, as Constrained by U‐Pb Dating

et al. 2019

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Shear zones typically interact to form connected systems or networks to accommodate crustal deformation, but our knowledge of how this happens is fragmentary. Understanding branching and interacting shear zones requires knowledge of timing, deformation kinematics, and rheology. The Senador Pompeu, Tauá, and Cococi strike‐slip shear zones of the Borborema Province (NE Brazil) have a central role and location in the Neoproterozoic assembly of Gondwana and provide a means to understand shear zone interaction. We apply (i) U‐Pb in situ SHRIMP analysis of zircons from syntectonic plutons and dykes to constrain the timing of shearing and (ii) vorticity and strain analysis on pluton's megacrystic facies deformed in the magmatic state and during final stages of crystallization. Obtained ages show that the shear zone pair was active under high temperature at 583.5±4.6 Ma, while felsic dykes were emplaced in the brittle regime in the wall rocks. Average vorticity estimates of 0.70 indicate a strong component of pure shear in the shear zones. Despite the transpressional character, the dispersion in estimates of thinning and thickening for the Senador Pompeu shear zone highlights variations of offset rate for the interacting branches that leads to localized transtension. We conclude that the kinematic framework of the Senador Pompeu and Tauá conjugate pair involves the formation of a dextrally closing zipper structure involving the trailing Cococi shear zone to the southwest, which in turn caused the northeastward extrusion of the enclosed crustal wedge and possibly activation of the nappe system of the Ceará Central domain.

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The influence of partial melting and melt migration on the rheology of the continental crust

Cited by 29 publications

References 55 publications

Hot Versus Cold Orogenic Behavior: Comparing the Araçuaí‐West Congo and the Caledonian Orogens

Hot Versus Cold Orogenic Behavior: Comparing the Araçuaí‐West Congo and the Caledonian Orogens

An anticlockwise metamorphic P-T path and nappe stacking in the Reisa Nappe Complex in the Scandinavian Caledonides, northern Norway: evidence for weakening of lower continental crust before and during continental collision

Zippered Shear Zone Model for Interacting Shear Zones in the Borborema Province, Brazil, as Constrained by U‐Pb Dating

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