Horizontal contraction or horizontal extension? Heterogeneous Late Eocene and early Oligocene general shearing during blueschist and greenschist facies metamorphism at the Pennine-Austroalpine boundary zone in the Western Alps

Ring, Uwe

doi:10.1007/bf00240572

Cited by 31 publications

(46 citation statements)

References 43 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Divergence started there sometime after the middle Oligocene (Raouzaios et al 1996;Thomson et al 1998;Ring et al 1999), but yet we know that much of the exhumation of the Cycladic high-pressure rocks occurred earlier, during the Eocene and Early Oligocene, shortly after the rocks were subducted and accreted (Avigad et al 1997;Ring et al 1999). Forster & Lister (this volume) argue that deep exhumation in the Cyclades is a result of multiple episodes of normal faulting, with any single event involving only a modest amount of exhumation.…”

Section: Continental Riftsmentioning

confidence: 99%

“…Attenuation of stratigraphic or metamorphic units, by itself, is not diagnostic of tectonic thinning by normal faulting (Wheeler & Butler 1994;Ring & Brandon 1994;Ring 1995;Butler & Freeman 1996) (Fig. 8).…”

Section: N O R M a L F A U L T I N Gmentioning

confidence: 99%

“…The presence of a subhorizontal foliation is generally diagnostic of ductile thinning. The general observation of subhorizontal foliations in the internal zones of many orogens shows that ductile thinning commonly aids exhumation (Selverstone 1985;Wallis 1992Wallis , 1995Wallis et al 1993;Platt 1993;Mortimer 1993;Ring 1995;Krabbendam & Dewey 1998;Ring et al 1999). Ductile thinning by itself cannot fully exhume rocks and an additional exhumation process is required to bring rocks back to the Earth's surface (Platt et alo 1998;Feehan & Brandon 1999).…”

Section: Ductile Thinningmentioning

confidence: 99%

See 2 more Smart Citations

Exhumation processes

et al. 1999

View full text Add to dashboard Cite

Deep-seated metamorphic rocks are commonly found in the interior of many divergent and convergent orogens. Plate tectonics can account for high-pressure metamorphism by subduction and crustal thickening, but the return of these metamorphosed crustal rocks back to the surface is a more complicated problem. In particular, we seek to know how various processes, such as normal faulting, ductile thinning, and erosion, contribute to the exhumation of metamorphic rocks, and what evidence can be used to distinguish between these different exhumation processes.In this paper, we provide a selective overview of the issues associated with the exhumation problem. We start with a discussion of the terms exhumation, denudation and erosion, and follow with a summary of relevant tectonic parameters. Then, we review the characteristics of exhumation in different tectonic settings. For instance, continental rifts, such as the severely extended Basin-and-Range province, appear to exhume only middle and upper crustal rocks, whereas continental collision zones expose rocks from 125 km and greater. Mantle rocks are locally exhumed in oceanic rifts and transform zones, probably due to the relatively thin crust associated with oceanic lithosphere.Another topic is the use of P-T-t data to distinguish between different exhumation processes. We conclude that this approach is generally not very diagnostic since erosion and normal faulting show the same range of exhumation rates, reaching maximum rates of >5-10 km Ma -1 for both processes. In contrast, ductile thinning appears to operate at significantly slower rates. The pattern of cooling ages can be used to distinguish between different exhumation processes. Normal faulting generally shows an asymmetric distribution of cooling ages, with an abrupt discontinuity at the causative fault, whereas erosional exhumation is typically characterized by a smoothly varying cooling-age pattern with few to no structural breaks. Last, we consider the challenging problem of ultrahigh-pressure crustal rocks, which indicate metamorphism at depths greater than 100-125 kin. Understanding the exhumation of these rocks requires that we first know where and how they were formed. One explanation is that metamorphism occurred within a thickened crustal root, but it does seem unlikely that the crust, including an eclogitized mafic lower crust, could get much thicker than c. 110 km while maintaining a reasonable Moho depth (<70 km, assuming that the seismically defined Moho would be observed to lie above the eclogitized lower crust). Diamondbearing crustal rocks cannot be explained by this scheme. The alternative is to accrete the upper 10-40 km of lithospheric mantle into the orogenic root. This scenario will provide sufficient pressures for both coesite-and diamond-bearing eclogite-facies metamorphism, while maintaining a reasonable Moho depth (<70 km) and reasonable mean topography (<3 kin). We speculate that the detachment and foundering of the mantle root may contribute to the exhumation of any crust...

show abstract

Section: Continental Riftsmentioning

confidence: 99%

Section: N O R M a L F A U L T I N Gmentioning

confidence: 99%

Section: Ductile Thinningmentioning

confidence: 99%

See 1 more Smart Citation

Exhumation processes

et al. 1999

View full text Add to dashboard Cite

show abstract

“…In addition to lithological differences, the distinction between the UU and the LU is frequently based on the estimated metamorphic record in metabasites. Most of the studies distinct the two units by the presence or absence of eclogite facies mineral assemblages (Balle`vre and Merle 1993;Ring 1995;Reddy et al 1999Reddy et al , 2003Pleuger et al 2007;Beltrando et al 2008). The UU is considered to be greenschist (Balle`vre and Merle 1993;Reddy et al 1999) to blueschist facies (Bousquet 2008;Bousquet et al 2012a).…”

Section: Structure Of the Piemont-ligurian Nappe Stackmentioning

confidence: 99%

Thermal structure and metamorphic evolution of the Piemont-Ligurian metasediments in the northern Western Alps

et al. 2013

View full text Add to dashboard Cite

In the Western Alps, the Piemont-Ligurian oceanic domain records blueschist to eclogite metamorphic conditions during the Alpine orogeny. This domain is classically divided into two ''zones'' (Combin and ZermattSaas), with contrasting metamorphic evolution, and separated tectonically by the Combin fault. This study presents new metamorphic and temperature (RSCM thermometry) data obtained in Piemont-Ligurian metasediments and proposes a reevaluation of the P-T evolution of this domain. In the upper unit (or ''Combin zone'') temperatures are in the range of 420-530°C, with an increase of temperature from upper to lower structural levels. Petrological evidences show that these temperatures are related to the retrograde path and to deformation at greenschist metamorphic conditions. This highlights heating during exhumation of HP metamorphic rocks. In the lower unit (or ''Zermatt-Saas zone''), temperatures are very homogeneous in the range of 500-540°C. This shows almost continuous downward temperature increase in the PiemontLigurian domain. The observed thermal structure is interpreted as the result of the upper and lower unit juxtaposition along shear zones at a temperature of *500°C during the Middle Eocene. This juxtaposition probably occurred at shallow crustal levels (*15-20 km) within a subduction channel. We finally propose that the Piemont-Ligurian Domain should not be viewed as two distinct ''zones'', but rather as a stack of several tectonic slices.

show abstract

“…The tectonic juxtaposition of low-grade rocks above higher grade rocks was used as the major evidence for normal faulting. But subsequent work by Wheeler & Butler (1994), Ring & Brandon (1994), and Ring (1995) showed that this evidence is not conclusive, and Ring & Brandon (1994 and Bolhar & Ring (2001) showed that the Coast Range fault is an out-of-sequence thrust. Other well-studied accretionary wedges, such as the Olympic subduction complex at the North American west coast, also show no evidence for normal faulting .…”

Section: Introductionmentioning

confidence: 99%

Tectonic significance of Cretaceous bivergent extensional shear zones in the Torlesse accretionary wedge, central Otago Schist, New Zealand

Deckert

Ring

Mortimer

2002

New Zealand Journal of Geology and Geophysics

Self Cite

View full text Add to dashboard Cite

We describe two shear zones in the Otago Schist of the Torlesse accretionary wedge, South Island, New Zealand: the north-dipping Rise-and-Shine Shear Zone (RSSZ) and the south-dipping Cromwell Gorge Shear Zone (CGSZ). Kinematic indicators (shear bands and asymmetric folds) indicate top-north movement for the RSSZ and topsouth transport for the CGSZ. Back rotation of the shear zones into their Late Cretaceous orientation and consideration of the relationship of the shear zones to arching of the Otago Schist show that both shear zones are extensional. Offset of textural zones suggests up to 15 km of dip-slip displacement on the RSSZ and probably a similar amount of slip for the CGSZ. We speculate that the goldmineralised RSSZ may be the western continuation of the late Mesozoic gold-bearing Hyde-Macraes Shear Zone in eastern Otago, forming a c. 100 km long extensional shear zone on the northern flank of the Otago Schist. Age constraints suggest that shear zone formation took place between 135 and 105 Ma. The shear zones aided the final exhumation of the deeper parts of the Otago Schist. We discuss whether normal shearing is related to syn-orogenic supercritical tapering of the Torlesse wedge, or due to postorogenic New Zealand-wide Albian rifting.

show abstract

Horizontal contraction or horizontal extension? Heterogeneous Late Eocene and early Oligocene general shearing during blueschist and greenschist facies metamorphism at the Pennine-Austroalpine boundary zone in the Western Alps

Cited by 31 publications

References 43 publications

Exhumation processes

Exhumation processes

Thermal structure and metamorphic evolution of the Piemont-Ligurian metasediments in the northern Western Alps

Tectonic significance of Cretaceous bivergent extensional shear zones in the Torlesse accretionary wedge, central Otago Schist, New Zealand

Contact Info

Product

Resources

About