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11.
Asymmetry or symmetry of magma‐poor rifted margins refers commonly to the crustal architecture and the occurrence or absence of large‐scale extensional detachment faults. While distal parts of magma‐poor rifted margins are often considered to be asymmetric, the observation of downlapping sedimentary sequences over exhumed mantle domains at conjugate margins suggests a symmetric evolution during mantle exhumation. On the basis of seismic observations along the Iberia–Newfoundland and Australia–Antarctica margins, we propose that their most distal parts show evidence for the development of multiple, out‐of‐sequence asymmetric detachment faults. We present evidence for cyclic delocalization and re‐localization of deformation, resulting in an apparent symmetry of the exhumed mantle domain. The interaction between out‐of‐sequence detachment systems and the successive rise of the asthenosphere may explain the observed transition from fault‐controlled to magma‐controlled strain accommodation and the transition to more symmetric and localized accretion associated with the formation of a stable spreading center. 相似文献
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Alpine‐type orogens are interpreted to result from the collision of former rifted margins. As many present‐day rifted margins consist of hyper‐extended domains floored by thinned continental crust (<10 km) and/or exhumed mantle, this study explores the influence of rift inheritance on the architecture and final evolution of Alpine‐type orogens. We propose that rift‐related necking zones, separating weakly thinned 25‐ to 30‐km‐thick crust from hyper‐extended domains, may act as buttresses during the transition from subduction to collision. As a result, former necking zones may now be found at the boundary between a highly deformed and overthickened nappe stack, made of relics of hyper‐extended domains, and an external, weakly deformed fold‐and‐thrust belt, which largely escaped significant rift‐related crustal thinning and orogeny‐related thickening. Therefore, the role of rift inheritance is of critical importance and is largely underestimated in controlling the architecture and evolution of Alpine‐type orogens. 相似文献
13.
G.?MohnEmail author G.?Manatschal E.?Masini O.?Müntener 《International Journal of Earth Sciences》2011,100(5):937-961
The Austroalpine nappe systems in SE-Switzerland and N-Italy preserve remnants of the Adriatic rifted margin. Based on new
maps and cross-sections, we suggest that the complex structure of the Campo, Grosina/Languard, and Bernina nappes is inherited
largely from Jurassic rifting. We propose a classification of the Austroalpine domain into Upper, Middle and Lower Austroalpine
nappes that is new because it is based primarily on the rift-related Jurassic structure and paleogeography of these nappes.
Based on the Alpine structures and pre-Alpine, rift-related geometry of the Lower (Bernina) and Middle (Campo, Grosina/Languard)
Austroalpine nappes, we restore these nappes to their original positions along the former margin, as a means of understanding
the formation and emplacement of the nappes during initial reactivation of the Alpine Tethyan margin. The Campo and Grosina/Languard
nappes can be interpreted as remnants of a former necking zone that comprised pre-rift upper and middle crust. These nappes
were juxtaposed with the Mesozoic cover of the Bernina nappe during Jurassic rifting. We find evidence for low-angle detachment
faults and extensional allochthons in the Bernina nappe similar to those previously described in the Err nappe and explain
their role during subsequent reactivation. Our observations reveal a strong control of rift-related structures during the
subsequent Alpine reactivation on all scales of the former distal margin. Two zones of intense deformation, referred to as
the Albula-Zebru and Lunghin-Mortirolo movement zones, have been reactivated during Alpine deformation and cannot be described
as simple monophase faults or shear zones. We propose a tectonic model for the Austroalpine nappe systems that link inherited,
rift-related structures with present-day Alpine structures. In conclusion, we believe that apart from the direct regional
implications, the results of this paper are of general interest in understanding the control of rift structures during reactivation
of distal-rifted margins. 相似文献
14.
Mderic Amann Marc Ulrich Gianreto Manatschal Eric Pelt Marie‐Eva Epin Julia Autin Daniel Sauter 《地学学报》2020,32(1):75-88
Basalts exposed in the Platta and Tasna nappes (SE Switzerland) derive from the Alpine‐Tethys ocean–continent transitions (OCT) and overlie subcontinental lithospheric mantle (SCLM). We show that the trace element signatures of these basalts differ from mid‐ocean ridge basalts (MORB). Two types of basalts occur in the OCT: a type‐1 showing a ‘garnet signature’ that can be modelled by the partial melting of the SCLM in the spinel stability field and a type‐2 characterized by an enrichment in incompatible elements that can be explained by the mixing between garnet‐pyroxenite‐derived melts and the melting of either a depleted MORB mantle or a refertilized SCLM. Based on the geological and geochemical observations, we propose that the basalts from the Alpine‐Tethys OCTs result from a poly‐phase magmatic system that carries an inherited SCLM signature. These basalts should therefore be referred to as OCT‐basalts rather than as MOR‐basalts. 相似文献
15.
It is commonly accepted that collisional orogens involve the reactivation of former rifted margins. While it remains debated how rift inheritance can be identified and how it controls the architecture of orogens this case study analyses the importance of rift-inheritance during reactivation of a passive margin. The study analyses complex, non-layer cake rift structures within the well-exposed Err and Platta nappes (SE Switzerland), representing the former distal Adriatic margin of the Alpine Tethys. Diagnostic criteria for rift inheritance include: (1) typical fault rocks with a mantle derived fluid signature, and (2) tectono-sedimentary breccias made of reworked exhumed basement and grading upwards into late syn- and post-rift sediments. Based on the study of “recognisable” features, a methodology is etablished, which enables to (1) map rift-related detachment faults and (2) to analyse their role during reactivation and formation of a thrust stack. First, second and third order thrust systems are defined. First order thrust systems juxtapose different rift domains (proximal, necking, and distal). Second order systems are dominantly made up of basement sheets sampling the former footwall of an extensional detachment fault. Third order systems mainly consist of the former hanging wall of an extensional detachment fault. A major result of this study is that thrust faults commonly reactivate former extensional detachment faults, especially in the exhumed mantle domain (Platta nappe), while in the hyperextended domain (Err nappe) reactivation of rift-inherited structures is more complex and often incomplete. The results of this study may help to better identify remnants of former distal margins and to define and analyse their complex stacking patterns observed in many internal parts of collisional orogens. 相似文献
16.
Hölker Andreas B. Manatschal Gianreto Holliger Klaus Bernoulli Daniel 《Marine Geophysical Researches》2002,23(4):319-334
The tectonic interpretation of basement structures in seismic reflection profiles from ocean-continent transitions (OCT) of magma-poor rifted margins is notoriously difficult due to the scarcity of borehole information. Low-angle intra-basement reflections are frequently interpreted as detachment faults, and in certain locations the drilled top of the basement is interpreted as exhumed detachment fault. The seismic expression of such detachment faults is, however, poorly understood. We address this problem by comparing synthetic seismic data from the Tasna OCT, an exposed remnant of a Tethyan margin, with seismic reflection data from Hobby High, a drilled basement high within the west Iberian margin. Both sites are widely considered as being representative of OCT zones. Their geological similarity and the complementary nature of the data enable us to perform a detailed investigation of the seismic structure and response of these OCT zones. This provides insights into the seismic imaging of OCT zones in general and the tectonic evolution of the associated detachment systems in particular. On the basis of the Tasna OCT models and their seismic responses we have identified some potential characteristics of intra- and top-basement detachments: (i) variable amplitudes and numerous diffractions from the top of exhumed subcontinental mantle, (ii) a continuous and strong reflection imaging the top of exhumed lower crustal rocks, and (iii) a weak and discontinuous reflection of inverse polarity representing a shallow intra-basement crust-mantle detachment. Similar features are consistently observed at geologically equivalent positions in the seismic data from Hobby High and may thus serve as guidelines for interpretation of seismic data from un-drilled OCT zones. 相似文献
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Natasha Stanton Gianreto Manatschal Julia Autin Daniel Sauter Marcia Maia Adriano Viana 《Marine Geophysical Researches》2016,37(3):185-205
This study investigates the magnetic and gravity signatures and associated seismic character of hyper-extended, exhumed and embryonic oceanic domains along the conjugate Iberia–Newfoundland rifted margins. As these margins have been drilled down to basement along their distal parts, it is possible to explore and test different geophysical techniques and interpretations. The aims of this work are twofold: (1) to investigate the location and nature of the two main marginal boundaries—the necking zone and the J Anomaly, which define the limits of major domains; and (2) to map the lateral variations of gravity and magnetic signatures and their detailed correlation with seismic data, from the proximal margin until the first unequivocal oceanic magnetic anomaly (e.g. C34 Anomaly). The results point out that the J Anomaly corresponds to a first-order tectono-magmatic boundary, with a basement formed by polyphase magmatism. It marks the boundary between the exhumed mantle domain, with little magmatic additions, from a domain oceanwards that reveals comparable trends, frequencies and a general magnetic pattern at both sides of the Atlantic, suggesting a coeval evolution. We propose that the domain between the J and the C34 Anomalies was formed by an embryonic spreading system, with intermittent budgets of magma, similar to those observed at very slow spreading systems. The J Anomaly may thus correspond to the location of lithospheric breakup though its origin and the nature of the domain oceanwards remains to be constrained. 相似文献