Abstract Ultra‐large rift basins, which may represent palaeo‐propagating rift tips ahead of continental rupture, provide an opportunity to study the processes that cause continental lithosphere thinning and rupture at an intermediate stage. One such rift basin is the Faroe‐Shetland Basin ( FSB ) on the north‐east Atlantic margin. To determine the mode and timing of thinning of the FSB , we have quantified apparent upper crustal β‐factors (stretching factors) from fault heaves and apparent whole‐lithosphere β‐factors by flexural backstripping and decompaction. These observations are compared with models of rift basin formation to determine the mode and timing of thinning of the FSB . We find that the Late Jurassic to Late Palaeocene (pre‐Atlantic) history of the FSB can be explained by a Jurassic to Cretaceous depth‐uniform lithosphere thinning event with a β‐factor of ~1.3 followed by a Late Palaeocene transient regional uplift of 450–550 m. However, post‐Palaeocene subsidence in the FSB of more than 1.9 km indicates that a Palaeocene rift with a β‐factor of more than 1.4 occurred, but there is only minor Palaeocene or post‐Palaeocene faulting (upper crustal β‐factors of less than 1.1). The subsidence is too localized within the FSB to be caused by a regional mantle anomaly. To resolve the β‐factor discrepancy, we propose that the lithospheric mantle and lower crust experienced a greater degree of thinning than the upper crust. Syn‐breakup volcanism within the FSB suggests that depth‐dependent thinning was synchronous with continental breakup at the adjacent Faroes and Møre margins. We suggest that depth‐dependent continental lithospheric thinning can result from small‐scale convection that thins the lithosphere along multiple offset axes prior to continental rupture, leaving a failed breakup basin once seafloor spreading begins. This study provides insight into the structure and formation of a generic global class of ultra‐large rift basins formed by failed continental breakup.
The southern rifted margins of the South Atlantic are commonly regarded as some of the best examples of magma-rich margins with the Pelotas, Uruguay, Argentine and Namibia margins showing prominent Seaward Dipping Reflectors (SDRs). These volcanic SDRs are commonly interpreted as resulting from enhanced decompression melting during rifting and breakup from regionally elevated asthenosphere temperatures associated with the Parana-Etendeka mantle plume. We investigate the lateral variability of breakup volcanic addition along-strike of the Pelotas segment of the southern South Atlantic rifted margin offshore SE Brazil. Our analysis of regional seismic reflection profiles shows that magmatic addition on the Pelotas margin varies substantially along strike from extremely magma-rich to magma-normal within a distance of approximately 300 km.In the north of the Pelotas margin, where SDRs are thickest, the Torres High shows SDRs up to  20 km thickness. In contrast, in the south of the Pelotas margin, the magmatic addition is normal and SDRs are very thin or absent. Further south of the Pelotas margin, offshore Uruguay and northern Argentina, margins are again magma-rich with SDRs thickness reaching 10 km or more.The very thick SDRs of the northern Pelotas margin lay offshore of the thick Serra Geral volcanics of similar Cretaceaous age found onshore in the Santa Catalina, Parana, Sao Paulo and northern Rio Grande do Sul states of SE Brazil. Further south, Serra Geral volcanics are absent in the cratonic southern Rio Grande do Sul, which is onshore of the southern Pelotas margin with thin or absent SDRs and normal magmatic addition. The abrupt decrease in rift and breakup decompression melting from north to south along the Pelotas margin, and its increase to the south on the Uruguay and northern Argentina margins is inconsistent with the simple Parana-Etendeka mantle plume model. The correlation of magma-normal breakup in the southern Pelotas margin with cratonic geology onshore implies a significant contribution of lithosphere inheritance to decompression melting during rifting and breakup to form the southern South Atlantic margins.A relationship is observed between the amount of volcanic material and the two way travel time (TWTT) of first proximal volcanics in seismic sections.  First volcanics are observed at 1.25s TWTT for the highly magmatic Torres High profile while, in contrast, for the normally magmatic profiles in the south, first volcanics are observed at 4.2s TWTT or deeper. The observed inverse relationship between post-breakup accommodation space and SDR thickness is consistent with predictions of a simple isostatic model of continental lithosphere thinning and decompression melting during breakup. This relationship between TWTT of first volcanics in seismic sections and the magnitude of magmatic addition may provide an effective means of mapping the distribution of breakup magmatic volume for the southern South Atlantic margins and its correlation with onshore geological inheritance.
The distribution of oceanic and continental crust in the eastern Mediterranean region is not well understood but has major implications for tectonic evolution of this region and its petroleum systems. In particular the location of the continent-ocean boundary (COB), the ocean-continent transition (OCT) structure, and crustal thickness within the basin regions is a topic of much debate. While seismology, especially refraction seismology, is an ideal method for locally determining crustal thickness, it is limited to 2D as 3D mapping of crustal thickness is not practical or affordable over large areas. However, a recent development in 3D crustal thickness mapping uses gravity anomaly inversion. We illustrate the application of this technique using the example of the eastern Mediterranean (Figure 1). The new 3D gravity inversion technique, incorporating a lithosphere thermal gravity anomaly correction, is used to map Moho depth, crustal basement thickness, and continental lithosphere thinning. We then use this to determine the distribution of oceanic and continental crust, and ocean-continent transition structure, for the eastern Mediterranean.
Abstract Determining the volume and timing of magmatism during rifting and breakup is challenging due to the similar density and seismic velocity of inherited continental crust, magmatic additions and serpentinized mantle; and the difficulty of dating magmatic additions. Here rules of thumb to estimate these are proposed based on the characteristics of the top basement and Moho on seismically imaged margins. A simple kinematic model is used to generate first‐order crustal shapes of margins as a function of magma volume and timing of emplacement, which are successfully compared to a representative number of rifted margins. It appears that ‘magma‐rich margins’ require melt emplacement in advance of crustal thinning but not necessarily enhanced melt volume, while margins with exhumed mantle require a delay in melt emplacement but not necessarily a low magmatic volume. An alternative classification for the magma‐poor/magma‐rich dichotomy is proposed to better represent the crustal shape variability of rifted margins.
Research Article| December 01, 2003 Mechanism for generating the anomalous uplift of oceanic core complexes: Atlantis Bank, southwest Indian Ridge A. Graham Baines; A. Graham Baines 2 Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA Search for other works by this author on: GSW Google Scholar Michael J. Cheadle; Michael J. Cheadle 2 Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA Search for other works by this author on: GSW Google Scholar Henry J.B. Dick; Henry J.B. Dick 3Woods Hole Oceanographic Institution, Woods Hole Road, Woods Hole, Massachusetts 02543, USA Search for other works by this author on: GSW Google Scholar Allegra Hosford Scheirer; Allegra Hosford Scheirer 4U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Barbara E. John; Barbara E. John 5Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA Search for other works by this author on: GSW Google Scholar Nick J. Kusznir; Nick J. Kusznir 6Department of Earth Sciences, University of Liverpool, Liverpool L69 3BX, UK Search for other works by this author on: GSW Google Scholar Takeshi Matsumoto Takeshi Matsumoto 7Nippon Marine Enterprises, Ltd., 14-1 Ogawacho, Yokosuka 238-0004, Japan Search for other works by this author on: GSW Google Scholar Author and Article Information A. Graham Baines 2 Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA Michael J. Cheadle 2 Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA Henry J.B. Dick 3Woods Hole Oceanographic Institution, Woods Hole Road, Woods Hole, Massachusetts 02543, USA Allegra Hosford Scheirer 4U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA Barbara E. John 5Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA Nick J. Kusznir 6Department of Earth Sciences, University of Liverpool, Liverpool L69 3BX, UK Takeshi Matsumoto 7Nippon Marine Enterprises, Ltd., 14-1 Ogawacho, Yokosuka 238-0004, Japan Publisher: Geological Society of America Received: 16 May 2003 Revision Received: 15 Aug 2003 Accepted: 19 Aug 2003 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2003) 31 (12): 1105–1108. https://doi.org/10.1130/G19829.1 Article history Received: 16 May 2003 Revision Received: 15 Aug 2003 Accepted: 19 Aug 2003 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation A. Graham Baines, Michael J. Cheadle, Henry J.B. Dick, Allegra Hosford Scheirer, Barbara E. John, Nick J. Kusznir, Takeshi Matsumoto; Mechanism for generating the anomalous uplift of oceanic core complexes: Atlantis Bank, southwest Indian Ridge. Geology 2003;; 31 (12): 1105–1108. doi: https://doi.org/10.1130/G19829.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Atlantis Bank is an anomalously uplifted oceanic core complex adjacent to the Atlantis II transform, on the southwest Indian Ridge, that rises >3 km above normal seafloor of the same age. Models of flexural uplift due to detachment faulting can account for ∼1 km of this uplift. Postdetachment normal faults have been observed during submersible dives and on swath bathymetry. Two transform-parallel, large-offset (hundreds of meters) normal faults are identified on the eastern flank of Atlantis Bank, with numerous smaller faults (tens of meters) on the western flank. Flexural uplift associated with this transform-parallel normal faulting is consistent with gravity data and can account for the remaining anomalous uplift of Atlantis Bank. Extension normal to the Atlantis II transform may have occurred during a 12 m.y. period of transtension initiated by a 10° change in spreading direction ca. 19.5 Ma. This extension may have produced the 120-km-long transverse ridge of which Atlantis Bank is a part, and is consistent with stress reorientation about a weak transform fault. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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