Deep seismic reflection data of EDGE U.S. mid-Atlantic continental-margin experiment: Implications for Appalachian sutures and Mesozoic rifting and magmatic underplating

The seismic reflection Moho beneath the United Kingdom and adjacent areas

A continuous seismic reflection profile extends from the continental slope off Cape Hatteras to the Bermuda Rise with sub-bottom penetration to about 2.0 sec (≈2.0 km). Each physiographic province is underlain by distinctive patterns of reflection interfaces which may correspond to sequences of well-stratified sediment. The continental slope is underlain by strata with low seaward gradients (< 0.9 × 10−2 radian SE) which are consistent with seaward projections of Cretaceous through Cenozoic coastal plain strata. The strata terminate against a thin mantle of sediment draped with a gradient of 10.5 × 10−2 radian SE nearly parallel to the sediment-water interface. The stratal terminations appear to have resulted from rotational slumping and retreat of the continental slope at least 5 km. The continental rise does not fit previous concepts that it is underlain either by unstratified sediment or by homogeneously stratified sediment. The continental rise is underlain to at least 0.5-sec two-way travel time (450 meters) primarily by extensive sedimentary strata with about 1.0 × 10−2 radian SE seaward gradients nearly parallel to the sediment-water interface. The strata are divided into a mosaic of units. Each unit is tens of kilometers wide (NW-SE) by hundreds of meters thick, contains a uniform pattern of strata, and is bounded by discontinuities. The discontinuities are interpreted as products of erosional and lateral gravitational displacement processes including, in particular, gravitational gliding. Gravitational gliding of units would explain the observed configuration of strata on the lower continental rise and is consistent with values of shear stress calculated for glide units buoyed by interstitial fluid pressure and with measured sediment shear strength. The continental rise may have extended primarily by gravitational gliding for a distance of the order of tens of kilometers over the margin of the Hatteras abyssal plain. A possible relict continental rise extends at least 150 km over a relict abyssal plain (horizon A). It is inferred from the configuration of the stratigraphic boundary that continental rise extension and abyssal plain formation may have alternated in time. The post-Late Cretaceous evolution of the continental margin has apparently involved tilting of the continental terrace including the coastal plain and two major extensions of the continental rise over two abyssal plains.

Chapter 14 The Atlantic Margin Basins of North America

Research Article| April 01, 1987 Crustal structure of the Basin and Range–Sierra Nevada Transition from COCORP deep seismic-reflection profiling P.L.K. KNUEPFER; P.L.K. KNUEPFER 1Institute for the Study of the Continents (INSTOC), Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar P. J. LEMISZKI; P. J. LEMISZKI 2Department of Geological Sciences and INSTOC, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar T. A. HAUGE; T. A. HAUGE 3INSTOC, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar L. D. BROWN; L. D. BROWN 4Department of Geological Sciences and INSTOC, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar S. KAUFMAN; S. KAUFMAN 4Department of Geological Sciences and INSTOC, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar J. E. OLIVER J. E. OLIVER 4Department of Geological Sciences and INSTOC, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar Author and Article Information P.L.K. KNUEPFER 1Institute for the Study of the Continents (INSTOC), Cornell University, Ithaca, New York 14853 P. J. LEMISZKI 2Department of Geological Sciences and INSTOC, Cornell University, Ithaca, New York 14853 T. A. HAUGE 3INSTOC, Cornell University, Ithaca, New York 14853 L. D. BROWN 4Department of Geological Sciences and INSTOC, Cornell University, Ithaca, New York 14853 S. KAUFMAN 4Department of Geological Sciences and INSTOC, Cornell University, Ithaca, New York 14853 J. E. OLIVER 4Department of Geological Sciences and INSTOC, Cornell University, Ithaca, New York 14853 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 98 (4): 488–496. https://doi.org/10.1130/0016-7606(1987)98<488:CSOTBA>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation P.L.K. KNUEPFER, P. J. LEMISZKI, T. A. HAUGE, L. D. BROWN, S. KAUFMAN, J. E. OLIVER; Crustal structure of the Basin and Range–Sierra Nevada Transition from COCORP deep seismic-reflection profiling. GSA Bulletin 1987;; 98 (4): 488–496. doi: https://doi.org/10.1130/0016-7606(1987)98<488:CSOTBA>2.0.CO;2 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 SocietyGSA Bulletin Search Advanced Search Abstract Deep seismic-reflection data collected by COCORP along a 145-km-long line in westernmost Nevada and easternmost California as part of the 40°N latitude transect of the western Cordillera reveal the geometry of three crustal-scale features associated with the Walker Lane and the transition from the Basin and Range extensional province to the Sierra Nevada crustal block. The Walker Lane, a zone of late Cenozoic strike-slip and normal faults crossed in the central third of the line, is underlain by a zone of moderately west-dipping reflections that terminate at a discontinuous mid-crustal zone of subhorizontal reflections extending across most of the line at depths ranging from 14 to 23 km. We interpret the mid-crustal reflections as an active detachment accommodating strike-slip and extensional displacements. It may coincide with the base of the Sierran batholith, a shear zone, and/or the transition from brittle to ductile crustal deformation. The dipping reflections are inferred to be from a moderately dipping (45°) fault that soles in this mid-crustal detachment and accommodates the strike-slip and normal displacement of the northern Walker Lane. Discontinuous reflections at 9.5–10.2 s two-way travel time (28–30 km) on the eastern half of the line are interpreted as the Moho, similar to the Moho imaged by COCORP lines farther east in Nevada. Moho reflections are imaged at 11.0–11.5 s (33–35 km) in the western third of the line, and project westward toward similar reflections as deep as 12–13 s (37–41 km) beneath the eastern Sierra Nevada, and so the crust appears to thin gradually from the Sierra Nevada into the Basin and Range. The lower crust east of the Walker Lane is relatively highly reflective, characteristic of COCORP data from other Nevada lines, but the lower crust west of the Walker Lane is less reflective, similar to COCORP data from the northern Sierra Nevada. The change in reflectivity of the lower crust also appears to occur gradually, with no sharp offsets or boundaries. On the basis of the COCORP data, therefore, the transition between the Basin and Range and Sierra Nevada appears to be a wide (∼100 km) zone of crustal thinning possibly accompanied by a change in deformation fabric that may correspond to changes in lower crustal rheology or degree of deformation. This transition zone is dominated by a moderately dipping fault underlying the Walker Lane and accommodating strike-slip and normal displacement down to a mid-crustal detachment level. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Deep penetrating MCS imaging of the rift-to-drift transition, offshore Douala and North Gabon basins, West Africa

In summer 2014, the U.S. Geological Survey conducted a 21-day geophysical program in deep water along the Atlantic continental margin by using R/V Marcus G. Langseth (Field Activity Number 2014-011-FA). The purpose of the seismic program was to collect multichannel seismic reflection and refraction data to determine sediment thickness. These data enable the United States to delineate its Extended Continental Shelf (ECS) along the Atlantic margin. The same data can also be used to understand large submarine landslides and therefore assess their potential tsunami hazard for infrastructure and communities living along the eastern seaboard. Supporting geophysical data were collected as marine magnetic data, gravity data, 3.5-kilohertz shallow seismic reflections, multibeam echo sounder bathymetry, and multibeam backscatter. The survey was conducted from water depths of approximately 1,500 meters to abyssal seafloor depths greater than 5,000 meters. Approximately 2,761 kilometers of multi-channel seismic data was collected along with 30 sonobuoy profiles. This field program had two primary objectives: (1) to collect some of the data necessary to establish the outer limits of the U.S. Continental Shelf, or Extended Continental Shelf, as defined by Article 76 of the United Nations Convention of the Law of the Sea and (2) to study the sudden mass transport of sediments down the continental margin as submarine landslides that pose potential tsunamigenic hazards to the Atlantic and Caribbean coastal communities.

北山造山带处于中亚造山带南缘，研究其岩浆事件对于推演中亚造山带地质构造演化具有重要意义。在甘肃北山南带的双鹰山-花牛山岛弧带中，分布有大量花岗质岩体。本文选取甘肃北山南带双峰山南复式岩体中的花岗闪长岩和二长花岗岩，开展LA-ICP-MS锆石年代学、Hf同位素、全岩地球化学和Sr-Nd同位素研究。研究结果表明该复式岩体成岩时代、地球化学与同位素特征基本一致，具体如下：（1）锆石年代学结果显示二长花岗岩年龄为367.5±1.7Ma、368.0±1.8Ma，花岗闪长岩年龄为366.3±2.2Ma，均为晚泥盆世；（2）复式岩体SiO₂含量为64.39%~74.95%、碱含量为5.01%~9.21%，属准铝质（A/CNK=0.88~1.00），P₂O₅含量低（0.02%~0.17%），且与SiO₂呈负相关，具有典型的I型花岗岩特征；（3）样品总体富集轻稀土元素（（La/Yb）_N=6.23~23.0），具有较强烈的Eu负异常（δEu=0.31~0.55），富集Rb、Th、U等大离子亲石元素，亏损Nb、Ti、P等高场强元素；（4）锆石ε_Hf（t）值为-3.1~+6.0，t_DM2为928~1327Ma，全岩（⁸⁷Sr/⁸⁶Sr）_i在0.705607~0.708523之间，ε_Nd（t）在-4.1~-1.9之间。结合区域构造环境，实验数据表明，双峰山南晚泥盆世复式岩体是在活动大陆边缘的环境下，由幔源岩浆底侵加热下地壳使之部分熔融，并与之混合形成的，代表了晚泥盆世柳园洋向北俯冲的构造事件。;Beishan orogenic belt (BOB) is located on the southern margin of the Central Asian Orogenic Belt (CAOB). The study of magmatic events in BOB is of great significance for understanding the tectonic evolution of the CAOB. A large number of granitiod plutons are distributed in the south of BOB, where the Shuangyingshan and Huaniushan arcs are located. In this study, we focus on granodiorite and monzogranite from the south Shuangfengshan complex in the southern BOB. We present whole rock geochemistry, Sr-Nd isotopic composition, in situ U-Pb dating and Hf isotopic composition of zircons from this complex, from which the following results are obtained:(1) The granodiorites and monzogranites have similar zircon U-Pb chronology, whole rock geochemistry and isotopic composition. (2) Zircon LA-ICP-MS U-Pb dating yields ages of 367.5±1.7Ma and 368.0±1.8Ma for the monzogranite, and 366.3±2.2Ma for the granodiorite, suggesting they were formed in the Late Devonian. (3) The SiO₂ contents from samples collected in the complex are 64.39%~74.95%, with alkali contents of 5.01%~9.21%, suggesting it belongs to metaluminous (A/CNK=0.88~1.00); the measured samples have low P₂O₅ contents (0.02%~0.17%), which are negatively correlated to SiO₂. These features indicated they are of typical I-type granite characteristics. (4) For the REE compositions, this complex is characterized by enriched light rare earth elements ((La/Yb)_N=6.23~23.0), negative Eu anomaly (δEu=0.31~0.55), enriched large ion lithophile elements, such as Rb, Th, U, and depleted high field strength elements such as Nb, Ti, and P. (5) The complex has ε_Hf(t) values of -3.1~+6.0, two stage model ages (t_DM2) of 928~1327Ma, (⁸⁷Sr/⁸⁶Sr)_i values of 0.705607~0.708523, and ε_Nd(t) values of -4.1~-1.9. Combined with the regional geology and tectonic environment, these data reveals that the south Shuangfengshan complex was formed in an active continental margin in Late Devonian, and during its evolution, the lower crust was partially melted by the underplating of mantle-derived magma and mixing with mantle-derived materials, which represented a northward subduction of the Liuyuan Ocean plate in the Late Devonian.

Results from two deep seismic reflection lines are presented. When combined, these lines span the rifted continental margin off Nova Scotia, from crust unaltered by rifting to the ocean basin. These data provide crustal and upper mantle reflection geometry to depths of over 50 km and elucidate the rifting process on this margin which occurred during the Mesozoic breakup of Pangaea. The continental crust below the continental shelf and slope becomes progressively thinner toward the ocean–continent boundary. In the upper crust, normal faults accommodated Mesozoic extension, and these flatten and terminate at 5–6 s (two-way time). In the lower crust and upper mantle Mesozoic rifting may be reflected in dipping events, which are interpreted to be normal faults. All Mesozoic extensional faulting could be controlled by the preexisting fabric of the crust, which in this region would be related to Appalachian compression within the Meguma Terrane. Below the continental rise, there is some evidence for magmatic underplating of the thinned continental crust, but the presence of synrift diapiric salt prevents clear definition of deeper structure. The extreme seaward end of the profile lies in a region interpreted in most other, earlier studies to be oceanic in nature. However, the seismic profile described here shows that relief on basement is associated with listric normal faults, which flatten in decollement, and that linear, landward-dipping intrabasement reflections characterize the area. These features can be explained in either a continental or an oceanic context.

A deep seismic reflection survey across the Betic Chain (southern Spain): first results

Simultaneous inversions for one‐ (1‐D) and three‐dimensional (3‐D) seismic structure and hypocenters (SSH) for both the central and western Virginia seismic regions are performed, using direct and refracted phases from about 60 earthquakes. Optimal inversion models are computed by employing regularization techniques of Tikhonov and of Backus and Gilbert. Improvements for the residual sum squared, of up to 70% are obtained for the 3‐D models and somewhat less for the 1‐D models. For the central Virginia seismic region the SSH 1‐D velocity models show a strong negative bias in the deduced Pn velocity which could only be alleviated after a ray‐tracing travel time correction for the Pn phases due to the east‐west downdipping Moho has been applied. A 4° Moho dip turns out to be optimal for best explaining the observed travel time residuals and returning a realistic Pn velocity of 8.2–8.3 km/s. However, the deduced velocity in the lower crust is only ∼ 6.35 km/s, which is lower than that predicted from gravity modeling but can be explained in terms of a lower crustal petrology of anorthosite‐rich granulite. A more detailed analysis of the lower crust shows that the hypothesized high‐velocity layer at the bottom of the crust (Pratt et al., 1988) is not clearly identifiable by the present travel time data and so can neither be corroborated nor refuted. Many of the 1‐D crustal results are further substantiated by the 3‐D model, which also provides a reduced lower crustal velocity under the Goochland Terrane. Positive velocity anomalies, which are found in the upper and middle crust under the Blue Ridge/Piedmont boundary, correlate qualitatively with the high‐density, thrust‐faulted slab deduced by Pratt et al. (1988) from gravity modeling. The vertical movements of the relocated hypocenters in the central region are of O(2–5 km) and are such as to further widen the aseismic gap under the Goochland Terrane. In the eastern section of the seismic zone (at the Piedmont/Atlantic Coastal Plain boundary) the downward focal shifts at the lower seismic boundary place events well into the Grenville basement, indicating a lowering of the brittle‐ductile transition boundary. For the western Virginia seismic region the SSH 1‐D velocity models result in a gradual increase in velocity with depth. Significant shifts in the hypocentral relocations are obtained which indicate a further deepening of the brittle‐ductile transition. This and results of thermomechanical creep models favor a quartz‐poor, diorite rich, middle and lower crust in the western region. The 3‐D velocity model of the western region shows a variety of features which can be related to the geology and the tectonics of the Valley and Ridge province. In the surficial layer a velocity low in the Mississippian‐Permian molasse of the West‐Virginian Valley and Ridge province and a velocity high in the thicker Cambrian‐Ordovician carbonate thrust and fault sheets of the Giles county area of the Valley and Ridge are obtained. In the lower crust, higher velocities are detected in the western Valley and Ridge province, which correlates well with the thickening of the crust in the western section of the Virginian Appalachian.

Cretaceous magmatic underplating and delamination beneath continental SE Brazil and their tectonic implications: Evidence from the PABBRISE wide-angle reflection and refraction seismic profile

Research Article| January 01, 2004 Structure and evolution of the central Gulf of Mexico continental margin and coastal plain, southeast United States D.L. Harry; D.L. Harry 1Department of Geological Sciences, University of Alabama, Box 870338, Tuscaloosa, Alabama 35487-0338, USA Search for other works by this author on: GSW Google Scholar J. Londono J. Londono 1Department of Geological Sciences, University of Alabama, Box 870338, Tuscaloosa, Alabama 35487-0338, USA Search for other works by this author on: GSW Google Scholar Author and Article Information D.L. Harry 1Department of Geological Sciences, University of Alabama, Box 870338, Tuscaloosa, Alabama 35487-0338, USA J. Londono 1Department of Geological Sciences, University of Alabama, Box 870338, Tuscaloosa, Alabama 35487-0338, USA Publisher: Geological Society of America Received: 13 Aug 2002 Revision Received: 01 Jul 2003 Accepted: 24 Jul 2003 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2004) 116 (1-2): 188–199. https://doi.org/10.1130/B25237.1 Article history Received: 13 Aug 2002 Revision Received: 01 Jul 2003 Accepted: 24 Jul 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 D.L. Harry, J. Londono; Structure and evolution of the central Gulf of Mexico continental margin and coastal plain, southeast United States. GSA Bulletin 2004;; 116 (1-2): 188–199. doi: https://doi.org/10.1130/B25237.1 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 SocietyGSA Bulletin Search Advanced Search Abstract As in many continental margins, Mesozoic rifting in the Gulf of Mexico trended subparallel to older tectonic structures created by opening and closure of a prior ocean basin. Unlike the situation in most other margins, however, extension in the Gulf of Mexico did not involve widespread reactivation of these older tectonic features. This difference may be related to the unusual facts that (1) the antecedent passive continental margin was a transform rather than a rift margin and (2) the prior orogeny did not substantially thicken the crust. In order to characterize the interaction between Mesozoic rifting and prior tectonic events, two geophysical transects were constructed across the central Gulf of Mexico coastal plain and continental shelf. The transects show that the early Paleozoic passive continental margin buried beneath the late Paleozoic Ouachita orogen was little affected by compressional tectonism or Mesozoic extension during opening of the Gulf of Mexico. The thickness of the crust on this ancient margin decreases from 35 km to 10 km over a distance of only 50 km, consistent with previous interpretations that this was a transform margin. The Ouachita fold-and-thrust belt is shown to be a thin-skinned doubly vergent orogen that formed above a well-preserved southward-dipping subduction system. Relict Cambrian oceanic crust may exist beneath the southern part of the orogen, but its presence is not required by the data. The thin crust and shallow mantle in the Ouachita suture created a zone of relatively high strength that acted as a barrier to Mesozoic extension, which is restricted to regions south of the orogen. Extension was initially distributed over a broad area that included the Mississippi Interior Salt Basin and regions south of the Wiggins Arch. Extension became progressively more focused south of the Wiggins Arch with time, culminating in the onset of seafloor spreading beneath the modern continental rise. Mesozoic extension factors are β = 1.4–1.9 beneath the Mississippi Interior Salt Basin, β ≈ 2.9 immediately south of the Wiggins Arch, and β ≈ 4 adjacent to the oldest oceanic crust in the central Gulf of Mexico. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

GLIMPCE Seismic reflection evidence of deep-crustal and upper-mantle intrusions and magmatic underplating associated with the Midcontinent Rift system of North America

Modification of Archean lower crust of the North China Craton by magma underplating during the Mesozoic: Evidence from zircon U-Pb-Hf-O isotopes of granulite xenoliths

Phanerozoic magma underplating associated with remelting of the lower crust beneath the Cathaysia Block: Evidence from zircon U[sbnd]Pb ages and Hf[sbnd]O isotopes of granulite xenoliths from Daoxian, South China