An official website of the United States government
The New England Appalachians provide a fascinating window into a host of fundamental geological problems. These include the modification of crustal and mantle lithospheric structure via orogenesis, terrane accretion, and continental rifting, the evolution of individual terranes through processes such as channel flow and ductile extrusion, and the causes and consequences of the Northern Appalachian Anomaly (NAA), a prominent geophysical anomaly in the upper mantle. Recent and ongoing deployments of dense seismic arrays in New England are providing images of the crust and upper mantle in unprecedented detail, allowing us to address both new and longstanding science questions. These deployments include the Seismic Experiment for Imaging Structure beneath Connecticut (SEISConn, 2015-2019), the New England Seismic Transects (NEST, 2018-present), and the GEology of New England via Seismic Imaging Studies (GENESIS, 2022-present) arrays. Here we present results from these experiments that are shedding new light on the tectonic evolution of New England and the ways in which structures and processes in the upper mantle can affect the structure of the overlying lithosphere. These include detailed new images of crustal architecture beneath central and southern New England, including a sharp transition from thick (~48 km) crust Laurentia terranes to thin (~32 km) crust beneath Appalachian terranes. The character of this offset beneath the SEISConn and NEST arrays suggests an overlap of two Moho boundaries, forming an overthrust-type structure that may have resulted from reactivation of faults during the compression and shortening associated with the formation of the hypothesized Acadian Altiplano. Beneath SEISConn, there is evidence for multiple relict structures preserved in the lithosphere from past episodes of terrane accretion and suturing, as well as anisotropic layering that constrains the kinematics of past lithospheric deformation events. Beneath the NEST line in central New England, we infer a relatively shallow (~80 km) lithosphere-asthenosphere boundary above the NAA upper mantle geophysical anomaly, providing evidence for lithospheric thinning above a presumed asthenospheric upwelling. Finally, preliminary results suggest layered crustal anisotropy beneath the GENESIS array, perhaps corresponding to a past episode of channel flow in the mid-crust.
more »
« less
New insights into crustal and mantle structure beneath the New England Appalachians from temporary broadband seismic deployments and integration with geological constraints
The New England Appalachians provide a fascinating window into a host of fundamental geological problems. These include the modification of crustal and mantle lithospheric structure via orogenesis, terrane accretion, and continental rifting, the evolution of individual terranes through processes such as channel flow and ductile extrusion, and the causes and consequences of the Northern Appalachian Anomaly (NAA), a prominent geophysical anomaly in the upper mantle. Recent and ongoing deployments of dense seismic arrays in New England are providing new images of the crust and upper mantle in unprecedented detail, allowing us to address both new and longstanding science questions. These deployments include the Seismic Experiment for Imaging Structure beneath Connecticut (SEISConn, 2016-2019), the New England Seismic Transects (NEST, 2018-present), and the GEology of New England via Seismic Imaging Studies (GENESIS, 2022-present) arrays. Here we present initial results from the SEISConn and NEST experiments and discuss science targets and hypothesis testing for the GENESIS experiment. In combination with constraints from geological investigations (including structural studies and geochronology work), our new seismic investigations are shedding new light on the tectonic evolution of New England and the ways in which upper mantle processes can affect the structure of the overlying lithosphere.
more »
« less
- Award ID(s):
- 2147463
- PAR ID:
- 10428830
- Date Published:
- Journal Name:
- AGU Fall Meeting Abstracts
- Volume:
- 2022
- Page Range / eLocation ID:
- S45C-05
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The New England Appalachians provide a fascinating window into a host of fundamental geological problems. These include the modification of crustal and mantle lithospheric structure via orogenesis, terrane accretion, and continental rifting, the evolution of individual terranes through processes such as channel flow and ductile extrusion, and the causes and consequences of the Northern Appalachian Anomaly (NAA), a prominent geophysical anomaly in the upper mantle. Recent and ongoing deployments of dense seismic arrays in New England are providing images of the crust and upper mantle in unprecedented detail, allowing us to address both new and longstanding science questions. These deployments include the Seismic Experiment for Imaging Structure beneath Connecticut (SEISConn, 2015-2019), the New England Seismic Transects (NEST, 2018-present), and the GEology of New England via Seismic Imaging Studies (GENESIS, 2022-present) arrays. Here we present results from these experiments that are shedding new light on the tectonic evolution of New England and the ways in which structures and processes in the upper mantle can affect the structure of the overlying lithosphere. These include detailed new images of crustal architecture beneath central and southern New England, including a sharp transition from thick (~48 km) crust Laurentia terranes to thin (~32 km) crust beneath Appalachian terranes. The character of this offset beneath the SEISConn and NEST arrays suggests an overlap of two Moho boundaries, forming an overthrust-type structure that may have resulted from reactivation of faults during the compression and shortening associated with the formation of the hypothesized Acadian Altiplano. Beneath SEISConn, there is evidence for multiple relict structures preserved in the lithosphere from past episodes of terrane accretion and suturing, as well as anisotropic layering that constrains the kinematics of past lithospheric deformation events. Beneath the NEST line in central New England, we infer a relatively shallow (~80 km) lithosphere-asthenosphere boundary above the NAA upper mantle geophysical anomaly, providing evidence for lithospheric thinning above a presumed asthenospheric upwelling. Finally, preliminary results suggest layered crustal anisotropy beneath the GENESIS array, perhaps corresponding to a past episode of channel flow in the mid-crust.more » « less
-
null (Ed.)Abstract The eastern margin of North America has been affected by a range of fundamental tectonic processes in the geologic past. Major events include the Paleozoic Appalachian orogeny, which culminated in the formation of the supercontinent Pangea, and the breakup of Pangea during the Mesozoic. The southern New England Appalachians exhibit a particularly rich set of geologic and tectonic structures that reflect multiple episodes of subduction and terrane accretion, as well as subsequent continental breakup. It remains poorly known, however, to what extent structures at depth in the crust and lithospheric mantle reflect these processes, and how they relate to the geological architecture at the surface. The Seismic Experiment for Imaging Structure beneath Connecticut (SEISConn) was a deployment of 15 broadband seismometers in a dense linear array across northern Connecticut. The array traversed a number of major tectonic boundaries, sampling across the Laurentian margin in its western portion to the Avalonian terrane at its eastern end. It also crossed the Hartford rift basin in the central portion of the state. The SEISConn stations operated between 2015 and 2019; data from the experiment are archived at the Incorporated Research Institutions for Seismology Data Management Center and will be publicly available beginning in 2021. A suite of imaging techniques is being applied to SEISConn data, with the goal of providing a detailed view of the crust and mantle lithosphere (including discontinuities, seismic velocities, and seismic anisotropy) beneath the southern New England Appalachians. Results from these analyses will inform a host of fundamental scientific questions about the structural evolution of orogens, the processes involved in continental rifting, and the nature of crustal and mantle lithospheric deformation during subduction, terrane accretion, and continental breakup.more » « less
-
Abstract In this study, we use data from the SEISConn seismic experiment to calculate Sp receiver functions in order to characterize the geometry of upper-mantle structure beneath southern New England (northeastern United States). We image robust negative-velocity-gradient discontinuities beneath southern New England that we interpret as corresponding to the lithosphere-asthenosphere boundary (LAB) and identify a well-defined step of 15 km in LAB depth at a longitude of 73°W, which we interpret to be the boundary between Laurentian and Appalachian lithosphere, although the offset may be larger if the putative LAB phase is reinterpreted to be a mid-lithospheric discontinuity. We infer that the lithosphere throughout the region is substantially thinner than elsewhere in the continental interior, consistent with regional tomographic studies and previously published Sp receiver function results. The presence of thinned lithosphere suggests that the low-velocity Northern Appalachian Anomaly (NAA) in the upper mantle may extend as far south as coastal Connecticut. The presence of regionally thinned lithosphere and a step in lithospheric thickness suggests that inherited structure may be preserved in present-day lithosphere, even in the presence of more recent dynamic processes associated with the NAA.more » « less
-
Abstract Seismic tomography observations show a low‐velocity feature in the upper mantle beneath eastern North America known as the Northern Appalachian Anomaly (NAA). Proposed models for the formation of the NAA include a remnant high‐temperature feature resulting from the passage of the Great Meteor Hotspot, edge‐driven convection, and ongoing asthenospheric upwelling. We investigate the structure of the lithosphere above the central portion of the NAA using data from the New England Seismic Transects (NEST) experiment. Ps receiver functions reveal two consistent interfaces beneath the dense northern line of NEST: the Moho (the base of the crust) and a deeper negative velocity gradient (NVG) feature located at depths between 60 and 110 km. We consider several potential explanations for this NVG feature; based on comparisons with previous results, we propose that it likely corresponds to the lithosphere‐asthenosphere boundary. Our results indicate that the lithosphere beneath New England is nonuniform and has likely been thinned.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- The DOI is not currently available.
