Crustal Heating and Lithospheric Alteration and Erosion Associated With Asthenospheric Upwelling Beneath Southern New England (USA)

Abstract

The Northern Appalachian Anomaly (NAA), a region of exceptionally low seismic velocities in the asthenosphere beneath southern New England and easternmost New York State, has been interpreted as a site of mantle upwelling. We synthesize a combination of new and previously published data that indicates the following: (1) The upwelling has eroded or delaminated the lithosphere in a localized region centered in southern Vermont that we call the “Green Mountains Anomaly.” Forty‐second period Rayleigh wave phase velocities, which have peak sensitivity at lithospheric depths, are slow in this region, and S wave receiver functions are dominated by shallow (60‐km depth) mantle structures indicating reduced velocities. Thermal springs and sites with anomalously high concentrations of mantle‐derived helium‐3 are concentrated at the borders of the Green Mountains anomaly, perhaps due to stress concentrations produced by geologically recent, uncompensated delamination of the lower lithosphere. (2) S wave receiver functions indicate intense (>10%), shallow (60‐km depth) short wavelength structures along the southern and western edges of the NAA, indicating that the lithosphere there is being intensely altered, possibly by a combination of shearing and introduction of volatiles. And (3) Notwithstanding the localized thinning and alteration, the NAA lithosphere as a whole does not appear to have experienced pervasive heating, for the compressional wave quality factor of QP = 870 inferred from the decay rate of Po waves is very significantly above the QP ≈ 60 value previously reported for the NAA asthenosphere.

Seismotectonic implications of the Berne earthquake swarms west-southwest of Albany, New York

“…The ultimate source of the stresses that caused the fault reactivations of the Berne swarms is beyond the scope of this report, but it may be linked to two alternative models: (1) geodynamics of the asthenospheric edge-driven upwelling centered in southern New England (Menke et al, 2016(Menke et al, , 2018, or (2) adjustments of the slightly undercompensated mafic bodies modeled for the Scranton gravity high (Benoit et al, 2014) in response to the present stress field.…”

“…The approximate, relatively sharp, steeply dipping western boundary of the low-velocity zone lies parallel to, and ~15-30 km west of, the western thrusts on Figure 1 (and ~10 km east of the Berne swarm; Menke et al, 2016), or lies up to 75 km farther west (~45-55 km west of the Berne swarm; Schmandt and Lin, 2014;Pollitz and Mooney, 2016). The low-velocity zone is thought to indicate upwelling asthenosphere that is related to mantle processes functioning at the continental margin ("edge-driven upwelling"; e.g., Menke et al, 2016Menke et al, , 2018. Abbott and Menke (2019) proposed that geothermal springs and seismicity are linked to the edge-driven upwelling.…”

“…A significant low-velocity zone is located in the shallow mantle (100-300 km depth) that marks thinned lithosphere beneath southern New England, called the Northern Appalachian anomaly (e.g., Levin et al, 1995Levin et al, , 2000Li et al, 2003;Skryzalin et al, 2015;Pollitz and Mooney, 2016;Menke et al, 2016Menke et al, , 2018. The approximate, relatively sharp, steeply dipping western boundary of the low-velocity zone lies parallel to, and ~15-30 km west of, the western thrusts on Figure 1 (and ~10 km east of the Berne swarm; Menke et al, 2016), or lies up to 75 km farther west (~45-55 km west of the Berne swarm; Schmandt and Lin, 2014;Pollitz and Mooney, 2016).…”

“…Abbott and Menke (2019) proposed that geothermal springs and seismicity are linked to the edge-driven upwelling. The field of identified geothermal springs extends from southern New England into eastern New York along the Hudson River valley (Menke et al, 2018). Menke et al (2018) suggested that He +3 anomalies such as those in the spring water at Saratoga Springs (Siegel et al, 2004) indicate that mantle sourcing is occurring along deep fracture systems that extend to the mantle and that are open because of the geodynamics of the edge-driven upwelling.…”

“…The field of identified geothermal springs extends from southern New England into eastern New York along the Hudson River valley (Menke et al, 2018). Menke et al (2018) suggested that He +3 anomalies such as those in the spring water at Saratoga Springs (Siegel et al, 2004) indicate that mantle sourcing is occurring along deep fracture systems that extend to the mantle and that are open because of the geodynamics of the edge-driven upwelling. Saratoga Springs is located along the Saratoga-McGregor fault (which is on-strike with the epicenters of the Berne earthquake swarms; Fig.…”