NJK /Sept 2016 1 North Atlantic 2016 – Durham Mapping Crustal Thickness, OCT Structure and Crustal Type Using Satellite Gravity Anomaly Inversion for the North Atlantic: Some Answers but Many Questions Nick Kusznir Earth and Ocean Sciences, University of Liverpool, Liverpool, L69 3BX, UK Email: [email protected]Aim •To present evidence for Iceland being underlain by lithosphere with some continental component? •To make some observations of analogous phenomena using global crustal thickness mapping from satellite gravity inversion
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NJK /Sept 2016
1
North Atlantic 2016 – Durham
Mapping Crustal Thickness, OCT Structure and Crustal Type Using
Satellite Gravity Anomaly Inversion for the North Atlantic: Some
Answers but Many Questions
Nick KusznirEarth and Ocean Sciences, University of Liverpool, Liverpool, L69 3BX, UK
Gravity anomaly inversion of satellite derived free-air gravity incorporating a lithosphere thermal gravity anomaly correction data now provides a useful and reliable methodology for mapping global crustal thickness in the marine domain (Chappell & Kusznir, GJI, 2008). The resulting maps of crustal thickness and continental lithosphere thinning factor may be used to determine continent-ocean boundary location, and the distribution of oceanic lithosphere, micro-continents and oceanic plateaux (e.g. Alvey et al., EPSL 2008). Crustal cross-sections using Moho depth from gravity inversion allow continent-ocean transition structure and magmatic type (magma poor, “normal” or magma rich) to be determined. Using crustal thickness and continental lithosphere thinning factor maps with superimposed shaded-relief free-air gravity anomaly, we can improve the determination of pre-breakup rifted margin conjugacy and sea-floor spreading trajectory during ocean basin formation.
Gravity anomaly inversion of satellite derived free-air gravity incorporating a lithosphere thermal gravity anomaly correction data now provides a useful and reliable methodology for mapping global crustal thickness in the marine domain (Chappell & Kusznir, GJI, 2008). The resulting maps of crustal thickness and continental lithosphere thinning factor may be used to determine continent-ocean boundary location, and the distribution of oceanic lithosphere, micro-continents and oceanic plateaux (e.g. Alvey et al., EPSL 2008). Crustal cross-sections using Moho depth from gravity inversion allow continent-ocean transition structure and magmatic type (magma poor, “normal” or magma rich) to be determined. Using crustal thickness and continental lithosphere thinning factor maps with superimposed shaded-relief free-air gravity anomaly, we can improve the determination of pre-breakup rifted margin conjugacy and sea-floor spreading trajectory during ocean basin formation.
Crustal thickness mapping (figure 1b) shows large crustal thicknesses (> 30 km) under SE Iceland (Torsvik et al., PNAS, 2015) extending offshore to the NE and consistent with SE Iceland being underlain by continental crust associated with a southern continuation of the Jan Mayen micro-continent. This interpretation is supported by geochemical evidence.
Plate restoration to 83 Ma of crustal thickness derived from gravity inversion for the S Atlantic (figure 2) shows the Rio Grande Rise and Walvis Ridge forming a single feature which is analogous to Iceland. Some continental component has been proposed for the Rio Grande Rise. Similar features with anomalously thick crust within the ocean domain with continental affinity are also observed within the Indian Ocean (Torsvik et al., Nature Geoscience, 2014) and appear to be attractors for ocean ridge jumps. Some of many questions are whether these regions clearly within the oceanic domain are underlain by lithosphere with some continental compositional component and whether the ridge jumps are attracted by rheological weaknesses controlled by compositional or thermal anomalies.
NJK /Sept 2016
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•3D spectral inversion for Moho depth - Parker (1972)- Low pass Butterworth filter ( λ = 100 km)
•Smith’s theorem – unique solution for assumptions made
•Lithosphere thermal gravity anomaly correction
- Oceanic and rifted continental margin lithosphere have elevated geothermal gradients- Large negative thermal gravity anomaly (< -350 mgal) - Correction needed to determine Moho depth from gravity inversion
•Magmatic addition prediction uses decompression melting model of White & McKenzie (1989)
•Sediment density model assumes normal
compaction
Global Oceanic Crustal Thickness Mapping using Satellite Gravity Inversion
