Constructing a High-Resolution Temporal Record of Spreading-Rate Variations Along the Mid-Atlantic Ridge
Abstract
Paleoclimate records provide an opportunity to investigate links between major changes in Earth's climate and long-term forcing mechanisms. While changes in atmospheric CO2 appear to drive trends in climate, global ocean cooling in the late Miocene remains an enigma: most CO2 proxies do not show a corresponding decline over this period. To improve constraints on the global carbon cycle over this time, we are constructing a new global synthesis of variations in ridge spreading rates with high temporal resolution over the past 20 Myr. We utilize newly available compilations of seafloor fabric and marine magnetic anomalies that are provided by the Global Seafloor Fabric and Magnetic Lineation Data Base Project (Matthews et al., 2011; Seton et al., 2014). Our initial focus is the northern Mid-Atlantic Ridge, where spreading is preserved on both ridge flanks, and dense data sets of magnetic anomalies are available. To obtain accurate and precise values of time, we use a new orbital timescale for magnetic reversal ages. Tectonic flow lines are generated from seafloor fabric, using continuous fracture zones extending from transform faults along the current ridge out to seafloor > 30 Myr. The cumulative distance each point on the flow line has traveled from the ridge is computed. Nearby magnetic anomalies are projected onto the flow line along lines normal to the flow line. Spreading rate as a function of seafloor age is then determined from age-distance relationships; both ridge flanks are treated separately to investigate spreading asymmetry. To improve the profiles' signal to noise ratios, we then stack the anomaly crossings onto composite east and west spreading profiles. Our preliminary analysis shows that spreading rates have decreased significantly from the mid-Miocene to the present, beginning around 15 Ma and experiencing a pronounced reduction during 8 to 5 Ma. This trend mirrors the decline observed in global sea surface temperatures, suggesting that tectonic forcing, through reductions in mantle CO2 release over time, may have triggered global cooling. Future work will yield spreading rate histories for all major ridge systems, estimations of variations in global crustal production at ridges over the past 20 Myr, and a new perspective on the link between climate change and long-term tectonic forcing.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.T33A3007C
- Keywords:
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- 7245 Mid-ocean ridges;
- SEISMOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICSDE: 8163 Rheology and friction of fault zones;
- TECTONOPHYSICSDE: 8416 Mid-oceanic ridge processes;
- VOLCANOLOGY