Whole-earth geodynamics Flashcards
What does the lower mantle host? Surrounded by?
The lower mantle hosts two large, warmer LLSVPs. These are surrounded by colder graveyards of subducted slabs that have transformed into denser post-perovskite
What has accumulated over time?
Two large LLSVPs and two massive slab graveyards that have accumulated over time
What does this control?
This controls patterns of mantle heat transport and their control of mantle plumes and lithospheric processes, including the physics and chemistry of plate margins and hot spots and their dynamic and hazard implications
What is the cycle?
Material is taken from the earth’s surface into the boundary of the lower mantle and outer core, material is then taken back to the earth’s surface into the hotspots. Therefore, what happens at the plate margins is controlled by what happens in the lower mantle
What does it provide?
It also (2) provides ‘top-down regulation’ of compositional convection in the outer core. Post-perovskite has anomalously high thermal conductivity, further amplifying heat transport across the core-mantle boundary
What are slab graveyards coupled with?
Cold slab graveyard is coupled with the downwelling in the outer core.
Where is downwelling focused?
Downwelling is focussed in two main areas which is coupled with downwelling’s in the outer core
What are LLSVPs paired with?
Upwellings are the warmer part of the outer core which is paired with the LLSVPs
What does compositional convection affect?
Compositional convection in the outer core affects the shape of the earth’s magnetic field as well as heat exchange with the inner core, affecting the latter’s growth vs. melting as well as crystal structure
What do heavier materials do?
Heavier materials will stay at the boundary of the inner core and lighter ones will rise again- this compositional change fuels convection in the outer core
What does this cause?
Lopsided growth on the boundary of the inner core- melts one side which results in upwelling and fuelling volcanism at the earth’s surface and the downwelling arm couples with the ‘freezing’ of the inner core boundary, causing a lopsided growth
What to LLSVPs and slab graveyards represent?
The LLSVPs and slab graveyards therefore represent the central hub of consistent dynamic coupling of the entire earth, from the inner core to the earth surface
What do mid-ocean ridges generate?
Mid-ocean ridge generates the lithospheric plate and carries ocean ridge basalts which will eventually subduct into the upper mantle and reach the slab graveyard. The mid-ocean ridge basalts (MORBs) can be transferred into the ULVZ which will end up in the mantle plumes which will melt due to decompression melting and then fuel hot spot volcanism.
What can MORBs do?
MORBs can probably be ‘recycled’ by slab transport into graveyards and subsequent transfer into LLSVPs and then mantle plumes. This is an elegant way to explain the asthenospheric signatures of lava sampled at hot spot locations
What do LLSVPs sit underneath?
Wherever we have hotspots and mid-ocean ridges, this is where the LLSVPs are sitting underneath. Heat is upwelled as mantle plumes are being generated which fuels mid-ocean ridges and hotspots.
