A parcel of lherzolite in an upwelling mantle beneath 8-10 ?N of the East Pacifi

Question

A parcel of lherzolite in an upwelling mantle beneath 8-10 ?N of the East Pacific Rise ( about 100km deep) contains Pb, Ce and Yb at levels common for depleted MORB mantle. a) If the pathway of these elements in this setting stayed the same, discuss the processes that affect them over a time span of the next 200 million years b) Compare how the same elements will be processed over the next 200 million years in a parcel of lherzolite beneath Central Iceland (100 km deep) and highlight how pathways may diverge for some of the elements in Iceland relative to the EPR.

Explanation / Answer

a)MORB or mid oceanic ridge basalt , lies underwater like a moutain system and it is usually known by the phenomena of sea floor spreading. When there is a mantle upwelling new seafloor is formed and this flows as magma in the oceanic crust which later after cooling forms new crust.

As we know tectonic plates do move closer consistently every single second nevertheless speed of the movement might be very slow so over the span of 200 Million years the chemical composition of the parcel of Lherzolite in the region of East pacific Rise will go through several processess and the upper mantle will melt over time to a certain depth.Initally when there is a magma rise in MORB they releases Mg and Si . Furthermore when it settles the sillica content continues to increase along with other oxides of Na or K.Lherzolite contain large amont of olivine which later after the depletion of MORB mantle changes to other forms with the course of time considering they have stayed in the same setting.

b)Iceland is usually famous for conducting several study on seismic experiments.So if a parcel of Lherzolite containing elements like Pb , Ce , Yb etc goes through substantial differentaition. Over a span of 200 million years the composition will change along with several other things like the original place of occurance etc.

The compositional range of icelandic basalt usually overlaps normal MORB and their temperatures is also high in comparision of the mid oceanic ridge basalt.After 200 Million years there will be a theoretical movement of tectonic plates and it is also supposed that their will be one super continent by then.So the pathway of the elements of Lherzolite will have a drastic change and not only that the elements too will change due to internal heat and pressure caused by the rise in upper mantle and the flow of magma etc.

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