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sunset landing EarthCache

Hidden : 05/27/2009
1.5 out of 5
3 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

there is a very cool rock at a beautiful beach in sunset, on deer isle. it is best accessed at half-tide or low tide.

i want to thank my friend, northwoods explorer, for his help on this earthcache and for sending me information about many other geologic features of deer isle. his description of the rock in this earthcache is as follows: The story of this earthcache begins during the Cambrian Period when the sediments formed from the rifting of Avalonia from Gondwana and the associated volcanism on Gondwana accumulate in the adjacent seas. These sediments would become Ellsworth Schist when they were metamorphosed by the colliding land masses during the Acadian orogeny. The Acadian orogeny is the name of a long-lasting mountain building disturbance that most greatly affected the Northern Appalachian region (New England northeastward into the Gaspé region of Canada). The "climax" of this orogeny is dated as early in the Late Devonian, but deformation, plutonism, and metamorphism related to this orogeny continued well into the Mississippian Period. The cause of this great period of deformation is a result of the plate docking of a small continental landmass called Avalonia (named after the Avalon Peninsula of Newfoundland). The docking of Avalonia onto the margin of Laurentia resulted in the closing of a portion of the Iapetus Ocean. The Acadian Orogeny spanned a period of about 50 million years (beginning roughly 375 million years ago). During the course of the orogeny, older rocks were deformed and metamorphosed, and new faults formed and older faults were reactivated.

A schist is a rock that has been so strongly metamorphosed, or altered by intense heat and pressure, that platy minerals called micas have formed. The micas in the schist allows it to break readily along closely-spaced irregular surfaces. The Ellsworth Schist started out as a sediment composed of sand grains derived from volcanic and granitic rocks. In this area the original sedimentary rock here were probably interlaminated beds of quartz-rich sand (lighter bands) and silt (darker bands). Viewed in the right direction, you will see that these laminations have been intensively deformed into very small folds. This is the type of deformation that occurs in subduction zones on the edge of the plates.

These plates are on the surface and part of the lithosphere. The lithosphere includes the crust and the uppermost mantle, which is joined to the crust across the mantle. The lithosphere is underlain by the asthenosphere, the weaker, hotter, deeper, and more plastic part of the upper mantle. The boundary between the lithosphere and the underlying asthenosphere is defined by a difference in response to stress: the lithosphere remains rigid for long periods of geologic time, whereas the asthenosphere flows much more readily. In addition, the colder rocks in the lithosphere are denser than those in the underlying asthenosphere, and thus tend to sink, given the opportunity. Thus when, for example, a section of the lithosphere is bowed down and breaks, perhaps as a result of loading by sediment eroded off a continent, the material on one side of the break may begin to sink into the asthenosphere. This process is called subduction. The swirls are the same as when you add cream to coffee except it takes a much longer time for it to take place. At the posted coordinates you will see evidence of this subduction in the small folds in the metamorphosed rocks. The event that formed these rocks took place 375 million years ago.

remember that because this is an earthcache, there is no physical container. to log the cache, you must post a photo of you (or your hand) with your gps, showing a view of one of the layers of the rock. please email me through my profile and tell me the thickness of the various layers of this rock. please include the name of the earthcache in your email.



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