Devens Disc Golf   Part 1 (Geologic History)

Why Devens?

Figure 1.  (Wood 2016) Basket #12 General

The Disc Golf Courses at Devens are unique. Two separate courses wind their way through thick forest, rocky terrain and steep elevations changes.  The Hill, on the west and south sides of Shepley’s Hill, is the original course,  and as its name implies is dominated by numerous and often very large (up to 90 ft) elevation changes.  The General is the newer course, lies on the north and east sides of Shepley’s Hill, is longer and straighter, and is not as extreme in its elevation changes (though it is still very hilly).  These courses are free to play, lie about an hour from much of the Boston Area, and have a local disc golf shop (The Hawks Nest) which is the hub for the local disc golf community.  The locals take strong ownership in the course, both in upkeep and in the largest weekly league in Massachusetts.  It is all of these factors that has made Devens my home course and it is the inspiration for this blog.  Nowhere else that I have played so beautifully and organically merges geology with disc golf.  The geology shapes the course and the course gives the disc golfer an avenue to experience the geology.

The Terranes of Eastern Massachusetts

This first entry is going to try to unravel the geologic history of the Devens area.  If you want to focus on what rocks are at Devens and how they affect the course, then wait for the next blog entry.  This section is about how this part of Massachusetts came to be. The geologic history of the Devens area is quite complicated and is still being figured out by geologists, but I am going to try to give you the basic idea of what we think we know at the current time.

First we need to introduce the main players in the tectonic history of eastern Massachusetts as we will be using these names a lot both in this entry and in other, including other courses.

Laurentia – this is the core of the current North American Continent, If we go back to the Early Paleozoic (500 MYA (million years ago)) the margin of Laurentia was around the Berkshires in Western Massachusetts.

Gondwana-  Name of the supercontinent that consisted of the cores of current continents of Africa, South America, Antarctica and the India subcontinent.      

Avalonia – (or Avalon Terrain)   a portion of the margin of the Gondwanan continent (Possibly an island arc like Japan) in Late Proterozoic and Cambrian time. It is now located in Eastern New England, the Maritime Provinces and Scotland.

Ganderia-  Another  portion of the margin of the Gondwana continent but separate from Avalonia.  It is now thought that this subcontinent was split into two pieces, often referred to as its leading edge and trailing edge.  Ganderia is present in New England and the Maritime Provinces.  The Devens area is likely on the trailing edge segment of Ganderia.

The Merrimack Belt (terrane)-  A belt of meta-sediments and igneous intrusions thought to be a part of, or deposited on the trailing edge of the Ganderia subcontinent.  The rocks in and around Devens are from this belt, which trends from southern Maine to the Connecticut coast.

The Nashoba terrane-  a group of highly metamorphosed and deformed metamorphic and igneous rocks that lie between the Merrimack terrain (Ganderia) and the Avalon Terrane (Avalonia).  Only present in Massachusetts.

Figure 2.  From Pollock et al. 2009.  This map shows the location of the various terranes that now make up Eastern Massachusetts In  Proterozoic- Ordovician time.

 Geotectonics of the Devens region.

Ganderia was formed off the coast of Gondwana, along the margins of Gondowana, possibly as island arcs on the margins of these continents.  The time of its formation is not clear but is likely in Late Proterozoic time (before 550 MYA).   By Late Cambrian to Early Ordivician  time (515 MYA to 485 MYA) both Ganderia and Avalonia separated  from Gondwana as a new spreading center formed between them and the main Gondwana landmass.  As this rift expanded Ganderia and Avalonia were separated from Gondwana and moved towards Laurantia.  During this time of separation and transit rifting also occurred within the Ganderia landmass, splitting it into two pieces so that when Ganderia finally approached Laurantia it likely came in two large chunks.   When the leading edge of Ganderia eventually slammed into the Laurentian coast the Taconic orogeny occurred (Ordivician Time 485 MYA to 440 MYA) building mountains along the margin of Laurentia, forming new volcanic arcs, and deforming the edge of Laurentia and this portion of Ganderia.  Evidence of this event is found father to the west in Massachusetts.   After the Taconic Orogeny finished, sedimentary basins formed just off the margin of the now expanded Laurentia, taking sediment from the both Laurentia  and from the trailing edge of Ganderia which was now approaching the Laurentian Continent.  It is in this environment that it is thought that the sediments that would become the Merrimack Belt were first emplaced.  Some of these sediments can be seen in other parts of the Merrimack belt such as at Coggshall Disc Golf course in Fitchburg.  By Early Silurian time (440MYA- 420 MYA) the trailing edge of Ganderia slammed into Laurentia in the Salinic Orogeny.  At this point deposition of sediments sifted farther eastward continuing till early Devonian time (415 -400 MYA).  It is at this time that the sediments that would become the main components of the Merrimack Terrane in the Devens area were likely deposited.  Next, The Avalon terrain slammed into Laurentia /Ganderia to the East and pushed the Nashoba terrane underneath the Merrimack terrane.  This event is called the Acadian Orogeny (415- 375 MYA) and it is this subduction of the Nashoba terrane that triggered the emplacement of the igneous plutons in the Merrimack, including the Ayer Granite. Compression from this event likely formed many of the deformational features we see in Merrimack Belt rocks like folds, shear zones and fractures.   Much later, in the Permian, Gondwana itself crashed against Laurantia in the Alleghanian Orogeny (300- 250 MYA) , this event and subsequent rifting in the Mesozoic do not seem to have had as much impact as the earlier events in the Devens Area but are important in other parts of New England.  Basically Eastern Massachusetts consists of a series of terranes that subsequently collided with and were accreated to the edge of the North American continent.  Devens sits in one of these terranes whose origin if much more Aftrican or South American than North American and has been heavily deformed and altered by these numerous collisions.  

Figure 3:  from Sorota 2013.  Cross sections showing the area of the Merrimack terrane (MT) during Silurian to Devonian time.  In Silurian time (A) sediments are derived from both Laurentia and Ganderia (block to right of picture).  In Devonian time (B) Avalonia collides with Laurantia, subducting under the Merrimack Terrane, triggering formation of igneous intrusions (in red). 

References and Links

Devens Disc Golf Course Review Page  -   http://www.dgcoursereview.com/course.php?id=1186

The Hawks Nest  -  http://www.hawksnestdg.com/

Devens League Website -  http://devensdg.blogspot.com/

Gannett Fleming Inc.  and US EPA Region 1.  Shepley’s Hill Bedrock Investigation. Environmental Proctection Agency: 2012. Electronic URL  https://www3.epa.gov/region1/superfund/sites/devens/507276.pdf

Kopera, Joseph P.  Preliminary Bedrock Geologic Map of the Ayer Quadrangle, Massachusetts [map]. 1:24000. Office of the Massachusetts State Geologist. University of Massachusetts.  Electronic URL ftp://128.119.45.20/pub/stategeologist/for_Ray/ayer_prelim_final.pdf

Pollock, Jeffrey C, Hibbard, James P, and Sylvester Paul J.  “Early Ordovician Rifting of Avolonia and Birth of the Rheic Ocean: U-Pb Detrital zircon constraints from Newfoundland.”  Journal of the Geological Society. May 2009.

Robinson Peter and Goldsmith, Richard, “Stratigraphy of the Merrimack Belt, Central Massachusets.”  U.S. Geological Survey Professional Paper 1366 E-J. Washington D.C.: 1991. Electronic URL  http://pubs.usgs.gov/pp/1366e-j/report.pdf

Skehan, James W. Roadside Geology of Massachusetts. Missoula: Mountain Press Publishing Company, 2006. Print

Skehan, James W. Roadside Geology of Connecticut and Rhode Island. Missoula: Mountain Press Publishing Company, 2008. Print

Sorota, Kristin Joy.  Age and Origin of Merrimack Terrane, Southeastern New England: A Detrital Zircon U-Pb Geochronology Study.  M.S. Thesis. Boston College. 2013. Online.  Persistent link: http://hdl.handle.net/2345/3043

Zen, E-an, Gildsmith, Richard, Ratcliffe, N.M., Robinson, Peter, Stanley R.S., Hatch, N.L., Shride, A.F.,Weed, E.G.A., and Wones, D.R.  Bedrock Geologic Map Of Massachusetts[map]. 1:250,000. U.S. Geological Survey. 1983