The Bloody Bluff Fault Zone

The Bloody Bluff fault in Massachusetts, USA is actually a fault zone and consists of many faults along a linear trend.   It forms an arc that trends east-west to northeasterly at its northeast end near Newbury, Massachusetts along the Atlantic coast.   In Massachusetts the fault zone is approximately 80 miles long.   The fault zone curves southwestward to Reading and Wilmington, and then southwestward into the state of Connecticut.

Geologic evidence suggests that the Bloody Bluff fault zone formed toward the end of the Paleozoic era, at a shallow depth, so the resulting faulting was brittle (Skehan, 2001).   The fault zone is named after Bloody Bluff in Minute Man National Historic Park in Lexington, Massachusetts and consists of reddish-orange Indian head granite that formed during the Mississippian period.   It is named for a location where British troops gathered during an early battle of the Revolutionary War.  The bluff is shown in the picture on the right.

Bedrock south and east of the Bloody Bluff fault zone is of the Avalon terrane.   It formed as a late Precambrian chain of volcanic and plutonic islands along the edge of the supercontinent Gondwana.   Because of subsequent plate tectonics movements which included formation of the Atlantic Ocean during the Jurassic period, part of the Avalon terrane is now in Great Britain and Belgium.

Bedrock north and west of the Bloody Bluff fault zone is of the Nashoba terrane.   It consists of mafic, intermediate, and felsic volcanic, volcanogenic, and plutonic rocks.

Plate Tectonics

Plate tectonics theory suggests that eastern Massachusetts has undergone at least three plate collisions in the last 500 million years (Skehan, p. 6).   At plate boundaries, the denser plate, usually consisting of oceanic crust, sinks under the less dense continental crust in a trench at a subduction zone.

The most recent movements along the Bloody Bluff fault zone probably occurred near the end of the Paleozoic era when a collision of continental blocks took place during the creation of the Pangean supercontinent.

Parallel with this fault zone to the north and west is the Clinton-Newbury fault zone which also transects eastern Massachusetts from the Atlantic coast near Newbury into the state of Connecticut.    The Clinton-Newbury fault zone separates Nashoba terrane from Merrimack terrane.

Some Useful Links

The above discussion provides basic information and illustrations for the Bloody Bluff fault zone.   To further explore this subject, excellent publications or the resources of the internet can be explored.   Following are some hyperlinks that may help with the evaluation and description of faults:

• Historical Perspective – Pangaea, Laurentia, and Gondwana (U.S. Geological Survey website):  Website that explains Plate Tectonics and the evolution of Supercontinents.
• Faults (University of Leeds, School of Earth and Environment, UK):  Material describing faults and faulting with pictures and drawings.   Based on information presented in their first year course in structural geology.
• This Dynamic Earth:  The Story of Plate Tectonics (US Geological Survey website):  Illustrated online version of a publication by W. Jacquelyne Kious and Robert I. Tilling printed by the U.S. Printing Office in 1996.
• Earthquake Watch - Current information based on earthquakes reported to the USGS in the last 24 hours and information about recent earthquakes.

• USGS maps, products, and publications - Online information resource on the U.S. Geological Survey website.