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Directions: Several glacially polished and rounded outcrops are located near the entrance to a highway depot in the southeast comer of Chain of Ponds Township (about 10 miles southeast of Coburn Gore and about 10 miles northwest of Eustis). See Map 6.
The Chain Lakes Complex holds up much of the rugged terrain between here and Jackman due to the high quartz content of its metamorphic rocks. Although grossly uniform, the metamorphic rocks display a complex fabric up close (FIG).
The high quartz content of the Chain Lakes Complex indicates a continental affniity. The complex was probably a scrap of continental crust or sediment rafted away from Laurentia or another continent (see Stage II). The island of Madagascar, a scrap of African crust now isolated in the Indian Ocean, provides a modern analog.
As the oldest rock unit in northern Maine, the Chain Lakes Complex has suffered a long history. It was 1) intruded by Ordovician granite, 2) bevelled by erosion and covered by Silurian sediment, 3) structurally covered by the Boil Mt. Complex, 4) intruded by Devonian granite, 5) ruptured by a strike-slip fault (to the north), and 6) bevelled again by erosion.
Directions: This outcrop is located on the low ridge top between the northernmost outlet of Moosehead Lake and Rockwood.
The outcrops here consist of green volcanic rocks of intermediate composition (FIG). A matrix of fine ash encloses scattered fragments of lava and abundant crystals of white feldspar. Such ash deposits imply explosive eruptions.
These volcanic rocks typify the marine island are volcanic deposits that accumulated during subduction of the Iapetus Ocean (STAGE III-A).
Directions: Park at the scenic vista south of Jackman overlooking Attean Pond. Outcrops are located at the south end of the parking lot. If arriving from Moosehead Lake, a three mile drive on a good logging road will save backtracking from Jackman on Rt. 201.
The Attean Granite (FIG) is coarse-grained, composed of orange feldspar and gray quartz. It is one of only a few Ordovician-age granites in New England. The mottling of the feldspars is a result of metamorphism (the younger Devonian granites are generally unmetamorphosed).
The Attean Granite may be related to the Ordovician intermediate volcanic rocks (stop 21). It signifies collision of the Taconica arc with Laurentia (STAGE III).
Directions: The vista of Attean Pond includes a good view of Sally Mountain north of the Pond. The actual site requires a several mile hike. From Jackman, drive to the railroad bridge between Attean Pond and Wood Pond. Follow the railroad track to the Sally Mt. Trail.
The Attean Granite is overlain by Silurian sediments which form the summit of the mountain (FIG). The boundary between the granite and sediments is an erosional surface or unconformity (as at Stop 2). The sediments are very immature, indeed hardly recognizable as sediments in places. They are composed largely of fragments of the granite. Silurian corals have been reported from nearby.
The Sally Mountain unconfomiity signifies uplift of the arc region as a result of its collision with Laurentia (STAGE III-B).
Directions: The interior of Misery Ridge is exposed at its northeast end. Look for a long roadcut on the west side of Routes 15 and 6 less than a mile south of Rockwood.
Misery Ridge, perhaps the longest straight ridge in the state, is made of light weathering gray sandstones and shales. The quartzitic sandstones resist erosion. The top of the sequence can be determined by looking for "graded beds" (FIG) having sandy bases grading into muddy tops. The sequence becomes younger towards Mt. Kineo. Note the brachiopod fossils (FIG) at the base of several layers. These indicate shallow water conditions.
During early Devonian time, the Misery Ridge sediments were the last ones to be deposited in the diminishing puddles of the once vast Iapetus Ocean. They mark the transition from dominantly deep marine to terrestrial conditions (STAGE IV-B).
Directions: Mt. Kineo (FIG) itself can only be reached by boat from Rockwood. The Kineo Rhyolite, however, is exposed at both ends of Blue Ridge in roadcuts.
The Kineo Rhyolite forms a resistant layer which dips to the north (FIG). The rhyolite is a fine-grained, flinty gray rock. Close inspection may reveal some small quartz and/or feldspar crystals. Both the Kineo Rhyolite and Katahdin Granite crystallized from the same magma; in a general way, the granite at Phillips (stop 26) is also the underground equivalent of the Kineo Rhyolite.
The Kineo and related magmas were generated by the melting of continental materials during the full-scale continent-continent collision between Avalonia and Laurentia. Significantly, the Kineo Rhyolite is also the youngest unit to have been folded by the collision.
Directions: This fault can not be observed exactly, but is located between the southernmost exposure of the Chain Lakes Complex (stop 13) and the Boil Mt. Complex (stop 19).
This fault juxtaposes metamorphosed continental rocks (stop 13) and nearly unmetamorphosed oceanic crust (stop 19). While shown as a thrust fault on the state geologic map, its sense of movement is uncertain.
The Squid Gun Fault, which elsewhere affects rocks as young as Devonian, probably resulted from the convergence of Avalonia and Laurentia (STAGE IV).
Directions: The northern stop (19a) is located where the road passes over a prominent ridge. It consists of outcrops on both sides of the road. The southern stop (19b) consists of two large roadcuts likewise on both sides of the road.
The southern roadcuts (stop 19b) consist of pillowed basalt lavas similar to the ones at Thetford Mines (stop 10). Stop 19a is pyroxenite (FIG), a coarse-grained plutonic rock composed entirely of the green mineral pyroxene. The pyroxenite formed as crystals grew and solidified in the magma chamber beneath the lava pile. Is the original "up direction" of the igneous complex to the north or south?
The Boil Mountain Complex is another scrap of oceanic crust (STAGE II). In at least a general way, it correlates with the Thetford Mines Complex.
Directions: This unit is poorly exposed and no accessible exposures have been located to date.
The Hurricane Mountain Complex is a melange (as in stop 6) of shale matrix enclosing blocks of various sizes and compositions . The blocks include oceanic crustal materials and other volcanic and sedimentary rocks. Indeed, the oceanic crust at stop 19 is probably a giant block within this complex.
The Hurricane Mountain Complex may represent an accretionary prism that accumulated in a subduction zone setting. The complex is currently thought to have formed somewhere in the central part of the Iapetus Ocean during one of the earliest destructive episodes (see final paragraph in discussion of STAGE III). Later collisions have somewhat obscured this early event.
