Granite is found throughout mainland Nova Scotia and Cape Breton in
plutons of various sizes and represents about 20-25 per cent of the
bedrock across the province. The largest pluton is the South
Mountain Batholith, which is the dominant feature in the landscape
of southwestern Nova Scotia. It extends in an arc from Yarmouth to
Halifax.
AGE AND GENESIS
Over the years, there has been much discussion about the
formation of granitic rocks. The theories generally are variants on
two themes: (1) separation from a basaltic melt, and (2) extreme
recrystallization, or even melting, of pre-existing rocks.
Combinations of these two are also possible. There is general
agreement that most of the Nova Scotia granites were once molten
(magma). Age studies show that, since the Precambrian, granites
have formed in Nova Scotia during at least two periods of intense
crustal disturbance when sediments may have been thrust deep into
the earth's crust and melted. These two major occasions were during
the Cambrian and the Devonian periods. The older group of granite
plutons, around 550 to 500 million years old, is composed of
relatively small bodies which are found exclusively north of the
Cobequid-Chedabucto Fault in northern mainland Nova Scotia and Cape
Breton. The younger group, roughly 370 million years old, is found
throughout the province, but predominantly south of the
Cobequid-Chedabucto Fault, within the sedimentary rocks of the
Meguma Zone. These were generated during the Acadian Orogeny, when
the thick Meguma sedimentary pile would have been squeezed against,
and possibly over, the Avalon Zone.
The South Mountain Batholith a very large body of granite which
underlies about half of western Nova Scotia, falls within this
younger group. It has been studied extensively during the past
twenty years or so and is the best known of the granite bodies in
the province. The description which follows is basically that of
the South Mountain Batholith, although most other
Devonian/Carboniferous plutons are likely to share similar
characteristics. The South Mountain Batholith is Late Devonian in
age (ca. 370 million years) and is the largest body of granitoid
rocks in the entire Appalachian system. The margin tends to be a
granodiorite phase, but towards the centre of the batholith there
are several other phases, including monzogranite and granite. Some
of these rocks contain magmatic cordierite, andalusite or garnet.
The Batholith as a whole is broadly concordant with the regional
trends in the surrounding Meguma rocks, although locally, of
course, it must cut across structures within them. Near its margin,
it can contain screens of metamorphosed sedimentary rocks, or
myriads of xenoliths (small fragments of the country rocks). Any
foliation in the granite is due to movement in the viscous magma
itself and was not imposed upon the rock by later tectonic
stresses.
The South Mountain
Batholith
MODE OF EMPLACEMENT
Ascent of the Molten Rock A hot magma which forms at a depth of
20-40 km in the earth's crust may rise either by forcing a path
along lines of weakness or by breaking off and incorporating
overlying rocks. There are no signs of strain within the
sedimentary rocks surrounding the South Mountain Batholith, which
might indicate forced passage, but several signs indicative of
ascent by incorporation of blocks from the overlying strata (called
country rock). The contact with the surrounding Meguma country rock
is generally steep, and in several places, blocks of sediment, some
with obvious sedimentary banding, are incorporated into the granite
mass. These blocks, or xenoliths, were gradually assimilated by the
hot magma and can be found in various degrees of alteration in
several localities near the margins of the granite; for example, at
Portuguese Cove. The process of ascent by invasion and
incorporation of country rock is called "stoping".
To claim the
earthcache you must send me the answers 3 questions.
Question #1
How large is the South Mountain Batholith?
Question #2
What is the most(possible 8) abundant mineral found in the South
Mountain Batholith?
Question #3
From this waypoint what the estimated height above sea
level?
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group & gps with cliffs in the background.
You do not
need to wait for confirmiation from me before posting online.
However, any logs that do not fulfill ALL requirements will be
deleted.