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Dolerite intrusion Hobart district, Tasmania

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Leaman, DE (1970) Dolerite intrusion Hobart district, Tasmania. PhD thesis, University of Tasmania.

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Abstract

Jurassic dolerite intrusions ot the Hobart district,
Tasmania, have been examined geologically and gravimetrically
in order to determine their form. The dolerite intrudes flat lying
shallow marine Permian and continental Triassic rocks.
A major problem was the resolution of more recent faulting
superimposed upon Jurassic structures.
The intrusions are the result or a limited series of
injections (four or five). Each individual intrusion has an
irregular flattened trumpet shape. Synchronous intrusions
have interconnected to produce a cross-wave pattern in which
each hollow represents the site or one or more massive feeders.
The feeders are basically dykes up to a mile across, although
some are pipe-like extensions or wedges from dykes, and most
are related to pre-existing faults.
Sheets have been initiated above feeder wedges at a point
where effective intrusion pressure (about 7x10,gm/cm2) has
exceeded the load pressure. Dislocation by fracturing was
followed by hydrostatic intrusion. The actual form of the
sheets, termed chonoliths, is determined at any place by any previous and concomitant fracturing. Fractures are controlled
by rock heterogeneities, plastic confining beds, fluid
content and distance from the feeder, or proximity of the
tree surface. Each sheet is about l,000-1,500 feet thick.
Initial intrusions are normally placed low in the
sedimentary column, while later intrusions generally found a
higher level. Ultimately a lava plateau could be produced
if the magma supply was adequate, although no evidence exists
for this feature in Tasmania.
Extreme products of differentiation are to be found
only in those parts of the intrusion ad3acent to, or above,
a feeder. There is no evidence of assimilation within the
area.

Item Type: Thesis (PhD)
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Date Deposited: 11 Aug 2011 00:41
Last Modified: 11 Mar 2016 05:56
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