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the maar. According to them, continued activity led to the subsidence of the dia-
treme portion and collapse of the crater rim. This was followed by subsidence of the
interbeded pyroclastic and epiclastic
floor deposit within the diatreme. They further
suggested that the explosive activity resulted in the removal of groundwater as
steam, subsequently a cone of depression was formed. This allowed downward
extension of the diatreme. The pheratomagmatic activity stopped, when the dia-
treme penetrated deep enough into dry mudstone of the Fair
d formation. The
magma then ascended in a non-explosive manner and intruded as diatreme and
formed lava lakes of olivine lamproite and lava domes of leucite lamproite within
the initial maar crater. Smith and Lorenz (1986) found that in case of many leucite
lamproite pipes, early pheratomagmatic eruption was followed by ascent of the
magma (small microphenocrysts of phlogopite) into the maar crater. In the next
stage, the lamproite magma with large phlogopite phenocrysts ascended from a
strati
ed magma reservoir. The predominant rock types of the West Kimberley area
are:
fitzroyite, cedricite, and mamilite. Wolgidite is the most predominant rock type
at Moulament Hill, Mt. North, and Wolgidee Hill. Fitzroyite is the most common
rock type found along the Fitzroy River basin, where it often includes quartz
amygdules. Cedricite and mamilite are typical rock types in the Mt. Credric and
Mamilu Hills, respectively. There are also some other varieties, which are transi-
tional in character between cedricite and
fitzroyite, and are similar to the wyom-
ingite of the Leucite Hills. Some of the transitional rocks are found in
“
P
”
Hills.
Analyses of K-rich lamproitic rocks from West Kimberley, Australia, are given in
Table
4.5
, but for comparison between geochemistry of West Kimberley rocks with
that of Spanish rocks, see Nixon et al. 1984).
4.2.2 New South Wales, Australia
The potassic lava
flows extend over a small area in fold belts of Southern Highlands
(Wellman 1970). This region has a peneplaned basement complex comprising
goesynclinal sediments and granitic rocks, which are overlain by a thin Cainozoic
sedimentary sequence. The fault planes and major lineaments strike along north-
northwest direction. According to Cundari (1973), the general outcrop patterns of
the K-rich volcanic rocks are distributed along the same trends (Fig.
4.7
).
The K
10 Ma years
ago (Wellman 1970). The volcanoes at Lake Cargelligo and Tullibigeal are well
preserved but at Bygalorie the domal structure of the volcano has been reduced to a
'
Ar ages of the rocks suggest that the lavas were erupted 14
-
-
. The other notable localities of K-rich lavas include El Capitan,
Bergargo Hills, Flagstaff Hills, Byrock, Condoblin, Grif
volcanic skeleton
'
th and Harden. The K-rich
rocks cover an extensive area at Tullibigeal (43 km
2
), Bygalorie (46 km
2
) and Lake
Cargelligo (12 km
2
), but in other localities such as El Capitan (6 km
2
), Begargo
Hills (2 km
2
), Flagstaff Hills (1 km
2
), Byrock (1 km
2
), Condoblin (2 km
2
), Grif
th
(1 km
2
) and Harden (0.1 km
2
), they cover relatively small areas.
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