Geology Reference
In-Depth Information
(b)
(a)
0.6
0.6
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
7.6
7.8
8.0
7.6
7.8
8.0
Σ
Cations
Σ
Cations
Fig. 2.9 a The distribution of Ti and the sum of cations in phlogopite from 3 specimens. Open
squares: Shiprock lamproite, New Mexico; open circles: wolgidite, Mount North, West
Kimberley, Australia; solid stars: Sisco lampriote, Corsica. b The distribution of Ti and the
sum of cations in phlogopites from 5 specimens. Solid triangles: Concarix lamproites, Corsica;
solid circles: Calasparra lamproite, Murcia, Spain; solid squares: lamproites from Jumilla, Murcia,
Spain; asterisk: lamproites from Barqueros, Murcia, Spain; open triangles: Smoky Butte lamproite
Montana, U.S.A (after Wagner and Velde 1986)
TiO
2
plot, the mica from the lamproitic rocks of Smoky Butte was
found to have the highest TiO
2
content (Mitchell et al. 1987). Optically zoned micas
have in general a trend of increasing TiO
2
coupled with slight decrease in the Al
2
O
3
content. In a similar plot of Al
2
O
3
versus TiO
2
contents, micas from K-rich rocks of
Alto Paranaiba (Brazil), have chemistry similar to those of micas from West
Kimberley, Smoky Butte and Leucite Hills (Gibson et al. 1994). Micas occurring in
the K-rich dikes of Trace Ranchos, Limeira I, Indaia I and Pantano, are TiO
2
-poor
tetra-ferriphlogopites. In other intrusives (e.g. Mata do Lenco) phlogopite shows
enrichment in TiO
2
from core to the rim. Phlogopites from Bociana intrusives have
moderate TiO
2
(4
In an Al
2
O
3
-
5 wt%), Al
2
O
3
(12
13 wt%) and total FeO (11 wt%) and plot in
-
-
the same
fields as the groundmass micas of madupites of Leucite Hills. The micas
of the lavas from Olegario, Serra do Bueno and Corrego Verjao have high TiO
2
(5
9 wt%) contents. These are
quite similar to the micas from West Kimberley and Leucite Hills. The phlogopites
7 wt%), moderate Al
2
O
3
(7
11 wt%) and FeO (6
-
-
-
Search WWH ::
Custom Search