Tjie Contact Between 
THE (jRAxrnc Kocks and the (’ardup 
Series 
AT AKilADALE. 
:]7 
Under tiie nn('ros<' 0 ])e the most proiiouiuT'd feiiluri' is the i)r(*si*neo of 
dark cdots, elong’nt(‘d i)arall(‘l to the l)nnding‘, whieh are made u]) ot' brownish 
green biotite, eidiedi'al apatite, s])h(m(‘, magnetite, and rare blue-grecm liorn- 
bleiide (fig. 3A). These (-lots are undoubtedly deriveal fi'oni the basic 
xenoliths wliieh are so abundantly seatler(‘d tliroiigh this gneiss (plate 2^ 
fig. 1). The other constituents are eonsitlerably (*pidotised plagicxdase (most 
abundant), clear microcline' and (juartz. Tlu' <|uartz is all slightly strained. 
Both quartz and miciHxdine hav(‘ emdosial the ])lagio<dase. 
An analysis t)f this rock is sliown in Table I., column 2, and this indi- 
cates that there has Ixam a considerable addition of i>oth silica and soda 
to the original basic rock. As mentioned above some of the {piartz of the 
hybrid gneiss may be xenolithi(' although the greatei* part, as seen from its 
relations with the introdneed microeline, has undoul)todly been introdueed 
during the graiiitisation in-oecss. 
Head (192(i, p. Ifir)) has desciabed 11u‘ process of hybridisation of a 
gi'anitic magma l)y nltrabasic mat<'rial and his nanarks api)ly etpially well 
to the Armadale hybridised roc'ks. The basic xenoliths, in tinur high biotite 
content, are clearly hybrid typos laqna'senting basic igneous nuitfu’ial which 
has been [)ermealed with potassic solutions from an intrusive granite. ’’I’his 
gi’anite, wliitdi re[)resents the first period of granite intrusion in this area, 
was itself consid(*rably hyl>ridis(‘d by the incorporation of this basic hybrid 
and is now represented by the mesocratic hybridised gneiss described above. 
(B) The ‘ffounger granite { A])Iogra}ii(e) . 
The aplogranites are leucocratic, medium to coarse grained (in ])la('es 
]>egmaiilie) rocks compose<l of (piartz and felspar with practi<*ally no ferro- 
magnesians. Tin* texture is allotriomorphic! granular and the constituents 
seen in ihiit slice are (piartz, slightly pertliitic microcliru* and oligoclaso- 
albite with an ueeasional shred of gre(‘nish biotite. Both tin* microeline and 
finely twinned jilagioclase are slightly dusted wi(h inclusions and a notice- 
able feature is the fiaxpient (K'currence of myrmokiti(' structur(*s in flie 
])lagioclase when it occurs in contact with microeline. Most of tlie quartz 
shows slight strain shadows. 
Tin's acid granite may hav(* possibly bt'on the intrusion which caused 
the earli(‘r grauitisation effects that have Ix'en iiot(*d al)Ove but in its field 
relations app(*ars to Ix'long to a distinctly later pci’iod of intrusion. 
(C) .^ — The fine bandeA granitic gneisnes (forming the western edge of the 
granitic rocks). 
Tn many respe('t-s th(*S(* rocks are .similar to the various gneiss(‘s and 
acid I'ocks of the bb.nids Board (piarry, alfhougli no dark coloured xenolithic 
bodies hav(' lieen found in them. Their structure vari(*s from i)lac(' to ]i]ace, 
from finely band(‘d granitic gneiss('s to almost massive granites in which no 
banded structures are visilile. The massiv(* structured rocks hav(* a granitic 
texture and art* nnnh* \\\^ of (piartz, fr(*sh mi('rocline and slightly liirliid 
oligoclnS(* and so a])poar to he very similar to tin* afdogranites of' llu* eastern 
half of the area. The finely banded gneisses contain quartz, mic-rocline, 
oligoclase, clotted shr(*ds of strongly pleochroic. greeiiish-hrowu bi<)fit(‘ and 
some muscovite, which appears to be developing from a fiirlnd sericitis(*d 
felspar. The microeline is perfectly fi*esh. 
