Classification - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 69

8

Navajo Complex
Dulce Dyke
Espanola Basin
Two Buttes

Spanish Peaks

6

high - K

4

2

medium - K

low - K

0

38 42 46 50 54 58

SiO (wt %)
2

Fig. 3.1 SiO 2 versus K 2 O diagram showing classification of potassium-rich rocks into low-K,
medium-K and high-K series (after Gibson et al. 1993)

cation. The
diagram is based on 24,000 analyses of different rock types. Regarding this clas-
si

fields. They however, point out some limitations for this type of classi

cation, they suggested that there are several constraints:

1. It is purely a descriptive classi cation.

2. The plot has been made independent of any field location or field association.

3. No generic relationships are employed.
4. In these analyses, the CO 2 and H 2 O contents are not taken into consideration,
and their concentration has been subtracted

first and then, all analyses were

recalculated to 100.
5. The name basanite is used if olivine content exceeds 10 % in the CIPW norm.

Fig. 3.2 Total alkali versus
SiO 2 diagram classifying
potassic rocks into different
types (after Le Bas et al.
1986)

15

Phonolite

13

Te p h r i -
phonolite

Trachyte

11

Foidite

Phono-
tephrite

9

Trachy-
andesite

Trachydacite

Te p h r i t e
basanite Basaltic trachy-
andesite
Trachy-
basalt

7

5

Dacite

Basaltic
andesite

Andesite

Basalt

3

Picro-
basalt

1

37 41 45 49 53 57 61 65 69 73 77

ULTRABASIC BASIC INTERMEDIATE ACID

SiO (wt%)
2