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Distribution Regularities of Trace Elements in Granitoid Intrusions of the Batholith and Hypabyssal Types
Distribution Regularities of Trace Elements in Granitoid Intrusions of the Batholith and Hypabyssal Types L. V. TAUSON
Institute of Geochemistry, Academy of Sciences U.S.S.R., Irkutsk, U.S.S.R.
Abstract The distribution character of trace elements divides the granitoid intrusions into four groups: abyssal batholiths, meso-abyssal batholiths, hypabyssal intrusions with a low volatile content and hypabyssal intrusions with a high one. Abyssal batholiths go with a deep differentiation of the magmatic substance and a strong difference of many rare elements in the marginal members of the magmatic series. This is not apparent in meso-abyssal batholiths. In hypabyssal intrusions magmatic differentiation processes of rare elements are reduced but increase because of their emanation transportation to the apical parts.
Investigation of distribution characteristics of trace elements in granitoids shows two tendencies of behaviour due to processes of crystallization and differentiation of magma. A large part of their atoms is dispersed in the lattices of rockforming or accessory minerals (crystallochemical dispersion). Other atoms, owing to a strong relation to volatiles, remain a long time in the melt. At the end phase of crystallization these atoms either form minute amounts of their own minerals or concentrate in the residual melts and solutions together with the volatiles (remain concentrating). The geochemical history of the rare elements in magmatic process and especially their distribution in rocks depends mainly on the ratio of their atoms which are in a state of crystallochemical dispersion to those which remain in solution. This ratio will change with composition, size and depth of intrusion. As a consequence, the distribution regularities of trace elements in abyssal, meso-abyssal batholiths and in hypabyssal intrusions are considerably different. In abyssal granitic batholiths, forming at great depth under quiet tectonic conditions, processes of crystallo-differentiation develop fully. There the volatile components together with a part of the rare elements, concentrate
630
L. V. Taus on
in the latest intrusive phases, and only - ^ is in the batholith. For the main phases of this type of intrusion homogeneity of composition is characteristic. For instance, in the Susamir batholith the main intrusive phase is composed mainly of porphyry granodiorites and biotite granites. Plagiogranites, tonalités and adamellites play minor roles, and therefore the main faciès difference among the rocks of this phase is the predominance of granites in certain parts and that of granodiorites in others. Fully developed processes of crystallo-differentiation in this type of intrusion reveal sharp contrasts in the behaviour of some rare elements in the marginal members of differentiation series (Table 1). TABLE 1. CONTENT OF RARE ELEMENTS IN INTRUSIVE PHASES OF THE SUSAMIR BATHOLITH (CENTRAL TYAN-SHAN, U.S.S.R.)
Intrusive phases I. Phase diorites and gabbro-diorites II. (main) phase porphyry granodiorites and granites III. phase leucocratic granites Vein granitoaplites
Li
Rb
Tl
U
STRce
XTR Y
Pb
Zn
Cu
F
0/
/o
ppm 28
70
0-7
1-4
205
105
9
96
33
0070
32
170
1-3
3-4
350
60
25
56
12
0100
55 7
250 280
2-7 4-7
5-8 81
250 70
120 220
34 34
30 12
9 10
0125 0025
Table 1 shows, that the difference in content between rocks of the first phase and the vein granite-aplites is 6-8 times for uranium, thallium, zinc, and 2-3 times for many other elements. In characterizing the depth of differentiation processes it is useful to use the ratio of elements chemically alike but undergoing a differently directed concentration change in a genetically related rock series ; in this respect it is of interest to consider the ratio Zn/Pb and Σ TR Ce /E TR Y . Table 2 shows that in the granitoids of Susamir batholith the ratio Zn/Pb changes from the first phase to the vein aplites by up to 33 times. In the meso-abyssal batholiths, differentiation processes are less intense and the difference in the ratio Zn/Pb decreases to 7-15 times and in hypabyssal intrusions it decreases to 2-3 times or disappears. Useful also is the ratio change of Σ TR Ce /Z TR Y . In the Susamir batholith the maximum is in granitoids of the main phase leucocratic granites and in phase vein aplites. The variation is 19 times. It is important that at the magmatic stage, the geochemical history of elements used in connection with the ratio of indicating pairs, must be dominated by the tendency of crystallochemical dispersion, and therefore the given ratio answers fully the question of the intensity of processes of crystallo-differentiation at this magmatic chamber.
631
Distribution Regularities of Trace Elements
Meso-abyssal batholiths forming at a depth of 4-6 km are characterized by a great faciès rock variation of their main intrusive phase. For instance, among the rocks of the main intrusive phase of the Djidinski meso-abyssal batholith (Western Transbaikalia) there occur monzonites, syenite-diorites, syenites, quartz syenites, grano-syenites, adamellites and porphyry granites. In the Verchne-Undinski meso-abyssal batholith there is among the rocks of the main phase a facies variation from quartz diorites to leucocratic TABLE 2. Z N / P B RATIO GRANITE INTRUSIONS OF DIFFERENT TYPES
Abyssal batholiths Intrusive phases
VerchneUndinski
Djidinski
Cent. Tyan- Eastern TransbaiShan kalia
Western Transbaikalia
Susamirski
I II (main) III Vein series I stage (aplite)
Meso-abyssal batholiths
10 2-2 0-9 0-3
6 3-2 2 0-4
51 2-8 1-6 0-7
Hypabyssal intrusions Shakhtaminski
Soktuyski
Eastern Transbaikalia 2-7 1-7 11
21 20 2-2
granites. The number of facies in the main phases of meso-abyssal batholiths comes from a disturbed tectonic condition for the crystallization of magmatic melts and also from the heterogenetic composition due to contamination. The difference between the homogeneity of rock composition in the main phases of abyssal and of meso-abyssal batholiths is reflected in the distribuZTR Ce /ZTR Y Granitoids of the main phase Leucocratic granites Vein granite-aplites
5-8 21 0-3
tion characteristics of the rare elements in these rocks. Table 3 gives the average contents and the concentration dispersion of some trace elements in the rocks of the main intrusive phases in abyssal (Susamir) and mesoabyssal (Verchne-Undinski, Djidinski) batholiths. So, with an equal level of contents of the given elements their concentration dispersion in the rocks of the main phases in meso-abyssal batholiths (Verchne-Undinski and Djidinski) is much higher than that in rocks of O.D.E.—21*
632
L. V. Tauson
abyssal batholith (Susamir). The cause of dispersion growth of element concentrations in the rocks of the main intrusive phases of the meso-abyssal batholiths is apparently the lower stability of crystallization conditions for magmatic melts of this type of intrusion compared with those of depth. This holds water because of the great number of faciès variations of rocks of the main intrusive phases of meso-abyssal batholiths. Probably, this is related to the fact that by rock crystallization of the main intrusive plases of mesoabyssal batholiths degassing of intrusions is smooth. Because of a higher gradient of pressure of fluid phases meso-abyssal batholiths volatile compoTABLE 3. AVERAGE CONTENT AND DISPERSION OF CONCENTRATION LI, R B , PB, Z N , U, Mo IN THE MAIN INTRUSIVE PHASES OF ABYSSAL AND MESO-ABYSSAL BATHOLITHS
Batholiths
Lithium c a2 ppm
Rubidium c ppm
σ2
Lead
Zinc
c a2 ppm
c a2 ppm
Uranium c ppm
Molybdenum
a2
c ppm
o2
Susamirski, Central Tyan-Shan, U.S.S.R.
32
180 170 1000
25
24
56
206 3-4
215
0-6
010
Verchne-Undinski, Eastern Transbaikalia, U.S.S.R.
42
260 129 2460
14
54
45
427 3-2
5-92 1 0
1-89
Djidinski, Western Transbaikalia, U.S.S.R.
35
295 130 1239
19
30
55
420
—
11
—
1-6
nents migrate to the upper parts of the magma chamber and are dispersed in granitoids and rocks enclosing them. The main result of this process is the impletion of late acid differentiates of those magma chambers with volatile components. For instance, the decrease of fluorine and the associated lithium in the third intrusive phase of meso-abyssal batholiths (Table 4). Table 4 shows both the accumulation of F and Li in the third phase of the Susamir (abyssal) batholith and the impletion of the rocks of the third phases in meso-abyssal batholiths with these elements, and the stability of the F/Li ratio in a differentiation sequence indicating the genetic unity of these magmatic series and the geochemical association of lithium and fluorine. The stability of F/Li is also apparent in rock-forming minerals concentrating these elements. For instance, the ratio F/Li in the biotites from different faciès of main phase granitoids of the Verchne-Undinski meso-abyssal batholith is stable and near to the mean value of this ratio for rocks of the given phase.
633
Distribution Regularities of Trace Elements TABLE 4. AVERAGE CONTENT OF F AND LI IN ABYSSAL AND MESO-ABYSSAL BATHOLITHS
Fluorine (%)
Lithium (ppm)
F/Li
I phase
II (main) phase
III phase
Vein aplites
Susaminskit
0070
0100
0125
0025
Verchne-Undinski Djidinski Kalbinskit (Kazakhstan, U.S.S.R.)
0045 0082
0068 0098
0058 0079
0015
0070
0150
0066
0018
Susamirski
28
32
55
7
Verchne-Undinski Djidinski Kalbinskit
25 34 85
42 35 123
39 32 77
8 10-5 26
Susamirski
25
31
23
—
Verchne-Undinski Djidinski Kalbinski
18 24 8
16 28 12
15 25 9
—
t Data by Stavrov, 1963.
The graphical illustration of the relation between the fluorine and lithium contents is given in figure 1. This does not only stress the genetic unity of the series, but shows also the difference in the concentration levels 0.15 . 0.14. 0.13 .
*v
0.12. o,ii . 0.10.
. /
ΙΝ^
/
c-/
V
* /ill"
• / 'ί
0,09.
/
0.080.07-
4
0.060.05-
^y 20
30
//«
*'IIImt
,^«.
ΛΟ
SO
9o
ioo
no
120
Li
ppm
FIG. 1. The correlation of the contents of Li and F in granite batholiths. I, the first intrusive phase ; II, the second (main) intrusive phase ; III, the third intrusive phase.
634
L. V. Tauson
of these elements and the degree of degassing of acid differentiates in mesoabyssal batholiths. It is supposed, that the degassing of late members of the magmatic series of the meso-abyssal type are strongly associated with post-magmatic processes. Therefore, this degassing process of late differentiates is one more proof for the conclusion from the occurrence limit of differentiation in intrusions of this type.
Quartz-diorites and granodiorites (margin faciès) Porphyry granites and granodiorites (main fades) Leucocratic granites (deep-seated faciès)
F wt. %
Li ppm
F/Li
0-38 0-64 112
270 410 790
14 15-5 14
Thus, although the processes of crystallochemical dispersion are dominant in determining the rare element distribution in abyssal and meso-abyssal batholiths, the distribution characteristics of the two types of granitoid intrusions are different. In the abyssal batholiths the processes of crystallo-differentiation proceed strongly and in acid differentiates bring about a high concentration of some elements and a sharp decrease of others. At the same time acid differentiates intensively accumulate elements crystallo-chemically associated with potassium (Rb, Cs, Tl, Pb, etc.) or those which build up stable compounds with volatiles (Li, Be, U, etc.), but decrease contents of elements crystallo-chemically related to magnesium and iron (Zn, Cu, Ni, Co, etc.). The homogeneity of the magmatic melts gives these intrusions a low dispersion of element concentration. In the meso-abyssal granite batholiths, an instability of the intrusive crystallization condition, leading to a non-uniformity of magmatic melts, together with crystallo-chemical differentiation and the degassing of late acid differentiates, all play a part in determining the element distribution pattern. This is reflected in the decrease of the degree of variation of element contents between the first and last members of differentiated sequences, the increase of element concentration in the main intrusive phases and a concentration decrease in the acid differentiates of some volatile components and their associated rare elements (fluorine-lithium). The distribution of trace elements in hypabyssal intrusions differs considerably from that in batholiths. For this intrusion type the characteristics of rare element distribution are due apparently to their small volume, at a relatively shallow depth of formation and their composition characteristics. The latter, first of all, includes the content level of volatile components in magmatic melts. At the same time it should be pointed out that these intrusions very often reveal only their apical parts. That makes the investigation of rare element distribution characteristics in the intrusive body difficult and
635
Distribution Regularities of Trace Elements
sometimes gives an indication of abnormally high contents of some rare elements therein. In addition, in the first phases of such intrusions, contamination processes have given rise to a higher content and greater dispersion of some rare elements. The small size of hypabyssal intrusions, the low depth of formation and the relatively high rate of crystallization bring about a process of crystallodifferentiation, which is characteristic for all intrusions of this type, and so is characterized by the example of intrusions with a low content level of volatile components (Table 5). TABLE 5. RARE ELEMENT DISTRIBUTION IN INTRUSIVE PHASES OF THE SHAKHTAMINSKI MASSIF (EASTERN TRANSBAIKALIA)
Li
Rb
Tl
Intrusive phases
Be
Pb
Zn
Sn
ppm
Diorites and monzonites (1st phase) Granodiorites and adamellites of the main phase Granites of the additional intrusion phase (3rd phase)
F wt.
%
28
110
0-6
20
20
54
7-2 0 0 8
33
181
1-3 2-3
24
40
2-5
54
249
1-9 3-2
28
33
3-7 0 0 9
008
It is clear, that in a given differentiation sequence the average contents of the investigated elements do not change more than 2-3 times and do not exceed the level of the dark content for this rock type. In our case, the high content of lithium in granites of the third phase is left without explanation. The high tin content in the granitoids of the first phase, it seems, is a result of the contamination process. For this intrusion type very low values of dispersion are characteristic and particularly for the main intrusive phases (Table 6). As in the batholith intrusions so here the processes of crystallo-chemical dispersion dominate the rare element distribution. TABLE 6. DISTRIBUTION OF RARE ELEMENTS IN THE MAIN INTRUSIVE PHASES OF THE MESOZOIC M A G M A T I C COMPLEXES OF EASTERN TRANSBAIKALIA
Lithium Complexes
Rubidium
c c a2 a2 ppm ppm
Thallium
Beryllium
c c a2 a2 ppm ppm
Shakhtaminski 32 71 150 211 11 AmudjikanoSretenski 66 357 190 2123 1-9 Kukulbeiski 84 571 350 3546 4-5
Lead
Zinc
Tin
c c c a2 a2 ppm a2 ppm ppm
3 0 0-28 25
Fluorine wt.
%
68 41 150 2-9 0-41 0 0 8 0
32 21 39 162 4-3 0140 6-6 4-75 30 116 57 629 6-3 6-83 0-300
636
L. V. Tauson
The most difficult is the distribution of rare elements in the hypabyssal intrusions differing with a high content of volatile components in magmatic melts; the crystallo-differentiation processes there are also weakened. Because a great pressure gradient of fluid phases and a high content of volatiles are usual in these intrusions we often find the processes of gas transportation of volatile compounds carry some trace element into the upper parts of the magma chambers and there is also a distinctly expressed tendency for the residual concentration of volatiles and related rare elements in the late acid differentiates. Consequently the processes of intrusion degassing and the migration of rare elements appear not only in the magmatic stage but also in all post-magmatic stages. On the whole, a considerably higher content of some trace elements and a very high concentration dispersion of the elements is characteristic. A detailed investigation of rare element distribution in the mesozoic magmatic complexes of Eastern Transbaikalia showed these common characteristics of rare element distribution in intrusions of a similar type and their difference in this case from hypabyssal intrusions with a low volatile content (Table 6). These data show that in the granitoids of the Kukulbey complex the average content of all studied elements, taking out lead and zinc, is 2-4 times higher than in the granitoids of the Shakhtaminski complex, but the greatest differences are in the element concentration dispersion. In the granites of the Kukulbey complex the value of this distribution parameter for rubidium, beryllium and tin is 17 times and for lithium 8 times that in the Shakhtaminski complex granitoids. The lead and zinc contents in the Kukulbey complex granites do not differ from those of the Shakhtaminski complex granitoids, but the concentration dispersion of these elements in the Kukulbey complex is 2 and 4 times higher than in the Shakhtaminski complex. Granites of the Kukulbey complex are characterized by a high concentration of volatile components, as proved by the fluorine content. This is the cause of the characteristic feature of these granitoids in which a sharp increase of rare element content in the rockforming minerals appears at the end phases of the crystallization process. Significant also are the contents of several trace elements in biotites from the granites of the Shakhtaminski and Kukulbey complexes (Table 7). The investigation of the granitoids of the Shakhtaminski and the Kukulbey complexes shows that the biotites are evolved at the end phases of crystallization. From the data of Table 7 it is clear that biotites from granites of the Kukulbey complex are enriched in rare elements, especially tin, lead and zinc. It should be stressed, that in biotites from granites rich with fluorine are concentrated not only elements bound up with the volatiles (Li, Rb, Be, Sn), but also elements for which such relations are not established (Pb and Zn). This can be understood as indirect proof for the enrichment in these granitoids of other volatile components helping most of the rare elements to remain
637
Distribution Regularities of Trace Elements
in the melt until the end phase of crystallization. But all these characteristics of rare element distribution in hypabyssal intrusions with a high level of volatiles apply to the upper parts of intrusives. It is regrettable to be without observations on the distribution character of rare elements in the upper as well as the lower parts of some definite intrusion of this type. At present we have only indirect evidence relating to the problem of degassing of such intrusions. TABLE 7. TRACE ELEMENTS IN BIOTITES. (THE CONTENT IS IN PPM; IN BRACKETS IS THE ELEMENT CONTENT IN ROCKS)
Complexes Shakhtaminski Kukulbey
Li
Rb
Be
Pb
Zn
Sn
426 (45) 1350 (84)
695 (198) 1300 (350)
5 (2-9) 12 (65)
2-5 (18) 27 (29)
155 (32) 990 (68)
6-3 (35) 200 (71)
A known example of degassed portions of acid magmatic melts is vein granite-aplite. In these formations, the content of several rare elements is high whereas the content of volatile components is low, particularly fluorine. While investigating the distribution characteristics of rare elements in granitoids of the Kukulbey complex a zone in one of the massifs was found to be composed of quartz syenites and grano-syenites which is in this case regarded as a degassed phase of the main intrusion. As a result of the supposed degassing process the magmatic melt producing these rocks lost a notable part of rare elements (Table 8). TABLE 8. THE RARE ELEMENT DISTRIBUTION IN THE ROCKS OF THE SOKTUY MASSIF, EASTERN TRANSBAIKALIA, U.S.S.R.
Rocks Granite phases of additional intrusions (late differentiate) Biotite granites of the main phase Granosyenites and quartz-syenites (degassed faciès of biotite granites)
Li Rb Tl
Be Pb Zn Sn ppm
F wt. /o
84 372 4-4 6-9 70 343 4-3 6-6
19 30
42 7-4 0-33 61 6-2 0-30
12 142 11 2-5
22
85 2-6 006
The degassing processes of hypabyssal granite intrusions, characterized with a high content of volatile components help the migration of rare elements into the upper parts of the magmatic chamber not only in the magmatic stage of the history of these intrusions but also by the autometasomatosis and also at high-temperature metasomatic processes. As a result, the apical parts of such intrusions can have zones highly enriched with some of the rare elements, especially Li, Rb, Be, Sn, W and others.
638
L. V. Tauson
This shows, that the distribution of rare elements in hypabyssal intrusions is considerably different from that in intrusions of the batholithic type and particularly those with hypabyssal intrusions with a high content of volatile components. The above-mentioned allow us to conclude: 1. The characteristics of rare element distribution in granitoids is determined by the intrusion size, depth of forming and composition. These features give abyssal and meso-abyssal intrusions of the batholithic type and hypabyssal intrusions with high and low contents of volatile components. 2. In the abyssal batholiths the rare element distribution is mainly controlled by processes of crystallo-differentiation, leading to a strong difference in the contents of rare elements between the margin members of the magmatic series. The rare element distribution in the crystallization process of rocks there is dominated by the crystallochemical dispersion. 3. The meso-abyssal batholiths forming at moderate depth and usually under quiet tectonic conditions are characterized by a crystallo-differentiation process and the degassing of late differentiates. The rare element distribution dominates the process of the crystallochemical dispersion, going with many variations in the main phases and this brings about an element concentration dispersion that is higher than in abyssal batholiths. 4. In hypabyssal intrusions with a low level of volatiles, crystallo-differentiation processes are weak. In the end members of the magmatic series there is a small difference in rare element contents. The element concentration dispersion is insignificant except where due to contamination or some redistribution of elements bound up with volatiles. The element distribution is mainly determined by the crystallochemical dispersion. 5. In hypabyssal intrusions with a high content of volatiles and a great pressure gradient of fluid phases, elements associated with volatiles (Li, Be, Rb, Sn, W, Nb, Ta, etc.) are concentrated in the apical parts of intrusions. That holds especially for the late differentiates of the magmatic series. For this intrusion type there is a distinctive process of crystallo-differentiation. There is a wide development of emanation transportation of rare elements with a degassing of deep-seated intrusion parts, particularly appearing at late magmatic or early post-magmatic stages of the formation of the intrusion. This leads to the concentration of several rare elements in the upper parts of intrusions and also a 15-20 times higher concentration dispersion of these elements than is found in hypabyssal intrusions, with a low volatile content. References LEONOV, L. L. and BALASHOV, U. A. (1963) The distribution of uranium, thorium and rareearth elements in granitoids of the Susamirski batholith (Central Tyan-Shan). Geochimiya No. 2, 1008-1015.
Distribution Regularities of Trace Elements
639
STAVROV, O. D. (1963) Geochemical features of lithium, rubidium and caesium at the forming process of granitic intrusives and their pegmatites. Geologiay mestorozhdeniy redkich elementov 21, Moskva, Gosgeoltechizdat.
ZLOBIN, B. I., BELAYEV, U. I. and TAMONTYEV, V. P. (1967) Copper in intrusions of the
Central-North Tyan-Shan along with metallogenic problems. Geologiya redkich mestorozhdeniy 9, 45-56.
Institute of Geochemistry, Academy of Sciences U.S.S.R., Irkutsk, U.S.S.R.
Abstract The distribution character of trace elements divides the granitoid intrusions into four groups: abyssal batholiths, meso-abyssal batholiths, hypabyssal intrusions with a low volatile content and hypabyssal intrusions with a high one. Abyssal batholiths go with a deep differentiation of the magmatic substance and a strong difference of many rare elements in the marginal members of the magmatic series. This is not apparent in meso-abyssal batholiths. In hypabyssal intrusions magmatic differentiation processes of rare elements are reduced but increase because of their emanation transportation to the apical parts.
Investigation of distribution characteristics of trace elements in granitoids shows two tendencies of behaviour due to processes of crystallization and differentiation of magma. A large part of their atoms is dispersed in the lattices of rockforming or accessory minerals (crystallochemical dispersion). Other atoms, owing to a strong relation to volatiles, remain a long time in the melt. At the end phase of crystallization these atoms either form minute amounts of their own minerals or concentrate in the residual melts and solutions together with the volatiles (remain concentrating). The geochemical history of the rare elements in magmatic process and especially their distribution in rocks depends mainly on the ratio of their atoms which are in a state of crystallochemical dispersion to those which remain in solution. This ratio will change with composition, size and depth of intrusion. As a consequence, the distribution regularities of trace elements in abyssal, meso-abyssal batholiths and in hypabyssal intrusions are considerably different. In abyssal granitic batholiths, forming at great depth under quiet tectonic conditions, processes of crystallo-differentiation develop fully. There the volatile components together with a part of the rare elements, concentrate
630
L. V. Taus on
in the latest intrusive phases, and only - ^ is in the batholith. For the main phases of this type of intrusion homogeneity of composition is characteristic. For instance, in the Susamir batholith the main intrusive phase is composed mainly of porphyry granodiorites and biotite granites. Plagiogranites, tonalités and adamellites play minor roles, and therefore the main faciès difference among the rocks of this phase is the predominance of granites in certain parts and that of granodiorites in others. Fully developed processes of crystallo-differentiation in this type of intrusion reveal sharp contrasts in the behaviour of some rare elements in the marginal members of differentiation series (Table 1). TABLE 1. CONTENT OF RARE ELEMENTS IN INTRUSIVE PHASES OF THE SUSAMIR BATHOLITH (CENTRAL TYAN-SHAN, U.S.S.R.)
Intrusive phases I. Phase diorites and gabbro-diorites II. (main) phase porphyry granodiorites and granites III. phase leucocratic granites Vein granitoaplites
Li
Rb
Tl
U
STRce
XTR Y
Pb
Zn
Cu
F
0/
/o
ppm 28
70
0-7
1-4
205
105
9
96
33
0070
32
170
1-3
3-4
350
60
25
56
12
0100
55 7
250 280
2-7 4-7
5-8 81
250 70
120 220
34 34
30 12
9 10
0125 0025
Table 1 shows, that the difference in content between rocks of the first phase and the vein granite-aplites is 6-8 times for uranium, thallium, zinc, and 2-3 times for many other elements. In characterizing the depth of differentiation processes it is useful to use the ratio of elements chemically alike but undergoing a differently directed concentration change in a genetically related rock series ; in this respect it is of interest to consider the ratio Zn/Pb and Σ TR Ce /E TR Y . Table 2 shows that in the granitoids of Susamir batholith the ratio Zn/Pb changes from the first phase to the vein aplites by up to 33 times. In the meso-abyssal batholiths, differentiation processes are less intense and the difference in the ratio Zn/Pb decreases to 7-15 times and in hypabyssal intrusions it decreases to 2-3 times or disappears. Useful also is the ratio change of Σ TR Ce /Z TR Y . In the Susamir batholith the maximum is in granitoids of the main phase leucocratic granites and in phase vein aplites. The variation is 19 times. It is important that at the magmatic stage, the geochemical history of elements used in connection with the ratio of indicating pairs, must be dominated by the tendency of crystallochemical dispersion, and therefore the given ratio answers fully the question of the intensity of processes of crystallo-differentiation at this magmatic chamber.
631
Distribution Regularities of Trace Elements
Meso-abyssal batholiths forming at a depth of 4-6 km are characterized by a great faciès rock variation of their main intrusive phase. For instance, among the rocks of the main intrusive phase of the Djidinski meso-abyssal batholith (Western Transbaikalia) there occur monzonites, syenite-diorites, syenites, quartz syenites, grano-syenites, adamellites and porphyry granites. In the Verchne-Undinski meso-abyssal batholith there is among the rocks of the main phase a facies variation from quartz diorites to leucocratic TABLE 2. Z N / P B RATIO GRANITE INTRUSIONS OF DIFFERENT TYPES
Abyssal batholiths Intrusive phases
VerchneUndinski
Djidinski
Cent. Tyan- Eastern TransbaiShan kalia
Western Transbaikalia
Susamirski
I II (main) III Vein series I stage (aplite)
Meso-abyssal batholiths
10 2-2 0-9 0-3
6 3-2 2 0-4
51 2-8 1-6 0-7
Hypabyssal intrusions Shakhtaminski
Soktuyski
Eastern Transbaikalia 2-7 1-7 11
21 20 2-2
granites. The number of facies in the main phases of meso-abyssal batholiths comes from a disturbed tectonic condition for the crystallization of magmatic melts and also from the heterogenetic composition due to contamination. The difference between the homogeneity of rock composition in the main phases of abyssal and of meso-abyssal batholiths is reflected in the distribuZTR Ce /ZTR Y Granitoids of the main phase Leucocratic granites Vein granite-aplites
5-8 21 0-3
tion characteristics of the rare elements in these rocks. Table 3 gives the average contents and the concentration dispersion of some trace elements in the rocks of the main intrusive phases in abyssal (Susamir) and mesoabyssal (Verchne-Undinski, Djidinski) batholiths. So, with an equal level of contents of the given elements their concentration dispersion in the rocks of the main phases in meso-abyssal batholiths (Verchne-Undinski and Djidinski) is much higher than that in rocks of O.D.E.—21*
632
L. V. Tauson
abyssal batholith (Susamir). The cause of dispersion growth of element concentrations in the rocks of the main intrusive phases of the meso-abyssal batholiths is apparently the lower stability of crystallization conditions for magmatic melts of this type of intrusion compared with those of depth. This holds water because of the great number of faciès variations of rocks of the main intrusive phases of meso-abyssal batholiths. Probably, this is related to the fact that by rock crystallization of the main intrusive plases of mesoabyssal batholiths degassing of intrusions is smooth. Because of a higher gradient of pressure of fluid phases meso-abyssal batholiths volatile compoTABLE 3. AVERAGE CONTENT AND DISPERSION OF CONCENTRATION LI, R B , PB, Z N , U, Mo IN THE MAIN INTRUSIVE PHASES OF ABYSSAL AND MESO-ABYSSAL BATHOLITHS
Batholiths
Lithium c a2 ppm
Rubidium c ppm
σ2
Lead
Zinc
c a2 ppm
c a2 ppm
Uranium c ppm
Molybdenum
a2
c ppm
o2
Susamirski, Central Tyan-Shan, U.S.S.R.
32
180 170 1000
25
24
56
206 3-4
215
0-6
010
Verchne-Undinski, Eastern Transbaikalia, U.S.S.R.
42
260 129 2460
14
54
45
427 3-2
5-92 1 0
1-89
Djidinski, Western Transbaikalia, U.S.S.R.
35
295 130 1239
19
30
55
420
—
11
—
1-6
nents migrate to the upper parts of the magma chamber and are dispersed in granitoids and rocks enclosing them. The main result of this process is the impletion of late acid differentiates of those magma chambers with volatile components. For instance, the decrease of fluorine and the associated lithium in the third intrusive phase of meso-abyssal batholiths (Table 4). Table 4 shows both the accumulation of F and Li in the third phase of the Susamir (abyssal) batholith and the impletion of the rocks of the third phases in meso-abyssal batholiths with these elements, and the stability of the F/Li ratio in a differentiation sequence indicating the genetic unity of these magmatic series and the geochemical association of lithium and fluorine. The stability of F/Li is also apparent in rock-forming minerals concentrating these elements. For instance, the ratio F/Li in the biotites from different faciès of main phase granitoids of the Verchne-Undinski meso-abyssal batholith is stable and near to the mean value of this ratio for rocks of the given phase.
633
Distribution Regularities of Trace Elements TABLE 4. AVERAGE CONTENT OF F AND LI IN ABYSSAL AND MESO-ABYSSAL BATHOLITHS
Fluorine (%)
Lithium (ppm)
F/Li
I phase
II (main) phase
III phase
Vein aplites
Susaminskit
0070
0100
0125
0025
Verchne-Undinski Djidinski Kalbinskit (Kazakhstan, U.S.S.R.)
0045 0082
0068 0098
0058 0079
0015
0070
0150
0066
0018
Susamirski
28
32
55
7
Verchne-Undinski Djidinski Kalbinskit
25 34 85
42 35 123
39 32 77
8 10-5 26
Susamirski
25
31
23
—
Verchne-Undinski Djidinski Kalbinski
18 24 8
16 28 12
15 25 9
—
t Data by Stavrov, 1963.
The graphical illustration of the relation between the fluorine and lithium contents is given in figure 1. This does not only stress the genetic unity of the series, but shows also the difference in the concentration levels 0.15 . 0.14. 0.13 .
*v
0.12. o,ii . 0.10.
. /
ΙΝ^
/
c-/
V
* /ill"
• / 'ί
0,09.
/
0.080.07-
4
0.060.05-
^y 20
30
//«
*'IIImt
,^«.
ΛΟ
SO
9o
ioo
no
120
Li
ppm
FIG. 1. The correlation of the contents of Li and F in granite batholiths. I, the first intrusive phase ; II, the second (main) intrusive phase ; III, the third intrusive phase.
634
L. V. Tauson
of these elements and the degree of degassing of acid differentiates in mesoabyssal batholiths. It is supposed, that the degassing of late members of the magmatic series of the meso-abyssal type are strongly associated with post-magmatic processes. Therefore, this degassing process of late differentiates is one more proof for the conclusion from the occurrence limit of differentiation in intrusions of this type.
Quartz-diorites and granodiorites (margin faciès) Porphyry granites and granodiorites (main fades) Leucocratic granites (deep-seated faciès)
F wt. %
Li ppm
F/Li
0-38 0-64 112
270 410 790
14 15-5 14
Thus, although the processes of crystallochemical dispersion are dominant in determining the rare element distribution in abyssal and meso-abyssal batholiths, the distribution characteristics of the two types of granitoid intrusions are different. In the abyssal batholiths the processes of crystallo-differentiation proceed strongly and in acid differentiates bring about a high concentration of some elements and a sharp decrease of others. At the same time acid differentiates intensively accumulate elements crystallo-chemically associated with potassium (Rb, Cs, Tl, Pb, etc.) or those which build up stable compounds with volatiles (Li, Be, U, etc.), but decrease contents of elements crystallo-chemically related to magnesium and iron (Zn, Cu, Ni, Co, etc.). The homogeneity of the magmatic melts gives these intrusions a low dispersion of element concentration. In the meso-abyssal granite batholiths, an instability of the intrusive crystallization condition, leading to a non-uniformity of magmatic melts, together with crystallo-chemical differentiation and the degassing of late acid differentiates, all play a part in determining the element distribution pattern. This is reflected in the decrease of the degree of variation of element contents between the first and last members of differentiated sequences, the increase of element concentration in the main intrusive phases and a concentration decrease in the acid differentiates of some volatile components and their associated rare elements (fluorine-lithium). The distribution of trace elements in hypabyssal intrusions differs considerably from that in batholiths. For this intrusion type the characteristics of rare element distribution are due apparently to their small volume, at a relatively shallow depth of formation and their composition characteristics. The latter, first of all, includes the content level of volatile components in magmatic melts. At the same time it should be pointed out that these intrusions very often reveal only their apical parts. That makes the investigation of rare element distribution characteristics in the intrusive body difficult and
635
Distribution Regularities of Trace Elements
sometimes gives an indication of abnormally high contents of some rare elements therein. In addition, in the first phases of such intrusions, contamination processes have given rise to a higher content and greater dispersion of some rare elements. The small size of hypabyssal intrusions, the low depth of formation and the relatively high rate of crystallization bring about a process of crystallodifferentiation, which is characteristic for all intrusions of this type, and so is characterized by the example of intrusions with a low content level of volatile components (Table 5). TABLE 5. RARE ELEMENT DISTRIBUTION IN INTRUSIVE PHASES OF THE SHAKHTAMINSKI MASSIF (EASTERN TRANSBAIKALIA)
Li
Rb
Tl
Intrusive phases
Be
Pb
Zn
Sn
ppm
Diorites and monzonites (1st phase) Granodiorites and adamellites of the main phase Granites of the additional intrusion phase (3rd phase)
F wt.
%
28
110
0-6
20
20
54
7-2 0 0 8
33
181
1-3 2-3
24
40
2-5
54
249
1-9 3-2
28
33
3-7 0 0 9
008
It is clear, that in a given differentiation sequence the average contents of the investigated elements do not change more than 2-3 times and do not exceed the level of the dark content for this rock type. In our case, the high content of lithium in granites of the third phase is left without explanation. The high tin content in the granitoids of the first phase, it seems, is a result of the contamination process. For this intrusion type very low values of dispersion are characteristic and particularly for the main intrusive phases (Table 6). As in the batholith intrusions so here the processes of crystallo-chemical dispersion dominate the rare element distribution. TABLE 6. DISTRIBUTION OF RARE ELEMENTS IN THE MAIN INTRUSIVE PHASES OF THE MESOZOIC M A G M A T I C COMPLEXES OF EASTERN TRANSBAIKALIA
Lithium Complexes
Rubidium
c c a2 a2 ppm ppm
Thallium
Beryllium
c c a2 a2 ppm ppm
Shakhtaminski 32 71 150 211 11 AmudjikanoSretenski 66 357 190 2123 1-9 Kukulbeiski 84 571 350 3546 4-5
Lead
Zinc
Tin
c c c a2 a2 ppm a2 ppm ppm
3 0 0-28 25
Fluorine wt.
%
68 41 150 2-9 0-41 0 0 8 0
32 21 39 162 4-3 0140 6-6 4-75 30 116 57 629 6-3 6-83 0-300
636
L. V. Tauson
The most difficult is the distribution of rare elements in the hypabyssal intrusions differing with a high content of volatile components in magmatic melts; the crystallo-differentiation processes there are also weakened. Because a great pressure gradient of fluid phases and a high content of volatiles are usual in these intrusions we often find the processes of gas transportation of volatile compounds carry some trace element into the upper parts of the magma chambers and there is also a distinctly expressed tendency for the residual concentration of volatiles and related rare elements in the late acid differentiates. Consequently the processes of intrusion degassing and the migration of rare elements appear not only in the magmatic stage but also in all post-magmatic stages. On the whole, a considerably higher content of some trace elements and a very high concentration dispersion of the elements is characteristic. A detailed investigation of rare element distribution in the mesozoic magmatic complexes of Eastern Transbaikalia showed these common characteristics of rare element distribution in intrusions of a similar type and their difference in this case from hypabyssal intrusions with a low volatile content (Table 6). These data show that in the granitoids of the Kukulbey complex the average content of all studied elements, taking out lead and zinc, is 2-4 times higher than in the granitoids of the Shakhtaminski complex, but the greatest differences are in the element concentration dispersion. In the granites of the Kukulbey complex the value of this distribution parameter for rubidium, beryllium and tin is 17 times and for lithium 8 times that in the Shakhtaminski complex granitoids. The lead and zinc contents in the Kukulbey complex granites do not differ from those of the Shakhtaminski complex granitoids, but the concentration dispersion of these elements in the Kukulbey complex is 2 and 4 times higher than in the Shakhtaminski complex. Granites of the Kukulbey complex are characterized by a high concentration of volatile components, as proved by the fluorine content. This is the cause of the characteristic feature of these granitoids in which a sharp increase of rare element content in the rockforming minerals appears at the end phases of the crystallization process. Significant also are the contents of several trace elements in biotites from the granites of the Shakhtaminski and Kukulbey complexes (Table 7). The investigation of the granitoids of the Shakhtaminski and the Kukulbey complexes shows that the biotites are evolved at the end phases of crystallization. From the data of Table 7 it is clear that biotites from granites of the Kukulbey complex are enriched in rare elements, especially tin, lead and zinc. It should be stressed, that in biotites from granites rich with fluorine are concentrated not only elements bound up with the volatiles (Li, Rb, Be, Sn), but also elements for which such relations are not established (Pb and Zn). This can be understood as indirect proof for the enrichment in these granitoids of other volatile components helping most of the rare elements to remain
637
Distribution Regularities of Trace Elements
in the melt until the end phase of crystallization. But all these characteristics of rare element distribution in hypabyssal intrusions with a high level of volatiles apply to the upper parts of intrusives. It is regrettable to be without observations on the distribution character of rare elements in the upper as well as the lower parts of some definite intrusion of this type. At present we have only indirect evidence relating to the problem of degassing of such intrusions. TABLE 7. TRACE ELEMENTS IN BIOTITES. (THE CONTENT IS IN PPM; IN BRACKETS IS THE ELEMENT CONTENT IN ROCKS)
Complexes Shakhtaminski Kukulbey
Li
Rb
Be
Pb
Zn
Sn
426 (45) 1350 (84)
695 (198) 1300 (350)
5 (2-9) 12 (65)
2-5 (18) 27 (29)
155 (32) 990 (68)
6-3 (35) 200 (71)
A known example of degassed portions of acid magmatic melts is vein granite-aplite. In these formations, the content of several rare elements is high whereas the content of volatile components is low, particularly fluorine. While investigating the distribution characteristics of rare elements in granitoids of the Kukulbey complex a zone in one of the massifs was found to be composed of quartz syenites and grano-syenites which is in this case regarded as a degassed phase of the main intrusion. As a result of the supposed degassing process the magmatic melt producing these rocks lost a notable part of rare elements (Table 8). TABLE 8. THE RARE ELEMENT DISTRIBUTION IN THE ROCKS OF THE SOKTUY MASSIF, EASTERN TRANSBAIKALIA, U.S.S.R.
Rocks Granite phases of additional intrusions (late differentiate) Biotite granites of the main phase Granosyenites and quartz-syenites (degassed faciès of biotite granites)
Li Rb Tl
Be Pb Zn Sn ppm
F wt. /o
84 372 4-4 6-9 70 343 4-3 6-6
19 30
42 7-4 0-33 61 6-2 0-30
12 142 11 2-5
22
85 2-6 006
The degassing processes of hypabyssal granite intrusions, characterized with a high content of volatile components help the migration of rare elements into the upper parts of the magmatic chamber not only in the magmatic stage of the history of these intrusions but also by the autometasomatosis and also at high-temperature metasomatic processes. As a result, the apical parts of such intrusions can have zones highly enriched with some of the rare elements, especially Li, Rb, Be, Sn, W and others.
638
L. V. Tauson
This shows, that the distribution of rare elements in hypabyssal intrusions is considerably different from that in intrusions of the batholithic type and particularly those with hypabyssal intrusions with a high content of volatile components. The above-mentioned allow us to conclude: 1. The characteristics of rare element distribution in granitoids is determined by the intrusion size, depth of forming and composition. These features give abyssal and meso-abyssal intrusions of the batholithic type and hypabyssal intrusions with high and low contents of volatile components. 2. In the abyssal batholiths the rare element distribution is mainly controlled by processes of crystallo-differentiation, leading to a strong difference in the contents of rare elements between the margin members of the magmatic series. The rare element distribution in the crystallization process of rocks there is dominated by the crystallochemical dispersion. 3. The meso-abyssal batholiths forming at moderate depth and usually under quiet tectonic conditions are characterized by a crystallo-differentiation process and the degassing of late differentiates. The rare element distribution dominates the process of the crystallochemical dispersion, going with many variations in the main phases and this brings about an element concentration dispersion that is higher than in abyssal batholiths. 4. In hypabyssal intrusions with a low level of volatiles, crystallo-differentiation processes are weak. In the end members of the magmatic series there is a small difference in rare element contents. The element concentration dispersion is insignificant except where due to contamination or some redistribution of elements bound up with volatiles. The element distribution is mainly determined by the crystallochemical dispersion. 5. In hypabyssal intrusions with a high content of volatiles and a great pressure gradient of fluid phases, elements associated with volatiles (Li, Be, Rb, Sn, W, Nb, Ta, etc.) are concentrated in the apical parts of intrusions. That holds especially for the late differentiates of the magmatic series. For this intrusion type there is a distinctive process of crystallo-differentiation. There is a wide development of emanation transportation of rare elements with a degassing of deep-seated intrusion parts, particularly appearing at late magmatic or early post-magmatic stages of the formation of the intrusion. This leads to the concentration of several rare elements in the upper parts of intrusions and also a 15-20 times higher concentration dispersion of these elements than is found in hypabyssal intrusions, with a low volatile content. References LEONOV, L. L. and BALASHOV, U. A. (1963) The distribution of uranium, thorium and rareearth elements in granitoids of the Susamirski batholith (Central Tyan-Shan). Geochimiya No. 2, 1008-1015.
Distribution Regularities of Trace Elements
639
STAVROV, O. D. (1963) Geochemical features of lithium, rubidium and caesium at the forming process of granitic intrusives and their pegmatites. Geologiay mestorozhdeniy redkich elementov 21, Moskva, Gosgeoltechizdat.
ZLOBIN, B. I., BELAYEV, U. I. and TAMONTYEV, V. P. (1967) Copper in intrusions of the
Central-North Tyan-Shan along with metallogenic problems. Geologiya redkich mestorozhdeniy 9, 45-56.