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On the occurrence of analcime in the northeastern Azerbaijan volcanics (northwestern Iran)
On the occurrence of an lcime in the northeastern Azerbaijan volcanics (northwestern Iran) P. COMIN-CHIARAMONTI, S. MERIANI, R. MOSCA & S. SINI{301
LITHOS
Comin-Chiaramonti, P., Meriani, S., Mosca, R. & Sin~-,oi,S. 1979: On the occurrence of analcime in the northeastern Azerbaija~a volcanics (northwestern lran). L/tb~ 12, 187-198. Oslo. ISSH {A}24-4937. Euhedral, phenocryst-like crystals of anslcime, as well as microlites, are rather common in phoaoliti: and tephritic lavas and in some anaicitic dikes and lenses of the Upper Cretaceous and Lower Tertia~ volcanics of eastern Azerbaijan (Iran). The mineralogy and petrology of these extrusive rocks are described with the aim of establishing the orig/n of the big analcime crystals. While the mineralogica! data (e.g. true symm~Rry, AUSi disorder and Na atom distribution, struct~ar~l refinements) are nol conclusive, the paragenesis and microprobe analyses of analcime and a~s~ated phases, m a i ~ feldspars, lead us to believe they are of a secondary, metasomatic origin. It is s~ggested that during hte or post-magmatic stages analcime may have originated eith~.r from ion-exchan,~d leucite or by alteratio~ or interaction between preexisting Na-rich phases such as nepheline, f e l d s ~ and glass at subsolidus temperatures. P. Comin-Chiaramonli & S. Sinigoi, istituto di Mineralogia e Petrografia, gries:e University - Piazza~ Europa, I - 1-34100 Trieste, Italy. S. Meriani, Istituto di Chimica Applicata e ladustriale. R. Mosca, istituto di Chimica. Trieste University - Piazz~le Europa, I - 1-34100 fries~e, i t a l y .
Analcime occurs in extrusive rocks in amygdales of volcanics ranging from basalts to tephritic types (late hydrothermal stage of crystallization), or as devitrification products or replacing other minerals such as leucite, feldspars and nepheline (metasomatic, secondary origin). However, well-developed euhedral (icositetrahedra) analcime phenocrysts in some marie phonolites (Lupata phonolites of Wolley & Symes 1976) and blairmorites (Crowsnest blairmorites of Pearce 1970), as well as in trachybasalts and analcimites, provide at least textural evidence of a primary origin and crystallization at liquidqs temperatures (primary intratelluric origin: Peters et al. 1966; Wilkinson 1968). Doubts have long been expressed as to the origin of such phenocryst-like crystals. A recent experimental study by Roux & Hamilton (1976) has demonstrated that primary igneous analcime c~n only exist at very high H20 pressure and moderately low temperatures between 600' and 640". It is therefore timely to examine critically all associations in which anaicime is assumed to be an equilibrium primary (intratelluric) phase. In the Upper Cretaceous and Tertiary volcanics of the northeastern Azerbaijan (Iraa) volcanic province, analcime was found in several modes ~ffoccurrences. For at least some of these occurrences, phenocryst-like analcime~ pre-
dominate. Didon & Gemain {19~6) proposed that they were of a primary intra~'0~q~uricorigin. This interpretation was extended b~ Lescuyer & Riou (1976) and by Lescuyer et al. 1976)to analcimebearing 'shoshonitic types' of E~:ene age in Iranian Aze~ijan. The purpose of this study i~ to determine on chemical and mineralogical ~,~-~ia and by consideration of the parage~:,sis, whether the phenocryst-like analcime (Fig. t) present both ~n dikes and lenses and in iav~ flows can be considered to be of primary intratelluric o r ~ n or whether it should rather be regarded as secondary. All cases of unquestionable hydrothermal origin in which analcime is ~ssociated with other zeolites (chabazite, thomsonite, stilbite and meso~ite) have obviously been disregardeL
Outline of the northeastern Azerbaijan volcanisin Eastern Azerbaijan has been the s~te of re~a~c= J and varied volcanic activity in Upper L~eta~~e. ous, Tertiary and Quaternary time~;. AI~leas~ ~ou~ main magmatic cycles have occurred ,[A|be~'tie~ al. 1976; Didon & Gemain 1976; St6ck~in & Nabavi 1973):
i!88 Comin.Chlaramontiet al.
LITHOS
12(1979)
(c) A moderately alkaline and foid-free cycle occurred in the southern district in the Upper Miocene (9-11 m.y.: Aiberti !~,t al. 1976). Products of this volcanism range from latitic rocks to alkali-quartz trachytes (Comin-Chiaramonti et al. 1975, 1978). Limited occurre.,,,ces o f Miocene analcime-bearing alk~ine volcanics are also reported from the northern district.
Fig. I. Phenocryst-like analcime in a lava-flow of northeastern Azerbaijan (Sample AZi73).
(a) One cycle started at the top of the Turonian in the northernmost part of the volcanic province, spanning all the Upper Cretaceous, and was first submarine and then subaefial. It has limited areal extent and was charact,:rized by a strong explosive activity. The lavas of the largely volcanoclasfic, submarine formation belonging to this cycle are analcime-bearing tephrilles and basanites; they are subaerial towards the top of the formation. Didon & Ge~ain (1976) call it the 'Sehjafarlu Formation' and attribute a blairmoritic character to the lavas. T~:le same authors state that analcime gradually disappears as it approaches the subaeriai c~_~nditions towards the top of the formation. Some dike swarms and lense~; (e.g. the Teic Dam analcimite: CominChiaramonti 1977) are possibly connected to the Upper Cretaceous volcanism, but should more probably be linked to the later, more widespread Eocene volcanism. (b) A shoshonitic cycle took place in the northern district during Eocene, reaching its climax at the Eocene-Oiigoceae transition: K/At age degerminations give 39-50 m.y., but the activity possibly extended ovcr some 10 million years through Oligocene times ~30 m.y.: Alberti et al. 1976). This cycle has been predominantly fissural and in places has buih lava sequences of up to some hundred meters thick, but central type volcanic structures and pyroclastic rocks are also well represented at various stages. The most abundant rocks are Ne-normative tephritic lavas in which the foids are mainly represented by analcime (analcime-bearing tephritic phonolites of the Harbab Khandi area: Alberti et al. 1978a).
(d) A highly explosive, Plio-Quaternary volcanism in the central part of the volcanic province displays a subalkaline ch,~acter (following the classification of Irvine & Baragar 1971) and a continuous variation from quartz-latiandesites to rhyodacites (Alberti & Stolfa 1973; Alberti et al. 1975; Bruni 1976). This recent cycle gave rise to the big Savalan strato-volcano and to minor occurrences both to the east and west of the same volcano. A high-K calc-alkaline affinity is reported by Dostal & Zerbi (1978).
Analcime-bearing volcanics: petrography and mineralogy The analytical data on selected aryalcime-phyric rocks are given in Table 1: one Sehj~.farlu type is taken from Didon & Gemain (1976), and the Harbab Khandi volcanics from Alberti et al. (1978b). The normative v a l u e s - C I P W norms with FeZ+/Fe"+ + Fe a+ atomic ratios calculated according to the oxidation ratio after LeMaitre (1976) show that the Teic Dam 'analcimite' and the Razi dike can be classitied as phonolites, the Sehjafarlu type and the Harbab Khandi volcanics being tephritic phonolites. -
Tephrites and phonolites of Sehjafarlu The,,ie lava flows exhibit a porphyritic texture and a seemingly intratelluric paragenesis with large analcime 'phenocrysts' (pink colored, mow. than 1 cm in diameter, 25% by volume as average), diopsidic clinopyroxene (C,'60Mg35Fe15: 30%), ore minerals (magnetite and/or martite and ilmeni~e: 5%), occasional oliviae and alkali-feldspar in a glassy to intersertal mesostasis with abundant clinopyroxene and aria!time microlites. In some rocks the cli~opyroxene is distinctly zoned and its content in +.]~e intratelluric par:~genesis is lower; a labradoritic plagioc[ase jacketed by alkalifeld,,;par is present, while, the mesostasis is intersertal with abundant clinopyroxene micro-
Analcime in Azerba~ia~ voicanics 189
(1979)
LITHO$12
7able !. C~:emical analyses and CIPW norms of anaicime phyric volcanics o f the Seluafarlu ($2), Teic Dam (,~7.15 I), l~azi (AZ79) and Harbab Khandi area (AZ45, AZ60, AZ62, AZ64, AZI73). AZI51GM and AZ79GM: gromglmasses. $2
AZI51
AZi51GM
AZ79
AZ79GM
AZ45
AZ60
AZ62
AZ64
AZI73
SiO2 46.31 TiO2 0.87 AI2Oa 15.80 FesOs* 6.56 MnO 0.25 MgO 9.25 Ca{) 5.68 lqa~O 5.20 K20 5.36 P,,Os 0.10 HzO + 3.00 COs n.d.
49.42 0.21 21.96 2.19 0.18 0.96 3.46 9.29 4.08 0.04 6.55 1.88
54.97 0.39 22.01 1.65 0.37 0.72 3.42 10.03 n.d. n.d. n.d.
52.23 0.75 18.68 5.67 0.1,.3 3.0~ 3.17 8.42 2.0~; 0.6~ 5,5 | n.d.
57.1 0.2 22.9 !.6 0.9 1.7 7.5 6.8 n.d. n.d. n.d.
55.5 i 0.72 18.35 4.84 0.11 0.98 5.23 5.01 5.30 0.43 1.52 1.23
54.52 0.85 18.63 5.60 0.11 1.51 5.54 6.02 3.72 0.61 2.48 0.26
55.27 0.83 17.64 5.54 01~: 2,23 3..c:7 5.87 4.79 0.53 2.09 0.57
55.83 0.76 18.59 5.00 0.10 !.21 4. i 5 5.80 5.49 0.45 1.66 0.77
54.~ 0.80 18.43 5.55 0.12 1.72 4.38 6.02 4.97 0.46 2.4| 0.39
98.38
100.22
93.56
100.35
98.5
99.23
99.85
99.42
99.81
100.13
24.13 27.93 5.06 27.41 . 0.40 2.09 1.81 0.40 0.10 4.27
59.3 15. I 3.6 7.5
12.29 45.95 47.~3 13.67 . . 3 3~1 5.~} 4.27 1.43 1.61 -
24.9 37.3 9.4 |9.7 .
31.35 39.91 I i.87 1.32
22.00 40.85 12.78 5.44
28.33 41.06 7.59 4.63 .
32.47 38.10 8.42 5.92
29.41) 33.96 8 54 8.99
3.48 1.50 3.96 ! .44 t.05 1.75
6.16 i.74 4.29 1.52 t.07 0.89
CIPW NORM or ab an ne ic C di ol mt il ap cc
27.24 3.89 23.83 3.49 -
18.53 ! 1.45 4.73 1.66 0,23 -
.
. 4.2 2.3 0.8 -
.
. .
3.8 0.4 -
. . 2.83 1.54 3.68 i .37 i .00 2.80
. .
. 7.30 1.20 4.09 1.62 1.42 0.59
. 3.81 3.47 4.18 1.58 i .2~; ! .30
* Total Fe as Fe~Os.
lites. In the latter cases analcime may have labradoritic plagioclase inclu~ionz (crystals up to one mm long), apparently eq~filibrated with the host phase. Carbonation a~d zeolitization are pre~ent affecting all the rt~cks to a variable extent, carbonation being mainly the alteration of olivines. "fhe lava flows, as well as the dikes, of the Sehjafarlu Formation are likened by Didon & Gemain (1976) to blairmorites: however, acco~'ding to the petrographic features these volcanics are not blairmorites sensu strictu because the latter rocks have an intratelluric paragenesis with analcime, melanitic garnet, sanidine (Or about 85 %) and aegirinaugitic clinopyroxene in a groundmass of sanidine, analcime and aegirinaugite (Pearce 1970).
cm) of induration. This rock has a distinct porphyritic texture with conspicuous analcime 'phenocrys~s' ranging from 50 to 70% by volume (Comin-Chiaramonti 1977): these crystals usually occur as well developed icositetrahedra, ranging in diameter from several mm to 5 era, white or pink colored and of stone-like appearance (Fig. 2); the likeness with the Crowsnest
Teic Dam analcimite and Razi dike The Teic Dam analcimite is a lens-like body extruded in a volcanic brecciia which experienced very limited effects of thermal metamorphism, restricted to a small zone (few
Fig. 2. Teic Dam analcimite showing large idiomorphic crystals of an~cime.
190 Comin-Chiaramonti et ai.
Fig. 3. Potassic rim (K) around analcime (A) in Sample AZISI. Phenocryst of sanidine (S) is also shown. Nicols//.
bi~irmorite (Plate 1 of Roux & Hamilton 1976) should be noted. Sanidine can also be found as elongated (a few mm long), translucent phenocrysts. Under the microscope the analcime crystals are lightly colored isotropic minerals 9ccasionally surrounded or replaced by cmbonates. Anisotropic rims sometimes envelop the analcime (Fig. 3): microprobe analyses give a composition of SiO2 61.35, AlamO:: 19.81, FeO 0.25, MgO 0.04, Na20 1.02, K:,O 14.59 wt.%, corresponding to Or 92.9, Ab 4.8, Ne 2.3. The alkali-feldspar phenocrysts (Or 7'7-66, Ab 20-31, An 2-3: 3% by volume) have elongated habit, frequent Carlsbad twinning, a 2 V , =5-100 and belong to the sanidine H.T.-albite H.T. series. Plagioc[ase and clinopyroxene relics, almost complelely replaced by carbonates, can also be distinguished. Very rare olivine appears to be substitt~ted by a limonite-iddiwgsite..carbonate association. The groundmass is microfeldspathic with all, all feldspar microlites having a mean composition of Or 58.4, Ab 38.0, An 3.6; carbo-
Fig. 4..~,nalcime of the Razi dike Ni¢ols//.
LITHOS 12(1979) nate microgranulations are frequent. The carbonate material appears to have a late origin and has ankeritic composition in all textural positions. This rock is unusual among the volcanics of northeastern Azerbaijan and because of the abundance of analcime is comparable with an analcime-phyric glassy dike of Eocene age occurring dose to the Harbab Khandi lava flows (Razi dike). The Razi dike, Which is also extruded into a volcanic breccia with no appreciable thermal metamorphic effects, contains 'phenoc, r3"sts' of a clear, isotropic analcime (0. I-3 mm in diameter with .~ubrounded outlines and sometimes also in glomeroporphyritic aggregates) plus fresh clinopyrexene (Ca 42, Mg 42, Fe 16 atom%) and apatite in brown unaltered glass with olivine relics and titanomagnetite microlites. "[he approximate mode of the rock is analcime 30, clinopyroxene 7, olivine 2, opaque c,xides 4, apatite 2, glass 55 vol.%.
Harbab Khandi phonolitic rocks These rocks are generally pc,rphyritic lav~ts with a micro or cryptocrystaUine groundmas:~. The most distinctive feature is the abundance cf large (from a few mm to some cm long) phenc,crysts of placioclase (18-30% by volume). The plagioclase is sometimes zoned, and can range from Or 2.4, Ab 25.9, An 71.7 at the core to Or 10.0, Ab 51.5, An 38.5 at the rim, but the most common composition is close to Or 6.7, Ab 46.6, An 46.'/. Alkali feldspar (about Or 45, Ab 49, An 6) often mantles the plagioclase. Clear or pink analcime is abundant both as 'phenocrysts' (up to 3 mm in diameter) and micrelites (7-22% by volume). The analcime 'phenocrysts' show weak birefringenc,~, especially when they are interfaced with plagioclase. Other phases, present either as phenocrysts or microlites, are olivine (Fa 25--40°~,, often iddingsitized and bowlingitized: I-7% by volume), augitic clinopyroxene (Ca 44, Mg41, Fe 15 atom %, Na~O 0.51 wt. % as an average for phenocrysts; Ca 44, Mg 40, Fe 16 atom%, Na20 0,35 wt.% as an average for microtites: 5-10% by vo~,ume); titanomagnetite (with 40 to 30 mole % Fe2TiO4, calculated on the ulvrspinel basis) and occasional ilmenite (only in samples AZ45 and AZ64). A feldspathic ground.mass (microlites rangm:g from Or 35, Ab 60, An 5 to Or 50, Ab 46, An 4 with prevailing compositions around Or 46, Ab 48, An 6, very similar to the alkali feldspar jacketing the plagioclase) with
~
Analcime in Azerbaijan volcanics
LITHOS 12 (1979)
191
Table 2. Analyses 9 f analcime 'phenocrysts' and microlites (M) from northeastern Azerbaij/tn volcanics. $2 SiO2 Al2Oa Fe,zOa MgO Cad Nard KgO H20 +
55.91 21.64 ! .05 0.09 0.19 12.00 0.25 8.50
AZISIW 51.39 23.48 !.55 0.21 0.20 12.78 1.92 8.20
AZI51
AZ79
AZ45
AZ60
AZ62
AZ64
AZ64M
AZI73 AZ!73M
53.50 23.46 0.33 0.06 0.04 13.17 0.06 .
55.0 22.9 0.7 0.9 12.1 0.6
54.8 23.2 0.43 0.22 0.66 12.0 0.24 .
55.3 23.2 0,42 0. ~2 0.54 11.8 0.16 .
54.53 21.99 0.20 0.16 !3.22 0.20
55.32 22.73 0,3! 0.23 12.36 0.06 .
53.33 23.24 0.09 0.37 13.32 0.06
56.04 21. ~I 0.21 0.48 0.19 ~3.07 0.18
54.08 22.44 0.45 0.09 0.43 13.67 0.33
.
92.2
91.55
91.27
91.01
90.38
91.25
91 4 9
33 65 2 27 73 13.705(2)
35.0 64. ! 0.9 24 76 1.488(2) 2.30 13.718(2)
36.3 63. I 0.6 21 79 13.721(4)
31.6 67.4 i.0 31 69 1.484(2; 2.27 13.715(I)
34.9 64.9 0,2 24 76 ! .484(2) 2.27 13.716(2)
33.2 f~. I 0.7 28 72 !.489(6) 2.~9 13.720(4)
29.5 69. i i.4 36 64 13.708{2)
3 ! .76 16.39 0.15 0.05 0.03 15.13 0.02
32.15 15.77 0.31 0.57 13.69 0.~5
32.11 15.99 0.19 0.19 0.41 13.61 u. ~
32.31 15.95 0.19 0. ! ! 0.34 13.35 0.12
32.48 15.41 0.09 0.10 15.24 0.15
32.5 ! 15.72 0.14 0.14 14.06 0.04
3 ! .78 16.29 0.04 0.23 15.36 0.04
32.95 14.61 0.09 0.42 (~.I 1 14.87 0.14
32.02 15.63 0.19 0.07 0.28 15.62 028
48.30
48.23
48.29
48.45
47.98
48.37
48. I I
47.o5
47.84
15.21
15.28
14.61
14.15
15.59
14.38
15.86
15.25
16.46
.
.
.
.
.
,!
99.63 Qz Ne Ks Ne Ab n D ao
35.6 63.4 1.0 21 79 1.494(2) 2.30 13.70
99.73 26.7 66.0 7.3 39 61 1.491(3) 2.294(2) 13.713(8)
Atomic ratios on 96 oxygens basis Si 32.87 30.82 AI 14.97 16.57 Fe +++ 0.46 0.70 Mg 0.08 0.19 Ca 0.12 0.13 Na 13.65 14.83 K 0.18 1.47 Si+AI+ +Fe :j+ 48.30 48.09 Na+K+ +2Ca 14.07 16.56
90.60 3 i .5 68. I 0.4 31 .9 -
90.30
30.3 69.5 0.2 34 66 13.710(5)
Microprobe analyses: Ba and Sr were also analyzed but found to be absent; water loss was not determined. W: wet analysis. Physical parameters are aiso reported (n: refraction index; D: density; ao: lattice parameter assuming a cubic structure. Esti~nated standard deviations are given in parentheses).
small amounts of interstitial glass, has a volume of 45-56°A. Attemp1:s to define the equilibration conditions for the Harbab Khandi volcanics by means of olivine-clinopyroxene geothermometry (Powell & Powell 1974) indicate temperatures of about 1008*C. The empirical plagioclase geothermometer (Kudo & Weill 1970, refined by Mathez 1973) gives 9390C as an average at 0.5 Kbs of Pn,o. Microprobe analyses reveal the presence of coexisting oxide phases (titanomagnetite and ilmenite) in samples AZ45 and AZ64 (molecular percent of ulvtspinei in the spinel phases is 31.4 and 33.3 and molecular percent of R203 in rhombohedral phases is 9.1 and 7.2 respectively). The quenching te;mperatures estimated according to Buddington & LindsJey (1964) are 790° (A2'A5 ,,~,;,!.., ,,,1 ['th = 10 -14"3) and 770°C (AZ64 with fo, = 10-~5"z). An equilibration solution for the pheno,.~ryst phases was obtained from sample AZ45 utilizing the reactions: Ca'[:i + SiO~ = An;
Jd + SiO2 = Ab; CaMgSi2Oe + I/2SiO~ + AIzOa CaAI2Si2Oa + l/2Mg2SiO4 (Bacon & Carmichael 1973; Carmichaei et al. 1974, 1976j. The results are close to 94TC at 3.8 Kbs of total pressure, according to the temperature of the plagioclase geothermometer at 0.5 Kbs of PH,o. =
Analcime mineralogy General features In order to gain evidence of physical and/or chemical differences among the analcimes, chemical analyses, X-ray diffraction patterns, density and refractive index measurements were performed for Teic Dam, Razi an~ Halbab Khandi samples. Thermal behavior was also investigated by means of differential thermal analyses. Literature data were used foc the Sehjafarlu analcime (Didov~,& Gemain 1976). The results are shov, n in Table 2.
192 Comin-Chiaramonti et al.
LITHOS
I
i
I
SA
A
12(1979)
N
I
13.73
13.72 AZ
~S57 13.71
.
/"" /
i~-~'--"~ A Z 173M ~
AZ 79
13.70 !
AI Si
12 36
Z Ca.~.Na÷K
15 33
The refractive indices and densi' y data do not provide useful information, the diffi.'rences being within the confidence limits of the experimental error. The atomic ratios calculated on the basis of 96 oxygens show that Si, AI and Fe +++ almost always sum to 48, thus indicating .,~aturation of ~h~ equivalent positions avaihble in the flamework of the tetracoordinated cations. X~.y diffraction patterns are generally in close agreement with Ia3d space group, although weak forbidden reflection,~ (as 200) appear on the powder patterns and on the single-crystals photograms of optically anisotropic analcimes of the Harbab Khandi samples (they are referable to a tetra: real 14dacd or orthorhombic Ibca symmetry, according to, Mazzi & Galli 1978). The relationships between the chemical composition and the unit cell parameter of anaicime may be derived from Ithe Coombs & Whetten (1967) diagram which relates 'ao' values with atomic frequencies (Fig. 5). The line in Fig..5 represents Coombs & Whetten's 'be~t fit' curve based on natural and synthetic data The main outcome is that: (a) In the analcime 'phenocrysts' of the Harbab Khandi voicanics, silica content and structural parameters show a good correlation with stoichiometric ana[cime. However, these analcimes are oversaturated relative to their alkalies content. Representative points fall above the 'best fit' curve of Coombs & Whetten and ,4:his can
17 31
L_ 19
29
Fig. 5. Si (dots), A! (squares) and 2Ca + Na + K (diamonds) versus ao(A) diagram for analcimes of northeastern Azerbaijan, SA: stoichiometfic aaalcime; A: albite; N: natrolite (after Saha 1959 and Coombs & Whetten 1967).
perhaps be related to their prevailingly anisotropic appearance under the microscope. (b) The Teic Dam and Razi analcimes as well as the analcime microlites of Harbab Khandi have rather small unit cell parameters compared with the 'best fit' curve; but whereas the Teic Dam ar~alcime is strongly silica undersaturated (wet a~alysis), the remainder are stoichiometric. (c) There is good correlation between chemical arid structural parameters of the Sehjafarlu analcime even though this mineral is chemically closer to albite. (d) The represented analcimes are split into two groups: the 'phenocrysts' of the Harbab Khandi volcanics which show birefringence and forbidden reflections on the X-ray powder patterns and the optically isotropic analcimes of all other occurrences.
In this context it should be noted that the analcime 'phenocrysts' show very low contents of Fe2Oa; the higher values in samples $2 and AZI51 are referable to haematite which confers a more reddish color (Aurisicchio et al. 1975). T1Re K20 content is also very low, except for the T,~c Dam analcime. Moreover, the analyzed phases of Table 2 are closer to the stoichiometric analcime (Ab65 Ne35) than to the highest thermal stable synthetic analcime (Ab50Nes0: Roux & Hamilton 1976). They would conform even more closely to the stoichiometric corn-
LITHOS
Analcime in Azerbaijan volcanics 193
12(1979)
Figs. 6, 7, 8, 9. Photomicrographs of selected analcime occurrences in Harbab Khandi lava flows. (Fig. 6) Analcime of type I, Sample AZ62. (Fig. 7) Analcime of type If, Sample AZ64; Anl: analcime; Pi: plagioclase. (Fig. 8) Analcime of type Ill, Sample AZI73. All with Nicolsll (see text for explanativn). CFig. 9) Analcime of type II1 wdh a ghost str,acture indicating almost total resorption of plagioclase, Sample AZI73, crossed Nicols.
position if loss of Na had occurred during microprobe analyses (cf. wet and microprobe analyses of AZ 151 analcime). Differential thermal analysis studies give identical results for all examined samples. DTA patterns indicate two enaothermie events: at 320"C (dehydration, reversible transformation) and at 760"C (irreversible transformation into nepheline+albite). The latter transformation was confirmed by X-ray diffraction analyses; it was found that a 24-hour heating at 800"C was enough to get the whole analcime transformed into nepheline + albite (beth in powdered specimens and in analcime crystals with a diameter of some cm).
Textural relationships of the Harbab Khandi analcimes While the textural relationships of the phenocryst-like analcimes of the Sehjafarlu, Teic Dam and Razi occurrences have been mentioned
in the previous sections, it is worthwhile to describe in detail the main features of the Harbab Khandi analcimes. In the tephritic phonolites of the Harbab Khandi area three main types of textural positions can be noted for analcimes: (I)
Euhedral or subeuhedral or subrounded analcime in the groundmass (Figs. I and 6). (II) Wedge-shaped analcime interfaced predominantly with large plagioclase phenocrysts. Reaction textures can involve plagioclase-analcime groundma~s (~ig. 7). (III) Subrounded analcime (frequently including plagioclase) interfaced with plagioclase and groundmass (Fig. 8). All these types can be present in the same sample, (I) and (II) occurring most frequently, and they are noteworthy for birefringence and twinning of analcime and sometimes (type Ill) for complete resorption of plagioclase inclusions indicated by ghost structures (Fig. 9).
194 Comin-Chiaramonti et al.
LITHOS 12 (1979)i
i Fig. lO. Enlargement of a smaller area of Fig. 7 identified by the bleb in both figures. Marked points represent microprobe analyses {Table 3).
Fig. 11. Compositional relationslfips for analcime of Type III. Marked points represent microprobe analyses {Table 4). Sample AZ62, Nieols//.
Compositional relations across analcimeplagioclase and groundmass interfaces were studied in detail using the electron microprobe. Some specific examples, illustrating practically all types of relations, are reported here. In Fig. 6, showing an analcime of type (I), points marked A represent a glassy material with composition SiP2 53.22, AI2Oa 23.92, MgO 0.21, CaP 5.48, Na20 6.35, K20 3.22, corresponding to Or 19.0, Ab 36.2, An 27.2, Ne 9.5 wt.%. Points marked B are feldspar microlites aligned along the analcime outlines (CaP 0.7, Na~O 5.0, K20 10.0 wt.%) and points marked C are roughly similar to mean composition of the groundmass microlites (CaP 1.1, Na20 6.4, K20 7.8: Or 44, Ab 51, An 5).
Fig. 10, representing an enlargement of a small area of Fig. 7, belongs to type (II); analytical data are shown in Table 3. Fig. 11 (analytical data recorded in Table 4) shows the compositional relationships of type (Ill) positions. In the last case the upper rim (point 10) has a composition close to Anl 83 Lc 17 (incomplete analcimization?). Resorption of plagioclase and K~O concentration at the ana2cime borders is therefore a general trait.
Tabh, 3. CaP, Na~O and K~O distribution 0~y microprobe analyses) as shown in Fig. 10.
CaP Na20 K20
!
2
3
4
5
6
9.7 5.3 13
8.9 6,0 0.7
0.4 3.9 10.6
0.2 12.9 0.1
0.1 0.4 1 2 . 7 13.5 OI 0.g
7
8
0.3 4.0 10.4
0.3 4.1 10.3
Discussion Didon & Gemain (1976) suggested a primary intrateiluric origin for the Sehjafarlu analcime and pointed out a PT field around 0.5 Kbs and 640°C on the basis of the experimental data of Roux & Hamilton (1976) on the Ne-Ab-H.,O and Ne-Or-Ks-H20 systems. In order to justify the persistence of anal¢ime under extrusion conditions, they suggested a 'fossilization' of thermodynamic conditions caused by the quick magma ascent and subsequent extrusion. However, whereas pyroclastic units and flows are
Tabh, 4. Microprobe analyses across ar~aicime of type II1 (of. Fig. i I). 1
SiO~ 56.80 AI.,O~ 25.36 Fc~()a 0.5 t) MgO 0.06 CaP 8.06 NazO 6.32 K20 E.77
2
3
4
5
6
7
8
9
10
54.89 26.82 0.5 i 0.05 8.83 7.42 0.78
65.00 19.54 0.34 0.08 1.62 6.24 8.13
59,38 17.10 4,07 3.43 0.23 2.42 10.79
54.53 21.83 0,20 0. i ! 13.13 0.16
54.50 21.99 0.16 0.16 13.22 0.20
55.89 23.44 2.20 0.83 5.66 6.50 2.93
54.17 26.88 0.77 0.08 10.03 5.39 1.35
54.45 22.00 0.18 0.12 13.18 0.20
57.82 21.66 0.15 0.03 0.08 12.59 3.65
LITHOS 12 (1979)
cc,mmonplace in the Sehjafarlu volcanics, the arJalcime-beafing lava flows appear to be extruded in a quiet way. The same reasoning holds for the Harbab Khandi occurrences in which, moreover, there is very meagre evidence of e×p~osive activity throughout the complex. In the northeastern Azerbaijan volcanic rocks the systematic absence of hydrous phases such a~ amphibole and biotite must be taken as evidence that water contents of the melts before extrusion were relatiw:ly low and most probably insufficient to depress liquidus temperatures to values adequate for analcime crystallization as a primary phase in the residua system. Moreover, tl~e fact that the Teic Dam lens and Razi dike were emplaced without producing effects of thermal metamorphism on enclosing rocks, ¢:ould also be consistent with rather dry magmas. In natural basalt-H~O systems a calciferous amphibole and not a pyroxene is the dominant mafic phase above 5 Kbs at temperatures below 900°C (Yoder & Tilley 1962; Wyllie 1974; Nakamura & Yoder 1974). Recent experiments on a sample of crinanite (Henderson & Gibb 1977) produced substantial amounts of amphibole, notably from glass-starting materials, between 700° and 1020°C at 1 Kb of Pn,o pressure. Since the total pressure" calculated for sample AZA5 is 3.8 Kbs (which is a value consistent with equilibration data obtained for phenocryst phases belonging to a high-K basalt and to a slaoshonitic basalt of the Harbab Khandi area: Alberti e t a l . , unpublished data) it can be assumed that crystallization started at a total pressure significantly less than 5 Kbs. Wh:h Pu~o'~Ptota~, as previously suggested, the physical conditions prevent the precipitation of primary analcime even at quenching temperatures (of. experhnental data of Peters e t a l . 1966; Boettcher & WyUie 1969; Kim & Burley 1971 and DiSabatino & Giampaolo 1975). Furthermore, the values indicated by tl~e geothermometry and the evidence of rapid analcime transformation into nepheline +albite at altmospheric pressure and 800°C (which is a rather low value for lava flows) makes survival of the analcime very unlikely, The hypothesis of a primary origin for analcime in the northeastern Azerbaijan volcanics should therefore be disregarded. Consequently the analcime 'phenocrysts' are in all likelihood secondary after some earlier phases.
Analcime in Azerba~lan volcanics
195
During late or post-magmatic shages, analcime may have originated from: (1) ion-exchanged leucite. According to Gupta & Fife (1975), if sufficient Na-bearing water ~K+/ Na + as low as 0.3) is present, the conversion vail proceed even at surface temperatures from twoway diffusion involving Na + and H~O, and K + across original leucite-groundmass interfaces; (2) alteration or interaction between pre-existing Na-rich phases such as nepheline, feldspar~ and glass at subsolidus temperatures. According to Henderson & Gibb (1977) nepheline and alkali feldspar can react to completion, giving analcime in presence of water vapor. In the examined samples neither leucite nor nepheline were discovered by means of X-ray and microprobe analyses. While normative nepheline appears in variable amounts in all whole-rock analyses, the Sehjafarlu sample only presents normative leucite. It is therefore a question of finding the phases from which analcime may have grown in these rocks. The undersaturated quadrilateral in the residua system Ne-Ks-Qz (after Schairer 1957 and Fudali 1963) can give some information (Fig. 12A and B). The residuum of the Teic Dam 'analcimite' (sample AZISI) plots at a more K-rich composition than the host, defining an anomalous relationship characterized by a higher liquidus temperature relative to the l,ost. If equilibrium was involved, this implies a crossing of the thermal v~ley in the residua system both at I bar and at 1 Kb of Pu,o pressure (Fig. 12A). The same goes for the Razi dike (sample AZ79), assuming a 1~o~1Kb. However, the two rocks, if related to the volcanic cycle (b) of northeastern Azerbaijan, have a too high N~OIK20 ratio (2.28 and 4.05 respectively) compared with the rocks of cycle (b) with a 1.12 ratio (standard deviation 0.33:54 chemical analyses with SiO~ ranging from 46 to 56 wt.%). The same also goes for a smaller silica range (1.28 ratio; standard deviation 0.23. 15 chemical analyses with SiO~ ranging from 49 to 53%). Hence they have a marked sodic character in volcanic sequences belonging to :~.a as~ociation of shoshonitic affiaity (Albev3 et ~. 1978a). An easy explanation of such anomalou~ relationships would kest on the assuml~fion of a complete transformation, induced by metasoma-
196
LITHOS 120979)
Comin.Chiaramonti et al.
Fig. 12. Part of the phone;ire
An
O •
f
Lc
\
Ab
Or
Lc 1200
Ks
tic processes, of an earlier (highly) potassic phase such as leucite, a trace of which could be found in the potassic rims, with K,O at about 15%, around the analcime of Teic Dam. The idea of a possible devitfification in the Razi dike can be, in our opinion, disregarded because of the size of analcime 'phenocrys, ts'. Such an interpretation is not new: for example Wilkinson has recently explained (1978) that the analcime 'phenocrysts' of a vitrophiric analcimite ffoug]hly similar to, the Razi glassy dike) are ion-exchanged leuc~tes. Conversion of leucite to armlcime must have been completed during the hydration: the main influx of water from the enclosing volcanic breccia most probably occurred following fracturing when the Teic Dam lens and Razi dike were practically consolidated. No data is available for the Sehjafarlu ($2) groundmass, but the bulk composition is also consistent with the possibility of earlier leucite crystallization at a low pressure of H20 (Fig. 12A). For the Harbab Khandi occurrences the more probable path of crystallization, considering the composition of bulk-rock, glasses and microrites, leads to nepheline + alkali feldspars as final products (Fig. 12b). It can be consequently argued that the reaction to form analcime, in the presence of water vapor with nepheline and alkali feldspars as re~ctants, is virtually completed ff nepheline were e~ther a real phase or a
pentahedron with the tertiary feldspar plane rotated into KAISiO4-NaAISiOc-SiOz plane. Phase relationships between nepheline, alkali feldspar and leucite are represented at I bar (solid lines) and at 1 Kb (dashed lines) water-vapor pressure (after Schairer 1957; Fudali 1963; Carmichael et al. 1974). Full circles represent normative salic constituents of the lavas (R: Razi; TD: Teic Dam; S: Sehjafarlu; HK: Harbab Khandi); open circles: groundmass or glass; squares: analcime. Compositions of feldspars phenocrysts and of groundmass sanidine (F: phenocr)sts; M: microlites for Teic Dam'analcimite') are represented by dots with arrows showing the direction of zoning from core to margit~s. The star represents K-rich rim around analcime of AZ 151 sample.
latent phase in glass in the last stage of crystallization. We have also previously seen that there is textural and compositional evidence that analcimization has taken place by involving also plagioclases with Na extraction and K-enrichment into feldspar. In the light of the above data we can conclude that any hypothesis of a primary (intr~aelluric) origin of analcime in eastern Azerbaijan is untenable. The problem, as to the nature of the pre-existing phases from which analcime originated is still open from the structural~.crystallographic point of view. AccorOing to Mazzi et al. (1976) and to Galli et al. (1978), the isotropic, cubic analcime (Sehjafarlu, Teic Dam and Razi occurrences) is a disordered phase structurally in agreement with No-exchanged leueites, ~vhile anisotropic analcime (Harbab Khandi occt~rrences) is a partially-ordered phase in agreement with growth in the sodic form from net~helinefeldspars reactions. However, a metasomatic origin and subsolidus reactions for the analcime occurrences seem to be established in the northeastern A zerbaijan. Acknowledgements. - The authors would like to thank Profes-
sors T. H. Pearce and J. F. G. Wilkinson for comments on an early draft of the text. The manuscript was improved through helpful discussion with Dr. A. A. Alberti. Thanks are also due to Professors G. Gottardi and E. Ga]li for their caStical reading of the final manuscript. We gratefully ackno~ Jedge the financial support of the 'National Research Council' of Italy (con-
LITHOS 12 (1979) tribution N • 75.00028,05) as well as financing for the installation and maintenance (for all scientists affiliated vdth the 05 Committee of CNR) of an electron microprobe ial:~ratory at the Institute of Mineralngy and Petrology at Modena University, whose facilities were used in the present work.
References Alberti, A. A., Comin-Chiaramonti, P., DiBattistini, G., Sinigni, S. & Zerbi, M. 1975: On the magmatism of the Savalan Volcano (North-West Iran). Rend. Soc. Ital. Min. Petrol. 31, 337-350. Alberti, A. A., Comin-Chiaramonti, P., DiBattistini, G., Sinigni, S. & Zerbi, M. 1978a: Shoshonitic volcanism in the northeastern Azerbaijan at the Eocene-Oligocene transition. Neues Jahrb. Miner. Abh., in press. Alberti, A. A., Comin-Chiaramonti, P., DiBattistini, G., Fioriti, R. & Sinigoi, S. 1978b: New chemical analyses of the Tertiary volcanics from the northeastern Azerbaijan highlands (Iran). lstituto di Mineralogia e Petrografia, Trieste University. Alberti, A. A., Comin-Chiaramonti, P., DiBattistini, G., Nicoletti, M., Petrucciani, C. & Sinigoi, S. 1976: Geochronology of the Eastern Azerbaijan Volcanic Plateau (northwest Iran). Rend. Sac. ltaL Min. Petrol. 32, 57~590. Alberti, A. A. & Stolfa, D. 1973: First data on the Savalan Volcano (eastern Azerbaijan, Iran): the Upper Series. Rend. Sac. ltal. Min. Petrol. 29, 369--385. Aurisicchio, C., DeAngelis, G., Dolfi, D., Farinalo, R., Loreto, L., Sgarlata, F. & Trigila, R. 1975: On the red-coloured analcime in the volcanics 6f the Crowsnest alkaline complex (Alberta-Canada). Preliminary Report. Rend. Soc. ital. Mln. Pem, I. 31,653-671 (in Italian). Bacon, C. R. & Carmichael, I. S. E. 1973: Stages in the P-T path of ascending basalt magma: an example from San Quintin, Baja California. Contr. Mineral. Petrol. 41, 1-22. Boettcher, A. L. & Wyllie, P. J. 1969: Phase relationship in the system NaAISiO4-SiO2-H20 to 35 gbars pressure. Am. J. Sci. 267, 875. Bruni, P. 1976: Petrochemical study of the Savalan Volcano fin Italian). Unpublished thesis ETH, Zurich. Buddington, A. F, & Lindsley, D. H. 1964: Iron-titanium oxide minerals and synthetic equivalents. J. Petrol. 5, 310-357. Carmichael, 1. S., Turner, F. J. & Verhoogen, J. 1974:Igneous Petrology, McGraw-Hill Book Co., New York. Carmichael, I. S. E., Nicholls, J., Spera, F. J., Wood, B. J. & Nelson, S. A. 1976: High-temperature properties of silicate liquids: applications to the equilibration and ascent of basic magma. LBL-5238preprint, Lawrence Berkeley Laboratory. Comin-Chiaramonti, P. 1977:The Teic Dam analcimite (eastern Azerbaljan, northwestern 1;ran). Bull. Soc. jr. Miniral. Cristaliogr. 100, 113. Comin.Chiaramonti, P., DiBattistini, G., Mosca, R. & Sinigoi, S. 1978: Miocene volcanism in the Nir district (eastern Azerbaijan, Iran). Neues Jahrb. Miner./lbh. 133, 23-32. Comin-Chiaramonti, P., Nardin, G. & Sinigoi, S. 1975: The alkali quartz-trachytes of the Gasr Dagh (Azerbaijan, northwest Iran). Rend. Sac. ltal. Min. Petrol. 31,297-308. Coombs, D. S. & Whetten, J. T. 1967: Composition of analcime from sedimentary and burial metamorphic rocks. Bull. Geol. Sac. Am. 78, 268-282. Didon, G. & Gemain, Y. M. |976: Le Savalan, Volc~m
A n a , c i m e in A z e r b a i j a n v o i c a n i c s
197
Piio-Quaternaire de l ' A z e r ~ Oriental (Iran): i ~ t ~ GeoloBique et P~trographique de I'~lificie et de son environment r~gional. Th~se 3~ cycle, Grenoble. DiSabafino, N. & Giampaolo, C. 1975: Stability fields of primary and secondary analcimes (in ltalianL Rend. Sac. ha!. Min. Petrol. 31, 63 i-640. Dostal, J. & Zerbi, M. 1978: Geochemistry of the Savalan volcano (northwestern h'an). Chem. Geol. 22, 31-42 Fudali, R. F. 1963: Experimental studies bearing on the origin of pseudoleucite and associated problems of alkalic rock. Geol. Sac. Am. Bull. 74, 1101-1125. Gaili, E., G~ttardi, G. & Mazzi, F. 1978: The natural and synthetic phases with the ieucite framework (in preparaUon). Gupta, A. K. & Fyfe, W. S. 1975: Leucite survival: the alteration to analcime. Can. Mineral. 13. 36 !-363. Hamilton, D. L. & MacKenzie, W. S. 1965: Phase equilibrium studies in the system NaAISiO~-KAISiOc-HzO. Mineral. Mar. 34, 214-231. Henderson, C. M. B. & Gibb, F. G. F. 1977: Formulation of analcime in the Dippin sill, Isle of Arran. Mineral. Mar. 41. 534-537. Irvine, T. N. & Baragar, W. R, A. 1971: A guide to the chemical classification of the common volcanic rock s. C~n. J. Earth Sci. 8, 532-549. Kim, K. & Burley, B. J. 1971: Phase equilibria in t~e system NaAISi3Os-NaAISiO4-H20 with special emphasis on the stability of analcite. Can. J. Earth Sci. 8, 311-337, Kudo, A. M. & Weill, D, F. 1970: An igneous plagioclase thermometer. Contr. Mineral. Petrol. 2'J, 52-65. LeMaitre, R. W. 1976: Some problems of the projectior~ of chemical data into .mineralogical classifications. Contr. Mineral. Petrol. 56, 181-189. Lescuyer, J. L. & Riou, R. 1976. G~ologie de la r~gion de Mianeh (Azerbaijan): contribution it F6tude du volcanism tertiaire de I'iran. Th~se 30 cycle, Grenoble. Lescuyer, J. L., Riou, R. & Vivier, G. 1976: Etude g6ochimique du volcanism tertiaire de la r68ion de Mianeh (Azerbaijan, iran). Gi,ol. Alpine 52. 85-98. Mathez, E. A. 1973: Refinement of the Kudo-Weill plagioc~ase thermometer and its application to b~-,altic rocks. Contr. Mineral. Petrol. 41, 61-72. Mazzi, F., Galli, E. & Gottardi, G. 1976~The crystal structure of tetragonal leucite. Am. Mineral. 61, 108--I15. Mazzi, F. & Galli, E. 1978: Is each analcime different? Am. Mineral. 63, 448-460. Nakamura, Y. & Yoder, H. $. 1974: Analcite, hyalophane and phiilipsite from the Highwood Mountains, Montana. Carnegit Inst. Wash. Year Book 73. 354-358. Pearce, T. H. 1970: The analcite-bearing volcanic rocks of the Crowsnest Formation, Alberta. Can. J. Earth Sci. 7, 46-/06. Peters. T., Luth, W. C. & Turtle, O. F. 1966: The melting of analcite solid solutions in the system NaAISiOaOaNaAISiO,-H20. Am. Mineral. 51,736-763. Powell, M. & Powell, R. 1974: An olivine-clinopyroxene geothermometer. Contr. Mineral. Petrol. 48, 24~-264. Roux, J. & Hamilton, D. L 1976: Primary igneous analcite: an experimental study. J. Petrol. 17, 244-257. Saha, P. 1959: Geochemical and X-ray investigation of natural ~nd synthetic analcites. Am. Mint ral. 44, 300-3|3. Schairer, J. F. i957: Melting relatior~s of the common rockforming silicates Am. Ceram. Sac. J. 40, 215-235. St6cklin, J. & Nabavi, M. H. 1973: Tectonic map of Iran 112,500,000. Geol. Surv. of lran, Teheran. Wilkinson, J. F. G. 1968: Analcites from some potassic igneous rocks and aspects of analcite rich igneous assemblage5. Contr. Mineral. Petrol. 18, 252-269.
198
L I ~ O S 12 (1979)
C o m i n - C h i a r a m o n l r i et al.
Wilkinson, J. F. G. 1978: An~lcime pher~ocrysts in a vitrophyric analcimiteo Primary o r secondary? Cc~tr. Mineral. Petrol 64, 1-10. Wolley, A. R. & Symes, R. F. 1976: The analcime-phyric phonolites (blairmorites) and associated analcime kenytes of the Lupata Gorge, Mocambique. Litnos 9, 9-15. Wyllie, P. 1974: The Dynamic Earth, Wiley, New York.
Yeder, H. S, Jr. & Tilley, C. E. 1962: Origin of basaltic magmas and experimental study cf natural a n d synthetic rock systems. J. Petrol. 3, 342-352. Accepted for publication November 1978 Printed July 1979
LITHOS
Comin-Chiaramonti, P., Meriani, S., Mosca, R. & Sin~-,oi,S. 1979: On the occurrence of analcime in the northeastern Azerbaija~a volcanics (northwestern lran). L/tb~ 12, 187-198. Oslo. ISSH {A}24-4937. Euhedral, phenocryst-like crystals of anslcime, as well as microlites, are rather common in phoaoliti: and tephritic lavas and in some anaicitic dikes and lenses of the Upper Cretaceous and Lower Tertia~ volcanics of eastern Azerbaijan (Iran). The mineralogy and petrology of these extrusive rocks are described with the aim of establishing the orig/n of the big analcime crystals. While the mineralogica! data (e.g. true symm~Rry, AUSi disorder and Na atom distribution, struct~ar~l refinements) are nol conclusive, the paragenesis and microprobe analyses of analcime and a~s~ated phases, m a i ~ feldspars, lead us to believe they are of a secondary, metasomatic origin. It is s~ggested that during hte or post-magmatic stages analcime may have originated eith~.r from ion-exchan,~d leucite or by alteratio~ or interaction between preexisting Na-rich phases such as nepheline, f e l d s ~ and glass at subsolidus temperatures. P. Comin-Chiaramonli & S. Sinigoi, istituto di Mineralogia e Petrografia, gries:e University - Piazza~ Europa, I - 1-34100 Trieste, Italy. S. Meriani, Istituto di Chimica Applicata e ladustriale. R. Mosca, istituto di Chimica. Trieste University - Piazz~le Europa, I - 1-34100 fries~e, i t a l y .
Analcime occurs in extrusive rocks in amygdales of volcanics ranging from basalts to tephritic types (late hydrothermal stage of crystallization), or as devitrification products or replacing other minerals such as leucite, feldspars and nepheline (metasomatic, secondary origin). However, well-developed euhedral (icositetrahedra) analcime phenocrysts in some marie phonolites (Lupata phonolites of Wolley & Symes 1976) and blairmorites (Crowsnest blairmorites of Pearce 1970), as well as in trachybasalts and analcimites, provide at least textural evidence of a primary origin and crystallization at liquidqs temperatures (primary intratelluric origin: Peters et al. 1966; Wilkinson 1968). Doubts have long been expressed as to the origin of such phenocryst-like crystals. A recent experimental study by Roux & Hamilton (1976) has demonstrated that primary igneous analcime c~n only exist at very high H20 pressure and moderately low temperatures between 600' and 640". It is therefore timely to examine critically all associations in which anaicime is assumed to be an equilibrium primary (intratelluric) phase. In the Upper Cretaceous and Tertiary volcanics of the northeastern Azerbaijan (Iraa) volcanic province, analcime was found in several modes ~ffoccurrences. For at least some of these occurrences, phenocryst-like analcime~ pre-
dominate. Didon & Gemain {19~6) proposed that they were of a primary intra~'0~q~uricorigin. This interpretation was extended b~ Lescuyer & Riou (1976) and by Lescuyer et al. 1976)to analcimebearing 'shoshonitic types' of E~:ene age in Iranian Aze~ijan. The purpose of this study i~ to determine on chemical and mineralogical ~,~-~ia and by consideration of the parage~:,sis, whether the phenocryst-like analcime (Fig. t) present both ~n dikes and lenses and in iav~ flows can be considered to be of primary intratelluric o r ~ n or whether it should rather be regarded as secondary. All cases of unquestionable hydrothermal origin in which analcime is ~ssociated with other zeolites (chabazite, thomsonite, stilbite and meso~ite) have obviously been disregardeL
Outline of the northeastern Azerbaijan volcanisin Eastern Azerbaijan has been the s~te of re~a~c= J and varied volcanic activity in Upper L~eta~~e. ous, Tertiary and Quaternary time~;. AI~leas~ ~ou~ main magmatic cycles have occurred ,[A|be~'tie~ al. 1976; Didon & Gemain 1976; St6ck~in & Nabavi 1973):
i!88 Comin.Chlaramontiet al.
LITHOS
12(1979)
(c) A moderately alkaline and foid-free cycle occurred in the southern district in the Upper Miocene (9-11 m.y.: Aiberti !~,t al. 1976). Products of this volcanism range from latitic rocks to alkali-quartz trachytes (Comin-Chiaramonti et al. 1975, 1978). Limited occurre.,,,ces o f Miocene analcime-bearing alk~ine volcanics are also reported from the northern district.
Fig. I. Phenocryst-like analcime in a lava-flow of northeastern Azerbaijan (Sample AZi73).
(a) One cycle started at the top of the Turonian in the northernmost part of the volcanic province, spanning all the Upper Cretaceous, and was first submarine and then subaefial. It has limited areal extent and was charact,:rized by a strong explosive activity. The lavas of the largely volcanoclasfic, submarine formation belonging to this cycle are analcime-bearing tephrilles and basanites; they are subaerial towards the top of the formation. Didon & Ge~ain (1976) call it the 'Sehjafarlu Formation' and attribute a blairmoritic character to the lavas. T~:le same authors state that analcime gradually disappears as it approaches the subaeriai c~_~nditions towards the top of the formation. Some dike swarms and lense~; (e.g. the Teic Dam analcimite: CominChiaramonti 1977) are possibly connected to the Upper Cretaceous volcanism, but should more probably be linked to the later, more widespread Eocene volcanism. (b) A shoshonitic cycle took place in the northern district during Eocene, reaching its climax at the Eocene-Oiigoceae transition: K/At age degerminations give 39-50 m.y., but the activity possibly extended ovcr some 10 million years through Oligocene times ~30 m.y.: Alberti et al. 1976). This cycle has been predominantly fissural and in places has buih lava sequences of up to some hundred meters thick, but central type volcanic structures and pyroclastic rocks are also well represented at various stages. The most abundant rocks are Ne-normative tephritic lavas in which the foids are mainly represented by analcime (analcime-bearing tephritic phonolites of the Harbab Khandi area: Alberti et al. 1978a).
(d) A highly explosive, Plio-Quaternary volcanism in the central part of the volcanic province displays a subalkaline ch,~acter (following the classification of Irvine & Baragar 1971) and a continuous variation from quartz-latiandesites to rhyodacites (Alberti & Stolfa 1973; Alberti et al. 1975; Bruni 1976). This recent cycle gave rise to the big Savalan strato-volcano and to minor occurrences both to the east and west of the same volcano. A high-K calc-alkaline affinity is reported by Dostal & Zerbi (1978).
Analcime-bearing volcanics: petrography and mineralogy The analytical data on selected aryalcime-phyric rocks are given in Table 1: one Sehj~.farlu type is taken from Didon & Gemain (1976), and the Harbab Khandi volcanics from Alberti et al. (1978b). The normative v a l u e s - C I P W norms with FeZ+/Fe"+ + Fe a+ atomic ratios calculated according to the oxidation ratio after LeMaitre (1976) show that the Teic Dam 'analcimite' and the Razi dike can be classitied as phonolites, the Sehjafarlu type and the Harbab Khandi volcanics being tephritic phonolites. -
Tephrites and phonolites of Sehjafarlu The,,ie lava flows exhibit a porphyritic texture and a seemingly intratelluric paragenesis with large analcime 'phenocrysts' (pink colored, mow. than 1 cm in diameter, 25% by volume as average), diopsidic clinopyroxene (C,'60Mg35Fe15: 30%), ore minerals (magnetite and/or martite and ilmeni~e: 5%), occasional oliviae and alkali-feldspar in a glassy to intersertal mesostasis with abundant clinopyroxene and aria!time microlites. In some rocks the cli~opyroxene is distinctly zoned and its content in +.]~e intratelluric par:~genesis is lower; a labradoritic plagioc[ase jacketed by alkalifeld,,;par is present, while, the mesostasis is intersertal with abundant clinopyroxene micro-
Analcime in Azerba~ia~ voicanics 189
(1979)
LITHO$12
7able !. C~:emical analyses and CIPW norms of anaicime phyric volcanics o f the Seluafarlu ($2), Teic Dam (,~7.15 I), l~azi (AZ79) and Harbab Khandi area (AZ45, AZ60, AZ62, AZ64, AZI73). AZI51GM and AZ79GM: gromglmasses. $2
AZI51
AZi51GM
AZ79
AZ79GM
AZ45
AZ60
AZ62
AZ64
AZI73
SiO2 46.31 TiO2 0.87 AI2Oa 15.80 FesOs* 6.56 MnO 0.25 MgO 9.25 Ca{) 5.68 lqa~O 5.20 K20 5.36 P,,Os 0.10 HzO + 3.00 COs n.d.
49.42 0.21 21.96 2.19 0.18 0.96 3.46 9.29 4.08 0.04 6.55 1.88
54.97 0.39 22.01 1.65 0.37 0.72 3.42 10.03 n.d. n.d. n.d.
52.23 0.75 18.68 5.67 0.1,.3 3.0~ 3.17 8.42 2.0~; 0.6~ 5,5 | n.d.
57.1 0.2 22.9 !.6 0.9 1.7 7.5 6.8 n.d. n.d. n.d.
55.5 i 0.72 18.35 4.84 0.11 0.98 5.23 5.01 5.30 0.43 1.52 1.23
54.52 0.85 18.63 5.60 0.11 1.51 5.54 6.02 3.72 0.61 2.48 0.26
55.27 0.83 17.64 5.54 01~: 2,23 3..c:7 5.87 4.79 0.53 2.09 0.57
55.83 0.76 18.59 5.00 0.10 !.21 4. i 5 5.80 5.49 0.45 1.66 0.77
54.~ 0.80 18.43 5.55 0.12 1.72 4.38 6.02 4.97 0.46 2.4| 0.39
98.38
100.22
93.56
100.35
98.5
99.23
99.85
99.42
99.81
100.13
24.13 27.93 5.06 27.41 . 0.40 2.09 1.81 0.40 0.10 4.27
59.3 15. I 3.6 7.5
12.29 45.95 47.~3 13.67 . . 3 3~1 5.~} 4.27 1.43 1.61 -
24.9 37.3 9.4 |9.7 .
31.35 39.91 I i.87 1.32
22.00 40.85 12.78 5.44
28.33 41.06 7.59 4.63 .
32.47 38.10 8.42 5.92
29.41) 33.96 8 54 8.99
3.48 1.50 3.96 ! .44 t.05 1.75
6.16 i.74 4.29 1.52 t.07 0.89
CIPW NORM or ab an ne ic C di ol mt il ap cc
27.24 3.89 23.83 3.49 -
18.53 ! 1.45 4.73 1.66 0,23 -
.
. 4.2 2.3 0.8 -
.
. .
3.8 0.4 -
. . 2.83 1.54 3.68 i .37 i .00 2.80
. .
. 7.30 1.20 4.09 1.62 1.42 0.59
. 3.81 3.47 4.18 1.58 i .2~; ! .30
* Total Fe as Fe~Os.
lites. In the latter cases analcime may have labradoritic plagioclase inclu~ionz (crystals up to one mm long), apparently eq~filibrated with the host phase. Carbonation a~d zeolitization are pre~ent affecting all the rt~cks to a variable extent, carbonation being mainly the alteration of olivines. "fhe lava flows, as well as the dikes, of the Sehjafarlu Formation are likened by Didon & Gemain (1976) to blairmorites: however, acco~'ding to the petrographic features these volcanics are not blairmorites sensu strictu because the latter rocks have an intratelluric paragenesis with analcime, melanitic garnet, sanidine (Or about 85 %) and aegirinaugitic clinopyroxene in a groundmass of sanidine, analcime and aegirinaugite (Pearce 1970).
cm) of induration. This rock has a distinct porphyritic texture with conspicuous analcime 'phenocrys~s' ranging from 50 to 70% by volume (Comin-Chiaramonti 1977): these crystals usually occur as well developed icositetrahedra, ranging in diameter from several mm to 5 era, white or pink colored and of stone-like appearance (Fig. 2); the likeness with the Crowsnest
Teic Dam analcimite and Razi dike The Teic Dam analcimite is a lens-like body extruded in a volcanic brecciia which experienced very limited effects of thermal metamorphism, restricted to a small zone (few
Fig. 2. Teic Dam analcimite showing large idiomorphic crystals of an~cime.
190 Comin-Chiaramonti et ai.
Fig. 3. Potassic rim (K) around analcime (A) in Sample AZISI. Phenocryst of sanidine (S) is also shown. Nicols//.
bi~irmorite (Plate 1 of Roux & Hamilton 1976) should be noted. Sanidine can also be found as elongated (a few mm long), translucent phenocrysts. Under the microscope the analcime crystals are lightly colored isotropic minerals 9ccasionally surrounded or replaced by cmbonates. Anisotropic rims sometimes envelop the analcime (Fig. 3): microprobe analyses give a composition of SiO2 61.35, AlamO:: 19.81, FeO 0.25, MgO 0.04, Na20 1.02, K:,O 14.59 wt.%, corresponding to Or 92.9, Ab 4.8, Ne 2.3. The alkali-feldspar phenocrysts (Or 7'7-66, Ab 20-31, An 2-3: 3% by volume) have elongated habit, frequent Carlsbad twinning, a 2 V , =5-100 and belong to the sanidine H.T.-albite H.T. series. Plagioc[ase and clinopyroxene relics, almost complelely replaced by carbonates, can also be distinguished. Very rare olivine appears to be substitt~ted by a limonite-iddiwgsite..carbonate association. The groundmass is microfeldspathic with all, all feldspar microlites having a mean composition of Or 58.4, Ab 38.0, An 3.6; carbo-
Fig. 4..~,nalcime of the Razi dike Ni¢ols//.
LITHOS 12(1979) nate microgranulations are frequent. The carbonate material appears to have a late origin and has ankeritic composition in all textural positions. This rock is unusual among the volcanics of northeastern Azerbaijan and because of the abundance of analcime is comparable with an analcime-phyric glassy dike of Eocene age occurring dose to the Harbab Khandi lava flows (Razi dike). The Razi dike, Which is also extruded into a volcanic breccia with no appreciable thermal metamorphic effects, contains 'phenoc, r3"sts' of a clear, isotropic analcime (0. I-3 mm in diameter with .~ubrounded outlines and sometimes also in glomeroporphyritic aggregates) plus fresh clinopyrexene (Ca 42, Mg 42, Fe 16 atom%) and apatite in brown unaltered glass with olivine relics and titanomagnetite microlites. "[he approximate mode of the rock is analcime 30, clinopyroxene 7, olivine 2, opaque c,xides 4, apatite 2, glass 55 vol.%.
Harbab Khandi phonolitic rocks These rocks are generally pc,rphyritic lav~ts with a micro or cryptocrystaUine groundmas:~. The most distinctive feature is the abundance cf large (from a few mm to some cm long) phenc,crysts of placioclase (18-30% by volume). The plagioclase is sometimes zoned, and can range from Or 2.4, Ab 25.9, An 71.7 at the core to Or 10.0, Ab 51.5, An 38.5 at the rim, but the most common composition is close to Or 6.7, Ab 46.6, An 46.'/. Alkali feldspar (about Or 45, Ab 49, An 6) often mantles the plagioclase. Clear or pink analcime is abundant both as 'phenocrysts' (up to 3 mm in diameter) and micrelites (7-22% by volume). The analcime 'phenocrysts' show weak birefringenc,~, especially when they are interfaced with plagioclase. Other phases, present either as phenocrysts or microlites, are olivine (Fa 25--40°~,, often iddingsitized and bowlingitized: I-7% by volume), augitic clinopyroxene (Ca 44, Mg41, Fe 15 atom %, Na~O 0.51 wt. % as an average for phenocrysts; Ca 44, Mg 40, Fe 16 atom%, Na20 0,35 wt.% as an average for microtites: 5-10% by vo~,ume); titanomagnetite (with 40 to 30 mole % Fe2TiO4, calculated on the ulvrspinel basis) and occasional ilmenite (only in samples AZ45 and AZ64). A feldspathic ground.mass (microlites rangm:g from Or 35, Ab 60, An 5 to Or 50, Ab 46, An 4 with prevailing compositions around Or 46, Ab 48, An 6, very similar to the alkali feldspar jacketing the plagioclase) with
~
Analcime in Azerbaijan volcanics
LITHOS 12 (1979)
191
Table 2. Analyses 9 f analcime 'phenocrysts' and microlites (M) from northeastern Azerbaij/tn volcanics. $2 SiO2 Al2Oa Fe,zOa MgO Cad Nard KgO H20 +
55.91 21.64 ! .05 0.09 0.19 12.00 0.25 8.50
AZISIW 51.39 23.48 !.55 0.21 0.20 12.78 1.92 8.20
AZI51
AZ79
AZ45
AZ60
AZ62
AZ64
AZ64M
AZI73 AZ!73M
53.50 23.46 0.33 0.06 0.04 13.17 0.06 .
55.0 22.9 0.7 0.9 12.1 0.6
54.8 23.2 0.43 0.22 0.66 12.0 0.24 .
55.3 23.2 0,42 0. ~2 0.54 11.8 0.16 .
54.53 21.99 0.20 0.16 !3.22 0.20
55.32 22.73 0,3! 0.23 12.36 0.06 .
53.33 23.24 0.09 0.37 13.32 0.06
56.04 21. ~I 0.21 0.48 0.19 ~3.07 0.18
54.08 22.44 0.45 0.09 0.43 13.67 0.33
.
92.2
91.55
91.27
91.01
90.38
91.25
91 4 9
33 65 2 27 73 13.705(2)
35.0 64. ! 0.9 24 76 1.488(2) 2.30 13.718(2)
36.3 63. I 0.6 21 79 13.721(4)
31.6 67.4 i.0 31 69 1.484(2; 2.27 13.715(I)
34.9 64.9 0,2 24 76 ! .484(2) 2.27 13.716(2)
33.2 f~. I 0.7 28 72 !.489(6) 2.~9 13.720(4)
29.5 69. i i.4 36 64 13.708{2)
3 ! .76 16.39 0.15 0.05 0.03 15.13 0.02
32.15 15.77 0.31 0.57 13.69 0.~5
32.11 15.99 0.19 0.19 0.41 13.61 u. ~
32.31 15.95 0.19 0. ! ! 0.34 13.35 0.12
32.48 15.41 0.09 0.10 15.24 0.15
32.5 ! 15.72 0.14 0.14 14.06 0.04
3 ! .78 16.29 0.04 0.23 15.36 0.04
32.95 14.61 0.09 0.42 (~.I 1 14.87 0.14
32.02 15.63 0.19 0.07 0.28 15.62 028
48.30
48.23
48.29
48.45
47.98
48.37
48. I I
47.o5
47.84
15.21
15.28
14.61
14.15
15.59
14.38
15.86
15.25
16.46
.
.
.
.
.
,!
99.63 Qz Ne Ks Ne Ab n D ao
35.6 63.4 1.0 21 79 1.494(2) 2.30 13.70
99.73 26.7 66.0 7.3 39 61 1.491(3) 2.294(2) 13.713(8)
Atomic ratios on 96 oxygens basis Si 32.87 30.82 AI 14.97 16.57 Fe +++ 0.46 0.70 Mg 0.08 0.19 Ca 0.12 0.13 Na 13.65 14.83 K 0.18 1.47 Si+AI+ +Fe :j+ 48.30 48.09 Na+K+ +2Ca 14.07 16.56
90.60 3 i .5 68. I 0.4 31 .9 -
90.30
30.3 69.5 0.2 34 66 13.710(5)
Microprobe analyses: Ba and Sr were also analyzed but found to be absent; water loss was not determined. W: wet analysis. Physical parameters are aiso reported (n: refraction index; D: density; ao: lattice parameter assuming a cubic structure. Esti~nated standard deviations are given in parentheses).
small amounts of interstitial glass, has a volume of 45-56°A. Attemp1:s to define the equilibration conditions for the Harbab Khandi volcanics by means of olivine-clinopyroxene geothermometry (Powell & Powell 1974) indicate temperatures of about 1008*C. The empirical plagioclase geothermometer (Kudo & Weill 1970, refined by Mathez 1973) gives 9390C as an average at 0.5 Kbs of Pn,o. Microprobe analyses reveal the presence of coexisting oxide phases (titanomagnetite and ilmenite) in samples AZ45 and AZ64 (molecular percent of ulvtspinei in the spinel phases is 31.4 and 33.3 and molecular percent of R203 in rhombohedral phases is 9.1 and 7.2 respectively). The quenching te;mperatures estimated according to Buddington & LindsJey (1964) are 790° (A2'A5 ,,~,;,!.., ,,,1 ['th = 10 -14"3) and 770°C (AZ64 with fo, = 10-~5"z). An equilibration solution for the pheno,.~ryst phases was obtained from sample AZ45 utilizing the reactions: Ca'[:i + SiO~ = An;
Jd + SiO2 = Ab; CaMgSi2Oe + I/2SiO~ + AIzOa CaAI2Si2Oa + l/2Mg2SiO4 (Bacon & Carmichael 1973; Carmichaei et al. 1974, 1976j. The results are close to 94TC at 3.8 Kbs of total pressure, according to the temperature of the plagioclase geothermometer at 0.5 Kbs of PH,o. =
Analcime mineralogy General features In order to gain evidence of physical and/or chemical differences among the analcimes, chemical analyses, X-ray diffraction patterns, density and refractive index measurements were performed for Teic Dam, Razi an~ Halbab Khandi samples. Thermal behavior was also investigated by means of differential thermal analyses. Literature data were used foc the Sehjafarlu analcime (Didov~,& Gemain 1976). The results are shov, n in Table 2.
192 Comin-Chiaramonti et al.
LITHOS
I
i
I
SA
A
12(1979)
N
I
13.73
13.72 AZ
~S57 13.71
.
/"" /
i~-~'--"~ A Z 173M ~
AZ 79
13.70 !
AI Si
12 36
Z Ca.~.Na÷K
15 33
The refractive indices and densi' y data do not provide useful information, the diffi.'rences being within the confidence limits of the experimental error. The atomic ratios calculated on the basis of 96 oxygens show that Si, AI and Fe +++ almost always sum to 48, thus indicating .,~aturation of ~h~ equivalent positions avaihble in the flamework of the tetracoordinated cations. X~.y diffraction patterns are generally in close agreement with Ia3d space group, although weak forbidden reflection,~ (as 200) appear on the powder patterns and on the single-crystals photograms of optically anisotropic analcimes of the Harbab Khandi samples (they are referable to a tetra: real 14dacd or orthorhombic Ibca symmetry, according to, Mazzi & Galli 1978). The relationships between the chemical composition and the unit cell parameter of anaicime may be derived from Ithe Coombs & Whetten (1967) diagram which relates 'ao' values with atomic frequencies (Fig. 5). The line in Fig..5 represents Coombs & Whetten's 'be~t fit' curve based on natural and synthetic data The main outcome is that: (a) In the analcime 'phenocrysts' of the Harbab Khandi voicanics, silica content and structural parameters show a good correlation with stoichiometric ana[cime. However, these analcimes are oversaturated relative to their alkalies content. Representative points fall above the 'best fit' curve of Coombs & Whetten and ,4:his can
17 31
L_ 19
29
Fig. 5. Si (dots), A! (squares) and 2Ca + Na + K (diamonds) versus ao(A) diagram for analcimes of northeastern Azerbaijan, SA: stoichiometfic aaalcime; A: albite; N: natrolite (after Saha 1959 and Coombs & Whetten 1967).
perhaps be related to their prevailingly anisotropic appearance under the microscope. (b) The Teic Dam and Razi analcimes as well as the analcime microlites of Harbab Khandi have rather small unit cell parameters compared with the 'best fit' curve; but whereas the Teic Dam ar~alcime is strongly silica undersaturated (wet a~alysis), the remainder are stoichiometric. (c) There is good correlation between chemical arid structural parameters of the Sehjafarlu analcime even though this mineral is chemically closer to albite. (d) The represented analcimes are split into two groups: the 'phenocrysts' of the Harbab Khandi volcanics which show birefringence and forbidden reflections on the X-ray powder patterns and the optically isotropic analcimes of all other occurrences.
In this context it should be noted that the analcime 'phenocrysts' show very low contents of Fe2Oa; the higher values in samples $2 and AZI51 are referable to haematite which confers a more reddish color (Aurisicchio et al. 1975). T1Re K20 content is also very low, except for the T,~c Dam analcime. Moreover, the analyzed phases of Table 2 are closer to the stoichiometric analcime (Ab65 Ne35) than to the highest thermal stable synthetic analcime (Ab50Nes0: Roux & Hamilton 1976). They would conform even more closely to the stoichiometric corn-
LITHOS
Analcime in Azerbaijan volcanics 193
12(1979)
Figs. 6, 7, 8, 9. Photomicrographs of selected analcime occurrences in Harbab Khandi lava flows. (Fig. 6) Analcime of type I, Sample AZ62. (Fig. 7) Analcime of type If, Sample AZ64; Anl: analcime; Pi: plagioclase. (Fig. 8) Analcime of type Ill, Sample AZI73. All with Nicolsll (see text for explanativn). CFig. 9) Analcime of type II1 wdh a ghost str,acture indicating almost total resorption of plagioclase, Sample AZI73, crossed Nicols.
position if loss of Na had occurred during microprobe analyses (cf. wet and microprobe analyses of AZ 151 analcime). Differential thermal analysis studies give identical results for all examined samples. DTA patterns indicate two enaothermie events: at 320"C (dehydration, reversible transformation) and at 760"C (irreversible transformation into nepheline+albite). The latter transformation was confirmed by X-ray diffraction analyses; it was found that a 24-hour heating at 800"C was enough to get the whole analcime transformed into nepheline + albite (beth in powdered specimens and in analcime crystals with a diameter of some cm).
Textural relationships of the Harbab Khandi analcimes While the textural relationships of the phenocryst-like analcimes of the Sehjafarlu, Teic Dam and Razi occurrences have been mentioned
in the previous sections, it is worthwhile to describe in detail the main features of the Harbab Khandi analcimes. In the tephritic phonolites of the Harbab Khandi area three main types of textural positions can be noted for analcimes: (I)
Euhedral or subeuhedral or subrounded analcime in the groundmass (Figs. I and 6). (II) Wedge-shaped analcime interfaced predominantly with large plagioclase phenocrysts. Reaction textures can involve plagioclase-analcime groundma~s (~ig. 7). (III) Subrounded analcime (frequently including plagioclase) interfaced with plagioclase and groundmass (Fig. 8). All these types can be present in the same sample, (I) and (II) occurring most frequently, and they are noteworthy for birefringence and twinning of analcime and sometimes (type Ill) for complete resorption of plagioclase inclusions indicated by ghost structures (Fig. 9).
194 Comin-Chiaramonti et al.
LITHOS 12 (1979)i
i Fig. lO. Enlargement of a smaller area of Fig. 7 identified by the bleb in both figures. Marked points represent microprobe analyses {Table 3).
Fig. 11. Compositional relationslfips for analcime of Type III. Marked points represent microprobe analyses {Table 4). Sample AZ62, Nieols//.
Compositional relations across analcimeplagioclase and groundmass interfaces were studied in detail using the electron microprobe. Some specific examples, illustrating practically all types of relations, are reported here. In Fig. 6, showing an analcime of type (I), points marked A represent a glassy material with composition SiP2 53.22, AI2Oa 23.92, MgO 0.21, CaP 5.48, Na20 6.35, K20 3.22, corresponding to Or 19.0, Ab 36.2, An 27.2, Ne 9.5 wt.%. Points marked B are feldspar microlites aligned along the analcime outlines (CaP 0.7, Na~O 5.0, K20 10.0 wt.%) and points marked C are roughly similar to mean composition of the groundmass microlites (CaP 1.1, Na20 6.4, K20 7.8: Or 44, Ab 51, An 5).
Fig. 10, representing an enlargement of a small area of Fig. 7, belongs to type (II); analytical data are shown in Table 3. Fig. 11 (analytical data recorded in Table 4) shows the compositional relationships of type (Ill) positions. In the last case the upper rim (point 10) has a composition close to Anl 83 Lc 17 (incomplete analcimization?). Resorption of plagioclase and K~O concentration at the ana2cime borders is therefore a general trait.
Tabh, 3. CaP, Na~O and K~O distribution 0~y microprobe analyses) as shown in Fig. 10.
CaP Na20 K20
!
2
3
4
5
6
9.7 5.3 13
8.9 6,0 0.7
0.4 3.9 10.6
0.2 12.9 0.1
0.1 0.4 1 2 . 7 13.5 OI 0.g
7
8
0.3 4.0 10.4
0.3 4.1 10.3
Discussion Didon & Gemain (1976) suggested a primary intrateiluric origin for the Sehjafarlu analcime and pointed out a PT field around 0.5 Kbs and 640°C on the basis of the experimental data of Roux & Hamilton (1976) on the Ne-Ab-H.,O and Ne-Or-Ks-H20 systems. In order to justify the persistence of anal¢ime under extrusion conditions, they suggested a 'fossilization' of thermodynamic conditions caused by the quick magma ascent and subsequent extrusion. However, whereas pyroclastic units and flows are
Tabh, 4. Microprobe analyses across ar~aicime of type II1 (of. Fig. i I). 1
SiO~ 56.80 AI.,O~ 25.36 Fc~()a 0.5 t) MgO 0.06 CaP 8.06 NazO 6.32 K20 E.77
2
3
4
5
6
7
8
9
10
54.89 26.82 0.5 i 0.05 8.83 7.42 0.78
65.00 19.54 0.34 0.08 1.62 6.24 8.13
59,38 17.10 4,07 3.43 0.23 2.42 10.79
54.53 21.83 0,20 0. i ! 13.13 0.16
54.50 21.99 0.16 0.16 13.22 0.20
55.89 23.44 2.20 0.83 5.66 6.50 2.93
54.17 26.88 0.77 0.08 10.03 5.39 1.35
54.45 22.00 0.18 0.12 13.18 0.20
57.82 21.66 0.15 0.03 0.08 12.59 3.65
LITHOS 12 (1979)
cc,mmonplace in the Sehjafarlu volcanics, the arJalcime-beafing lava flows appear to be extruded in a quiet way. The same reasoning holds for the Harbab Khandi occurrences in which, moreover, there is very meagre evidence of e×p~osive activity throughout the complex. In the northeastern Azerbaijan volcanic rocks the systematic absence of hydrous phases such a~ amphibole and biotite must be taken as evidence that water contents of the melts before extrusion were relatiw:ly low and most probably insufficient to depress liquidus temperatures to values adequate for analcime crystallization as a primary phase in the residua system. Moreover, tl~e fact that the Teic Dam lens and Razi dike were emplaced without producing effects of thermal metamorphism on enclosing rocks, ¢:ould also be consistent with rather dry magmas. In natural basalt-H~O systems a calciferous amphibole and not a pyroxene is the dominant mafic phase above 5 Kbs at temperatures below 900°C (Yoder & Tilley 1962; Wyllie 1974; Nakamura & Yoder 1974). Recent experiments on a sample of crinanite (Henderson & Gibb 1977) produced substantial amounts of amphibole, notably from glass-starting materials, between 700° and 1020°C at 1 Kb of Pn,o pressure. Since the total pressure" calculated for sample AZA5 is 3.8 Kbs (which is a value consistent with equilibration data obtained for phenocryst phases belonging to a high-K basalt and to a slaoshonitic basalt of the Harbab Khandi area: Alberti e t a l . , unpublished data) it can be assumed that crystallization started at a total pressure significantly less than 5 Kbs. Wh:h Pu~o'~Ptota~, as previously suggested, the physical conditions prevent the precipitation of primary analcime even at quenching temperatures (of. experhnental data of Peters e t a l . 1966; Boettcher & WyUie 1969; Kim & Burley 1971 and DiSabatino & Giampaolo 1975). Furthermore, the values indicated by tl~e geothermometry and the evidence of rapid analcime transformation into nepheline +albite at altmospheric pressure and 800°C (which is a rather low value for lava flows) makes survival of the analcime very unlikely, The hypothesis of a primary origin for analcime in the northeastern Azerbaijan volcanics should therefore be disregarded. Consequently the analcime 'phenocrysts' are in all likelihood secondary after some earlier phases.
Analcime in Azerba~lan volcanics
195
During late or post-magmatic shages, analcime may have originated from: (1) ion-exchanged leucite. According to Gupta & Fife (1975), if sufficient Na-bearing water ~K+/ Na + as low as 0.3) is present, the conversion vail proceed even at surface temperatures from twoway diffusion involving Na + and H~O, and K + across original leucite-groundmass interfaces; (2) alteration or interaction between pre-existing Na-rich phases such as nepheline, feldspar~ and glass at subsolidus temperatures. According to Henderson & Gibb (1977) nepheline and alkali feldspar can react to completion, giving analcime in presence of water vapor. In the examined samples neither leucite nor nepheline were discovered by means of X-ray and microprobe analyses. While normative nepheline appears in variable amounts in all whole-rock analyses, the Sehjafarlu sample only presents normative leucite. It is therefore a question of finding the phases from which analcime may have grown in these rocks. The undersaturated quadrilateral in the residua system Ne-Ks-Qz (after Schairer 1957 and Fudali 1963) can give some information (Fig. 12A and B). The residuum of the Teic Dam 'analcimite' (sample AZISI) plots at a more K-rich composition than the host, defining an anomalous relationship characterized by a higher liquidus temperature relative to the l,ost. If equilibrium was involved, this implies a crossing of the thermal v~ley in the residua system both at I bar and at 1 Kb of Pu,o pressure (Fig. 12A). The same goes for the Razi dike (sample AZ79), assuming a 1~o~1Kb. However, the two rocks, if related to the volcanic cycle (b) of northeastern Azerbaijan, have a too high N~OIK20 ratio (2.28 and 4.05 respectively) compared with the rocks of cycle (b) with a 1.12 ratio (standard deviation 0.33:54 chemical analyses with SiO~ ranging from 46 to 56 wt.%). The same also goes for a smaller silica range (1.28 ratio; standard deviation 0.23. 15 chemical analyses with SiO~ ranging from 49 to 53%). Hence they have a marked sodic character in volcanic sequences belonging to :~.a as~ociation of shoshonitic affiaity (Albev3 et ~. 1978a). An easy explanation of such anomalou~ relationships would kest on the assuml~fion of a complete transformation, induced by metasoma-
196
LITHOS 120979)
Comin.Chiaramonti et al.
Fig. 12. Part of the phone;ire
An
O •
f
Lc
\
Ab
Or
Lc 1200
Ks
tic processes, of an earlier (highly) potassic phase such as leucite, a trace of which could be found in the potassic rims, with K,O at about 15%, around the analcime of Teic Dam. The idea of a possible devitfification in the Razi dike can be, in our opinion, disregarded because of the size of analcime 'phenocrys, ts'. Such an interpretation is not new: for example Wilkinson has recently explained (1978) that the analcime 'phenocrysts' of a vitrophiric analcimite ffoug]hly similar to, the Razi glassy dike) are ion-exchanged leuc~tes. Conversion of leucite to armlcime must have been completed during the hydration: the main influx of water from the enclosing volcanic breccia most probably occurred following fracturing when the Teic Dam lens and Razi dike were practically consolidated. No data is available for the Sehjafarlu ($2) groundmass, but the bulk composition is also consistent with the possibility of earlier leucite crystallization at a low pressure of H20 (Fig. 12A). For the Harbab Khandi occurrences the more probable path of crystallization, considering the composition of bulk-rock, glasses and microrites, leads to nepheline + alkali feldspars as final products (Fig. 12b). It can be consequently argued that the reaction to form analcime, in the presence of water vapor with nepheline and alkali feldspars as re~ctants, is virtually completed ff nepheline were e~ther a real phase or a
pentahedron with the tertiary feldspar plane rotated into KAISiO4-NaAISiOc-SiOz plane. Phase relationships between nepheline, alkali feldspar and leucite are represented at I bar (solid lines) and at 1 Kb (dashed lines) water-vapor pressure (after Schairer 1957; Fudali 1963; Carmichael et al. 1974). Full circles represent normative salic constituents of the lavas (R: Razi; TD: Teic Dam; S: Sehjafarlu; HK: Harbab Khandi); open circles: groundmass or glass; squares: analcime. Compositions of feldspars phenocrysts and of groundmass sanidine (F: phenocr)sts; M: microlites for Teic Dam'analcimite') are represented by dots with arrows showing the direction of zoning from core to margit~s. The star represents K-rich rim around analcime of AZ 151 sample.
latent phase in glass in the last stage of crystallization. We have also previously seen that there is textural and compositional evidence that analcimization has taken place by involving also plagioclases with Na extraction and K-enrichment into feldspar. In the light of the above data we can conclude that any hypothesis of a primary (intr~aelluric) origin of analcime in eastern Azerbaijan is untenable. The problem, as to the nature of the pre-existing phases from which analcime originated is still open from the structural~.crystallographic point of view. AccorOing to Mazzi et al. (1976) and to Galli et al. (1978), the isotropic, cubic analcime (Sehjafarlu, Teic Dam and Razi occurrences) is a disordered phase structurally in agreement with No-exchanged leueites, ~vhile anisotropic analcime (Harbab Khandi occt~rrences) is a partially-ordered phase in agreement with growth in the sodic form from net~helinefeldspars reactions. However, a metasomatic origin and subsolidus reactions for the analcime occurrences seem to be established in the northeastern A zerbaijan. Acknowledgements. - The authors would like to thank Profes-
sors T. H. Pearce and J. F. G. Wilkinson for comments on an early draft of the text. The manuscript was improved through helpful discussion with Dr. A. A. Alberti. Thanks are also due to Professors G. Gottardi and E. Ga]li for their caStical reading of the final manuscript. We gratefully ackno~ Jedge the financial support of the 'National Research Council' of Italy (con-
LITHOS 12 (1979) tribution N • 75.00028,05) as well as financing for the installation and maintenance (for all scientists affiliated vdth the 05 Committee of CNR) of an electron microprobe ial:~ratory at the Institute of Mineralngy and Petrology at Modena University, whose facilities were used in the present work.
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