Geol. Surv. Iran, 40, 239-260, 1977 239 THREE ... - Manuel berberian

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The metamorphic complexes of the Hajiabad Quadrangle are divided into three .... Saudi Arabia, the Hall Group is folded and metamorphosed to Amphibolite ...
Geol. Surv. Iran, 40, 239-260, 1977

THREE

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QUADRANGLE (Southeastern extremity of the Sanandaj-Sirjanstructural zone): Paleotectonic Discussion by M. BERBERIAN GEOLOGICAL AND MINING SURVEY OF IRAN ABSTRACT The effects of two important syntectonic regional metamorphismsin the exposed rocks of the Hajiabad Quadrangle (southeastern extremity of the $anandaj-Si~an structural zone) show that the area has undergone two important metamorphisms during Precambrian and Early Kimmerian orogenic movements. The possibility of a Hercynian diastrophic movementtogether with a questionable regional metamorphism is under investigation.

INTRODUCTION There are three syntectonic regional metamorphic complexes in the Hajiabad Quadrangle (southeastern extremity of the Sanandaj-Sirjan structural zone; Berberian 1976), 180kmnorth of Bandar Abbas (Figs. 1 and 2). These complexes have different metamorphicgrades and different ages, and are covered by unaffected Jurassic basal conglomerate (with metamorphic rock fragments) and volcano-detritic rocks. The complexes have been traced continuously from Hajiabad in the southeast to Neyriz Quadrangle in the northwest, within the Sanandaj-Sirjan Zone. The metamorphic complexes of the Hajiabad Quadrangle are divided into three units from bottom to top: 3. 2. 1.

Upper Complex (low grade) Middle Complex (medium to low grade) Lower Complex (high grade)

The complexesare briefly discussed here:

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1.

Lower Complex: High Grade Complex of Garnet-Amphibolite

Facies.

This unit always makes the basement outcrops in the region and is usually tectonically covered by the younger complexes (middle and upper), or has a fault contact with them. The rocks are highly deformed and flow structures are developed perfectly. The age of this comple× is pre-Silurian-Devonian (Precambrian?). It is divided lithologically into two units (Berberian and Nowgol 1974): 1. 1. Zarab Kyanite-Sillimanite The type paragenesis Kyanite+biotite+almandine

Schist, Gneiss and Amphibolite.

of this upper high grade unit (garnet-amphibolite facies).

of the Lower Complex is:

The major rock types of the Zarab unit are as follows :

GULF OF

Fig, 1.

Position of the Hajiabad Quadrangleon the main Iranian seismotectonic provinces. The Hajiabad Quadrangleis shownby a small square (after Berberian 1976).

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- kyanite-sillimanite-tourmaline-biotite-muscovite schist. - orthoclase-biotite-muscovite schist. - hornblende schist. - garnet amphibolite. - garnet-biotite schist. - sillimanite-garnet-biotite-muscovite gneiss. - arkosic-garnet-biotite-muscovite gneiss. It should be noted that this unit normally overlies Bareh Koshan garnet amphibolite, and that there is no faulted contact or unconformity between them.

Fig.

2. Seismotectonic situation of the Hajiabad Quadranglearea (after BeJberian 1976).

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1.2.

Bareh Koshan Garnet Amphibolite.

These are highly deformed meta-basic volcanics with type paragenesis of almandine +hornblende+plagioclase (garnet-amphibolite facies), which form the lower high grade unit of the Lower complex. The varieties observed in this unit, which is the highest grade and the oldest exposed metamorphic rock of the Hajiabad area, are as follows : -

pegmatitic or mobilized amphibolite. hornblende-epidote amphibolite. almandine-hornblende-biotite amphibolite. almandine-hornblende-plagioclase amphibolite.

Fig. 3. Quartzo-feldspathic mobilized layer in Bareh Koshan~arnet amphikolite, Hajiabad Quardrangle.

Fig. 4. Recumbentfolds (L1) in Bareh Koshangarnet amphibolite (natural size).

Fig. 5. A folded (L1) Bareh Koshangarnet amohibolite (natural size).

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Figs. 6 and 7. First deformational style (L1) in the Bareh Koshangarnet ~mphibolite.

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Figs. 8. and 9. First

deformational

phase (F1) in Bareh Koshan garnet amphibolite.

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In some places where the grade of the metamorphismwas high enough, the feldspathic patches became flattened and a pegmatitic appearance becomes more marked by metamorphic differentiation. In a few cases the homogeneousquartz-feldspathic mobilized rock is intruded in the adjacent rocks (Figs. 3 to 9). 1.3. Discussion on the high grade lower complex. Since the lower complex of high grade metamorphicrocks is older than the middle complex, and the age of the sediments of the middle complex is Silurian-Devonian (see section 3), the age of the rocks of the lower complexshould be considered at least "Pre-Silurian-Devonian" at this stage. The potassium-argon radiometric age determination of a sample of the Zarab kyanite-sillimanite schist in the Neyriz Quadrangle (Watters and Sabzehei, 1970) gave 404+~8m.y. which is at the Silurian-Devonian boundary; another sample of the same unit gave 362+7m.y. which is at the top of the Middle Devonian. The age for a sample of the Bareh Koshan garnet-amphibolite (?) was determined by the same methodas 170~-8m.y. (Watters and Sabzehei, 1970), which is at the lower part of the Middle Jurassic. It should be observed that potassium-argon age determinations on crystalline metamorphosedrocks usually give rise to difficulties of interpretation because in many places the dates obtained refer not to the original period of crystallization but rather to later events. The 362+~7m.y.age (top of the Middle Devonian) is not the correct age of the metamorphismof the rocks of the Zarab kyanite-sillimanite schist, because as stated before, the rocks are older than Silurian-Devonian. Again the metamorphism age of the rocks of the Bareh Koshan garnet-amphibolite should not be 170+8m.y. (lower part of the Middle Jurassic), because metamorphismof the lower complexof the high grade metamorphic recks of this region took place before Silurian-Devonian time (possibly in Precambrian). Berberian and Nowgol(1974) considered these grade metamorphic rocks to be pre-Devonian, possibly of Precambrian age. Since field study suggests a "pre-Silurian-Devonian age for metamorphismof this complex, the high grade lower complexcan be said to be related to the syntectonic regional metamorphism of the late Precambrian orogenic movements. The metamorphic minerals are folded, and the garnet-amphibolites were highly epidotized, sericitized and chloritized during the younger orogenic movementsand their related syntectonic metamorphism (metamorphism of the middle and upper complexes). In some cases the newly formed metamorphic minerals of the younger phases cut the trend of the original minerals of the garnet-amphibolite. Twodifferent B-lineations have been found in the lower complex of the Hajiabad Quadrangle. The first and the older set(L1)has a N-S trend (Fig. 10)and the second which is younger(L2)hasa trend of nearly E-W(Fig.10.B).Interestingly, the first (older) B-lineation (L1) present in the lower high grade complex is absent in the middle complex (Silurian-Devonian-Carboniferous) and the upper complex (Permian - Triassic). Thus those complexes younger than the lower complex (Precambrian) did undergo the compression and stress system which produced L1 in the lower complex.

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Fig. 10.

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Equal area plot of B-lineations in the Precambrian high grade lower complex of the Hajiabad Quadrangle: LI= first (older) lineation, L2 = second (younger) lineation. For location of the diagrams see Fig. 19. A-L1 : 16.6~oo,9.2~o, 5.5~oo,3.7~o. B-L1 : 13.1~o,11.1,°,~,7.0~o,2.0~. C-L1 : 16.3~,8.1°/oo,6/1%,20°//oo. D-L1 : 10.8~o,5.4~,2.7~. E-L2 : 14.2~, 11.4~,5.7~o,2.8~. Upper hemisphere of Schmidt stereonet

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Fig.. 11 Equal area plot of the first schistosity in the Precambrianhigh grade lower complexof the Hajiabad Quadrangle. For the location of the diagrams see Fig. 19. A- SI : 8.2~,5.4~o, 2.7~o, 1.3~o. B- S1 : 13.2~,8.4~,4.7~,0.9~. C- S1 : 14.1~,9.71,5.4~,1.0~ D- S1 : 11.5~,7.6~,3.8~. Upper hemisphereof Schmidtstereonet.

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The schistosity in the lower complexhas a variable trend but the schistosity plane is roughly oriented N-S to NE and SWwith variable dips (Fig.ll). According to Schmidt et al. (1973), "during Asir Tectonism (Precambrian) Saudi Arabia, the Hall Group is folded and metamorphosed to Amphibolite facies (it consists mostly of garnet amphibolite, gneiss, and garnet-biotite schist). During the Bishah Orogeny (570 m.y. ago) the rocks were folded about N-S axes. During the latest Precambrian and Early Cambrian (520 m.y. ago) the N-S folds and faults were cross-cut by the Najd NW-SEleft-lateral Wrench Fault System that affected large parts of the eastern and northern parts of the Arabian Shield. Movementsmore than 100 kmtook place in the northwesternmost fault zone. Small granite plutons were emplaced in the Najd Fault System near the end of the period of faulting which may have extended into Cambrian time." Bareh Koshan Garnet-Amphiboite may be the equivalent of the Hali Group of Saudi Arabia, but will require further study before such a conclusion can be drawn. 2,

Middle Complex: Metamorphicsof Green-Schist Facies.

This complex is composed of metamorphoseddetritic rocks, meta-volcanics and some limestones. The mineral assemblages indicate metamorphismin the green-schist facies. The general rock types of this complexare as follows. -

Carbonaceous black low-grade schist with Devonian pollen. Meta-biotite-quartz diorite. Meta-ignimbrite Schistosed meta crystal-tuff. Epidote-muscovite schist. Biotite schist. Muscovite-chlorite schist. Muscovite-biotite-chlorite schist. Meta-quartzite.

In certain sections of this complex, some badly preserved crinoid stem fragments and a few corals and one sample of bryozoa have been discovered. In the carbonaceous black schists, "Devonian pollen and spore" were found (72.M.B.34) and determined by Prof. A. Kimiai of Tehran University (Berberian 1976). The coral samples (76.M.B.26 and 119) were determined by Prof. M. Kato of Hokkaido University as "Hexagonaria (a Devonian Rugosa)" and a bryozoan (76.M.B.119.b) belonging to "’Trepostornata" (Low,er Paleozoic) was determined by Prof.S. Sakagami of Ehime University. The generic and specific nameof this last fossil is unknownbecause of bad preservation due to the regional metamorphism. A few Blerophontid type gastropods have been collected in these metamorphics.

POLYMETAMORPHISM

Fig. 12.

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The extreme recumbencyof these drag folds causes their apices to be almost entirely sheared out. A b - lineation is created by the parallelism of the drag - fold axes. Metamorphosed limestone of northern Khabr, Hagiabad Ouadrangle.

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Figs. 13. and 14. Recumbentisoclinal folds (L1), developedby ductile flow, in the metamorphicrocks of Hajiabad Quadrangle area.

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Figs. 15. and 16. Recumbentisoclinal folds with boudins developedin the metamorphicrocks of Hajiabad Quadrangle area (first deformational phase in Silutian-Devonian rocks of middle complex).

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2.1. Discussion on the middle complex. Since a part of this complex has a proved Devonian age,they were metamorphosed during the later movements. The only possible diastrophic phases responsible for the syntectonic regional metamorphism of these Devonian rocks were the "Hercynian" and "Early Kimmerian" movements. Earlier authors described these metamorphics as Precambrian basement rocks (St6cklin 1968), but Hushmandzadeh et al. (1972), Sabzehei, Berberian (1972), (1972), Berberian (1972, 1973), Hushmandzadeh (1973), Berberian, Nowgol (1974), Sabzehei (1974), Majidi (1974), and Berberian (1976) stated that Early Kimmerian movements were responsible for the syntectonic regional metamorphism of this complex. Majidi (1973) stated that detrital rock fragments of Precambrian rocks have been found in the Early Kimmerian metamorphic conglomerates. It is important to note that the metamorphic grade and the style of deformation of this complex (middle complex) is not the same as the grade of the upper complex .(Permian-Triassic rocks). The Permian-Triassic Complex is slightly metamorphosed

w

Fig. 17.

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Equal area plot of B-lineations in the Silurian-Devonian-Carboniferous middle complex of the Hajiabad Quadrangle. L1 : first lineation. For the location of the diagramssee Fig. 19 E-L1 : 11.9~/o,7.1~o,4.76~oo.,2.38~o. F-L1 : 18.1%,12.1~,6.0~. Upper hemisphere of Schmidt stereonet

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Equalarea plot of first schistosity in the Silurian - Devonian- Carboniferousmiddlecomplex of the Hajiabad Ouadrangle. For the location of diagrams see Fig. 19. E- S1 : 15.5~,6.8~,3.4~. F- SI : 14.2~o,8.5~,5.7~o. G- S1 : 16.6~o, 12.5~o, 4.1~ Upperhemisphere of Schmidtstereonet.

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Fig. 19.

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Main structural and physiographic units of the Haiiabad Quadrangle. 1 - Preeambrian high grade lower complex outcrops. 2 - Hercynides (?) 3 - Permo-Triassic metamorphosedduring Early Kimmerian orogenic phase. 4 - Zagros Acti’~e Folded Belt. 5 - Jurassic - lower Cretaceous rift 6 - Coloured Melange rift. 7 - Eocene flysch rift 8 - Hihg Angle Reverse Fault 9 - Measured B - lineations, see (Figs. 10, 11, 17, 18.). 10- First - class road.

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and is rich in microfauna, while the middle complex(Devonian) is a green schist facies and has few fossils. One.maytherefore..consider the "Hercynian movements’" responsible for the metamorphismof the middle complex (?). (Figs. 12 to The13-1ineations in the middle complex (Silurian- Devonian-Carboniferous) have a dominant E-Wtrend (Fig. 17) and a shistosity of nearly N-S (Fig. 18)The B-lineation and B-axes observed in the middle complex are present in the lower complex~ as the younger B-lineation (L2). Thus the compression system responsible for the formation of the E-WB-lineations in the middle complex refolded the N-S older B-lineations and B-axes of the older complex(Fig. 10. B). Thiele (1968) stated for the first time that someof the metamorphicsof Golpayegan Quadrangle in the Sanandaj-Sirjan Zone were metamorphosed during "Hercynian movements" and that they have NE-SWfold axes. The effects and the importance of the Hercynian movementsin Iran may, in the light of recent evdence, now be susceptible of confirmation in the field. Resrearch to this end is underway. 3~ UpperComplex:Slightly metamorphosedfossiliferous

Permian-Triassic rocks.

This unit is composedof a basal polygenetic conglomerate, associated detritics, meta-volcanics, phyltite~ crystallized Fusulina-Schwagerinabearing limestone of Lower to Middle Permian age (Chahzar ensemble), and Lentieulina bearing limestone (73. M.B.309) and dolomite of Lower Triassic age (Khabr ensemble). The grade of metamorphismin these rocks ~s upper green-schist facies to slightly crystallized rocks. ’3. 1o Discussion on the upper complex. The slightly metamorphosedfossiliferous Permian-Triassic rocks are unconformably covered by Jurassic sediments and post-tectonic lava flows. Since the Jurassic sediments are not metamorphosed, the Early Kimmerian orogenic movementis responsible for the metamorphismof the Permian-Triassic beds.

4.

CONCLUSION

The oldest knownhigh grade metamorphic rocks’~6~’ garnet-amphibolite facies of probably Precambnan (pre-Sllurlan-Devom~)’~, In the Hajlabad Quadrangle are exposed as a basement complex in the area, witl~ Older N-S and younger E-WB-lineations. After the diastrophic phase (probably of late Precambrian) reponsible for the metamorphismof the older and low6r complex,the horsts of Baikalides were developed in the area. The trend of Baikalid horstS in H@~bad was E-Wand it swings to NW-SE towards the northwest of the area. The horsts were bounded by major faults with the same trends (Fig. 19). During ?Silurian, Devonian and Carboniferous, several detritic and volcanic rocks, together with some carbonates, were deposited in the E-Wto NW-SEgrabens existing then betweenthe Baikalides. After this deposition and during a younger phase, probably Hercynian, the rocks were metamorphosed in the green-schist facies and

Fig. 20. Direction of maximum horizontal shortening deduced from Neogeneaxes of folding in Hajiabad Quadranglearea (cf. Fig. 19).

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an E-WB-lineation developedfor the first time. The compressionin this period refolded the N-S B-lineations previously formed in the highgrade lower complex and a second E-WB-lineation was formed. The Permian sea transgressed from the north but could not cover the still preserved Baikalides and Hercynides (?), and just covered the northern foothills of the high lands. During the Early Kimmerianorogeny, the area underwent another syntectonic regional metamorphismin the lower green-schist facies. The Baikalides, Hercynides (?) and the horsts of the Early Kimmerian remained as high lands during the Jurassic and the Lower Cretaceous, and some parts remain high lands to day. The JurassicLower Cretaceous sea covered the grabens or the rifts developed in these periods. A separate rift (the Coloured Melangerift) system developed in the southwestern marginal part of Central Iran (along the present Zagros line) (Fig. 19) During Eocene another rift openedand Eoceneflysch were deposited along the Zagros line. The OligoMiocene sea only covered the lowlands of the northern Hajiabad area. The study of the B-axes of the post Neogenefolds in this area shows a uniforn E-Wdirection for the B-axes and a nearly local N-S stress direction during the Zagros Orogeny (Wallachian diashophism) in this region (Fig. 20).

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REFERENCES

Berberian, M., 1972. Twoimportant defo~mational and metamorphicpha:es in the belt northeast o the Zagros thrust line (Iran). Geol. Surv. lran. Petrological Department,Int. Rep.-13p. Berberian, M., 1973. Twoimportant deformational and metamorphicphases in the belt northeast of the Zagrosthrust line (lran). A brief structural review of the Sal,~andaj-Sirjan Belt. Geol. Surv, lran, lnt. Rep- No. 27 35p Berberian, M., 1976, Anexplanatory note on the First Seismotectonic Mapof Iran: a seismoectonic review of the country. In Geological, Survey of Iran, Rep. No. 39, pp. 7-142,53 Figures, 5 Maps, 135p. Berberian, M., Nowgol,M., 1974. Preliminary explanatory text of the geology of DehSard and Khabr maps with some remarks at a the metamorphiccomplexes and the tectonics of the area (two geological sheets on scale o~" 1:100.000 from the Hajiabad Quadranglemap). Geological Surveyof lran, Int. Rep., 60p., 24 Figures, 2 geological maps. Hushmandzadeh,A., 1973. Precambrian metamorphicepisodes in Iran; A short revi:w. Geol. Surv. Iran, Int; Rep., 62, 20p. Hushmandzadeh,A., Sabzehei, M., and Berberian, M., 1972. A brief note on Early Kimmerianorogeny and high grade metamorphismin the Sanandaj-Sirjan Belt (Sirjan-Esfandagheh), Iran. Geol. Surv. Iran, Int. Rep., 3p. Majidi, B., 1972. Preliminary report of the Hadjiabad Quadrangle. Geol. Surv. Iran, Int. Rep. Majidi, B., 1973. Petrographic character and age of metamorphiccomplexesof south Iran. Geol. Surv. Iran, Int. Rep. Majidi, B., 1974. Metamorphicproblems of south Iran. MemoirsFaculty Engineering, Tehran University, No. 28. Sabzehei, M., 1974. Los m~langesophiolitiques de la region d’Esfandagheh(Iran Meridional)-6tude petrologique et structurale, interpretation darts le cadre Iranian. Thesis, Grenoble,306 p. Sabzehei, M., 13erberian, M., 1972. Preliminary note on the structural and metamorphichistory of the area between Dowlatabadand Esfandagheh, south-east Central Iran. Geol. Surv. Iran, Int. Rep. 30p. ; and 1st Iranian Geol. Syrup., NIOC,1973 (abst.), Schmidt, D.L, Hadley, D.G., Greenwood, W.R., Gonzalez, L., Coleman, R.G., and Broun, G.F., 1973. Stratigraphy and tectonism of the southern part of the PrecambrianShield of Saudi Arabia. Mineral Resources Bulletin, No. 8, Directorate General of Mineral Resources, Jiddeh. Stocklin, J., 1968. Structural history and tectonics of Iran: a review. Bull. Am.Assoc. petrol. Geol., 52 (7), 1229-1258. Thiele, O., et al., 1968. Explanatory text of the GolpayganQuadranglemap,1,250,£120. Geol. Surv. lran, Rep. 17, 24 p. Watters, W.A., Sabzehei, M., 1970. Preliminary report, geology and topography of the metamorphic and igneous complexof the central part of the Neyriz Quadrangle. Geol. Surv. Iran, Int. Rep.