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Paleozoic to Triassic ocean opening and closure preserved in Central Iran: Constraints from the geochemistry of meta-igneous rocks of the Anarak area

July 2013
Lithos 172(12):267-287

July 2013
172(12):267-287

DOI:10.1016/j.lithos.2013.02.009

Authors:

David Buchs

Cardiff University

Sasan Bagheri

University of Sistan and Baluchestan

Laure Martin

University of Western Australia

Joerg Hermann

Universität Bern

Show all 5 authorsHide

The Anarak area belongs to an ophiolitic belt along the northern border of the Central-East Iranian Microcontinent, and is thought to contain fragments of the former Paleotethys and Neotethys oceans. A wide range of meta-igneous rocks from the Late Paleozoic to Triassic Anarak Metamorphic Complex (AMC) and nearby Meraji area have been studied to constrain the origins and modes of emplacement of oceanic remnants in Central Iran. Our samples occur as layers and lenses embedded in extensive sequences of deformed meta-sediments and smaller bodies of serpentinized ultramafic rocks. Petrographical and geochemical data combined with field and satellite observations allow recognition of seven types of meta-igneous rocks preserved from low grade to blueschist facies conditions. Their origins based on relative abundances of immobile trace elements include subduction zone, mid-ocean ridge, ocean intraplate, and continental rift settings. These data and existing geochronological constraints show the AMC formed an accretionary complex formed/exhumed incrementally during the Carboniferous, Permo-triassic and Triassic. Igneous rocks from Meraji formed in the Early Devonian due to opening of the Paleotethys, and belong to a rift sequence extending over 300 km along the edge of the Central-East Iranian Microcontinent. The AMC and nearby rock associations record the evolution of the Paleotethys during a complete Wilson Cycle between ca. 450 and 225 Ma, with implications for: (1) continental rifting; (2) ocean opening; (3) subduction initiation; (4) ocean intraplate and continued mid-ocean volcanism; (5) ridge subduction; and (6) final closure of the ocean during continent–continent collision. Alternate interpretations of the Anarak metabasites are possible, but require radical departures from the widely accepted model for tectonic evolution of the Paleotethys, with the existence of Paleotethyan backarc basin(s) and Permian or earlier collision of continental blocks in Central Iran. In any case, our results show accretionary complexes preserved along suture zones contain an important record of the evolution of oceanic crust from ancient ocean basins.

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Paleozoic to Triassic ocean opening and closure preserved in Central Iran:

Constraints from the geochemistry of meta-igneous rocks of the Anarak area

David M. Buchs

a,c,

⁎, Sasan Bagheri

, Laure Martin

, Joerg Hermann

, Richard Arculus

Research School of Earth Sciences, The Australian National University, 0200 Canberra, Australia

Department of Geology, University of Sistan and Baluchestan, Iran

GEOMAR, Kiel, Germany

abstractarticle info

Article history:

Received 27 November 2012

Accepted 16 February 2013

Available online 26 February 2013

Keywords:

Accretionary complex

Subduction

Paleotethys

Central Iran

Wilson Cycle

The Anarak area belongs to an ophiolitic belt along the northern border of the Central-East Iranian

Microcontinent, and is thought to contain fragments of the former Paleotethys and Neotethys oceans. A

wide range of meta-igneous rocks from the Late Paleozoic to Triassic Anarak Metamorphic Complex (AMC)

and nearby Meraji area have been studied to constrain the origins and modes of emplacement of oceanic

remnants in Central Iran. Our samples occur as layers and lenses embedded in extensive sequences of de-

formed meta-sediments and smaller bodies of serpentinized ultramaﬁc rocks. Petrographical and geochem-

ical data combined with ﬁeld and satellite observations allow recognition of seven types of meta-igneous

rocks preserved from low grade to blueschist facies conditions. Their origins based on relative abundances

of immobile trace elements include subduction zone, mid-ocean ridge, ocean intraplate, and continental

rift settings. These data and existing geochronological constraints show the AMC formed an accretionary

complex formed/exhumed incrementally during the Carboniferous, Permo-triassic and Triassic. Igneous

rocks from Meraji formed in the Early Devonian due to opening of the Paleotethys, and belong to a rift se-

quence extending over 300 km along the edge of the Central-East Iranian Microcontinent. The AMC and near-

by rock associations record the evolution of the Paleotethys during a complete Wilson Cycle between ca. 450

and 225 Ma, with implications for: (1) continental rifting; (2) ocean opening; (3) subduction initiation;

(4) ocean intraplate and continued mid-ocean volcanism; (5) ridge subduction; and (6) ﬁnal closure of the

ocean during continent–continent collision. Alternate interpretations of the Anarak metabasites are possible,

but require radical departures from the widely accepted model for tectonic evolution of the Paleotethys, with

the existence of Paleotethyan backarc basin(s) and Permian or earlier collision of continental blocks in Cen-

tral Iran. In any case, our results show accretionary complexes preserved along suture zones contain an im-

portant record of the evolution of oceanic crust from ancient ocean basins.

1. Introduction

The Wilson Cycle postulates the evolution of ocean basins com-

mences with continental break-up (rifting) followed in sequence by

ocean spreading, subduction initiation, mid-ocean ridge subduction,

and concludes with continent–continent collision. Note that in this

simplest form, the Wilson Cycle does not consider the consequences

of creation and destruction of backarc basins, or formation, transport

and accretion of elongated slivers of preexisting continent from one

continental block to another. More generally, our understanding of

the nature and tectonic evolution of ancient ocean basins is strongly

limited by their near total subduction along convergent margins; con-

sequently, accretionary complexes that preserve fragments of former

ocean ﬂoor are the optimal locations for determining the nature and

evolution of vanished oceans (e.g. Buchs et al., 2011; Isozaki et al.,

1990; Nokleberg et al., 2000; Ueda and Miyashita, 2005). Even though

circum-Paciﬁc complexes have been extensively studied, our knowl-

edge of accretionary complexes preserved in continental orogenic

belts (e.g. Jian et al., 2009; Sayit et al., 2010) is still very limited. New

data are needed to evaluate the potential record in accretionary com-

plexes of the evolution of ocean basins during a complete Wilson Cycle.

The tectonic development of Iran during the Paleozoic and Mesozoic

is intrinsically related to the opening and closure of the Paleotethys and

Neotethys oceans, which are documented at regional scale by elongated

strips of ophiolites and mélanges juxtaposed to microcontinentalblocks

(Fig. 1). There is a consensus that the evolution of the Paleotethys

Ocean, recorded from Turkey to Thailand, was dominated by two con-

secutive events of microcontinental drift during which pieces of the

Gondwana margin migrated northwards and sutured with the southern

Eurasian margin (Berberian and King, 1981; Boulin, 1991; Golonka,

2004; Sengör, 1979; Stampﬂi and Borel, 2002; Stöcklin, 1974). The

ﬁrst drift event initiated during the Late Ordovician and Silurian in

Lithos 172–173 (2013) 267–287

⁎Corresponding author.

E-mail address: BuchsD@cf.ac.uk (D.M. Buchs).

http://dx.doi.org/10.1016/j.lithos.2013.02.009

Contents lists available at SciVerse ScienceDirect

Lithos

journal homepage: www.elsevier.com/locate/lithos

response to south-dipping subduction below Gondwana, and caused

opening of the Paleotethys in a backarc position (Stampﬂi, 2000;

Stampﬂietal.,1991). The second drift event corresponds to the migra-

tion of the Gondwanan continental sliver known as the Cimmerian

microcontinent (or several microcontinental blocks) that broke up

diachronously from Gondwana between the Late Carboniferous and

late Early Permian due to northward slab pull of the subducting

Paleotethys (Stampﬂi and Borel, 2002). Drift of the Cimmerian

microcontinent away from Gondwana allowed concurrent closure of

the Paleotethys Ocean (north of the microcontinent) and opening of

the Neotethys (south of the microcontinent). The Central-East Iranian

Microcontinent (CEIM) (Takin, 1972) is commonly considered as a

tectonized remnant of the Cimmerian microcontinent that sutured

with Eurasia in the Late Triassic during a regional Eocimmerian

orogenic event (Berberian and King, 1981; Stöcklin, 1974; Zanchi

et al., 2009a)(Fig. 1). Although this general scheme of evolution

can successfully explain Eocimmerian orogenesis in northern

Iran, the number of continental blocks forming the rest of Iran

and, therefore, the number and mode of closure of oceanic basins

in the late Paleozoic and early Mesozoic remain actually poorly un-

derstood (Zanchi et al., 2009b and references therein). We provide

here new petrographical and geochemical data for metabasites and

maﬁc igneous rocks from the Anarak Metamorphic Complex, Cen-

tral Iran, which contains the remnants of a late Paleozoic to Late

Triassic active margin (Bagheri and Stampﬂi, 2008; Zanchi et al.,

2009b). We show that metabasites and igneous rocks preserved

from low grade to blueschist facies conditions outline successive

events of accretion/exhumation, which we propose record the

complex phases of ocean evolution during a complete Wilson

Cycle.

2. Geology of the Anarak Metamorphic Complex

The Anarak Metamorphic Complex (AMC) is located at a major geo-

logical boundary between central and northern Iran at the NW border

of the CEIM (Figs. 1 and 2). It broadly consists of a tectonic assemblage

of Paleozoic to Triassic meta-sediment, meta-igneous rocks and

serpentinized ultramaﬁc rocks onlapped or tectonically interﬁngered

with Jurassic to Neogene sediments. The AMC occurs south of the Great

Kavir–Doruneh strike–slip fault (Walker and Jackson, 2004)andthe

Nakhlak area that contains Triassic sediments thrust onto ultramaﬁc

and maﬁc rocks of unclear relationship with the AMC (Alavi et al., 1997;

Bagheri, 2007; Balini et al., 2009; Davoudzadeh and Seyed-Emami,

1972). Two gabbroid samples embedded in the ultramaﬁcrocksofthe

Nakhlak area have an ~ 387 Ma age of formation determined based on zir-

con dating (Bagheri, 2007). The sediments found in the Nakhlak area in-

clude a 2400 m-thick forearc succession of turbiditic, shallow-marine

and ﬂuvial deposits (i.e. “Nakhlak Group”after Balini et al., 2009)thatre-

cord the erosion of a nearby volcanic arc and metamorphic basement,

presumably the AMC (Bagheri and Stampﬂi, 2008; Balini et al., 2009;

Zanchi et al., 2009b). A forearc origin for the Nakhlak area is further sug-

gested by supra-subduction and boninitic geochemical afﬁnities of the

~387 Ma gabbroid samples (Bagheri, 2007; Bagheri and Stampﬂi, 2008).

In the south, the AMC is thrusted upon Paleozoic sedimentary cover of

the Yazd (Cimmerian) block. In the west, the AMC is bounded by the

“coloured mélange”of the Mesozoic Nain–Baft ophiolites that corre-

sponds to the Neotethys suture in Central Iran (e.g. Ghasemi and Talbot,

2006).

The AMC is composed mostly of metapelite with minor metabasite,

marble and ultramaﬁc rocks that have been affected by Mesozoic–

Cenozoic tectonics. This assemblage is locally tectonically juxtaposed

46° 62°58°50° 54°

38°

34°

30°

26°

38°

34°

30°

26°

Oman Sea

Caspian Sea

Persian Gulf

ARABIAN

PLATE

EURASIAN

PLATE

Lut

Block

Tabas Block

Great Kavir-Doruneh

Fault

Yazd Block

Zagros fold belt and foreland

Makran

Central

Domain

CEIM

EIR

Sanadaj-Sirjan zone

Ophiolites

Major fault zones

Units with "Variscan" or

Cimmerian deformation

Neotethys sutures

Fig.2

Paleotethys sutures

Fig. 1. Map of Iran with main tectonic subdivisions, also showing ocean sutures and their spatial relationships with ophiolites and units with “Variscan”or Cimmerian deformation.

Modiﬁed after Pollastro et al., 2000; Zanchi et al., 2009b.

268 D.M. Buchs et al. / Lithos 172–173 (2013) 267–287

with Cenozoic terrigenous sediments, and does not preserve original

stratigraphic or structural relationships (Bagheri and Stampﬂi, 2008;

Zanchi et al., 2009b). Six fault-bounded units were previously recognized

in the studied area based on distinct lithostructural and metamorphic

characteristics (Bagheri and Stampﬂi, 2008; Sharkovski et al., 1984;

Zanchi et al., 2009b)(Figs. 2 and 3). The Morghab,Chah Gorbeh and Patyar

units are predominantly composed of phyllites and micaschists with

minor amounts of metabasites and felsic volcanic products. Most of the

primary textures were obliterated by syn-metamorphic polyphase

deformation, but turbiditic facies are locally preserved that suggest a

slope or deep-sea fan environment of deposition for some parts of

these units (Bagheri and Stampﬂi, 2008). The Morghab unit is exclu-

sively preserved in greenschist metamorphic conditions, whereas

greenschists and blueschists are reported from the Chah Gorbeh and

Patyar units. Blueschist samples from the Chah Gorbeh Unit indicate

a transition from blueschist- to greenschist-facies condition, with

estimated conditions of peak metamorphism of P = 0.4–0.9 GPa

and T > 300 °C (Zanchi et al., 2009b). Meter-scale layers of marble

Nain

Nakhlak

Chah Gorbeh

Lak

Patyar

Doldol

Palhavand

Meraji

(30 km E)

Biabanak Fault

Ashin

Chah Kharbozeh

Dareh Anjir

Anarak

0510 15 20 Km

Serpentinized ultramafic

rocks with minor blueschist,

263.3±1.0 Ma trondjhemites,

and altered mafic dikes.

Patyar Unit

Schistose metasediments and

metabasites with black

quartzite and dolomite. In

greenschist to blueschist facies

conditions (undated).

Doshakh Unit

Schists and slates with basalts and

gabbros in low grade metamorphic

conditions with Kungurian-Roadian,

~276-268 Ma, and late Ladinian-middle

Carnian,~240-230 Ma, conodonts.

Chah Gorbeh Unit

Schistose metasediments and

metabasites with marble. In

greenschist to blueschist facies

conditions (metamorphic ages

of ~280 and 232 Ma).

Lak Marble

Marble (undated).

Nakhlak Group

Shale, limestone, and

conglomerate (Early to Middle

Triassic).

"PALEOTETHYAN" FOREARC

"PALEOTETHYAN" ACCRETED SEQUENCES (ANARAK METAMORPHIC COMPLEX)

YAZD BLOCK

Nain-Ashin ophiolitic mélange

(Upper Cretaceous-Paleocene).

Syn-rift deposits: shallow-water

terrigenous sediment and limestones

(Upper Jurassic-Lower Cretaceous).

NEOTETHYAN SEQUENCES

PERMO-TRIASSIC DOMAIN

CARBONIFEROUS DOMAIN

TRIASSIC DOMAIN

Morghab Unit

Schistose metasediments and

metabasites in greenschist facies

conditions with metamorphic ages

of ~334 to 320 Ma.

Flysch, shallow-marine, lacustrine

and continental sediments,

with minor volcanic rocks

(Lower Cretaceous-Neogene).

fault Neotethys

suture

Paleotethys

suture

thrust

locality

and road

Limestone, sandstone/siltstone,

shale, marl, and dolomite

(Lower Palaeozoic to Middle

Triassic).

33°15'N

33°30'N

54°00'E

53°45'E

53°30'E

Anarak

Metamorphic

Complex

Nakhlak

Nain-Ashin

ophiolitic

mélange

Yazd

Block

Neotethyan

sediments

Fig. 2. Simpliﬁed geological map of the Anarak area (after Bagheri and Stampﬂi, 2008). The inset shows the major complexes of the area.

269D.M. Buchs et al. / Lithos 172–173 (2013) 267–287

or black cherts and dolomites are included in the Chah Gorbeh and Patyar

units, respectively; they do not occur in the Morghab Unit. Bagheri and

Stampﬂi (2008) provide 333.65 ± 2.26 and 320.39 ± 1.72 Ma meta-

morphic ages for the Morghab Unit using

Ar/

Ar step-heating on

two muscovite–schists. A similar 326.50 ± 1.79 Ma metamorphic age

is reported for a sample of muscovite–gneiss tectonically juxtaposed

with the Morghab Unit south of Lak (i.e. the “Palhavand gneiss subunit”

after Bagheri and Stampﬂi, 2008). A 232.80 ± 2.35 Ma total fusion age

was also provided for a metabasalt and a metagreywacke from the

Chah Gorbeh Unit based on a stilpnomelane separate. These ages

are in broad agreement with previous K–Ar radiometric ages

obtained on mineral separates and bulk rock samples, which range

between 420 and 208 Ma with a main cluster between 375 and

300 Ma (Sharkovski et al., 1984).

Ultramaﬁc rocks of unclear origin occur essentially as large slivers

of serpentinite within the Chah Gorbeh Unit in the central part of

the AMC, or smaller slivers along the Morghab Unit and Biabanak

Fault in the south of the complex (Lensch and Davoudzadeh, 1982).

The ultramaﬁc rocks include mostly schistose harzburgites with

chromian spinel porphyroclasts. Domains with a preserved massive tex-

ture locally occur. These contain clinopyroxene and spinel with Al-rich

original cores that possibly represent a primary phase (Sharkovski et

al., 1984; Zanchi et al., 2009b). Locally in the central part of the AMC,

the serpentinites comprise decametric-scale lenses of variously-

deformed pillow lavaspreserved in blueschist metamorphic conditions,

trondhjemites, gabbros, and dikes of maﬁc rocks suggesting several

phases of magmatism and metamorphism (Bagheri and Stampﬂi,

2008; Sharkovski et al., 1984; Torabi, 2011, 2012; Zanchi et al.,

2009b). The blueschists have an OIB geochemical afﬁnity (Bagheri

and Stampﬂi, 2008; Torabi, 2011), whereas the trondjhemites have

a supra-subduction origin and yielded a U–Pb zircon age of 262.3 ±

1.0 Ma (Bagheri and Stampﬂi, 2008; Torabi, 2012). A poorly

constrained 285.42 ± 1.65

Ar/

Ar age based on a crossite separate

was also reported from a blueschist basalt embedded in the ultramaﬁc

rocks (Bagheri and Stampﬂi, 2008).

The Lak Marble comprises thick layers of meta-carbonate essentially

devoid of silicicilastic or terrigenous component, juxtaposed with other

metamorphic units along faulted contacts. Sharkovski et al. (1984) de-

scribe this unit as a series of klippen and propose an Early–?Middle

Cambrian age based on the occurrence of archaeocyathids. However,

these fossils have not been illustrated and could not be encountered

by subsequent workers. Bagheri and Stampﬂi (2008) propose that

the Lak Marble represent the remnant of Permian atoll carbonates

originally deposited on top of OIB-like metabasites found in the

Patyar Unit.

The Doshakh Unit occurs in the Palhavand area, south of the AMC. It is

composed of a low-grade metamorphic succession that includes pillow

lavas, gabbros (as blocks or small stocks), shales, marly limestones and

schistose greywackes (Bagheri, 2007; Bagheri and Stampﬂi, 2008).

Conodonts in the marly limestones provided a Kungurian–Roadian

(~276–268 Ma) age (Bagheri, 2007). The Chah Palang area located

~40 km SW of Anarak may represent a lateral equivalent of the sequence

in the Palhavand area and provided a late Ladinian–middle Carnian

(~240–230 Ma) age based on conodont assemblages in a chert sample

(Bagheri and Stampﬂi, 2008). An alkaline within-plate or OIB geochem-

ical afﬁnity has been reported for the pillow lavas and gabbros in the

Palhavand area (Bagheri and Stampﬂi, 2008; Bayat and Torabi, 2011).

Arc-derived material and blueschist facies rocks demonstrate that

the AMC and Nakhlak areas constitute an ancient arc-trench and sub-

duction system, which was active from the Paleozoic and sutured

with a Cimmerian block in the Late Triassic (Bagheri and Stampﬂi,

2008; Zanchi et al., 2009b). The original site of emplacement of the

complex remains however unclear (Zanchi et al., 2009b and refer-

ences therein). The AMC could have formed further north along the

main Paleotethys suture and was subsequently displaced southward

in association with counterclockwise rotation of the CEIM (Bagheri

and Stampﬂi, 2008; Davoudzadeh et al., 1981) or, alternatively, the

AMC could be parautochthonous (Zanchi et al., 2009b), suggesting

formation along an oceanic basin distinct from the main Paleotethys

Ocean or along a marginal branch of this ocean. Bagheri and Stampﬂi

(2008) propose that the AMC represents an accretionary complex of

the Paleotethys Ocean, with a “Variscan”, Permo-triassic and Triassic ac-

cretionary unit. They further propose that OIB represents the accretion

of a large, structurally well-preserved seamount in the Permo-triassic

unit and several smaller seamounts in the Triassic (i.e. Doshakh)

unit. Bayat and Torabi (2011) consider however, that alkaline igne-

ous rocks in the Triassic unit are part of a larger “lamprophyre prov-

ince”in Central Iran, which includes suites of intrusives found in the

Bayazeh, Chah Palang, Meraji and Palhavand areas (Fig. 2 in Bayat

and Torabi, 2011), and formed by low degrees of mantle melting in

response to continental rifting. In order to better constrain the ori-

gins of the AMC, we provide here new data on the composition

and spatial distributions of metabasites collected in distinct units

of the AMC. We also discuss possible origins of newly-analyzed alka-

line rocks from the Meraji area, which may share a similar origin

with alkaline igneous rocks of the Doshakh Unit.

3. Analytical techniques

Landsat 7 ETM + data complementing ﬁeld work allowed gener-

al observations of the structures and composition of the AMC. These

data were processed in a geographic information system (ArcGIS) to

produce a natural color composite image based on bands 1 (blue-green),

1000

5 km

2000

Altitude (m)

1500

1000

2000

1500

LakPatyar

Patyar Unit

Chah Gorbeh Unit

Permo-triassic domain

Carboniferous domain

Triassic domain

Morghab Unit

Doshakh Unit

Lak Marble

Serpentinized ultramafic rocks

Neotethyan flysch

Yazd Block

Dol DolChah Gorbeh

AB C

Dareh Anjir

Sebarz

Fig. 3. Cross-section views of the Anarak Metamorphic Complex (location shown in Fig. 2).

270 D.M. Buchs et al. / Lithos 172–173 (2013) 267–287

Group 1 (NMORB-like)

Group 2 (EMORB-like)

Group 3 (BABB-like)

Group 4 (Arc-like)

Group 5 (OIB-like)

Geological domains Geochemical groups

Carboniferous

33°25'

33°20'

33°15'

33°10'

53°30' 53°35' 53°40' 53°45' 53°50' 53°55'

33°25'

33°20'

33°15'

33°10'

53°30' 53°35' 53°40' 53°45' 53°50' 53°55'

Permo-triassic

Triassic

5 km

Fig. 4. Satellite views of the studied area with location of analyzed samples and interpreted geological domains in the Anarak Metamorphic Complex. (a) Natural color composite

image based on Landsat 7 ETM + data, bands 1 (blue-green), 2 (green) and 3 (red). (b) Grayscale image based on Landsat 7 ETM + data, band 5 (Mid-IR)/band 7 (Short Wave IR)

ratio. Larger symbols represent samples analyzed in this study; smaller symbols represent a selection of samples analyzed by Bagheri and Stampﬂi (2008).

271D.M. Buchs et al. / Lithos 172–173 (2013) 267–287

2(green)and3(red)(Fig. 4a), and a grayscale image based on band 5

(Mid-IR)/band 7 (Short Wave IR) ratio (Fig. 4b).

Bulk rock samples of metabasite were reduced to powder at the

Research School of Earth Sciences (RSES), Australian National Universi-

ty, using a pre-contaminated agate mill. The Environmental Laboratory

at the Central Analytical Facility of the University of Stellenbosch deter-

mined major element contents by X-ray ﬂuorescence (XRF) and mea-

sured loss on ignition (LOI). Trace element contents were measured

by laser ablation inductively coupled plasma source mass spectrometry

(LA-ICP-MS) on tetraborate glasses at the RSES following procedures

given in Longerich et al. (1996) and Eggins (2003). Glass disks used

for LA-ICP-MS analyses were prepared by fusion of 0.5000 g dried sam-

ple powder and 1.5000 g of “12–22”eutectic lithium metaborate–lithi-

um tetraborate. A pulsed 193 nm ArF Excimer laser, with 50 mJ energy

at a repetition rate of 5 Hz, coupled to an Agilent 7500S quadrupole

ICP-MS were used. A synthetic glass (NIST 612) was used as standard

material. Four ablations with a 120 μm pit size were used to obtain

the composition of each sample. Si values obtained from XRF analysis

were used as internal standard. BCR-2 standard was additionally mea-

sured in each analytical series to check quality and consistency of the

results.

Comparison of our geochemical results with former data from the

AMC was limited by the use of different analytical techniques in

different studies (e.g., measurement of Th, Nb, Ta, Zr and Y by XRF

in Bagheri and Stampﬂi, 2008), an absence of analysis of some partic-

ular elements (e.g. no Nb measurements for some samples in Bayat

and Torabi, 2011), or elemental variations probably related to analyti-

cal uncertainties. Therefore, the use of former regional data was mostly

restricted to PM-normalized rare earth element (REE) diagrams and

semi-quantitative assessment of available Nb, Zr and Y contents in dia-

grams of tectonic discrimination.

4. Results

The AMC can be subdivided into Carboniferous, Permo-triassic

and Triassic domains that are generally in accordance with geologi-

cal or accretionary units deﬁned by previous studies (Bagheri and

Stampﬂi, 2008; Sharkovski et al., 1984). The Carboniferous domain

corresponds to the Morghab Unit, the Permo-triassic domain corre-

sponds to the Chah Gorbeh, Patyar, Lak and ultramaﬁcunits,andthe

Triassic domain corresponds to the Doshakh Unit south of the AMC.

This subdivision is in good agreement with lithological differences

observed by ﬁeld work and remote sensing, as well as differences

in the composition and metamorphic grade of embedded metabasites

(Fig. 4). Landsat 7 ETM + data allowed remote recognition of meta-

igneous rocks interlayered with meta-sediments in low grade to

blueschist facies conditions. Meta-igneous rocks appear as dark areas

on a greyscale image showing ratio of bands 5/7 (Fig. 4b). 35 samples

of igneous and meta-igneous rocks were analyzed in the AMC and

Meraji area (Tables 1–3). The rocks from the AMC were subdivided

into six groups of distinct petrological afﬁnities: (1) Normal mid-ocean

ridge (NMORB)-like; (2) Enriched mid-ocean ridge (EMORB)-like;

(3) Backarc basin basalt (BABB)-like; (4) arc-like; and (5) two types

of ocean island basalt (OIB)-like. Spatial relationships, petrography

and geochemistry of these rocks are detailed below. In contrast, rocks

from the Meraji area have broadly similar OIB-like afﬁnities. Their con-

textual and geochemical characteristics are out of the primary scope of

Table 1

Sample type and location.

Sample Rock type Metamorphic facies Geochemical group Unit/area Geological domain Coordinates (WGS84)

Latitude Longitude

DS09-001 Greenschist Greenschist Group 3 (BABB-like) Chah Gorbeh Permo-triassic 33.3232 53.7082

DS09-002 Blueschist Blueschist Group 5a (OIB-like) Ultramaﬁc rocks Permo-triassic 33.3952 53.7543

DS09-006 Gabbro Greenschist Group 2 (EMORB-like) Ultramaﬁc rocks Permo-triassic 33.3945 53.7262

DS09-008 Greenschist Greenschist Group 5a (OIB-like) Chah Gorbeh Permo-triassic 33.3449 53.6847

DS09-009 Greenschist Greenschist Group 5a (OIB-like) Chah Gorbeh Permo-triassic 33.3449 53.6847

DS09-010 Greenschist Greenschist Group 4 (Arc-like) Chah Gorbeh Permo-triassic 33.3464 53.6855

DS09-011 Greenschist Greenschist Group 3 (BABB-like) Chah Gorbeh Permo-triassic 33.3488 53.6878

DS09-014 Greenschist Greenschist Group 3 (BABB-like) Patyar Permo-triassic 33.2974 53.9174

DS09-015 Greenschist Greenschist Group 3 (BABB-like) Chah Gorbeh Permo-triassic 33.3523 53.6800

DS09-018 Greenschist Greenschist Group 3 (BABB-like) Chah Gorbeh Permo-triassic 33.3647 53.6651

DS09-019 Greenschist Greenschist Group 3 (BABB-like) Chah Gorbeh Permo-triassic 33.3533 53.6795

DS09-020 Greenschist Greenschist Group 4 (Arc-like) Morghab Carboniferous 33.3326 53.6182

DS09-022 Greenschist Greenschist Group 4 (Arc-like) Chah Gorbeh Permo-triassic 33.3379 53.6183

DS09-024 Greenschist Greenschist Group 4 (Arc-like) Morghab Carboniferous 33.3309 53.5918

DS09-025 Greenschist Greenschist Group 5a (OIB-like) Chah Gorbeh Permo-triassic 33.3546 53.7040

DS09-026 Microgabbro (dike) Greenschist Group 2 (EMORB-like) Ultramaﬁc rocks Permo-triassic 33.4442 53.5280

DS09-027 Basalt (dike) Greenschist Group 2 (EMORB-like) Ultramaﬁc rocks Permo-triassic 33.4442 53.5280

DS09-028 Greenschist Greenschist Group 5a (OIB-like) Chah Gorbeh Permo-triassic 33.4216 53.5107

DS09-030 Greenschist (dike) Greenschist Group 2 (EMORB-like) Ultramaﬁc rocks Permo-triassic 33.4353 53.5150

DS09-032 Greenschist (dike) Greenschist Group 2 (EMORB-like) Ultramaﬁc rocks Permo-triassic 33.4214 53.7655

DS09-034 Gabbro Low P-T Group 5b (OIB-like) Doshakh Triassic 33.1840 53.8935

DS09-035 Basalt Low P-T Group 5b (OIB-like) Doshakh Triassic 33.1946 53.9170

DS09-036 Basalt Low P-T Group 5b (OIB-like) Doshakh Triassic 33.1924 53.9096

DS09-037 Basalt Low P-T Group 5b (OIB-like) Doshakh Triassic 33.1920 53.9080

DS09-040 Basalt Low P-T Group 5b (OIB-like) Doshakh Triassic 33.1802 53.9190

DS09-041 Basalt Low P-T Group 5b (OIB-like) Doshakh Triassic 33.1851 53.9221

DS09-042 Gabbro Low P-T Group 5b (OIB-like) Doshakh Triassic 33.1851 53.9221

DS09-043 Nepheline syenite Low P-T Meraji Meraji area Undeﬁned 33.1782 54.2324

DS09-044 Nepheline syenite Low P-T Meraji Meraji area Undeﬁned 33.1782 54.2324

DS09-045 Alkaline gabbro Low P-T Meraji Meraji area Undeﬁned 33.1906 54.2480

DS09-046 Alkaline gabbro Low P-T Meraji Meraji area Undeﬁned 33.1874 54.2528

DS09-047 Nepheline syenite Low P-T Meraji Meraji area Undeﬁned 33.1853 54.2554

DS09-048 Nepheline syenite Low P-T Meraji Meraji area Undeﬁned 33.1853 54.2554

DS09-049 Blueschist Blueschist Group 1 (NMORB-like) Chah Gorbeh Permo-triassic 33.4311 53.7543

DS09-050 Blueschist Blueschist Group 5a (OIB-like) Chah Gorbeh Permo-triassic 33.4315 53.7470

272 D.M. Buchs et al. / Lithos 172–173 (2013) 267–287

this paper and only brieﬂy described below for comparison with the

AMC.

4.1. Spatial relationships

Important loss of original lithostratigraphic relationships exists in

the Carboniferous and Permo-triassic domains, with at least three

phases of deformation seen from outcrop to regional scales (Fig. 4).

Metabasites in these domains occur as elongated, schistose or de-

formed bodies that range broadly from a few to 500 m in thickness

and a few meters to several kilometers in length. The Carboniferous do-

main (Morghab Unit) includes arc-like with possible NMORB, EMORB

and BABB-like greenschist metabasites embedded in a volumetrically-

predominant matrix of phyllite and micaschist (i.e. meta-sediment).

In the Permo-triassic domain, Chah Gorbeh and Patyar Units

include NMORB-like, BABB-like, arc-like and OIB-like greenschist-

blueschist metabasites that, similar to metabasites of the Carbonifer-

ous domain, occur as elongated rock bodies in an abundant matrix of

meta-sediment. However, layers of metabasites found in the Car-

boniferous domain (Morghab unit) are generally thinner and more

abundant than those in the Permo-triassic domain (Fig. 4). In the

Permo-triassic domain (Chah Gorbeh Unit), thin (10–50 m) marble

layers occur locally in contact with layers of metabasite, which

may represent original sequences of volcanic rocks associated with

their sedimentary cover. Metabasites are locally juxtaposed with

the Lak Marble along faulted contacts and it is therefore unclear

whether the marble represents an original cover of the metabasites.

Unequivocal observations supporting a primary stratigraphic relation-

ship between the marble and metabasites (such as deformed basalt

breccias or dikes within the marble) have not been made. Metabasites

of the Permo-triassic domain also occur in serpentinized ultramaﬁc

rocks as EMORB-like greenschist dikes, decametric-scale lenses of

OIB-like greenschist–blueschist basalts, and gabbroid stocks with a

cumulative fabric. Basalts in blueschist metamorphic conditions lo-

cally preserve a pillow lava fabric.

The Triassic domain (i.e. Doshakh Unit south of the AMC) includes

decametric-scale lenses of OIB-like alkaline basalts and gabbros inter-

calated with siliciclastic and carbonate sediments. Sampled rocks

have a preserved igneous fabric that contrasts markedly with strong

deformation seen in the Carboniferous and Permo-triassic domains.

Table 2

Major elements (analyzed by XRF).

Sample SiO

wt.%

TiO

wt.%

MnO

wt.%

MgO

wt.%

CaO

wt.%

Total

wt.%

LOI

wt.%

Group 1 (NMORB-like)

DS09-049 48.57 1.34 15.05 12.93 0.18 7.74 10.24 2.91 0.03 0.12 99.12 3.72

Group 2 (EMORB-like)

DS09-006 33.05 1.90 22.16 16.46 0.25 19.68 5.04 0.07 1.52 0.26 100.39 11.79

DS09-026 49.28 1.38 15.50 9.77 0.17 7.91 10.49 4.06 0.10 0.18 98.85 2.85

DS09-027 40.01 2.11 20.74 14.60 0.20 8.56 9.34 2.30 0.66 0.35 98.88 5.69

DS09-030 47.90 1.62 17.70 10.45 0.13 5.64 10.41 5.17 0.32 0.19 99.52 7.56

DS09-032 40.67 2.18 29.93 5.88 0.13 3.45 11.66 0.07 4.83 0.23 99.02 5.30

Group 3 (BABB-like)

DS09-001 50.17 1.34 14.16 13.06 0.19 6.30 9.73 2.99 0.82 0.13 98.89 2.42

DS09-011 52.60 1.59 14.30 12.24 0.17 4.94 10.91 2.15 0.21 0.15 99.25 2.93

DS09-014 56.74 0.47 13.49 8.27 0.15 6.68 9.76 2.17 1.65 0.05 99.44 2.48

DS09-015 48.57 1.71 14.80 12.60 0.18 7.07 10.68 2.82 0.52 0.15 99.11 2.67

DS09-018 54.79 1.44 13.19 12.11 0.19 5.72 8.58 3.27 0.06 0.16 99.50 2.98

DS09-019 49.72 1.49 15.07 12.54 0.18 6.21 11.98 1.88 0.14 0.14 99.35 3.57

Group 4 (Arc-like)

DS09-010 49.98 1.50 14.00 10.97 0.15 5.54 15.09 1.52 0.07 0.12 98.95 1.75

DS09-020 76.16 0.21 12.22 1.58 0.01 0.42 0.32 0.89 7.92 0.05 99.79 1.01

DS09-022 50.45 1.04 16.52 10.47 0.15 5.65 10.64 3.43 0.49 0.11 98.95 2.26

DS09-024 54.24 1.86 17.31 10.92 0.15 4.04 6.94 3.40 0.11 0.33 99.30 3.28

Group 5a (OIB-like)

DS09-002 58.06 2.10 12.03 10.57 0.08 5.48 3.84 5.83 0.71 0.44 99.15 3.31

DS09-008 46.65 2.61 12.75 14.72 0.16 8.75 10.36 2.26 0.68 0.06 99.00 3.63

DS09-009 47.22 1.96 12.26 13.19 0.17 9.21 12.36 2.10 0.19 0.13 98.78 2.94

DS09-025 46.32 2.04 16.30 12.48 0.16 7.77 9.55 2.86 0.85 0.34 98.66 3.55

DS09-028 51.22 3.16 15.29 14.80 0.16 5.12 5.12 4.38 0.26 0.27 99.80 6.40

DS09-050 47.45 3.69 17.13 12.76 0.15 2.38 9.77 3.99 0.77 0.60 98.69 2.75

Group 5b (OIB-like)

DS09-034 46.78 2.13 17.31 11.01 0.15 5.72 12.39 3.27 0.22 0.36 99.35 5.17

DS09-035 54.15 1.80 18.76 8.21 0.19 2.54 3.39 7.26 1.23 1.14 98.67 2.62

DS09-036 47.31 3.41 18.04 11.10 0.14 3.82 7.14 4.04 3.05 0.98 99.03 2.41

DS09-037 46.65 3.60 16.08 15.48 0.20 4.74 5.02 4.88 1.57 0.85 99.05 3.54

DS09-040 45.24 2.33 13.77 12.44 0.17 7.72 12.85 4.09 0.25 0.38 99.24 5.57

DS09-041 49.38 2.97 17.60 14.48 0.15 1.91 5.15 6.66 0.20 0.81 99.30 4.02

DS09-042 50.82 2.18 17.30 12.36 0.21 1.88 6.31 6.08 0.77 0.53 98.45 2.06

Meraji area (OIB-like)

DS09-043 50.13 1.73 17.08 12.54 0.05 2.85 4.07 4.43 5.33 1.04 99.25 1.48

DS09-044 51.36 1.70 17.70 8.70 0.06 2.73 5.01 4.49 5.34 1.02 98.11 1.76

DS09-047 51.18 2.05 18.05 10.97 0.03 4.00 1.80 5.22 4.45 1.00 98.75 2.57

DS09-048 56.09 1.46 18.53 6.77 0.04 1.56 4.57 7.62 2.11 0.40 99.15 3.22

DS09-045 48.29 2.06 15.62 12.54 0.03 7.64 3.03 4.07 4.64 0.65 98.57 2.41

DS09-046 47.44 1.73 18.16 10.83 0.10 7.04 9.20 3.40 1.04 0.19 99.13 3.67

273D.M. Buchs et al. / Lithos 172–173 (2013) 267–287

Table 3

Trace elements (analyzed by LA-ICP-MS).

Sc V Cr Mn Ni Cu Zn Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U

Sample ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

Group 1 (NMORB-like)

DS09-049 49.5 378 109 1296 65 99 81 0.3 184 30.5 75 3.3 0.03 8 4.15 11.1 1.73 9.56 3.35 1.24 4.31 0.77 5.57 1.16 3.59 0.52 3.48 0.50 2.09 0.22 3.39 0.35 0.21

Group 2 (EMORB-like)

DS09-006 36.4 299 717 1674 370 24 90 27.8 46 36.6 148 13.0 2.00 246 11.5 26.2 3.50 17.8 5.26 1.72 6.10 1.02 7.08 1.48 4.27 0.62 4.02 0.58 3.73 0.80 2.19 1.30 0.25

DS09-026 43.6 260 125 1144 67 56 56 0.8 413 24.5 104 13.7 0.10 69 11.6 23.2 3.07 14.2 3.68 1.31 4.08 0.68 4.64 0.94 2.75 0.40 2.58 0.38 2.54 0.89 0.97 1.32 0.28

DS09-027 65.0 449 27 1497 39 234 67 4.6 2261 42.9 157 20.1 0.12 798 17.5 34.6 4.54 21.4 5.72 1.95 6.72 1.12 7.89 1.64 4.85 0.72 4.95 0.76 3.97 1.35 2.89 1.66 0.43

DS09-030 45.0 323 70 851 72 57 77 4.4 169 27.1 107 15.9 0.60 31 13.2 27.4 3.37 15.6 4.06 1.35 4.38 0.76 5.24 1.10 3.09 0.47 3.13 0.45 2.75 0.97 2.41 1.62 0.77

DS09-032 71.8 510 519 897 256 134 56 84.9 1255 49.0 131 13.8 1.76 997 10.1 24.3 3.55 18.7 6.26 2.25 7.67 1.33 9.45 1.99 5.63 0.79 5.09 0.71 3.51 0.70 22.8 1.05 19.42

Group 3 (BABB-like)

DS09-001 46.0 340 92 1362 54 127 77 16.7 216 24.5 86 5.7 0.50 174 8.36 18.5 2.48 12.0 3.39 1.14 4.03 0.67 4.64 0.97 2.78 0.39 2.73 0.40 2.31 0.37 2.42 1.19 0.28

DS09-011 40.0 327 74 1231 49 138 73 4.1 95 27.1 108 7.6 0.23 88 6.83 17.7 2.72 14.4 4.19 1.16 4.86 0.80 5.40 1.06 3.06 0.44 2.77 0.39 2.88 0.51 2.14 1.02 0.23

DS09-014 44.2 228 73 1039 41 4 42 37.9 360 9.9 23 1.2 0.72 368 2.41 5.20 0.74 3.80 1.18 0.47 1.47 0.25 1.87 0.39 1.18 0.16 1.14 0.17 0.68 0.08 2.81 0.36 0.11

DS09-015 42.2 320 204 1314 79 100 73 13.2 163 23.2 97 7.0 0.48 90 7.51 18.8 2.65 13.3 3.88 1.28 4.35 0.70 4.60 0.92 2.55 0.36 2.27 0.31 2.57 0.45 0.80 0.88 0.22

DS09-018 37.6 340 60 1342 32 48 77 1.2 144 32.3 90 4.6 0.09 21 5.74 15.2 2.23 12.1 3.93 1.30 5.17 0.82 5.98 1.26 3.72 0.55 3.76 0.54 2.50 0.30 1.94 0.86 0.31

DS09-019 37.2 336 98 1287 72 105 76 3.5 92 22.9 88 7.0 0.21 33 6.81 17.4 2.47 12.4 3.71 1.05 4.56 0.66 4.43 0.91 2.53 0.36 2.31 0.30 2.35 0.44 1.95 0.95 0.23

Group 4 (Arc-like)

DS09-010 40.3 316 133 1118 60 73 60 1.1 185 25.8 117 8.2 0.06 19 13.6 27.9 3.72 17.6 4.65 1.48 5.00 0.77 5.11 1.02 2.85 0.41 2.65 0.36 3.13 0.55 4.58 1.55 0.33

DS09-020 8.5 49 12 75 9 8 22 133.4 49 39.2 188 7.5 0.62 910 62.4 107 12.4 46.5 8.67 0.99 7.76 1.22 7.43 1.42 4.21 0.59 3.72 0.58 5.31 0.68 11.3 15.61 2.29

DS09-022 35.4 255 114 1070 63 81 64 10.8 213 19.1 76 5.6 0.35 104 9.01 18.4 2.38 11.3 3.08 1.04 3.36 0.54 3.68 0.76 2.20 0.31 2.07 0.29 1.99 0.37 2.88 1.22 0.27

DS09-024 34.0 351 4 1010 9 23 90 1.6 175 50.4 128 5.9 0.11 36 23.7 50.8 6.59 30.7 8.02 2.18 8.57 1.35 9.19 1.92 5.48 0.79 5.13 0.77 3.62 0.33 5.97 5.51 1.53

Group 5a (OIB-like)

DS09-002 26.1 230 384 527 176 181 64 11.8 40 26.1 134 25.1 0.57 38 19.3 39.9 5.33 25.3 6.27 2.13 6.29 0.87 5.33 0.96 2.37 0.29 1.71 0.22 3.26 1.53 1.29 1.90 0.28

DS09-008 39.2 310 366 1186 197 232 90 15.2 1993 26.5 198 20.5 0.76 237 19.2 45.6 6.25 29.5 7.46 2.54 7.03 1.04 6.27 1.11 2.87 0.38 2.38 0.32 4.80 1.32 3.35 2.24 0.28

DS09-009 32.6 211 555 1265 365 126 74 4.2 1097 22.6 146 14.3 0.25 41 13.4 29.1 4.21 21.0 5.44 1.73 5.52 0.80 4.88 0.90 2.39 0.32 1.94 0.26 3.81 0.98 2.55 1.40 0.24

DS09-025 32.7 242 283 1159 200 52 82 12.7 471 27.3 179 26.2 0.21 179 21.4 41.6 5.19 23.0 5.47 1.84 5.64 0.85 5.59 1.09 2.95 0.39 2.51 0.37 4.21 1.72 2.72 3.17 0.61

DS09-028 41.4 429 141 1135 77 235 99 4.3 73 30.3 195 15.9 0.46 25 17.9 41.6 5.91 29.2 7.22 2.23 7.02 1.01 6.50 1.25 3.38 0.46 2.95 0.43 5.03 1.10 3.02 1.10 0.52

DS09-050 27.3 203 37 1060 80 11 123 16.5 684 41.7 313 35.4 0.75 237 37.2 74.6 9.20 41.5 10.1 3.78 9.88 1.44 8.79 1.61 4.21 0.55 3.48 0.45 7.40 2.36 6.29 5.04 0.85

Group 5b (OIB-like)

DS09-034 38.5 291 44 1071 80 207 67 3.4 896 22.1 149 31.6 0.19 164 25.7 50.5 6.25 27.6 6.19 2.06 5.72 0.82 5.05 0.90 2.29 0.29 1.82 0.25 3.84 1.91 4.52 3.03 0.66

DS09-035 5.9 36 4 1317 4 25 114 26.5 373 34.0 529 91.4 0.54 248 72.9 152.3 17.5 70.4 12.9 3.54 10.1 1.32 7.78 1.36 3.45 0.46 2.80 0.39 11.2 5.77 3.79 10.0 5.13

DS09-036 16.9 103 6 994 12 38 89 37.8 1732 29.8 455 92.8 0.32 1130 69.5 138.9 16.3 68.1 13.3 4.00 10.6 1.36 7.34 1.20 2.85 0.33 2.00 0.26 9.94 5.87 5.54 8.56 1.55

DS09-037 11.2 125 6 1398 21 41 105 33.3 323 29.8 404 83.2 0.74 180 59.8 119.9 13.9 57.3 11.4 3.31 9.26 1.25 6.99 1.19 2.95 0.38 2.24 0.31 8.86 5.27 3.91 7.86 1.65

DS09-040 29.8 246 403 1187 249 68 94 4.3 227 23.3 206 33.6 0.15 158 25.7 52.7 6.6 28.7 6.33 1.94 5.77 0.84 5.22 0.95 2.49 0.34 2.16 0.29 4.80 2.15 2.93 3.08 0.69

DS09-041 13.6 118 6 1036 12 40 77 3.4 287 34.5 327 61.0 0.14 209 47.0 95.8 11.5 50.1 10.4 3.34 9.34 1.29 7.60 1.38 3.50 0.46 2.85 0.39 7.28 3.77 1.68 5.49 1.34

DS09-042 8.0 69 4 1444 3 53 92 7.4 1145 42.3 392 74.7 0.08 504 48.4 101.4 11.9 50.6 10.7 3.20 9.60 1.45 8.88 1.68 4.51 0.63 3.87 0.54 8.04 4.38 1.62 6.42 1.45

Meraji area (OIB-like)

DS09-043 9.4 65 14 343 13 7 27 96.1 394 27.1 431 89.0 1.57 997 73.3 145 15.5 58.9 9.60 2.74 7.08 0.95 5.85 1.05 2.86 0.39 2.45 0.33 9.29 4.99 3.21 8.26 1.59

DS09-044 10.9 62 13 375 12 30 24 96.6 493 27.1 434 89.1 1.82 826 84.9 165 17.6 66.8 10.8 2.80 7.94 1.04 5.93 1.06 2.80 0.37 2.44 0.33 9.38 5.05 2.29 8.75 1.56

DS09-047 12.6 85 21 196 20 9 25 85.5 247 17.1 399 87.4 2.09 546 61.9 124 13.1 50.2 8.00 2.28 5.78 0.73 3.97 0.70 1.95 0.29 1.93 0.30 8.75 5.03 1.44 8.69 1.46

DS09-048 10.0 45 4 260 4 56 18 60.7 403 23.1 445 94.1 2.00 299 77.6 141 15.0 55.5 9.06 2.61 6.71 0.89 5.11 0.91 2.48 0.35 2.39 0.35 9.66 5.51 4.32 10.5 1.87

DS09-045 23.4 175 207 161 127 8 25 118.8 234 21.2 281 53.8 3.70 323 48.9 95.5 10.4 40.9 7.15 2.31 5.73 0.76 4.57 0.84 2.23 0.30 1.90 0.26 6.15 3.05 1.76 4.87 0.98

DS09-046 32.6 248 208 642 68 24 55 27.3 371 16.5 111 11.7 1.15 174 10.9 24.5 3.21 15.4 3.80 1.34 3.70 0.55 3.59 0.65 1.80 0.25 1.54 0.21 2.66 0.73 3.08 0.99 0.30

Standard

BGR-2G 33.2 429 14 1542 12 17 155 45.2 331 29.9 166 12.8 1.09 673 23.6 50.4 6.16 27.2 6.25 1.84 5.84 0.89 5.80 1.16 3.26 0.47 3.14 0.44 4.18 0.76 11.0 5.58 1.59

2σ(n = 28) 5.3 22 1 52 1 1 12 2.4 41 5.5 30 1.4 0.07 64 3.64 3.12 0.77 3.93 1.05 0.26 1.07 0.15 1.03 0.21 0.62 0.09 0.57 0.09 0.77 0.13 0.84 0.95 0.10

274 D.M. Buchs et al. / Lithos 172–173 (2013) 267–287

Sequences in the Triassic domain occur as lava ﬂows, pillow lavas

intercalated/capped with recrystallized limestone and red shale, as

well as dikes/sills cross-cutting gabbros. These sequences are clearly

different from those of the Meraji area, where several hundred meters

of poorly-deformed dolomitic–siliceous sediments are intruded by

sills of altered alkaline gabbros and nepheline syenites up to ~ 40 m

thick.

4.2. Petrography

Petrographical observations under optical microscope show that

the analyzed samples in the AMC have a variable metamorphic im-

print ranging from low pressure–temperature conditions where the

protolith fabric is well preserved to high pressure–low temperature

conditions (HP–LT) where the protolith fabric is mostly erased by

deformation and metamorphic reactions. Rocks metamorphosed in

the greenschist facies are characterized by a paragenesis composed

of chorite + epidote + albite ± white mica, zoisite, actinolite, and

quartz. Rocks metamorphosed in the blueschist facies are charac-

terized by a paragenesis composed of glaucophane + chlorite +

epidote + magnetite + albite + quartz ± white mica. No relation-

ship was found between the metamorphic degree and composition

of the rocks, but our observations conﬁrm metamorphic differences

observed by previous studies between the Permo-triassic (greenschist–

blueschist) and Triassic (low PT) domains. A petrographic summary is

given below that supports magmatic or proximal volcaniclastic origin

of the analyzed rocks and outlines remarkable petrographical consis-

tency amongour petrogenetic groups (see Table 4 for full mineralogical

inventory of each sample).

Group 1 (NMORB-like) is represented by one greenschist sam-

pled in the Chah Gorbeh Unit (Permo-triassic domain). This sample

is homogeneously recrystallized and composed of chlorite + epidote +

actinolite + albite and quartz (Fig. 5a).

Group 2 (EMORB-like), which includes dike samples within ultra-

maﬁc rocks of the Permo-triassic domain, is represented by ﬁve rocks

with different textures and mineralogy. They are mainly metamor-

phosed in the greenschist facies, but none of them contain actinolite.

A common petrological feature of this group (gabbro DS09-006

excepted) is the presence of epidote crystals pseudomorphing former

minerals likely including feldspar. Sample DS09-006 is characterized

by a matrix composed of chlorite + titanite ± white mica, epidote

and accessoryeuhedral carbonate crystals. Dolerite DS09-026 shows

relics of magmatic hornblende ± clinopyroxene in a chlorite, epidote,

albite, quartz and oxide/titanite matrix. Sample DS09-027 is fully

recrystallized as a greenschist facies rock composed of chlorite +

epidote + albite + Fe–Ti-rich mineral ± white mica and carbonate

(Fig. 5b). Sample DS09-030 has a heterogeneous structure where

chlorite + albite + quartz + epidote-rich areas are crosscut by

carbonate-rich cracks or veinlets. Glaucophane is rare and only ob-

served as inclusions in albite crystals, indicating a strong retro-

grade overprint in greenschist facies conditions. Sample DS09-032 is

characterized by a homogeneous texture composed of large zoisite

crystals in a chlorite + white mica-rich matrix. The widespread occur-

rence of carbonates, and the high content of white mica and/or chlorite

indicates that these rocks underwent severe metasomatism, most likely

related to seaﬂoor alteration.

Group 3 (BABB-like) is represented by six rocks sampled in the

Permo-triassic domain. All samples are metamorphosed in the

greenschist facies and contain actinolite. Sample DS09-001 is com-

posed of chlorite + actinolite + albite + quartz ± white mica and Fe–

Ti oxide or titanite. Samples DS09-011 and DS09-019 are characterized

by a strong schistosity marked by Fe–Ti minerals-rich thin layers. They

are otherwise composed of chlorite + epidote + actinolite + albite +

quartz ± white mica. Sample DS09-014 is characterized by relics of pleo-

chroic brown and green hornblende in a matrix composed of actinolite +

chlorite + albite + Fe–Ti-rich minerals and white micas (Fig. 5c).

Sample DS09-015 is composed of actinolite + epidote (including zoisite

and clinozoisite) + albite + quartz and white micas. Sample DS09-018

is composed of actinolite + chlorite + epidote + albite + quartz ±

white mica and carbonates.

Group 4 (arc-like) is represented by four rocks sampled in the

Carboniferous and Permo-triassic domains. These samples are weakly

metamorphosed in the greenshist facies conditions at the highest.

Sample DS09-020 is mainly composed of a quartz + white mica +

feldspar-rich matrix containing large feldspar porphyroclasts. These

large feldspar porphyroclast contain inclusions of Fe–Ti-rich minerals

and relics of biotite crystals that are also observed in the matrix. Large

euhedral zircons (150 μmlong)areobservedinthematrix.These

observations, together with the absence of carbon-rich material or

graphite, lead to the interpretation of a magmatic origin for this

rock. Sample 024 is composed of epidote (clinozoisite and zoisite) +

chlorite + albite + quartz + titanite ± white mica (Fig. 5d). Sample

DS09-022 is composed of actinolite + epidote (clinozoisite and

zoisite) + chlorite + albite + quartz + titanite ± white mica. Sam-

ple DS09-010 is characterized by chlorite + actinolite + epidote +

albite + quartz and Fe–Ti-rich minerals. Actinolite pseudomorphs

after pyroxene occur. Sample DS09-012 is composed of calcite +

chlorite + albite + quartz and Fe–Ti-rich minerals. Calcite is present

as a major mineral of the matrix.

Group 5a (OIB-like) is represented by 5 rocks from the Chah

Gorbeh Unit and Ultramaﬁc Rocks (Permo-triassic domain), which

are variably metamorphosed in the greenschist and blueschist facies.

Samples DS09-008 (Fig. 5e), DS09-009 and DS09-025 are character-

ized by a strong foliation marked by chlorite + actinolite and thin

layers of Fe-Ti-rich minerals. Epidote is also present as well as quartz,

albite and minor white micas. Samples DS09-050 (Fig. 5f) and

DS09-002 are recrystallized in the blueschist facies with paragenesis

composed of glaucophane + chlorite + epidote + quartz ± white

mica, albite, magnetite, titanite and carbonate (DS09-002 only).

Group 5b (OIB-like) is represented by seven rocks from the

Triassic domain. These rocks have almost no metamorphic overprint,

allowing magmatic fabric to be still well observed (DS09-034 excepted).

Gabbro DS09-034 is composed of large mineral relics recrystallized as

actinolite + epidote + chlorite and Fe–Ti-rich minerals. The rest of the

rock is composed of the same minerals associated with albite and car-

bonate. Basalt DS09-035 is characterized by an ophitic texture compris-

ing euhedral feldspar crystals interﬁlled with chlorite and actinolite,

probably replacing clinopyroxene. The sample is peppered with magne-

tite crystals. Basalts DS09-037, DS09-40 and DS09-41 are characterized

by an intersertal texture where skeletal feldspar and oxide, probably

magnetite, are interﬁlled with a microcrystalline material now replaced

by epidote and chlorite. Sample DS09-037 is characterized by large cav-

ities now ﬁlled by carbonates and probably representing former vesicles

(Fig. 5g). Basalt DS09-042 is coarse-grainedandcomposedoflargerelics

of minerals, now replaced by chlorite and epidote, feldspar and oxide

(probably magnetite), now partly replaced by titanite. Basalt DS09-036

is a coarse-grained rock characterized by large brown hornblende, feld-

spar, magnetite and minor apatite, partly recrystallized by albite, chlorite

and titanite (Fig. 5h).

4.3. Geochemistry

Most metabasite samples display petrographical and geochemical

evidence for signiﬁcant alteration with secondary chlorite and white

mica formation. LOI is generally high (1.01 to 7.56 wt.%, average of

3.53 wt.%, one sample with 11.79 wt.%) and elements mobile during

seaﬂoor alteration and metamorphism (e.g. large ion lithophile ele-

ments (LILE) or most of the major elements) show signiﬁcant variations.

Variations in LOI of the samples do not correlate with their metamorphic

grade. However, deformed greenschist dikes within serpentinized ultra-

maﬁc rocks display signiﬁcantly higher LOI (2.85 to 11.79 wt.%, average

of 6.64 wt.%) than other samples. Similar observations can be made

275D.M. Buchs et al. / Lithos 172–173 (2013) 267–287

Table 4

Petrographic observations in the AMC.

Group Sample Rock type Metamorphic facies Cpx* Fsp* Hbl* Bt* Ab Qz Act Chl WM Czo Zo Gln Spn Fe–Ti Ox Mag Cb Comment

1 (NMORB-like) DS09-49 Greenschist GS x x x x x Schistosity, complete metamorphic recrystallisation

2 (EMORB-like) DS09-006 Gabbro GS b1% x b1% b1% x x Inherited magmatic texture still present, euhedral carbonates

2 (EMORB-like) DS09-026 Dolerite GS x x x x x x x x Magmatic mineral relics, carbonate in veins

2 (EMORB-like) DS09-027 Greenschist GS x x b1% x x x

2 (EMORB-like) DS09-30 Greenschist GS/BS x x x b1% x x x Schistosity, carbonate in veins

2 (EMORB-like) DS09-32 Greenschist GS b1% x x x x x Schistosity, Zoisite pseudomorphes pre-existing mineral (Cpx?)

3 (BABB-like) DS09-001 Greenschist GS x x x x b1% x x

3 (BABB-like) DS09-011 Greenschist GS x x x x x x Schistosity

3 (BABB-like) DS09-014 Greenschist GS x x b1%xxx x

3 (BABB-like) DS09-015 Greenschist GS x x x x x x x

3 (BABB-like) DS09-018 Greenschist GS x x x x b1% x x x Schistosity

3 (BABB-like) DS09-019 Greenschist GS x x x x b1% x x Schistosity

4 (arc-like) DS09-024 Greenschist GS x x b1% x x Schistosity

4 (arc-like) DS09-022 Greenschist GS x x x x x x x x Schistosity

4 (arc-like) DS09-020 Greenschist GS ? x x x x x x Schistosity, Inherited Zircon and feldspar porphyroclasts

4 (arc-like) DS09-010 Greenschist GS x x x x x x Schistosity, Unidentiﬁed mineral relics

5a (OIB-like) DS09-050 Blueschist BS x x x x x x x

5a (OIB-like) DS09-002 Blueschist BS ? x x x x x x

5a (OIB-like) DS09-008 Greenschist GS x x x x x x x Schistosity, Unidentiﬁed mineral relics

5a (OIB-like) DS09-009 Greenschist GS/BS x x x x x x b1% x Schistosity, Unidentiﬁed mineral relics

5a (OIB-like) DS09-025 Greenschist GS x x x x x x Schistosity

5b (OIB-like) DS09-034 Gabbro low P-T x x x x x x Unidentiﬁed mineral relics

5b (OIB-like) DS09-035 Dolerite low P-T x x x x x Magmatic texture

5b (OIB-like) DS09-036 Basalt low P-T ? x x x x x Magmatic texture

5b (OIB-like) DS09-037 Basalt low P-T x x x? Magmatic, microcritalline texture

5b (OIB-like) DS09-040 Basalt low P-T x x x x x? x Altered basalt with carbonates in ocella

5b (OIB-like) DS09-041 Basalt low P-T x x x x x x? x Magmatic texture, basalt; carbonates and quartz in veins only

5b (OIB-like) DS09-042 Gabbro low P-T x x x x x x Magmatic texture, gabbro

Abbreviations: Cpx: clinopyroxenes; Fsp: Feldspar; Hbl: Hornblend; Bt: Biotite; Ab: Albite; Qz: Quartz; Act: Actinolite; Chl: Cholrite; WM: White Mica; Czo: clinozoisite; Zo: zoisite; Gln: glaucophane; Spn: Sphene; Fe–Ti Ox: Fe–Ti Oxide;

Mag: Magnetite; Cb: Carbonate; (*) minerals inherited from magmatic protolith; “b1%”: accessory mineral.

276 D.M. Buchs et al. / Lithos 172–173 (2013) 267–287

Fig. 5. Representative microscope images from the petrogenetic groups of metabasites recognized in the AMC. Group 1: NMORB-like, Group 2: EMORB-like, Group 3: BABB-like,

Group 4: arc-like, Group 5a: OIB-like, and Group 5b: OIB-like. Mineral abbreviates: Cpx: clinopyroxenes, Fsp: Feldspar, Hbl: Hornblend, Bt: Biotite, Ab: Albite, Qz: Quartz, Act:

Actinolite, Chl: Cholrite, WM: White Mica, Czo: clinozoisite, Zo: zoisite, Gln: glaucophane, Spn: Sphene, Fe–Ti Ox: Fe–Ti Oxide, Mag: Magnetite, and Cb: Carbonate.

277D.M. Buchs et al. / Lithos 172–173 (2013) 267–287

using ratios of mobile–immobile elements of samples with EMORB and

OIB-like afﬁnities (Fig. 6). These samples show a much larger variation

than typical OIB in terms of Cs/Th, Rb/Th, Ba/Th, and U/Th ratios

(Fig. 6a–d); the variation is particularly important for dikes found in

the serpentinized ultramaﬁc rocks. It is reduced to that seen in typical

OIB using ratio of immobile element ratios such as Nb/Th and La/Th

(Fig. 6e, f), indicating that petrogenetic characteristics of our samples

can be successfully evaluated based on immobile trace elements. Major

elements and mobile trace elements are unlikely to yield reliable infor-

mation on primary magmatic characteristics and were not considered

further.

Metabasites in the AMC deﬁne a broad compositional spectrum, but

six consistent petrogenetic groups can be recognized based on speciﬁc

characteristics of immobile trace elements (Figs. 7–10). Sample of

Group 1 has NMORB-like afﬁnities with low concentrations in the

most incompatible elements ([La/Sm]

= 0.78, N = PM-normalized),

ﬂat patterns of heavy (H)REE, and no negative Nb–Ta or Ti anomaly in

PM-normalized REE or multielement diagrams (Figs. 7aand8a). This

group plots in the subalkaline basalt ﬁeld in a Nb/Y vs Zr/TiO

*0.001 di-

agram (Winchester and Floyd, 1977)(Fig. 9a), and NMORB ﬁeld in a

2*Nb vs Zr/4 vs Y diagram (Meschede, 1986)(Fig. 9b). A broadly similar

composition was observed for some samples of Bagheri and Stampﬂi

(2008) (Figs. 7aand9c, d) that we consider belonging to the same

NMORB-like petrogenetic group.

Group 2 has EMORB-like afﬁnities shown bylarger abundance in the

most incompatible elements ([La/Sm]

=1.01–2.03), ﬂat patterns of

100

1000

Ba/Th

0.1

100

Rb/Th

0.01

0.1

DS09-032 (greenschist in Serpentinite Unit)

U/Th=18.5

Cs/Th

0.1

U/Th

La/Th

0 100 200 300 400 500 600 700

Zr (ppm) Zr (ppm)

Zr (ppm)

Blueschist facies EM1 and EM2 islands

HIMU islands

Mauna Kea

OIB and EMORB-like samples from

the Anarak Metamorphic Complex Modern OIB (unaltered)

Greenschist facies

Greenschist facies within serpentinite

Low metamorphic conditions

Zr (ppm)

Nb/Th

Fig. 6. Diagrams of mobile/immobile trace element ratios vs Zr for OIB (Ocean Island Basalts)-like and EMORB (Enriched Mid-Ocean Ridge Basalts)-like samples from the Anarak

Metamorphic Complex preserved in distinct metamorphic conditions. A selection of modern OIB samples is displayed to illustrate the possible range of compositional variability in

fresh protoliths of the studied samples. These samples include tholeiitic series of the Mauna Kea volcano, Hawaii (Huang and Frey, 2003) as well as alkaline series of EM and HIMU

isotopic end-members (compilation after Willbold and Stracke, 2006).

278 D.M. Buchs et al. / Lithos 172–173 (2013) 267–287

HREE and no negative Nb–Ta or Ti anomaly in PM-normalized REE or

multielement diagrams (Figs. 7band8b). This group plots in the

subalkaline to alkali basalt ﬁelds in a Nb/Y vs Zr/TiO

*0.001 diagram

(Fig. 9a), and within-plate tholeiite ﬁeld in a 2*Nb vs Zr/4 vs Y diagram

(Fig. 9b). A broadly similar composition was observed for some samples

of Bagheri andStampﬂi(2008)(Figs. 7aand8c, d) that we consider hav-

ing also EMORB-like afﬁnities. Larger compositional variability of these

samples in Fig. 8 likely results from analytical uncertainties due to Nb

determination by XRF.

Group 3 has BABB-like afﬁnities with slightly enriched nor-

malized patterns of incompatible elements ([La/Sm]

=0.92–

1.55 and [Sm/Yb]

= 1.12–1.86) and a variable Nb–Ta anomaly

in PM-normalized REE or multielement diagrams (Figs. 7cand8c). A

maﬁc character of this group is attested by its location in basalt

and andesite/basalt ﬁelds in Nb/Y vs Zr/TiO

*0.001 diagram (Fig. 8a).

Chemical characteristics intermediate between MORB and volcanic arc

basalt is displayed on a 2*Nb vs Zr/4 vs Y diagram (Fig. 9b). One sample

of Bagheri and Stampﬂi (2008) has a similar composition (Figs. 7aand

9c, d) and may belong to the same petrogenetic group.

Group 4 has arc-like afﬁnities with a progressive enrichment in the

most incompatible elements ([La/Sm]

=1.83–4.51 and [Sm/Yb]

1.62–2.53) and pronounced Nb–Ta and Ti negative anomalies in

PM-normalized multielement diagrams (Figs. 7dand8d). Some sam-

ples have a differentiated character with high Zr/TiO

*0.001 (Fig. 8a)

and Eu negative anomalies in PM-normalized multielement and

REE diagrams, which are likely to reﬂect fractionation of Fe–Ti

100