Petrology
Arefeh Heidarianmanesh; Seyed Mohsen Tabatabaimanesh; Narges Shirdashtzadeh
Abstract
Based on field observation and petrographic evidence, by progress in metamorphic degrees, a wide variety of metabasites have formed following the metamorphism at amphibolite facies (metamorphism M1) in the east of Jandaq. Thermobarometry of plagioclase- amphibole pairs indicate temperature ranges were ...
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Based on field observation and petrographic evidence, by progress in metamorphic degrees, a wide variety of metabasites have formed following the metamorphism at amphibolite facies (metamorphism M1) in the east of Jandaq. Thermobarometry of plagioclase- amphibole pairs indicate temperature ranges were 642-692ºC and 688-712 ºC for epidote amphibolites and garnet amphibolite, respectively, in a pressure range of 8 and 11 Kbar, correlating with transition from middle amphibolite to upper amphibolite facies. In addition to this metamorphic phase, petrographic signatures indicate further metamorphic phases concerning this region's geological phenomena. Based on brittle deformation in amphiboles, and epidote and quartz formation in their fractures, these rocks have undergone some degrees of retrograde metamorphism (<700 ºC; metamorphism M2) at greenschist to lower amphibolite facies. Rock foliation and mineral orientation, aggregate shape preferred orientation (ASPO) of titanite crystals along foliation, and syn-tectonic euhedral garnets indicate prograde metamorphism toward amphibolite-upper amphibolite facies (metamorphism M3). Finally, under greenschist facies condition, minerals such as chlorite and actinolite were formed in these rocks (metamorphism M4). The formation of chlorite and actinolite in the rims of the primary crystals shows that these rocks were finally affected by metamorphism at greenschist facies (M4 metamorphism).
S. Shekari; M. Sadeghian; M. Zhai; H. Ghasemi; Y. Zou
Abstract
Metamorphic - igneous Shotor-Kuh complex is located in the 80 km of SE Shahrood and in the northern edge of the central Iran structural zone. This complex includes a wide lithological composition range such as metapelite (micaschists and gneisses), metapsammites, metabasites (amphibolite and garnet amphibolite), ...
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Metamorphic - igneous Shotor-Kuh complex is located in the 80 km of SE Shahrood and in the northern edge of the central Iran structural zone. This complex includes a wide lithological composition range such as metapelite (micaschists and gneisses), metapsammites, metabasites (amphibolite and garnet amphibolite), metacarbonate (limestone and dolomitic marbles) and metrhyolites. Protolith of metabasites have been basaltic lavas, diabasic swarm dikes and small scale gabbro-dioritic intrusions. With respect to abundance and importance of metamorphosed basaltic intercalations and diabasic swarm dikes in comparison to the other basic rocks, this article specially advocated to investigation of their evolution. Based on the field evidence and petrography, increasing the degree of metamorphism of metabasites resulted in producing of amphibole schist, amphibolite, garnet amphibolite and eventually amphibolitic migmatites. Thermobarometery based on the chemical analysis of garnet, amphibole and plagioclase of the metabasites indicates that the thermal range of 602-711 °C and 9-11 Kbar pressure for their formation, stop of exchange and final equilibrium, which accommodate with P-T condition of amphibolite and upper amphibolites facies. From the geochemical points of view, the magmas forming of these metabasites have tholeitic to calc-alkaline nature. These magmas originated from the subcontinental lithospheric mantel source. Submarine basaltic lava flows and diabasic swarm dikes originated during extensional tectonic regimes which affected Late Neoproterozoic Iranian Gondwanan terrains. These extensional tectonic regimes are associated with producing of intracontinental sea to oceanic basins (riffitic or back arc). The mentioned basins closed in a short time and lead to generate tectonic melange or accretionary prisms on the continental crust. Based on the U- Pb age dating of the Zircons extracted from these metasbasites, these metamorphism event occurred in the interval time of 526-577 Million years (corresponds to the late Neoproterozoic and Cadomian orogeny in the Iranian Gondwanan landforms).
M. Advay; R. Hajialioghli; M. Moazzen
Abstract
The study area is located in the Central Iran Zone, in the view of tectonic subdivisions of Iranian terrains. The main outcropping rock types are metabasites and amphibolites having Precambrian age. The amphibolites have been classified as Ep-amphibolite, normal amphibolite, Grt-amphibolite and Grt-Cpx ...
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The study area is located in the Central Iran Zone, in the view of tectonic subdivisions of Iranian terrains. The main outcropping rock types are metabasites and amphibolites having Precambrian age. The amphibolites have been classified as Ep-amphibolite, normal amphibolite, Grt-amphibolite and Grt-Cpx amphibolite, considering characteristic mineral assemblages. The main textures are granoblastic and porphyrogranobastic. Mineral chemistry of Grt-Cpx amphibolites have been investigated in this contribution. The results have been used to estimate metamorphic P-T conditions. The compositions of amphiboles are pargasite and hornblende. Clinopyroxne is diopside. Plagioclases are rich in An content (An73.50-95.90) and Ab content is low (Ab3.90-24.70). Garnet have compositions as Alm (%45.90-%59.10)، Prp (%5.6-%16.1)، Sps (%10.90-%23.50)، GAU (%13.20-%23.70) . Garnet composition is non-uniform as increasing of Fe and Mg contents where Mn and Ca contents are decreased from the core to the rim. The peak metamorphic T-P obtained as 670 oC to 705 oC at 8.5 Kbar respectively. The estimated pressure is consistent with the depth of ~25Km correspending to the lower crustal condition. The recorded mid P-T conditions of Grt-Cpx ampgibolites belonge to Barrovian type regional metamorphism. On the basis of geological and petrological studies from the SE Qarehaghaj and the analogies with comparable rocks from adjucent Precambrian terrains, it seems that the Pan-African Orogeny is the phase causing metamorphism and consolidation of the basement rocks. The Precambrian metabasites and amphibolites have been probably formed in this regard. The subsequent mid P-T metamorphism of the metabasites under upper amphibolite facies (Barrovian type metamorphism) have been most likely recorded related to continental collision between the Arabian plate and the Central Iranian micocontinent correspending to the Alpian Orogeny during Cenozoic.
N Shirdashtzadeh; G Torabi; R Samadi
Abstract
Some dark green fragments of amphibolites are found within skarns at the south of Nain Ophiolite at the northeast of Nain city. They are similar to ortho-amphibolites (metamorphosed basic rocks) of this ophiolite in hand specimen, but mineralogically they are composed of amphibole (magnesio-hornblende, ...
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Some dark green fragments of amphibolites are found within skarns at the south of Nain Ophiolite at the northeast of Nain city. They are similar to ortho-amphibolites (metamorphosed basic rocks) of this ophiolite in hand specimen, but mineralogically they are composed of amphibole (magnesio-hornblende, Mg#>0.95), clinopyroxene (diopside, Mg#~0.61), garnet (grossular – andradite, with Grs~63-87 And~12-35), quartz, and minor amount of calcite and wollastonite. Accessory minerals are including chlorite and prehnite, mostly filling the fractures. Field studies, petrography and mineral chemistry indicate that amphibolitic fragments mineralogically differ from the skarns and ortho-amphibolites of this ophiolite; so they can be considered as olistoliths with sedimentary origin (calcic marls of sea floor), turned into amphibolitic rocks (para-amphibolite) during the regional metamorphism at amphibolite - granulite facies and low oxygen fugacity.
R Hajialioghli; H Fakharinezhad; M Moazzen
Abstract
The study area (Siyah-Cheshmeh), is located to the south Maku in the Khoy-Maku ophiolite zone. The various outcropped metamorphic rocks include serpentinites, metabasites (green schist, amphibolite) and meta-pelitic rocks (slate, mica-schist) with interlayers of marble and quartzite. The amphibolites ...
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The study area (Siyah-Cheshmeh), is located to the south Maku in the Khoy-Maku ophiolite zone. The various outcropped metamorphic rocks include serpentinites, metabasites (green schist, amphibolite) and meta-pelitic rocks (slate, mica-schist) with interlayers of marble and quartzite. The amphibolites can be classified as actinolite-amphibolite, epidote-actinolite- amphibolite, biotite-amphibolite, amphibolite and garnet-amphibolite. They have fine- to coarse-grained granoblastic texture. On the basis of whole rock chemistry, the protolith composition of the amphibolites has been determined as basalts with tholeiitic and less commonly, calc-alkaline affinities, developed in an island arc setting. The negative anomaly of Nb as well as small enrichments in LILE and LREE support arc related and tholeiitic signatures for the protolith. Considering the unknown age of the studied amphibolites, it is difficult to propose an appropriate tectonic model for formation of the investigated rocks. If the amphibolites are related to the Khoy-Maku ophiolitic complex, then they would be the result of subduction of the northern branch of the Neotethys ocean basin, development of an island arc and eventually metamorphism of the rocks due to closure and collision. Since the age is not clear, it is not possible to conclude unequivocally if the rocks are results of the Neotethys subduction system or they are related to an older, possibly a Precambrian subduction system. Dating the rocks will help to propose a suitable model for their formation.
A Gourabjeri; M.H Emami
Abstract
Gelmandeh Massive is located north-east of Saghand, in Yazd province. From tectonics point of view it belongs to Central Iran, the Kalmard_Posht-e-Badam Block. The metamorphic complex comprises amphibolites, marble, schist, quartz- feldspatic gneisses. The amphibolites are of three types. Namly: Hornblendite ...
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Gelmandeh Massive is located north-east of Saghand, in Yazd province. From tectonics point of view it belongs to Central Iran, the Kalmard_Posht-e-Badam Block. The metamorphic complex comprises amphibolites, marble, schist, quartz- feldspatic gneisses. The amphibolites are of three types. Namly: Hornblendite (composed of more than 90% hornblende), Garnet-amphibolites and amphibolitic gneiss. Deformations in Gelmandeh metamorphic complex are reflected in 6 types of rocks: 1-deformed igneous rocks, 2- mylonitic series rocks, 3-cataclastic series rocks, 4-regional metamorphic rocks, 5- mylonitic regional metamorphic, 6-cataclastic regional metamorphic rocks. Conspicuous deformational features comprise: tilted feldspars twining, erratic pertite, mirmecite, porphyroblasts, clasts with strain shadows, and strained & fish structure minerals showing right & left lateral sense.
A. N. Fazlnia
Abstract
A barrovian-type metamorphism occurred in the mafic rocks from the Qori complex (South Sanandaj - Sirjan zone), because of a regional arc-related metamorphism with a peak metamorphic condition of 700 °C and 8.5 kbar at 147 million years ago. As a result of the process, the rocks changed to migmatite. ...
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A barrovian-type metamorphism occurred in the mafic rocks from the Qori complex (South Sanandaj - Sirjan zone), because of a regional arc-related metamorphism with a peak metamorphic condition of 700 °C and 8.5 kbar at 147 million years ago. As a result of the process, the rocks changed to migmatite. Trondhjemitic granitoids were formed as the dike form because parts of the melts can be extracted from the migmatites. Decreasing and increasing trace and rare earth elements in the amphibolites and trondhjemites were resulted of stability or instability in the metamorphic minerals during peak of the metamorphism, which caused migmatization and also formation of trondhjemite. Based on the partition coefficients of elements in different minerals, light rare earth elements (LREE) were mostly controlled by hornblende and garnet and apatite (but not a lot) during the partial melting of the amphibolites. Related to the LREE, heavy rare earth elements (HREE) and Y were controlled by apatite and garnet. Elements with high field strength (HFS), such as Zr, Nb, Ta and Th were controlled and distributed by hornblende and ilmenite. Large ionic lithophile elements (LILE) such as Sr, Ba and Rb showed that plagioclase and biotite were main minerals to control and distribute the elements. The evidence suggests that the Qori trondhjemitic granitoids are similar to the Al-poor trondhjemites, which are the result of partial melting of the garnet-hornblende from the amphibolitic protolith in presence of calcic plagioclase as stable phase.