GEOSCIENCES
Year:2001 | Volume:10 | Issue:39-40|Papers Count:6

The magmatic suites in the Sungun area are a part of NW-SE trending Cenzoic magmatic belt of Iran. The Sungun porphyries occur as stocks and dikes ranging in composition from quartz monzo-diorite through quartz monzonite and granodiorite to granite. The stocks are divided into two groups, I and II.The porphyry stock II, hosting the copper ore experienced intense hydro-fracturing, jointing, and faulting.The mineralized porphyry stock II experienced multiple events of intense hydro-fracturing leading to the formation of stockwork-type and anastomozing veinlets and micro-veinlets of quartz, sulfides, carbonates, silicates, and sulfates. The veinlets are thought to have formed in three distinct, although continuous, hydro-fracturing stages. E-type quartz veinlets and micro-veinlets were formed during the early stage.Quartz-sulfide, quartz-moly, chalcopyrite, pyrite, molybdenite, dolomite, calcite, calcite-pyrite, and sericite veinlets and microveinlets were developed during the middle stage. Anhydrite (present gypsum), L-type quartz, chert, and some calcite and calcite-pyrite veinlets and micro-veinlets characterize the late stage of hydro-fracturing processes.

In this paper, the Damghan Fault System is introduced based on findings of detailed structural and morphotectonic studies and a comparison of neotectonics patterns within its various parts. This fault system on the southern margin of eastern Alborz comprises four segments including Dehmolla-Siahkuh, Siahkuh- Rudbar, Rudbar-Fooladmahalleh and Labrud-Shotorgardan. The Dehmolla-Siahkuh segments is a strike slip normal fault, while the mechanism of all the others is sinistral reverse. This system is one of the important tectonic elements within the left lateral transpression shear zone with a N60E trend which, in this paper, is being reported as the Astaneh-Attary transpression shear zone. The Astaneh and Attary faults forms its northern and southern boundaries respectively. The Dehmolla- Siahkuh and Siahkuh-Rudbar segments with distinct activity in the Quaternary form a clockwise rotational fault, which is separated from the Rudbar-Fooladmahalleh segment by the Labrud- Shotorgardan segment. The rotational part of the Dehmolla-Rudbar is a transfer fault for the Labrud-Shotorgardan tear fault.The Labrud-Shotorgardan segment has neither a structural relation nor a similar behavior in the development of sedimentary basin with the Attary fault in the Jam region. Although the area contained within the Astaneh-Attary left lateral shear zone was clearly active in the Quaternary and this activity has left clear evidences in the Dehmolla-Siahkuh, the Siahkuh-Labrud and the Labrud- Shotorgardan segments but its Quaternary activity in the western part (Rudbar-Fooladmahalleh segment), has mainly indicated a sinistral mechanism along the Astaneh fault.Young geological kinematic evidences for the existence of a left lateral transpression shear zone in this part of eastern Alborz, supports the dynamic findings resulting from analysis of earthquake focal mechanism and surface deformation of historical and instrumental earthquakes as well as the results of satellite studies conducted on the lithospheric plates. All these evidences confirm the application of a compressional oblique stress on the Astaeh-Attary region in a north-northeast direction which could mobilize the Damghan fault system according to the proposed model.

The Badamestan Anticline is stuated in the Zagros folded belt of Iran. Formations outcropping within the anticline are Gurpi-Pabdeh, Asmari, Gachsaran, Aghajari, and Bakhtiari in ascending order. Study of joint patterns in the Asmari limestone suggests that joint formation is synchronous with folding, and the stress field is symmetrically oriented with respect to the fold axis. Gomieh anticline shows gravitational slip of the Bakhtiari conglomerate on the lower ductile layers. The joints within this formation indicate another younger stress field.

A part of the Nakhlak area (NE. Nain, Central Iran) to the west of central Iran desert was studied. The Triassic rocks of the Nakhlak area with a thickness of 2701 meters are divided into 3 Formations: Alam Formation, Baqoroq Formation and Ashin Formation. Outcrops of these rocks are bounded by two thrust faults.The Alam Formation (1298 m.) with Late Scythian- MiddleAnisian age consists of carbonate facies at the base and turbiditic calstic facies (dominantly sandstone and shale) at the top. Carbonate facies rocks were derived from the continental shelf and the clastic facies rocks were dominantly derived from the continental slope as submarine fanlomerates. The Alam Formation was thrusted over the ophiolitic rocks of the Nakhlak arp.a and was covered by Baqoroq Formation with a disconform contact.The Baqoroq Formation (1122m) with Late Anisian? - Middle Ladinian age dominantly consists of conglomerate, sandstone and shale.These facies were derived from a continental environment and deposited as alluvialfans, by meandering and braided rivers. The Baqoroq Formation (281 m.) with Late Ladinian-Early Carnian? age consists of clastic facies (dominantly sandstone and shale) deposited at the end of continental slope to abyssal plain, as submarine fanglomerates (distal part). The Upper Cretaceous rocks of Nakhlak area were thrusted over to the Ashin Formation.From lithological and paleontological point of view, the Triassic rocks of Nakhlak area are not correlative to other Triassic rocks of Iran.The only correlative rock units similar to the Triassic rocks of Nakhlak area are Aghdarband Group of northeastern Iran. The present study has shown that these rocks were adjacent to each other as well as being in the same sedimentary basin at the time the southern active margin of Turanian continental block existed.

The Sikhoran Ultramafic- Mafic Complex is located in the Sanandaj-Sirjan metamorphic belt, Southeast Iran. This complex is surrounded by palaeozoic metamorphics, overlain by mesozoic glaucophane schists with Ashin reverse fault and consists of three main units including porphyroclastic harzburgites (mantle unit?), transitonal and layered Ultramafic-mafic unit. The Abshour isotropic gabbros with a late- middle Triassic age occurr as a huge intrusion cutting this complex. It has produced an intense contact metamorphism-in the palaeozoic metamorphics. Scattered diabasic dykes with late-middle Jurassic ages cut all of them. This polygenetic complex does not include certain essential units of a classic ophiolite sequence such as dyke swarms and pillow lavas, hence we can not name it an ophiolite sensce stricto. Porphyroclastic harzburgites and porphyroclastic dunites of the transitional zone have deformational fabrics and mineral and whole rock compositions of alpine mantle peridotites. The upper part of transitional zone composed of a rhythmic sequence of layered dunite-wehrlite-pyroxenite with mamgmatic origin. Layered ultramafic-mafic cumulates consist of an ultramafic (feldspathic peridotites) section in the lower and a thick mafic (gabbroic) section in the upper part. Detailed studies of the main lithologic units of this complex indicate, that the lower part (ultramafics) crystallized in an open system replenisihed by new magmatic injections and the upper (gabbroic) part in a closed system. This trend is similar to that of low-Ti Ophiolites magmatic secuerce.Field relations of different lithologic units, regional geology. and absolute age determinations show that this compex has been formed in an extensional tectonic environment by partial melting (29-30%) of an upper mantle diapir during the upper Carboniferous-Permian (simultaneously with Hercynian orogeny and Initation of riftng of Zagros and Sanandaj-Sirjan Neotethys basins) and subsequently by isotropic gabbros and diabasic dykes in the late- middle Triassic (Early Cimerian) and Jurassic (Late Cimerian) times respectively.