نشریه پترولوژی
پیاپی 42 (تابستان 1399)

The Fertile pegmatites are known as the most important source of strategic and rare elements. These coarse-grained granitic units are related to potentially granitic intrusions and the identification of the parental intrusion is the first step of their exploration and recognition. In the present paper, the Moshirabad granite-pegmatite system located in southwest of Qorveh has been studied using bulk-rock data and available geological information in order to consider rare elements behavior and their contents. The investigations show that the studied igneous units did not formed in a unique fractionation succession, but rather happened separately in parallel differentiation processes. During sequential injections and development of fractionation (Rb increase and K/Rb decrease), the metals such as Sr, Zn, Ba, REEs, Th, Zr, and Hf were depleted whereas, the elements including Nb, Ta, Be, and Ga were enriched. In addition, the evidences imply that hydrothermal activities, also, involved in the concentration and depletion of the elements.

Hanar intrusion located in 155 km South of Birjand in the east of Lut block and compositionally consist of tonalite, granodiorite, quartz-diorite and diorite that intruded as stock and dikes in volcanic sequence (basic to intermediate) outcropped in this area. Hanar granitoid rocks are metaluminous and show I-type granitoids affinity. In addition, they are belong to calk-alkaline series and reveal the active continental margin geochemical evidences. According to relation of studying intrusion to I type granitoids with oxide (magnesian) state, they have no potential to produce Sn and W mineralization. Also, Low Sr/Y and V/Sc ratios as well as the situation of the studying samples in barren domain of the fertile-barren discrimination diagrams show that Hanar granitoids have no potential for Cu porphyry mineralization. In other hand, Low degree of the magmatic evolution as well as location of the studying samples in different Fe-mineralization potential evaluation diagrams indicate that Hanar granitoids (Diorite unit) has high potential for formation of iron deposits that this case is supporting by occurrence of  Fe-mineralization (as vein-Iron deposit) in association with this intrusion.

The Ahar-Arasbaran Volcanic Belt (AAVB), in the Eastern Azerbaijan province, is located in the NW of Varzaghan. The area is a part of a large tectono-magmatic unit called Turkish-Iranian High Plateau (TIHP). The studied volcanic rocks composing of andesitic lavas and related pyroclastic deposits are the youngest volcanic rocks in the area. Mineralogically, these rocks are characterized by plagioclase, clinopyroxene and orthopyroxene as the main phenocrysts with dominant porphyritic texture. They have calc-alkaline to high-K calc-alkaline nature and on chondrite-normalized REE diagrams display less steep patterns (LaN/YbN=5.21-7.54) along with weak negative Eu anomaly (Eu/Eu*=0.82-0.89). The notable features of these rocks on MORB-normalized multi-element diagrams are LREEs and LILEs enrichment (i.e., Ba, Th, K, and Sr) relative to HREEs and HFSEs and TNT negative anomalies, which all are criteria of subduction-related magmas. The petrologic studies of above-mentioned rocks and their comparison with the comagmatic rocks from other places of TIHP (Ararat and Sahand) support this hypothesis that the parent magma of NW Varzaghan andesitic rocks was derived from partial melting of the subcontinental lithospheric mantle, which previously metasomatized by releasing fluids from subducting slab in a post-collisional setting and contaminated by upper continental crust during ascending to the surface.

The south Natanz volcanic zone located in the central part of Urumieh-Dokhtar magmatic arc and the north of Isfahan. The area is dominated by the Eocene volcanic rocks ranging from acidic to intermediate and relatively basic affinity. Petrologically, they consist of rhyolite, dacite, andesite, basaltic trachyandesite and basaltic andesite. Mineralogically speaking, except for the acidic rocks, the other rocks are mainly made of plagioclase and clinopyroxene up. According to EPMA, the composition of clinopyroxene and plagioclase is augite and andesine to bytownite. Having features such as zoning and sieve texture in phenocrysts of plagioclase, roundness, and corrosion gulf in minerals belonging to the volcanic rocks reflecting the existence of unequilibrium during magma solidification. Considering geochemical features of these rocks, we can realize that they are calc-alkaline with potassium from intermediate to high LILE enrichment, and negative Nb-Ti anomalies. On the spider diagram, primitive mantle- normalized with Pb-enrichment can be seen which may be attributed to crustal assimilation. The negative anomalies of Nb and Ti on the spider diagram reflect subduction process, the crustal involvement in magmatism processes, or an indication of deficiency of these elements at the origin, the stability of Nb-Ti bearing phases during partial melting or separating these elements in the course of fractional crystallization process. The chondrite- normalized REE pattern points to LREE enrichment in comparison with HREE. The volcanic rocks studied have been originated in a magmatic arc.

The Hormuz and the Gachin salt domes are located in the south of Bandar Abbas, the Hormozgan Province, in Zagros Structure Zone. The domes are dominated by andesite, trachy-andesite, basalt, dacite, and rhyolite belonging to Permian to Triassic age. Based on geochemical evidence, these rocks are calc-alkaline originated in orogenic setting related to subduction environment. The presence of oxide minerals (hematite and magnetite) in the volcanic rocks of the domes reflect oxidization conditions and high oxygen activity during their formation. Negative TNT and high LREE/HREE anomalies along with positive Pb anomalies and low Nb/U ratios (0.48 to 14.6), as well as tectonomagmatic diagrams indicate that the studied rocks are magmatic products of primary mantle origin, which has been metasomatized by continental crustal rocks. High Ba/Nb values, low Sr and Zr/Y>3 ratio along with geochemical diagrams, confirm the characteristics of arc magmas related to the formation of the rocks under study in a subduction environment.

In the north of Torud and the eastern part of the Trood- Chah Shirin magmatic arc, the Late Eocene- Early Oligocene subvolcanic rocks with andesite, trachyandesite and dacite composition intruded the Eocene volcanic- pyroclastic sequence. Mineralogically, they are dominated by plagioclase, hornblende, biotite, quartz and magnetite with microlithic porphyry and hyallomicrolithic porphyric textures. Plagioclase with polysynthetic twinning and oscillatory zoning is the most abundant mineral that sometimes having sieve texture, dissolution, and corroded margins. Biotite and amphibole phenocrysts are idiomorphs to subidiomprph with opacitic margins. Quartz phenocrysts sometimes have corrosion gulf. Microscopic evidence, including non- equilibrium textures (oscillatory zoning and sieve texture of plagioclases), dissolution, and corrosion of crystals point to assimilation and magmatic contamination. The geochemical signatures of the rocks studied including enrichment in LILEs (especially Rb, K, Th) and LREEs relative to HREEs and HFSEs (Ta, Nb, Ti), a calc- alkaline affinity and their position on discrimination tectonomagmatic diagrams, display that these rocks derived from a subduction- related environment. These mentioned signatures with a differentiated pattern of rare earth elements without Eu anomaly, depletion in Y and Yb, and high ratio of Sr/Y and La/Yb show these rocks belong to high silica adakites. The parent magma of adakitic rocks in this region originated from partial melting of subducted oceanic crust (in garnet stability depth) associated with fractional crystallization and assimilation processes.