جستجوی مقالات مرتبط با کلیدواژه "geodynamic" در نشریات گروه "زمین شناسی"

The Upper Cretaceous succession (UCS) of the north Sanandaj-Sirjan zone consists of five units. The units are 2000 m thick, including shale, sandstone, limestone, intrafomational conglomerate with interbedded basaltic- andesitic lava. This succession is unconformably underlain by Lower Cretaceous and overlain by Paleocene conglomerates. The geochemistry of the samples represents ratios of Al2O3/TiO2 (18-22), La/LuCN (5.43-24.4), La/Sc (0.51-2.53), Th/Sc (0.42-0.68), LREE/HREE (Nd/ErCN > 5), and negative anomalies of Eu/Eu* (0.26-0.89) and Nb/Nb* (0.14-0.82). These characteristics indicate that the samples are immature, first-order sediments, and were eroded from intermediate to acidic arcs in the subduction zone. The volcanic rocks were formed during the intracrustal melting of an altered oceanic slab at high pressures in the garnet-amphibolite facies. The geochemical compositions and vertical lithofacies stacking patterns of the UCS imply that the depositional environment has changed during sedimentation from a trench to trench slope and forearc basins arising from continent-ward migration of the magmatic arc. The activities of Late Cretaceous volcanism resulted in the upwelling of anoxic water, demise of planktonic, and formed pyrite in the deposits. Samples on the Th/Yb-Ta/Yb diagram fall in the ACM and WPVZ fields, indicating tectonic evolution from low-gradient subduction to extensional volcanic conditions.

Zagros ophiolites are mainly exposed in Oman، Neyriz، Kermanshah، Kurdistan and north western of Iraq. The Sawlava ophiolitic complex is a member of Kurdistan ophiolites. In this research petrogenesis and geodynamic of this part of Zagros ophiolites have been investigated. Basalt، microgabbro، gabbro with serpentinized dunite and wherlite are the main rock units of the complex. The phenocryst in the basalta and the microgabbros are plagioclase and clinopyroxene and the main textures in the basalts are porphyric and microlitic-glassy whereas intersertal and microgranular are dominant in the microgabbros. The main minerals in the gabbros are clinopyroxene (augite-diopside)، plagioclase with labrador composition. In the peridotites، the major minerals are olivine (Fo= 88-91)، clinopyroxene (diopside-clinoenstatite) and chromin spinels (picotite). By analogy with the global standards، the obtained geochemical data reveal that basalts and microgabbros in Sawlava ophiolitic complex are tholeiitic in nature، and their magma source tends towards N-MORB and E-MORB. Gabbros are in tholeiite to calc-alkaline magma series and show the abyssal MORB to oceanic ARC features. The chemistry of peridotites shows the abyssal to supra-subduction zone source. The high volume of basalt-microgabbro، low Ti value and high content of Al and Cr# in peridoitite chromian spinels، reveal a high rate of partial melting (25-35%) indicating that the depleted mantle subjected to high degree of partial melting can be the Sawlava complex source. According to geochemical data a depleted mantle may be the source of Sawlava ophiolitic complex. This feature is more remarkable in the studied gabbros and peridotites. Comparing the lithological and geochemical characteristics of the studied ophiolites with some other complexes in the world documented that the complex under discussion formed in an oceanic back arc setting.