In this paper, we use satellite images, field observations and aeromagnetic data to describe major tectonic features in the central portion of the Urumieh-Dokhtar Magmatic Arc (UDMA) in Central Iran.Most of the analyzed structures such as horsetail splays, rotated blocks, positive flower structures and sedimentary basins have not been previously recognized.The NW-SE-trending Zefreh Fault is the most important dextral transpressional active lineament in the area.Maps of filtered aeromagnetic anomalies confirmed that the fault also affects the basement.Based on our field observations and cross-cutting relationships, tectonic evolution of the central part of the UDMA is interpreted in terms of two main stages:(1) formation of main thrusts during shortening and exhumation of older rocks in the UDMA after Eocene-Oligocene, and (2) transpressional movements reactivating the main thrust faults to reverse-dextral strike-slip faults during the Pliocene-Quaternary.The present-day deformation of the UDMA is mostly dominated by strike-slip movements.These two stages are interpreted as reflecting a change in convergence vector between Arabian and Eurasian plates.
<p>Records of paleoclimate in the Middle East are particularly sparse in comparison with other regions around the world. In order to better resolve how Middle East climate responded to large global climate and environmental changes in the past, here we present the first glacial record of southwestern Iran climate constructed using speleothem climate proxies. We analyzed two stalagmites collected from a cave on the western side of the Zagros mountains, ~100 km north of the Persian Gulf. The average annual precipitation and temperature close to the cave site are ~350 mm and ~21.6 &#176;C, respectively. Our data yield continuous &#948;<sup>18</sup>O and &#948;<sup>13</sup>C records from 45-35 kyr and 25-10 kyr BP, which show prominent millennial-scale events during the last glacial period and Termination I. The timing of these events is in agreement with North Atlantic Heinrich events and Greenland Daansgard-Oeschger events, within the respective records&#8217; age errors. Moreover, unlike the generally stable NGRIP &#948;<sup>18</sup>O record, a proxy for high-latitude Northern Hemisphere temperatures, the stalagmite &#948;<sup>18</sup>O and &#948;<sup>13</sup>C records reveal clearly evident periodic variations during the Last Glacial Maximum. &#948;<sup>18</sup>O values are consistently heavier than eastern Mediterranean stalagmite &#948;<sup>18</sup>O values during both the glacial period and throughout Termination I, suggesting at least one source of moisture to the southwestern Iran site in addition to the westerlies.</p>
Terrestrial paleoclimate records from arid southwestern Asia are relatively sparse. Therefore, the regional impact of abrupt glacial climate variability remains poorly constrained for much of the Western Asia, particularly winter (wet season) dynamics during Marine Isotope Stage 3. Here, we present the first paleoclimate reconstructions of Southwestern and Central Iran, which span the interval ~50-30 ka, based on speleothem δ18O and δ13C. Stable-isotope signals in the two stalagmites are generally uncorrelated and do not exhibit a consistent response to Greenland stadials or interstadials; however, both show a positive δ18O excursion that coincides with Heinrich event 4. This behavior contrasts with that observed in northern Iran, Anatolia, and Levant for the last glacial period. We explore the potential mechanisms for intermittent coupling of speleothem δ18O across Iran through isotope-enabled atmospheric modelling outputs, from which we utilize the spatial δ18O gradient as a proxy for wintertime westerly vs. southerly jet strength. Our results suggest that during Heinrich event 4 and several Greenland stadials, stronger westerly winds enhanced Mediterranean moisture contributions to both sites and reduced aridity in southern Iran. We emphasize the importance of analyzing spatial trends in speleothem δ18O to interpret atmospheric dynamics, rather than relying on time series from single sites.
Kalahroud Cave is located in central Iran, ~50 km north of Isfahan. The landscape is a typical mountain desert morphology of cuestas dissected by ravines and gorges created during rare surface run-off events; crest lines are ~2800 m asl and lowlands at ~2100 m asl. Kalahroud Cave (4500 m of mapped passages, ~60 m deep) is entered through breakdown in the eastern wall of a gorge. The host rock is a Cretaceous limestone and mudstone formation 60 m in thickness, underlain by sandstones and conglomerates and overlain by weakly permeable calcareous marl strata, all dipping 15-20o. Below the entrance breakdown, two corrosion notch chambers give access to a rectilinear, quasi-horizontal maze of joint-guided passages extending ~500 m eastwards. Rock solution morphology created by slowly flowing phreatic waters predominates (solution pockets, partitions, paragenetic forms, etc). Seven shafts are known that discharged water into the maze and chambers from inaccessible passages below. From XRD analysis, the paragenetic sediments derive from the mudstone interbeds. There are small displays of frostwork, helictites and thin flowstones typical of vadose speleothem deposition in arid caves. Below the level of the corrosion notch, more complex sub-aqueous and shelfstone calcites are overlain by accumulations of calcite rafts up to 70 cm in depth. Raft deposition continues today. It is proposed that the cave is of hypogene origin, serving to discharge interformational groundwaters into the gorge, and becoming de-watered as the latter was deepened. The corrosion notches are due to cessation of deepening. From U series dating, the modern phase of raft deposition began about 10,000 years ago. The sequence and ages of older events will be investigated in future work.
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