Lut Block Research Articles

Whole rock geochemistry and Sr-Nd isotopes of mafic to intermediate subvolcanics bodies of Kashmar, evidence for subduction of Sabzevar back arc basin beneath Lut block

Whole rock geochemistry and Sr-Nd isotopes of mafic to intermediate subvolcanics bodies of Kashmar, evidence for subduction of Sabzevar back arc basin beneath Lut block

Geometric-kinematic characteristics of the main faults in the W-SW of the Lut Block (SE Iran)

The area to the W-SW of the Lut Block in Iran has experienced numerous historical and recent destructive earthquakes. We examined a number of faults in this area that have high potential for generating destructive earthquakes. In this study a number of faults are introduced and named for the first time. These new faults are Takdar, Dehno, Suru, Hojat Abad, North Faryab, North Kahnoj, Heydarabad, Khatun Abad and South Faryab. For a group of previously known faults, their mechanism and geological offsets are investigated for the first time. This group of faults include East Nayband, West Nayband, Sardueiyeh, Dalfard, Khordum, South Jabal-e-Barez, and North Jabal-e-Barez. The N-S fault systems of Sabzevaran, Gowk, and Nayband induce slip on the E-W, NE-SW and NW-SE fault systems. The faulting patterns appear to preserve different stages of fault development. We investigated the distribution of active faults and the role that they play in accommodating tectonic strain in the SW-Lut. In the study area, the fault systems with en-echelon arrangement create structures such as restraining and releasing stepover, fault bend and pullapart basin. The main mechanism for fault growth in the region seems to be ‘segment linkage of preexisting weaknesses’ and also for a limited area through ‘process zone’. Estimations are made for the likely magnitudes of separate or combined failure of the fault segments. Such magnitudes are used in hazard analysis of the region.

Origin of 1.8 Ga zircons in Post Eocene mafic dikes in the Roshtkhar area, NE Iran

ABSTRACTThe Roshtkhar area is located in the Khaf-Kashmar-Bardaskan volcano-plutonic belt to the northeastern Iran along the regional E–W trending Dorouneh Fault, northeastern of the Lut Block. There are several outcrops of subvolcanic rocks occurring mainly as dikes in the area, which intruded into Cenozoic intrusive rocks. We present U–Pb dating of zircons from a diabase dike and syenite rock using LA-ICP-MS that yielded an age of 1778 ± 10 Ma for the dike, indicating this Cenozoic dike has zircon xenocrysts inherited from deeper sources; and 38.0 ± 0.5 Ma, indicating an Late Eocene crystallization age for the syenite. Geochemically, the dikes typical of high-K calc-alkaline to shoshonitic magmas. Petrographic observations and major and trace element variations suggest that diabase melts underwent variable fractionation of clinopyroxene, olivine, and Fe-Ti oxides and minor crustal contamination during the differentiation process. Primitive mantle-normalized multi-element diagrams display enrichment in LILE, such as Rb, Ba, Th, U, and Sr compared to HFSE, as well as negative anomalies of Nb, Ta, P, and Ti, suggesting derivation from subduction-modified mantle. Chondrite-normalized REE plots show moderately LREE enriched patterns (<3.83 LaN/YbN <8.27), and no significant Eu anomalies. Geochemical modelling using Sm/Yb versus La/Yb and La/Sm ratios suggests a low-degree of batch melting (~1–3%) of a phlogopite-spinel peridotite source to generate the mafic dikes. The geochemical signatures suggest that the Roshtkhar mafic dikes cannot be related directly to subduction and likely resulted from melting of upper mantle in an extensional setting where the heat flow was provided from deeper levels. These dikes presumably derived the zircon xenocrysts from the assimilation of upper crust of Gondwanian basement. Processes responsible for partial melting of metasomatized lithospheric mantle and post-collision magmatism in NE Iran was triggered by heating due to asthenospheric upwelling in an extensional setting.

Comparison of various knowledge-driven and logistic-based mineral prospectivity methods to generate Cu and Au exploration targets Case study: Feyz-Abad area (North of Lut block, NE Iran)

Motivated by the recent successful results of using GIS modeling in a variety of problems related to the geosciences, some knowledge-based methods were applied to a regional scale mapping of the mineral potential, special for Cu-Au mineralization in the Feyz-Abad area located in the NE of Iran. Mineral Prospectivity Mapping (MPM) is a multi-step process that ranks a promising target area for more exploration. In this work, five integration methods were compared consisting of fuzzy, continuous fuzzy, index overlay, AHP, and fuzzy AHP. For this purpose, geological maps, geochemical samples, and geophysics data were collected, and a spatial database was constructed. ETM + images were used to extract the hydroxyl and iron-oxide alterations, and to identify the linear and fault structures and prospective zones in regional scale; ASTER images were used to extract SiO2 index, kaolinite, chlorite, and propylitic alterations in a district scale. All the geological, geochemical, and geophysical data was integrated for MPM by different analysis. The values were determined by expert knowledge or logistic functions. Based upon this analysis, three main exploration targets were recognized in the Feyz-Abad district. Based on field observation, MPM was proved to be valid. The prediction result is accurate, and can provide directions for future prospecting. Among all the methods evaluated in this work, which tend to generate relatively similar results, the continuous fuzzy model seems to be the best fit in the studied area because it is bias-free and can be used to generate reliable target areas.

New insights into the geodynamics of Neo-Tethys in the Makran area: Evidence from age and petrology of ophiolites from the Coloured Mélange Complex (SE Iran)

The Coloured Mélange Complex is part of the North Makran domain (SE Iran) and consists of an assemblage of metric- to decametric-thick slices mainly represented by volcanic rocks, locally stratigraphically associated with radiolarian cherts. In this paper, we present new geochemical data on volcanic rocks and biochronological data on the associated cherts. Our data indicate the occurrence of a wide range of volcanic rocks-types, which are: 1) normal-type mid-ocean ridge basalts (N-MORB); 2) oceanic plateau basalts (OPB); 3) alkaline basalts; 4) calc-alkaline basalts, basaltic andesites, and andesites; 5) volcanic arc tholeiitic basalts and andesites, and high pressure - low temperature metabasalts formed in deep levels of an accretionary wedge. The volcanic arc tholeiites range from Early (late Hauterivian - early Aptian) to Late (latest Cenomanian - lower late Campanian) Cretaceous, whereas the calc-alkaline rocks and OPBs are Late Cretaceous in age (early Coniacian - Santonian and early Turonian - early Campanian, respectively). Alkaline basalts, OPBs, and N-MORBs represent remnants of the Mesozoic Neo-Tethys oceanic branch located between the Arabian plate and the Lut block. In this paper we document that this oceanic sector was characterized by the development of an oceanic plateau in the Late Cretaceous. In contrast, calc-alkaline and volcanic arc tholeiitic rocks represent remnants of a continental volcanic arc and forearc, respectively, developed onto the southernmost realm of the Lut block. The petrogenesis and age of volcanic rocks allow us to propose a new tectono-magmatic model for the evolution of the convergent margin developed in the northern sector of the Neo-Tethys from Early to Late Cretaceous. This model is basically constrained by the collision of the oceanic plateau with the continental arc, which led to the jump of the subduction toward the south, as well as to the formation of the imbricate pile of different units today observed in the North Makran area.

Fracture mapping of lineaments and recognizing their tectonic significance using SPOT-5 satellite data: A case study from the Bajestan area, Lut Block, east of Iran

Syste'm Pour l‘Observation de la Terre (SPOT) remote sensing satellite data have useful characteristics for lineament extraction and enhancement related to the tectonic evaluation of a region. In this study, lineament features in the Bajestan area associated with the tectonic significance of the Lut Block (LB), east Iran were mapped and characterized using SPOT-5 satellite data. The structure of the Bajestan area is affected by the activity of deep strike-slip faults in the boundary of the LB. Structural elements such as faults and major joints were extracted, mapped, and analyzed by the implementation of high-Pass and standard kernels (Threshold and Sobel) filters to bands 1, 2 and 3 of SPOT-5 Level 2 A scene product of the Bajestan area. Lineament map was produced by assigning resultant filter images to red-green-blue (RGB) colour combinations of three main directions such as N-S, E-W and NE-SW. Results derived from image processing technique and statistical assessment indicate that two main orientations, including NW-SE with N-110 azimuth and NE-SW with N-40 azimuth, were dominated in the Bajestan area. The NW-SE trend has a high frequency in the study area. Based on the results of remote sensing lineament analysis and fieldwork, two dextral and sinistral strike-slip components were identified as main fault trends in the Bajestan region. Two dextral faults have acted as the cause of shear in the south and north of the Bajestan granitoid mass. Furthermore, the results indicate that the most of the lineaments in this area are extensional fractures corresponding to both the dykes emplacement and hydrothermal alteration zones. The application of SPOT-5 satellite data for structural analysis in a study region has great capability to provide very useful information of a vast area with low cost and time-consuming.

سنگ شناسی، سن سنجی، ژئوشیمی و تعیین منشأ توده های گرانیتوئیدی منطقه بجستان، شمال فردوس، استان خراسان رضوی

سنگ شناسی، سن سنجی، ژئوشیمی و تعیین منشأ توده های گرانیتوئیدی منطقه بجستان، شمال فردوس، استان خراسان رضوی

Using airborne geophysical data in identifying tectonic lineaments in east of Iran

In this paper we tried to identify the main tectonic lineaments in Eastern Iran including Lut block and Sistan suture zone from the airborne geomagnetic data together with tilt filter. As the map of obtained lineaments from airborne geomagnetic data has been studied, four distinct set of lineaments has been identified: (i) north–south, (ii) east–west, (iii) northeast–southwest, and (iv) northwest–southwest that are concurrently with structural zones and area’s big faults. New faults which have been identified in this investigation are lineaments with trend northeast–southwest and east–west. The depth of these lineaments has been calculated through Euler modeling. Magnetic lineaments trending east–west have the most depth, so these lineaments are related to basement faults.

U-Pb geochronology and petrogenesis of intrusive rocks: Constraints on the mode of genesis and timing of Cu mineralization in SWSK area, Lut Block

The South-West Sorkh-Kuh (SWSK) area, part of the Tertiary volcanic-plutonic rocks in the Lut Block, eastern Iran, comprises volcanic rocks intruded by intrusive rocks of hornblende diorite and biotite quartz monzonite compositions. Biotite quartz monzonite has been intensively affected by quartz-sericite-pyrite, argillic and silicification alterations and hornblende diorite shows weak propylitic and carbonate alterations. Disseminated, stockwork and vein-type styles of mineralization are associated with intrusive rocks. The vein-type mineralization with NW-SE trend is hosted by hornblende diorite. The ore in vein-type mineralization consist of quartz, chalcopyrite, pyrite, and secondary Cu-Fe minerals. Disseminated and stockwork mineralizations consist of quartz, pyrite, chalcopyrite, and secondary minerals replacing biotite quartz monzonite and hornblende diorite intrusive rocks. The highest grades in terms of Cu (3%), As (1.3%), Mo (150ppm), Pb (362ppm), Zn (743ppm), and Au (278ppb) are associated with vein-type mineralization. Intrusive rocks causing mineralization, are of metaluminous to peraluminous types with calc-alkaline to high-K calc-alkaline affinity formed in a volcanic arc setting. The enrichment of LILE (Ba, K, Cs, Sr), depletion of HFSE (Nb, P, Ti) and enrichment of LREE relative to HREE indicate the formation of source magmas above a subduction zone. The results of zircon U–Pb dating give constraints on the timing of emplacement of biotite quartz monzonite and hornblende diorite bodies at 40.16±0.72 and 20.1±2.1Ma, respectively. The younger date extends the time span of mineralizations in the Lut Block from Middle Eocene to Early Oligocene (42–33Ma.) reported by previous researchers to more recent Early Miocene times. The initial 87Sr/86Sr ratios and εNd values of both biotite quartz monzonite and hornblende diorite reside in the restricted ranges of 0.7055–0.7066 and −0.33 to +1.88, respectively, consistent with an origin above a subduction zone followed by crustal contaminations of the initial magma compositions, especially with regard to biotite quartz monzonite. The zircon U-Pb ages as well as geochemical and radiogenic isotope data for the intrusive bodies associated with mineralization in this study are in accordance with previous studies on intrusive bodies related to porphyry copper deposits in the Lut Block. In contrast to previous studies, this study further extends the span of mineralization events to at least Early Miocene times.

Lithospheric structure of the Eastern Iranian plateau from integrated geophysical modeling: A transect from Makran to the Turan platform

We present a 2D profile of density and temperature distribution in the lithosphere across Iran along a more than 1600km long profile extending from the Oman Gulf in the South to the Kopeh-Dagh and the Turan platform in the North. Gravity, geoid, topography and surface heat flow data were used for modeling, assuming local isostatic equilibrium. As much as possible, crustal structure has been constrained by seismic data. Crustal thickening is found under the Taftan-Bazman volcanic-arc (up to 47km), under the Binalud foreland (∼54km) and beneath the Kopeh-Dagh mountains (up to 50km) whereas thin crust has been obtained under the Oman Gulf (20km). Moho depth under the Lut block and the Turan platform is about 40km. The lithospheric thickness is ∼90km under the Oman Gulf and increases slightly until the Jazmourian depression. Then the lithospheric-asthenospheric boundary (LAB) bends significantly and sinks to ∼260km under the Taftan-Bazman volcanic-arc. The LAB depth is about 190km beneath the Lut block. A slight increase of LAB depth under the Binalud foreland towards the North may indicate a suture zone. Under the Turan platform, the LAB depth reaches ∼210km. We also modeled two possible positions of the deep suture zone in NE Iran (along the main Kopeh-Dagh fault or along the Atrak River) and concluded that, when the suture zone is along the Atrak River, we obtained the better fit between calculated and measured data.

Petrogenesis of Plio-Quaternary basanites in the Gandom Beryan area, Kerman,Iran: geochemical evidence for the low-degree partial melting of enriched mantle

In the Gandom Beryan area, basanitic lava flows erupted from fractures in the Nayband fault zone and formed an area of about 300 km2 of basanitic rocks in the western part of the Lut Block. Olivine and clinopyroxene are the major phenocrysts in a microlitic groundmass for these basanitic rocks. The geochemical data show that Gandom Beryan rocks are basanite in composition and belong to intercontinental rifts related to alkali basanites. These rocks have low Fe/Mg ratios (Fe2O3t/MgO = 1.07-1.43) with low silica content (SiO2 = 44.89-48.26 wt.%) and are high-Ti basanites. The investigated rocks are characterized by a significant enrichment of total REE and LREE relative to chondrite. Moreover, the REE patterns of these rocks are linear without any negative Eu anomalies. The low abundances of HREE in basanitic rocks and the REE modeling together reflect the relation between these elements and residual garnet in the partially melted mantle. The 207Pb/204Pb and 206Pb/204Pb ratios of the basanitic rocks fall near the field of enriched mantle II (EM-II). The Gandom Beryan volcanism, which was related to partial melting of mantle within an extensional setting, resulted from a left-step, pull-apart basin in the Nayband N-S trending strike-slip fault system. Although the fault system is older than Gandom Beryan volcanism, it seems that it has been reactivated during and after the volcanism.

Iranshahr blueschist: subduction of the inner Makran oceanic crust

AbstractThe Makran accretionary prism in SE Iran and SW Pakistan is one of the most extensive subduction accretions on Earth. It is characterized by intense folding, thrust faulting and dislocation of the Cenozoic units that consist of sedimentary, igneous and metamorphic rocks. Rock units forming the northern Makran ophiolites are amalgamated as a mélange. Metamorphic rocks, including greenschist, amphibolite and blueschist, resulted from metamorphism of mafic rocks and serpentinites. In spite of the geodynamic significance of blueschist in this area, it has been rarely studied. Peak metamorphic phases of the northern Makran mafic blueschist in the Iranshahr area are glaucophane, phengite, quartz±omphacite+epidote. Post peak minerals are chlorite, albite and calcic amphibole. Blueschist facies metasedimentary rocks contain garnet, phengite, albite and epidote in the matrix and as inclusions in glaucophane. The calculated P–T pseudosection for a representative metabasic glaucophane schist yields peak pressure and temperature of 11.5–15 kbar at 400–510 °C. These rocks experienced retrograde metamorphism from blueschist to greenschist facies (350–450 °C and 7–8 kbar) during exhumation. A back arc basin was formed due to northward subduction of Neotethys under Eurasia (Lut block). Exhumation of the high‐pressure metamorphic rocks in northern Makran occurred contemporarily with subduction. Several reverse faults played an important role in exhumation of the ophiolitic and HP‐LT rocks. The presence of serpentinite shows the possible role of a serpentinite diapir for exhumation of the blueschist. A tectonic model is proposed here for metamorphism and exhumation of oceanic crust and accretionary sedimentary rocks of the Makran area. Vast accretion of subducted materials caused southward migration of the shore.

Albian and Cenomanian ammonites of the eastern margin of the Lut block (East Iran)

Upper Albian and Lower Cenomanian ammonites occur on the eastern margin of the Lut block in eastern Iran. The ammonite assemblages described herein are from the Nimbolook and Kerch sections located west of Qayen. The following taxa are described: Mantelliceras mantelli (J. Sowerby, 1814), Mantelliceras saxbii (Sharpe, 1857), Mantelliceras sp. 1, Mantelliceras sp. 2, Mantelliceras sp. 3, Sharpeiceras laticlavium (Sharpe, 1855), Sharpeiceras schlueteri (Hyatt, 1903), Puzosia (Puzosia) mayoriana (Orbigny, 1841), Hyphoplites costosus C.W. Wright & E.V. Wright, 1949, Mortoniceras (Mortoniceras) cf. fallax (Breistroffer, 1940), Mantelliceras cf. mantelli (J. Sowerby, 1814), Calycoceras (Gentoniceras) aff. gentoni (Brongniart, 1822), Idiohamites fremonti (Marcou, 1858), Mariella (Mariella) sp., Mariella (Mariella) dorsetensis (Spath, 1926), and Turrilites costatus Lamarck, 1801. The ammonite assemblages clearly indicate a late Albian-middle Cenomanian age for the Nimbolook section and late Albian-early Cenomanian age for the Kerch section.

Foraminifera biozonation and morphogroups from Nimbolook section, east margin of Lut block, Iran

One stratigraphic section named Nimbolook succession in the northwest of Qayen city was measured and sampled. Based on identified foraminifera Berthelina intermedia assemblage zone, Rotalipora appenninica and Biticinella subbreggiensis interval zones were proposed. These biozones coincide with global biozones. According to foraminifera fauna, an Early–Late Albian age was suggested for this study. Palaeoecological studies led to the recognition of three benthic foraminifera (MG1–3) and two planktonic morphogroups (MG4–5). In the lower and middle part of the section, the abundance of benthic and agglutinated foraminifera (MG1–3) is more than planktonic foraminifera (MG4–5), respectively. Calcareous benthic morphogroups could be attributed to aerobic, shallow to slightly deep water, and eutrophic to mesotrophic environment. Agglutinated benthic morphogroups suggested that aerobic, mesotrophic, to eutrophic environments are characteristic by a dominance of arenaceous shallow infaunal specimens which are active deposit feeders. Planktonic foraminifera morphogroups with trochospiral and smooth test have been seen near the surface water, aerobic to semi-aerobic environment. Increasing planktonic foraminifera and specially keeled species could be a suggested recovery in paleoenvironmental conditions.

Multistage dolomitization in the Qal'eh Dokhtar Formation (Middle‐Upper Jurassic), Central Iran: petrographic and geochemical evidence

The late Jurassic Qal'eh Dokhtar Formation lithologically comprises three parts, from bottom to top, a lower sandstone unit, middle shale unit and an upper carbonate unit, which extend in a N–S direction over a wide area to the east of the Shotori Range and west of the Lut Block (Central Iran). This succession was deposited on a mixed carbonate–siliciclastic ramp. Carbonate rocks of the Qal'eh Dokhtar Formation vary from undolomitized, to partly dolomitized, to completely dolomitized. Field observations from two measured sections (the type section, 955 m thick, and the Sorond section, 639 m thick), combined with detailed petrographic and geochemical analyses, revealed the diverse types of dolomite in this formation. Five types of replacement dolomite and one type of dolomite cement were distinguished. Replacement dolomites (RD) consist of: (1) fine crystalline planar‐s (RD1); (2) medium crystalline planar‐s (RD2); (3) medium crystalline planar‐e (RD3); (4) coarse crystalline planar‐s (RD4); and (5) coarse crystalline planar‐e (RD5). Coarse crystalline planar dolomite cements (DC) were observed in low abundance and filling dissolution voids and fractures. Variation in dolomite types is mainly related to early to late diagenetic processes leading to changes in composition of the dolomitizing fluids. Replacement dolomites are non‐stoichiometric (Ca43‐56–Mg34‐45) with Sr, Mn and Fe concentrations of 41–138 ppm, 168–919 ppm and 5000–21000 ppm, respectively. These dolomites are characterized by δ18O values ranging from 0.0 to –11.8 ‰ VPDB and δ13C values of +1.1 to +3.2 ‰ VPDB. These values are depleted in δ18O relative to the postulated values for late Jurassic dolomites precipitated in equilibrium with seawater, while δ13C values are within the range of Jurassic seawater dolomite values. Fluid inclusion data of RD4, RD5 and DC yield homogenization temperatures of 72 to 118 °C. Based on petrographic, fluid inclusion microthermometric data and geochemical results, the replacement dolomites in the Qal'eh Dokhtar Formation are interpreted to have formed in the subsurface at shallow to intermediate burial depths. These dolomites were then recrystallized at increased burial depths and temperatures. Seawater was the major source of Mg2+ for early diagenetic dolomite (DR1), while Mg2+ for late diagenetic dolomites was provided from diagenesis of clay minerals in shales and mechanical compaction of mudstone in the Qal'eh Dokhtar Formation. The dolomite cement is postdated by coarsely crystalline mosaic calcite cement indicating that diagenetic fluids eventually became undersaturated with respect to dolomite and oversaturated with respect to calcite. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Petrogenesis and tectonic setting of the Bazman Batholith, Southeast Iran

The Bazman batholith is located in the south of Lut block, southeastern Iran. The intrusive rocks include alkali granite, intermediate granitoid (quartz-monzonite, quartz-monzodiorite and granodiorite), gabbro and some leucocratic dykes (aplitic) which have been intruded into upper Paleozoic sedimentary rocks and causing a contact metamorphic aureole. In the granitoids, A/NK>1 and A/CNK<1 ratios are indicative of metaluminous nature. Initial 87Sr/86Sr ratios for the Bazman samples (<0.706), are consistent with I-type magmatic sources. Furthermore, based on chemical characteristics and mineralogy, the granitoids are I-type. In the Harker diagrams major and trace elements variations are not consistent with generation of granitoids from gabbros via magmatic differentiation process which is also confirmed by the normalized REEs and multi-element diagrams. In the normalized multi-element diagrams, light ion lithophile elements (LILE) such as K and Rb display positive anomaly whereas high field strength element (HFSE) such as Ti, Nb and Ta represent negative anomaly. Based on major elements geochemistry including low (Na2O+K2O)/(MgO+FeO+TiO2), K2O/Na2O and Al2O3/(MgO+FeO+TiO2) ratios and high CaO/Al2O3 and CaO+FeO+MgO+TiO2 contents, intermediate granitoids are similar to those ofpartial melts of amphibolite/metabasalt sources. In addition, trace elements modeling show that the intermediate granitoids can be produced by dehydration partial melting (10 to 30%) from an amphibolitic source and restite minerals assemblage of plagioclase, clinopyroxene, orthopyroxene and Fe-Ti oxides. Based on major element geochemistry, the intermediate granitoids are comparable with the partial melts originating from a metabasaltic/amphibolitic source. Geochemical characteristics suggest that the Bazman batholith has been formed in a volcanic arc setting (active continental margin). Therefore, it seems that during upper-Cretaceous, the southern margin of the Lut block was an active continental margin due to the subduction of a Neo-Tethyan slab beneath southern margin of Eurasia. Here we proposed a new model in which the oceanic basin of southern Lut was probably different from the ocean which is now subducting beneath the Makran. Instead it was a closed oceanic basin beneath Jazmurian depression.

Geodynamics and underlying bedrock of the magnetically active crust layer of the Lut block, Eastern Iran

The Curie point depth map of Eastern Iran was constituted from spectral analysis of the aeromagnetic data. The reduction to pole (RTP) was applied to the magnetic anomaly data. The Curie point depth values from 165 overlapping blocks, 100 × 100 km in size, have been estimated. The Curie point depth method provides a relationship between the 2-D FFT power spectrum of the magnetic anomalies and the depth of magnetic sources by transforming the spatial data into the frequency domain. The centroid and top depth of the magnetic sources (respectively Z0 and Zt) is calculated from radially averaged log power spectrum for each block. Finally, the Curie point depth of Eastern Iran is obtained by Zb = 2Z0–Zt. The highest value of 24 km is located in eastern and western boundaries of the Lut block, and the lowest value of 12 km is located at north of study area. The shallow depths in the Curie-point depth map are well correlated with the young volcanic areas and geothermal potential fields. Geothermal gradient ranging from 24 to 45°C/km. The deduced thermal structure in eastern Iran has a relationship with orogenic collapse associated with delamination of thickened lithospheric root between the Lut and Afghan continental blocks.

The Chahnaly Low-Sulfidation Epithermal Gold Deposit, Western Makran Volcanic Arc, Southeast Iran

The Chahnaly low-sulfidation epithermal Au deposit and nearby Au prospects are located northwest of the intermittently active Bazman stratovolcano on the western end of the Makran volcanic arc, which formed as the result of subduction of the remnant Neo-Tethyan oceanic crust beneath the Lut block. The arc hosts the Siah Jangal epithermal and Kharestan porphyry prospects, near Taftan volcano, as well as the Saindak Cu-Au porphyry deposit and world-class Reko Diq Cu-Au porphyry deposit, near Koh-i-Sultan volcano to the east-northeast in Pakistan. The host rocks for the Chahnaly deposit include early Miocene andesite and andesitic volcaniclastic rocks that are intruded by younger dacitic domes. Unaltered late Miocene dacitic ignimbrites overlie these rocks. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb zircon geochronology data yield ages between 21.8 and 9.9 Ma for the acidic-intermediate regional volcanism. The most recent volcanic activity of the Bazman stratovolcano involved extrusion of an olivine basalt during Pliocene to Quaternary times. Interpretation of geochemical data indicate that the volcanic rocks are synsubduction and calc-alkaline to subalkaline. The lack of a significant negative Eu anomaly, a listric-shaped rare earth element pattern, and moderate La/Yb ratios of host suites indicate a high water content of the source magma. Gold and electrum are temporally and spatially related to a series of structurally controlled, 030°-trending, subvertical hydrothermal breccias with chalcedony-adularia that cut porphyritic andesite and andesitic volcaniclastic rocks. Gold is associated with pyrite, a siliceous matrix of hydrothermal breccia, and previously formed vein clasts, as well as with iron oxides and hydroxides in oxidized zones. Rare silver minerals include Ag-bearing electrum and naumannite, iodargyrite, an unnamed silver diiodide, and hessite. Hydrothermal alteration is generally well developed surrounding the ore-bearing hydrothermal breccia. The main types of alteration in the area include an inner ~0.5- to 20-m-thick gold-bearing hydrothermal breccia composed of quartz-chalcedonyadularia-illite-pyrite, a ~5- to 50-m-thick zone of quartz, chalcedony, pyrite, illitic phengite, phengite, illitic muscovite, illite, illitic paragonite, paragonite, muscovite, montmorillonite and, rarely, siderite, and a 30- to 70-m outer propylitic zone of Fe-Mg chlorite, calcite, ankerite, dolomite, epidote, palygorskite, and pyrite. The Chahnaly Au deposit formed during the early stages of magmatism. LA-ICP-MS zircon U-Pb geochronology of host andesite and 40Ar/39Ar dating of two samples of gold-associated adularia show that the ore-stage adularia (19.83 ± 0.10 and 19.2 ± 0.5 Ma) is younger, by as much as 1.5 million years, than the volcanic host rock (20.32 ± 0.4 Ma). Therefore, either hydrothermal activity continued well after volcanism or a second magmatic event rejuvenated hydrothermal activity. This second magmatic event may be related to eruption of porphyritic andesite at ~20.32 ± 0.40 Ma, which is within error of ~19.83 ± 0.10 Ma adularia. The new LA-ICP-MS zircon U-Pb host rock and vein adularia 40Ar/39Ar ages suggest that early Miocene magmatism and mineralization in the Bazman area is of a similar age to that of the Saindak porphyry and Tanjeel porphyry center of the giant Reko Diq deposit. This confirms the existence of early Miocene arc magmatism and mineralization along the Iranian part of the Makran volcanic arc. Ore, alteration mineralogy, and alteration patterns indicate that the Chahnaly deposit is a typical low-sulfidation epithermal Au deposit, located in a poorly explored part of the Makran volcanic arc in Iran.

Geochemistry, zircon U-Pb age, and tectonic constraints on the Bazman granitoid complex, southeast Iran

The Bazman granitoid complex (BGC), including a large zoned pluton, intrudes into the upper Paleozoic sedimentary cover of the Lut block. It crops out on the southern slope of the Bazman volcano in Baluchestan Province of Iran. The intrusive rocks range from gabbro to various metaluminous to weakly peraluminous granites, and they are classified as I-type magmatic series. They display geochemical characteristics of typical volcanic arc magmatism at continental margins. Major- and trace-element variation diagrams show that fractional crystallization was the major process and crustal contamination, a subordinate process during the evolution of the BGC. The decrease in CaO, MgO, Al2O3, Fe2O3, TiO2, P2O5, and Sr, as well as the increase of K2O and Rb with increasing silica, are possibly related to the fractionation of plagioclase, hornblende, apatite, and titanite, whereas the increasing K, Rb, Cs, Pb, and light rare earth elements (LREEs) can be explained by crustal contamination. The BGC rocks are enriched by large ion lithophile elements (e.g., Rb, K, Cs) and the LREEs with respect to the high field strength elements (e.g., Zr, Hf, Nb, Ta, Y) and heavy rare earth elements. New ID-TIMS U-Pb dating performed on zircon and titanite extracted from the granitic samples indicates that the BGC was emplaced during the late Cretaceous period at 83?72 Ma by subduction of the Neo-Tethyan oceanic crust beneath the Eurasian continent. Subsequently, the complex became part of the Lut block when it probably rotated counter-clockwise with respect to the Sanandaj-Sirjan zone and the Urumieh-Dokhtar volcano-plutonic belt.

Geomorphic signal of active faulting at the northern edge of Lut Block: Insights on the kinematic scenario of Central Iran

AbstractRecent works documented Neogene to Quaternary dextral strike‐slip tectonics along the Kuh‐e‐Sarhangi and Kuh‐e‐Faghan intraplate strike‐slip faults at the northern edge of the Lut Block of Central Iran, previously thought to be dominated by sinistral strike‐slip deformation. This work focuses on the evidence of Quaternary activity of one of these fault systems, in order to provide new spatiotemporal constraints on their role in the active regional kinematic scenario. Through geomorphological and structural investigation, integrated with optically stimulated luminescence dating of three generations of alluvial fans and fluvial terraces (at ~53, ~25, and ~6 ka), this study documents (i) the topographic inheritance of the long‐term (Myr) punctuated history of fault nucleation, propagation, and exhumation along the northern edge of Lut Block; (ii) the tectonic control on drainage network evolution, pediment formation, fluvial terraces, and alluvial fan architecture; (iii) the minimum Holocene age of Quaternary dextral strike‐slip faulting; and (iv) the evidence of Late Quaternary fault‐related uplift localized along the different fault strands. The documented spatial and temporal constraints on the active dextral strike‐slip tectonics at the northern edge of Lut Block provide new insights on the kinematic model for active faulting in Central Iran, which has been reinterpreted in an escape tectonic scenario.