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New detrital U–Pb zircon ages from the Sanandaj–Sirjan metamorphic zone in the Zagros orogenic belt allow discussion of models of the late Neoproterozoic to early Palaeozoic plate tectonic evolution and position of the Iranian microcontinent within a global framework. A total of 194 valid age values from 362 zircon grains were obtained from three garnet-micaschist samples. The most abundant detrital zircon population included Ediacaran ages, with the main age peak at 0.60 Ga. Other significant age peaks are at c. 0.64–0.78 Ga, 0.80–0.91 Ga, 0.94–1.1 Ga, 1.8–2.0 Ga and 2.1–2.5 Ga. The various Palaeozoic zircon age peaks could be explained by sediment supply from sources within the Iranian microcontinent. However, Precambrian ages were found, implying a non-Iranian provenance or recycling of upper Ediacaran–Palaeozoic clastic rocks. Trace-element geochemical fingerprints show that most detrital zircons were sourced from continental magmatic settings. In this study, the late Grenvillian age population at c. 0.94–1.1 Ga is used to unravel the palaeogeographic origin of the Sanandaj–Sirjan metamorphic zone. This Grenvillian detrital age population relates to the ‘Gondwana superfan’ sediments, as found in many Gondwana-derived terranes within the European Variscides and Turkish terranes, but also to units further east, e.g. in the South China block. Biogeographic evidence proves that the Iranian microcontinent developed on the same North Gondwana margin extending from the South China block via Iran further to the west.

Staurolite stability in rocks of zonal metamorphic complexes and the subsequent decomposition of this mineral in the rocks at increasing temperature is a criterion for distinguishing the staurolite metamorphic zone. Along with other metamorphic zones, this zone reflects the temperature distribution configuration when the metamorphic zoning was formed. Staurolite-bearing mineral assemblages are formed in metapelites of appropriate chemical composition at metamorphic temperatures of ~500–650°C. The fact that staurolite is stable within a relatively narrow temperature range makes it possible to predict the presence or absence of this mineral in rocks if representative data on the composition of their protoliths are available. We propose a method for identifying potentially staurolite-bearing rocks using computational petrochemical modules, whose values are calibrated on natural rocks and modeled rock compositions that can occur in nature. Four petrochemical modules are proposed in the form of specified proportions of major chemical components in metamorphic rocks: Al2O3/SiO2, CaO/FM (where FM = FeOt + MgO), K2O/FM, and Na2O/FM. They can be used as criteria for estimating the possibility of staurolite crystallization in rocks when a suitable temperature (and pressure) is reached. These modules make it possible to select and more reliably specify the boundaries of the staurolite zone when, for example, maps of metamorphism are produced.

Metamorphic rock units of Toutak and Surian complexes located in the Sanandaj–Sirjan metamorphic zone, NE Shiraz, Iran, were mapped using the matched filtering (MF) method on the visible near-infrared (VNIR) and shortwave infrared (SWIR) bands of advanced spaceborne thermal emission and reflection radiometer (ASTER) sensor. These complexes host magnetite and Cu–Zn–Ag volcanogenic massive sulfide (VMS) deposits. Mixed pixels of lithologic–mineralogic indicators of these deposits were detected to identify the prospecting areas. The spectra of end-members were extracted from imagery using sequential maximum angle convex cone (SMACC) model and were compared to the field and laboratory spectra to examine their characteristics. The key minerals including chlorite + epidote (greenschist), muscovite + biotite (mica schist), calcite + dolomite (marble), and muscovite + oligoclase (gneiss) were identified and were input to the algorithm for estimating the sub-pixel fractions of desired minerals. A generalized map of lithologies was then produced by combining the fraction maps of greenschist, mica schist, marble, and gneiss using a GIS. Finally, this lithologic association was applied to define the prospecting areas. The accuracy of results was assessed using R2 coefficient, field observations, and XRD analysis. The R2 coefficient was 0.74 for greenschist, 0.63 for mica schist, 0.65 for marble, and 0.53 for gneiss. The results also showed good agreement with field evidence, and thus, they can be used for finding potential targets for copper and iron deposits.

International audience; The North Pyrenean Zone inverts remnants of an Aptian–Cenomanian rifting during which subcontinental mantle was exhumed. These remnants contain a synrift HT–LP metamorphic domain, the Internal Metamorphic Zone. New field data, Raman spectroscopy on carbonaceous material data and structural cross-sections constrain the structural and metamorphic relationships between the Internal Metamorphic Zone and the underlying low-grade North Pyrenean Zone. The Internal Metamorphic Zone is a tectonic nappe that overthrusts the European margin along the 3M Fault. Along this contact, the Tuc de Haurades peridotite is surrounded by tectonic breccia composed of ductilely deformed carbonate and sparse lherzolite clasts that passes upward into foliated marbles. Marbles contain top-to-south ductile shear, recording continuing extensional deformation that marks the onset of HT metamorphism. During Early Cretaceous rifting, European Mesozoic sedimentary cover metamorphosed and its base brecciated as it slid basinward on Triassic salt onto exhumed mantle. As the exhumed mantle domain closed during early convergence, the detached metamorphosed cover was transported northward and thrust onto the distal European margin, sampling lherzolite tectonic lenses. This triggered the first tectonic loading on the European plate. This study highlights the role of the Internal Metamorphic Zone in the early Pyrenean orogenic phase and gives new insights into the east–west diversity of structural setting of the North Pyrenean Zone peridotites. Supplementary material : A table with Raman spectroscopy on carbonaceous material temperatures and original and high-quality photographs of the samples are available at https://doi.org/10.6084/m9.figshare.c.5539260

The Central Qilian Block is a Precambrian block in the Qilian Orogen, which has long drawn international attention for the study of orogeny and continental dynamics. The Huangyuan Group in the Datong area is one of the Precambrian metamorphic basement units in the Central Qilian Block and reflects metamorphism in the Barrovian garnet zone and sillimanite zone from south to north. Based on detailed fieldwork, this study presents a systematic study of petrography, mineral chemistry and phase equilibria of schists and gneisses from the two metamorphic zones. The garnet metamorphic zone is composed of micaschist, garnet-bearing micaschist and felsic leptynite, with interlayered plagioclase amphibolite. The sillimanite metamorphic zone consists of garnet-bearing biotite micaschist, sillimanite-bearing biotite-plagioclase gneiss and felsic leptynite. Garnet from the garnet metamorphic zone shows growth zoning with increasing almandine and pyrope and decreasing spessartine from core to rim. Garnet from the sillimanite metamorphic zone is almost homogeneous. Towards the outer rim, the contents of almandine and pyrope slightly decrease and grossular slightly increase. Biotite in both metamorphic zones is ferro-biotite. Plagioclase is oligoclase in garnet metamorphic zone and andesine in sillimanite metamorphic zone. Phase equilibrium modeling of a sample from garnet metamorphic zone resulted in a clockwise P-T path with a prograde stage (4.5–5.0 kbar, 520–530 °C), a peak P stage (9.8–10.2 kbar, 560–570 °C), a stage of thermal relaxation (8.0–8.5 kbar, 580–590 °C) and finally a retrograde stage (6.8–7.0 kbar, 560–580 °C). Thermodynamic modeling of a sample from the sillimanite metamorphic zone indicates a prograde stage (5.5–6.0 kbar, 540–550 °C) and a peak stage (7.8–8.5 kbar, 660–690 °C). The results indicate that the Huangyuan Group experienced medium-pressure amphibolite-facies metamorphism, which resulted from continental-continental collision between the Qaidam Block and the Central Qilian Block.

Awi 18-1 is an injection well drilled in the Cianten Caldera, near the western margin of the Salak (Awibengkok) reservoir in west Java, Indonesia. As the initial well injectivity was low, a long-term hydraulic stimulation was conducted to improve the permeability and establish a better connection to existing natural fractures. A geologic model of the area was built by integration of surface mapping, log and core data, and well performance information. The well penetrated pre- and post-caldera volcanics, the caldera ring fault intrusion and contact metamorphic zone, and marine sedimentary rocks. Permeability was found primarily near the caldera margin in pre-caldera lavas and ring fault intrusion along steeply dipping N to NW and NE trending fractures that were partially sealed by mineral precipitation. A geomechanical simulation model was developed from the geologic model to understand the injectivity evolution mechanisms and behaviours under different injection conditions, and also predict long term future injectivity performance. The model domain contains the completed interval of a deviated injection well (Awi 18-1) and covers the majority of microseismic events observed during the course of the stimulation. It simulates injectivity evolution using fully coupled processes of heat and mass transfers in poro-elastic media. The model was history-matched against the injection data (i.e. pressure) by calibrating rock mechanical and fracture properties. A few what-if scenarios under different operation conditions were simulated to evaluate the effects of injection pressure and temperature on the injectivity. These what-if scenario simulations indicate that both colder injection temperature and higher wellhead pressure lead to better injection efficiency. Also, the higher pressure had prolonged impacts while the colder temperature impacts are limited at the early time.

In recent years, a variety of remote sensing data have been widely used in mineral exploration, particularly at the reconnaissance stage for mapping alteration zones and investigating the relationship between tectonic structures and target mineralization. Moreover, different image processing methods such as band ratios, dimensionality reduction, and classification have been developed for enhancing target features in various mineralization systems. The Sanandaj-Sirjan metamorphic zone in Iran is a potential zone for different types of metallic mineralization, such as copper, molybdenum, and gold. Contrary to other metallic deposits, only a few studies have been carried out to map gold deposits in this region using remote sensing data. This study aims to map tectonic lineaments and those alteration zones known to be relevant to orogenic gold deposits in the Qolqoleh-Kasnazan shear zone, a portion of the Sanandaj-Sirjan zone in the southwest of Saqez, Iran. We use two well-known and efficient image processing methods, i.e., band ratios and principal component analysis, for processing ASTER images and mapping alteration zones. Moreover, we map tectonic lineaments using the first principal component of Landsat 8 data. The study of alteration zones and lineaments reveals a major trend of NW-SE for gold mineralization in the study area. It is observed that mineralized zones are associated with iron oxides and argillic alteration zones and the phyllic alteration is predominant at the margin and away from the center of mineralization zones.

International audience; Deformation processes related to early stages of collisional belts, especially the inversion of rifted systems remain poorly constrained, partly because evidence of these processes is usually obliterated during the subsequent collision. The Pyrenean belt resulting from the inversion of a Cretaceous hyperextended rifted margin associated with a HT/LP metamorphism in the Internal Metamorphic Zone (IMZ), is a good example for studying the early stage of orogenic deformation. This study is focused on the Eastern Pyrenees where the relation between inverted Mesozoic rifted basins and their basement are well-preserved. By using maximum temperatures (Tmax) estimated by the Raman Spectroscopy of Carbonaceous Materials geothermometer and structural data, we describe the spatial distribution of the various tectono-metamorphic units. Tmax recorded in the sedimentary cover exposed to the north and to the south of a Paleozoic basement block (Agly massif), exceed 550°C, while the Paleozoic metasediments and their autochthonous Mesozoic cover show Tmax

The Lesser Zab River (LZR), the largest tributary in Iraq, with a catchment area of about 20,000 km2, and majority of its basin lying in Iraq, drains into the Tigris River. It runs through highly folded and faulted igneous and metamorphic zone in the northeastern part of Iraq. We studied the heavy minerals in recent sediments of the Lesser Zab River Basin (LZRB) to determine their mineralogies, assemblages pattern, distribution manner, spatial variability, microtexture, provenance, and tectonic setting. We analyzed 24 sediment samples for heavy mineral assemblage determination, using the standard petrographic method. Scanning Electron Microscopy was used to determine the morphology of the grains of selected heavy minerals. Heavy minerals identified in the studied sediments include: dark color such as magnetite, ilmenite, hematite, and goethite; and transparent minerals represented by hornblende, tremolite–actinolite; pyroxenes, epidotes, zircon, tourmaline, rutile, garnet, staurolite, kyanite, and layered minerals assemblage such as muscovite, chlorite, biotite, and phlogopite. The studied sediments are considered immature, because they have the lowest concentration of ultrastable minerals compared to unstable heavy minerals, which confirms that the surface sediments of LZR and its sub-basin tributaries were deposited in an active continental-margin tectonic setting.

A detailed knowledge of the thickness of crust and upper mantle structure is important for understanding a plate tectonics and geodynamics in the region. We use body wave for detecting details of the subsurface structure. The information in this research is collected from a seismic linear profile that extends across the Sanandaj-Sirjan metamorphic zone in seismic states of Central Iran and Zagros. We compute P receiver functions to investigate crustal and upper mantle discontinuities. We use teleseismic events (mb ≥ 5.5, 30° < Δ < 95°) registered between 1996 and 2018 and recorded at 10 short-period stations with 3 components and 17 broadband stations with high signal to noise ratio. The observed depth of Moho in the study area is approximately 50 km and rises to 70 km at the end of the seismic linear profile beneath Sanandaj-Sirjan zone. In Central Iran, depths discontinuities in the transition zone are shown by the reference model of deviation, which can be attributed to the convergence of Arabian plate with the Central Iran plateau. Also, the study area was identified as geothermal susceptibility by SUNA and this observation was confirmed.

The spatiotemporal relationship between granitoid intrusions and low-pressure/temperature type regional metamorphism in the Ryoke belt (Mikawa area) is investigated to understand the tectono-thermal evolution of the upper- to middle-crust during a Cretaceous flare-up event at the Eurasian active continental margin. Three plutono-metamorphic stages are recognized; (1) 99–84 Ma: intrusion of granitoids (99–95 Ma pulse) into the upper crust and high-T regional metamorphism reaching sillimanite-grade (97.0 ± 4.4 Ma to 88.5 ± 2.5 Ma) in the middle crust, (2) 81–75 Ma: intrusion of gneissose granitoids (81–75 Ma Ma pulse) into the middle crust at ~19–24 km depth, and (3) 75–69 Ma: voluminous intrusions of massive to weakly-foliated granitoids (75–69 Ma pulse) at ~9–13 km depth and formation of contact metamorphic aureoles. Cooling of the highest-grade metamorphic zone below the wet solidus of granitic rocks is estimated at 88.5 ± 2.5 Ma. At ca. 75 Ma, the upper-middle crustal section underwent northward tilting, resulting in the exhumation of regional metamorphic zones to ~9–13 km depth. Although the highest-grade metamorphic rocks and the 99–95 Ma pulse granitoids preserve similar U–Pb zircon ages, the absence of spatial association suggests that the regional metamorphic zones were mainly produced by a transient thermal anomaly in the mantle and thermal conduction through the crust, supplemented by localized advection due to granitoid intrusions. The successive emplacement of granitoids into shallow, deep and shallow levels of the crust was probably controlled by the combination of change in thermal structure of the crust and tectonics during granitoid intrusions.

Subduction is a key process for linking the carbon cycle between the Earth's surface and interior. Carbonates in oceanic crust can be recycled into the deep mantle by plate subduction. In recent years, Mg isotopes have been successfully applied to trace the deep recycled carbonates (Li et al., 2016 and references thereafter). However, it remains unclear whether Mg isotopes can trace all recycled carbonate in the subduction zones. In this study, we petrologically and geochemically studied carbonated eclogite and marble from the S.W. Tianshan UHP metamorphic zone that was formed by the Late Palaeozoic oceanic subduction. Carbonate from carbonated eclogites predominantly consists of Fe-rich {Fe# = Fe / (Fe + Mg) ∗ 100 = 19–43} dolomite with minor Fe-rich (Fe# = 24–43) magnesite inclusions, whereas the carbonate from marble is major calcite and minor Fe-poor (Fe# = 0–7) dolomite. The bulk Mg isotopic composition (−0.19 ≤ δ26Mg ≤ 0.24‰) of carbonated eclogite from the S. W. Tianshan is fairly higher than typical mantle-source rock (−0.25 ± 0.07‰, 2SD). Meanwhile, carbonate separated from carbonated eclogite shows mantle-like Mg (−0.33 ≤ δ26Mg ≤ 0.09‰), C (−6.9 ≤ δ13C ≤ −3.3‰), and O (11.0 ≤ δ18O ≤ 12.3‰) isotopic characteristics, indicating most or at least part of their carbon stems from Earth's mantle. Although recycling of the carbonated eclogite in the subduction zone could partly affect mantle carbon budgets, it should have no relationship with the low δ26Mg signature of the mantle. In contrast, bulk marble shows sedimentary carbonate-like Mg (−2.72 ≤ δ26Mg ≤ −2.15‰), C (0.1 ≤ δ13C ≤ 1.9‰), and O (16.7 ≤ δ18O ≤ 22.1‰) isotopic characteristics, indicating all of the carbon in marble precipitated from seawater. Recycling of this marble in the subduction zone should play a key role in modifying mantle isotopic composition and formation of the local mantle-domain with a low-δ26Mg signature. Both petrologic and geochemical studies show that there are two different sources of recycled carbon in the S.W. Tianshan UHP oceanic subduction zone.

The Mesozoic accretionary complex in Northeast China, which mainly consists of the Jilin-Heilongjiang high-pressure (HP) metamorphic belt and the Nadanhada accretionary complex, are the key area to understand the Paleo-Pacific subduction-accretion. The Jilin-Heilongjiang HP belt is a HP metamorphic zone between the Jiamusi and Songliao blocks and consists of the Heilongjiang blueschist belt and the Zhangguangcai Complex. Previously published and our new geochronological data indicate that the collision between the Jiamusi and Songliao blocks along the Jilin-Heilongjiang HP belt occurred between 210 and 180 Ma, suggesting that the Jilin-Heilongjiang HP belt is an important unit for characterizing the geodynamic switch from the north-south closure of the Central Asian Orogenic Belt to the onset of westward accretion related to subduction of Paleo-Pacific plate in the Latest Triassic to Early Jurassic. Early Permian igneous rocks with arc affinity in the eastern margin of the Jiamusi Block are more likely related to the Mongol-Okhotsk subduction rather than the Paleo-Pacific subduction or the collision between the Jiamusi and Khanka blocks as previously considered. The Nadanhada accretionary complex lies to the east of the Jiamusi Block, and is composed of the Yuejinshan and Raohe complexes. Compilation of published geochronological data indicate that the Yuejinshan Complex was probably formed between 210 Ma and 180 Ma, similar to ages for the Jilin-Heilongjiang HP belt along the western margin of the Jiamusi-Khanka Block. The Raohe Complex was formed later in the Late Jurassic to Early Cretaceous (170–137 Ma), likely more related to the subduction-accretion of Paleo-Pacific plate. The final accretion in the target area took place in the Early Cretaceous (137–130 Ma).

Deformed low-grade metabasites from the western segment of the Beihuaiyang zone in the Hong’an orogen, central China can be divided into two types, i.e. meta-gabbro and meta-basalt. These lithologies have been studied by using whole-rock elemental and Sr-Nd-Pb isotopic analyses, and zircon SHRIMP U-Pb dating. Concordant zircon U-Pb ages of 631 ± 5 Ma and 623 ± 14 Ma are obtained for the meta-gabbros, consistent with a previously reported U-Pb age of 635 ± 5 Ma. The meta-basalt was dated to have a protolith age of middle Neoproterozoic (∼750 Ma) and a metamorphic age at ca. 240 Ma. The all studied metabasites occur as block or slice within a metamorphosed Ordovician volcanic zone (originally named as the Dingyuan Formation) and are in tectonic contact to each other. The gabbro and basalt emplaced at ∼630 Ma and ∼750 Ma, respectively in a continental rifting setting, whereas their present country rocks were erupted at ∼465 Ma in an arc setting. The Pb-isotope compositions of the low-grade meta-gabbros and meta-basalts are similar to those from the Dabie ultrahigh-pressure (UHP) meta-igneous rocks with an upper continental crust affinity. The protolith ages of the studied relatively low-grade meta-basic rocks are in good agreement not only with ages for two episodes of middle and late Neoproterozoic mafic and felsic magmatism in the Suizhou to Zaoyang areas at the northern margin of the South China Block, but are also in agreement with the protolith ages of UHP meta-igneous rocks in the Dabie-Sulu orogenic belt. Therefore, these Neoproterozoic low-grade metabasites are considered to be exotic and they may have been detached and offscraped from the subducting upper crust of the South China Block at shallow depths during continental collision in the Triassic. They were subsequently exhumed in the initial stage of continental subduction, and thrusted over the Paleozoic metamorphosed rocks in the southern margin of the North China Block or as foreign slices within the UHP metamorphic zone. They are a kind of the accretionary wedge involved in the Paleozoic oceanic subduction, and Triassic crustal detachment and tectonic overthrusting during the early stage of continental subduction.

This study focuses on the Cenozoic provenance and tectonic evolution of the southwestern Qaidam Basin through geochemical analysis of detrital garnet, tourmaline and rutile. The variation of detrital mineral compositions indicates that the Cenozoic evolution can be divided into three stages: (i) before the deposition of the upper Xiaganchaigou Formation (before 37.8 Ma); (ii) between the deposition of the upper Xiaganchaigou Formation and the Shangganchaigou Formation (from 37.8 to 22 Ma); (iii) since the deposition of the Xiayoushashan Formation (since 22 Ma). In the first stage, abundant garnets from high‐grade meta‐basic and ultramafic rocks in the sediments from the Ganchaigou area support a provenance from the South Altyn Tagh HP/UHP metamorphic zone. The low percentage of tourmalines from granitoid rocks in the sediments in the Kunbei‐Lucaotan area suggests a provenance from the East Kunlun fault zone, indicating that the Qimen Tagh Shan was not high enough to prevent the transport of sediments from the southern Qaidam Basin. The sediments in the Qigequan area were derived from both the Altyn Tagh fault zone and the East Kunlun fault zone. In the second stage, the tectonic activity consisted in the rapid uplift of the Altyn Shan. Changes in garnet composition indicate a lower detrital contribution from high‐grade metamorphic rocks. In the third stage, the disappearance of garnets from high‐grade metamorphic rocks and scattered temperatures of rutiles in the Ganchaigou area suggest that the source area shifted from the South Altyn Tagh HP/UHP metamorphic rocks to weakly metamorphosed Meso‐Neoproterozoic sedimentary rocks. The increase in granitoid‐derived tourmalines in the Kunbei‐Lucaotan area is indicative of the rapid uplift of the Qimen Tagh Shan. The provenance evolution in the southwestern Qaidam Basin indicates that the tectonic activity along the Altyn Tagh fault zone can be divided into an early stage of Altyn Shan uplift and a later stage of left‐lateral slip. At the same time, tectonic movement along the East Kunlun fault zone initiated.

The Tengchong terrane comprises a sequence of linear dome-like zones, cored by granite and migmatitic layers. These cores are mantled by predominantly gneiss and subordinate schist sequences, decreasing in deformation intensity outward from extensive mylonitization to weak mylonitization. The pre-doming deformation was characterized by the formation of large-scale top-to-the-east shearing (D1) in the gneiss terrane, locally preserved flat-lying foliation (S1), weak folding (F1) and emplacement of the Mangbang granite during the Cretaceous (114-104 Ma). The second stage of deformation (D2) consisted of map-scale east-verging folds (F2, dome amplification) and minor lateral strike-slip shear zones between the anticlines in the gneiss and migmatitic sequences. Extensive partial melting and emplacement of 67-30 Ma synkinematic granitoid bodies/veins occurred, leading to the emplacement of wedges of granite into the easterly directed F2 fold cores. These wedges formed kilometer-scale granitoid domes. The post-doming D3 deformation with transpression recorded strain partitioning with simple shear-dominated high-strain zones along the Gaoligong and Nabang dextral lateral strike-slip shear zones (active during 30-11 Ma). Late transtensional deformation (D4) during cooling of the entire terrane involved the localized low-temperature Gaoligong west and east detachment faults that controlled the late exhumation of the Gaoligong metamorphic zone (since 10 Ma). Our structural observations, combined with previous studies, suggest that this style of doming is a representative type of intra-continental deformation in the Cenozoic during the oblique India-Asia collision. The actual dome shapes reflect formation of antiforms during compression-dominated transpression, prior to localized strike-slip shearing, in the accommodation belt around the Eastern Himalayan Syntaxis. Vertical exhumation of crustal material by contractional doming played an important role in absorbing the vast majority of the internal deformation of crustal fragments during oblique collision.

SUMMARY We have constructed a 3-D shear wave velocity (Vs) model for the crust and uppermost mantle beneath the Middle East using Rayleigh wave records obtained from ambient-noise cross-correlations and regional earthquakes. We combined one decade of data collected from 852 permanent and temporary broad-band stations in the region to calculate group-velocity dispersion curves. A compilation of >54 000 ray paths provides reliable group-velocity measurements for periods between 2 and 150 s. Path-averaged group velocities calculated at different periods were inverted for 2-D group-velocity maps. To overcome the problem of heterogeneous ray coverage, we used an adaptive grid parametrization for the group-velocity tomographic inversion. We then sample the period-dependent group-velocity field at each cell of a predefined grid to generate 1-D group-velocity dispersion curves, which are subsequently inverted for 1-D Vs models beneath each cell and combined to approximate the 3-D Vs structure of the area. The Vs model shows low velocities at shallow depths (5–10 km) beneath the Mesopotamian foredeep, South Caspian Basin, eastern Mediterranean and the Black Sea, in coincidence with deep sedimentary basins. Shallow high-velocity anomalies are observed in regions such as the Arabian Shield, Anatolian Plateau and Central Iran, which are dominated by widespread magmatic exposures. In the 10–20 km depth range, we find evidence for a band of high velocities (>4.0 km s–1) along the southern Red Sea and Arabian Shield, indicating the presence of upper mantle rocks. Our 3-D velocity model exhibits high velocities in the depth range of 30–50 km beneath western Arabia, eastern Mediterranean, Central Iranian Block, South Caspian Basin and the Black Sea, possibly indicating a relatively thin crust. In contrast, the Zagros mountain range, the Sanandaj-Sirjan metamorphic zone in western central Iran, the easternmost Anatolian plateau and Lesser Caucasus are characterized by low velocities at these depths. Some of these anomalies may be related to thick crustal roots that support the high topography of these regions. In the upper mantle depth range, high-velocity anomalies are obtained beneath the Arabian Platform, southern Zagros, Persian Gulf and the eastern Mediterranean, in contrast to low velocities beneath the Red Sea, Arabian Shield, Afar depression, eastern Turkey and Lut Block in eastern Iran. Our Vs model may be used as a new reference crustal model for the Middle East in a broad range of future studies.

The South China Block (SCB) is tectonically bounded by the Tethyan and Pacific subduction zones and the Qinling-Dabie HP-UHP metamorphic zone. Triassic tectonic activity was a key phase in the tectonic history of the SCB and in creating the fundamental framework of East Asia. The geometry and kinematics of the Triassic deformation sheds light on the mechanism driving intra-continental orogenesis in the SCB. Our new field- and mapped- based structural analysis, along with thermo-chronological dating results, reveal two-stage distinct Triassic deformations in the southern SCB involving top-to-north dextral thrusting at ~250–225 Ma and NE-trending sinistral transpression at ~230–190 Ma. Early Triassic dextral transpression is marked by WNW-trending high-strain zones and thrust nappes/sheets, which might have been rooted beneath the Hainan-Yunkai basement along a low angle, middle-upper crustal basal detachment. It transformed from a thick-skinned fold-and-thrust belt to thin-skinned Jura-like patterns with northerly-propagating deformation. Late Triassic NE-trending sinistral transpression was accompanied by a series of the parallel folds and thrusts in the SCB interior, resulting in the development of the regional positive-flower geometry and reactivation of the pre-existing structures. Such signatures, in combination with the available geological, geochronological, and paleogeographic observations, suggest two-stage (early-middle and late Triassic) intra-continental orogenesis in the SCB, were controlled by the clockwise scissor-like closure of the Paleotethyan Ocean and its interactions with the adjoining blocks including deep-subduction beneath the North China Block and limited lateral extrusion due to the obstructing paleo-Pacific plate.

Several outcrops of spectacular feather-like hornblende aggregates occur in the phyllites of the Gol-e-Gohar complex (southeast of Iran) and form special Garbenschiefer rock types. The Gol-e-Gohar complex, as a part of the southern Sanandaj-Sirjan metamorphic zone, contains a succession of metabasites, phyllites, and slates intruded by dioritic intrusions. There are two types of hornblendes in the phyllites; the first one is concentrated around the fractures and the second one is randomly distributed in the rocks and forms radial feather-like hornblende aggregates. Petrographical and chemical characteristics of these two shapes of hornblendes are the same, except the latter is developed parallel to the foliation planes. The hornblendes occur as unstrained needle-shaped porphyroblasts with oriented quartz and feldspar inclusions as well as polygonal grains in the matrix with mosaic texture, which implies the matrix has been recrystallized. On the basis of field observations, petrography, and chemical compositions of the hornblendes, we inferred that the Garbenschiefer phyllites formed during hydrothermal metamorphism in association with penetration of hot fluids. The compositions of hornblende aggregates are similar to those formed in hydrothermal systems and differ from regional and thermal metamorphic amphiboles. All evidence shows that, in the studied area, ascending of dioritic intrusions increases fluid temperature, the hot fluids leach some elements from the metabasites, and finally the enriched fluids flow upward via the fractures. In the upper levels, the fluids penetrate into the phyllites along their foliation planes and, with a decrease in temperature and pressure, they crystallize hornblende aggregates under static hydrothermal conditions.

The first occurrence of two-step growth of textural sector- and sigmoidal-zoned garnet of metapelitic rocks of the San Lorenzo Schists in the Sierra Nevada de Santa Marta massif is documented here. This textural type of zoned garnets occurs in the staurolite metamorphic zone of the San Lorenzo Schists. They are generally coarse-grained (up to 2.5 mm in diameter), and occur in quartz-rich domains. Together with staurolite, garnet is a porphyroblastic mineral in these rocks. Two periods of garnet growth have been observed: (1) a xenoblastic core, with a sector-zoned garnet; and (2) a subidioblastic rim with a sigmoidal-zoned garnet. Garnet preserves chemical zoning, with decreasing XMn and increasing XMg from core to rim (a patch trend), suggesting that garnet grew during increasing temperature. XCa and XFe follow a radial trend. Study of this type of garnet indicates that it has grown during the late emplacement of gabbroic rocks of the Santa Marta Batholith close to thepeak regional of metamorphism of the San Lorenzo Schists. During the first steps of garnet growth, it develops a textural sector-zoning, characterized by the cleavage domes, pressure shadows and shearing away cleavage domes, whereas during the last steps a textural sigmoidal-zoned garnet overgrowth occurred after textural sector-zoned garnet. This type of textural sector- and sigmoidal-zoned garnet from the San Lorenzo Schists is very important as a key piece for interpretation of thetectono-metamorphic history of this metamorphic unit.Keywords: San Lorenzo Schists, two-step growth, sector- and sigmoidal-zoned, garnet, metamorphism.

Columnar tourmaline in Cenozoic granitic mylonites from the Chongshan metamorphic zone (CMZ), Yunnan, China has deformed, at 450–300 °C, by tensile fractures normal to the foliation and lineation. Sequential fracturing and separation of the fragments during progressive cooling and exhumation upward the brittle-ductile transition produced a series of microboudins with decreasing length/width ratios. Here we present a method to apply the microboudinage paleopiezometry, combined with strain analyses, microstructural observations and thermochronological data to provide constraints on strain rates ( e ˙ ), differential stresses (σ) and their correlations with temperature for the polycrystalline quartz matrix in which tourmaline grains have been fragmented into microboudins. The results yield a flow law of e ˙ = Aσnexp(-Q/RT) with n = 4, Q = 184 kJ/mol and A = 7.180 × 10−7 MPa-ns−1 for naturally deformed quartzite. The differential stresses calibrated by this flow law are very close to the geometrical mean of the lower and upper bounds given by Luan and Paterson (1992) and Gleason and Tullis (1995), respectively. Utilization of this flow law to the present-day crust of the CMZ provides a reliable interpretation for the distribution of focal depths and electrical resistivity structure. The microboudinage piezometer also permits to estimate the mechanical strengths of rocks deformed in the elastic-brittle regime.

International audience; The architecture of the Pyrenean‐Cantabrian belt results from the inversion of a series of former Cretaceous rift basins. A HT‐LP metamorphic event dated at 105 to 85 Ma ago is commonly associated with an Albo‐Cenomanian episode of hyperextension of the continental crust. This metamorphism is well known in the eastern Basque‐Cantabrian Basin within the Nappe des Marbres Unit (NMU) that is preserved from intense compressional deformation during the Pyrenean orogeny. Based on a structural study at the scale of the eastern Basque‐Cantabrian Basin (BCB) and on a dense sampling for TRSCM estimates with the RSCM method (Raman Spectrometry on Carbonaceous Material), we show following results: (1) the NMU has recorded two major phases of deformation, related to a localized extensional ductile foliation (S1) during the Cretaceous rifting and later by the regional N‐S shortening, recorded by a regional cleavage (S2) observed only in shale sediments; (2) The NMU is affected by early salt tectonics related to several diapirs and salt walls fed by the Upper Triassic evaporitic layer; (3) The NMU recorded maximum temperatures exceeding 550°C, which represent some of the highest temperatures along the Pyrenees. These new data demonstrate that there is no E‐W lateral metamorphic gradient across the belt and that hyperextension rifting occurred consistently within a high‐thermal regime; (4) metamorphic isograds are oblique in respect of the main structures, suggesting that the metamorphic event postdates most of the early salt related deformations prior to or coeval with early stages of rifting. As it represents one of the best preserved example of pre‐orogenic hyperextended basin, the eastern BCB record may be used regionally to better understand the rift to orogen evolution of the Pyrenean Internal Metamorphic Zone but also more generally as an analog of salt‐bearing hyper‐extended rift record.

The Anjerd Cu skarn deposit is located 40 km north of Ahar, NW Iran, which comprises three different stages of skarn–type mineralization and metasomatic alteration including (i) prograde, (ii) early retrograde and (iii) late retrograde. Prograde stage is identified by garnet as andradite–grossularite and diopsidic pyroxene crystallization, whereas retrograde stage overprinted the prograde skarn and is predominantly composed of tremolite, actinolite, quartz, epidote and chlorite. Metasomatic alteration started with generation and evolution of the mineralizing fluids in the Shayvar batholith, followed by the fluids ascending into fractures of the skarn in the metamorphic zone. Subsequently, retrograde alteration continued to the end of the skarnification process. Based on mineral chemistry studies, garnet is dominated by andradite (27–78 mol. %) and grossularite (20–67 mol. %) compositions and pyroxenes by diopside (65–98 mol. %) and hedenbergite (2–34 mol. %) compositions. Based on detailed petrography studies, three types of fluid inclusions were recognized including two–phase liquid–rich (LV), vapor–rich (VL), and three–phase (LVS) inclusions. The characteristic of the mineralizing fluids during the skarn evolution was changed significantly from early retrograde stage with (i) high temperature (up to 460 °C) and high salinity (up to 39 wt% NaCl equiv.), through late retrograde stage with (ii) moderate to high temperature (334 to 446 °C) and low salinity (0.3 to 0.8 wt% NaCl equiv.), (iii) low to moderate temperature (158 to 362 °C) and moderate salinity (1.7 to 12.3 wt% NaCl equiv.), suggesting that high–temperature and moderately saline fluids are indicative of a magmatic source within the minerals belonging to the prograde skarn, while the fluids with lower temperature and low to moderate salinity indicating a meteoric source for the retrograde skarn assemblage. The δ18O values for prograde garnet and magnetite vary from ∑0 to 8.2‰, whereas δ18O and δD values for retrograde calc–silicates in equilibrium with fluid including epidote range from 6.7 to 9.2‰ and −10.2 to −31.4 and for chlorite range from 1.9 to 2.7‰ and −37.5 to −48.1‰, respectively, pointing out that mixing of magmatic fluids with meteoric water in the retrograde alteration. Moreover, the δ34S values of pyrite and chalcopyrite (−3.6 and +4.9‰), suggesting a magmatic source for sulfur which was largely responsible for the mineralization in the Anjerd deposit.

The subduction of the Paleotethyan Ocean and subsequent continental collision along the Lancang tectonic belt of the southeastern Paleotethyan belt is a major tectonic event in Southwest China, but the event of the subduction preceding the final collision is still not well-constrained. The mafic blueschists exposed in the Lancang accretionary complex provide crucial records of the Paleotethyan subduction process. In this paper, we present a set of new petrologic, geochronological and geochemical data for the Suyi mafic blueschists in the Lancang metamorphic zone. The mineral assemblage of these blueschists consists of zoned sodic amphibole (25–30%), albite (15–20%), epidote (25–30%), phengite (5–10%), chlorite (~ 5–10%), and minor amounts of actinolite, apatite, sphene, zircon, ilmenite, quartz and secondary limonite. This suggests a prograde metamorphism from ~ 0.5 to ~ 0.9 GPa and retrograde metamorphic overprinting (back to ~ 0.6 GPa) within the temperature range of 300–450 °C. The Suyi blueschists give a zircon U–Pb age of 260 ± 4 Ma and glaucophane minerals formed during prograde metamorphism yield a 40Ar/39Ar plateau age of 242 ± 5 Ma (MSWD = 0.77; P = 0.54). The blueschists have geochemical compositions of subalkaline basalt and show typical OIB-type REE and multi-elemental patterns and eNd(t) values ranging from + 3.35 to + 4.85. Based on available data, it is inferred that the protolith formed at 260 Ma and originated from a basaltic seamount. The basaltic rocks subducted down to 30–35 km depths beneath the Lincang arc to form the epidote blueschists at ~ 242 Ma. The blueschists were subsequently transported to shallower crustal levels in response to the continuous underthrust of the subducted slab and the continent–continent collision in the middle–late Triassic. These results provide a systematic constraint on the tectonic evolution and temporal framework of the southeastern Paleotethyan belt in Southwest China.

Comprehension of the genesis of Pb-Zn ore systems is currently limited by a poor understanding of where these metals are sourced from. Our study of metal mobility during regional metamorphism in the Mt. Lofty Ranges, South Australia, demonstrates that in staurolite-absent siliciclastic metasedimentary rocks, biotite contains >80 % of the bulk rock Zn, as well as a considerable proportion of the total Pb. Fluid flow through these metasedimentary rocks led to a continuous depletion of Pb and Zn on a mineral and bulk rock scale during prograde regional metamorphism. We calculate that ∼80 % of the bulk rock Zn and ∼50 % of the bulk rock Pb were mobilised, mainly through reactions involving biotite. These reactions led to a calculated Pb and Zn “loss” of ∼2.7 and 27 Mt, respectively, in the high-grade metamorphic zone. Halogen contents of apatite and biotite and bulk rock Zn isotope data provide evidence that Cl-rich metamorphic fluids were important for metal transport. Hence, fluid flow accompanying prograde metamorphism of typical sedimentary rocks can mobilise base metals to the degree required to potentially supply significant Pb-Zn ore systems.

The Matthew Creek Metamorphic Zone (MCMZ) exposes what is inferred to be the lowest structural level of the lower Aldridge Formation in the Canadian portion of the Belt–Purcell Supergroup. Zircon, monazite, and titanite were dated using the U–Pb system by LA–ICP–MS. The detrital zircon populations of quartzite layers in these rocks define a provenance dominated by sources of Laurentian affinity with a minor component of non-North American ages between 1600 and 1490 Ma. Special attention was paid to monazite in sillimanite-grade metapelitic schists that was analyzed using in situ LA–ICP–MS techniques guided by BSE imaging and compositional mapping. Textural and geochronological evidence indicate that coupled dissolution–reprecipitation affected detrital monazite at 1413 ± 10 Ma. This was followed by prograde monazite growth at 1365 ± 10 Ma, synchronous with crystallization of the nearby Hellroaring Creek peraluminous granite at 1365 ± 5 Ma. Late-stage pegmatite emplacement and ductile shearing along the contact of the MCMZ and overlying rocks occurred at 1335 ± 5 Ma, interpreted as a period of post-collisional extension, core complex formation, exhumation, and decompression melting. The entire package was subsequently affected by a pervasive ∼1050 Ma hydrothermal overprint that partially reset U–Pb dates in monazite, zircon, and titanite contained in all lithologies examined. The lowermost Belt–Purcell stratigraphy in southeast British Columbia preserves a detailed record of sedimentary provenance and a long history of episodic collision and extension that must be reconciled with plate reconstruction models for the break-up of the Nuna supercontinent and assembly of Rodinia.

New geologic mapping delimits major structures associated with the later stages of exhumation of high-pressure (HP) metamorphic rocks of the Sambagawa belt of central Shikoku. The main sets of structures define an inclined N-dipping wedge, bounded by S-vergent thrust faults below and N-vergent normal faults above. Such faults bound every metamorphic mineral zone of the Sambagawa belt. Faults also occur within metamorphic mineral zones, such as the Asemigawa detachment, which is entirely within the oligoclase–biotite zone, the highest-grade metamorphic zone. This fault is the structurally lowest of the N-vergent normal faults. These D2 structures accommodate the exhumation of the higher-grade rocks relative to the lower-grade rocks within the Sambagawa belt, rather than relative to units bounding the belt, so they are termed an “internal” extrusional wedge. The extrusional wedge is truncated to the east against footwall chlorite zone rocks by the Hamegano out-of-sequence thrust (OOST). The OOST divides the traditional chlorite zone into an upper unit consisting of varicolored schist (L tectonite), and a lower unit consisting of regionally extensive pelitic schist. To the north, the metamorphic mineral zones are stacked over the OOST, forming the Tomisato duplex, and these structures are further modified by the Oboke anticline and Tsuneyama syncline. The evolution of exhumation structures of the Sambagawa suggests progressive localization of strain as exhumation proceeded, as well as a change in movement direction from D1 oblique (orogen-subparallel) exhumation to the D2 structures with dip-parallel (orogen-normal) transport that we describe in detail. The evolution of exhumation structures in the Sambagawa belt differs from that of the HP rocks of the Franciscan Complex of California in that the exhumation of the latter is accommodated entirely by discrete faults and the Franciscan lacks internal normal faults. The internal extrusional wedge structure of the Sambagawa HP rocks resembles that of HP rocks of Leti Island of eastern Indonesia.

The Dorud–Azna region of the Sanandaj–Sirjan metamorphic zone (SSMZ) in NW Iran is part of the Zagros orogenic belt and exposes an amphibolite-grade metamorphic succession of mixed continental (e.g., the granitic Galeh–Doz orthogneiss) and oceanic or rift (e.g., various amphibolites) origin, which is intruded by the Darijune gabbro. Laser-ablation ICP–MS U–Pb zircon ages of 608 ± 18 Ma and 588 ± 41 Ma of the granitic Galeh–Doz orthogneiss indicate a Panafrican basement similar to that of the Yazd block of Central Iran. We therefore interpret this part of the SSMZ to represent a previously subducted part of the Panafrican basement of the Iranian microcontinent. Based on geochemistry, amphibolites and metagabbros from the Amphibolite unit representially potentially the cover on the Panafrican Galeh–Doz orthogneiss are interpreted to have their origin in a likely Upper Paleozoic to Mesozoic rift or E-MORB ophiolite succession. One of the metagabbros, here termed Dare-Hedavand metagabbro yield a 206Pb/238U mean age of 314.6 ± 3.7 Ma. Talc-bearing greenschists to epidote amphibolites of the Triassic June complex formed in a similar, but younger environment. Furthermore, the metamorphic complex is intruded by the Darijune gabbro, which yields a mean ICP–MS U–Pb zircon age of 170.2 ± 3.1 Ma. The final stage of likely Jurassic greenschist facies-grade metamorphism postdates the gabbro intrusion. We interpret the Darijune gabbro to have resulted from the initial subduction of Neotethyan oceanic lithosphere in a continental arc setting. The new data combined with data from literature indicate that the SSMZ represents a tectonic element of a mixed continental and oceanic origin, likely accreted to Central Iran during a Jurassic tectonic process. The new data also constrains thick-skinned nappe stacking within the Sanandaj–Sirjan zone.

The detailed analysis of the isotope-geochronological and isotope-geochemical data obtained in recent years by different researchers, including the authors of this study, is performed for the metamorphic formations of the Sredinny Range in Kamchatka formed within the Cretaceous sedimentary basin of the continental margin. It is concluded that all metamorphic complexes have the same age. They do not show stratification by the age of their formation, but the sequence of metamorphic facies from the ultra-high-temperature in the core of the metamorphic zone to the low-temperature on the flanges, which resulted from the metamorphic processes, granitization, and the formation of granite-gneiss domes ∼52 Ma ago. These processes resulted in the sharp uplift of the central parts of the metamorphic zone of the Range and their intense erosion, controlling widespread relationships between the deeply and weakly metamorphosed formations.

The high pressure metamorphic zone of As Sifah area in the Saih Hatat window, NE Oman plays a vital role to study global tectonic setting, metamorphism, transport direction and age of initial ophiolite emplacement. Scientists and researchers are keen in determining the protolith, structural evolution, and timing and metamorphic conditions of the Saih Hatat area. In this study, mapping of the metamorphic zone and discrimination of associated rock formations occurred in the As Sifah region is carried out using visible and near infrared–shortwave infrared (VNIR–SWIR) spectral bands of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and well known image processing methods such as image decorrelation, Principal Component Analysis (PCA) and Spectral Angel Mapper (SAM). The study delineated the region of metamorphic zone and discriminated the different metamorphic and carbonate rocks of the study area characterized by hydroxyl (OH) and carbonate bearing minerals. The assessment of accuracy for the occurrence and spatial distribution of major lithological units provided the overall accuracy of 96.06% with Kappa Coefficient = 0.95 in the matrix of Maximum Likelihood (ML) and compared with the Spectral Angle Mapper (SAM) and Spectral Information Divergence (SID) algorithms. The occurrence of such minerals are detected and confirmed by SAM supervised classification method. The study also describes the spectral character of metamorphic and carbonates minerals. The metamorphic zone and associated rock types interpreted over the images are verified in the field and checked for their occurrences and spatial distributions. The occurrence of CO 3 bearing carbonate minerals and OH bearing metamorphic minerals are confirmed further under microscope, XRD analysis and PIMA spectral measurements in the laboratory studies. The study proved sensor capability of ASTER to discriminate metamorphic rocks from associated formations and detection of different mineral occurrences. It is recommended to use the studied technique to map metamorphic zone occurred in the rugged topography, where it is difficult to do conventional geological mapping in similar arid regions.

Detrital heavy mineral analysis coupled with a regional geological review provide key elements to re-evaluate the distribution of the Rhodope metamorphic zone (SE Europe) in the region and its role in determining the evolution of the Thrace basin. We focus on the Eocene-Oligocene sedimentary successions exposed in the southern Thrace basin margin to determine the dispersal pathways of eroded crustal elements, of both oceanic and continental origins, as well as their different contributions through time. Lithological aspects and tectonic data coupled with geochemistry and geochronology of metamorphic terranes exposed in the area point to a common origin of tectonic units exposed in NW Turkey (Biga Peninsula) with those of NE Greece and SE Bulgaria (Rhodope region). The entire region displays (1) common extensional signatures, consisting of comparable granitoid intrusion ages, and a NE-SW sense of shear (2) matching zircon age populations between the metapelitic and metamafic rocks of the Circum-Rhodope Belt (NE Greece) and those of the Camlica-Kemer complex and Cetmi m,lange exposed in NW Turkey. Detrital heavy mineral abundances from Eocene-Oligocene sandstones of the southern Thrace basin demonstrate the influence of two main sediment sources mostly of ultramafic/ophiolitic and low- to medium-grade metamorphic lithologies, plus a third, volcanic source limited to the late Eocene-Oligocene. Detrital Cr-spinel chemistry is used to understand the origin of the ultramafic material and to discriminate the numerous ultramafic sources exposed in the region. Compositional and stratigraphic data indicate a major influence of the metapelitic source in the eastern part (Gallipoli Peninsula) during the initial stages of sedimentation with increasing contributions from metamafic sources through time. On the other hand, the western and more external part of the southern Thrace margin (Gok double dagger eada, Samothraki and Limnos) displays compositional signatures according to a mixed provenance from the metapelitic and metamafic sources of the Circum-Rhodope Belt (CamlA +/- ca-Kemer complex and Cetmi m,lange). Tectonic restoration and compositional signatures provide constraints on the Palaeogene palaeogeography of this sector of the central-eastern Mediterranean region.

The Piranshahr-Sardasht-Saqqez Zone (PSSZ) in the north-west of the Sanandaj-Sirjan metamorphic zone (SSZ) hosts some major Iranian gold deposits. In the south-east of PSSZ, there is a north-east trending orogenic gold belt which contains three gold deposits/occurrences (Qolqoleh, Kervian and Ghabaghloujeh). In this research, studies are focused on processing and analysing airborne magnetic and radiometric data in order to find applicable indicators for prospecting gold in this area. Former studies on the gold deposits/occurrences in the study area suggest three essential factors in local orogenic gold mineralisation: (1) intersecting deep bending structures/shear zones, (2) Fe-rich mafic meta-volcanic lithologies (primary source and host rocks) and (3) altered mylonitic granites (secondary host rock). Geological structures and lithological contacts can be mapped based on locating edges in the magnetic field at different depths. In this study, we extracted the structure from aeromagnetic data by reduction to the pole, upward continuation and applying a tilt derivative filter to the horizontal derivative of the upward continued data. Upward continuation was to several levels from 500 to 4000m. Afterwards, a 3D architecture was built based on extracted subsurface lineaments in different levels. This 3D model can assist in the visualisation of the underground shape of structures that may influence gold mineralisation. Moreover, mafic meta-volcanic rocks in the study area, which contain magnetic minerals such as magnetite, titanomagnetite and ilmenite, can be mapped using aeromagnetic data. Mylonitic granites, which are the other host rock in the deposits, were mapped using airborne radiometric data.

A wide band magnetotelluric study of the ophiolitic zone of the Zagros orogenic belt was conducted in the Neyriz area of southwestern Iran. The purpose of the study was to image subsurface structures electrically and relocate the main Zagros thrust fault in the region. The thrust fault has a complex structure with obscure behavior and is believed to be located within a zone of ongoing continental plate convergence. The fault zone with a NW–SE geological trend is parallel to the Zagros orogenic belt and separates the Neyriz ophiolite assemblage from the adjacent Sanandaj-Sirjan metamorphic zone. Magnetotelluric data were collected along a SW–NE profile across the geologic strike; the study included 18 stations and modeling was performed using a 2-D inversion scheme. Analysis of both modes of magnetotelluric data (TE and TM) clarifies the signatures of large resistivity variation in the study area. Due to the presence of a high contrast in resistivity between the ophiolites and neighboring rocks, we are able to discern two sharp boundaries as faulting planes and borders of the ophiolite–radiolarite zone in the north-eastern and southwestern parts of the 2-D resistivity models, respectively.

Multiphase solid (MS) inclusions in both garnet and omphacite were investigated for zoisite-bearing eclogite from the ultrahigh-pressure (UHP) metamorphic zone in the Sulu orogen. The results provide petrological evidence for local anatexis during exhumation of deeply subducted continental crust. There are three types of MS inclusions: (1) plagioclase + quartz, (2) plagioclase + quartz + K-feldspar, and (3) barite + plagioclase + K-feldspar ± zoisite/epidote. The host minerals mostly exhibit radial fractures surrounding the MS inclusions. The first and second types of MS inclusions were analyzed for their bulk compositions, yielding high SiO 2 and Na 2 O but very low FeO + MgO + TiO 2 with variable K 2 O for the second type. Trace element analyses of representative MS inclusions yield generally very low concentrations except such large ion lithophile elements as Sr, Ba and Rb. These features suggest different origins for the three types of MS inclusions. The first type of MS inclusions would be primarily derived from dehydration melting of paragonite, whereas the second type of MS inclusions would be derived from dehydration melting of both paragonite and phengite. The third type of MS inclusion may result from the interaction between metamorphic fluid and host mineral in view of the occurrence of barite as a filling phase in the fractures of host minerals. Zoisite breakdown is also indicated by its highly cuspate shape in coexistence with quartz, providing components for growth of garnet during the exhumation. Therefore the anatexis of zoisite-bearing UHP eclogite is primarily driven by the breakdown of hydrous minerals such as phengite and paragonite. The major and trace element compositions of MS inclusions in the eclogites mainly depend on the species of hydrous minerals involved in the mineralogical reactions of dehydration melting in subduction channel.

High-precision secondary-ion mass spectrometry (SIMS) U–Pb and Hf–O isotopic microanalyses of zircons from the central Sanandaj–Sirjan metamorphic zone (SSMZ) of the Zagros orogen, Iran, provide evidence of the presence of 2.7 Ga xenocrystic zircons, suggesting that the SSMZ records Neoarchean crustal components that have not previously been reported in Iran. The two amphibolite samples analyzed from the Muteh–Golpaygan metamorphic complex during this study include one sample (GQ-10) that yielded xenocrystic zircons with ages clustered around ca 2.7 Ga. The second sample (GC-15) contains zircons that show two distinct xenocrystic zircon domains with ages of (i) ca 2.7 and 2.5 Ga, and (ii) ca 52 Ma. The ca 2.7 Ga zircons and zircon domains have homogeneous, mantle-like δ18O values with a mean of 6.10 ± 0.69‰. They have eHf(t) values that vary between +0.2 to +6.8 with TDMC ages of 3.1–2.7 Ga, suggesting they crystallized from granitoid melts derived from juvenile components. However, the younger ca 2.5 Ga zircons yield an average δ18O value of 6.17 ± 0.24‰ and have evolved Hf isotopic compositions (eHf(t) −0.8 to −3.4; TDMC = 3.2–3.1 Ga), indicating that the older crust in this region underwent more intense later reworking than is the case for crustal material formed at ca 2.7 Ga. These data provide evidence of Neoarchean basement rocks in this region, indicating that the SSMZ records ancient crustal growth events. The youngest ca 52 Ma xenocrystic zircons within these samples most likely reflect the late Paleocene–Eocene magmatic ‘flare-up’ within Iran. These zircons have slightly elevated δ18O values (7.69 ± 0.21‰) and negative Hf isotopic compositions (eHf(t) −8.3 to −12.1; TDMC = 1.9–1.6 Ga), suggesting intensive crustal reworking at ca 50 Ma.

This study reports new zircon U–Pb and Hf isotopes and whole-rock elemental and Sr–Nd isotopic data for the gneissic granite and leucogranite from the Nabang metamorphic zone, Yingjiang area (West Yunnan, SW China). The metamorphosed granitoids crystallized during the early Eocene (~ 55–50 Ma) with zircons showing eHf(t) values from + 11 to − 5.3 and crustal model ages of 1.5 to 0.42 Ga, comparable to those of coeval I-type granitoids from the Gangdese batholith, southern Lhasa. The rocks are characterized by metaluminous and weakly peraluminous hornblende-bearing gneissic granites with A/CNK = 0.95–1.09, Na2O > K2O, coupled with low initial Sr isotopic values of 0.7049–0.7070 and high eNd(t) values from + 1.1 to − 7.1. The rocks were derived from crustal materials involving ancient upper crust/sedimentary and juvenile mantle-derived rocks. Together with available data from nearby regions, it is proposed that the early Eocene granitoids in the Nabang and Tengliang area can be correlated to the Gangdese granitoids and represent the southeastward continuation of the magmatic arc resulting from the Neotethyan subduction in southern Tibet. The petrogenesis of early Eocene granitoids in western Yunnan was probably related to the rollback of the subducting Neotethyan slab that caused the remelting of the crustal materials newly modified by the underplated basaltic magma.

The general classification of intermediate-acid intrusive rocks in the metamorphic zone of Gaoligong Mountains as one of the metamorphic terranes of Proterozoic Gaoligong Mountains is problematic regarding the intrusion stage and age, as well as the subsequent metamorphism and deformation. In this study, we investigated granitic gneiss in the metamorphic zone of Gaoligong Mountains based on the 1:50,000 regional geological survey of Qushi Street (2011–2013) and SHRIMP U-Pb zircon geochronology. Results showed that the SHRIMP U-Pb zircon dating of granitic gneiss ranged from 163.5±5.7 Ma to 74.0±2.0 Ma. Thus, the granitic gneiss was grouped into orthometamorphic rocks (metamorphic intrusions). The dating data of granite rocks associated with intense metamorphism and deformation were divided into three groups, 163.5±5.7 to 162.3±3.1 Ma, 132.2–101.0 Ma and 99.4±3.5–74.0±2.0 Ma, which respectively represented three independent geologic events including an important magma intrusion with superimposed metamorphic effects in the late Middle Jurassic, regional dynamic metamorphism and superimposed reformation of fluid action in the early Cretaceous, and dynamic metamorphism dominated by ductile shear and metamorphism starting from the late Cretaceous.

The geometry of intra-continental lithosphere boundaries along the Zagros orogenic belt in the Arabia-Eurasia collision is investigated by means of teleseismic data. The data are gathered over a seismic linear profile extending across south Zagros, the Sanandaj–Sirjan metamorphic zone, the Urumieh–Dokhtar magmatic arc, Central Iran, and the Kopeh Dagh - Binalud mountains. We exploit the P and S receiver functions leading to map the geometry of the crustal and subcrustal interfaces. The migrated depth sections reveal an abrupt crustal thickening and a gentle crustal thinning ~ 60 km north and ~ 30 km south of the Zagros suture, respectively. Associated to the buckled antiformal Moho south of the suture, a deeper synform in the lithospheric lid of the lower Arabia plate is shown by migrated depth sections affecting the lithospheric mantle of the Arabia plate beneath the suture zone. This geometry implies an unexpected intra-lid decoupling. These features imply that the Central Iran lithosphere acts as a relatively strong backstop producing significant internal deformation expressed by shortening and thickening at the edge of the Arabian lithosphere. The 410 km and 660 km transition zones are imaged by P to S converted phases and showed lateral continuity implying an originally low dip angle subduction of the oceanic Arabian plate beneath Central Iran.

The Jian copper deposit, located on the eastern edge of the Sanandaj–Sirjan metamorphic zone, southwest of Iran, is contained within the Surian Permo-Triassic volcano-sedimentary complex. Retrograde metamorphism resulted in three stages of mineralization (quartz ± sulfide veins) during exhumation of the Surian metamorphic complex (Middle Jurassic time; 159–167 Ma), and after the peak of the metamorphism (Middle to Late Triassic time; approximately 187 Ma). The early stage of mineralization (stage 1) is related to a homogeneous H2O–CO2 (XCO2 > 0.1) fluid characterized by moderate salinity ( 370°C, >3 kbar). Early quartz was followed by small amounts of disseminated fine-grained pyrite and chalcopyrite. Most of the main-ore-stage (stage 2) minerals, including chalcopyrite, pyrite and minor sphalerite, pyrrhotite, and galena, precipitated from an aqueous-carbonic fluid (8–18 wt.% NaCl equivalent) at temperatures ranging between 241 and 388°C during fluid unmixing process (CO2 effervescence). Fluid unmixing in the primary carbonaceous fluid at pressures of 1.5–3 kbar produced a high XCO2 (>0.05) and a low XCO2 (

Two fresh types of eclogites, namely the massive eclogite and foliated eclogite, are discernible in large eclogite bodies surrounded by country rock gneisses from the Dabie (大别)-Sulu (苏鲁) UHP metamorphic zone. They are different in mineral assemblage, texture and structure at various scales. The massive eclogite has a massive appearance with a metamorphic inequigranular and granoblastic texture, which consists mainly of nominally anhydrous minerals such as garnet, omphacite, rutile with inclusions of coesite and rare microdiamond. Massive eclogites which formed at the peak UHP metamorphic conditions (∼3.1–4.0 GPa, 800±50 °C) within the coesite to diamond stability field recorded the deep continental subduction to mantle depths greater than 100 km during the Triassic (∼250–230 Ma). The diagnostic UHP minerals, mineral assemblages and absence of notable macroscopic deformation indicate the peak metamorphic’ forbidden-zone’ P-T conditions, an extremely low geothermal gradient (≤7 °C·km−1) and low differential stress. The foliated eclogite is composed of garnet+omphacite+rutile+phengite+kyanite+zoisite+talc+nyboite±coesite/quartz pseudomorphs after coesite. It is quite clear that the foliated eclogite bears relatively abundant hydrous mineral, and shows well-developed penetrative foliation carrying mineral and stretching lineation reflecting intense plastic deformation or flow of eclogite minerals. The foliated eclogite occurred at mantle levels and recorded the earliest stages of exhumation of UHP metamorphic rocks. At a map scale, the foliated eclogites define UHP eclogite-facies shear zones or high-strain zones. Asymmetric structures are abundant in the zones, implying bulk plane strain or dominant non-coaxial deformation within the coesite stability field. The earliest stages of exhumation, from mantle depths to the Moho or mantle-crust boundary layering, were characterized by a sub-vertical tectonic wedge extrusion, which occurred around 230-210 Ma. The three-dimensional relationship between the massive and foliated eclogites is well displayed a typical ‘block-in-matrix’ rheological fabric pattern indicating the partitioning of deformation and metamorphism in the UHP petrotectonic unit. The existing data support the now widely accepted concept of deep continental subduction/collision and subsequent exhumation between the Yangtze and Sino-Korean cratons. The pressure is a constitutive geological variable. The influence of tectonic overpresure on UHP metamorphism is rather limited.

Northwest Hubei province is located in Mount Wudang metamorphic zone, where the geological conditions are very complex. The carbonaceous schist is relatively rare in this area, however, compared with other schists, it has some quite special characteristics. This paper focuses on lithologic features, physical and mechanical characteristics of carbonaceous schist, and Huashigou tunnel is researched as the engineering background. Analysis of carbonaceous schist shows that it has typical rheological, anisotropic and water-sensitive properties. Through a large number of monitoring measurement data analysis, deformation law of carbonaceous schist are summarized.

A Cu-bearing skarn zone occurs north of the Shayvar Mountain in northwestern Iran. Skarn-type metasomatic alteration and mineralization occur along the contact between Upper Cretaceous impure carbonates and a Miocene Cu-bearing granitic stock. Both endoskarn and exoskarn developed in the rocks. Exoskarn is the principal skarn zone and is enclosed by a skarnoid–hornfelsic zone. Skarn formation occured during stages: (1) prograde, (2) middle stage and (3) late stage. In the prograde stage, there were two main processes: (a) metamorphic–bimetasomatic and (b) prograde metasomatic. The metamorphic process began immediately after intrusion of the pluton into the enclosing impure carbonates. The prograde metasomatic stage commenced with segregation and evolution of a fluid phase in the pluton and movement into fractures and micro-fractures in the skarnoid–hornfelsic rocks developed in a metamorphic zone. The introduction of considerable amounts of Fe, Si and Mg led to the development of voluminous medium- to coarse-grained anhydrous calc-silicates. During the middle stage, the previously formed skarn zones were affected by intense multiple hydrofracturing in the Cu-bearing stock. In addition to Fe, Si and Mg, substantial amounts of Cu, Pb and Zn, along with volatile components such as H2S and CO2 were added to the skarn system. Consequently, substantial amounts of hydrous calc-silicates (epidote, tremolite–actinolite), sulfides (pyrite, chalcopyrite and molybdenite), oxides (magnetite, hematite) and carbonates (calcite) replaced the anhydrous calc-silicates. The retrograde stage was synchronous with the incursion of relatively low-temperature, more oxidized fluids into skarn system, resulting in partial alteration of the early-formed calc-silicates and development of a series of very fine-grained aggregates of chlorite, clay, hematite and calcite. Zircon grains from the endoskarn zone provide constraints on the timing of solidification of the granite stock (9.91 ± 0.31 Ma) that caused mineralization in the Anjerd area. One sample of primary hornblende from the monzogranitic Shayvar batholith has an 40Ar/39Ar age of 26.54 ± 0.65 Ma and indicates that intrusion of the Miocene stock and associated Cu skarn formation occurred a considerable time after intrusion of the batholith.

The Gaoligong metamorphic zone is located southeast of the Eastern Himalayan Syntaxis in western Yunnan, China. The zone is characterized by four stages of deformation (D1–D4). D1 structures record early compressive deformation during the Indosinian orogeny, which formed tight to isoclinal F1 folds of bedding with a penetrative S1 foliation developed parallel to fold axial planes. Mid-crustal horizontal shearing during D2 resulted in overprinting of D1 structures. D1 and D2 structures are associated with granulite facies metamorphism. D3 doming resulted in late crustal thickening and the development of a regional NW–SE trending F3 antiform. Synchronous with or slightly subsequent to D3 deformation, the zone experienced D4 ductile strike-slip shearing, resulting in its exhumation to shallow crustal levels and retrograde metamorphism. Granitic D4 mylonites predominantly yield 40 Ar/ 39 Ar mica ages of 15–16 Ma, indicating that D4 dextral strike-slip shearing occurred in the Miocene. Weakly deformed leucogranite and protomylonite yield 40 Ar/ 39 Ar ages of 10–11 Ma, suggesting that ductile strike-slip shearing continued to the Late Miocene. The new 40 Ar/ 39 Ar data indicate that escape-related deformation along the Gaoligong strike-slip shear zone occurred in the Miocene. In association with recent geophysical studies, and on the basis of the structural, crystal preferred orientation (CPO), and geochronological data presented in this paper, we suggest that the Gaoligong metamorphic zone formed in response to intracontinental transpression in the southeast of Tibet, characterized as intense deformation and metamorphism at middle–upper crustal levels.

The Qinling–Dabie–Sulu orogenic belt in east-central China is the largest high and ultrahigh pressure (HP and UHP) metamorphic zone in the world. The Dabie Mountains are the central segment of this orogenic belt between the North China and Yangtze cratons. This work studies the nature of the crustal structure beneath the Dabie orogenic belt to better understand the orogeny. To do that, we apply ambient noise tomography to the Dabie orogenic belt using ambient noise data from 40 stations of the China National Seismic Network (CNSN) between January 2008 and December 2009. We retrieve high signal noise ratio (SNR) Rayleigh waves by cross-correlating ambient noise data between most of the station pairs and then extract phase velocity dispersion measurements from those cross-correlations using a spectral method. Taking those dispersion measurements, we obtain high-resolution phase velocity maps at 8–35 second periods. By inverting Rayleigh wave phase velocity maps, we construct a high-resolution 3D shear velocity model of the crust in the Dabie orogenic belt. The resulting 3D model reveals interesting crustal features related to the orogeny. High shear wave velocities are imaged beneath the HP/UHP metaphoric zones at depths shallower than 9 km, suggesting that HP/UHP metaphoric rocks are primarily concentrated in the upper crust. Underlying the high velocity HP/UHP metamorphic zones, low shear velocities are observed in the middle crust, probably representing ductile shear zones and/or brittle fracture zones developed during the exhumation of the HP/UHP metamorphic rocks. Strong high velocities are present beneath the Northern Dabie complex unit in the middle crust, possibly related to cooling and crystallization of intrusive igneous rocks in the middle crust resulting from the post-collisional lithosphere delamination and subsequent magmatism. A north-dipping Moho is revealed in the eastern Dabie with the deepest Moho appearing beneath the Northern Dabie complex unit, consistent with the model of Triassic northward subduction of the Yangtze Craton beneath the North China Craton.

An Epithemal Au-Ag mineralized zone is developed in the Moisan area of Hwangsan-myeon, Haenam-gun, Jeol-lanam-do, Korea, which is located in the southwestern part of the Ogcheon metamorphic zone. It is hosted in the Hwangsan volcaniclastics of the Haenam Formation of the Late Cretaceous Yucheon Group. This research investigated the characteristics of bedding arrangement, fold, fault, fracture system, quartz vein and the time-relationship of the fracture system to understand the geological structure related to the formation of the mineralized zone. On the basis of this result, the tectonic environment at the time of the mineralization was considered. Beds mainly trend east-northeast and gently dip into north-northwest or south-southeast. Their poles have been rearranged by subhorizontal-upright open fold of (east)-northeast trend as well as dip-slip fault. Fracture system was formed through at least 6~7 different deformation events. D1 event; formation phase of the main fracture set of EW (D1-1) and NS (D1-2) trends with a good extensity, D2 event; that of the extension fracture of NW trend, and conjugate shear fracturing of the EW (dextral) and NS (sinistral) trends, D3 event; that of the extension fracture of NE trend, and conjugate shear refracturing of the EW (sinistral) and NS (dextral) trends, D4 event; that of the extension fracture of NS trend showing a poor extensity, D5 event; that of the extension fracture of NW trend, and conjugate shear refracturing of the EW (dextral) and NS (sinistral) trends, D6 event; that of the extension fracture of EW trend showing a poor extensity. Frequency distribution of fracture sets of each deformation event is D1-1 (19.73 %)> D1-2 (16.44 %)> D3

The geological setting of Sichuan-Tibet Railway is complicated, while magmatic and metamorphic rocks are widely distributed. Reference to the other engineering experience of underground works under similar geological conditions at home and abroad, the analysis shows that it exists the hazardous possibility that the inorganic gas are toxic and harmful in the tunnels of Sichuan-Tibet Railway. Combining the conditions that inorganic gas produced and the geological conditions along the Sichuan-Tibet Railway, it analyzes and predicates that CH4, CO2, H2S, SO2, CO, NO2, NH3 and H2 are the main types of poisonous gas along the Sichuan-Tibet Railway. The poisonous gas is mainly distributed in the three suture zones, three crustal fault zones and more than three basement fault zones and mafic and ultrabasic rock zone, granites zone, volcanic zone and contact metamorphic zone. All these zones are the favorable migration point to area and gathering area to the toxic and harmful gas. It should be highly mentioned on the construction of the tunnels.