Compressional Tectonic Setting Research Articles

Geochronology and geochemistry of granitoids of the Yanghuidongzi porphyry Cu deposit, Heilongjiang Province: Implications for petrogenesis and metallogenic setting during the Early Jurassic in the Northeast of China

AbstractThe Yanghuidongzi Cu deposit is a newly discovered porphyry Cu deposit in the eastern segment of the Central Asian Orogenic Belt. The Cu mineralization is associated with granodiorite porphyry and granodiorite. This paper presents new zircon U–Pb dating, Hf–O isotopes, whole‐rock major and trace elements data for this deposit, to constrain the ore‐forming age and the magma source of the granitoids. LA–ICP–MS U–Pb dating of zircons from granodiorite porphyry and granodiorite samples yielded ages of 192.8 ± 1.7 Ma, and 198.1 ± 1.4 Ma, respectively, which are interpreted as the emplacement ages of granitoids. These age data confirm that the granodiorite porphyry is associated with the porphyry Cu deposit, and both granitic intrusion and Cu mineralization were associated with the Early Jurassic magmatism in NE China. The granodiorite porphyry has high SiO2, Al2O3, and Sr contents together with low concentrations of Y and Yb. It is enriched in LILE, and depleted in HFSE, classified as adakitic. The granodiorite has high SiO2 and K2O, enriched in LILE, depleted in HFSE, and is classified as high‐K calk‐alkaline I‐type granite. The granodiorite porphyry and granodiorite have variable εHf(t) values (5.2 to 9.5), Mesoproterozoic two‐stage Hf models (TDM2) of 629–905 Ma, and δ18O values (4.26‰ to 7.50‰). These geochemical data and zircon Hf–O isotopes suggest that the granodiorite porphyry originated from the partial melting of thickened juvenile crustal materials and granodiorite derived from the partial melting of juvenile crustal materials with an additional of mantle‐derived magmas input. Combining our new data with the regional tectonic setting, the Yanghuidongzi Cu deposit and the related granitoids formed in a compressional tectonic setting associated with the subduction of the Paleo–Pacific Plate beneath the Eurasian continent.

Stratigraphic and structural evidence of transpressional Quaternary fault reactivation along the SE Korean Peninsula

Comprehending the nature, extent, and distribution of seismogenic structures, along with their seismogenic potential to induce destructive earthquakes in low seismic strain regions, holds significant socio-economic significance. Analyzing historical and paleoearthquakes becomes essential to understanding the influencing factors controlling the origin of earthquakes in intraplate regions, such as the Korean Peninsula. Based on current knowledge, the seismic pattern within the intraplate region, particularly along the Korean Peninsula, exhibits greater heterogeneity. This observation is drawn from historical seismic records, instrumentally detected seismic patterns, and paleoseismological analyses. Comprehensive paleoseismological studies play a crucial role in providing new evidence for fault activity, and hence they are an important contribution to the understanding of the seismic and structural evolution of faults. Existing paleoseismic investigations have predominantly focused on southeastern Korea, primarily along the Yangsan or Ulsan faults, with less attention given to other faults in the southeastern part of the Korean Peninsula. In the ongoing Korean Active Fault Mapping Project, this study specifically identifies a fault trace approximately 5.5–7 km long along the Ulsan-Dongnae Fault system named as Seokgye fault, named after the locality. Detailed paleoseismic investigations were carried out along the Seokgye fault. The fault presents a clear example of fault reactivation under the present compressional tectonic setting with a paleoearthquake during the late Pleistocene (∼121 ± 6 ka). Based on the length of the fault traced and observed displacement in the trench, Seokgye fault is capable of generating an earthquake of magnitude similar to the 2016 Gyeongju earthquake (Mw 5.8). This research enhances our understanding of the ongoing tectonic processes and Quaternary activities of fault systems in the southeastern Korean peninsula. Additionally, it contributes valuable insights for local-scale seismic hazard analysis in the area.

Petrogenesis of Jurassic granitic plutons in the Yanbian area, NE China: Implications for the subduction history of the Paleo-Pacific Plate

It is widely accepted that the subduction of the Paleo-Pacific Plate beneath the Eurasian continent began during the early Mesozoic; however, the details of the subduction process remain uncertain. This paper presents new zircon U–Pb–Hf and whole-rock geochemical data for Jurassic intrusive rocks from the Yanbian area of NE China to provide a better understanding of the subduction history of the Paleo-Pacific Plate. Zircon U–Pb dating results reveal that three stages of Jurassic magmatism are recorded in the Yanbian area, namely, Early Jurassic (188–179 Ma), Middle Jurassic (172–163 Ma), and Late Jurassic (158–156 Ma). Early Jurassic intrusive rocks from the Yanbian area are predominantly calc-alkaline gabbro, gabbro-diorite, quartz monzonite, granodiorite, and syenogranite. These geochemical features and rock associations are indicative of formation in an active continental margin setting related to the initial subduction of the Paleo-Pacific Plate beneath the Eurasian continent. The Early Jurassic granitoids were formed mainly by the partial melting of heterogeneous lower crust. The Middle Jurassic granitoids are geochemically similar to adakites and have εHf(t) values of + 2.0 to + 10.1. These rocks are inferred to have been derived from magmas generated by the partial melting of thickened juvenile lower-crustal material. Their formation was related to the subduction of the Paleo-Pacific Plate. Late Jurassic adakites in the Yanbian area formed in a compressional tectonic setting. Their negative εHf(t) values (−17.2 to − 8.6) and TDM2 ages (2025–1552 Ma) indicate that the primary magma was derived from the partial melting of ancient continental crust. Combining our data with the distribution of Late Jurassic igneous rocks in the NE Asian continental margin and the northward migration of Jurassic accretionary complexes along the margin, we conclude that the subduction of the Paleo-Pacific Plate beneath the Eurasian continent during the Late Jurassic–earliest Early Cretaceous had a low angle of obliquity.

Devonian to Early Carboniferous Retreating—Advancing Subduction Switch in the Northwestern Patagonia Accretionary Orogen: U‐Pb and Lu‐Hf Isotopic Insights

AbstractIn this contribution, we present new early middle Devonian igneous and metaigneous units with a major juvenile magmatic source input in the North Patagonian Massif, which were discovered through U‐Pb and Lu‐Hf zircon analyses. Afterward, we assessed their tectonic implications for northwestern Patagonia and then for southern South America, combining our results with available database information consisting of igneous crystallization ages and isotopic data of the Devonian to early Carboniferous magmatic units, tectonic‐metamorphic analyses, and thermochronologic record. This study allows for distinguishing retreating and advancing subduction switching in northwestern Patagonia (38°30′ to 44°S) and a contrasting coetaneous evolution for basement outcrops exposed further north (27°30′ and 37°30′S). The early middle Devonian (400–380 Ma) northwestern Patagonian magmatism is characterized by widespread magmatism and positive εHf–εNd linked to forearc and backarc magmatism that evolved within a retreating subduction stage. A tectonic switching toward advancing orogeny stage began in the late Devonian, evidenced by a lull in magmatic activity with a negative εHf–εNd trend, possibly contemporaneous with the first tectonic‐metamorphic event in western Patagonia. An early Carboniferous magmatic gap, followed by the subsequent development of the main foliation in the basement during the Carboniferous‐Permian period, denotes the acme of this contractional stage. In contrast, the Devonian period in the northern segment is characterized by mostly negative εHf–εNd values, reverse shear zone activity in the foreland, and an inboard magmatism migration, evidencing a compressive tectonic setting that changed to an extensional configuration in the early Carboniferous with widespread arc magmatism development.

Petroleum system modelling in a compressional tectonic setting: The eastern Kuqa Depression, Tarim Basin, Northwestern China

Petroleum system modelling in a compressional tectonic setting: The eastern Kuqa Depression, Tarim Basin, Northwestern China

Evidence for structural control of mare volcanism in lunar compressional tectonic settings

One of the long-standing enigmas for lunar tectonic-thermal evolution is the spatiotemporal association of contractional wrinkle ridges and basaltic volcanism in a compressional regime. Here, we show that most of the 30 investigated volcanic (eruptive) centers are linked to contractional wrinkle ridges developed above preexisting basin basement-involved ring/rim normal faults. Based on the tectonic patterns associated with the basin formation and mass loading and considering that during the subsequent compression the stress was not purely isotropic, we hypothesize that tectonic inversion produced not only thrust faults but also reactivated structures with strike-slip and even extensional components, thus providing a valid mechanism for magma transport through fault planes during ridge faulting and folding of basaltic layers. Our findings suggest that lunar syn-tectonic mare emplacement along reactivated inherited faults provides important records of basin-scale structure-involved volcanism, which is more complex than previously considered.

The relationship between Carlin-type Au mineralization and magmatism in the Youjiang Basin-a case study from the Mingshan gold deposit in northwest Guangxi, China

The Youjiang Basin in Southwest (SW) China is the second-largest Carlin-type goldfield in the world after Nevada, USA; however, the spatial, temporal, and genetic links between Carlin-type Au mineralization and magmatism in SW China remain controversial compared with those in Nevada. The Mingshan gold deposit is one of the few Carlin-type gold deposits that exhibits a close spatial relationship between gold orebodies and magmatic rocks in the Youjiang Basin. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) uranium-lead (U-Pb) dating of magmatic zircons from quartz porphyry dikes and hydrothermal apatite associated with gold yields the intrusive and gold mineralization ages of 96.34 ± 0.89 and 139.9 ± 4.8 Ma, respectively, indicating that the magmatism was much younger than the gold mineralization at Mingshan. Petrography and microthermometry of the fluid inclusions from ore-stage quartz and calcite suggest a low to moderate temperature (140–240 °C), low salinity (3–8 wt% NaCleqv), and moderate to low density fluid. The hydrogen and oxygen isotope compositions of the ore-stage quartz indicate a metamorphic fluid source of the ore fluid. Thus, we propose that the close spatial contact between the gold orebodies and igneous dikes could have resulted from the same NWW-trending fault space during the Early Cretaceous precipitation of ore fluid and the Late Cretaceous intrusion of the quartz porphyry dikes. However, the genetic link between the quartz porphyry and Carlin-type Au mineralization was not observed at Mingshan. The primary metamorphic fluid associated with Early Cretaceous gold mineralization in the Youjiang Basin was derived from syn-orogenic shortening deformation and metamorphism in the compressional tectonic setting caused by the subduction of the Paleo-Pacific Plate. Subsequent post-orogenic extension during the rollback of the subducted Pacific slab led to significant extensional faults and intrusions of Early Cretaceous concealed granites, which may have provided heat, materials, and energy for the transport of ore fluid. The ore fluid was transported through permeable extensional structures from the deep crust and reacted with the carbonaceous and Fe-rich host rocks in the shallow crust, resulting in the Early Cretaceous gold mineralization event in the Youjiang Basin.

Evolution of the Paleo–Asian Ocean in south‐eastern Inner Mongolia, China: Evidence from zircon U–Pb ages, Hf isotopes data and specific deformation of the Linxi and Sunjiafen formations

The crystallization age of the Sunjiafen Formation volcanic rocks is 253.9 ± 1.1 Ma. Geochemical data show that these volcanic rocks belong to the shoshonitic and metaluminous series and have high Sr and low Y contents (461–582 and 5.60–6.74 ppm, respectively), MgO = 1.32–2.65 wt%, and Na2O/K2O = 0.81–1.40. In MgO−SiO2, Cr−SiO2, Sr/Y−Y and (La/Yb)N−YbN diagrams, data for the samples plot in the adakite and “adakite related to thickened lower crust” fields. As such, we suggest that the Sunjiafen Formation C−type adakitic andesites formed in a compressional tectonic setting. The youngest age (youngest peak age) of two sandstone samples from the Linxi Formation are 251 Ma (257 Ma) and 237 Ma (254 Ma). Detrital zircons with ages of >1500 Ma have εHf(t) values of −5.87 to +6.31. A comparison of the age spectra and εHf(t) values of the detrital zircons in the Linxi Formation with those of igneous zircons from the Central Asian Orogenic Belt and North China Craton indicates the formation was derived from both the belt and the craton. We identified “Jura–type Folds” that formed in peripheral foreland basin in the Linxi Formation, and along with plant fossil fragments (Paracalamites frigidus). These and previously published results indicate the Paleo–Asian Ocean closed along the Xar Moron–Changchun Suture zone during the Late Permian. The study area was in a continuous compressional setting during the Late Permian and formed a peripheral foreland basin that was related to continent–continent collision.

Modelling of pore pressure evolution in a compressional tectonic setting: The Kuqa Depression, Tarim Basin, northwestern China

The Kuqa Depression is part of a Mesozoic-Cenozoic foreland basin located at the northern margin of the Tarim Basin. High fluid overpressures were reported in the Mesozoic section related to both the complex tectonic evolution and the sealing by the salt-bearing sequence within the Paleogene Kumugeliemu Group. The role of structural evolution and compressional shortening in the generation of overpressures is poorly understood and requires a model-based understanding of the basin structure for different time steps. Structurally restored geometries based on a present-day geological section interpreted from a 2D seismic line, has been used as input for a basin and petroleum system model to simulate pore pressure history through geological time. In this simulation, we demonstrate structural dependencies of pore pressure development, and examine the impact of disequilibrium compaction, tectonic compression, opening and closing of faults over time, as well as folding on overpressure evolution. The poroelastic model is used to quantitatively evaluate the contribution of horizontal shortening due to tectonic compression on overpressure. We found that the pressure increase caused by 12.5% shortening can account for a maximum of more than 60% of overpressure, depending on lithology and deformation strength. We also simulated the effect of salt content within the seal layer on overpressure and found that the increase in salt has promoted the onset time and magnitude of overpressure in the underlying strata, which favors porosity preservation. A heat flow sensitivity analysis was performed, suggesting that the pressure increase caused by extremely high heat flow is rather low.

Origin of the dolomite in the Buqu Formation (Mid-Jurassic) in the south depression of the Qiangtang Basin, Tibet: Evidence from petrographic and geochemical constraints

The Qiangtang Mesozoic sedimentary basin is a new field of hydrocarbon exploration, in which the Buqu Formation dolostone reservoirs have attracted increasing attention in recent years. To determine the origin of these reservoirs, petrographic study, fluid inclusion thermometry dating, and C-O and Sr isotopic dating were performed. The results revealed the genesis and evolution of different types of dolomite matrix and cement, as follows: 1) The dolomite texture in the study area is closely related to its formation environment and process and can be categorized as primary fabric well-preserved dolomite (Rd1), primary fabric poorly-preserved dolomite, and dolomite filling. The primary fabric-poorly-preserved dolomite includes fine-grained euhedral dolomite (Rd2), fine-grained planar subhedral dolomite (Rd3), and medium-to coarse-grained anhedral dolomite (Rd4). The dolomite filling includes fine-grained planar subhedral cave-filling dolomite (Cd1) and medium-to coarse-grained anhedral, saddle dolomite (Cd2). 2) Rd1 has δ13C‰PDB of 3.42‰–4.23‰, δ18O‰PDB from −4.22‰ to −3.37‰, and 87Sr/86Sr of 0.707654–0.708176 and was formed in the contemporaneous or penecontemporaneous stage at low temperatures by mimic replacement related to seawater evaporation. Abundant supersaturated dolomitization fluids favored the preservation of its primary dolomite texture. 3) Rd2 has δ13C‰PDB of 3.18‰–4.11‰, δ18O‰PDB from −4.56‰ to −4.23‰, and 87Sr/86Sr (0.707525–0.708037), while Rd3 has δ13C‰PDB of 2.72‰–4.42‰, δ18O‰PDB from −6.57‰ to −5.56‰, and 87Sr/86Sr of 0.707432–0.707990. Both were formed at low temperatures in the shallow-burial stage, when the dolomitization fluid was mainly derived from seawater. Excessive dolomitization during the late shallow-burial stage caused the destruction of the dolomite crystals from euhedral to subhedral. 4) Rd4 has δ13C‰PDB of 3.24‰–4.14‰, δ18O‰PDB from −8.22‰ to −6.37‰, and 87Sr/86Sr of 0.707234–0.707884 and resulted from dolomitization or recrystallization at high temperatures in the medium-to deep-burial stage. The crystal curvature was caused by high environmental temperatures. 5) Cd1 has δ13C‰PDB of 3.02‰, δ18O‰PDB of −5.13‰, and 87Sr/86Sr of 0.708147 and was formed during cavern filling before the shallow-burial stage. Cd2 has δ13C‰PDB of −0.09‰−3.38‰, δ18O‰PDB from −10.41‰ to −8.56‰, and 87Sr/86Sr of 0.708180–0.708876 and was related to the collisional orogeny between the Lhasa termite and the Qiangtang Basin in the late Early Cretaceous. Fluids in the overlying and underlying clastic strata of the Buqu Formation were driven by the thermal hot spot during compressional tectonic setting. These fluids caused negative shifts in the oxygen isotope compositions of the earlier dolomite.

Mesozoic Magmatic and Geodynamic Evolution in the Jiaodong Peninsula, China: Implications for the Gold and Polymetallic Mineralization

The intrusive age ranges of Linglong, Guojialing, Weideshan, and Laoshan granites in the Jiaodong Peninsula are 155–154 Ma, 131–130 Ma, 118–111 Ma, and 116 Ma, respectively. Together with the Shidao granite (227–200 Ma), five phases of magmatism can be classified by the time, all of which have different degrees of gold and polymetallic mineralization. The type of granites evolved from A–, S–type to I–, A–type from the Late Triassic to the Early Cretaceous, thus reflects the evolution of geodynamics in the Mesozoic, indicating the switch from North China Craton (NCC)–Yangtze Craton (YC) collision to subduction of the Paleo–Pacific Plate (PPP), with crustal thickening switching to lithospheric thinning and a compressional tectonic setting changing to an extensional setting. It directly leads to a series of extensional structures evolving in the Jiaodong Peninsula and demonstrates affinity for the extensive mineralization in the Early Cretaceous. The key markers of Jiaodong gold and polymetallic mineralization are magmatism, fluid activity and extensional structure. Extensive magmatic uplift and extensional structures in the Early Cretaceous formed the extensional tectonic system. During the formation process, a large proportion of crust and mantle materials exchanged and mixed, and the fluid interaction was highly active, resulting in a magmatic fluid metallogenic system, which provided favorable metallogenic conditions for gold and nonferrous metal hydrothermal deposits. Thus, a large-scale explosive mineralization occurred in Jiaodong in the middle and late Early Cretaceous.

Pore Pressure Prediction Using Velocity-Mean Effective Stress Relationship in Madura Sub-basin, East Java Basin - Indonesia

DOI:10.17014/ijog.9.2.247-262Pore pressure prediction using velocity-mean effective stress relationship is introduced in Madura Subbasin which is located in a compressional tectonic setting. The new workflow accommodates the three principal stresses, those are vertical stress, maximum horizontal stress, and minimum horizontal stress in a form of mean stress as the compaction main inducing agent. The application of this new workflow has resulted in a more accurate pore pressure prediction where the normally used pore pressure prediction method tends to underestimate the actual data. In Dukuh-1 well, as an example, the pore pressure prediction from the new work flow is able to explain the continuous hole problems such as well flows and well kicks that were recorded during drilling. In MDA-2 well, the new pore pressure prediction closely matches the well data in comparison to the normally used prediction. As a result, a more accurate regional pore pressure prediction map using mean stress is generated to aid both hydrocarbon exploration and development activities in the study area

Mesozoic tectonic transition of the northeastern North China Craton: Evidence from adakitic rocks in southeastern Jilin Province, China

ABSTRACT Chronological and geochemical studies of adakites and adakitic rocks are important in understanding the tectonic evolution and geodynamic processes. We present new zircon U–Pb ages, Hf isotope, and geochemical analyses of adakitic rocks exposed in the Baishan area, southeastern Jilin Province, China. These new ages, together with existing age data, indicate that adakitic magmatism in southeastern Jilin Province can be subdivided into four stages: Early–Middle Triassic (251–235 Ma), Late Triassic (221–219 Ma), late Early–early Late Jurassic (176–156 Ma), and Early Cretaceous (ca. 130 Ma). Early–Middle Triassic adakitic rocks occur in a nearly E–W-trending belt within the northern margin of the northeastern North China Craton, indicating a compressional tectonic setting caused by the scissor-like closure of the Paleo-Asian Ocean from west to east. Late Triassic adakitic rocks occur in the Tonghua area and formed in an extensional setting caused by delamination after subduction and collision between the Yangtze Craton and NCC. Late Early–early Late Jurassic adakitic rocks occur in the Baishan and Kaiyuan areas and originated from partial melting of thickened lower crust in a compressional setting related to subduction of the Paleo-Pacific Plate. Early Cretaceous adakitic rocks occur in the Baishan area and were derived from partial melting of thickened lower crust above the subduction zone and delaminated lower crust, indicating that the subducting Paleo-Pacific Plate retreated to the eastern part of southern Jilin Province during the Early Cretaceous (ca. 130 Ma) and that the tectonic setting of the northeastern part of the NCC changed from compression to extension, starting in the east and progressing westward. In summary, the northeastern part of the NCC has been affected by a series of tectonic events during the Mesozoic, such as the closure of the Paleo-Asian Ocean, the collision between the NCC and YC, and the subduction of the Paleo-Pacific Plate.

Progressive accretion recorded in sedimentary rocks of the 3.28–3.23 Ga Fig Tree Group, Barberton Greenstone Belt

Abstract One of the major challenges in early Earth geology is the interpretation of the nature of the crust and tectonic processes due to the limited exposures of Archean rocks. This question is predominantly addressed by numerical modeling, structural geology, geochemical analyses, and petrological approaches. Here we report on the reconstruction of one of the oldest, well-preserved volcano-sedimentary sequences on Earth, the 3.28–3.22 Ga Fig Tree Group in the Barberton Greenstone Belt, South Africa, based on geochronology, provenance, and stratigraphy to provide new constraints on the nature of tectonic processes in the Archean. The Fig Tree basin was asymmetric and the onset of deposition varied across the greenstone belt. The Fig Tree Group is now preserved in east-west oriented bands of fault-bounded structural belts with those preserved in the southern parts of the greenstone belt showing an onset of deposition at 3.28 Ga, those in the center at 3.26 Ga, and those in the north at 3.24 Ga. Stratigraphically, the rocks display a general up-section trend from deeper to shallower-water deposition and/or from finer- to coarser-grained sedimentary rocks. Associated with this up-section stratigraphic trend, the sedimentary rocks show a change in provenance from more regionally similar to more locally variable, and an increase in felsic volcanic activity, especially toward the closure of Fig Tree deposition. The data is consistent with formation of the Fig Tree Group in a compressional tectonic setting by deposition in a foreland basin that experienced progressive accretion of crustal terranes onto a northward prograding fold-and-thrust belt.

Genesis of the Yanghuidongzi Cu deposit, NE China: Constraints from H-O-Pb isotopic compositions and geochronological study

• The Yanghuidongzi Cu deposit classified as a porphyry type Cu deposit. • H-O isotopes indicate a mixing of magmatic water and meteoric water for ore fluids. • Pb-Re isotopes indicated a deep seated magma mixed with crustal materials for ore metals. • The Yanghuidongzi Cu deposit formed during Early Jurassic . The newly-discovered Yanghuidongzi porphyry Cu deposit is located in the southeastern part of Heilongjiang Province in NE China and represents one of the rare Jurassic porphyry Cu deposits within the easternmost segment of the Central Asian Orogenic Belt (CAOB). The Cu mineralization occurs as veins and disseminations hosted by granodiorite porphyry, associated with typical porphyry copper deposit alteration zoning, which is characterized by from an inner K-silicate zone through to a quartz–sericite zone to an outer propylitic zone, the K-silicate alteration and quartz–sericite alteration are closely related to mineralization. LA-ICP-MS zircon U-Pb data, sericite Ar-Ar and Molybdenite Re-Os data, and H-O and Pb isotopic compositions are used to constrain the ore-forming age and genesis of the Yanghuidongzi Cu deposit. LA-ICP-MS U-Pb dating of zircons from three granodiorite porphyry samples yielded weighted mean 206 Pb/ 238 U ages of 194.3 ± 1.2 Ma, 192.0 ± 2.0 Ma, and 194.6 ± 2.1 Ma respectively, whereas zircon U-Pb age of granodiorite in the study area yielded weighted mean 206 Pb/ 238 U age of 199.5 ± 1.5 Ma that are interpreted to be the emplacement age of these intrusions. 40 Ar- 39 Ar dating of sericite from a quartz-pyrite vein and a quartz-polymetallic sulfide vein yielded plateau ages of 193.9 ± 2.1 Ma and 193.6 ± 1.9 Ma, respectively, whereas five molybdenite samples yielded a Re-Os isochron age of 194.8 ± 2.1 Ma, with a weighted mean model age of 193.6 ± 1.2 Ma. Mineralization ages are consistent with the emplaced ages of the granodiorite porphyry within the analytical uncertainties, indicating that the Cu mineralization is genetically related to the granodiorite porphyry. The fluid δ 18 O fluid and δ 18 D fluid values range from −4.22‰ to 6.5‰ and from −92.8‰ to −65.7‰, respectively, indicating that the ore fluids were mixtures of magmatic and meteoric water. The 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb values of the pyrite and chalcopyrite are 17.547–18.327, 15.446–15.505, and 37.408–38.113, respectively, suggesting a common, magmatic source for the sulfur. Taking Re (6.75–29.53 ppm) data into consideration, the sources of ore-forming materials may be from a mixture of crustal and mantle sources. Combining our new data with the Jurassic regional tectonic setting, the Yanghuidongzi Cu deposit and the related granitoids formed in a compressional tectonic setting are associated with the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.

Evolution of a magmatic to a phreatomagmatic volcanic system: The birth of a monogenetic volcanic field, Tilocálar volcanoes, northern Chile

The Tilocálar volcanic complex comprises four monogenetic volcanoes located at the southeastern edge of the Salar de Atacama Basin, northern Chile. These monogenetic volcanic centers are the Tilocálar Norte lava, the El Maní dome, the Tilocálar Sur small–lava shield, and the Tilocálar Sur maar, respectively, and were formed between 460 ± 50 ka to < 1 Ma ago along the north–south-striking Tilomonte ridge that underlies the Tucúcaro Ignimbrite (3.2 ± 0.3 Ma). Their formation is the result of an intermediate magma rising to the surface during a local transtensional regime, which is observed at El Maní, under a dominantly compressional tectonic setting. The Tilocálar monogenetic centers provide a rare opportunity to examine the variability from individual and small–volume magma batches to the development of a monogenetic volcanic field. These volcanoes and the control on their eruption styles were studied by geological mapping and stratigraphic considerations, morphometric analysis, textural studies (density and vesicularity), petrographic observations, and geochemical analyzes. The Tilocálar Norte lavas have an intermediate composition (mostly andesite, 62.02 wt.% SiO2) that reach a maximum distance of 3.9 km to the north and 1.2 km to the southwest from their vent, with a dense–rock equivalent (DRE) volume of 8.73×107 m3. The El Maní lava dome is small (covering 750 m2 area and consisting of 1.06×103 m3 DRE volume) that presents mingled mafic (63.89 wt.% SiO2) and felsic (73.73 wt.% SiO2) products of the original magma source, related to shallow crustal melts. The Tilocálar Sur small lava–shield is characterized by a pyroclastic fall deposit and lavas. The pyroclastic fall deposit is characterized by agglutinated andesite scoria–spatter fall units, covering 2.81 km2 and consisting of 7.75×105 m3 DRE volume. In contrast, the lavas are characterized by an andesitic composition (57.64 wt.% SiO2), which is 1.8 km in length to the northwest and 1.4 km to the east of their source. These lavas cover an area of 3.78 km2 with 9.15×107 m3 DRE volume. Tilocálar Sur maar crater has an elliptical shape in map view (363 m diameter east–west and 288 m diameter north–south), surrounded by individual conglomerates, sandstones, granitoids, and tuff fragments that lie on the present–day surface around the crater rim. The Tilocálar volcanic complex is interpreted as a small monogenetic volcanic field that shows an eruption history defined by a spectrum of eruptive processes determined by internal and external parameters at any given time from the four independent volcanic centers.

Features That Favor the Prediction of the Emplacement Location of Maar Volcanoes: A Case Study in the Central Andes, Northern Chile

Maar volcanoes are monogenetic landforms whose craters cut below the pre-eruptive surface and are surrounded by a tephra ring. Both the maar crater and the surrounding tephra rim deposits are typically formed due to magma–water explosive interactions. Northern Chile is located in the Central Volcanic Zone of the Andes where, in literature, 14 maars have been recognized as parasite (6) and individual (8) volcanoes. Amongst these individual maars, 3 of them, namely the Tilocálar Sur, Cerro Tujle, and Cerro Overo volcanoes, are not related to calderas and were emplaced &lt;1 Ma ago by magmatic explosive-effusive and phreatomagmatic eruptions. Based on the evolution and control of the volcanic eruptive styles of these three maars, which have been determined in previous research through fieldwork, stratigraphic, morphometric, textural (density and vesicularity), petrographic, and geochemical analyses, a set of key features that favor a prediction of the emplacement location of maar volcanoes in Central Andes, northern Chile are proposed. The set of features that permit and favor the growth mechanisms for maar formations corresponds to (i) a compressive tectonic setting (e.g., ridge structures), (ii) groundwater recharge (e.g., snowmelt and seasonal rainfall), (iii) the lithological setting (e.g., layers of low permeability), (iv) the presence of aquifer and/or endorheic basins (e.g., lakes or salars), and (v) a period of stress relaxation that permits magma ascent to the surface in volcanically active areas. Considering these characteristics, it is possible to identify places where phreatomagmatic eruption can occur. If the magma ascent flux is lower than the groundwater flux, this can lead to a phreatomagmatic eruption because of groundwater coming into contact with the magma. These eruptive features evidence internal—and external—factors that play an essential role in the transition from explosive-effusive magmatic to phreatomagmatic volcanic eruption styles during the same eruptive period that is one of the biggest challenges in volcanic hazard evaluations. Although, in this contribution, a set of features that permit and favor the growth mechanisms for a prediction of the emplacement location of maars in northern Chile is proposed, these considerations could also be applied to identify potential locations in other parts of the world where magma–water interaction eruption could occur. Therefore, this approach could be useful in the prediction of hydromagmatic volcanic eruptions and, thus, in mitigating the impact of volcanic hazard for the inhabitants of the surrounding areas.

Late Mesozoic Paleo-Pacific Plate “scissors-like” subduction: Insight from the magmatism in the Gan-Hang Belt, Southeast China

Abstract Though it is widely accepted that the Paleo-Pacific Plate has a subducted beneath the eastern Asian continent, controversy still exists regarding the initial timing and geodynamic model of the subduction. In this contribution, we report new geochronology and geochemical data of granitic plutons within the Gan-Hang Belt in Southeast China. The Damaoshan pluton yields zircon U-Pb ages of 139.60 ± 0.69 Ma and 133.90 ± 1.70 Ma, and the Qianshan and Fenglonggu plutons are dated at 135.70 ± 1.30 Ma and 135.33 ± 0.93 Ma, respectively. The Hecun and Huangtuling plutons yield ages of 157.85 ± 0.77 Ma and 167.10 ± 7.50 Ma, respectively. The Damaoshan pluton has an obvious A-type geochemical signature in terms of major and trace element compositions, such as high K2O + Na2O contents (average 8.46 wt%) and FeOT/MgO ratios (average 10.29). The low CaO/Na2O ratios but high Al2O3/TiO2 (average is 110.05), Rb/Ba (average is 9.14), and Rb/Sr (average is 22.53) ratios indicate a derivation from pelite-derived melt. Meanwhile, we also studied the Mesozoic adakites related to magmatic ore formed during a compressive tectonic setting as well as the later bimodal dikes and A-type granitic plutons formed during the extensional tectonic setting in the Gan-Hang Belt. The multiphase qualitative plutons with geochemical characteristics of the adakitic and island arc types (175–150 Ma) related to the northwestward subduction of the Paleo-Pacific Plate, several bimodal dikes, and A-type granitic plutons (135–123 Ma) related to the subducted slab roll-back are found within the Gan-Hang Belt. All of these plutons show a decreasing trend of isotopic ages from the inland area to the coast, from SW to NE. We propose that the distribution pattern of these plutons in Southeast China was controlled by a scissors-like subduction and slab roll-back of the Paleo-Pacific Plate, which occurred roughly from SW to NE along the continental margin approximately during the Middle Jurassic to the Early Cretaceous.

Compressional origin of the Aegean Orogeny, Greece

The Aegean Sea area is thought to be an actively extending back-arc region, north of the present day Hellenic volcanic arc and north-dipping subduction zone in the Eastern Mediterranean. The area shows extensive normal faulting, ductile ‘extensional’ shear zones and extensional S-C fabrics throughout the islands that have previously been related to regional Aegean extension associated with slab rollback on the Hellenic Subduction Zone. In this paper, we question this interpretation, and suggest the Cenozoic geodynamic evolution of the Aegean region is associated with a Late Cretaceous–Eocene NE-dipping subduction zone that was responsible for continent-continent collision between Eurasia and Adria-Apulia/Cyclades. Exhumation of eclogite and blueschist facies rocks in the Cyclades and kyanite-sillimanite grade gneisses in the Naxos core complex have pressures that are far greater than could be accounted for purely by lithospheric extension and isostatic uplift. We identify four stages of crustal shortening that affected the region prior to regional lithospheric extension, herein called the Aegean Orogeny. This orogeny followed a classic Wilson cycle from early ophiolite obduction (ca. 74 Ma) onto a previously passive continental margin, to attempted crustal subduction with HP eclogite and blueschist facies metamorphism (ca. 54–45 ​Ma), through crustal thickening and regional kyanite – sillimanite grade Barrovian-type metamorphism (ca. 22–14 ​Ma), to orogenic collapse (<14 ​Ma). At least three periods of ‘extensional’ fabrics relate to: (1) Exhumation of blueschists and eclogite facies rocks showing tight-isoclinal folds and top-NE, base-SW fabrics, recording return flow along a subduction channel in a compressional tectonic setting (ca. 50–35 ​Ma). (2) Extensional fabrics within the core complexes formed by exhumation of kyanite- and sillimanite gneisses showing thrust-related fabrics at the base and ‘extensional’ fabrics along the top (ca. 18.5–14 ​Ma). (3) Regional ductile-brittle ‘extensional’ fabrics and low-angle normal faulting related to the North Cycladic Detachment (NCD) and the South(West) Cycladic Detachment (WCD) during regional extension along the flanks of a major NW–SE anticlinal fold along the middle of the Cyclades. Major low-angle normal faults and ductile shear zones show symmetry about the area, with the NE chain of islands (Andros, Tinos, Mykonos, Ikaria) exposing the NE-dipping NCD with consistent top-NE ductile fabrics along 200 ​km of strike. In contrast, from the Greek mainland (Attica) along the SE chain of islands (Kea, Kythnos, Serifos) a SW-dipping low-angle normal fault and ductile shear zone, the WCD is inferred for at least 100 ​km along strike. Islands in the middle of the Cyclades show deeper structural levels including kyanite- and sillimanite-grade metamorphic core complexes (Naxos, Paros) as well as Variscan basement rocks (Naxos, Ios). The overall structure is an ~100 ​km wavelength NW–SE trending dome with low-angle extensional faults along each flank, dipping away from the anticline axis to the NE and SW. Many individual islands show post-extensional large-scale folding of the low-angle normal faults around the domes (Naxos, Paros, Ios, Sifnos) indicating a post-Miocene late phase of E–W shortening.

On the architecture of intra-formational Mass-Transport Deposits: Insights from the carbonate slopes of Great Bahama Bank and the Apulian Carbonate Platform

Large sub-tropical carbonate platforms shed huge volumes of sediment onto their adjacent slopes. Resulting carbonate successions are comprised of gravity-flow beds (turbidites, debrites), which are occasionally reworked into mass-transport deposits (MTDs) by the failure of inconsistently lithified portions of slope strata. Despite their significance in the depositional record, the internal architecture of MTDs along relatively tectonically stable and sediment-producing carbonate platforms is poorly understood in comparison with counterparts in active compressional tectonic settings. This study compares carbonate-slope-derived MTDs imaged in seismic reflection data with those observed in outcrop. The internal architecture of MTDs from two case studies is presented: the seismically-imaged MTDs in Miocene-Recent carbonate-slope deposits from the Bahamas, and MTDs off the Cretaceous Apulian carbonate margin exposed in outcrops of the Ionian Basin (Albania). Understanding the large-scale (kilometers to tens of kilometers) internal architecture of MTDs in seismic is crucial for identification of these structures in outcrop. In turn, only outcrop studies allow the detailed analysis of the reworking style within these massive sediment bodies at a smaller scale (meters to kilometers). The internal architecture of the studied carbonate MTDs testifies to the existence of an along-slope continuum of deformation structures, characterized by vertical partitioning into distinct mass flows during single mass-transport events. Mass-wasting processes are inferred from strain-partitioning structures, recording along-slope and slope-parallel architectural heterogeneities. Three deformation domains are recognized: extensional headwall domain, translational body domain, and contractional toe domain. Confined MTDs are limited by steep and deep lateral margins and frontal ramps that mark the boundaries between failed deposits and undisturbed strata. Vertical strain-partitioning is pronounced in the toe domain. Upward intensification of deformation within MTDs is common and corresponds to a top-down reorganization of failed strata during downslope transport. Intra-formational MTDs along carbonate slopes that are lacking exotics, such as the ones studied here, differ from extra-formational MTDs occurring in compressional tectonic settings that form sedimentary mélanges. Ductile-layer deformation structures are predominant in carbonate MTDs as opposed to block-in-matrix fabrics in sedimentary mélanges. The development of shear surfaces, rather than ductile shear zones, in the body and toe domains presents predictive (in modern environments) and diagnostic criteria (in fossil examples) of mass-wasting events along carbonate slopes.