Regional Geodynamic Evolution Research Articles

Hydrothermal activity near the Permian–Triassic transition in the south‐western Ordos Basin, China: Evidence from carbonate cementation in Upper Permian sandstones

ABSTRACTCarbonate cementation in the Upper Permian sandstones informs the timing and temperature of hydrothermal activity in the south‐western Ordos Basin. This study presents a detailed examination of these hydrothermally influenced carbonate cements, constraining their age, carbonate diagenesis and relationship with regional geodynamic evolution. Sedimentological analyses demonstrate the development of deltaic plain and front sand bodies in the study area, which resulted in interbeds of volcanic matrix‐rich sandstones with matrix‐free sandstones. Petrography and electron microprobe analysis reveal four carbonate mineral growth phases of matrix‐free sandstones in the following sequence; scarce pure siderite, scarce Mg‐rich siderite, abundant blocky calcite and moderately abundant grain‐replacing calcite. The fluid inclusion data show anomalies of homogenization temperature of blocky carbonate cements during early diagenesis, over a wide range of ca 148 to 228°C. In addition, blocky carbonate cements show low δ13C (−5.9 to −13.1‰ Vienna PeeDee Belemnite) and δ18O (clustered tightly from −12.4 to −14.6‰ Vienna PeeDee Belemnite) values, interpreted to result from elevated temperatures during cementation, associated with activation of basement faults and concomitant hydrothermal fluid intrusion triggered by oceanic crust subduction in the south‐west margin of the Ordos Basin. Using in situ calcite U–Pb geochronology, the timing of hydrothermal activity was constrained to ca 247.0 ± 11 to 248.2 ± 4.7 Ma. This work provides a case study for applying intergranular calcite U–Pb dating to determine the absolute timing of fluid flow in sedimentary basins, offering tremendous potential to capture snapshots of various diagenetic evolution stages in sediments. The proposed diagenetic model can also provide new insights and understanding regarding hydrothermally influenced sediments. More importantly, hydrothermal activity may have commenced earlier than previously thought. The North Qinling Orogen uplift and associated Mianlue oceanic crust subduction may have begun at the Permian–Triassic transition with a protracted hydrothermal event in the south‐western Ordos Basin.

Zircon U-Pb and Whole-Rock Geochemistry of the Aolunhua Mo-Associated Granitoid Intrusion, Inner Mongolia, NE China

The Aolunhua Mo deposit is a typical porphyry deposit, which is located in the middle southern section of the Da Hinggan Range metallogenic belt. Here, we report LA-ICP-MS zircon U-Pb age data from the Mo-associated granitoid, together with the element geochemistry of the zircons, discussing the source material of the ore-forming rock of the deposit. The zircon data constrain the crystallization age of the granite porphyry as 135.0 ± 1.0 Ma, correlating it with the widespread Yanshanian intermediate–felsic magmatic activity. The Th/U ratio of the zircon is greater than 0.1, with a significant positive Ce anomaly (Ce* = 1.72–188.71) and a negative Eu anomaly (Eu* = 0.05–0.57). The zircons show depleted LREE and enriched HREE patterns, as well as low La and Pr contents, suggesting crystallization from crust-derived magmas. Based on the geology of the ore deposit and the age data, in combination with the regional geodynamic evolution, we infer that the Aolunhua Mo deposit was formed near the peak stage of Sn poly-metallic metallogenesis in the Da Hinggan Range region at around 140 Ma, associated with a tectonic setting, characterized by the transition from compression to extension. Based on a comparison with the newly found Mo deposits along the banks of the Xilamulun River, we propose that the Tianshan–Linxi is an important Mo-metallogenic belt. It also suggests an increased likelihood for the occurrence of Mo along the north bank of the Xilamulun River.

Jurassic to early Cretaceous geodynamic evolution of the eastern Hellenides

Remarkably well-preserved crustal sections from the Eastern Hellenides offer the chance to evaluate the regional geodynamic evolution of continental crust. Here, we identify and geodynamically interpret eclogite facies metamorphism in the Triassic–Jurassic volcano-sedimentary series of the West Circum Rhodope zone in the eastern Hellenides. Equilibrium phase diagrams and measured mineral compositions were used to inform reconstructions of geodynamic evolution during the early Alpine period. We newly define the existence of the Eohellenic HP belt, consisting of pre-Alpine basement, continental volcano-sedimentary formations, and a Jurassic magmatic arc. We suggest that the Eohellenic HP-Belt was subducted in the late Jurassic to early Cretaceous beneath the European plate margin. Detailed geodynamic reconstructions such as ours provide a robust anchor for future computational models of long-term crustal evolution in the Eastern Hellenides.Graphical abstract

Did the Western and the Eastern Vardar ophiolites originate through a single intra-oceanic subduction? Insight from numerical modelling

The ophiolites of the Balkan Peninsula are distinguished into the Western and the Eastern Vardar ophiolites and it is generally accepted that both of them resulted from the latest Jurassic/earliest Cretaceous closure of the Vardar branch of the Tethys Ocean (Vardar Tethys). This study is aimed at testing the possibility that the origin and emplacement of these two ophiolite belts can be explained in terms of a single NE-dipping intra-oceanic subduction, which commences in mid Jurassic and lasts until the lowermost Cretaceous, and then transitions into collision between the African and the European plate. The subduction is accompanied by creation of a new oceanic lithosphere in the back-arc. In order to test this hypothesis, we use 2D numerical thermomechanical modeling for investigating the nucleation of the East Vardar Ocean in the back-arc and intra-arc region. Our numerical results suggest that a single intra-oceanic subduction can indeed be simultaneously responsible for both the westward obduction of the Western Vardar ophiolites and for complex active margin processes along the western rim of the European plate. The simulations show that the single intra-oceanic subduction zone is able to produce a pronounced extension and oceanic spreading along the European margin, which can be associated with the formation of the Eastern Vardar ophiolites in this subduction related setting (SSZ and BAB). The comparison of the numerical modeling results with available natural data suggests that our models are capable to approximate the regional geodynamic evolution during and immediately after the closure of Vardar Tethys.

Mafic–felsic igneous rocks in the north‐eastern North China Craton, eastern Jilin, NE China: Petrogenesis and implications for regional geodynamic evolution during the Cretaceous

We present zircon U–Pb ages, major and trace element analyses and zircon Hf isotope data on the Cretaceous mafic–felsic igneous rocks in the north‐eastern North China Craton (NCC) of NE China. These data have been used to discuss the petrogenesis of the mafic–felsic igneous rocks in order to constrain the geodynamical and magmatic evolution of the region. Zircon U–Pb dating results indicate that these igneous rocks crystallized during the Cretaceous (ca. 123–90 Ma). These mafic igneous rocks display low SiO2 contents, high MgO contents and marked enrichments in large‐ion lithophile elements (LILEs) and depletions in high‐field‐strength elements (HFSEs), combined with their εHf(t) values and La/Nb versus La/Ba diagram, suggesting they were derived from lithospheric mantle that experienced gradually increasing fluid metasomatism from 123 to 90 Ma. The felsic igneous rocks with high SiO2 values are metaluminous to weakly peraluminous and belong to the high–K calc–alkaline series. These felsic igneous rocks are all enriched in light rare earth elements (LREEs) and LILEs and relatively depleted in HFSEs, with barely negative Eu anomalies, combined with their εHf(t) values, these felsic igneous rocks were derived from partial melting of a lower crust. A synthesis of these new data with previous researches shows that the subduction and rollback of the Palaeo‐Pacific slab played a major role in the destruction of the north‐eastern NCC. The diagenetic temperatures of igneous rocks indicate that the mechanism of destruction of the NCC may be heterogeneous, most likely a thermal erosion mechanism in eastern Jilin area and a delamination mechanism in Liaodong Peninsula.

Petrochemistry, Petrogenesis and Geodynamic Implications of Mantle Plume Generated Dhanjori Volcanics, Singhbhum Craton (Eastern India)

Abstract New geological and geochemical data have been presented in this paper to improve the understanding of the petrogenesis and regional geodynamic evolution of the 2.8-2.5 Ga Dhanjori volcanics. These volcanics exhibit porphyritic texture and classified as picritic basalt. The Dhanjori volcanics are MgO-rich (9.97 - 15.81 wt%) with moderate SiO2 (51.62 - 53.82 wt%), FeOT (9.97- 12.57 wt%) and TiO2 (0.73 -1.21 wt%) but relatively higher Ni (123.56 - 545.35 ppm) and Cr (241.87- 1158.41). The rare earth element (REE) patterns and their ratios indicate their derivation from the garnet to spinel stability field due to decompressive melting of a mantle plume head near the crust-mantle boundary, which is supported by the presence of high positive gravity anomaly over the Dhanjori lavas. The thermo-barometric studies indicate that the primary magma had an initial mantle potential temperature between 1350 and 1500oC in a pressure range of 1 to 1.8 GPa, thus conforming with the mantle origin, which is further endorsed by supplementary geophysical studies.

Long-term evolution of a carbonate reservoir submitted to fresh, saline and thermal waters interactions – Jurassic carbonates in the coastal area of the Gulf of Lion margin (southern France)

Securing and managing underground water resources requires a good knowledge of the structure, texture and connections of the reservoir, in order to develop realistic and reliable hydrogeological models. On the coastline of the Gulf of Lion Margin (S. France), the Balaruc-les-Bains deep karst reservoir is subjected to interactions between fresh, marine and deep thermal waters, respectively. Water resource usage for drinking, spa resort, and fish-farming raises important economic and social issues. These were addressed by an integrated research program, involving drilling of an exploratory borehole across the Jurassic carbonate reservoir. This contribution analyses the 750 m cores, in order to (i) characterise the architecture and evolution of the karst reservoir and (ii) investigate the paleo-fluids circulations, witnessed by calcite and dolomite mineralization in the fractures, karst cavities, and as cement of tectonic beccia. The structure of the reservoir is characterised by the superposition of several aquifers separated by marly intervals. At shallow level, the initial grainstone is incompletely dolomitized in metre-thick intervals, while limestone in the 210–340 m interval was completely dolomitized at an early stage. Dolomite has been subjected to penetrative extensional cataclastic deformation, while the preserved limestone is affected by normal faulting, resulting from NNE–SSW extension. Distinct types of karsts have been documented, from the top of the reservoir (paleo-lapiaz filled with Burdigalian marine marls), down to 500 m depth (paleo-endokarst filled with continental silts). The upper reservoir (75–150 m) is intensely karstified, and includes 0.1 to 1 m-wide cavities, where present day water fluxes are documented. Analyses of calcite and dolomite crystallisation under natural light and cathodoluminescence indicate precipitation from distinct fluids: formation water in chemical equilibrium with the host rock, water rich in oxides and hydroxides, ascending hydrothermal fluid and corrosive water of meteoric origin. Alternate dolomitization and calcitization observed in the upper reservoir suggests alternate flows of karstic freshwater and marine salt-water. Vertical, metre-long and centimetre wide open cracks are presently used for large water flows; several generations of syntaxial calcite growth provide evidence for varying chemistry of the circulating fluids. Structural cross cutting relationships allowed us to establish a relative chronology of events, which can be correlated with the regional geodynamic evolution. The study reveals that the present-day reservoir architecture results from the superimposition of structures formed during the Early Cretaceous extension, Maastrichtian-Eocene Pyrenean shortening, and Oligocene rifting of the Gulf of Lion. The reservoir was also shaped by successive karstification episodes and marine transgressions. Although the present-day hydrological system is controlled by, and reactivates structures inherited from a long-term evolution, it is characterised by frequent turn-overs of the water flow, tuned by high-frequency external forcings such as sea-level changes driven by Pleistocene glacio-eustasy, or varying precipitation rates.

Petrogenesis of Bonai volcanic rocks from Singhbhum Craton (Eastern India): Geophysical and geodynamic implications for pervasive plume-lithospheric interaction

• Petrogenesis and geodynamic evolution of Bonai volcanic, Singhbhum Craton. • Volcanic rocks generated by mantle plume within spinel lherzolite stability field. • Mantle potential temperature of 1300-1700°C and pressure 0.5-3.5 GPa. • Lower crustal exhumation, highly denudated lithospheric keel and magma underplating. • Crust-mantle thermal interaction, contamination and fractional crystallization. Singhbhum Craton of the Indian Shield is one of the oldest Eoarchean segments on the Earth, which contains several well-preserved Mesoarchean-Paleoproterozoic volcanic suites. In this study, we investigate petrogenesis of the Bonai suite of volcanic rocks located in the western part of the craton on the basis of detailed geological, geochemical and geophysical data, which provide a new understanding of its regional geodynamic evolution. These volcanics are generally fine to medium-grained, exhibit porphyritic texture and contain plagioclase and pyroxene as primary minerals and amphiboles, epidote, sericite and chlorite as secondary minerals. The accessory phases are mainly zircon, ilmenite, pyrite and chalcopyrite. They can be petrographically and geochemically classified as basalt and basaltic andesite of tholeiitic nature. They are characterized by moderate to high contents of SiO 2 (49.35-57.81 wt%), MgO (7.14-11.39 wt%), Al 2 O 3 (10.21-14.68 wt%), CaO (5.14-11.15 wt%), TiO 2 (0.48-2.03 wt%), Cr (32-483 ppm) and Ni (34-175 ppm). Their HFSE/REE ratios and REE patterns indicate their derivation from a relatively low melting of a similar mantle source within the spinel lherzolite stability field. They are formed as a result of decompressive melting of the mantle plume near the crust-mantle boundary, which underwent fractional crystallization and crustal contamination. The plume had an initial mantle potential temperature between 1300°C and 1700°C with corresponding pressure of 0.5 to 3.5 GPa. In Nb/Y-Zr/Y plot, almost all the samples fall in the field of oceanic plateau basalt with mantle plume affinity. This region is underplated by about 14 km thick magmatic rocks above the Moho, over which gravity field and regional elevation are consistently high and the lithosphere is extremely thin. These characteristics corroborate well with the mantle plume signatures. Subduction related geochemical signatures appear absent.

Geochronology, geochemistry, and Sr–Nd–Pb–Hf isotopes of ore-related diorites in the Erdaohe Pb-Zn-Ag deposit, Great Hinggan Range, NE China: Constraints on timing, petrogenesis and tectonic setting

The Erdaohe deposit is a newly discovered large-sized skarn Pb-Zn-Ag deposit located in the middle segment of the Great Hinggan Range, NE China. Geochronologic and geochemical data for the ore-related diorites in the deposit are presented here to explore the age, petrogenesis and geodynamic setting of these rocks. Zircon U–Pb LA-ICP-MS dating results show that the ore-related diorites were emplaced at 145–142 Ma. Geochemically, the ore-related diorites are generally characterized by high Y (22.5–32.7 ppm) and Yb (2.23–3.28 ppm) contents, low Sr/Y (14–40) ratios, light rare earth element (LREEs) and large ion lithophile element (LILE) (e.g., Rb and K) enrichments, and high field strength element (HFSE) (e.g., Nb, Ta, and Ti) depletions. These geochemical features are similar to those of arc magmas. Furthermore, the diorites have low (87Sr/86Sr)i compositions, fairly variable εNd(t) values and positive εHf(t) values, corresponding to 0.70604 to 0.70720, −7.8 to +2.6 and +4.5 to +8.0, respectively. These diorites have relatively young Sm–Nd and Hf model ages of 1564 to 721 Ma and 955 to 619 Ma, respectively. The whole-rock Pb isotopes show a narrow range. These isotopic data suggest that the parental magma was sourced mainly from juvenile crustal components, followed by assimilation and fractional crystallization in the crust with limited concomitant input of ancient crustal materials during magma ascent. In the Late Jurassic, the Great Hinggan Range was under compression due to the closure of the Mongol–Okhotsk Ocean, while in the Early Cretaceous, it was under extension related to the influence of the Paleo-Pacific plate. Based on the geochemical evidence and regional geodynamic evolution, we conclude that the formation of the Erdaohe deposit was associated with Paleo-Pacific plate subduction.

Eocene intra-plate shortening responsible for the rise of a faunal pathway in the northeastern Caribbean realm.

Intriguing latest Eocene land-faunal dispersals between South America and the Greater Antilles (northern Caribbean) has inspired the hypothesis of the GAARlandia (Greater Antilles Aves Ridge) land bridge. This landbridge, however, should have crossed the Caribbean oceanic plate, and the geological evolution of its rise and demise, or its geodynamic forcing, remain unknown. Here we present the results of a land-sea survey from the northeast Caribbean plate, combined with chronostratigraphic data, revealing a regional episode of mid to late Eocene, trench-normal, E-W shortening and crustal thickening by ∼25%. This shortening led to a regional late Eocene-early Oligocene hiatus in the sedimentary record revealing the location of an emerged land (the Greater Antilles-Northern Lesser Antilles, or GrANoLA, landmass), consistent with the GAARlandia hypothesis. Subsequent submergence is explained by combined trench-parallel extension and thermal relaxation following a shift of arc magmatism, expressed by a regional early Miocene transgression. We tentatively link the NE Caribbean intra-plate shortening to a well-known absolute and relative North American and Caribbean plate motion change, which may provide focus for the search of the remaining connection between 'GrANoLA' land and South America, through the Aves Ridge or Lesser Antilles island arc. Our study highlights the how regional geodynamic evolution may have driven paleogeographic change that is still reflected in current biology.

Slab break-off origin of 105 Ma A-type porphyritic granites in the Asa area of Tibet

AbstractThe study of the petrogenesis of some magmatic rocks with special geochemical attributes provides effective information for us to explore the deep geodynamic background of their formation. A series of granitic porphyry dykes have been found in the mélange zone of the Asa region in southern Tibet, whose genesis may be closely related to the evolution of the Meso-Tethyan Ocean. Regional geodynamic evolution is investigated by whole-rock geochemical analysis, zircon U–Pb dating and Lu–Hf isotopic analysis of two porphyritic granites. The Asa porphyritic granites have high SiO2(74.29–78.65 wt %) and alkalis (Na2O + K2O = 6.51–9.35 wt %) contents, and low Al2O3(11.60–14.51 wt %), CaO (0.04–0.19 wt MgO (0.01–0.10 wt %) contents. They are enriched in Zr, Nb, Ce, Y and Hf and depleted in Ti, Ba, Sr and P, consistent with A-type granites. The samples are relatively rich in LREEs, with LREE/HREE ratios of 1.73–3.04. They display negative Eu anomalies (Eu/Eu* = 0.24–0.28) and obvious Ce anomalies in some samples. Zircon U–Pb analyses show that the porphyritic granites formed in late Early Cretaceous time, 107.4 to 105.5 Ma. Zircon εHf(t) values are in the range of 6.9 to 12.0. These data indicate that the porphyritic granites were sourced from interaction between mantle-derived and juvenile lower crust-derived melts, with the addition of oceanic sediment-derived melts. This occurred when the subducting Bangong–Nujiang oceanic crust split to create a slab window. Rising asthenosphere triggered re-melting of lower crust basalts, resulting in the formation of the late Early Cretaceous A-type granites around Asa.

Geochronology, geochemistry and petrogenesis of the Dengfuxian lamprophyres: Implications for the early Cretaceous tectonic evolution of the South China Block

The middle–late Mesozoic tectonic evolution of the South China Block is not well constrained due to limited studies of synchronous mafic rocks in this area. The Dengfuxian area is located at the central to northern parts of the Nanling Range in the South China Block with many lamprophyre dikes seen cross-cutting the late Jurassic granites. This contribution is the first to report the whole-rock geochemistry, zircon U–Pb age and Sr–Nd–Hf isotope signature of these lamprophyres; provide a geochronological and petrogenetic studies that sheds new light on regional geodynamic evolution. The Dengfuxian lamprophyre dikes have variable contents of major oxides like SiO2 (58.45–65.19 %), Al2O3 (12.18–15.73 %), Fe2O3T (6.31–6.93 %), MgO (2.48–4.14 %), CaO (4.21–5.19 %), Na2O (1.08–3.02 %), K2O (2.78–4.00 %), TiO2 (0.59–1.00 %), MnO (0.15–0.33 %) and P2O5 (0.28–1.22 %). Identified as high-K calc-alkaline rock series, the lamprophyres are enriched in large ion lithophile elements (e.g., Rb, U, K and Pb) but depleted in Ba, Sr and high field strength elements (e.g., Nb, Ta, Zr and Hf). The HREEs are relative depleted compared to LREEs, with weak Ce anomalies (Ce/Ce* = 0.99–1.06) but marked negative Eu anomalies (Eu/Eu* = 0.61–0.79). A total of 30 magmatic zircon grains from the studied lamprophyre yields weighted mean U–Pb ages of 141–143 Ma, suggestive of an early Cretaceous emplacement. The Negative εNd(t) (–4.3 to –6.0) and εHf(t) (–4.1 to –10.9) values, old Nd depleted mantle model ages (TDM = 1231–1628 Ma) and Hf single stage model ages (TDM = 998–1243 Ma), with high initial 87Sr/86Sr (0.71057–0.71322) indicate that the parent magma was sourced from a subduction-modified enriched mantle. Together with integrated major and trace elements studies, it can be inferred that the parent magma of the Dengfuxian lamprophyres originated from low degree (1–3 %) partial melting of an enriched mantle source (garnet peridotite) that was altered by subduction sediments in a progressive intra-plate extension environment. The magma experienced significant fractional crystallization of olivine, clinopyroxene, plagioclase, Fe-Ti oxides and apatite with little crustal contamination. A two-stage geodynamic model is presented to constrain the tectonic evolution of the South China Block during the early Cretaceous.

Geodynamic Evolution of Flat‐Slab Subduction of Paleo‐Pacific Plate: Constraints From Jurassic Adakitic Lavas in the Hailar Basin, NE China

AbstractSubduction of the Paleo‐Pacific Plate caused widespread Mesozoic magmatism, lithospheric deformation and thinning, and mineralization along the continental margin of East Asia. However, the details of this subduction process remain unclear. To investigate the regional geodynamic evolution and subduction processes of the Paleo‐Pacific Plate, we carried out a geochronological, geochemical, and Sr‐Nd‐Hf isotopic study of Middle‐Late Jurassic adakitic lavas in the Hailar Basin, northeast (NE) China. These rocks have relatively high Sr contents (434–877 ppm), low heavy rare earth element and Y (6.81–14.37 ppm) contents, and high Sr/Y ratios (56–83), which are characteristic of adakites. The rocks are classified into Middle Jurassic high‐K and Late Jurassic low‐K adakitic lavas. The high‐K adakitic lavas were derived by dehydration melting of thickened garnet‐bearing amphibolite‐facies lower crust. In contrast, the low‐K adakitic lavas could be considered as pristine slab‐melts that were likely generated by hydrous melting of subducted eclogitic oceanic crust, followed by limited interaction between the slab melt and peridotite as a consequence of flat‐slab subduction. Combined with previous data, our results demonstrate that the late Mesozoic magmatism in NE China records the entire temporal‐spatial evolution of subduction of the Paleo‐Pacific slab from initial shallowing of the subduction angle to flat‐slab subduction, followed by basalt‐eclogite phase transformation and finally slab rollback.

Mafic–intermediate igneous rocks in the East Kunlun Orogenic Belt, northwestern China: Petrogenesis and implications for regional geodynamic evolution during the Triassic

Mafic–intermediate igneous rocks can provide important insights into the geodynamic evolution of orogenic belts. Here, we investigate the petrogenesis of mafic–intermediate intrusive igneous rocks in the East Kunlun Orogenic Belt (EKOB) to constrain regional geodynamic and magmatic evolution. These intrusive rocks are all located in the Permian-Triassic magmatic arc and parallel to the Paleo-Tethys ophiolite belt. Zircon UPb dating results indicate that these various igneous rocks crystallized during the Triassic. The 250–248 Ma appinites display low SiO2 contents, high MgO contents, and marked enrichments in large-ion lithophile elements and depletions in high-field-strength elements; combined with their enriched εHf(t) values, these appinites were considered to be derived from lithospheric mantle modified by subducted slab-derived fluids. The Harizha host granodiorites and MMEs have indistinguishable crystallization ages of 235 Ma but distinct SiO2 contents and δ18OSMOW values, which, together with enriched Sr–Nd–Hf–Pb isotopes, suggest that their primary magmas were derived from the Mesoproterozoic lower crust (MLC) and subduction-modified lithospheric mantle (SMLM), respectively. The 241 Ma Baidungou quartz diorite and the 218 Ma Huanglonggou diorite porphyry show characteristics of medium SiO2 contents, moderate Mg# and εHf(t) values relative to contemporaneous mafic and granitic rocks; therefore they probably represent the mixing products of MLC-derived felsic and SMLM-derived mafic magmas. Different from the Baidungou diorite and Harizha granodiorite, the Huanglonggou diorite porphyries have adakitic characteristics, which suggests crustal thickening during the Late Triassic. A synthesis of these new data with previous researches shows that the EKOB undergone three magmatic peaks corresponding to three extension events (slab-rollback, slab-breakoff, and delamination) during the Triassic evolution.

Microthermometric evidence for the formation of Permian VHMS deposits in Tasik Chini area, Central Belt of Peninsular Malaysia

The VHMS deposits of Tasik Chini area are located in the Pahang State of Central Belt, Peninsular Malaysia. The deposits occur in a package of Permian volcanics within mixed volcano-sedimentary sequence, and have been exploited from the Bukit Botol and Bukit Ketaya deposits. They have many similarities with Kuroko-style massive sulfide deposits. The host rocks at both deposits are felsic volcanic rocks of rhyolitic to rhyodacitic composition. Mineralization occurs as distinct ore zonation forming a stringer to massive sulfide zone at the footwall followed by barite lenses and exhalite layers (Fe + Mn ± Si ore) at the stratigraphic top. The sulfide phases are characterized by pyrite as the major sulfide mineral, with subordinate chalcopyrite, sphalerite and rare galena; traces of gold, silver- and Sn-bearing minerals occur in the massive sulfide and barite ores. Primary fluid inclusions within quartz and barite occur as two types: (1) type I: two phase, liquid-vapour inclusions without daughter minerals, and (2) type II: three phase, liquid CO2-bearing carbonic inclusions. These three phase inclusions include liquid H2O, liquid CO2 and vapour CO2, with variable CO2 content, and often decrepitate before complete homogenization. Microthermometric measurements of the type I inclusions show that the temperature of homogenization (Th) varies between 180 °C and 310 °C with salinities ranging from 1.0 to 15.0 wt% NaCl equivalent in the quartz samples. Homogenization temperatures (Th) of 190 °C to 300 °C and salinities between 1.0 and 13.0 wt% NaCl equivalent are recorded from the barite samples. Type II inclusions have an initial melting temperature range of −57.1 °C to −57.5 °C, clathrate melting temperature (Tmclathrate) of 7.4 °C to 8.0 °C and CO2 homogenization temperature (ThCO2) between 30.1 °C and 30.3 °C, and salinity ranging from 4.0 to 5.1 wt% NaCl equivalent. Densities, pressure and depth of ore forming fluids range from 0.711 to 0.970 g/cm3, 12 to 93 bars, and ∼1500 m depth of seawater. Laser Raman spectroscopic analysis shows the presence of CO2 in the carbonic inclusions. The fluid inclusion results suggest that the main ore fluid during the formation of the Tasik Chini VHMS deposit is a seawater-dominated fluid, but contribution from a modified seawater or possibly magmatic origin is also indicated by higher salinities relative to seawater (3.2 wt% NaCl) and the presence of CO2. Taking into account the regional geodynamic evolution, it is also concluded that the formation of VHMS deposits in the Tasik Chini area occurred in a back-arc geotectonic setting.

Incremental emplacement and syn-tectonic deformation of Late Triassic granites in the Qinling Orogen: Structural and geochronological constraints

Granitoids are important components of major orogenic belts, and provide important information about the regional geodynamic evolution. The emplacement mechanism of granite plutons and its relationship with regional tectonics has long been discussed, although it still remains debated. The Qinling Orogen within the Central China Orogen was marked by the emplacement of numerous Late Triassic granitic plutons. Although the petrology, geochemistry and geochronology of these intrusions have been addressed in various studies, their tectonic setting remains controversial, particularly since the structural aspects not been evaluated in detail. In this study, we attempt to reconstruct the emplacement process of the Late Triassic Dongjiangkou pluton in the South Qinling Belt. Field observations show extensive syn-plutonic deformations both in the pluton and its contact zones. Microstructural observations demonstrate that fabrics in the pluton were mainly acquired during submagmatic flow to high-T solid-state deformation. Zircon U–Pb ages reveal that the pluton is a composite intrusion which is composed of two juxtaposed small plutons with distinct ages (~210 Ma and ~200 Ma). Al-in-hornblende thermobarometer indicates that the pluton was formed at depths ranging from 4.7 km to 8.8 km, with an increasing depth trend from the inner unit to the outer unit. Distribution of the internal fabrics shows two concentric patterns which are concordant with pluton margins at the pluton scale and were probably induced by the regional sinistral transpression. Integrating these analyses, an incremental emplacement model is proposed for the syn-tectonic pluton. This model not only solves the ‘room problem’ but also accounts for the zoned petrological features of the pluton. Combined with previous studies, we suggest that the Late Triassic granite plutons in the Qinling Orogen were emplaced under a syn-collisional convergence setting, and that the granite magmatism was probably controlled by regional tectonics. Additionally, the incremental emplacement model may be a common mechanism for the Late Triassic granite plutons.

Ages and petrogenesis of the Late Mesozoic igneous rocks associated with the Xiaokele porphyry Cu–Mo deposit, NE China and their geodynamic implications

The genesis of igneous rocks associated with the newly discovered Xiaokele porphyry Cu-Mo deposit, located in the eastern Erguna Block, NE China, can give insights into the regional geodynamic evolution during the Late Mesozoic. Several ore-bodies have been identified in a granodiorite porphyry stock, which intruded the rhyolite and was subsequently intruded by diorite porphyry and granite porphyry. The U–Pb ages of zircons from rhyolite, mineralized granodiorite porphyry, diorite porphyry and granite porphyry associated with the Xiaokele deposit are 152.5 ± 1.7, 150.0 ± 1.6, 147.9 ± 1.3, and 123.2 ± 1.7 Ma, respectively. The rhyolite and granite porphyry have high SiO2 and low MgO, Cr, Co, and Ni contents. Their isotopic data show negative εNd(t) values of −4.76 to −0.87, initial 87Sr/86Sr ratios of 0.7066 to 0.7134 and positive zircon εHf(t) values of 0.33–5.56, indicating that they were derived from a basaltic lower continental crust. The mineralized granodiorite porphyry is characterized by high Sr/Y values and low Y (3.7–8.0) contents, showing adakite affinity. The low K2O/Na2O (0.51–0.7) ratios, high CaO contents, weakly negative εNd(t) (−1.17 to −0.27), and low zircon εHf(t) (1.49–5.4) values from the adakitic samples indicate that they were derived from the partial melting of an altered oceanic slab together with assimilation of mantle peridotite and crustal materials. The 148 Ma diorite porphyry has high Mg# (51–58), weakly negative and positive εNd(t) (−0.09 to 0.01) values, and lower (87Sr/86Sr)i (0.7055–0.7057) ratios, suggesting an enriched mantle wedge source. Considering the late Mesozoic regional tectonic evolution of the Erguna Block and adjacent area, we propose that the formation of the Xiaokele deposit is linked to the southward flat-slab subduction of the Mongol–Okhotsk oceanic plate during the Later Jurassic-Early Cretaceous.

U-Pb zircon geochronology of the Paleogene – Neogene volcanism in the NW Anatolia: Its implications for the Late Mesozoic-Cenozoic geodynamic evolution of the Aegean

The northern Aegean region was shaped by subduction, obduction, collision, and post-collisional extension processes. Two areas in this region, the Rhodope-Thrace-Biga Peninsula to the west and Armutlu-Almacık-Nallıhan (the Central Sakarya) to the east, are characterized by extensive Eocene to Miocene post-collisional magmatic associations. We suggest that comparison of the Cenozoic magmatic events of these two regions may provide insights into the Late Mesozoic to Cenozoic tectonic evolution of the Aegean. With this aim, we present an improved Cenozoic stratigraphy of the Biga Peninsula derived from a new comprehensive set of U-Pb zircon age data obtained from the Eocene to Miocene volcanic units in the region.The compiled radiometric age data show that calc-alkaline volcanic activity occurred at ~43–15Ma in the Biga Peninsula, ~43–17Ma in the Rhodope and Thrace regions, and ~53–38Ma in the Armutlu-Almacık-Nallıhan region, which are slightly overlapping. We discuss the possible cause for the distinct Cenozoic geodynamic evolution of the eastern and western parts of the region, and propose that the Rhodope, Thrace and Biga regions in the north Aegean share the same Late Mesozoic to Cenozoic geodynamic evolution, which is consistent with continuous subduction, crustal accretion, southwestward trench migration and accompanying extension; all preceded by the Late Cretaceous – Paleocene collision along the Vardar suture zone. In contrast, the Armutlu-Almacık-Nallıhan region was shaped by slab break-off and related processes following the Late Cretaceous – Paleocene collision along the İzmir-Ankara suture zone. The eastern and western parts of the region are presently separated by a northeast-southwest trending transfer zone that was likely originally present as a transform fault in the subducted Tethys oceanic crust, and demonstrates that the regional geodynamic evolution can be strongly influenced by the geographical distribution of geologic features on the subducting plate.

Early Cretaceous magmatism and associated polymetallic mineralization in South China: the Tiantang example

ABSTRACTThe Tiantang Cu–Pb–Zn polymetallic deposit in western Guangdong, South China, is hosted in the contact zone between the monzogranite porphyry and limestone of the Devonian Tianziling Formation. Orebodies occur in the skarn and skarnized marble as bedded, lenses, and irregular shapes. In this study, we performed LA-ICP-MS zircon U–Pb dating, zircon trace elements, and Hf isotopic analyses on the Tiantang monzogranite porphyry closely related to Cu–Pb–Zn mineralization. Twenty-two zircons from the sample yield excellent concordia results with a weighted mean 206Pb/238U age of 104.5 ± 0.7 Ma, which shows that the emplacement of the monzogranite porphyry in the Tiantang deposit occurred in the Early Cretaceous. The zircon U–Pb age is largely consistent with the sulphide Rb–Sr isochron ages, indicating that both the intrusion and Cu–Pb–Zn mineralization were formed during the Early Cretaceous in South China. The εHf(t) values of three inherited zircons from the monzogranite porphyry are 13.1, 11.9, and 12.9, respectively, and the two-stage Hf model ages are 1096 Ma, 1087 Ma, and 1055 Ma, respectively. Except for the three inherited zircons, all εHf(t) values of zircons are negative and have a range of −7.6 to −3.4, with the two-stage model ages (TDM2) of 1380–1643 Ma, which indicates the rock-forming materials were mainly derived from the partial melting of Mesoproterozoic to Neoproterozoic crust rocks, and probably included some Neoproterozoic arc-related volcanic-sedimentary materials. In this study, the monzogranite porphyry from the Tiantang deposit has calculated Ce4+/Ce3+ ratios of zircon ranging from 91 to 359, indicative of a more oxidized signature and significant prospecting potential for ore-related magmatism. Based on ore deposit geology, isotope geochemistry, and geochronology of the Tiantang Cu–Pb–Zn deposit and regional geodynamic evolution, the formation of Early Cretaceous magmatism and associated polymetallic mineralization in South China is believed to be related to large-scale continental extension and subsequent upwelling of the asthenosphere.

Paleozoic intrusive rocks in the Nalati mountain range (NMR), southwest Tianshan: Geodynamic evolution based on petrology and geochemical studies

A synthesis involving the data for the Nalati mountain region (NMR) in west Tianshan with a dataset including zircon U-Pb ages, Hf isotopic composition, major and trace elements of Paleozoic intrusions are presented to improve the understanding of regional geodynamic evolution. Paleozoic intrusive rocks in the NMR could be classified into four categories based on chronological and geo-chemical data: 480±5 Ma, 445-410 Ma, 345-320 Ma, and 295 Ma, which correspond to (1) closure of the Terskey Ocean and the opening of the south Tianshan back-arc basin, which was followed with the opening of the south Tianshan Ocean, (2) initial subduction of the south Tianshan oceanic crust, (3) major subduction stage, and (4) collision to post-collisional stage, respectively. Following the closure of the Terskey Ocean, the south Tianshan Ocean opened at Early Silurian and subducted under Yili-central Tianshan by the end of Early Carboniferous Period. The following breakoff of the subducted slab triggered partial melting of continental crust and formed voluminous granitic rocks in the NMR.