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The Tarim Craton is an ancient Precambrian continental block, and detailed knowledge of its thermo‐tectonic history is crucial for understanding the early history of continental evolution. Abundant layered mafic rocks, which have commonly been regarded as basalts, occur within the Ediacaran Sugetbrak Formation (Fm.) in the Aksu region of the northwestern Tarim Craton. Clear intrusive features have now been discovered, including mafic rocks truncating Ediacaran sedimentary layers, exhibiting an intrusion‐baked margin where they interact with both the overlying and bottom wall rocks, and displaying a fine‐grained transition zone from their interior to their margins. The new findings demonstrate that these mafic rocks within the Aksu Ediacaran strata were not erupted basalts but instead are intrusive diabase dykes. Therefore, these mafic rocks cannot be used to constrain the timing of the Sugetbrak Fm. in the Aksu area, nor as marker layers for regional stratigraphic correlation. Furthermore, the Ediacaran thermo‐tectonic evolution in this region, deduced from the assumption that the mafic rocks are lavas, needs to be revised. [ABSTRACT FROM AUTHOR]

Purpose: To investigate diabetic retinopathy (DR) as a potential marker of cardiovascular disease (CVD) in adults with type 1 diabetes attending the Danish DR‐screening programme and non‐diabetes adults. Methods: In this registry‐based matched case–cohort study, we identified 16 547 adults with type 1 diabetes, who were registered in the Danish Registry of Diabetic Retinopathy (DiaBase). Each case was age‐ and sex‐matched by five non‐diabetes individuals (n = 82 399), and odds ratios (ORs) and hazard ratios (HRs) were estimated for incident and upcoming CVD in multivariable models. Results: Adults with type 1 diabetes (median age 44.5 years, 57.6% male) were more likely to have prevalent CVD (OR 1.29; 95% CI, 1.20–1.38) and to develop CVD within 5 years (HR 1.19; 95% CI, 1.08–1.30) as compared to non‐diabetes control. However, adults without DR were less likely to develop CVD (HR 0.84; 95% CI, 0.72–0.97) compared to the reference population. For adults with type 1 diabetes, there was an increasing risk for incident CVD for increasing levels of DR (HR 1.33, 1.95, 1.71 and 2.39 for DR‐levels 1–4, respectively). Patients with CVD at the time of the first screening had a higher risk to develop DR during follow‐up (HR 1.23; 95% CI, 1.02–1.49). Conclusion: In a nationwide matched case–cohort study adjusted for potential confounders, DR was identified as an independent marker of prevalent and incident CVD in type 1 diabetes with increasing risk demonstrated for higher levels of DR. Likewise, CVD also independently predicted the risk of incident DR. [ABSTRACT FROM AUTHOR]

The energy budget and the interplay between stable friction evolution and dynamic stick‐slips are tested here under continuous slip along rough faults. We conducted 34 direct‐shear experiments coupled with precise roughness measurements on diabase and limestone fault samples. The faults broad roughness ranges from highly rough and interlocked fractured interfaces to smooth polished surfaces. The analysis focuses on two slip phases: (a) the evolution of the shear strength of rough sample under stable, cumulative displacement; and (b) the dynamic of unstable stick‐slip sliding. We found that the breakdown work during frictional strength evolution increases with roughness increase across multiple scales. The diabase samples are more sensitive to roughness increase than limestone samples in terms of the breakdown work implied by frictional evolution. We attribute this increased diabase sensitivity with fault roughness to its higher bulk elasticity and not to the fault shear stiffness. The diabase faults displayed multiple periodic system‐size stick‐slips, and the measured stored energy during the preparatory stage were surprisingly independent of the fault roughness. This finding suggests that during the preparatory stage a balance between the intracycle fault stiffness and stress drop govern the stored energy magnitude. Further, this energy balance suggests that some interface conditioning occurs before the spontaneous slip overcomes a sticking barrier. Plain Language Summary: The breakdown energy dissipated as work during friction evolution along laboratory faults can be determined by integration of the shear stress versus shear displacement. In this study, we quantitatively analyze the relationship between the roughness of laboratory faults and the dissipated energy during sliding. The experiments with rough diabase and limestone faults show an increase of breakdown work implied by the frictional strength with increasing fault roughness, and breakdown work increase with increasing host rock rigidity. We also find that the energy dissipated during frictional evolution of rough faults is four orders of magnitude larger than the energy dissipated during system size stick‐slip cycles in the same experimental setting. We attribute this observed discrepancy to the difference in contact area between interlocked, and sheared, surfaces. Surprisingly, our examination of breakdown work during stick‐slip cycles reveals a roughness‐independent behavior. We ultimately show that the energy components of both stick‐slip and friction evolution follow the same power law relationship when scaled to the sliding displacement. Key Points: The breakdown work implied by the evolution of frictional strength scales with roughness (RMS) height and elasticity of intact rockThe stored energy within stick‐slip cycles is four orders of magnitude lower than the energy accommodated during friction evolutionThe stored energy at the onset of breakdown during stick‐slip cycles is generally independent of fault roughness [ABSTRACT FROM AUTHOR]

It is well established that Cretaceous magmatism in the South China Block (SCB) is related to the Paleo‐Pacific subduction. However, the starting time and the associated deep crust‐mantle processes are still debatable. Mafic dike swarms carry important information on the deep earth (including mantle) geodynamics and geochemical evolution. In the Jiangnan Orogen (South China), there is no information on whether the Mesozoic magmatic activities in this region are also directly related to the Pacific subduction or not. In this study, we present detailed zircon U‐Pb geochronological, whole‐rock element and Sr‐Nd isotope data for Early Cretaceous Tuanshanbei dolerite dikes, and provide new constraints on the condition of the lithospheric mantle and mantle dynamics of the SCB during that time. LA‐ICP‐MS zircon U‐Pb dating suggests that this dolerite erupted in the Early Cretaceous (∼145 Ma). All samples have alkaline geochemical affinities with K2O + Na2O = 3.11–4.04 wt%, K2O/Na2O = 0.50–0.72, and Mg# = 62.24–65.13. They are enriched in LILE but depleted in HFSE with higher initial 87Sr/86Sr ratio (0.706896–0.714743) and lower εNd(t) (–2.61 to –1.67). They have high Nb/U, Nb/La, La/Sm and Rb/Sr, and low La/Nb, La/Ta, Ce/Pb, Ba/Rb, Tb/Yb and Gd/Yb ratios. Such geochemical signatures suggest that the fractional crystallization is obvious but crustal contamination play a negligible role during magmatic evolution. Tuanshanbei dolerite were most likely derived from low‐degree (2%–5%) partial melting of a phlogopite‐bearing mantle material consisted of ∼85% spinel peridotite and ∼15% garnet peridotite previously metasomatized by asthenosphere‐derived fluids/melts with minor subduction‐derived fluids/melts. Slab‐rollback generally lead to the upwelling of the hot asthenosphere. The upwelling of asthenosphere consuming the lithospheric mantle by thermo‐mechanical‐chemical erosion. The lithospheric mantle may have partially melted due to the heating by the upwelling asthenosphere and lithospheric extension. It is inferred that the Tuanshanbei dolerite might be associated with the initial slab rollback and corresponding lithospheric extension occurred potentially at ca. 145 Ma. [ABSTRACT FROM AUTHOR]

In this study, field descriptions of the dolerite dykes cross‐cutting the Pan‐African basement (DPB) and the dolerite and gabbroic dykes cross‐cutting the Cretaceous sedimentary basin (DGCSB) are used together with petrographic, bulk‐rock geochemistry, as well as Sr–Nd–Pb isotopic data to constrain the geodynamic setting and origin of these mafic (basanite, basalt and basaltic andesite in composition) rocks that outcrop in the Figuil–Léré area. The DPB dykes are alkaline with SiO2 of 46.63–49.03 wt% and MgO of 3.93–7.11 wt%. In contrast, the DGCSB dykes are subalkaline with SiO2 ranging between 50.24 and 53.16 wt% and MgO fluctuating between 5.22 and 7.90 wt%, comparable to dykes described in other regions of the Cameroon Line (CL). The rocks studied belong to the tholeiitic series and were emplaced in within‐plate basalts (WPB) and mid‐ocean ridge basalts (MORBs) setting. The variations in major and trace elements from the basanite to basaltic andesite compositions are dependable with fractional crystallization (FC) of different mineral phases such as opaque minerals, olivine, clinopyroxene, amphibole and alkali feldspar. Most samples exhibit negative Nb–Ta and positive Sr anomalies, which together with the negative correlation between MgO and 87Sr/86Sr, and isotopic ratio of 206Pb/204Pb <19.5 (18.27–19.49) suggests interactions of crustal components. Nevertheless, this contamination seems limited because there is a positive correlation between SiO2 and 143Nd/144Nd plot and low Ba contents (72–210 ppm) of the samples compared to the mid‐continental crust (259–628 ppm). Trace element modelling proposes a derivation of the Figuil–Léré dykes from parental melts generated by 4%–15% partial melting of a source containing garnet peridotite in the mixed lithospheric–asthenospheric mantle. The isotopic data of the dykes studied with hybrid magma composition are characterized by more radiogenic 87Sr/86Sr, 143Nd/144Nd and 206Pb/204Pb isotopic ratios with a dominant mixing of depleted MORB mantle (DMM)–enriched mantle 1 (EM1)–enriched mantle 2 (EM2), like those of other mafic dykes of the CL. [ABSTRACT FROM AUTHOR]

Here we present an analytical method for Zinc (Zn) isotopic measurements using "standard‐sample bracketing" on a Nu Sapphire multi‐collector inductively coupled plasma‐mass spectrometer. The effects of Zn mass fraction and HNO3 molarity mismatch between the standard and the sample, as well as the presence of matrix elements have been evaluated. Long‐term reproducibility of better than ±0.03‰ for δ66Zn (2s) was routinely obtained. Accurate measurements were achieved when CNi/CZn < 0.001, CTi/CZn < 0.03, CBa/CZn < 0.05, CNa/CZn and CAl/CZn < 0.5, CMg/CZn < 0.1, CFe/CZn < 5 and CCu/CZn as well as CCd/CZn < 10. High‐precision Zn isotopic determination were performed on twenty‐one widely available geological certified reference materials, with an overall range of ~ 0.62‰ (0.15 to 1.07‰), which is nearly twenty times the current analytical precision (0.03), and the results are in agreement with most previously published data within 2s. Among them, δ66ZnJMC 3‐0749L of eleven geological certified reference materials are reported for the first time: 0.22 ± 0.03‰ (dolerite, DR‐N), 0.23 ± 0.02‰ (gabbro, GSR‐10), 0.20 ± 0.04‰ (microgabbro, PM‐S), 0.15 ± 0.02‰ (andesite, GSR‐2), 0.22 ± 0.08‰ (diorite, GSR‐9), 0.19 ± 0.07‰ (syenite, GSR‐7), 0.30 ± 0.06‰ (granite, GSR‐1), 0.25 ± 0.00‰ (rhyolite, GSR‐11), 0.37 ± 0.01‰ (shale, GSR‐5), 0.21 ± 0.03‰ (limestone, GSR‐6) and 0.20 ± 0.03‰ (hornblendite, GSR‐15). The novel Zn isotopic data from these certified reference materials can be used for future interlaboratory comparisons. [ABSTRACT FROM AUTHOR]

Large‐scale magmatic activity and associated mineralization in South China are linked to the subduction of the palaeo‐Pacific Plate, although specific processes have remained controversial including the timing of subduction initiation and lithospheric extension. We present new geochemical data and zircon U–Pb and Lu–Hf isotope measurements on volcanic rocks, granites and mafic dikes from coastal south‐eastern China along the Eurasian continental margin. The biotite monzogranites show I–type granitoid affinity and fractional crystallization with zircon εHf(t) values ranging from −10.15 to +0.50, suggesting magma derivation from the melting of lower crust with the addition of juvenile crustal or mantle components. The biotite granites are typical of highly fractionated A‐type granites with εHf(t) values ranging from −3.63 to +1.35, indicating magma hybridization between anatectic granitic and mantle‐derived mafic magmas. The diabase dikes have zircon εHf(t) values ranging from −2.99 to +1.71, with high La/Nb and La/Ta ratios. This suggests derivation from partial melting of a lithospheric mantle metasomatized by fluid from a subducting–slab, with contributions of depleted asthenospheric mantle components. Our data, combined with those from previous studies, suggest that the shallow subduction of the palaeo–Pacific Plate beneath the Eurasian continent had begun by ca. ~170 Ma at least and the subduction orientation changed to oblique with respect to the continental margin. Steepening of the subduction angle likely caused a slab rollback during the Early Cretaceous, resulting in a tectonic transition from compression to extension in South China at ca. 145 Ma. [ABSTRACT FROM AUTHOR]

Understanding the nature of parental melts for pyroxenite veins in supra‐subduction zone (SSZ) ophiolites provides vibrant constraints on melt infiltration processes operating in subduction zones. The Zedang ophiolitic massif in the eastern Yarlung–Zangbo suture zone in Tibet consists of mantle peridotites and a crustal section of gabbro, diabase, and basalt. Veins of two pyroxenite varieties cut the southern part of the Zedang massif. These pyroxenite rocks have different geochemical characteristics, where the first variety (type‐I) has relatively higher contents of SiO2 (51.82–53.08 wt%), MgO (20.08–23.23 wt%), and ΣPGE (3.42–13.97 ppb), and lower Al2O3 (1.59–2.28 wt%) and ΣREE (1.63–2.94 ppm). The second pyroxenite variety (type‐II) is characterized by SiO2 (45.44–49.61 wt%), MgO (16.68–19.78 wt%), Al2O3 (4.24–8.77 wt%), ΣPGE (14.46–322.06 ppb), and ΣREE (5.82–7.44 ppm). Pyroxenite type‐I shows N‐MORB‐like chondrite‐normalized REE patterns. Zircon U‐Pb ages of pyroxenite type‐I (194 ± 10 Ma), associated ophiolitic gabbro (135.3 ± 2.0 Ma), and plagiogranite (124.2 ± 2.3 Ma) evidently imply episodic evolution of the Zedang ophiolites. The mineralogical and geochemical characteristics of the investigated pyroxenites can be explained by subduction‐initiated hydrous melting of metasomatized sub‐arc mantle, later overprinted by sub‐slab mantle melting triggered by upwelling asthenosphere during the Jurassic–Early Cretaceous times. The geochemical variations in pyroxenite vein composition, coupled with age differences amongst the other ophiolite units, may correspond to intermittent emplacement of pyroxenite dikes and isotropic gabbroic intrusions where the geodynamic setting progressed from arc maturation and slab rollback to slab tearing and delamination. [ABSTRACT FROM AUTHOR]

Supported by laboratory experimental results, the reduction in elastic thickness (Te ${T}_{e}$) and flexural rigidity (D $D$) at trench outer rise, which enables bending, is attributed to damage. A series of laboratory experiments were performed on intact and thermally treated diabase and peridotite (400°C–800°C) under increasing confining pressures (3–200 MPa) at room temperature. Simultaneous porosity and elastic wave velocity (P and S) measurements were obtained under dry and fluid saturated conditions. The velocity and porosity inversions indicated a significant variation in crack properties (crack density, aspect ratio) and reduction in Young's modulus, of thermally treated samples in comparison to the intact samples. Hence the experimental results suggested weakening in elastic properties of a damaged oceanic lithosphere. Subsequently created lithospheric strength profiles showed a strength reduction in wet models in comparison to dry models. Under the assumption of different cooling models, the aging of the plate resulted in an increase in strength with deeper neutral zones. The outcome of the strength profiles was utilized to estimate Te ${T}_{e}$ and D $D$, which are also dependent on the elasticity of the lithosphere. The results showed a reduction in D $D$ with increasing damage and suggest that the bending at the subduction zone is facilitated by weakened elastic properties of a damaged lithosphere. While most of the geophysical observations of Te ${T}_{e}$ were able to be constrained by the proposed damaged models, some shallow observations indicated enhanced damage triggered either by increased depth to brittle‐ductile transition or by large bending related faulting events. Plain Language Summary: In this investigation, we propose that the bending of the plate at the subduction zone is facilitated by cracks that are present in the rocks. To test this idea, we conducted several experiments in the laboratory on rocks which represent the oceanic plate (diabase and peridotite). By increasing the temperature inside a furnace, we induced cracks (damage) in the samples before the experiments and compared the results with the undamaged samples. During the experiment, we measured the wave velocity and porosity. From the comparison, it was understood that the damaged rocks have weak elastic properties. Following the results of the experiments, we calculated the lithospheric strength profiles, for both dry and wet models for different ages of the oceanic plate and found that the strength decrease markedly when water is present. From this strength estimations, we calculated the thickness of the elastic layer which can transmit bending stress and the flexural rigidity which is the resistance to bending. The results showed that with more damage present in the plate, the elastic thickness and flexural rigidity decrease. Finally, we compared these results with the actual geophysical data and have shown the validity of our model. Key Points: Hydrostatic experiments were conducted on thermally treated diabase and peridotite with simultaneous velocity and porosity measurementsDamaged models showed significant weakening in the elastic properties of the rocks due to the development of cracksSupported by the experimental results, elastic thickness, and rigidity of dry and wet oceanic lithospheres were estimated [ABSTRACT FROM AUTHOR]

Recent studies highlight the debates about the role of the northwestern China blocks, for example, north Tarim block, south Tarim block (STB), Altyn Tagh block (ATB) and Qaidam‐Qilian block (QQB) during the assembly of Rodinia. We herein present a combined paleomagnetic, geochronological, and geochemical study on 16 mafic dikes in the northern ATB. After removing a recent viscous remanent magnetization, three characteristic remanent magnetization components (CHs) were isolated. CH1 was identified in eight NW‐trending diabase dikes, one of which was newly dated at 895.3 ± 7.7 Ma through use of SHRIMP baddeleyite U‐Pb methodology. It yields a mean direction (D/I) of 123.3°/−42.2° (α95 = 12.1°). The paleopole (40.9°S/184.6°E, A95 = 11.7°) was calculated by averaging eight virtual geomagnetic poles (VGPs) from each dike. A partial baked‐contact test supports the primary origin of CH1. CH2 was isolated from three E‐W trending diabase dikes, pointing northwest with considerably shallower downward inclinations. CH3 was obtained from five lamprophyre dikes, directing southeast with moderate to shallow upward inclinations. However, the VGPs of either CH2 or CH3 are insufficient to average a precise mean pole. Geochemical analyses also reveal petrogenetic discrepancy among the dikes with distinct CHs. Combining the new ∼895 Ma pole of CH1 with the global paleomagnetic database and being aided by geological evidence, we propose that the STB‐ATB‐QQB and the north China craton were located along the northwestern side of Laurentia in Rodinia at ∼895 Ma, and suggest the connection might have been intact until ∼780 Ma. Plain Language Summary: The paleogeographic positions of the northwestern China blocks, including the north Tarim block, the south Tarim block, the Altyn Tagh block (ATB) and the Qaidam‐Qilian block in the Rodinia supercontinent, remain enigmatic and highly controversial. Here we present new paleomagnetic geochronological and geochemical data from three groups of the mafic dikes in the northern ATB. Our new results, in combination with other coeval paleomagnetic poles and geological evidence, support a specific proximity among the south Tarim, Altyn Tagh, Qaidam‐Qilian blocks and the north China craton along the northwestern side of Laurentia between ∼895 and ∼780 Ma. Key Points: A new paleomagnetic pole was obtained from eight early Neoproterozoic mafic dikes in the northern Altyn Tagh blockThe pole was dated at 895.3 ± 7.7 Ma using baddeleyite U‐Pb SHRIMP methodologyThe adjacent south Tarim‐Altyn Tagh‐Qaidam‐Qilian block and north China craton were located at NW side of Laurentia on the periphery of Rodinia [ABSTRACT FROM AUTHOR]

Structural and petrological data suggest that the Xigaze ophiolite from the Yarlung Zangbo Suture Zone (YZSZ) in south Tibet was a typical slow‐spreading ridge. A new field, geochemical, mineral, and U‐Pb zircon dataset of plagiogranite intrusions were used to constrain the dynamic processes of oceanic accretion in this slow‐spreading ridge. Plagiogranites mainly occur as dykes or intrusions intruded into the whole sequence of the ophiolite and have a similar orientation to the dolerite dykes developed in the late stage of detachment faulting. U‐Pb zircon ages of 122–123 Ma were obtained for two types of plagiogranites and associated dolerite dykes. Detailed geochemical and mineralogical examinations suggest that the plagiogranites are the product of low‐pressure (2–3 kbar) fractional crystallization of mid‐ocean ridge basalt‐like magma and unlikely to have been derived from the partial melting of hydrous gabbroic rocks. The complex cross‐cut relationship between the plagiogranites and ophiolite sequence reflects that they are controlled by small discontinued melt lenses rather than a big magma chamber under the ridge axis and reveals multiple injections during the oceanic crust accretion. The formation of plagiogranites possibly reflects the complex characteristic of oceanic accretion at slow‐spreading ridges, time‐dependent on structural (external) and magmatic (internal) processes. [ABSTRACT FROM AUTHOR]

To better image complex geological structures and explore for the gold‐bearing quartz pebble conglomerate (locally termed Kimberley Reef) near Burnstone mine in the South Rand goldfield (South Africa), we reprocessed legacy 2D reflection seismic data using up‐to‐date seismic processing algorithms. The mining region is dominated by steeply dipping normal and reverse faults, as well as dolerite intrusions that crosscut the tabular gold mineralization and complicate the extraction of the ore. The legacy seismic data were acquired in 1993 in the South Rand goldfield as part of the gold exploration programme by the Gold Division of Anglo‐American Corporation. The pre‐stack data quality was improved by cautiously removing noise and applying static corrections to enhance the continuity of the reflection events. Improved structural imaging was then achieved using pre‐stack time migration and pre‐stack depth migration through careful velocity analysis. In particular, pre‐stack depth migration provided better imaging of near‐surface stratigraphic units and deep‐seated complex structures, relative to older post‐stack migrated images produced in 1993. Other reprocessing improvements included accurate imaging of key seismic reflective interfaces that can be used as proxies to 2D map the gold deposit, its dip variations, and geological structures (faults/dykes) crosscutting it. Synthetic shot gathers data computed using a 2D finite‐difference algorithm provided some insight into the source of seismic reflectivity observed on the reprocessed seismic data. The new structural information from reprocessing is essential for enhancing ore resource evaluation and guiding future exploration projects in the region. [ABSTRACT FROM AUTHOR]

Early arrival traveltime tomography and full waveform inversion were conducted on downward continued streamer seismic data at Dante's Domes oceanic core complex (OCC), providing unprecedented details of shallow P wave velocity structure. Together with reverse time migration images, seafloor morphology, in situ geological samples, magnetic and gravity data, the seismic constraints are used to infer the lithological distribution along the seismic profiles. Based on the striking similarity in velocity structure beneath the corrugated domes with other OCCs and drilling results from Atlantis Massif, we confidently reconfirmed the Southern Dome as dominantly gabbroic rocks, and the Northern Dome as serpentinized peridotites. A series of isolated gabbroic bodies embedded in the diabase and basaltic layers is observed in the breakaway zone, suggesting that the initiation of Dante's Domes OCC occurred over a long period during which there were several failed attempts to form a long‐lived detachment fault. This early development of the OCC probably occurred under a regime of alternating magma starvation and magma replenishment. The predominantly gabbroic section, beneath the Southern Dome and extending to termination, indicates the OCC has been created with relatively high magma flux. We also imaged distinct shallow subseafloor reflections which are also termed as D reflectors underneath the corrugated domes. The location of the D reflectors is similar to those in the Atlantis Massif, with depths well correlated with the top of exhumed gabbroic bodies and the discontinuities in the D reflectors between gabbroic bodies. Our findings contribute to the understanding of processes controlling the OCCs initiation and evolution at slow spreading ridges. Plain Language Summary: The lithospheric structure generated along the mid‐ocean ridges is determined by the magmatic accretion and tectonic extension, the spatiotemporal variation of which generally depends on the spreading rates. Along slow spreading ridges, tectonic extension dominates and sometimes forms oceanic core complexes (OCCs) generated by heterogeneous exhumed lower crustal and upper mantle section caused by long‐lived, large‐offset detachment faults. The Dante's Domes OCC, located between 26°32′N and 26°40′N on the African plate along the Mid‐Atlantic Ridge, was created by a ∼18‐km‐long detachment fault. Here detailed structural variability within the Dante's Domes OCC was obtained from advanced seismic imaging techniques. The lithological distribution interpreted from seismic imaging, which could be employed to infer magmatic accretion and tectonic extension behaviors, improved our understanding of the initiation and evolution of Dante's Domes OCC. A series of linear ridges are interpreted as breakaways where the OCC initiated, suggesting that the Dante's Domes OCC experienced several failed attempts to form long‐lived detachment fault, and was not exhumed quickly as previously postulated. Key Points: Detailed structure of Dante's Domes oceanic core complex (OCC) was obtained from downward continued streamer waveform inversion and reverse time migrationA series of narrow ridges interpreted as breakaways indicates that the initiation of Dante's Domes OCC was not fast as previously postulatedVelocity contrasts of the shallow low‐velocity and fractured layer and deeper high‐velocity gabbros contributes to the shallow reflectivity [ABSTRACT FROM AUTHOR]

New geochronologic and paleomagnetic data from the North American Midcontinent Rift (MCR) reveal the synchronous emplacement of the Beaver River diabase, the anorthosite xenoliths within it, and the Greenstone Flow—one of the largest lava flows on Earth. A U‐Pb zircon date of 1091.83 ± 0.21 Ma (2σ) from one of the anorthosite xenoliths is consistent with the anorthosite cumulate forming as part of the MCR and provides a maximum age constraint for the Beaver River diabase. Paired with the minimum age constraint of a cross‐cutting Silver Bay intrusion (1091.61 ± 0.14 Ma; 2σ), these data tightly bracket the age of the Beaver River diabase to be 1091.7 ± 0.2 Ma (95% CI), coeval with the eruption of the Greenstone Flow (1091.59 ± 0.27 Ma; 2σ)—which is further supported by indistinguishable tilt‐corrected paleomagnetic pole positions. Geochronological, paleomagnetic, mineralogical and geochemical data are consistent with a hypothesis that the Beaver River diabase was the feeder system for the Greenstone Flow. The large areal extent of the intrusives and large estimated volume of the volcanics suggest that they represent a rapid and voluminous ca. 1,092 Ma magmatic pulse near the end of the main stage of MCR magmatism. Key Points: New geochronology on an anorthosite xenolith tightly constrains the timing of the Beaver River diabase intrusionsPaleomagnetic and geochronological data support that the Beaver River diabase is comagmatic with the very high‐volume Greenstone FlowWide conduits of magma to the surface are indicated by large anorthosite xenoliths [ABSTRACT FROM AUTHOR]

Mesozoic mafic dykes in the Litun ore district provide an opportunity to study the nature of the Mesozoic lithospheric mantle beneath the Luxi area of the North China Craton. U–Pb dating of zircon from the Litun diabase using laser ablation inductively coupled plasma mass spectrometry yields an age of 124.6 ± 1.7 Ma, indicating an Early Cretaceous emplacement age. Samples from the Litun diabase display a medium‐ to fine‐grained texture, consisting of plagioclase (60–65 vol%), clinopyroxene (30–35 vol%), and minor biotite (~2 vol%). They are characterized by enrichment of large‐ion lithophile elements (LILEs, such as Rb, Ba, Th, and U) and light rare‐earth elements (LREEs) without significant Eu anomalies (0.83–1.07), depletion of high‐field‐strength elements (HFSEs, such as Nb, Ta, and Ti). The Litun diabase has relatively high initial 87Sr/86Sr ratios (0.7049–0.7060) and negative εNd(t) values (−11.7 to −9.7). The Litun diabase also shows high MgO (10.52–13.84 wt%), Cr (956–1,162 ppm), Co (26.5–65.6 ppm), and Ni (240–514 ppm) contents and low Rb/Sr ratios (0.01–0.03). These geochemical features suggest that the Litun diabase may have originated from an enriched lithospheric mantle source with amphibole as an essential phase, and that the Litun diabase was not significantly affected by fractional crystallization and crustal contamination. In combination with the Sr–Nd isotopic compositions of mafic rocks in the Luxi area (such as the Mengyin mafic dykes and Jinan gabbro), our results suggest that the lithospheric mantle beneath the Luxi area may have been rapidly enriched between ~144 and ~124 Ma, which was induced by sequential hybridization of sinked lower crust. [ABSTRACT FROM AUTHOR]

The Western Dharwar Craton (WDC) exhibits numerous exposures of NNW–SSE to NW–SE trending mafic dykes. Geochemistry of four 2.21 Ga NNW–NW trending dykes and 21 other similar trending dykes provides new insights into the geochemical behaviour, mantle source characteristics, and tectonic history of mafic magmatic event, which have also affected the Eastern Dharwar Craton (EDC). Based on modal mineralogy and texture, these dykes can be classified into dolerite, olivine dolerite, gabbro, and olivine gabbro. They show basaltic to basaltic‐andesitic composition and have sub‐alkaline tholeiitic nature. LaN/LuN ratio classifies the dykes into two groups: Group I, with values close to 2, shows relatively flat REE patterns while, Group II, with values 4–6, has inclined REE patterns. In general, both groups show LREE enrichment and most of the samples exhibit negative Nb–Ta and Ti anomalies, indicating crustal contamination. However, negative Zr–Hf anomaly and low Th/Nb values (0.14–0.73) noticed within the samples preclude significant crustal inputs. Petrogenetic modelling using batch melting equation suggests that the dykes fractionated from two distinct mantle melts and had slightly different sources, both within the spinel–garnet transition zone. The overall composition of these 2.21 Ga dykes is consistent with a mantle plume‐induced heterogeneous source that was previously modified by some ancient subduction event. Coeval dykes from EDC exhibit similar geochemical behaviour, mantle source characteristics, and tectonic history. These and other synchronous dykes from distant cratons, viz. Superior, Slave, Greenland, represent a 2.21 Ga large igneous province event, which is linked with the Sclavia/Superia supercraton. [ABSTRACT FROM AUTHOR]

Non-metamorphosed, autochthonous Lesser Himalayan sediments (LHS), which are correlated to the Kuncha and Naudanda Formations, were found in a narrow belt between the Main Boundary Thrust and the Lesser Himalayan Thrust at the base of the Kuncha nappe in southeastern Nepal. The autochthonous Naudanda Formation is comprised of cross-bedded and rippled orthoquartzite and yielded a maximum depositional age of 1795.1 Ma ±5.1 Ma using detrital zircons. Low-grade metamorphosed quartzite in the Kuncha nappe yielded a maximum depositional age of 1867.4 Ma ±3.4 Ma, although it is totally recrystallized. These ages and age distribution patterns of detrital zircon grains indicate that the meta-quartzite of the nappe is originally Naudanda Formation. A zircon fission-track age of the autochthonous Naudanda Formation shows partially annealed age of 864 Ma ±56 Ma, in contrast, that of the Kuncha nappe shows a totally annealed age of 11.9 Ma ±1.6 Ma. These results suggest that the autochthonous LHS have never undergone metamorphism during the Himalayan orogeny. We also discovered a non-metamorphosed Heklang Formation that rests on the Naudanda Formation, and designated it as a sub-type section on the basis of detailed lithostratigraphic study. It is characterized by black and light green slate with dolerite sills and ill-sorted quartzose sandstone, and correlated to the metamorphosed Dandagaon Phyllites in the Kathmandu area. Nonmetamorphosed autochthonous formations distributed to the south of the nappe front suggest that they escaped from thermal metamorphism by hot nappe. [ABSTRACT FROM AUTHOR]

The Taishu Group is a folded, Eocene-Lower Miocene, thick sedimentary package exposed widely on Tsushima Island between the Japan Sea and East China Sea. This location makes the strata important to understand tectonics and paleo-environments in the Far East, but the timing of the folding is controversial. We studied the styles of brittle deformations of the strata. It was found that flextural-slip folds were dominant. Mesoscale faults were classified into two groups: NE-SW trending reverse faults and NW-SE trending strike-slip faults. Members of both the groups showed movements largely perpendicular to the fold axes. The latter group consisted of sinistral and dextral faults. Accordingly, we interpreted that they were transfer faults activated during the folding. Consequently, mesoscale faults and flexural-slip faults evidence the map-scale plane strain of the Taishu Group in the plane perpendicular to the NE-trending fold axes. There were few transpressional deformations in the group. This is inconsistent with the transpression hypothesis for explaining the simultaneous folding and Japan Sea opening. Another hypothesis in which the folds in Tsushima are regarded as an onshore part of the Taiwan- Shinji fold belt is inconsistent with the timing of folding suggested by mining geologists to be consistent with and contemporaneous with this deformation. On the other hand, we found that dolerite dikes and sills were involved in the folding. Therefore, we conclude that the folding began during the late Early Miocene time and climaxed during the ore mineralization at around 15 Ma. We suggest that the folding in Tsushima was the easternmost manifestation of the compressional regime around the Yellow Sea and East China Sea in the Early to early Middle Miocene, and that the compression was brought about by the arrival of the Philippine Sea plate to initiate buoyant subduction under Kyushu. [ABSTRACT FROM AUTHOR]

The Qingchengzi Pb–Zn–Au–Ag–Mo polymetallic ore field located in the Liaodong Peninsula, Liaoning Province, China, is spatially associated with multiple magmatism, which provide a classic example for studying the multiple tectonic and metallogenetic events. In this paper, we report some new geochemical and geochronological data of igneous rocks in the Qingchengzi ore field, including diabase, lamprophyre, microdiorite, granite porphyry, and quartz porphyry. Zircon U–Pb dating yielded the formation ages of these rocks as Triassic, Jurassic, and Early Cretaceous. Low‐Mg adakitic granite porphyries formed at 233 Ma have zircon εHf(t) values of −17.7 to −14.5, suggesting that they were mainly derived from partial melting of thickened lower crust. Mafic dykes formed during 226–203 Ma have zircon εHf(t) values of −28.6 to −12.8, suggesting that they were mainly derived from partial melting of ancient lithospheric mantle. Zircons from the 168Ma Jurassic diabase have high Nb/Ta and low Nb/Th ratios, with zircon εHf(t) values of −25.2 to −18.5. This suggests that ancient lithospheric mantle was influenced by melts/fluids from the subducted Palaeo‐Pacific Plate. The Early Cretaceous microdiorites (126 Ma) are high‐Mg adakite rocks, with zircon εHf(t) values of −27.3 to −19.6. Melting of delaminated eclogitic lower crust might produce these high‐Mg adakitic microdiorites. The upwelling asthenosphere could heat the residual lower crust to form the quartz porphyries. The Early Cretaceous diabase (100 Ma) shows low Nb/Ta and high Nb/Th ratios, with zircon εHf(t) values of −0.7 to 5.8, implying a depleted mantle source. The characteristics of Triassic–Cretaceous intermediate‐mafic intrusions show that the lithospheric mantle evolved from enriched ancient mantle to depleted juvenile mantle. This transformation of the lithospheric mantle might have resulted from the delamination of the lower crust that was caused by subduction of the Palaeo‐Pacific Plate. Based on the field observation and geochemical data, Au, Pb–Zn–Ag, Mo mineralization in the Qingchengzi ore field show closely spatial and genetic relationship with intrusive rocks, indicating that the Mo, Pb–Zn–Ag mineralization might be related to the Jurassic magmatic activity, whereas Au mineralization related to the Early Cretaceous magma. [ABSTRACT FROM AUTHOR]

Faults in the rock mass of dam foundation are crucial in controlling dam deformation and stability. In particular, long‐term stability of dam foundation is an important factor for the safety of dam operations. The rock in the foundation of Dagangshan hydropower station is mostly granite, and there are many diabase dikes distributed in granite. Geological survey indicates that many faults exist along the interfaces between granite and diabase. Lots of diabase were metamorphosed to chlorites, which have very low strength. In order to investigate the deformation of faults in diabase dikes under long‐term loading, in situ shear creep tests were performed to estimate the creep performance of a fault. The shear creep displacement and the influence of displacement history of the specimen during multi‐level loading tests were measured and analyzed. The isochronous stress‐strain method was used to determine the long‐term strength of the fault in shear creep tests. Considering the instantaneous damage and strain softening, a new viscoelastic‐plastic softening creep model was proposed to describe the shear creep behavior of the fault. Comparisons confirmed that this creep model is capable of describing the shear creep behavior of the fault and the creep parameters were estimated accordingly using this model. [ABSTRACT FROM AUTHOR]

The Karoo Basin covers much of South Africa and is an area of prospective shale gas exploration, with the Whitehill Formation the target shale unit. However, the sedimentary succession, including the Whitehill, has been intruded by a series of sills and dykes associated with the Karoo Large Igneous Province (~183 Ma), which are expected to have modified the thermal history of the basin dramatically. Here, we investigate a secondary effect of these intrusions: a series of hydrothermal vent complexes, or breccia pipes, focusing on using O, H, and C isotopes to constrain the origin and evolution of fluids produced during the intrusion of basaltic sills. A cluster of breccia pipes have been eroded down to the level of the Ecca Group at Luiperdskop on the western edge of the Karoo basin; a small isolated pipe of similar appearance crops out 13 km to the east. The Luiperdskop pipes are underlain by a Karoo dolerite sill that is assumed to provide the heat driving fluidization. The pipes consist of fine‐grained matrix and about 8% clasts, on average, of mostly sedimentary material; occasional large rafts of quartzite and dolerite are also present. The presence of clasts apparently from the Dwyka Group is consistent with the depth of formation of the pipes being at, or near, the base of the Karoo Supergroup, between 400 and 850 m below present surface. The presence of chlorite as the dominant hydrous mineral is consistent with an emplacement temperature between 300 and 350°C. The major and trace element, and O‐ and H‐isotope composition of the Tankwa breccias is homogenous, consistent with them being derived from the same source. The δ18O values (vsVSMOW) of the breccias are relatively uniform (7.1‰–8.7‰), and are similar to that of the country rock shale, and both are lower than expected for shale. The water content of the breccia is between 2.7 and 3.1 wt.% and the δD values range from −109‰ to −144‰. Calcite in vesicles has δ13C and δ18O (VSMOW) values of −4.2‰ and 24.0‰, respectively. The low δD value of the breccia rocks does not appear to be due to the presence of methane in the fluid. Instead, it is proposed that low δD and δ18O values are the result of the fluid being derived from the breakdown of clay minerals that formed and were deposited at a time of cold climate at ~290 Ma. [ABSTRACT FROM AUTHOR]

The Dingqing ophiolite is located in the eastern segment of the Bangong‐Nujiang suture zone. This suture zone is W–E trending parallel with the Yarlung–Zangbo suture zone and is an strategic area for exploring chromite deposits in China. The Dingqign ophiolite is distributed in near SE‐NW direction. According to the spatial distribution, the Dingqing ophiolite is sudivided into two massifs, including the East and the West massifs. The Dingqing ophiolite covers an area of nearly 600 km2. This ophiolite is composed of peridotite, pyroxenite, gabbro, diabase, basalt, plagiogranite and chert (Fig. 1). The peridotite is the main lithology of the Dingqing ophiolite. The peridotite covers about 90% of the total area of the Dingqing ophiolite. The Dingqing ophiolite is dominated by harzburgite with a small amounts of dunite. The Dingqing harzburgite displays different textures, such as massive, Taxitic, oriented and spherulitic textures (Fig. 2d–i). These four types of harzburgite occur in both the East and West massifs, especially in the Laraka area of the eastern part of the East massif. Dunites have different occurrences in the field outcrops, such as lenticular or strip‐shaped, thin‐shell and agglomerate varieties (Fig. 2a–c). On the basis of detailed field work, we have discovered 83 chromitite bodies, including 27 in the East massif and 56 in the West massif. According to the occurrence scale and quantity of the chromitite bodies, we have identified four prospecting areas, namely Laraka, Latanguo, Langda and Nazona. Chromitites in the Dingqing ophiolite show different textures, including massive, disseminated, veined and disseminated‐banded textures (Fig. 3). On the basis of the Cr# (=Cr/(Cr+Al)×100) of chromite, we have classified the Dingqing chromitite into high‐Cr, medium high chromium type, medium chromium type and low chromium type chromitite (Figs. 4, 5). Among them, low chromium type chromitite Cr# is extremely low, ranging from 9.23 to 14.01, with an average of 11.89; TiO2 content is 0.00% to 0.04%, and the average value is 0.01%, which may be a new output type of chromitite. These different types of chromitites have different associations/assemblages of mineral inclusions. The inclusions in high chromium type chromitite are mainly clinopyroxene and a small amount of olivine; medium high chromium chromitite are mainly amphibole, a small amount of clinopyroxene and phlogopite; while low‐chromium chromite rarely develops mineral inclusions, and micron‐sized clinopyroxene inclusions are common in olivines which are gangue mineral in it. These different types of chromite ore bodies have a certain correspondence with the field output, and may also restrict their genesis. This part will be further developed in the follow‐up work. [ABSTRACT FROM AUTHOR]

The ages and source of Late Cretaceous mafic dolerite dykes of the Songliao Basin were determined using geochronological, geochemical, zircon Hf, whole‐rock Sr–Nd isotopic, and zircon fission tract. The results show that (a) petrographic data reveal doleritic, poikiloblastic textures, and amygdale structures of the dolerite dykes. (b) LA‐MC‐ICP‐MS U–Pb analysis of zircons yielded an age of 70.0 ± 3.0 Ma of one of these mafic dykes in agreement with the zircon fission track age (69–68 Ma) of host rocks within uncertainty, placing them within the Late Cretaceous. (c) Geochemical researches indicate that the dykes are classified as the alkaline and tholeiitic series according to their major elements and characterized by high Na2O (2.79–4.89 wt.%), TiO2 (1.63–2.71 wt.%), and low K2O (0.46–2.45 wt.%). And they have enrichment of incompatible elements (e.g., K, Ti, Rb, Ba, Th, U, Nb, Ta, and REEs), high Rb/Sr (0.026–0.066), LaN/YbN (3.83–15.93), near‐chondritic HREEs ([Gd/Yb]N = 1.78–3.37), low Sm/Nd (0.202–0.282) ratios, and with negligible Eu anomalies (Eu/Eu* = 0.98–1.06). The dykes contain relatively low amounts of radiogenic Sr, as shown by (87Sr/86Sr)i values (0.7037–0.7045), and have positive values of εNd(t) (3.66–5.40) and εHf (t) (2.66–7.45), suggesting that the mafic dykes have been derived from partial melting of the depleted lithospheric mantle and contaminated by crust in the source region and formed in back‐arc rift settings caused by the subduction of the Pacific Oceanic Plate. All the above indicate large‐scale extensional event in Songliao Basin NE China at about 70 Ma. [ABSTRACT FROM AUTHOR]

Diabase dikes are extensively distributed in the Xiongcun porphyry copper–gold district in the southern margin of the Lhasa terrane. Here, we report zircon U–Pb ages determined by laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) along with Hf isotopic, whole‐rock elemental, and Sr–Nd–Pb isotopic data for these diabase dikes. Zircons from one of the Xiongcun diabase dikes yielded an emplacement age of 165.3 ± 1.0 Ma. The Xiongcun diabase dikes display subalkaline features and tholeiite compositions. They are enriched in large‐ion lithophile elements (e.g., Rb, Ba, and K) and light rare earth elements and are depleted in high‐field‐strength elements (e.g., Nb, Ta, and Ti). The Xiongcun diabase dikes exhibit relatively low ratios of (87Sr/86Sr)i (0.70386–0.70501), (206Pb/204Pb)i (18.15–18.40), (207Pb/204P)i (15.52–15.57), and (208Pb/204Pb)i (38.06–39.46) and relatively high values of εNd(t) (5.85–6.92) and εHf(t) (+12.58 to +14.03). Combined with previous research results, these findings suggest that the Xiongcun diabase dikes and Early Mesozoic magmatic rocks in the southern margin of the Lhasa terrane formed in an active continental margin magmatic arc setting related to the northward subduction of the Neo‐Tethys oceanic slab; however, the possibility that the Xiongcun diabase dikes were formed in an intra‐oceanic arc setting cannot be excluded. Their parental magmas were formed by the partial melting of the depleted mantle source that was modified by fluids released from the Neo‐Tethys oceanic slab. The magmas experienced fractional crystallization of olivine and clinopyroxene and underwent limited crustal contamination during magma emplacement. The ~165 Ma Xiongcun diabase dikes, which probably originated under an extensional stress condition in a magmatic arc setting, correspond to the timing of Middle Jurassic subduction‐related porphyry copper mineralization (161–172 Ma) in the southern margin of the Lhasa terrane, likely suggesting that this episode of mineralization occurred during a period of changing stress from compression to extension. [ABSTRACT FROM AUTHOR]

From the east of the Xuefengshan tectonic zone (XTZ) to the Pacific coast of the South China Block, there exist widespread Mesozoic magmatic rocks, which attract a great deal of attention for their forming mechanism and evolutional history. Among them, the Mesozoic Jishou diabase located at the west of the XTZ is reported in this study. Based on our geochronologic analysis, the diabase has a U–Pb age of 134 ± 2.3 Ma. The diabase belongs to calc‐alkaline series in a SiO2‐K2O diagram and illustrates significant enrichment in light rare earth elements and flat heavy rare earth elements without obvious Eu anomalies. Meanwhile, the diabase has negative εHf(t) and εNd(t) values and higher radiogenic 87Sr/86Sr(t) ratios, suggestive of EM2‐like Sr‐Nd isotopic compositions. The diabase shows high variations in 207Pb/204Pb(t; 15.609–15.671), 206Pb/204Pb(t; 17.943–18.742), and 208Pb/204Pb(t; 38.268–39.302). It is suggested that the Jishou diabase may be generated from the lithospheric mantle in response to the decompression melting accompanied by lithospheric extension during Pacific subduction process. During the Early Cretaceous (145–120 Ma), the upwelling and melting of the mantle occurred under the XTZ, causing intraplate Jishou diabase magma. Subsequently, the significantly descending of the subducted Paleo‐Pacific slab led progressively eastward generation and migration of subduction‐related magmas, resulting in a widespread distribution of igneous rocks in the Cathaysia Block. [ABSTRACT FROM AUTHOR]

Metavolcanics and mafic intrusive rocks of the Paleoproterozoic Birimian terrane in the southeastern part of the West African Craton, Ghana, were analyzed for major and trace elements and Nd and Sr isotopic data to constrain the geodynamic evolution of the Birimian Supergroup. The metavolcanic rocks consist of metabasalts, meta‐andesites, and amphibolites, whereas the mafic intrusions are mainly gabbros, hornblendites, and dolerites. The rocks are tholeiitic in composition and show the classic features of arc magmatism. The metavolcanics display significant enrichments in large ion lithophile elements (LILE) and light rare earth elements, relative to high field strength elements (HFSE) and heavy rare earth elements. The multielement patterns of the rocks also show positive Pb, Ba, Th, and Sr and negative Nb, Ta, and Ce anomalies that are typical characteristics of subduction‐related magmas. They also have La/Nb ratios <3 and La/Ta ratios <43 that are similar to other Archean and Birimian greenstone belts in West Africa. The rocks have εNd (2.1 Ga) values of −0.96 to +2.60, and Nd model ages of 2.24–2.51 Ga (TDM1) and 2.16–2.45 Ga (TDM2), indicating their juvenile character with possible contributions from pre‐Birimian crustal materials in their sources. The εNd values suggest a depleted source and further indicate that they were probably produced in an almost entirely oceanic environment with minor influence from the continental crust. The Nd isotopic results are consistent with the island arc model, which views Paleoproterozoic terranes of the West African Craton in the context of subduction–accretion processes. Accordingly, these processes may have played a role in the formation of the Columbia supercontinent during the Paleoproterozoic (2.1–1.8 Ga) orogenic events. [ABSTRACT FROM AUTHOR]

This study presents new geochemical data on dolerites from the Plussulien and Beulin Neolithic quarries in the Massif Armoricain (France) and for dolerite samples from their surrounding local regions. Using the major and trace element data obtained on these rocks, the two quarries and regional dolerite occurrences appear to be clearly distinct. Consequently, a set of chemical criteria is proposed to identify the dolerite axes produced uniquely at the Beulin quarry and to discriminate between the axes produced in the surrounding local region of Beulin, but outside the quarries, and those produced in the local region of Plussulien. These results could also be used, for example, to identify the existence of undiscovered quarries in the Beulin region. This work may provide the breakthrough needed to understand stone axe exchanges during the Neolithic times in north-western France and beyond. [ABSTRACT FROM AUTHOR]

This paper reports peculiar alternating augite-plagioclase wedges in basement dolerites of Lockne impact structure, Sweden. The combined microscopic and spectroscopic studies of the micro/nanoscale wedges reveal that these are deformation-induced features. First, samples showing wedges, 12 out of 18 studied, are distributed in the impact structure within a radius of up to 10 km from the crater center. Second, the margins between the augite and labradorite wedges are sharp and the {110} prismatic cleavage of augite develops into fractures and thereafter into wedges. The fractures are filled with molten labradorite pushed from the neighboring bulk labradorite grain. Third, compared to the bulk labradorite, the dislocation density and the residual strain in the labradorite wedges are significantly higher. A possible mechanism of genesis of the wedges is proposed. The mechanism explains that passing of the shock waves in the basement dolerite induced (i) formation of microfractures in augite and labradorite; (ii) development of the augite prismatic cleavages into the wedges, which overprint the microfracture in the labradorite wedges; and (iii) thereafter, infilling of microfractures in the augite wedges by labradorite. [ABSTRACT FROM AUTHOR]

The article discusses geochronology and tectonic impacts of diabase intruded into Xiangshan Group in the Southeastern Alxa Block, North West China.Topics discussed include tectonic junction between the North China Block and the western Qinling–North Qilian Orogenic Belt, use of sensitive high-resolution ion microprobe II to measure zircon ages of the diabase, and high potassium content in the region.

Early Permian (272±2Ma) diabase dikes from the Linxi area in central Inner Mongolia of NEChina have high MgO(10.4-12.3wt%),Cr (301-448ppm) and Ni (167-233ppm) concentrations, and show enrichments in large ion lithophile element (LILE) and light rare earth elements (REE) but depletions in high field strength element (HFSE, e.g., Nb and Ta), with depleted mantle-type Sr [87Sr/86Sr (i)=0.70315 - 0.70362], Nd [εNd (t)=+6.8 - +7.4], Pb [206Pb/204Pb (i)=18.10 - 18.16] and zircon Hf [εHf (t)=+14.7 - +19.1] isotopic compositions, but slightly higher zircon δ18O (5.2 - 6.0 ‰ with an average of 5.7 ‰) than normal mantle. The combined geochemical data indicate their derivation from a depleted mantle metasomatized by recycled crustal component. Elemental and isotopic modeling results suggest that the primary magma was produced through 5 % to 10 % melting of a depleted mantle, which contained approximately 1 % sediment fluid released from the subducted paleo-Asian Ocean. Considering the widespread distribution of contemporaneous mafic rocks across the central Inner Mongolia, which show REE patterns from E-MORBs to normal MORBs, we propose a petrogenetic link between the Early Permian mafic magmatism and a back-arc extension in response to northward subduction of the paleo-Asian Ocean. The Permian mafic magmatism and the new age constraints from the metamorphic and sedimentary records in this area tend to indicate the ultimate closure of the paleo-Asian Ocean by the end of Paleozoic. [ABSTRACT FROM AUTHOR]

The Bangong- Nujiang suture ( BNS) between the Lhasa and Qiangtang terranes is an important boundary and its petrogenesis is controversial. Diabase from the accretionary prism in the southern Qiangtang terrane yields a zircon U- Pb age of 181.3 ± 1.4 Ma. All the diabases show tholeiitic basalt compositions, gentle enrichment patters of light rare earth elements ( REE), variable enrichment in incompatible element concentrations (e.g. Th and Rb), and no anomaly in high field strength elements (e.g. Nb and Ta), similar to that of enriched mid-ocean ridge basalt ( E- MORB). They have relatively homogeneous whole rock Nd (ε Nd(t) = 7.3-9.1) and zircon Hf- O isotopic compositions (ε Hf(t) = 14.8-16.1, and δ18 O = 4.57-6.12‰), possibly indicating melting of the depleted mantle and no significant crustal contamination during the petrogenesis. The element variations suggest that the diabases were formed by plume-ridge interaction at a mid-ocean ridge within the Bangong- Nujiang ocean. [ABSTRACT FROM AUTHOR]

Once a mafic intrusive rock has become altered, it is generally difficult to obtain a reliable intrusion age using conventional isotopic dating methods. To overcome this problem, this study used zircon fission track ( ZFT) thermochronometry to determine the timing of crystallization of altered mafic intrusions. ZFT dating was carried out on samples of baked granite country rock adjacent to dolerite dikes (5-10 m thick) in the Takato area of central Japan. Three granite samples collected within 8 mm of a dike contact yielded consistent ZFT ages of 17-16 Ma, with confined track lengths indicative of the complete annealing of pre-existing tracks by reheating due to dike intrusion. An older ZFT age was obtained for one granite sample collected within 20 mm of the contact, but confined track length measurements indicate that this is an incompletely reset age that lies between the ZFT age of the unbaked granitic country rocks ( ca. 55 Ma) and the emplacement age of the dike. Petrographic examinations suggest that post-intrusion hydrothermal activity did not influence the ZFT ages. We conclude that the 17-16 Ma ZFT age represents the emplacement age of the dikes. Our results show that ZFT dating of baked country rock is an effective tool for dating altered mafic intrusions, for which other dating techniques are not applicable. In the eastern part of Southwest Japan, dispersed volcanic activity occurred in the late Early to early Middle Miocene (18-15 Ma), and the volcanic belt extended into the forearc. This pulse of activity was possibly related to the injection of asthenospheric material into the trench-side mantle wedge beneath the Japan arc. We also present young apatite fission track ages ( ca. 4 Ma) that may reflect a Middle Miocene or later thermal event associated with local magmatic activity near the Takato area. [ABSTRACT FROM AUTHOR]

The geology of the Snowdonia National Park in North Wales comprises a mixture of Lower Palaeozoic shallow marine sediments, acidic igneous rocks and basic intrusions of the Welsh Basin that were subsequently deformed during the Caledonian Orogeny. Thin igneous intrusions are challenging to map due to variable surface exposures, their intrusive origin, structural deformation and burial by glacial sediments. This study used a combination of traditional geological techniques, near-surface geophysical surveys and remote sensing to detect and map a buried dolerite sheet intrusion. Both simple and mathematical analysis of magnetic anomalies and numerical modelling allowed the dolerite position, depths and target widths to be determined. Results showed that calibrated magnetic surveys can characterize buried igneous bodies in such mountainous environments. [ABSTRACT FROM AUTHOR]

Weathering extends to shallower depths on diabase than granite ridgetops despite similar climate and geomorphological regimes of denudation in the Virginia (United States) piedmont. Deeper weathering has been attributed to advective transport of solutes in granitic rock compared to diffusive transport in diabase. We use neutron scattering (NS) techniques to quantify the total and connected submillimeter porosity (nominal diameters between 1 nm and 10 µm) and specific surface area (SSA) during weathering. The internal surface of each unweathered rock is characterized as both a mass fractal and a surface fractal. The mass fractal describes the distribution of pores (~300 nm to ~5 µm) along grain boundaries and triple junctions. The surface fractal is interpreted as the distribution of smaller features (1-300 nm), that is, the bumps (or irregularities) at the grain-pore interface. The earliest porosity development in the granite is driven by microfracturing of biotite, which leads to the introduction of fluids that initiate dissolution of other silicates. Once plagioclase weathering begins, porosity increases significantly and the mass + surface fractal typical for unweathered granite transforms to a surface fractal as infiltration of fluids continues. In contrast, the mass + surface fractal does not transform to a surface fractal during weathering of the diabase, perhaps consistent with the interpretation that solute transport is dominated by diffusion in that rock. The difference in regolith thickness between granite and diabase is likely due to the different mechanisms of solute transport across the primary silicate reaction front. [ABSTRACT FROM AUTHOR]

Introduction: Constraining the amount of a meteoritic signature within rocks of an impact structure provides important information on the fate of the projectile, as well as on the processes that occur during and after an impact cratering event. In 2016, the IODP-ICDP Expedition 364 drilling recovered a ~829 m continuous core (M0077A) of impactites and basement rocks within the peak ring of the ~200-km-diameter Chicxulub impact structure [1]. An iridium anomaly and a near-chondritic highly siderophile element (HSE) signature were identified within the transitional unit of core M0077A, at the top of the peak ring, corresponding to the settling of atmospheric fallout of finegrained extraterrestrial material [2]. Previous works on other drill cores recovered from the Chicxulub structure have shown that most Chicxulub impactites contain a rather minor, heterogeneously distributed, chondritic component, up to 0.1% in a few samples [3, and references therein]. This study focuses on the search for a meteoritic component within impact melt rock samples recovered from the peak ring. Methods: To identify a possible meteoritic contribution within the impact melt rock units from the peak ring, detailed geochemical investigations, including selected moderately (Cr, Co, Ni; 25 samples), and HSE (Ir, Pt, Re, Os; 12 samples) contents, as well as Re-Os isotopic analyses (12 samples), were completed. In addition, two suevite samples, as well as pre-impact lithologies (one amphibolite, one dolerite, one dacite, and two granite samples) of the Chicxulub peak ring, were also analyzed. Details on the methods used for this study are provided in [3]. Results and discussion: Impact melt rock samples are generally of andesitic composition. The moderately siderophile element contents (Cr, Co, Ni) of impact melt rocks reflect primarily a mixture of a felsic (granite) and a mafic (dolerite) components, with the incorporation of carbonate material in the upper impact melt rock unit (from 715.60 to 747.02 meters below seafloor). Concentrations of the HSEs in impact melt rock and suevite samples are generally low (<39 ppt Ir, <96 ppt Os, <149 ppt Pt), similar to upper continental crust [4]. Only three impact melt rock samples exhibit an enrichment in Os (125, 344, and 410 ppt) and/or Ir (250 and 324 ppt) by one order of magnitude relative to the other samples investigated. However, the dolerite sample shows a similar enrichment in the HSEs (245 ppt Os, 156 ppt Ir, and 346 ppt Pt) by roughly one order of magnitude relative to the other pre-impact lithologies. In contrast, granite, dacite, and suevite samples are depleted in Ir, with contents ranging from 1 to 10 ppt. The 187Os/188Os ratios of the impact melt rocks range from 0.18 to 2.09, probably reflecting heterogenous target rock contributions. The presence of a significant (~20-60%, and up to 80-90%) mafic, unradiogenic dolerite (187Os/188Os of 0.17) component within the impact melt rocks may be the most likely explanation of the lowest 187Os/188Os ratios measured in impact melt rocks. Granite samples have unusually unradiogenic 187Os/188Os ratios (~0.16). Only one of the investigated samples of the upper impact melt rock unit could be interpreted in terms of a highly diluted (~0.01-0.05%) meteoritic component. Importantly, the impact melt rocks and pre-impact lithologies were affected by a long-lived (>1 Myr) post-impact hydrothermal system [5], locally remobilizing Re and Os. This study shows that the amount of meteoritic material incorporated within the Chicxulub impact structure seems to be rather low and heterogeneously distributed. In contrast, significant meteoritic contribution (up to ~5%) is found in distal K-Pg impact ejecta [6,7]. The low amount of meteoritic material preserved within the Chicxulub impact structure may result from a steeply inclined trajectory of the impactor (~45-60°), as suggested by numerical modeling [8], with most of the projectile material likely ejected and deposited outside the crater. Our study (see details in [3]) shows the challenges associated with the unambiguous identification of a meteoritic component at terrestrial impact structures. Acknowledgements: Thanks to ECORD, IODP-ICDP, the Yucatán Government, and Universidad Nacional Autónoma de México for drilling funding. University of Vienna doctoral school, FWO-Flanders, BELSPO, and VUB Strategic Research Program supported this research. [ABSTRACT FROM AUTHOR]

In highly heterogeneous aquifer systems, conceptualization of regional groundwater flow models frequently results in the generalization or negligence of aquifer heterogeneities, both of which may result in erroneous model outputs. The calculation of equivalence related to hydrogeological parameters and applied to upscaling provides a means of accounting for measurement scale information but at regional scale. In this study, the Permo-Triassic Lagan Valley strategic aquifer in Northern Ireland is observed to be heterogeneous, if not discontinuous, due to subvertical trending low-permeability Tertiary dolerite dykes. Interpretation of ground and aerial magnetic surveys produces a deterministic solution to dyke locations. By measuring relative permeabilities of both the dykes and the sedimentary host rock, equivalent directional permeabilities, that determine anisotropy calculated as a function of dyke density, are obtained. This provides parameters for larger scale equivalent blocks, which can be directly imported to numerical groundwater flow models. Different conceptual models with different degrees of upscaling are numerically tested and results compared to regional flow observations. Simulation results show that the upscaled permeabilities from geophysical data allow one to properly account for the observed spatial variations of groundwater flow, without requiring artificial distribution of aquifer properties. It is also found that an intermediate degree of upscaling, between accounting for mapped field-scale dykes and accounting for one regional anisotropy value (maximum upscaling) provides results the closest to the observations at the regional scale. [ABSTRACT FROM AUTHOR]

A method for the determination of total sulfur in geological materials by inductively coupled plasma-optical emission spectrometry (ICP-OES) is described. We show that good results were obtained using this method even for sample types with very low (< 20 μg g−1) sulfur concentration (e.g., peridotite). Sulfur was determined in fifteen geological reference materials with different sulfur contents. For reference materials with certified sulfur contents, the ICP-OES method gave results in excellent agreement with certified values, and uncertainties better than 4% RSD. ICP-OES results for sulfur in other reference materials yielded RSDs better than 10%, where S concentrations were > 100 μg g−1 (except for diabase W-2a, 16% RSD). Reference materials with lower sulfur contents (< 40 μg g−1) showed much higher RSDs (17-18%). Except for RMs with certified values for sulfur, most data obtained by the combustion infrared detection method generally showed higher concentrations than those measured by ICP-OES and a better RSD (≤ 8% for all materials except DTS-2b). [ABSTRACT FROM AUTHOR]

Diabase dyke swarms are widespread in the East Tianshan and Beishan regions. LA-ICP-MS zircon U-Pb ages of these diabase vary from 305 Ma to 278 Ma, showing that these dykes were formed during Late Carboniferous-Early Permian magmatism. All diabase samples are subalkali calc-alkali, characterized by slight LREE and LILEs enrichment, and weak negative Ti, Nb and Ta anomalies. The diabase samples have positive εNd( t) values (>+3), high Sr isotopic compositions (initial 87Sr/86Sr values=0.7030-0.7097), and large variation of Pb isotopic compositions, indicating they were derived from a deplete mantle source. Regional geology and geochemistry evidences indicate that these diabase dyke swarms were generated in a lithosphere extensional setting and had the same magma sources. Initial magmas may be a mixture of depleted asthenosphere mantle and enriched lithospheric mantle during rapid magma ascending. [ABSTRACT FROM AUTHOR]

Terra Nova, 24, 213-220, 2012 Abstract The Sudbury Structure is located <10 km from the Grenville Front; the northern boundary of the Grenville metamorphic terrane. Previous geological studies have suggested that late Grenvillian deformation (1000-1070 Ma) of the Sudbury Structure was limited to minor brittle deformation. Olivine diabase dykes, which were intruded at 1238 Ma, before the last pulse of Grenville deformation, cross much of the Sudbury Structure. Any Grenville age deformation of the Sudbury Structure therefore should produce systematic displacements in the geometry of the dykes. This study uses information derived from an aeromagnetic survey of the Sudbury Structure to map and measure fault displacements. Lateral displacements of dyke segments define a progressive increase in fault rotation from NE to SW across the basin. A two-dimensional inversion modelling of magnetic anomaly profiles across segments of the dykes outlines a series of fault blocks with common dip. The dyke dip detected by the inversion models suggests that displacement on the faults included rotation about an axis perpendicular to the trend of the fault. The resulting model of scissor, or splay faults is compatible with previously published palaeomagnetic studies of the olivine dykes in the Sudbury region. [ABSTRACT FROM AUTHOR]

A group of Copper Age shaft-hole axes from Caput Adriae (northeastern Italy, western Slovenia and northwestern Croatia) manufactured using meta-dolerite have been analysed for major and trace elements. All the samples show magmatic textures and well recognizable relicts of primary mineralogical phases. Petrographic observations suggest an ophiolitic provenance of the protolithic source(s) while geochemical data indicate that the original magmas originated in a fore arc or pre arc tectonic setting. Strong similarity has been found with several lithotypes from the Banija Ophiolite Complex (Croatia), here indicated as the most probable source area. Considering the available archaeometric data about shaft-hole axes found in northern Italy and Caput Adriae in comparison to those of axe blades discovered in the same area, it emerges that there is a utilization of different rock types, the source of which appears to be quite close to the discovery sites. In the investigated area the shaft-hole axes are largely made from ophiolitic-related rocks which are associated with copper deposits. Consequently there may have been a relation between the localization of the geological sources of shaft-hole axes and the development of metallurgical activities. [ABSTRACT FROM AUTHOR]

The Pan‐African event is widely distributed in East Antarctica craton. Many terranes or outcrops of the craton bear more or less signs of the event. From characteristics of the shear zones, granites, pegmatites, feature and time of high grade metamorphism and detrital zircon ages peaks of the downflowing sediments from the plateau, the Pan‐African event in the East Antarctica and adjacent areas in the Gondwana reconstruction, like SE Africa, southern India and SW Australia, wasdistributed as special zones or areas in many localities, including both the coastal regions and interior of the East Antarctica. In geochemistry, the granites are generally anorogenic, ocassionally with some gabbros or dolerite dykes, showing sign of bi‐modal feature. The water or fluid available along the shear zones were responsible for retrogression of the earlier, e.g., Grenville age, high grade outcrops to later Pan‐African amphibolite facies metamorphism. Meanwhile, the Pan‐African event has influenced most isotopic systems, including the U‐Pb, Sm‐Nd, Rb‐Sr and Ar‐Ar systems, giving younger apparent ages. Manifestation of the Pan‐African event is distributed from possibly locally granitic magmatism, to wider medium‐high grade metamorphism, and mostly widespread in resetting for some isotope systems, suggesting the prevailing thermal effect. Before Gondwana formation, local depressions in the East Antarctica could be filled with sediments, implying the initial breakup period of the Rodinia. The later Pan‐Gondwana counterrotating cogs shaped the interstitial fold belts between continent blocks and formed a set of shear zones. The mafic underplating in the Gondwana may be responsible for the widespread granites, pegmatites and more or less isotopic resetting due to strong thermal effect from the deep. That is, the Pan‐African event is a possible response of the plate movement surrounding the continent swarms in the non‐stable interior of theyet consolidated Gondwana. The Pan‐African event may be an overwhelmingly extensional and transcurrent tectonics in mechanism. [ABSTRACT FROM AUTHOR]

The Peng Co ophiolite is located to the west of Peng lake in the area of lakes in north Tibet, which belongs to the Baila‐Yilashan sub‐belt of the the middle Bangong Co‐Nujiang ophiolitic belt. The Peng Co ophiolite is mainly composed of mantle peridotites, cumulates, diabase dikes. About 70 percent peridotites are harzburgites and 30 percent are lherzolites. Mineral chemistry of the Peng Co lherzolitesare characterized by low Fo contents (88.85–90.33) of olivine and high Al2O3 content (4.26%–7.25%) in pyroxenes. Compared to the primitive mantle, the Peng Co peridotites have relatively higher MgO contents, lower CaO, Al2O3 and TiO2 contents. The total rare‐earth element (REE) contents of the lherzolites are 1.11–1.53 ppm, which are lower than those of the primitive mantle. The chondrite‐normalized REE patterns of the Peng Co peridotites display slight loss in LREE. In the primitive mantle‐normalized spider diagram, the Peng Co peridotites exhibit negative Rb and Zr anomalies and intensively positive U, Ta, Sr anomalies. The PGE contents of Peng Co lherzolites are between 22.9–27 ppb. The chondrite‐normalized PGE patterns of the Peng Co lherzolites are consistent with that of the primitive mantle. Mineral and whole‐rock geochemistry characteristics of the Peng Co lherzolites show an affinity to abyssal peridotites, indicating that it may have formed in the mid‐ocean ridge setting. Through quantitative modeling, we conclude that the Peng Co lherzolites formed after 5%–10% degree of partial melting of the spinel‐phase lherzolite mantle source. The sharp increase of Cr# (56.74 –60.84) in Spinel of harzburgites and relatively high Pd/Ir and Rh/Ir ratios suggest that they have experienced melt‐rock reaction. The crystallization sequence of Peng Co cumulate is olivine‐clinopyroxene‐plagioclase. The Mg# value of clinopyroxene in cumulate peridotite ranges from 86.92 to 89.93, and the mean value of Fo is 84.45, which is obviously higher than that of MOR‐type ophiolite cumulates. The mineral composition, sequence of magmatic crystallization and mineral components of Peng Co cumulate are similar to those of the cumulate formed by the SSZ‐type ophiolite in the subduction zone. Therefore, we can draw a preliminary conclusion that Peng Co lherzolites were formed in an environment of mid oceanic ridge and were remnants of the spinel lherzolite zone which experienced a partial melting of no more than 10%. In the later period, due to the intra‐oceanic subduction, it experienced the rock‐meltinteraction, and thus formed the SSZ‐type cumulate and harzburgite of high Cr value. [ABSTRACT FROM AUTHOR]

The article present the discovery of a ~1.37 Ga Granite in the Eastern Part of the Northern Margin of the North China Craton and its geological significance. Topic include the granite was collected from Huanglingzi town, west of Yitong County, Jilin Province (124°56′16″E, 43°27′46″N); and Zircons within the granite are of magmatic origin and yielded a weighted mean age of ~1.37 Ga, indicating crystallization during the Mid-Mesoproterozoic.

Chemical compositions and magnetic susceptibility data were compared for 12 dolerite bluestone implements including axes, axe-hammers and battle-axes, 11 Stonehenge monoliths (chemical data only), and potential source outcrops in Preseli, South Wales. Most of the studied artefacts are of spotted dolerite, a small number being unspotted dolerite. Bivariate graphs, discriminant analysis and t-tests were used singly and in combination to show, respectively, that the implements found at sites in England are mainly similar to Stonehenge monoliths, while the implements found in Wales have a variety of compositions and are much less similar to Stonehenge monoliths. The dichotomy between English and Welsh dolerite bluestone implements could be explained by exploitation of different Preseli outcrops or erratic assemblages derived from them. A small number of spotted dolerite implements have previously been shown to have chemical compositions atypical of and marginal to Preseli, suggesting the possibility of a source of spotted dolerite outside Preseli. Previously published analytical data in combination with the new implement/outcrop comparisons presented in this paper support derivation of the majority of analysed Stonehenge monoliths at one particular outcrop within the group of four identified by Thorpe et al. 15 years ago. Analysis of all the extant bluestone monoliths at Stonehenge (now possible using non-destructive methods) would allow progress in identifying monolith outcrop sources, and in understanding the links with the bluestone axe trade. [ABSTRACT FROM AUTHOR]

Abstract. Three granite inselbergs and six dolerite dykes and their surroundings were investigated in the Central Namib, at the interface between the Namib Desert and Nama Karoo biomes. The main objectives of this study included a phytosociological interpretation of the described plant communities, explanation of the correlation of the communities with environmental variables and quantification of the relative contribution of different types of variables to structuring plant communities. Nine grassland and shrubland plant communities were recognized, largely organized according to general habitat, elevation, size of inselberg and geology. Soil properties, often thought to play an important role in arid environments, showed no clear patterns in the level of analyses used in this study. Other environmental parameters of importance in arid mountain habitats, such as slope aspect and angle, also played a minor role. The main implications of the study are: 1. Central Namib inselbergs, particularly granite domes, harbour diverse plant communities, often with species from neighbouring higher rainfall areas, and are thus of high conservation value. 2. The poor contribution of environmental variables in this study, which are conventionally used in field studies of plant community - environment relationships, may demand a critical review of additional parameters to be included when analysing plant community - environment relations in arid environments. In particular between-season variation, phytogeographic aspects and the heterogeneity of microhabitats, often contained within a plant community, need to be taken into account. [ABSTRACT FROM AUTHOR]

Dolerite dykes which intrude dolomitic marble in the aureole of the Beinn an Dubhaich granite on the Isle of Skye have developed metasomatized margins close to the contact with the (younger) granite in the southern part of Torrin Quarry. These margins display well-defined mineralogical zones which can be divided into two groups on the basis of composition. Chlorite-bearing margins display the sequence dolerite | diopside+spinel | chlorite+calcite+magnetite | olivine+calcite+spinel | dolomite, whereas phlogopite-bearing sequences have a phlogopite+calcite±fluorapatite layer in place of the chlorite-bearing layer. No spatial pattern is seen in the distribution of the two margin types, but textural and compositional evidence points to an importance of metasomatism by localized infiltration of magmatic fluids in the development of the phlogopite-bearing sequences. Extensive patterning of the phlogopite-bearing margins by a process of self-organization during grain growth has resulted in the formation of alternating silicate-only/calcite-only layers parallel to the dyke margin on a millimetre to centimetre scale. Early development of chlorite-bearing sequences at the dolerite–dolomite contact during contact metamorphism was followed by metasomatism-controlled growth of phlogopite and patterning at or after the peak of metamorphism associated with the expulsion of aqueous fluids from the crystallizing pluton. [ABSTRACT FROM AUTHOR]

The article focuses on a collective geological prospecting prediction in the Shania gold deposit in Baise City, Guangxi Province in China, based on geophysical and geochemical anomaly characteristics and geological prospecting indicators, and mentions that the gold deposit is closely related to diabase. Topics discussed include basic geology of deposit, geophysical and geochemical anomaly characteristics in the mining area, and indicators for the deposit.

The article reports on the volcanic series of rocks on the southern and eastern flanks of Cader Idris in Harlech, Wales. The volcanic series of rocks of Cader Idris are composed of lavas and ashes with dolerite entry of slaty materials. Their determining factors are presence of lime in plants, existence of dripping water and ledges of good soil on rock-faces. They are dominated by calciferous rock namely pillow-lavas with calcite. They are also made up of acidic rocks with granophyres, rhyolites, ashy slates, mudstones, and dolerites.

The article presents a study which examines the relation of the distribution of floristically rich localities outside the transect in the Cadre Idris and Rhobell Fawr districts to the nature of the bed-rock in Wales. The study found that the rocks are chiefly composed of lavas and ashes with dolerite intrusions and intercalations of slaty material. The presence of lime in a form readily available for plants is the determining factor, but certain physical factors such as the presence of a head of water and of ledges and pockets of good soil on the precipitous rock-faces are also of considerable importance.

The article discusses the research on the discovery of diabase dike at the Shiquanhe ophiolite, a tectonic belt in western Tibet, China. Topics include the use of zircon uranium-lead dating geochronology to analyse rocks, the contamination of diabase by oceanic subduction during the Jurassic period, and the presence of silicon dioxide and magnesium in the rocks. According to the author the discovery is critical to understand the evolutionary history and petrology of Shiquanhe ophiolite.