Tectonic Style Associated with the Doleritic Dykes of the Téra-Ayorou Pluton (Liptako, Western Niger)

The doleritic dykes present in the Téra-Ayorou pluton crosscut the basement of the Nigerien Liptako and are part of the system of intrusive mafic dykes in the Paleoproterozoic domain of the Léo-Man ridge. In the previous work, emphasis was placed on the petrology, geochemistry and geochronology of the Liptako doleritic dykes. This study aims to analyze the tectonic style of intrusive doleritic dykes in the Téra-Ayorou pluton. The characterization of the deformation which affected the doleritic dykes of the Téra-Ayorou pluton is important for the evaluation of their economic potential. To this end, measurements of tectonic structure planes were taken in the field, and samples were taken from the chilled margin and cores of dolerite dykes, before being processed in the laboratory. Analysis of the tectonic structures collected revealed a brittle tectonic pattern, characterizing a phase of deformation subdivided into two episodes D1 and D2. Episode D1, with its subvertically dipping normal faults and simple N70˚ - N110˚ fractures, is compatible with N-S extension. On the other hand, episode D2, which created shear corridors by reactivation of pre-existing fractures and oriented N150˚ - N170˚, is associated with a WSW-ENE extension. These results open up prospects for the exploration of gold, uranium mineralization and diamonds in the north-west of Niger.

Assessing the Influence of Dykes on the Drainage Network of the Shivan River in North Maharashtra

The prominent linear dyke ridges outcropped in the Narmada-Tapi dykes’ swarm represent an intrusion in the Deccan Traps. Understanding the relationship among the underlying geological structures, the strike of the dykes, and the channel patterns is essential. Dykes act as obstructions to stream flow, causing diversions, and their geometry and patterns significantly impact the rivers and streams that drain and cross the dyke swarm zone. For this study, Google Earth images, LISS III images, and Cartosat DEM were used to delineate the Shivan basin and extract dyke features. The Shivan River basin is a sixth-order drainage system that reflects superimposed drainage systems within the Tapi dyke swarm zone. About 65% (169 km2) of its area is controlled by dyke orientation. The dyke ridges align predominantly in an East-West (E-W) direction, a pattern mainly followed by lower-order streams, which have developed an insequent, transverse drainage network within the dyke swarm zone. In the lower parts of the Shivan basin, where the number of dykes decreases, the drainage network follows the general slope and is oriented in a North-South direction. The Shivan River and its tributaries have partially adjusted to the dyke orientation, resulting in a transverse drainage pattern in areas characterized by parallel dyke ridges.

Dyke-Davidoff-Masson综合征临床及影像特征分析

目的分析Dyke-Davidoff-Masson综合征(DDMS)的临床表现与影像学特征。方法回顾性分析13例DDMS患者的临床及CT、MRI资料。12例行CT平扫,4例行MRI平扫,3例同时行CT及MRI平扫。结果后天性DDMS 8例,先天性DDMS 5例,临床表现为癫痫12例,偏瘫9例,肢体萎缩3例,智力低下及精神障碍各9例,面部不对称2例,性功能障碍1例,双侧耳廓畸形1例。DDMS分型:Ⅰ型6例,Ⅱ型4例,Ⅲ型3例。13例均见单侧大脑半球萎缩及同侧侧脑室扩大,中线结构向患侧移位12例,同侧基底神经节及大脑脚萎缩各10例,海马萎缩6例,交叉性小脑萎缩及双侧小脑萎缩各3例,脑软化9例,脑穿通畸形4例,胼胝体细小3例,脑裂畸形并透明隔缺如1例。13例均有不同程度同侧颅骨代偿性改变,表现为颅骨增厚、额窦及乳突过度气化。结论DDMS主要临床表现为癫痫、偏瘫、智力低下及精神障碍,典型影像征象为单侧大脑半球萎缩及同侧颅骨代偿性改变。

Geochronology,Geochemistry,and Implications of Aplite Dyke in the Giant Jiama Porphyry Copper System,Tibet

Jiama is a giant,high-grade porphyry copper system in the Gangdese metallogenic belt,Tibet.Multistage intermediate-felsic porphyries intruded in this deposit,some of which are strongly associated with copper-polymetallic mineralization.These ore-bearing porphyries include monzogranite,granodiorite,and quartz diorite porphyries.A new granite aplite dyke was found in the south of Jiama.Its age,genesis,and relationship with ore-related magmatism are obscure.Here,its emplacement age and petrogenesis were determined using mineralogy,zircon U-Pb dating,geochemistry,and Sr-Nd-Pb isotope studies.The zircon LA-ICP-MS U-Pb age of the aplite dyke is 16.66±0.21 Ma(n=14,MSWD=0.66),earlier than that of the ore-bearing porphyries(~15 Ma)in Jiama.Furthermore,the aplite exhibits high amounts of silicon(SiO_(2)=73.39%-74.74%),potassium(K_(2)O=5.12%-6.61%),aluminum(Al_(2)O_(3)=14.25%-14.69%),and light/heavy rare earth elements(LREE/HREE=12.12-16.19)as well as negative europium(δEu=0.47-0.72)and weak negative cerium anomalies(δCe=0.84-0.93).The aplite dyke is characteristic of metaluminous-peraluminous I-type granite,which is rich in large-ion lithophile elements(Rb,Ba,Th and U)and depleted in high-field-strength elements(Nb,P and Ti).The aplite dyke and ore-bearing porphyries in the Jiama deposit are the results of a partial melting of the juvenile lower crust,according to whole-rock geochemistry and Sr-Nd-Pb isotope data,but the dyke and ore-bearing porphyries were emplaced from the same magma chamber at different times.Thus,the aplite dyke shows the composition of the early evolution stage of shallow magma in the Jiama deposit and is the product of rapid condensation and crystallization.

Dyke-Davidoff-Masson综合征CT及MRI特征

目的 观察Dyke-Davidoff-Masson综合征(DDMS)CT及MRI特征。方法 回顾性分析8例DDMS患者临床及影像学资料,观察其CT及MRI表现。结果 8例CT和MRI均见患侧大脑半球萎缩、颅窝缩小;7例患侧侧脑室扩大,中线结构向患侧偏移,伴不同程度颅骨代偿性改变,包括颅骨代偿性增厚、鼻窦扩大、乳突过度气化等;5例丘脑萎缩;4例大脑脚萎缩;4例脑软化;1例豆状核萎缩伴钙化。结论 DDMS的CT及MRI表现具有一定特征性,包括受累侧大脑半球萎缩伴同侧颅骨代偿性改变。

Paleomagnetism of late Cretaceous dykes in the Gangdese belt: New constraints on the position and structure of the southern margin of Asia prior to the India-Asia collision

This paper report paleomagnetic data from late Cretaceous diorite dykes that sub-vertically intrude granodiorites in the eastern Gangdese belt near the city of Lhasa.Our research goals are to provide further constraints on pre-collisional structure of the southern margin of Asia and the onset of the India-Asia collision.Magnetite is identified as the main magnetic carrier in our study.The magnetite shows no evidence of metamorphism or alteration as determined from optical and scanning electron microscope observations.A strong mineral orientation is revealed by anisotropy of magnetic susceptibility analysis both for the intruded dykes and the country rocks.The authors interpret this AMS fabric to have formed during intrusion rather than deformation.Fifteen of 23 sites yield acceptable site mean characteristic remanences with dual polarities.A scatter analysis of the virtual geomagnetic poles suggests that the mean result adequately averaged paleosecular variation.The paleomagnetic pole from the Gangdese dykes yields a paleolatitude of 14.3°N±5.8°N for the southern margin of Asia near Lhasa.The paleolatitude corresponds to an in-between position of the Lhasa terrane during about 130‒60 Ma.Furthermore,the mean declination of the characteristic remanent magnetization reveals a significant counterclockwise rotation of 18°±9°for the sampling location since about 83 Ma.In the light of tectonic setting of the dykes,the strike of the southern margin of Asia near Lhasa is restored to trend approximately about 310°,which is compatible with the hypothesis that the southern margin of Eurasia had a quasi-linear structure prior to its collision with India.

斯德奇-韦伯综合征合并Dyke-Davidoff-Masson综合征1例

患儿男,10岁,间断左侧肢体抽搐9年、发作伴意识障碍2天;足月剖宫产,无窒息抢救史,无头颅外伤史、发热惊厥史及家族性癫痫史等。9年前无明显诱因首次抽搐发作后自行缓解,颅脑MRI示右侧大脑半球发育不良,双侧大脑半球、小脑半球脑表面多发软脑膜血管瘤,诊断为局灶性癫痫发作并予口服奥卡西平、丙戊酸钠等。

Mechanism for three types of mafic dyke swarms

This study proposes three models to explain the mechanism of the three major types of mafic dyke swarms. Parallel dyke swarms form in response to a regional stress field, e.g. the mafic dyke swarms in the North China Craton, whereas small radiating dyke swarm forms due to stress constructions around a plutonic or volcanic edifice, such as the dyke swarm at Spanish Peak, USA. The third type of radiating dyke swarm is giant fan-shaped dyke swarm such as the Mackenzie dyke swarm. Fractures that formed prior to magmatism may play a vital role in dictating the dyke swarm geometry. In most of the cases, the pre-existing fractures are induced by tectonic stresses and not by magma injection though magma injection can increase the fracture size by propagation at the dyke tip.

Does Geochronology of Few Dykes of a Swarm are True Representative of All Dykes of the Same Magmatic Event?: Constraints from the Geochemistry and Google^(TM) Earth Image–ArcG IS^(TM) Studies of the Paleoproterozoic Mafic Dyke Swarms of the Eastern Dharwa

A precise dating of a mafic dyke of a swarm in shield areas has great advantage to identify Large Igneous Provinces(LIPs;short-lived,mantle-generated magmatic event)(Bryan and Ernst,2008;Ernst et al.,2010).Such

Dyke-Davidoff-Masson综合征1例

Dyke-Davidoff-Masson综合征(DDMS)是一种罕见癫痫综合征,以1侧半球萎缩、同侧颅骨代偿性改变和对侧偏瘫为特点,本文介绍1例反复癫痫发作药物控制不佳案例,查体发现智力迟钝、面部不对称、右侧肢体轻偏瘫,MRI提示左侧大脑半球萎缩、颅骨增厚,正电子发射计算机断层显像(PET-CT)提示左侧大脑半球代谢减低,最终行多脑叶离断术缓解癫痫发作,术后随访1年,癫痫发作控制满意。

Neoproterozoic Mafic Dykes and Basalts in the Southern Margin of Tarim,Northwest China:Age,Geochemistry and Geodynamic Implications

Neoproterozoic rifting-related mafic igneous rocks are widely distributed both in the northern and southern margins of the Tarim Block,NW China.Here we report the geochronology and systematic whole-rock geochemistry of the Neoproterozoic mafic dykes and basalts along the southern margin of Tarim.Our zircon U-Pb age,in combination with stratigraphic constraint on their emplacement ages,indicates that the mafic dykes were crystallized at ca.802 Ma,and the basalt, possibly coeval with the ca.740 Ma volcanic rocks in Quruqtagh in the northern margin of Tarim. Elemental and Nd isotope geochemistry of the mafic dykes and basalts suggest that their primitive magma was derived from asthenospheric mantle（OIB-like） and lithospheric mantle respectively,with variable assimilation of crustal materials.Integrating the data supplied in the present study and that reported previously in the northern margin of Tarim,we recognize two types of mantle sources of the Neoproterozoic mafic igneous rocks in Tarim,namely the matasomatized subcontinental lithospheric mantle（SCLM） in the northern margin and the long-term enriched lithospheric mantle and asthenospheric mantle in the southern margin.A comprehensive synthesis of the Neoproterozoic igneous rocks throughout the Tarim Block led to the recognition of two major episodes of Neoproterozoic igneous activities at ca.820-800 Ma and ca.780-740 Ma,respectively.These two episodes of igneous activities were concurrent with those in many other Rodinian continents and were most likely related to mantle plume activities during the break-up of the Rodinia.

A Study of Sr, Nd and O Isotopes of the K-rich Melanocratic Dykes in the Late Mesozoic Gold Field in the Jiaodong Peninsula

Geologic, petrographic and petrochemical studies of the late Mesozoic K-rich melanocratic dykes, including lamprophyres, andesite porphyrites and dacite-porphyry in the gold field system in the Jiaodong Peninsula, China, have shown that these dykes are characterized by rich potassium and alkali but poor titanium. They belong to an ultra-high potassic, shoshonitic and high potassic calc-alkaline rock series. The parental magma has relatively high initial strontium ratios ((87Sr/86Sr),=0.70895-0.71140) and low (143Nd/144Nd)1 ratios (varying from 0.51135 to 0.51231); and its δ18Osmow, whole rock values vary from +5.8%c to +10.6%c with a mean of +7.1%c. These features suggest that the source region of the magma is an enriched mantle wedge transformed from a continental lithosphere mantle which has experienced metasomatism by mantle-derived fluids with H2O-dominated fluids that were provided during the underthrusting of an ocean crust. The initial magma was generated by low-degree partial melting of the enriched mantle in its mature stage in the back-arc spreading environment. The evolution of magmas is associated with two trends, i.e., fractional crystallization and mixing with or intensive contamination by palaeo-crust materials or metamorphic rocks. The former process is evident in the gold field system of quartz-vein type, whereas the latter is dominated in the gold field system of the altered-rock type. This conclusion is very important for more detailed study of petrogenesis and mineralization through the crust-mantle interaction (exchange) in the Mesozoic in this region.

SHRIMP Zircon U-Pb Dating of Alkaline Dykes in the Pobei Area,Beishan Rift,Xinjiang Autonomous Region,China:Implications for Tectonic Setting and Mantle Plume Events

In the Beishan rift in the eastern Tianshan orogen, Xinjiang Province, a N-S-trending dyke swarm is present in the Pobei area. The swarm cuts through the 270-290 Ma mafic-ultramafic intrusions associated with Ni-Cu sulphide mineralization. These mafic-ultramafic intrusions are typically found along E-W major faults in the Tianshan orogenic belts. We report SHRIMP U-Pb dating of zircons from a dyke of alkaline composition, which yielded a mean age of 252~9 Ma. Alkaline dykes of the same age are found in the Altay region of Siberia. This age is younger than the 270-290 Ma intraplate magmatic events that produced the mafic-ultramafic intrusions in the region, but in general agreement with the 250-260 Ma Permian plume event that gave rise to the Siberian traps and the Emeishan flood basalts in SW China. We suggest that there is a link between the Emeishan event and the dyke swarm in the Beishan rift and that the intraplate magmatism at 270-290 Ma reflects an early stage of mantle plume activity. The N-S trending dyke swarm in the Beishan rift may represent a later stage in the evolution of mantle plume activity in the NW and SW of China. We also speculate that in Beishan rift and possibly elsewhere in the Tianshan region, the dykes fed basaltic volcanism, whose products have since been eroded due to the strong uplift of the Tianshan orogen as a result of the IndiaEurasia collision in the Cenozoic.

Geochronology and geochemistry of mafic dykes in the Helanshan complex: Implications for Mesozoic tectonics in the North China Craton

The Helanshan tectonic belt(HTB) is a major tectonic divide between the Alxa and Ordos blocks in the North China Craton. The geochronology and petrogenesis of the mafic dykes in the northern HTB are keys to understanding the tectonic evolution of this belt. The mafic dykes, intruded into the Neoarchean-Paleoproterozoic metamorphic basement, are mainly composed of diabase with a mineral assemblage of plagioclase(45%-60%), pyroxene(25%-35%), minor quartz and Fe-Ti oxides. The LA-ICPMS U-Pb analysis of zircon grains from representative dykes yield a weighted mean age of 206 ± 1.9 Ma, which represents the crystallization age of the dyke. The diabases show high contents of Fe_2 O_3~T(11.88-17.55 wt.%), low contents of SiO_2(45.65-50.95 wt.%) and MgO(3.31-5.50 wt.%) with low Mg#(=100×MgO/(MgO + FeO) atomic ration) of 33-44. They are characterized by enrichment of light rare earth elements(LREEs) and large ion lithophile elements(LILEs)(e.g., Rb, Ba and Pb), and slight depletion of high field strength elements(HFSEs). These features suggest that the magma has undergone extensive fractionation of olivine and pyroxene but only minor crustal contamination during its evolution. Their high Sm contents and La/Sm ratios, and low Sm/Yb ratios indicate that magma from which the dykes formed was derived from low degree(about 5%) partial melting of an enriched garnet + spinel lherzolite mantle source. Together with regional geology, these geochemical and geochronological data suggest that the mafic dykes in the HTB were formed in an intracontinental extensional setting during the late Triassic.

Age and Tectonic Significance of the Mafic Dyke Swarm in the Kuruktag Region, Xinjiang

The mafic dykes are composed of a series of northwest-trending diabase in Kuokesu of the Kuruktag region, Xinjiang. Four whole-rock samples of the mafic dykes in the region give an 40Ar/36Ar–40K/36Ar isochron age of 282 Ma with the initial 40Ar/36Ar = 507. The characteristics of the major, trace and rare earth elements of the dyke rocks indicate that they belong to the calc-alkaline series and were emplaced in extensional structures at an intermediate depth of the crust. This shows that there was a large-scale extension in the Permian Period, which might be associated with the post-collisional extension of the ancient Tianshan Mountains.

U-Pb Zircon Age, Geochemical, and Sr-Nd-Pb Isotopic Constraints on the Age and Origin of Mafic Dykes from Eastern Shandong Province, Eastern China

U-Pb zircon age, geochemical, and Sr-Nd-Pb isotopic data of mafic dykes from eastern Shandong Province, eastern China is reported herein. Laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS） U-Pb zircon analyses of two samples from the investigated mafic dykes yield consistent ages ranging from 121.9 Ma ± 0.47 Ma to 122.9 Ma ± 0.61 Ma. The mafic dykes are characterized by high （87Sr/86Sr） i ranging from 0.7087 to 0.7089, low εNd（t） values ranging from -16.9 to -17.8, 206Pb/204Pb = 17.15 to 17.17, 207Pb/204Pb = 15.45 to 15.47, and 208Pb/204Pb = 37.59 to 37.68. Results from the current study suggest that the mafic dykes are derived from partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from foundered lower crustal eclogite. The mafic dykes may have been generated through subsequent insignificant crystal fractionation and very minor crustal contamination during magma ascent. Combined with previous studies, the current findings provide new evidence that the intense lithospheric thinning beneath the eastern Shandong Province of eastern China occurred at ~120 Ma, and that this condition was caused by the removal of the lower lithosphere （mantle and lower crust）.

Selenium and Sulfur Systematics of Mafic Dykes in Western Fujian Province,Southern China

Fifteen samples from three study areas （the Bancun diabase dykes, the Bali hornblende gabbro dykes, the Linzifen gabbro-diabase dykes） were collected and analyzed for selenium （Se）, sulfur （S）, copper （Cu）, major and trace elements. In general, Se, S and Cu do positively correlate to each other. The concentration of S and Se and the S/Se ratio are higher than the corresponding value of primitive mantle （PM）, and the Cu/S ratio falls in a narrow range （0.04-0.29）, which is consistent with that of primitive mantle （0.05-0.20）. The Bancun diabase dykes and the Bali hornblende gabbro dykes were located in an intraplate environment during the Late Mesozoic. Oceanic subduction was closely related to magmatic activities. The magmatic activities play an important role in the transportation mechanism of Se and S. Because those two groups were closer to fault zones, which may affect the distribution of S and Se and other elements. In the two groups, no crustal contamination was observed, indicating that all analyzed elements may come from enriched mantle metasomtism associated with slab subduction. However, the Linzifen gabbro-diabase dykes were located in an intraplate rift environment, and its invading age is older than the other two groups, the primitive magma comes from mantle, and there is an anomalous relation between S, Se and Al2O3, （La/Sm）N, and all these factors could result in higher S and Se concentration.

AMS studies on a 450 km long 2216 Ma dyke from Dharwar craton, India:Implications to magma flow

Anisotropy of magnetic susceptibility (AMS) studies were carried out on a precisely dated (2216.0 ± 0.9 Ma),450 km long NeS striking dyke in the Dharwar Craton,to determine the magma flow direction along the dyke length.In order to use the imbrication of the magnetic foliation,forty eight samples were collected from 13 locations along the length of the dyke.Magnetogranulometry studies show that AMS fabric is dominated by medium grained interstitial Ti-poor multidomain magnetite.The corrected anisotropy degree (Pj) of the samples was found to be low to moderate,between 1.007 and 1.072,which indicates primary magnetic fabric.The magnetic ellipsoid is either triaxial,prolate or oblate and clearly defines normal,intermediate and inverse magnetic fabrics related to magma flow during the dyke emplacement.The maximum susceptibility axes (Kmax) of the AMS tensor of the dyke is predominantly inclined at low angles (<30°),with no systematic variation in depth along the NeS profile,indicating sub-horizontal flow even at mid crustal levels which could probably be governed by location of the focal region of the magma source (mantle plume?),flow dynamics together with the compressive stresses exerted by the overlying crust.

Fenitized Wall Rock Geochemistry of the First Carbonatite Dyke at Bayan Obo, Inner Mongolia, China

The first carbonatite dyke at Bayan Obo is well exposed on the surface for a length and width of approximately 60 m and 1.1-1.5 m, respectively. Along its strike, the fenitized H1 （Qs） and H2 （Cs） quartzite is replaced by Na-amphiboles, aegirines, and alkali-feldspars, intermittently stretching as far away as 800 m in length. Based on petrographical characteristics, the dyke＇s fenitized wall rocks are divisible into different zones： （1） outer, （2） middle, and （3） inner. The outer zone is 5-17 m from the NW margin of the dyke. The middle zone is located at 3.5-5 m from the NW margin of the dyke. The inner contact zone is located between direct contact with the dyke and 3.5 m from the dyke. In the outer zone, upon visual examination, no evidence of outcrop fenitization was found and the major elemental rock composition is nearly identical to the unaltered H1 and H2 lithologies. In the thin sections, however, small amounts of Na-amphibole and phlogopite are present. Despite relatively poor development throughout the 5 m of fenitization, the wall rocks have retained at least a small geochemical signature comparable to the original sedimentary protolith. The fenites occurring in the inner zone exhibit distinct variations, not only for the sharp contact at the outcrop scale, but also for variations in major, rare earth elements （REE）, and trace elements and Sm-Nd isotope composition. The wall rocks within 3.5 m have undergone strong fenitization, inheriting the geochemical signature derived from the carbonatite dyke. Fenitization in the middle zone was not as strong, at least compared to the inner zone, but was stronger than the outer zone. Compared to some trace elements and REEs, the major elements are relatively immobile during fenitization. The Sm-Nd isotope data for the carbonatite dyke and the adjacent fenitized wall rocks, where the Sm and Nd originate solely from the dyke, plots as a six-point isochron with an age of 1308~56 Ma. This age is identical to that of ore-bearing dolomite carbonatite and the related ore-forming events, indicating that there may be a petrogenetic link between the two. Based on Sr and Nd isotope compositional data, the first carbonatite dyke may be derived from an enriched mantle.

Re-interpretation of zircon date in a carbonatite dyke at the Bayan Obo giant REE-Fe-Nb deposit,China

Recent ce-valuation of the dating of the carbonatite dykes associated with the REE-Re-Nb giant deposit at Bayan Obo