المؤلفون: Liu, Tong¹ (AUTHOR) liutong@mail.iggcas.ac.cn, Liu, Chuan-Zhou^1,2 (AUTHOR), Zhang, Zhen-Yu¹ (AUTHOR), Zhang, Wei-Qi¹ (AUTHOR), Ji, Wen-Bin³ (AUTHOR), Zhang, Chang¹ (AUTHOR), Mitchell, Ross N.¹ (AUTHOR)

المصدر: Contributions to Mineralogy & Petrology. May2024, Vol. 179 Issue 5, p1-19. 19p.

مصطلحات موضوعية: *PETROLOGY, *DIKES (Geology), *DIABASE, *GABBRO, *PLAGIOCLASE, *OCEANIC crust

مصطلحات جغرافية: TIBET (China), OMAN, TIBETAN Plateau

مستخلص: The dynamics and magma transport at the boundary between the upper and lower oceanic crusts (i.e., the dike–gabbro transition) are crucial for understanding the crustal accretion beneath mid-ocean ridges, which however have been studied at quite a few sites such as the East Pacific Rise and ophiolites like Troodos and Oman. Here we present detailed geological, petrological, and geochemical data for the dike–gabbro transition and associated basalts in the Yunzhug ophiolite, central Tibet, to constrain the complex magmatic processes in this specific horizon. The Yunzhug ophiolite contains a large (~ 20 km2) well-exposed sheeted dike complex, which is rooted in a dike–gabbro transition that consists of diverse lithologies, including diabase, gabbro, and minor porphyritic diabase. Petrographically, the Yunzhug gabbros could be grouped into the dominant Plg (plagioclase)-euhedral gabbros (euhedral–subhedral plagioclases enclosed in clinopyroxene oikocrysts) and a small amount of Cpx (clinopyroxene)-euhedral gabbros (with abundant euhedral clinopyroxenes). Plagioclases and their equilibrated melts of the two types of gabbros are similar, whereas clinopyroxenes and their equilibrated melts of the Cpx-euhedral gabbros are more primary and depleted than those of the Plg-euhedral gabbros. These petrographic and geochemical features suggest an earlier crystallization of clinopyroxene for the Cpx-euhedral gabbros, which is best explained by occasional water input in the magmatic system. Nevertheless, the modeled equilibrated melts of the two types of gabbros have compositions indistinguishable from the whole rock compositions of diabases and basalts, indicating a direct genetic linkage between these rocks. The unusual porphyritic diabases, on the other hand, provide evidence supporting for plagioclase accumulation and aggregation during magma upward migration, thus may have served as a unique way for magma to transport from the lower to upper crust. Studies of the Yunzhug ophiolite thus provide some key constraints on the complex magmatic processes in the oceanic dike–gabbro transition, regarding its dynamic accretion and magmatic plumbing mechanisms. [ABSTRACT FROM AUTHOR]

المؤلفون: González Guillot, Mauricio^1,2 (AUTHOR) mgonzalez@untdf.edu.ar, Torres Carbonell, Pablo J.¹ (AUTHOR) poltorrescarbonell@gmail.com, Cao, Sebastián² (AUTHOR) scao@untdf.edu.ar, Lobo, Constanza¹ (AUTHOR) clobo@untdf.edu.ar, Bordese, Sofía³ (AUTHOR) bordese.sofia@gmail.com, Hollanda, María-Helena B. M.⁴ (AUTHOR) hollanda@usp.br

المصدر: Journal of the Geological Society. May2024, Vol. 181 Issue 3, p1-19. 19p.

مصطلحات موضوعية: *DIKES (Geology), *GEOLOGICAL time scales, *PETROLOGY, *GEOLOGY, *PENINSULAS, *ANDESITE

مستخلص: We report the field geology, petrography, and geochemical and geochronological data for two dyke swarms in the Fuegian Andes, with the aim of correlating them with known suites and improving our knowledge of the magmatism of the Late Cretaceous rear arc and its relations with ductile deformation. We provide keys for correlation based on the K2O content of amphiboles. The Trapecio dyke swarm is mildly alkaline and ferriferous, with a zircon U–Pb age of 75 Ma, and therefore belongs to the Fuegian potassic magmatism (78–68 Ma). The Ushuaia peninsula dyke swarm, also known as the Ushuaia Peninsula Andesites, is shown to be high-K, calc-alkaline and magnesian, with new radiometric ages of 87–86 Ma. Although the Ushuaia peninsula dyke swarm exhibits foliation associated with ductile deformation, the Trapecio dyke swarm is post-kinematic and reveals emplacement controlled by the slaty cleavage in the metapelite host. Field and geophysical evidence suggest both swarms overlie small upper crustal plutons that are mostly buried. The variable composition of the dykes suggests a protracted history of dyke injection, mostly fed from deeper reservoirs. Contact metamorphism around both pluton–dyke systems is very weak. By comparison with adjacent plutons, we argue that the main variables controlling the development of the aureole are the small magma volumes and low rates of injection. Supplementary material: Full analytical procedures (Online Resource 1); detailed petrography of the investigated Trapecio dyke swarm samples (Table S1 and Fig. S1) with geochemical data (Table S3 and Fig. S2) (Online Resource 2); extended petrography and photomicrographs (Fig. S3) of the Ushuaia Peninsula Andesite dyke swarm (Online Resource 3); mineral chemistry data (Table S2) and the results of zircon U–Pb and hornblende Ar–Ar age measurements and ratios (Tables S4–S8) (Online Resource 4), and thermobarometric results (Table S9) (Online Resource 5) are available at https://doi.org/10.6084/m9.figshare.c.7097733Test [ABSTRACT FROM AUTHOR]

المؤلفون: Allgood, C.¹ (AUTHOR) ceri.allgood@durham.ac.uk, Llewellin, E. W.¹ (AUTHOR) ed.llewellin@durham.ac.uk, Humphreys, M. C. S.¹ (AUTHOR), Mathias, S. A.² (AUTHOR), Brown, R. J.¹ (AUTHOR), Vye‐Brown, C.³ (AUTHOR)

المصدر: Journal of Geophysical Research. Solid Earth. Apr2024, Vol. 129 Issue 4, p1-31. 31p.

مصطلحات موضوعية: *DIKES (Geology), *SURFACE of the earth, *VOLCANIC eruptions, *CRUST of the earth, *MAGMAS

مستخلص: Basaltic fissure eruptions, which are the most common type of eruption on Earth, are fed by dykes which mediate magma transport through the crust. Dyke propagation processes are important because they determine the geometry of the transport pathway and the nature of any geophysical signals associated with magma ascent. Here, we investigate small‐scale (mm–cm wide) banding features at the margins of dykes in the Teno Massif (Tenerife, Spain) and the Columbia River Basalt Province (CRBP) (USA). Similar marginal bands have been reported for dykes in numerous localities around the world. Dyke margins record valuable information about propagation because they are the first material to solidify against the host rock at the propagating dyke tip. We find that the marginal bands are defined by cyclic variations in phenocryst concentration and vesicularity, and we infer that these cyclic variations in texture are a product of cyclic variations in magma flow rates and pressures within the dyke tip. This indicates that dyke emplacement occurs in pulses, with propagation repeatedly hindered by the rapid cooling and solidification of magma in the narrow dyke tip. Using a 1D conduction model, we estimate the time taken for each band to cool and solidify, which provides a timescale of several minutes to tens of minutes for the pulses. The occurrence of similar bands in various volcanic settings suggests that pulsatory propagation is a common, if not ubiquitous, process associated with dyke emplacement. Plain Language Summary: Dykes are cracks in the Earth's crust through which magma rises, sometimes feeding volcanic eruptions. Here, we investigate small‐scale banding features that are commonly found in solidified magma in dykes, using examples from the Teno Massif (Tenerife, Spain) and the Columbia River Basalt Province (USA). The bands form at the margin of the dyke, against the crack wall, which means that they record what happened when the dyke first formed; that is, when magma first flowed into the crack. We find that the bands are defined by repeated variations in the amount of crystals and bubbles, which we infer to have resulted from variations in magma flow rates and pressures in the dyke tip. This shows that the dykes formed in steps, rather than all in one go. By calculating the time taken for the bands to cool and solidify, we find that each propagation step lasts several minutes to tens of minutes. The occurrence of similar bands in various volcanic settings around the world suggests that most or all dykes form this way. This is important because the stepwise formation of the cracks might create small earthquakes that can be detected as the magma rises toward the Earth's surface. Key Points: Banded textures at dyke margins are the result of pulsatory magma flow in the tip of the propagating dykeDyke propagation is not continuous, but occurs in steps via a cycle of cooling, stalling, inflating, rupturing and propagatingCooling and solidification of magma in the narrow dyke tip has a strong influence on dyke propagation [ABSTRACT FROM AUTHOR]

المؤلفون: Berra, Fabrizio¹ (AUTHOR) fabrizio.berra@unimi.it

المصدر: Sedimentology. Apr2024, Vol. 71 Issue 3, p827-849. 23p.

مصطلحات موضوعية: *DIKES (Geology), *DEFORMATIONS (Mechanics), *SALT tectonics, *METEORITES, *SEDIMENTATION & deposition, *CARBONATES, *SEISMITES, *PALEOSEISMOLOGY

مصطلحات جغرافية: SOUTHERN Alps/Ka Tiritiri o te Moana (N.Z.), ITALY

مستخلص: Identification of the processes producing soft‐sediment deformation structures, common in siliciclastic deposits and less abundant in carbonate successions, is complex, because different processes may produce similar structures. Thus, interpreting the origin of these structures may be challenging: it requires both a detailed sedimentological study, and the knowledge of the depositional environment and stratigraphic evolution, in order to provide hints to identify the processes affecting sediments after deposition. Among the potential causes of the formation of soft‐sediment deformation structures, seismic shock is one of the possibilities, but their origin could be also related to other triggering mechanisms, such as volcanic activity, sediment loading, salt tectonics, fluid expulsion, meteorite impacts and mass movements. Although it is a plausible option, the interpretation of these structures as 'seismites' is not obvious: it must be supported by different lines of evidence, considering that the correct interpretation of soft‐sediment deformation structures as a consequence of seismic shocks acquires important implications in palaeoseismology studies. The occurrence of diverse soft‐sediment deformation structures in a fault‐controlled basin (i.e. in a geological setting characterized by syndepositional tectonics) preserved in different subenvironments of a Norian carbonate system in the Southern Alps of Italy provides the chance to characterize different types of soft‐sediment deformation structures along a platform‐to‐basin depositional profile. Presence of pseudonodules in basinal resedimented limestone, sedimentary dykes and clinostratified breccias with unlithified clasts in slope settings and liquefaction of inner platform facies at the platform top testify to an origin compatible with multiple seismic shocks, repetitively affecting the same stratigraphic intervals. The diverse types of soft‐sediment deformation structures in the studied carbonate system provide a rich catalogue of structures related to seismic shocks, representing a possible reference for other similar settings. [ABSTRACT FROM AUTHOR]

المؤلفون: Sigmundsson, Freysteinn¹ fs@hi.is, Parks, Michelle², Geirsson, Halldór¹, Hooper, Andrew³, Drouin, Vincent², Vogfjörd, Kristín S.², Ófeigsson, Benedikt G.², Greiner, Sonja H. M.^4,5,6, Yilin Yang¹, Lanzi, Chiara¹, De Pascale, Gregory P.¹, Jónsdóttir, Kristín², Hreinsdóttir, Sigrún⁷, Tolpekin, Valentyn⁸, Friðriksdóttir, Hildur María², Einarsson, Páll¹, Barsotti, Sara²

المصدر: Science. 3/15/2024, Vol. 383 Issue 6688, p1228-1235. 8p. 1 Color Photograph, 2 Diagrams, 2 Graphs.

مصطلحات موضوعية: *DIKES (Geology), *MAGMAS, *STRESS fractures (Orthopedics)

مستخلص: Many examples of exposed giant dike swarms can be found where lateral magma flow has exceeded hundreds of kilometers. We show that massive magma flow into dikes can be established with only modest overpressure in a magma body if a large enough pathway opens at its boundary and gradual buildup of high tensile stress has occurred along the dike pathway prior to the onset of diking. This explains rapid initial magma flow rates, modeled up to about 7400 cubic meters per second into a dike ~15-kilometers long, which propagated under the town of Grindavík, Southwest Iceland, in November 2023. Such high flow rates provide insight into the formation of major dikes and imply a serious hazard potential for high-flow rate intrusions that propagate to the surface and transition into eruptions. [ABSTRACT FROM AUTHOR]

المؤلفون: Yan-Jun Wang^1,2 zhuweiguang@vip.gyig.ac.cn, Wei-Guang Zhu², Zheng-Xiang Li³, Hong Zhong^2,4, Zhong-Jie Bai², Cheng-Biao Leng¹, Jian-Bing Xu¹

المصدر: Geological Society of America Bulletin. Mar/Apr2024, Vol. 136 Issue 3/4, p1023-1036. 14p.

مصطلحات موضوعية: *SECONDARY ion mass spectrometry, *DIKES (Geology), *ZIRCON analysis, *MAGMATISM

مصطلحات جغرافية: HAINAN Sheng (China)

مستخلص: We report three sets of newly identified late Mesoproterozoic mafic intrusions in the southwestern Yangtze Block, China. Secondary ion mass spectrometry (SIMS) baddeleyite and zircon U-Pb analyses yield crystallization ages of ca. 1.15 Ga for the Boka dolerites, ca. 1.07 Ga for the Lanniping gabbros, and ca. 1.06 Ga for the Tong'an mafic dikes. These are tholeiitic to alkaline rocks with enriched mid-ocean-ridge basalt (E-MORB)-like trace-element patterns and superchondritic εNd(t) values, indicating a partial melting origin from the asthenospheric mantle. These results, along with existing data, define two episodes of late Mesoproterozoic, rift-related mafic magmatism in the southwestern Yangtze Block: an early phase at 1.17-1.14 Ga and a late phase at 1.07-1.02 Ga. Initiation of the two episodes of extensional events in the southwestern Yangtze Block coincided with high-grade Grenville-aged metamorphism in Hainan Island and possible early collision of Cathaysia with the southwestern Yangtze Block, indicating an impactogen model. Therefore, we interpret the observed two episodes to have resulted from local collision between the southwestern Yangtze Block and the Cathaysia Block (including Hainan Island), which was possibly a part of western Laurentia during the assembly of Rodinia. [ABSTRACT FROM AUTHOR]

المؤلفون: Hawkins, Louise M¹ (AUTHOR), Biggin, Andrew J¹ (AUTHOR) A.Biggin@liverpool.ac.uk, Liu, Yebo² (AUTHOR), Grappone, J Michael¹ (AUTHOR), Li, Zheng-Xiang² (AUTHOR)

المصدر: Geophysical Journal International. Jan2024, Vol. 236 Issue 1, p431-442. 12p.

مصطلحات موضوعية: *DIPOLE moments, *DIKES (Geology), *PHANEROZOIC Eon, *SCANNING electron microscopy, *MAGNETIC fields, *ARCHAEAN

مصطلحات جغرافية: WESTERN Australia, AUSTRALIA

مستخلص: Precambrian palaeointensity measurements provide fundamental constraints on the evolution of the deep Earth. Core evolution models predict trends in dipole moment on billion-year timescales that can be tested by palaeomagnetic records. Here, we report new palaeointensity results from the recently identified ∼2.62 Ga Yandinilling dyke swarm of the Yilgarn Craton, Western Australia, and consider them alongside published measurements spanning 500 Myr across the late Archaean to earliest Proterozoic. Rock magnetic and scanning electron microscopy analysis confirm that the magnetic mineralogy is fine-grained magnetite, appearing mostly as exsolved lamellae with ilmenite. Six sites produced acceptable palaeointensity estimates from thermal and microwave IZZI protocol Thellier experiments and from double-heating technique Shaw experiments. These site mean values of 9–26 µT translate to virtual dipole moments of 11–44 ZAm2 that are considerably lower than today's dipole moment of ∼80 ZAm2 and the value predicted for this time period by some thermal evolution models. Their average (median = 41 ZAm2) is, however, similar to the long-term average during both of the intervals 2300–2800 Ma (median = 44 ZAm2; N  = 103) and 10–500 Ma (median 41 ZAm2; N  = 997). While there is little evidence for a substantial net change in average dipole moment between the late Archaean and Phanerozoic, there is preliminary evidence that its variance has increased between the two intervals. This lower variance more than two billion years ago supports the idea that the geodynamo, even while not producing a stronger magnetic field, was more stable on average at the Archaean–Proterozoic transition than it is today. [ABSTRACT FROM AUTHOR]

المؤلفون: Kingsbury, C. G.¹ TheCGKings317@gmail.com, Altermann, W.² altermannw@gmail.com, Kramers, J.³ jkramers@uj.ac.za, Ernst, R. E.⁴ RichardErnst@cunet.carleton.ca, Söderlund, U.⁵ ulf.soderlund@geol.lu.se, Klausen, M. B.⁶ klausen@sun.ac.za

المصدر: South African Journal of Geology. Dec2023, Vol. 126 Issue 4, p471-484. 14p.

مصطلحات موضوعية: *IGNEOUS provinces, *DIKES (Geology), *RARE earth metals, *MAGMATISM, *CONTINENTAL crust, *RIFTS (Geology)

مصطلحات جغرافية: SOUTH Africa, CAPE Town (South Africa)

مستخلص: A new 130 to 140 Ma mafic dyke swarm, is identified in western South Africa. It consists of the previously undated Cederberg dyke swarm (CDS), for which we report U-Pb ID-TIMS baddeleyite ages of 131.4 ± 4.5 Ma (Knersvlake subswarm) and 133.0 ± 1.5 Ma (Doring-Tanqua subswarm). 40Ar/39Ar dates on these two samples and two additional dates of the Doring -- Tanqua subswarm cluster between 128.5 ± 1.4 Ma and 132.2 ± 1.5 Ma. We also report 40Ar/39Ar ages of 139.3 ± 3.5 Ma for an east-west trending dyke located further north: 27 km south of Kleinsee, and 140.3 ± 1.2 Ma for an east-west dyke near Garies. Together, these eight ages robustly date the emplacement of the northern part of a Greater Cederberg- False Bay Dyke Swarm (GCFDS) at ca. 130 to 140 Ma. Trace and rare earth element data reported herein suggest these dykes are compositionally E-MORB basalts that underwent modification either via subduction-modified lithospheric mantle, or by continental crust, or a combination thereof, and are petrogenetically similar to the ca. 132 Ma False Bay dykes around Cape Town. Therefore, we propose to unify all these coeval and compositionally similar dykes into one large igneous province (LIP) termed the Greater Cederberg-False Bay Large Igneous Province (GCF-LIP). [ABSTRACT FROM AUTHOR]

المؤلفون: Marjanović, Milena¹ marjanovic@ipgp.fr, Carbotte, Suzanne M.², Stopin, Alexandre³, Singh, Satish C.¹, Plessix, René-Édouard³, Marjanović, Miloš⁴, Nedimović, Mladen R.^2,5, Pablo Canales, Juan⁶, Carton, Hélène D.^1,2, Mutter, John C.², Escartín, Javier⁷

المصدر: Science Advances. 9/29/2023, Vol. 9 Issue 39, p1-12. 12p.

مصطلحات موضوعية: *VOLCANIC eruptions, *DIKES (Geology), *IMAGING systems in seismology, *IMAGING systems, *VOLCANIC hazard analysis, *NUCLEATION, *THERMAL boundary layer

مستخلص: The article focuses on exploring the architecture of magma plumbing systems and how magmas move through them in the context of volcanic activity. It discusses the use of advanced seismic techniques to study the shallowest parts of magmatic systems beneath the East Pacific Rise (EPR) and provides insights into the complex network of crustal magma bodies, shedding light on their characteristics and potential links to volcanic eruptions.

المؤلفون: Gao, Rui^1,2 (AUTHOR), Li, Jinke¹ (AUTHOR), Kerr, Andrew C.² (AUTHOR), Wu, Tao³ (AUTHOR) wutaocug@126.com, Xiao, Long⁴ (AUTHOR), Wang, Guocan⁴ (AUTHOR), He, Xinxing⁵ (AUTHOR)

المصدر: Geological Magazine. Sep2023, Vol. 160 Issue 9, p1711-1741. 31p.

مصطلحات موضوعية: *DIKES (Geology), *PETROGENESIS, *DIABASE, *OROGENIC belts, *DIORITE, *PETROLOGY

مصطلحات جغرافية: XINJIANG Uygur Zizhiqu (China), CHINA

مستخلص: Numerous Late Carboniferous – Early Permian dykes are found in West Junggar and represent an important part of the Central Asian Orogenic Belt. In this contribution, we use these dykes to assess the tectonic regime and stress state in the Late Carboniferous – Early Permian. The West Junggar dykes are mainly diorite/dioritic porphyrite with minor diabase and were formed in 324–310 Ma. They have been divided into two groups based on their orientation, petrology and geochronology. Group 1 dykes mostly comprise WNW-striking dioritic porphyrite and NE-striking diorite with minor diabase and resemble the Karamay-Baogutu sanukitoid. They were probably formed from depleted mantle at a relatively high temperature and pressure with the addition of 1–2% sediment/sedimental partial melt and 0–5% trapped oceanic crust-derived melts. Group 2 dykes are ENE-striking and are similar to sanukite in the Setouchi Volcanic Belt. These dykes were also derived from depleted mantle at a shallow depth but high temperature with the addition of 2–3.5% sediment/sedimental partial melt. Magma banding and injection folds in dykes and host granitoids indicate magma flow. Paleostress analysis reveals that both groups of dykes were formed in a tensile stress field. Their emplacement is favoured by presence of pre-existing joints or fractures in the host granitoids and strata. We conclude that large-scale asthenosphere mantle upwelling induced by trapped oceanic slab-off can explain the magmatism and significant continental crustal growth of West Junggar during Late Carboniferous to Early Permian. [ABSTRACT FROM AUTHOR]