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Despite extensive research on fault rocks, and on their commercial importance, there is no non-genetic classification of fault breccias that can easily be applied in the field. The present criterion for recognizing fault breccia as having no ‘primary cohesion’ is often difficult to assess. Instead we propose that fault breccia should be defined, as with sedimentary breccia, primarily by grain size: with at least 30% of its volume comprising clasts at least 2 mm in diameter. To subdivide fault breccias, we advocate the use of textural terms borrowed from the cave-collapse literature – crackle, mosaic and chaotic breccia – with bounds at 75% and 60% clast content. A secondary breccia discriminant, more difficult to apply in the field, is the ratio of cement to matrix between the clasts. Clast-size issues concerning fault gouge, cataclasite and mylonite are also discussed.

Multistage veinlet cataclastic rocks, composed of aphanitic veins typical of pseudotachylyte and unconsolidated fault gouge, and sediment veins composed of alluvial deposits are widely developed within a fault shear zone (<5 m wide) as simple veins, breccias, and complex networks along the active Shimotsuburai fault, central-southern segment of the Itoigawa-Shizuoka Tectonic Line active fault system (ISTL-AFS), central Japan. Early veins are generally fractured and overprinted by younger veins, indicating that vein-forming events occurred repeatedly within the same fault shear zone. Microstructurally, both the pseudotachylyte and fault gouge veins are characterized by a superfine- to fine-grained matrix and angular-subangular fragments ranging in size from submicron scale to several centimeters. Powder X-ray diffraction patterns show that the fault veins and injection veins of fault gouge and pseudotachylyte are characterized by crystalline materials composed mainly of quartz and feldspar, similar to the granitic cataclasite host. Based on the meso- and microstructural features of veinlet cataclastic rocks and the results of powder X-ray diffraction analyses, we conclude that (i) the pseudotachylyte veins were generated mainly by crushing rather than melting, (ii) multistage veinlet fault gouge and pseudotachylyte formed repeatedly within the fault-fracture zone via the rapid fluidization and injection of superfine- to fine-grained materials derived from the host granitic rocks during seismic faulting events, and (iii) veins of alluvial deposit formed by liquefaction associated with strong ground motion during large-magnitude earthquakes that occurred along the active Shimotsuburai fault of the ISTL-AFS. Our results show that the fluidized cataclastic veins and alluvial deposit veins record paleoseismic faulting events that occurred within a seismogenic fault zone; consequently, these features are a type of earthquake fossil, as is melt-origin pseudotachylyte.

Fault-related breccias, in Carboniferous limestone, have been well documented in the footwall damage zone to the reverse-oblique Dent Fault. This study describes breccias in the more complicated hanging wall, hosted in pre-deformed Ordovician and Silurian lithologies along the Dent Fault or one of its splays such as the Rawthey Fault. Brecciation style is shown to be influenced by lithology, with the most extensive brecciation in mechanically strong units: siliceous or calcareous mudstone, cemented sandstone and fine tuff. Most brecciation involves dilational strain in the fault damage zones. Attritional breccias are rare, even in fault cores. Dilation breccias are cemented sporadically by quartz or barite, but mostly by carbonate minerals. Transition matrix analysis shows that the sequence of hanging-wall carbonate cements matches that in the footwall: first dolomite or calcite, then ferroan dolomite, then ferroan calcite. This similarity suggests hydrological connectivity from hanging wall to footwall and through tens of cubic kilometres across the Dent-Rawthey fault system. Such connectivity is predicted across upper crustal faults that cut strong mechanical stratigraphy. It is proposed that fluid flow though the fault system was driven mainly by syntectonic topography above the hanging wall, and possibly also by thermal convection caused by a buried granite pluton in the footwall.

The Huaishuping gold deposit is located in the Xiong’ershan Mountains of the Qinling-Dabie Orogen of central China. The mineralisation is structurally controlled and hosted by faulted rhyolite, quartz andesite, volcaniclastic rocks and volcanic breccia assigned to the Jidanping Formation towards the top the Palaeoproterozoic Xiong’er Group. The deposit has a resource of around 32 t with an average grade of 5.5 g/t Au. Alteration at the deposit progressed from an early K-feldspar–quartz–pyrite assemblage through quartz–pyrite–gold, quartz–base-metal sulfides, to a late-stage assemblage of quartz–carbonate. The δ34S (V-CDT) values for pyrite in the ore range from − 13.3 to + 1.6‰. The calcite has C-isotopes ranging from − 6.1 to + 2.5‰ (V-PDB) and O-isotopes from + 10.6 to + 15.8‰ (V-SMOW). The δ18O quartz ranges from 10.5 to 15.1‰, and the δD values for fluid inclusions in quartz range from − 93 to − 76‰. The δ56Fe value for the mineralisation varies between 0.1 and 0.5‰ with corresponding δ57Fe values between 0.2 and 0.7‰. The isotope systematics indicates that the hydrothermal fluids were derived from metamorphic fluid, but the source of gold remains uncertain. Re–Os dating of molybdenite yields a date of 202 ± 8 Ma interpreted as the age of the gold mineralisation. This age is consistent with the Triassic onset of extensional tectonics following the collision between North and South China.

In the Early to Middle Miocene, the post‐orogenic intramontane lacustrine Sinj Basin that belonged to the Dinarides Lake System evolved in the area of the External Dinarides. A composite 770 m thick stratigraphic column was measured spanning the basin's stratigraphy. Eight facies were differentiated. Four facies are almost entirely composed of freshwater carbonate deposits. Carbonate facies are divided into calcareous mudstone, charophytic micritic limestone, calcisiltite and coquina facies. They are interpreted to belong to a prograding carbonate bench on a gently inclined lake margin. In addition, tuff/clays, carbonate conglomerate, carbonate breccia and coal were differentiated. The tuff/clays are the result of remote volcanic eruptions, while the coarse‐grained sediments belong to subaqueous shallow stream channels or were deposited by gravity flows. The coal at the top of the measured succession, mostly of allochthonous origin, was deposited as a fen forest peat, representing the final stage of the lake. The formation of the Sinj Basin might have been triggered by dissolution of Permo‐Triassic evaporites, within the mostly carbonate basement but also by breakdown and collapse of Mesozoic and Palaeogene carbonate rocks and coalescence of contiguous sinkholes. The non‐tectonic interpretation of the basin genesis is a novel hypothesis explaining the origin of one of the Dinarides intramontane basins and is in contrast to previous considerations that evolution of the Sinj Basin was controlled by strike‐slip or extensional tectonics. Miocene karstic Lake Sinj. A prograding carbonate bench on a gently inclined lake margin showing shallowing upwards tendency, and closing of the lake.

Atera Fault clay gouges were collected for age dating near Kawaue, Nakatsugawa City, Central Japan, and the results integrated within its complex geological history. The results form an internally consistent data set constrained by extensive geochronological data (AFTA, ZFTA, CHIME) and support the application of gouge dating in constraining timing of brittle deformation in Central Japan. The Atera illite age data complete recently obtained limited illite fault gouge age data from underground exposure in the Toki Granite; the new illite age data are identical within error. The age of the heterogenous welded tuff breccia zone (Atera 1) ranges from 40.6 ± 1.0 Ma to 60.0 ± 1.4 Ma, whereas ages of the fault core gouge sample (Atera 2) range from 41.8 ± 1.0 Ma to 52.7 ± 1.2 Ma. The finest < 0.1 µm fraction of the fault breccia and fault core gouge yield ages around 41 Ma, identical within error. The new illite age data indicate brittle faulting and a following geothermal event occurring in the Paleogene–Eocene, similar to the nearby Toki Granite area and confirm they were both synchronous with a post-intrusive pluton exhumation. The Atera Fault illite age data provide additional insights into an integrated, regional-scale record of the tectonic displacement of Central Japan and might be influenced by large-scale tectonic processes such as the Emperor sea mount kink around 55 to 46 Ma with fault initiation around 50 Ma and brittle fault cessation or reactivation around 40 Ma in the Eocene. Graphical Abstract

The activities of Alborz Tertiary magmatism are mainly attributed to the subduction and closure of Neo-Tethys. These phenomena, including the magma origin of this lesser area, are investigated in this study. In addition, the origin of the magma characteristics based on the geochemistry of main and rare elements is also studied, and a model is presented for their tectonomagmatic status. Volcanic Tertiary Alamut is part of magmatism in the central Alborz-west sequence of volcanic rocks (including basalt, trachyandesite, and basaltic andesite with alkaline geochemical properties, with porphyritic texture, pyroclastic rocks, and volcanic breccia) directly above the units belongs to the Karaj Formation (Middle Eocene age). Geochemical properties indicate that the parent magma is characterized by high ratios of LREE/HREE as well as Th/Nb, La/Nb, Ba/Nb, Zr/Nb, and low K/Nb ratios. The early basaltic magma is formed from a garnet lherzolite mantle by phlogopite/pargasite metasomatism at 2.5-5.3 GPa and depths of more than 80-150 km. Structural evidence suggests the formation of these volcanic rocks in a continental rift zone setting. The appearance of these rocks can be attributed to the effects of intercontinental extensional phases in deep faults during Eocene Alpine orogeny phases. The primary focus of this study is to provide the geological, petrographical, and geochemical data findings of the volcanic basaltic rocks along with the results of studying other rocks in this region. Aside from the mode and their formation, magma forming is also investigated. Moreover, for the rocks investigated in this study, the environment and the site of the tectonic-magmatic region are also clarified in detail.

The Tervu breccia zone was formed at the final stages of the Late Proterozoic magmatic and metamorphic activity (1.86 Ga ago) and healed with granitic material shortly after its formation. The Tervu breccia zone with granitic agmatites has a sublatitudinal orientation, which is discordant in relation to the earlier structures and Kurkijoki enderbite and Lauvatsaar–Impiniem diorite–tonalite complexes in the Svecofennian rocks of the Ladoga region. The largest granitic bodies in this area, the Tervu and Peltola intrusions, are located in the Tervu Zone. The U–Pb age of monazite from granites of the Peltola intrusion is determined as 1859 ± 4 Ma and coincides with the age of the granites of the Tervu intrusion (1859 ± 3 Ma), which indicates that the granites of both intrusions and some surrounding smaller bodies were intruded simultaneously into the tectonically weakened space at the late-orogenic stage while plastic deformations were turning to elasto-plastic ones. The results obtained reveal the features of the tectonic development of the junction zone of the two largest blocks of the Fennoscandinavian shield, the Karelian Craton and the Svecofennian Belt.

Organic carbon and nitrogen fixed in illite (I) clays were identified in a hydrothermal breccia structure from the Harghita Bãi area of the Neogene volcanism of the East Carpathians. The potassium-illite (K-I) alteration related to an early magmatic-hydrothermal event (9.5 ± 0.5 Ma) was later replaced by ammonium-illite (NH4-I) (6.2 ± 0.6 Ma) owing to circulation of an organic-rich fluid. Several textural evolutions of breccia structures were recognized, such as ‘shingle’, ‘jigsaw’, ‘crackle’ and hydraulic in situ fractures. The high-field-strength element behaviours of the K-I and NH4-I argillic altered andesite are close to chondritic ratios, indicating no contribution of hydrothermal fluid, especially on NH4-I andesite alteration and the CHArge-and-RAdius-Controlled (CHARAC) behaviour within silicate melts. The rare earth element normalized patterns show two distinct trends, one with a Eu* anomaly (K-I) and the other with a Nd* anomaly (NH4-I), indicating a boundary exchange with the organic-rich fluid. The strongly depleted δ13C (V-PDB) measured for the NH4-I clays reflects values (−24.39 to −26.67 ‰) close to CH4 thermogenic oxidation, whereas the δ15N (‰) from 4.8 to 14.8 (± 0.6) confirmed that the N2 originated from post-mature sedimentary organic matter. The last volcanism (6.3 to 3.9 ± 0.6 Ma) and simultaneous volcano-induced tectonics in the proximity of the eastern Transylvanian basin basement increased the heat flow, generating lateral salt extrusion, diapirism and increased pressure in the gas reservoir. New pathways were opened that provided new circulation routes for basinal fluids to new and old permeable zones and expelled seeps from the biogenic petroleum system.

Breccias associated with tectonic, fluid and sedimentary evolution of rifted margins can provide information on a variety of processes reflecting the modes of extension. In this paper, we analyse the numerous breccias exposed in the Agly Massif that was part of the European side of the Cretaceous rift now inverted in the eastern Pyrenees. Using a combination of petrologic and sedimentologic analyses, field-based structural study, and multivariate analysis of clast shape and diversity, binding lithology and size, and breccia fabrics, we distinguish 5 types of breccias reflecting depositional, tectonic, and salt-related processes. The integration of these processes in the tectonic history of the eastern Pyrenees confirms the attribution of these breccias to the Cretaceous rifting. We emphasize the major role played by the evaporitic Triassic particularly during the first stages of rifting as a major decoupling level at the basement/cover interface. Salt tectonics and shearing assisted by the circulation of fluids are reflected by hydrofracturing at the base of the Mesozoic cover. As this weak mechanical layer is later extracted as extension increases, a brittle detachment system developed along the cover-basement interface to exhume of deep crust and mantle. The relationships between brecciation and Cretaceous extension in the Pyrenees argue for a mixed mode of rifting associated with ductile and brittle deformation during the formation of the hyper-extended rift domain. Les brèches associées à l’évolution tectonique, sédimentaire et fluide des systèmes de rifts sont des marqueurs d’une variété de processus qui reflètent les modes d’extension. Dans ce papier, nous présentons une analyse des différentes brèches du Massif de l’Agly qui appartient à la partie européenne du rift crétacé inversé dans les Pyrénées Orientales. Cette étude pluridisciplinaire combine des données sédimentologiques, pétrologiques, structurales ainsi qu’une analyse statistique intégrant les formes et diversité des clastes, les lithologies et granulométrie du liant et la fabrique des brèches. Nous distinguons 5 types de brèches qui reflètent des processus sédimentaires et tectoniques, et la remobilisation des niveaux évaporitiques. L’intégration de ces processus dans l’histoire tectonique des Pyrénées Orientales confirme la formation de ces différentes brèches durant l’épisode de rifting crétacé. Nous mettons ainsi en évidence le rôle majeur des évaporites du Trias qui jouent le rôle de niveau de décollement aux interfaces socle/couverture durant les phases précoces du rifting. La tectonique salifère et le cisaillement sur ces interfaces socle/couverture, assistés par les circulations fluides sont exprimés par les nombreuses évidences de fracturation hydraulique à la base de la couverture mésozoïque. Avec l’augmentation de l’extension, ce niveau faible mécaniquement est extrait, entraînant la formation d’un système de détachement à comportement fragile. L’évolution de ce détachement préférentiellement localisé au niveau des interfaces socle/couverture, conduit à l’exhumation de la croûte profonde et du manteau. Les relations entre les processus de formation des brèches et l’extension crétacée mettent en évidence un mode de rifting dominé par un régime mixte à la fois cassante et ductile au cours de la formation des domaines hyper-étirées du rift pyrénéen.