Abstract Following continental collision, the distal European margin was overridden by the Alpine wedge and is now largely concealed beneath the mostly intact orogenic lid. Consequently, the geological evolution and nature of the hidden basement domains remain poorly constrained. We address this gap using 2,137 new LA‐ICP‐MS U‐Pb zircon ages from 16 samples representing indirect archives of the hidden European basement: (a) drill cores reaching the basement of the Bohemian spur beneath the northern wedge; (b) exotic boulders derived from the distal southern European slope and preserved in Jurassic–Eocene sediments (Gresten Formation, Buntmergelseries); and (c) Gresten Formation sandstones hosting the boulders. The latter two were basally accreted to the overriding Alpine wedge, transported northward, and are now exposed in the Ultrahelvetic nappe system. We find that basement drill core samples correlate well with exposed units of the Bohemian Massif. Provenance of the Ultrahelvetic boulders and sandstones is less straightforward, as zircon ages record Ordovician (∼467 Ma), early Variscan (380–350 Ma), late Variscan (350–310 Ma), and post‐Variscan Permian (280–270 Ma) magmatic events. These data are interpreted in the context of Penninic Ocean opening and closure. In the eastern study area, sediment was primarily derived from the Bohemian basement spur, whereas its influence decreases westward and detritus from the Tauern Window marginal high, and subordinately from Austroalpine units, becomes increasingly important. Overall, these results refine reconstructions of the concealed European margin and demonstrate that exotic boulders preserved in sediments retain pre‐collisional records, effectively lifting the orogenic lid.
Abstract Arc volcanism is commonly interpreted as the surface expression of subduction‐related magmatism and its spatial organization is often controlled by lithospheric structures. In arc‐back‐arc systems, slab retreat may promote the transition from compression to extension and the development of Subduction‐Transform Edge Propagator (STEP) faults. These latter accommodate the deformation along slab edges. A representative example of STEP fault is the Aeolian‐Tindari‐Letojanni fault system, a NNW–SSE‐striking shear zone affecting the central Aeolian arc and likely extending southward to the Ionian margin of Sicily. The Vulcano, Lipari, Salina islands form a NNW–SSE elongated Pleistocene volcanic belt emplaced on this shear zone. Here, we integrate and reinterpret available geological and geophysical data with new airborne gravity measurements to assess the structure of the Aeolian‐Tindari–Letojanni fault system and its relationship with volcanism. Our results indicate that the Vulcano–Lipari–Salina volcanoes can not be interpreted simply as the surface expression of aligned intracrustal magma reservoirs. Instead, they reflect a deeper tectonic structure related to a lithospheric‐scale discontinuity. Magnetic and gravity source distributions, basement uplifts, Moho undulations, and geometry of the magma plumbing systems reveal a tectono‐magmatic hierarchy in which lithospheric deformation primarily controls magma ascent and storage. We conclude that the Aeolian‐Tindari–Letojanni fault system acts as a lithospheric shear zone that dislocates both the crust and the Moho by focusing magma transfer along a NNW–SSE pathway. These results highlight the complexity of magma ascent across active shear zones and the broader role of STEP‐related volcanism in arc–back‐arc evolution.
Abstract Detrital zircon U–Pb geochronology from Triassic–Jurassic basins in the New England Orogen (NEO) constrains sediment provenance and episodic continental arc evolution along the eastern Gondwanan margin. Dominant zircon clusters at 270–230 Ma and 340–300 Ma in these basins were likely sourced from contemporaneous magmatism in the NEO. Integrating new and published data identifies three magmatic pulses at ∼320, ∼285, and ∼255 Ma. These pulses are interpreted in the context of arc migration based on the spatio‐temporal distribution of primary magmatic rocks and zircon trace‐element data. Landward arc migration during the early Carboniferous was possibly associated with slab shallowing. Elevated Eu/Eu*, Sm/Yb N , and U/Yb values are consistent with thicker crust and increased slab‐derived fluid input during the ∼320 Ma pulse. During the early Permian, trenchward arc migration and overriding‐plate extension reflect slab rollback (steepening). High zircon crystallization temperatures, reduced oxygen fugacity, and reduced slab‐derived fluid (lower U/Yb) suggest that the ∼285 Ma pulse was possibly generated by decompression melting in a backarc setting. Contraction of the overriding plate since the middle Permian, accompanied by crustal thickening (elevated Eu/Eu* and Sm/Yb N ), arc advance, and increasing slab‐derived fluid (increasing U/Yb), likely reflect slab shallowing. This contractional phase culminated in a major magmatic flare‐up at ca. 255 Ma. We suggest that episodic arc behavior in the NEO can be explained by alternations between slab steepening and slab shallowing, similar to processes documented in the Sierra Nevada batholith (North American Cordillera).
Abstract Strike‐slip faults play a pivotal role in controlling both the formation and spatial distribution of deep and ultra‐deep fault‐related karst reservoirs in the Central Shunbei region of the Tarim Basin. Three‐dimensional seismic interpretation has delineated five NE–striking major strike‐slip faults, each exhibiting relatively modest displacement magnitudes and variable along‐strike propagation extents. These major faults are stratigraphically partitioned into deep, middle, and shallow structural layers, with distinct deformation styles observed across different stratigraphic interfaces. Machine learning–enhanced fault detection has identified numerous low‐order strike‐slip faults—characterized by relatively short lengths and exhibiting either collinear or oblique geometric relationships with the major faults. A large‐scale sandbox experiment demonstrates that the development of major strike‐slip faults was predominantly controlled by pre‐existing basement faults and subduction of the Paleo‐Kunlun Ocean during the Middle–Late Ordovician. In contrast, subduction of the Paleo‐Altyn Tagh Ocean exerted only a secondary and spatially limited influence—restricted to a subset of faults located near the southeastern extremity. The major faults evolve through an east–to–west progressive propagation sequence; individual faults nucleate as en echelon R–type fractures and coalesce into continuous fault traces under progressive bulk shortening. A small‐scale sandbox experiment reveals that the low‐order strike‐slip faults function as kinematically subordinate structures, nucleating secondarily in response to the development of major strike‐slip fault system. Once developed, the major faults accommodated the bulk of compressional strain, thereby suppressing further reactivation and geometric modification of the low‐order faults.
Abstract The Coastal Cordillera of northern Chile, in the forearc of the Andean subduction zone, provides an ideal site to evaluate exhumation above the oldest active subduction under extreme aridity. This range lies parallel to a sediment‐starved trench, has experienced hyperaridity since the Miocene, and is transected by the ∼1,000‐km‐long Atacama Fault System (AFS). Previous thermochronology documents regional cooling since the Late Jurassic, but away from major structures, limiting assessment of fault‐controlled exhumation. Using a targeted sampling strategy, we test whether faulting has driven localized erosion within the Atacama's hyperarid core. We present new apatite and zircon (U‐Th)/He and apatite fission‐track data from a 720‐m‐relief transect crossing the Salar Grande Fault (SGF), the northern termination of the AFS. Dates range from 150 Ma to 30 Ma and thermal modeling indicates a multistage cooling history: (a) post‐emplacement cooling from ∼150 to 110 Ma); (b) slower cooling from ∼110 to ∼55–45 Ma with prolonged residence near ∼100°C; (c) renewed cooling between ∼50 and 35 Ma; and (d) very slow to negligible exhumation after ∼35 Ma. The cooling intervals align grossly with Andean tectonic phases and can be related to regional, plate boundary‐wide events (cooling intervals 1–3) as well as local fault deformation (interval 3). Specifically, we relate the mid Cenozoic cooling to pull‐apart basin formation along the SGF. Our findings show the value of low‐temperature thermochronology in low‐erosion environments such as the Atacama, where uplift‐driven exhumation occurs, albeit more slowly, ultimately preserving a long record of cooling.
