Continental arcs commonly experience brief, high-flux magmatic pulses, and the Late Jurassic Sierra Nevada arc records one such event as a compositionally diverse magmatic system that includes highly silicic plutonic, hypabyssal, and volcanic rocks, associated cumulate gabbros, and a regionally extensive Independence dike swarm. This study presents new constraints on the timing, magma sources, differentiation, and genetic relationships of this diverse magmatic episode. High-precision chemical abrasion−isotope dilution−thermal ionization mass spectrometry (CA-ID-TIMS) zircon geochronology, whole-rock Sr-Nd-Pb isotopic data, trace-element geochemistry, and zircon δ18O data were integrated to characterize the evolution of this magmatic system. Geochronological data constrain all magmatic activity to a narrow interval (152−149 Ma), indicating that the silicic rocks, cumulate gabbros, and Independence dike swarm are coeval features. Geochemical and isotopic data indicate that andesitic magma, best represented by the Independence dike swarm, served as the parental melt, from which high-silica, crystal-poor volcanic, hypabyssal, and plutonic rocks formed as interstitial melts, whereas the mafic cumulate gabbros represent the residuum. Geochemical patterns, including mantle-like zircon δ18O values, evolved Sr, Nd, and Pb isotopic signatures, and trace-element systematics, point to partial melting of the hydrated lower crust or subcontinental lithosphere to generate the parental andesitic magma, which then differentiated in shallow, deformation-influenced reservoirs to generate the bimodal suite of silicic rocks and mafic cumulates.

The relationship between late Cenozoic magmatism and extension in the central Basin and Range province (western United States) is complex, necessitating high- precision geochronology to understand its spatiotemporal connections. In the Death Valley region (California), the lack of high- precision U-Pb zircon ages has limited our understanding of the timing of pluton formation and its links to regional extension. We present new high- precision chemical abrasion- isotope dilution- thermal ionization mass spectrometry 206Pb/238U zircon ages and trace element analyses for eight Death Valley plutons. Our findings reveal three distinct phases of intrusive magmatism: (1) emplacement of shallow rapakivi granites at 13.2 Ma, (2) construction of the mid- crustal Black Mountains intrusive complex at 11.3 Ma, and (3) late emplacement of shallow, compositionally diverse intrusions at 8.2 Ma. A gap in zircon crystallization between 10 Ma and 8.2 Ma coincides with exhumation of the Black Mountains and a transition from sill to dike emplacement. The dominance of rapakivi granites in the Death Valley region, which is rare among Cenozoic granitoids, is likely a result of rapid crustal extension that induces adiabatic decompression. A comparison of the timing of volcanism, plutonism, and tectonic events in Death Valley reveals that intrusive magmatism closely tracks the locus of extension, underscoring the plutonic record as a vital link for understanding regional tectonics and changes in plate boundary dynamics during this period.

The San Albino deposit is a high-grade, vein-hosted, orogenic gold system that occurs within Mesozoic metamorphic rocks in the Central Highlands of NW Nicaragua. Despite active mining the timing of mineralization relative to a complex Jurassic to Paleogene tectonic evolution has remained enigmatic. This history includes several major orogenic episodes as part of Jurassic to Cretaceous arc activity, with related collisional events driving regional-scale fold-thrust belt formation. Widespread younger extensional to transtensional events are related to the formation and establishment of the Caribbean Plate, including translation of Central American crustal blocks hundreds of kilometers to the east from their original paleo-positions. Ongoing mining and related infrastructure development have produced abundant new exposures, providing key observational constraints as well as access to fresh, unweathered material for isotopic investigations. This contribution includes field observations to support U-Pb zircon LA-ICP-MS data from dike sets with key cross-cutting relationships relative to the primary ore zone, the San Albino vein system. Results indicate that the dike sets were emplaced at similar to 96 Ma, implying that mineralization must have occurred during Cretaceous or earlier events, likely as part of Aptian-Albion orogenesis driven by collision of Central American crustal blocks with nuclear Mexico (e.g., the Guerrero Terrane).

<p>Zircon megacrysts are unusually large crystals (> 5 mm) that are commonly associated with mantle-derived kimberlites, carbonatites, alkali basalts and syenitic pegmatites (e.g., Hoskin and Schaltegger 2003). Such zircons form during relatively short timespans and therefore, are often used as reference material for U-Pb geochronology. Here, we determine the geochemical and isotopic (U-Pb, Hf, O) characteristics of a little-known occurrence of zircon megacrysts at Kawisigamuwa, Sri Lanka.</p><p>The dark brown megacrysts are euhedral, commonly elongate crystals with double pyramidal terminations and have faintly corroded crystal surfaces. The zircons consist of oscillatory zoned and nearly featureless cathodoluminescence-bright patches, some of which appear to follow sealed cracks. All zircon domains show a low to moderate FWHM of the ν<sub>3</sub> (SiO<sub>4</sub>) Raman band (2.5 to 7.3 cm<sup>-1</sup>), have a low to moderate radiation damage (total α-dose mainly <0.5 x 10<sup>18</sup> events/g) and therefore are intermediate to well crystalline. Contents of most trace element (U, Th, REE, P) are elevated in the oscillatory zoned domains, while Hf content is elevated in the CL-bright domains and seems to be grain-dependant. The oscillatory zoned domains yielded a TIMS weighted mean <sup>206</sup>Pb/<sup>238</sup>U age of 532.39 ± 0.66 Ma (2sd). The<sup></sup><sup>206</sup>Pb/<sup>238</sup>U dates within the CL-bright domains are partially reset by a single event of recrystallisation at ~518 Ma. The mean Hafnium isotopic compositions of the tested grains show a narrow range of <sup>176</sup>Hf/<sup>177</sup>Hf from 0.281969 to 0.282003. Oxygen isotopes determined on two oscillatory zoned zircon megacrysts are homogeneous (mean δ<sup>18</sup>O of 12.1 and 12.2).    </p><p>While some of the trace and major element characteristics (Th/U, Zr/Hf, Hf content) of the Kawisigamuwa megacrysts resemble those of carbonatite zircons, their hafnium and oxygen isotope ratios are clearly different from mantle values. The isotopic values indicate that a significant amount of a crustal component must be involved in the formation of the zircons. Recently, several studies have found evidence for melting of carbonate rocks under high grade metamorphic conditions in Sri Lanka (e.g., Wang et al. 2021). It might be feasible that zircons grow from interaction of crustal derived carbonate melts and silicate melts or wall rocks under high grade metamorphic conditions.</p><p>Hoskin P.W.O. and Schaltegger U. (2003). The Composition of Zircon and Igneous and Metamorphic Petrogenesis. Reviews in Mineralogy and Geochemistry, 53 (1), 27–62.</p><p>Wang J., Su B.-X., Chen C., Ferrero S., Malaviarachchi S.P.K., Sakyi P.A., Yang Y.-H. and Dharmapriya P.L. (2021). Crustal derivation of the ca. 475-Ma Eppawala carbonatites in Sri Lanka. Journal of Petrology, 62 (11), 1-18.</p>

The Walker Lane belt and Eastern California shear zone of California, USA, are active, plate bound- ary-related dextral systems with transtensional and transpressional deformation, respectively. They are separated by the sinistral Garlock fault, creating a complex system without an overall integrated forma- tion and evolution model. We examine the deformation within the eastern segment of the Garlock fault zone over geologic timescales by determining the slip history of faults. We assess the progression of faulting and associated deformation along the WSW- striking Garlock fault zone and how it applies to the overall NNW- directed dextral system. Previous studies found that large synthetic fault strands take up 30% of the slip of the Garlock fault zone and have proposed multiple mechanisms to explore how to accommodate regional NNW- directed shear across the Garlock fault without cutting its trace.We analyze an unstudied section of faulting in one of the more complex areas of regional deformation via compiled and reinterpreted published geologic data for an analysis of total and incremental slip on the main faults of the eastern Garlock fault zone. We identify geologic offset features to interpret total slip, timing, and deformation evolution. We find that 30% of the total slip of the Garlock zone occurs on strands other than the Garlock fault sensu stricto, with the locus of main slip sidestepping during the evolution of accommodation of through- going, regional dextral shear. Our results support ideas of the creation and evolution of the regional dextral system via stress concentration on a sub- Garlock lithospheric anisotropy with a resulting lowering of the plastic yield stress. Our results also show an eastward increase in fault system complexity, which may imply an underappreciated seismic hazard of the eastern Garlock fault zone.

We characterise zircon megacrysts from the Kawisigamuwa carbonatite as a new potential reference material for laser ablation‐inductively coupled plasma‐mass spectrometry U‐Pb and Hf isotope measurement. We studied ten 0.5–4 cm long, brown megacrysts that consist of oscillatory zoned (OZ) and nearly featureless cathodoluminescence‐bright recrystallised (RX) zircon domains. The zircons have low to moderate radiation damage (total α‐dose < 0.5 x 10 18 events g ‐1 ), tested by the measured FWHM of the ν 3 (SiO 4 ) Raman band < 5 cm ‐1 . An ID‐TIMS weighted mean 206 Pb/ 238 U age of 532.39 ± 0.66 Ma (2 s uncertainty) was determined for OZ zircon domains of three grains. While hafnium content varies within and between crystals (6630–9960 μg g ‐1 ) the in situ mean 176 Hf/ 177 Hf ratios of ten crystals overlap within uncertainty. We recommend a mean 176 Hf/ 177 Hf ratio of 0.282003 ± 0.000020 (2 s ) as preliminary working value for OZ domains. Two OZ megacrysts yield indistinguishable δ 18 O VSMOW of 12.1 ± 0.4‰ and 12.2 ± 0.4‰ (2 s ). Elevated Th/U (> 1.5), Zr/Hf (59–75) and low hafnium contents in OZ domains are similar to those of zircons from carbonatites of mantle origin, while high δ 18 O and low εHf i (‐15.8 to ‐17.1) indicate a crustal contribution. The zircons probably grew from crustal‐derived carbonate melts under high grade metamorphic conditions.

This detailed geologic map and supplemental digital data set1 examine and demonstrate the complex deformational history and reactivation relationships of the Panamint Range (California, USA), from active transtension of the Walker Lane belt, Miocene extension of the Basin and Range, to multiple Mesozoic events related to subduction, and Neoproterozoic extension. This collection of map data focuses on the geometry, kinematics, and relative timing of deformation to understand the deformation history and effects of structural reactivation. A minor portion of this geologic mapping data was presented in the analysis and figures of Andrew and Walker (2009). The Neogene extension and subsequent dextral transtension deformation has created a complex network of faults via partial reactivation of Mesozoic and Neoproterozoic structures. Structural data show oblique normal slip overprinting earlier normal slip along the western range flank fault of the western Panamint Range. Jurassic and Cretaceous deformation is localized along the western range on the Goldbug fault. The hanging wall of this fault preserves migmatitic fabrics and intense deformation due to Jurassic contraction. The Goldbug fault places Paleoproterozoic to Mesoproterozoic rocks over Neoproterozoic rocks. The Jurassic contraction has top-to-the-northeast relative transport and the more discrete Cretaceous thrust faulting has top-to-the-east transport. A set of Late Cretaceous plutonic rocks and mylonitic gneisses derived from them, occur along the Goldbug fault and demonstrate the reactivated nature of this fault in the Late Cretaceous. New data for the Butte Valley fault show that this fault cuts Late Jurassic plutonic rocks and has normal slip. The Butte Valley fault ends northward at the linked sinistral slip Warm Spring Canyon fault, which was previously interpreted to be an intrusive contact. A previously unrecognized rim syncline structure occurs along the boundary of the Late Jurassic Manly Peak quartz monzonite. Neoproterozoic deformation is difficult to discern due to the overprinting deformations. Numerous Neoproterozoic deformation-related mass wasting deposits can be seen within this formation, including a set of conspicuous allochthonous deposits and clasts of older Beck Spring Dolomite that appear to be frozen in the process of breaking away from intact, normal thickness beds in the Surprise–Happy Canyons divide. This detailed geologic mapping and collection of structural data for the rocks in the central Panamint Range were created using digital in-the-field geographic information systems software running on a field-hardened laptop computer combined with an earlier set of field data that were digitized into the digital georeferenced database. This map is a simplification of detailed geologic mapping data collected at 1:2000–1:6000 scales and reduced to 1:20000 scale. Structural data include kinematic and relative timing of deformation information.

Digital map data files in ArcGIS shapefile format for data collection points, geologic contacts, and geologic unit polygons.

This detailed geologic map and supplemental digital data set1 examine and demonstrate the complex Neogene–Quaternary deformation in the Slate Range Crossing area (California, USA) of the active dextral transtension of the Death Valley region and Walker Lane belt. This map integrates the late Cenozoic structures and geologic units with the Mesozoic geologic units and deformation as a data set to examine the controls on reactivation of older structures. These geologic data were collected to study pre-, syn-, and post-kinematic rocks to examine the deformation history of the area and to find palinspastic markers to examine the late Cenozoic fault displacement and displacement history across Panamint Valley to the east, as reported in Andrew and Walker (2009). The study focused on defining the Miocene and Pliocene rocks and deposits and examining lateral changes and depositional sources of clasts. There are two different volcanic-sedimentary sequences in this area. A Miocene section contains mafic to felsic volcanic units, numerous debris-flow to laharic deposits, and several associated conglomerates and breccias containing exotic clasts. The exotic clasts are matched to rocks in the Panamint Range on the east side of Panamint Valley as reported in Andrew and Walker (2009) as displacement vectors for palinspastic reconstructions. These Miocene strata ubiquitously dip eastward 20–40º. A younger volcanic-sedimentary sequence contains relatively thin mafic lava flows and associated locally derived, coarse-grained mass wasting deposits. These younger basaltic lavas generally have gentle dipping lava flow features and foliation. Numerous faults cut the different age deposits allowing a chronology of Neogene to Quaternary faulting; additionally, there are numerous fabrics associated with Jurassic contraction and Cretaceous(?) dextral shear. The area near Slate Range Crossing has a conspicuous zone of earthquake foci; this study found that some of this seismic activity coincides with a zone of southwest-striking, moderately dipping to the north, sinistral-oblique normal faults, which cut across the northernmost Slate Range. These faults form a structural boundary between the Argus and Slate Ranges and link the fault networks in Panamint Valley with those in Searles Valley. This mapping and structural data demonstrate the two-stage Neogene fault history of the Walker Lane belt deformation in this area and show that regional tilting of rocks occurred after ca. 13 Ma and before ca. 4 Ma; this eastward down-tilting appears to be a discrete event and may mark the change from extension to transtension. This detailed geologic mapping and collection of structural data for the rocks in the eastern Argus and northern Slate Ranges and Panamint Valley were created using digital in-the-field geographic information systems software running on a field-hardened laptop computer. This map is a simplification of detailed geologic mapping data collected at 1:6000 scale and reduced to 1:20000 scale. Structural data includes kinematic and relative timing of deformation information.