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New U-Pb zircon ages are reported for granulite facies crustal xenoliths brought to the surface by mafic lavas in the Snake River Plain. All samples yield Meso-to-Neoarchean ages (2.4–3.6 Ga) that significantly expand the known extent of the Archean Wyoming Craton at least as far west as the west-central Snake River Plain. Most zircon populations indicate multiple growth episodes with complexity increasing eastward, but they bear no record of major Phanerozoic magmatic episodes in the region. To extrapolate this work further west to the inferred craton boundary, zircons from southwestern Idaho batholith granodiorites were also analyzed. Although most batholith zircons record Cretaceous formation ages, all samples have zircons with inherited cores—with some recording Proterozoic ages (approaching 2 Ga). These data enhance our perspectives regarding lithosphere architecture beneath southern Idaho and adjacent areas and its possible influence on Cenozoic magmatism associated with the Snake River Plain–Yellowstone "melting anomaly". [ABSTRACT FROM AUTHOR]

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We report the discovery of one of the largest ancient (>3.0 Ga) crustal terranes on Earth. Granitoids with crystallization ages >3.0 Ga and/or Sm-Nd depleted mantle model ages ≥3.2 Ga define a -1000 x 100 km belt on the western margin of the Rae craton, Canada, referred to herein as the Perry River terrane (PRT). Zircon U-Pb-Hf-O isotope and whole-rock geochemical data from granitoids show that the PRT is a predominantly juvenile 3.3--3.2 Ga terrane that was partially reworked by more evolved ca. 3.1 Ga magmatism. These findings call for a reassessment of the timing and extent of ancient continental growth on Earth. A global compilation of zircon Hf isotope data from 3.6 to 3.0 Ga igneous rocks reveals clusters of relatively juvenile (initial εHf -2 to +3) rocks at ca. 3.31 and ca. 3.23 Ga, which include samples from the PRT and 13 other terranes worldwide. Other global zircon data sets also document age peaks between 3.3 and 3.2 Ga, and a cluster of broadly chondritic initial εHf values around 3.2 Ga. The 3.3--3.2 Ga period may therefore have been a time of enhanced net continental growth on Earth, and the PRT is one of the largest terranes preserved from that time. Furthermore, zircon Hf isotope data from 3.3--3.1 Ga PRT granitoids and 3.5--3.0 Ga igneous rocks worldwide yield little evidence for parent magmas that interacted with or derived from pre--3.6 Ga continental material. Contrary to some continental-growth models, this latter observation suggests that the volume of continental crust established by 3.6 Ga was relatively small. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Polymetallic mineralization occurs as skarn-type, intermediate- and low-sulfidation. • Skarn-type is Cu-rich and close in age to felsic plugs dated at ∼51 Ma. • Intermediate-sulfidation veins are Ag-rich, ∼42 Ma, and ESE- to SE-striking. • Low-sulfidation veins are Au-rich, ∼29 Ma, and N-S-trending. Abstract Mineralization in the Zacatecas district is polymetallic (Ag, Zn, Pb, Cu, and Au) and occurs as skarn-type and epithermal veins formed in different metallogenetic stages. The oldest mineralization in the district is skarn-type, Cu-rich with lesser Zn-Pb-Ag, and is considered to be close in age to felsic dikes and plugs dated at ∼51 Ma. Epithermal mineralization occurs in both low- and intermediate-sulfidation styles. Intermediate-sulfidation veins (the Veta Grande, Mala Noche, El Bote, and La Cantera veins) are polymetallic, Ag-rich, hosted in ESE- to SE-striking structures, and were formed at ∼42 Ma (adularia 40Ar/39Ar isochron age from Veta Grande of 42.36 ± 0.18 Ma; 2σ, MSWD = 0.76). Low-sulfidation Au-(Ag) mineralization occurs in the N–S-trending El Orito vein system, which yielded an adularia 40Ar/39Ar isochron age of 29.19 ± 0.20 Ma (2σ, MSWD = 1.8). These ages and the differences in structural orientation indicate that the two styles of epithermal mineralization are temporally and tectonically unrelated. The mineral paragenesis of the Mala Noche deposit consists of early skarn-type Cu mineralization overprinted by later epithermal Pb-Zn-Ag veins. Skarn-type minerals include relicts of prograde silicate minerals (hedenbergite and garnets), retrograde silicate minerals (ilvaite, grunerite, stilpnomelane, epidote, clinochlore), and ore minerals (chalcopyrite, pyrite, sphalerite, galena, magnetite, wolframite, and minor bismuthinite). Epithermal mineralization is characterized by layered to vuggy quartz veins and breccias, with phyllic wallrock alteration (quartz, sericite-illite). The veins consist of quartz, calcite, dolomite, and ankerite with variable amounts of base metal sulfides (sphalerite, galena, pyrite, minor chalcopyrite, and rare acanthite and stromeyerite). The Veta Grande epithermal mineralization was emplaced in two main stages of Ag-rich quartz veining, with narrow selvedges of phyllic (quartz-sericite) wallrock alteration. Stage I consist of quartz, calcite, and minor adularia intergrown with pyrite, followed by sphalerite, galena, and lesser chalcopyrite, acanthite, pyrargyrite, and jamesonite. Stage II mineral paragenesis is similar to stage I but is characterized by amethystine quartz and contains less abundant sulfide minerals. The ore mineral paragenesis of the El Compas vein, within the El Orito System, consists of quartz, adularia, calcite, and chalcedony with minor pyrite, followed by rare aguilarite, naumannite, electrum, and native gold. The skarn-type and intermediate-sulfidation mineralization is coeval with Eocene subduction-related magmatism in the Zacatecas area, which is constrained by zircon U-Pb ages for igneous rocks between 51 and 42 Ma. The emplacement of these magmas was controlled by the same regional-scale, ESE- to SE-trending, transtensional structures that controlled the skarn-type and intermediate-sulfidation deposits. This mineralization is thus interpreted to be related to the last stages of subduction volcanism in central Mexico, under transtensional stress conditions. In contrast, no nearby magmatism is clearly related to the Oligocene low-sulfidation system. However, its age and structural orientation (N–S), combined with a regional change in magma composition from Eocene calc-alkaline to Oligocene bimodal volcanism in central Mexico, suggest that the low-sulfidation mineralization is related to post-subduction continental extension processes, reflecting the beginning of Basin and Range tectonics. [ABSTRACT FROM AUTHOR]