Assembly, configuration, and break-up history of Rodinia: A synthesis

Orogenic gold deposits : A proposed classification in the context of their crustal distribution and relationship to other gold deposit types

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Global continental and ocean basin reconstructions since 200 Ma

Adakitic magmas: modern analogues of Archaean granitoids

Review of global 2.1-1.8 Ga orogens: implications for a pre-Rodinia supercontinent

40Ar/39Ar Age Constraints on Caldera Formation of the Emmons Lake Volcanic Center, Alaska Peninsula, Alaska

fault: The Denali fault of the eastern Alaska Range Spatial variations in focused exhumation along a continental-scale strike-slip

U-pb and 40ar/39ar detrital geochronology of modern river sediments in the wrangell mountains, alaska: improved constraints on the age and tectonic evolution of jurassic-quaternary magmatism

The dunite–wehrlite–clinopyroxenite–gabbro massif in Eastern Chukotka, a key object for geodynamic reconstructions of the Vel’may terrane, which represents one of the segments of the southern border of the Chukotka folded system (Chukotka microcontinent, or Arctic Alaska–Chukotka microplate), is investigated. Mineralogical and petrological–geochemical studies of rocks of this massif are carried out. A comparative analysis of the primary mineralogy and formation conditions of cumulative rocks of dunite–wehrlite–pyroxenite–gabbro assemblages from modern island-arc systems, mantle transition zones, and crustal sections of ophiolites and ancient island arcs shows that the rocks studied are cumulates crystallized from a tholeiitic melt in an intraoceanic island arc at a moderately high pressure. The 40Ar/39Ar age of magnesian hornblende from gabbro indicates the massif was formed no later than in the Early–Middle Jurassic. The petrological and geochemical modeling suggests that the analyzed olivine clinopyroxenites and gabbros are probable plutonic comagmates of the Late Triassic island-arc basalts and dolerites of the Vel’may terrane. The arc segment represented by these rocks of the Vel’may terrane was probably part of the system of island arcs which had been reconstructed in this region for the age interval of 163 to 230 Ma. In addition, there is a tendency for the rejuvenation of the Middle Triassic–Late Jurassic island-arc magmatism in the direction from west to east, namely, from the South Anyui terrane of Western Chukotka through the Vel’may terrane of Eastern Chukotka to the Angayucham terrain of Alaska.

Tectonic and Geodynamic Settings of Formation of the Mesozoic Cumulative Dunite–Wehrlite–Olivine Clinopyroxenite—Gabbro Massif in Eastern Chukotka

High-grade epithermal Au–Ag veins of the Vodorazdelnaya district in far eastern Russia are hosted by Early Cretaceous volcanic rocks of the Tytylveem belt. The largest deposit is Zone 37, a 1-km long, northeast-striking vein that is up to 35-m wide, containing at least 32 t Au. The main shoot consists of crustiform—colloform banded quartz-chalcedony-adularia-sulfide veins, of low-sulfidation style. The vein is cut by late-mineral rhyolite sills and dikes. Zone 37 vein is dated at 117 ± 2 Ma, overlapping within error with the cross-cutting rhyolites (121–119 Ma) and with intrusions of the nearby Ilirney granitic pluton (119–117 Ma). The volcanic host rocks are dated at 121–115 Ma. At September Northeast, 15 km west-northwest of Zone 37, mineralisation consists of veins up to 4 m wide, with crustiform banded quartz ± chalcedony ± adularia ± chlorite, and Zn-Pb-Cu sulfides, of intermediate sulfidation style, in a 1-km-long, north-northeast striking trend. High grades are associated with gold dendrites in fine-grained quartz bands and with minor late-stage tellurides. The veins were disrupted by intrusion of rhyolite dikes and associated phreatic breccias. Some breccias host mineralisation as vein clasts and minor matrix sulfides. The Tytylveem belt is preserved below a regional unconformity that forms the base to the overlying Late Cretaceous (106–77 Ma) Okhotsk-Chukotka Volcanic Belt (OCVB). Intrusive rocks attributed to OCVB magmatism were emplaced at about 96 Ma and are associated with overprinting hydrothermal alteration, sub-economic veins and thermal resetting of some vein adularia ages at Zone 37, to 91–97 Ma.

Paul W. Layer

Papers

40Ar/39Ar Age Constraints on Caldera Formation of the Emmons Lake Volcanic Center, Alaska Peninsula, Alaska

fault: The Denali fault of the eastern Alaska Range Spatial variations in focused exhumation along a continental-scale strike-slip

U-pb and 40ar/39ar detrital geochronology of modern river sediments in the wrangell mountains, alaska: improved constraints on the age and tectonic evolution of jurassic-quaternary magmatism

Tectonic and Geodynamic Settings of Formation of the Mesozoic Cumulative Dunite–Wehrlite–Olivine Clinopyroxenite—Gabbro Massif in Eastern Chukotka

The Dvoinoye and September Northeast high-grade epithermal Au–Ag veins, Vodorazdelnaya district, Chukotka region, Russia