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Tectonic history of northern Nevada basement begins with amalgamation of the supercontinent Rodinia along the Cheyenne lineament, an east west Paleoproterozoic suture and mobile belt between Archean cratons on the north and Proterozoic terranes on the south. East of Park City, Utah this boundary is a suture, which becomes a widening mobile belt westward into northern Nevada. Rifting of Rodinia, initiated on mantle plumes in the early Neoproterozoic was complete by the end of Neoproterozoic time. In Nevada, continental ductile crust slid east off a plume head and created an orthogonal fracture pattern parallel with and normal to the cratonic boundary. Crustal thinning extended eastward from the continental margin near Winnemucca, Nevada to a hinge line near Salt Lake City. During late Neoproterozoic and much of Paleozoic time continental sediments shed westward onto a rectilinear North American margin and formed a passive platform that mimicked the rifted margin. In these environments carbonate sediments containing a high percentage of quartz silt grains formed favorable hosts for future mineral and gold deposits. Island arcs collided with western North America in late Devonian and late Permian times. This caused oceanic sediments between the island arcs and North America to obduct up to 160 kilometers southeastward over the continent in the Antler orogeny and up to 100 kilometers southeastward in the Sonoman orogeny. Break up of Pangea began in late Triassic time when North America began moving northwestward from South America. Rapid northeastward migration of the subducting slab formed an east-northeast directed flat subduction zone off North America's western coast from Mesozoic through Paleocene time creating a magmatic null. Old, favorably-oriented rift structures bounding Precambrian crustal blocks were reactivated with up-to-the-east reverse motion at this time. The thick skinned deformation may have translated to short-throw, thin-skinned detachment faults, imbricate faults and fault propagated folds associated with these periods of Mesozoic compression. The null was interrupted by two periods of slab roll back, centered at 160 Ma and 92 Ma, which produced a number of back arc intrusions in northern Nevada including stocks at Bald Mountain, Goldstrike and Cortez. Flat subduction ended at 48-45 Ma, after which the slab delaminated from both the north-northeast in Idaho and south-southeast in Mexico over the following 25 Ma. As the opposing wings delaminated, mantle was drawn between the sinking slab and the crust, creating a migrating magmatic arc south-southwest across Nevada. An enormous heat engine was created when mantle material invaded above the sinking slab beneath the continent that caused partial delamination of the lithospheric mantle from the crust and possibly some lower crust. Ore deposits, large apatite alteration haloes around the deposits and subsequent high heat flow within the Great Basin are considered to be reflections of these processes. A second phase of crust and lithospheric mantle delamination began in the Miocene after development of the Yellowstone mantle plume head centered near the McDermitt caldera. Fairly rapid emplacement blurred the age distinction between de-lamination and related gold deposits along the northern Nevada rift and the northern Carlin trend. This event concluded ore formation in north-central Nevada. Most Carlin-type deposits, including Bingham Canyon porphyry deposit, whether inboard or outboard of the platform margin, occur where this major heat engine has passed beneath the Cheyenne Belt mobile zone. Proximity to detritus shed off the Archean Wyoming and Siberian Cratons into the Trans Hudson and Cheyenne Belt mobile zones is empirically favorable for gold deposit formation because Homestake, Bingham Canyon, and Nevada's Carlin deposits totaling up to 300 million ounces of gold, are located in this environment. Also involved in ore formation are rectilinear structural intersections formed during the Neoproterozoic rifting of western North America focusing multiple periods of intrusion, and thin-skinned fault-propagated structural traps developed during multiple periods of Mesozoic crustal contraction. [ABSTRACT FROM AUTHOR]

The Valongo Anticline, near Porto, is situated in the Central Iberian Zone in Northern Portugal. Ordovician is well represented in the area consisting of three Formations. More recently volcanic rocks evidencing a continental rifting generated during the Early Ordovician (Tremadocian), representing an extensional episode in a passive continental margin of Gondwana related with the opening of Rheic Ocean, were described. Overlying this volcanic succession, shelf deposits represented by conglomerates, massive quartzites followed by interbedded quartzite, wacke, slate, ironstone and volcano-sedimentary intercalations occur. These last iron-rich layers with organic matter, algae and bryozoan remains are related with episodic development of anoxic conditions. Towards the top of Santa Justa Formation, a lingulid shell bed consisting in a phosphate-rich layer represent tempestites related with volcanic activity. The transition to the Valongo Formation (Dapingian-Darriwilian) gradually turns to pink siltites, grey siltites and slates. It is one of the most fossiliferous lithostratigraphic units of the Ordovician of Portugal. Among the fossil fauna more than a hundred species of trilobites were found besides graptolites, brachiopods, gastropods, cephalopods, bivalves, rostroshells, cystoids, crinoids, bryozoan and some very rare species. To the top of Valongo Formation a nodule-bearing layer overlain by a ferruginous horizon evidences a hiatus (paraconformity) of the Valongo Formation, missing upper Darriwilian, Sandbian and Katian strata (upper Middle Ordovician-lower Late Ordovician) from the succession. Sobrido Formation recently revised allowed to infer palaeogeographic patterns of the north Gondwana platform based on the relative locations of the ice margin, extent of deglaciated land, and position of the coastline during Hirnantian glaciation. [ABSTRACT FROM AUTHOR]

Peperites are recognised as a mixture of magma and sediment, which is generated by an interaction of partly emergent domes and lava flows with unconsolidated sediments. They commonly occur in back-arc and rift settings where progressive subsidence of basins occurs contemporaneously with magmatism. This presented research deals with peperites formed along the ephemeral lacustrine sediments and the overlying small- volume ultrapotassic lava flows in western Turkey. Ultrapotassic rocks occur as domes, dykes and lava flows and include peperitic basal contact zones. The peperitic contact zone with lava flows is defined by up-to-a metre thick layer of magma and sediment mixture. Magma clasts display fluidal and blocky morphologies with variable sizes ranging from few mm to a few decimetres. Fluidal clasts predominate with respect to blocky varieties. They were locally in-situ fragmented into blocky clasts that form a typical jig-saw texture. Blocky clasts are variably shaped and include digitate margins. Tapered clasts also occur along foliation planes of lava flows. Peperitic textures related to ultrapotassic lava flows closely resemble those generated by olivine basalt flows. Clast morphologies suggest a progressive fragmentation due to decreasing temperature along with increasing viscosity during peperite formation. Sediment fluidisation and low viscosity are presumed to be major controlling factors for fluidal clast generation and non-explosive emplacement. Common occurrences of peperite-bearing volcanic edifices in western Turkey suggest that magmatism developed within a progressively subsiding basin, probably corresponding to rift or back-arc extensional/transtensional environment. [ABSTRACT FROM AUTHOR]