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Paleomagnetic data bearing on vertical axis rotation of the Rio del Oso dike swarm, western Españ ola Basin, New MexicoThe Española Basin is one of a series of interconnected, asymmetrical basins in the Rio Grande rift that includes a number of north- and northeast-striking faults that accom- modated block tilting and basin subsidence. The western margin of the Española Basin, in particular, is characterized by a greater than 17-km wide zone of normal and oblique-slip faults. To clarify the involvement of block rota- tion in the tectonic evolution of the Española Basin, we carried out a paleomagnetic study of mafic intrusions (Rio del Oso dike swarm) that are genetically related to regionally exten- sive basalt flows of the mid-Miocene Lobato Formation. The primary hypothesis tested was that these intrusions experienced some degree of vertical axis rotation associated with mid-Miocene to recent continental rifting. In situ paleomagnetic results from forty-two sites yield a group mean declination (D) of 344.0°, an inclination (I) of 41.1°, α95 of 6.1°, and k of 14.1. The group mean result is discordant to the <10 Ma pole of D=356.0°, I=54.4°, α95 = 3.3° with a statistically significant inferred rotation (R) of -12.0°± 7.2° and flattening of +13.3° ± 5.5° relative to the <10 Ma pole field direction. These discordant results indicate that a modest degreemore »
Eruptive and magma feeding system evolution of Sośnica Hill Volcano (Lower Silesia, SW Poland) revealed from Volcanological, Geophysical, and Rock Magnetic DataThe Sośnica Hill volcano is part of the Oligocene to Miocene (30.9–20.0 Ma) Strzelin volcanic field. . It is located 100 km east of the Ohře Rift in the eastern part of the Fore-Sudetic Block, south of the town of Strzelin, Poland. Modern quarrying has exposed the sub-volcanic magma feeder system of the central part of the volcano and an extrusive volcanic succession that includes a 40 m thick sequence of lava flows and pyroclastic deposits that col- lectively form a complex scoria cone. Geophysical data (ground magnetometry and electric resistivity tomogra- phy (ERT)) reveal sharp linear anomalies that are interpreted to reflect normal faults dissecting the volcano. The ERT data map both high and low resistivity bodies, likely representing coherent clay-free dry rocks and partly argilized volcaniclastic deposits, respectively. Paleomagnetic data from 20 intrusive sites reveal two populations of reverse polarity site mean data; 11 sites are of low dispersion and yield a group mean direction that is discor- dant to the expected field direction, while six sites are highly scattered. Three sites did not yield interpretable re- sults. We interpret the 11 sites as time-averaged field directions that are discordant to the expected field. The high dispersion ofmore »
Distributed crustal shortening followed by transpressional shearing in the Superior Province, northeastern Canada: A Late Archean analogy to modern accretionary plate margins?The Canadian Superior Province has become one of the key test pieces to discuss tectonic processes and mechanisms of crustal growth in the Late Archean. The Province consists of a >2.8 Ga proto-cratonic core intruded by voluminous arc-like plutons and surrounded by a series of narrow, elongate ca. 2.8–2.7 Ga juvenile belts, also referred to as terranes or domains. The terranes seem to wrap around the proto-cratonic core and generally young outward, but the kinematics and geodynamic causes of their assembly remain debated. In this paper, we examine the Radisson pluton in northeastern Qu´ebec, which intruded the southern, outer edge of the presumed magmatic arc (Bienville domain) along its ~WNW–ESE-trending tectonic boundary with the protocratonic crust (La Grande domain). The pluton, dominated by porphyritic monzogranite to quartz monzonite, was emplaced at around 2712 Ma and exhibits complex internal structure resulting from superposed magmatic to solid-state deformations. An early margin-parallel ~WNW–ESE magmatic foliation containing a steep lineation, recognized by the anisotropy of magnetic susceptibility (AMS), is interpreted as recording vertical stretching and horizontal flattening of highly crystallized magma, either due to emplacement and/or pure shear dominated transpression. More widespread, however, is a horizontal lineation within the same foliation that is interpretedmore »