Geodetical and seismological evidences of stress transfer between Mauna Loa and Kilauea

<p>Different studies evidenced an anticorrelated pattern behavior the activity of Mauna Loa and Kilauea  volcanoes. We quantitatively demonstrate the existence of this pattern by using DInSAR SBAS time series, areal strain of horizontal GPS components and the spatial distribution of hypocenters. The DInSAR time series have been studied by using the Independent Component Analysis (ICA) statistical algorithm revealing an anticorrelated ground deformation pattern between sources located at shallow depths beneath Mauna Loa and Kilauea. Furthermore, ICA showed another independent source beneath Kilauea alone, being located at greater depth. A similar pattern was observed in the time series of areal strain of GPS data as well as by spatial distribution of earthquakes depths.</p><p>The anticorrelated behaviour of both volcanoes, has been explained by the crustal-level interaction of pulses of magma that cause pressure variations in shallow magma system [1]. Another explanation for this peculiar behaviour is due to the interaction by pore pressure diffusion in a thin accumulation layer of the asthenosphere [2]. Geochemical and petrological studies [5] however, points at the existence of separate reservoirs for Mauna Loa and Kilauea.</p><p>The aim of this work is to explain the mechanism that allows the crustal-level relationship between shallow ground deformation sources of both volcanoes. We applied inverse modelling to determine the geometries of the magmatic reservoirs beneath Mauna Loa and Kilauea and their dynamics. This method revealed to be a useful tool to better understand the dynamics and represent the interaction between Mauna Loa and Kilauea.  </p><p>Our results indicate that the interaction between ground deformation sources of Mauna Loa and Kilauea occurs at shallower depths, therefore we excluded a direct interconnection between their magmatic systems and, instead, we postulate a stress transfer mechanism that explain this interaction. This mechanism has been postulated by several authors to explain the intrusions along rift zones and the interaction between earthquakes and eruptions in these two volcanoes [3, 4]. The magma ascent in Mauna Loa edifice creates a stress field in Kilauea which makes more difficult for the magma to ascent into its shallower reservoir. The same mechanisms could act in an opposite scenario.</p><p>[1] A. Miklius and P. Cervelli, “Interaction between Kilauea and Mauna Loa,” Nature, vol. 421, no. 6920, pp. 229–229, 2003.</p><p>[2] H. M. Gonnermann, J. H. Foster, M. Poland, C. J. Wolfe, and B. A. Brooks, “Coupling at Mauna Loa and Kilauea by stress transfer in an asthenospheric melt layer,” Nat. Geosci., vol. 5, no. 11, pp. 826–829, 2012.</p><p>[3] P. Amelung, F., Yun, S.H, Walter, T. and Segall, “Stress Control of Deep Rift Intrusion at Mauna Loa Volcano, Hawaii,” Science (80-. )., vol. 316, no. MAY, pp. 1026–1030, 2007.</p><p>[4] D.A. Swanson, W. A. Duffield, and R.S. Fiske, “Displacement of the south flank of Kilauea Volcano: the result of forceful intrusion of magma into the rift zones,” U.S. Geol. Surv. Prof. Pap. 963, p. 39 p.1976.</p><p>[5] J.M. Rhodes and S. R. Hart, “Episodic trace element and isotopic variations in historical mauna loa lavas: Implications for magma and plume dynamics,” Geophys. Monogr. Ser.,vol. 92, pp. 263–288,1995.</p>

Polyphase deformation and metamorphism of the Cuiabá group in the Poconé region (MT), Paraguay Fold and Thrust Belt: kinematic and tectonic implications

Several deformation models have been proposed for the Paraguay Belt, which primarily differ in the number of phases of deformation, direction of vergence and tectonic style. Structural features presented in this work indicate that the tectonics was dominated by low dip thrust sheets in an initial phase, followed by two progressive deformation phases. The first phase of deformation is characterized by a slate cleavage and axial plane of isoclinal recumbent folds with a NE axial direction, with a recrystallization of the minerals in the greenschist facies associated with horizontal shear zones with a top-to-the-SE sense of movement. The second stage shows vergence towards the NW, characterized by crenulation cleavage axial plane to F2 open folds over S0 and S1, locally associated with reverse faults. The third phase of deformation is characterized by subvertical faults and fractures with a NW direction showing sinistral movement, which are commonly filled by quartz veins. The collection of tectonic structures and metamorphic paragenesis described indicate that the most intense deformation at the deeper crustal level, greenschistfacies, occurred during F1, which accommodated significant crustal shortening through isoclinal recumbent folds and shear zones with low dip angles and hangwall movement to the SE, in a thin-skinned tectonic regime. The F2 deformation phase was less intense and had a brittle to ductile behavior that accommodated a slight shortening through normal open subvertical folds, and reverse faults developed in shallower crustal level, with vergence towards the Amazonian Craton. The third phase was less pervasive, and the shortening was accommodated by relief subvertical sinistral faults.

Origin and tectonometamorphic history of the Repulse Bay block, Melville Peninsula, Nunavut: exotic terrane or deeper level of the Rae craton?

The Rae craton on Melville Peninsula, Nunavut, comprises several lithotectonic domains, including a structurally and lithologically distinct yet poorly known crustal terrane, the Repulse Bay block (RBb). This study presents new lithological and petrographic observations, combined with U–Pb zircon data, to better understand the Archean and Paleoproterozoic crustal evolution of the RBb. The new data demonstrate that the central-eastern RBb consists of the following: (i) upper amphibolite- to granulite-facies, ca. 2.73–2.71 Ga intermediate granitoid gneisses and gabbroic sheets; (ii) ca. 2.69 Ga two-pyroxene charnockite to enderbite intrusions; and (iii) thin slivers of both Archean and Paleoproterozoic supracrustal rocks. Inherited zircon also attests to the presence of a Mesoarchean to Paleoarchean substrate. A semi-pelitic gneiss from one of the Paleoproterozoic supracrustal panels was deposited sometime after ca. 1.89 Ga and shows a similar detrital zircon age profile to a <1.92 Ga semi-pelitic gneiss from the Lyon Inlet boundary zone at the northern extent of the RBb. Zircon in most rocks analyzed record metamorphism related to the Trans-Hudson orogeny between ca. 1.84 and 1.82 Ga. Results from this study are most consistent with the RBb, representing a piece of lower to middle crustal level of the Rae craton, rather than a distinct and separate crustal entity (i.e., an exotic block).