Cold avalanche, “super subduction”, mantle overturn, followed by buoyant subduction of an oceanic plateau and the formation of TTG´s during the Eocene in Viti Levu, Fiji islands

<p>Tonalite, Trondhjemite, Granodiorite (TTG) rocks in Viti Levu, Fiji islands formed through hydrous melting of gabbroic oceanic crust at low-pressure amphibolite-facies conditions caused by flat subduction of an oceanic plateau from Yavuna creek. During mid Miocene time, magmatic underplating took place and a Qtz-diorite unit was formed out of the gabbro under granulite-facies conditions. The investigated TTG´s occur as stocks and veins within the older gabbroic unit of the Yavuna Pluton.</p><p>Zircon ages show the parental gabbro to be ~47.5 Ma in age, whereas the TTG´s, which can be subdivided into a tonalite and a Qtz-diorite suite, are ~37.1 Ma and ~16.5 Ma, old respectively. The average d<sup>18</sup>O value of ~4.8 in zircon selected from the parental gabbro and the tonalite suggest a very homogenous mantle source. However, about 50% of the analyzed zircons from the gabbroic and tonalitic rock samples showing lower d<sup>18</sup>O values, and these are interpreted as reflecting interaction of hydrothermally altered seafloor with the deep depleted mantle source. eHf in zircon values of ~13 in the analyzed TTG´s are interpreted as reflecting typical juvenile continental crust. PerpleX whole-rock calculations suggest that the tonalite formed by melting of the gabbro through decompression under water-saturated amphibolite-facies conditions at a temperature of ~770 °C and a pressure of ~3.8 kbar, whereas the Qtz-diorite formed at a temperature up to ~900 °C at very shallow depth close to the Earth’s surface caused by the emplacement of a magmatic underplate during the mid Miocene. Our investigation provides new evidence for episodic growth of continental crust < 0.1 Ga in the South Pacific region.</p>

Genesis of Syntectonic Hydrothermal Veins in the Igneous Rock of Teschenite Association (Outer Western Carpathians, Czech Republic): Growth Mechanism and Origin of Fluids

Hydrothermal mineralization hosted by the Lower Cretaceous igneous rock of the teschenite association at Jasenice (Silesian Unit, Flysch Belt, Outer Western Carpathians) occurs in two morphological types - irregular vein filled by granular calcite and regular composite vein formed by both fibrous and granular calcite and minor chlorite, quartz, and pyrite. Crosscutting evidence indicates that the granular veins are younger than the composite vein. The composite vein was formed by two mechanisms at different times. The arrangement of solid inclusions in the marginal fibrous zone suggests an episodic growth by the crack-seal mechanism during syntectonic deformation which was at least partially driven by tectonic suction pump during some stages of the Alpine Orogeny. Both the central part of the composite vein and monomineral veins developed in a brittle regime. In these cases, the textures of vein suggest the flow of fluids along an open fracture. The parent fluids of both types of vein are characterized by low temperatures (Th=66-163 °C), low salinities (0.4 to 3.4 wt. % NaCl eq.), low content of strong REE-complexing ligands, and δ18O and δ13C ranges of + 0.2/+12.5 %. SMOW and -11.8/-14.1 %. PDB, respectively. The parent fluids are interpreted as the results of mixing of residual seawater and diagenetic waters produced by dewatering of clay minerals in the associ-ated flysch sediments. The flow of fluids was controlled by tectonic deformation of the host rock.

4. The resulting structure—a reef

‘The resulting structure—a reef’ shows that coral reef profiles, composed of reef flats, reef crests, and reef slopes, are remarkably consistent. The general structure is complicated by shifts of sea level over geological time, so the basic pattern will have superimposed upon it evidence of episodic growth and erosion. The environmental conditions on the reef slope are ideal for most corals and other reef life including the soft corals and sponges, so this is where most species are found. The cryptic, or hidden, life of the coral reefs is discussed along with the rugosity of the corals, and the structure and life of the sand in the back reef area.

Historical Set Points and the Development of U.S. Presidential Emergency Power

The recent outpouring of work on executive power during emergencies, inspired by the post-9/11 era, has significantly enhanced our legal and theoretical understanding of this crucial subject. A key flaw in this literature, however, is that it is historically un-rooted, either dismissing or ignoring important analytical and empirical insights from presidential research and from APD and historical-institutionalist perspectives. In this article, I argue that we can better explain patterns and variations in the use of presidential emergency power by paying careful attention to shifting historical set points for executive choice and action during security crises. In particular, the findings here underscore the episodic growth of new precedents, resources, and expectations for the White House in perilous contexts. The development of presidential emergency power reflects the potential for early executive choices to be repeated and legitimated over time, laying dormant as a “loaded weapon” to be used by future executives in similarly urgent circumstances.