Magmatic processes associated with caldera collapse at Ossipee ring dyke, New Hampshire

AbstractThe Palaeogene Slieve Gullion Igneous Complex comprises a layered central intrusion surrounded by a slightly older ring dyke. The ring dyke contains two major intrusive rock types. About 70% of the ring dyke is occupied by porphyritic granophyre and 30% by porphyritic felsite. Locally complex relationships between the two lithologies are observed. Major and trace element compositions suggest that there are two distinct chemical groups within each lithology: a Si-rich felsite, concentrated in a ~1 m wide zone at the outer margins of the dyke which grades into a less Si-rich felsite towards the interior. Similarly, a Si-rich granophyre, concentrated in the centre of the intrusion grades outwards into a Si-poor granophyre facies.These rock relationships and geochemical variations suggest that a complex magma chamber hosted a stratified granitic magma body and various wall/floor magma facies. Low density, high-Si felsite magma from the top of the chamber was tapped first, followed by less Si-rich felsite magma as evacuation proceeded. The granophyres probably originate from the chamber walls/floor, representing more mushy equivalents of the felsite magma. Little granophyre magma was tapped during the early stages of the evacuation sequence. As evacuation continued, probably aided by trap-door caldera collapse, the ‘granophyre magmas’ intruded the already emplaced and slightly cooled felsite, forming the complexly zoned structure of the Slieve Gullion ring intrusion.

Download Full-text

Characterization of the Outer Coast Tuff Formation- A way to unravelling the magmatic processes preceding and triggering Deception Island’s caldera - forming eruption (Antarctica)

10.5194/egusphere-egu21-2840 ◽

2021 ◽

Author(s):

Oriol Vilanova ◽

Meritxell Aulinas ◽

Adelina Geyer ◽

Joan Marti ◽

Antonio Álvarez-Valero ◽

...

Keyword(s):

Magma Mixing ◽

Austral Summer ◽

South Shetland Islands ◽

Caldera Collapse ◽

Deception Island ◽

The Past ◽

Magmatic Processes ◽

Magma System ◽

Research Initiatives ◽

Outer Coast

Deception Island (South Shetland Islands), discovered in 1820, is one of the most active volcanoes in Antarctica with more than 20 eruptions (including the historic eruptions of 1967, 1969 and 1970) and three documented volcanic unrest events (1992, 1999 and 2014-15) over the past two centuries. Deception Island currently hosts two scientific bases, which operate every year during the Austral summer, and is also one of the most popular tourist destinations in Antarctica. The island is a composite volcano with a centrally located caldera of 8.5 x 10 km dated at 3,980 &#177; 125 yr. BP. During the caldera-forming event, between 30 and 60 km3 (Dense Rock Equivalent-DRE) of magma, erupted in the form of dense basaltic-andesitic pyroclastic density current deposits. During the last decades, Deception Island has been intensively investigated but some aspects regarding the magmatic processes associated with the formation of its caldera collapse are still under research and debate. For instance, characterizing the magmatic conditions and processes that triggered the huge explosive event is crucial to understand the past (and in turn the future) magmatic and volcanic evolution of the island.This study is performing an exhaustive petrological and geochemical characterization (mineral and juvenile glass geochemistry) of the Outer Coast Tuff Formation (OCTF), the main syn-caldera depositional unit. The preliminary results confirm the existence of two different magmas coexisting, and interacting, prior to (and during) the caldera-forming event. Mineral analyses also allow shedding further light on the magmatic processes occurring in the magma system before the eruption (e.g. fractional crystallization, magma mixing). The presence of alteration minerals such as palagonite and zeolites indicate different magma-water interaction mechanisms occurred during the syn- and post-eruptive episodes in the island.This research is part of POLARCSIC and PTIVolcan research initiatives. This research was partially funded by the MINECO grants POSVOLDEC(CTM2016-79617-P)(AEI/FEDER-UE) and VOLGASDEC (PGC2018-095693-B-I00)(AEI/FEDER, UE). This research is also supported by the PREDOCS-UB grant.

Download Full-text

Malpractice & Negligence: State Supreme Courts Limit Therapists’ Duties to Third Parties

The Journal of Law Medicine & Ethics ◽

10.1017/s1073110500012985 ◽

1999 ◽

Vol 27 (2) ◽

pp. 204-205

Author(s):

Megan Cleary

Keyword(s):

Sexual Abuse ◽

Child Sexual Abuse ◽

Supreme Court ◽

New Hampshire ◽

Third Parties ◽

State Supreme Courts ◽

Recovered Memories ◽

Supreme Courts ◽

Repressed Memory ◽

University Of Colorado

In recent years, the law in the area of recovered memories in child sexual abuse cases has developed rapidly. See J.K. Murray, “Repression, Memory & Suggestibility: A Call for Limitations on the Admissibility of Repressed Memory Testimony in Abuse Trials,” University of Colorado Law Review, 66 (1995): 477-522, at 479. Three cases have defined the scope of liability to third parties. The cases, decided within six months of each other, all involved lawsuits by third parties against therapists, based on treatment in which the patients recovered memories of sexual abuse. The New Hampshire Supreme Court, in Hungerford v. Jones, 722 A.2d 478 (N.H. 1998), allowed such a claim to survive, while the supreme courts in Iowa, in J.A.H. v. Wadle & Associates, 589 N.W.2d 256 (Iowa 1999), and California, in Eear v. Sills, 82 Cal. Rptr. 281 (1991), rejected lawsuits brought by nonpatients for professional liability.

Download Full-text