Volcanism of the Late Silurian Eastport Formation of the Coastal Volcanic Belt, Passamaquoddy Bay, New Brunswick: GAC–MAC Halifax 2022 Pre-Meeting Field Trip

This field trip is an excursion through the exquisite, nearly pristine exposures of a Silurian, felsic-dominated bimodal volcanic and sedimentary sequence exposed in the Passamaquoddy Bay area of southwestern, New Brunswick (Eastport Formation). These rocks form the northwest extension of the Coastal Volcanic Belt that extends from southwestern New Brunswick to the southern coast of Maine. The sequence is significant because it is part of a large bimodal igneous province with evidence for supervolcano-scale eruptions that began to form during the close of the Salinic Orogeny (about 424 Ma), and continued into the Acadian Orogeny (421–400 Ma). The geochemical characteristic of the rocks can be explained by extension related volcanism but the specific drivers of the extension are uncertain. The Passamaquoddy Bay sequence is 4 km thick and comprises four cycles of basaltic-rhyolitic volcanism. Basaltic volcanism typically precedes rhyolitic volcanism in Cycles 1–3. Cycle 4 represents the waning stages of volcanism and is dominated by peritidal sediments and basaltic volcanics. A spectrum of eruptive and emplacement mechanisms is represented ranging from the Hawaiian and Strombolian-type volcanism of the basaltic flows and pyroclastic scoria deposits, to highly explosive sub-Plinian to Plinian rhyolitic pyroclastic eruptions forming pyroclastic density currents (PDC) and high grade rheomorphic ignimbrites. During this field trip we will examine key exposures illustrating this spectrum of eruptive and emplacement processes, and their diagnostic characteristics, along with evidence for the interaction between mafic and felsic magmas and a variety of peperitic breccias formed as a result of emplacement of flows on wet peritidal sediments. The constraints the depositional setting and voluminous bimodal volcanism places on tectonic models will also be considered.Cette sortie sur le terrain est une excursion à travers les magnifiques affleurements pratiquement non altérés d'une séquence volcanique et sédimentaire bimodale silurienne à dominance felsique exposée dans la région de la baie de Passamaquoddy, au sud-ouest du Nouveau-Brunswick (Formation d'Eastport). Ces roches forment le prolongement nord-ouest de la Ceinture volcanique côtière qui s'étend du sud-ouest du Nouveau-Brunswick à la côte sud du Maine. La séquence est importante car elle fait partie d'une grande province ignée bimodale comprenant des preuves de super éruptions volcaniques qui ont commencé à se former à la fin de l'orogenèse salinique (environ 424 Ma) et se sont poursuivies pendant l'orogenèse acadienne (421–400 Ma). La caractéristique géochimique des roches peut être expliquée par le volcanisme lié à l'extension, mais les facteurs spécifiques de l'extension sont incertains. La séquence de la baie de Passamaquoddy a une épaisseur de 4 km et comprend quatre cycles de volcanisme basaltique-rhyolitique. Le volcanisme basaltique précède généralement le volcanisme rhyolitique dans les cycles 1–3. Le cycle 4 représente les stades décroissants du volcanisme et est dominé par des sédiments péritidaux et des roches volcaniques basaltiques. Une variété de mécanismes éruptifs et de mises en place est représentée, allant du volcanisme de type hawaïen et strombolien des coulées basaltiques et des dépôts de scories pyroclastiques, aux éruptions pyroclastiques rhyolitiques hautement explosives sous-pliniennes à pliniennes formant des courants de densité pyroclastiques et des ignimbrites rhéomorphes à haute teneur. Au cours de cette visite sur le terrain, nous examinerons les affleurements clés illustrant cette gamme de processus éruptifs et de mises en place, et leurs caractéristiques diagnostiques, ainsi que les preuves de l'interaction entre les magmas mafiques et felsiques et une variété de brèches pépéritiques formées à la suite de la mise en place de coulées sur des sédiments péritidaux humides. Les contraintes que le contexte de dépôt et le vaste volcanisme bimodal imposent aux modèles tectoniques seront également examinées

South China Sea Rifted Margin Testing hypotheses for lithosphere thinning during continental breakup: Drilling at the South China Sea rifted margin

International Ocean Discovery Program Expedition 368 is the second of two consecutive cruises that form the South China Sea Rifted Margin program. Expeditions 367 and 368 share the common key objectives of testing scientific hypotheses of breakup of the northern South China Sea (SCS) margin and comparing its rifting style and history to other nonvolcanic or magma-poor rifted margins. Four primary sites were selected for the overall program: one in the outer margin high (OMH) and three seaward of the OMH on distinct, margin-parallel basement ridges. These three ridges are informally labeled A, B, and C. They are located within the continent-ocean transition (COT) zone ranging from the OMH to the interpreted steady-state oceanic crust (Ridge C) of the SCS. The main scientific objectives include 1. Determining the nature of the basement within crustal units across the COT of the SCS that are critical to constrain style of rifting, 2. Constraining the time interval from initial crustal extension and plate rupture to the initial generation of igneous ocean crust, 3. Constraining vertical crustal movements during breakup, and 4. Examining the nature of igneous activity from rifting to seafloor spreading. In addition, the sediment cores from the drill sites targeting primarily tectonic and basement objectives will provide information on the Cenozoic regional environmental development of the Southeast Asia margin. Expedition 368 was planned to drill at two primary sites (U1501 and U1503) at the OMH and Ridge C, respectively. However, based on drilling results from Expedition 367, Expedition 368 chose to insert an alternate site on Ridge A (Site U1502). In total, the expedition completed operations at four sites (U1501, U1502, U1504, and U1505). Site U1503, however, was not completed beyond casing to 990 m because of mechanical problems with the drilling equipment that limited the expedition from 25 May 2017 to the end of the expedition to operate with a drill string not longer than 3400 m. New alternate Site U1504 proposed during Expedition 367 met this condition. Site U1505 also met the operational constraints of the 3400 m drill string (total) and was an alternate site for the already drilled Site U1501. At Site U1501, we cored to 697.1 m in 9.4 days, with 78.5% recovery. We also drilled ahead for 433.5 m in Hole U1501D and then logged downhole data from 78.3 to 399.3 m. In 19.3 days at Site U1502, we penetrated 1679.0 m, set 723.7 m of casing and cored a total of 576.3 m with 53.5% recovery, and collected downhole log data from 785.3 to 875.3 m and seismic data through the 10¾ inch casing. At Site U1503, we penetrated 995.1 m, setting 991.5 m of 10¾ inch casing, but no cores were taken. At Site U1504, we took 40 rotary core barrel (RCB) cores over two holes. The cored interval between both holes was 277.3 m with 26.8% recovery. An 88.2 m interval was drilled in Hole U1504B. At Site U1505, we cored 668.0 m with 101.1% recovery. Logging data was collected from 80.1 to 341.2 m. Operations at this site covered 6.1 days. Except for Site U1505, we drilled to acoustic basement, which prior to the expedition, except for Site U1501, had been interpreted to be crystalline basement. A total of 6.65 days were lost due to mechanical breakdown or waiting on spare supplies for repair of drilling equipment. At Site U1501 on the OMH, coring ~45 m into the acoustic basement sampled highly lithified sandstone to conglomerate of presumed Mesozoic age overlain by siliciclastic Eocene pre- to synrift sediments of Oligocene age and topped by primarily carbonaceous postrift sediments of early Miocene to Pleistocene age. Site U1502 on Ridge A was cased to 723.7 m. At this site, we recovered 180 m of hydrothermally altered brecciated basalts comprising sheet and pillow lavas below deep-marine sediments of Oligocene to late Miocene age. Coring was not performed within the upper 380 m (~Pliocene-Pleistocene) at Site U1502. At Site U1503 on Ridge C, 991.5 m of casing was installed in preparation for the planned deep drilling to ~1800 m, but no coring was performed due to mechanical failures, and the site was abandoned without further activity. Coring at Site U1504 on the OMH ~45 km east of Site U1501 recovered metamorphic schist to gneiss (greenschist facies) below late Eocene (?) carbonate rocks (partly reef debris) and early Miocene to Pleistocene sediments. At Site U1505, we cored to 480.15 m through Pleistocene to late Oligocene mainly carbonaceous ooze followed at depth by early Oligocene to late Eocene siliciclastic sediments. Efforts were made at every drill site to correlate the core with the seismic data and seismic stratigraphic unconformities interpreted within the Eocene to Plio-Pleistocene sedimentary sequence prior to drilling. The predrilling interpretation of ages of these unconformities was in general confirmed by drilling results. As a result of the constraints on the length of drill string that could be deployed during the later part of Expedition 368, the secondary expedition objectives addressing the environmental history of the SCS and Southeast Asia received more focus than planned because these sites are located in shallower water depths and required less penetration depth. This forced change in emphasis, however, was without fatal consequences for the primary tectonic objectives. The two expeditions together provided solid evidence for a process of breakup that included vigorous synrift magmatism as opposed to the often-favored interpretation of the SCS margin as a magma-starved margin

Seismic stratigraphy of the central South China Sea basin and implications for neotectonics

Coring/logging data and physical property measurements from International Ocean Discovery Program Expedition 349 are integrated with, and correlated to, reflection seismic data to map seismic sequence boundaries and facies of the central basin and neighboring regions of the South China Sea. First-order sequence boundaries are interpreted, which are Oligocene/Miocene, middle Miocene/late Miocene, Miocene/Pliocene, and Pliocene/Pleistocene boundaries. A characteristic early Pleistocene strong reflector is also identified, which marks the top of extensive carbonate-rich deposition in the southern East and Southwest Subbasins. The fossil spreading ridge and the boundary between the East and Southwest Subbasins acted as major sedimentary barriers, across which seismic facies changes sharply and cannot be easily correlated. The sharp seismic facies change along the Miocene-Pliocene boundary indicates that a dramatic regional tectonostratigraphic event occurred at about 5 Ma, coeval with the onsets of uplift of Taiwan and accelerated subsidence and transgression in the northern margin. The depocenter or the area of the highest sedimentation rate switched from the northern East Subbasin during the Miocene to the Southwest Subbasin and the area close to the fossil ridge in the southern East Subbasin in the Pleistocene. The most active faulting and vertical uplifting now occur in the southern East Subbasin, caused most likely by the active and fastest subduction/obduction in the southern segment of the Manila Trench and the collision between the northeast Palawan and the Luzon arc. Timing of magmatic intrusions and seamounts constrained by seismic stratigraphy in the central basin varies and does not show temporal pulsing in their activities.Keywords: South China Sea, Neotectonism, Core-well-seismic integration, Seismic facies, Seismic stratigraphy, IODP Expedition 34

Geochemistry and source of ash layers in Bering Sea sediment at IODP site 323-U1341

IODP Expedition 323 to the Bering Sea drilled seven sites (U1339–U1345) with the aim of collecting high-resolution ocean and climate data for the last five million years. The Bering Sea has extremely high surface productivity allowing recovery of sediment with abundant microfossils and other paleoceanographic proxies. Sites were located along the slope edge of the Alaskan continental margin in the region of the Arctic gateway and Umnak Plateau, and on Bowers Ridge, a submarine high, formed by an extinct and submerged volcanic arc. Sediment cores recovered during IODP Expedition 323 contained numerous volcanic ash layers. This study concentrates on ash layers in Hole U1341B on the Bowers Ridge. This hole was about 600 m deep corresponding to an age at the bottom of the hole of approximately 3.9 Ma. Ash from U1341B was analysed for major and trace elements and the results compared with ash from surrounding volcanic sources and ash layers intersected in other drill holes in the region. The ash at Site U1341 varies in composition from felsic to mafic with a silica range from 40.35% to 79.90%. The high silica ashes cannot be matched with sources in Alaska or the Aleutians. While most siliceous ash from Japan has lower TiO₂, there are some ash layers that do overlap with the U1341B compositions, for example the Ah ash from Kikai caldera south of Kyushu. Basaltic and andesitic ash layers from U1341 are compared with volcanic ash analyses from the Aleutians, Alaska, Kamchatka and Japan. Some analyses overlap with analyses from Unimak Island in the Aleutians. Most analyses of Bering Sea ash have slightly higher TiO₂, FeO, and lower MgO compared to ash from nearby arc volcanoes.1 page(s

The University of the sea and the benefits to student learning of participation in a marine research expedition

The University of the Sea has provided university students from the Asia-Pacific region with experience on multi-week, marine research expeditions since 2004. The program is UNESCO-funded and generously supported by Geoscience Australia. During 2007 and 2008, students were surveyed to ascertain whether they felt the program was a valuable learning experience. The survey had both Likert-scaled and open-ended questions. The students enjoyed the experience, found it valuable, appreciated putting theory into practice, and liked the interaction with scientists. They gained skills and knowledge that will help guide their career paths. However, most felt they required more information prior to the expedition, and a greater knowledge of the research aims and their role in the expedition. Students incorrectly assumed the expedition would be tailored to their learning and would provide didactic learning experiences. They did not automatically see the experiential learning activity was valuable in itself.11 page(s

A high-nb OIB-like matic province in Northwestern NSW, Australia

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Using problem-based learning to bring the workplace into the classroom

A modified form of problem-based learning (PBL) with problems based on real workplace scenarios was trialled in a third year university class on Environmental Geology. Problems were developed in consultation with industry and based on their recent projects. These were then modified to allow for the shorter timeframe available, the less developed technical skills of the students, and their inability to collect data on working sites. Students worked in small “company” groups. Each problem required the students to produce a tender or request for proposal (RFP) document and a report based on the industry-standard guidelines. Problem topics included a preliminary investigation of a contaminated site, a geotechnical investigation of a landslide-prone area, and preparation of geological data for an environmental impact assessment of a proposed mine site. The unit was designed using PBL as this teaching format leads to increased student engagement with the subject matter and development of a range of graduate attributes. Our modified form of PBL provides a lecture series that gives background to the problems and in this instance, almost all lectures were given by industry representatives. Students enjoyed the overall format and the use of real workplace examples. Group work generally rated more poorly in the unit evaluation than expected. Working with industry brought new challenges largely due to the mobility and time commitments of industry representatives in a field-based and global industry.10 page(s

The ODP Undergraduate Student Trainee Program: Taking Part in Experiential Learning at Sea

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