Developing landslide chronologies using landslide-dammed lakes in the Oregon Coast Range

ABSTRACT The Oregon Coast Range is a dynamic landscape that is continually shaped by shallow and deep-seated landslides that can have disastrous consequences to infrastructure and human lives. Searching for evidence of potentially coseismic mass wasting is incredibly difficult, particularly when historical observations are limited. Landslide-dammed lakes with submerged “ghost forests” in the Oregon Coast Range present the unique opportunity to establish landslide chronologies with subannual accuracy when dendrochronology is applied. This field guide will visit the unique landslide-dammed Klickitat Lake and explore a drowned ‘ghost forest’ to discuss methods used to establish a prehistoric landslide chronology in western Oregon, USA. After exploring the lake and exposing its geomorphic secrets, the guide will end with a stop on Marys Peak, a mafic volcanic intrusion composed of gabbroic dikes and pillow basalt that forms the highest point in the Oregon Coast Range. With the landscape of western Oregon laid out before us, we will discuss short- and long-term geomorphic evolution of the Oregon Coast Range and Willamette Valley.

Raman estimates of the thermal effect on tree trunks in the Siberian Traps lavas and volcaniclastics

<p>Tree trunks in lava flows and volcaniclastics of the Siberian Traps witness volcanic activity's violent and rapid onset. Carbonized and petrified trees preserve the peak metamorphic temperatures, which can be estimated using Raman spectroscopy. We have conducted a Raman study of the tree trunks and wooden fragments trapped in the Siberian Traps volcaniclastics and lavas on the Tunguska basin's northwestern region (Norilsk area). The first sample set was taken from volcaniclastic rocks of the Kureika River. The second sample set was collected from the lowermost lava flow of Ivakinskaya Formation that erupted directly on the end-Permian boggy surface (Tunguska Group of Carboniferous-Permian age) and from the coal-bearing inter lava seam at Red Rocks outcrop near Talnakh. The third sample set was taken from in the basal part of the Ivakinskaya Fm lowermost lava flow erupted in a shallow water basin with pillow basalt formation (Ore Brook near Norilsk). The fourth sample set was taken from an open coal pit with shallow dolerites intruded into the late Permian part of the Tunguska Group (near Kajerkan). We analyzed carbonized wood with a Renishaw InVia Qontor with 532 nm laser and processed all spectra with Henry et al. (2018) recommendations. The peak metamorphic temperature was calculated from Deldicque et al. (2016) equation 2. The tree trunks of the first sample set (Kureika River volcaniclastics) have a narrow median temperature range (430-468oC with one sample of 612oC). The second sample set from tree trunks in lavas and the coal-bearing inter lava seam (Red Rocks near Talnakh) ranges between 343-658oC and 742-764oC. The third sample set from pillow basalt at the basal part of Ivakinskaya Fm. (Ore Brook near Norilsk) also has a narrow temperature range (503-535oC with one sample of 650oC). The last sample set from the open coal pit (near Kajerkan) has a wide median temperature range (388-632oC).</p><p>We explain these variations by different styles of the Siberian Traps eruption. At the Kureika River, the end-Permian forest was buried and carbonized by tephra. At the Talnakh area, lava flow erupted on the boggy surface, whereas in the Norilsk area, the lava flow erupted into the freshwater basin.</p><p> </p><p>Henry, D.G. et al. (2018). Int. J Coal Geol, 191: 135-151</p><p>Deldicque, D. et al. (2016). Carbon, 102: 319-329</p>

Determination of the microscopic mineralogy of inclusion in an amygdaloidal pillow basalt by fs-LIMS

Depth profiling and atomic intensity correlation studies on mineralogical inclusion embedded in calcium carbonate phase using a miniature laser mass spectrometer are presented. The method allows the determination of complex mineralogical phases.

Hyaloclastite formation during the effusion of the first lava flows of Siberian traps into a shallow freshwater basin

<p>Hyaloclastites have long been described within numerous volcaniclastic sequences in the Siberian Traps Large Igneous Province. They are typical for the southern and central parts of the Tunguska basin, and we inspected them in 2004-2010. In recent years, we have focused our attention on the northwestern region of the Tunguska basin (Norilsk area) with a volumetric manifestation of basaltic lava flows. We have completed fieldwork in this region from 2006 to 2019, with a recent focus on the understanding of the emplacement environments for the lowermost lava flow erupted directly on the end-Permian boggy surface. We studied pillow basalt at the basal part of the lowermost lava flow in the Norilsk region (Ivakinskaya Formation). In the upper part of this pillow basalt horizon, hyaloclastite is very common, and at the basal part, several tree trunks occur. The hyaloclastite includes black equant angular clasts and rusty red matrix and easily recognize at any outcrops. We studied hyaloclastite with optical microscopy and SEM-EDS. Black clasts composed of sideromelane cracked and altered to palagonite. Sideromelane fragments include crystals of olivine (Fo70), plagioclase (An63-70), and likely OPx altered to chlorite. Sideromelane glass has a basalt composition with elevated P2O5, CaO, and decreased amount of MgO and minor halogens (F, Cl). Some sideromelane clasts bear round inclusions (blobs) entirely infill with dolomite, siderite, and calcite. Every single carbonate inclusion has a specific structure and minerals infill.</p><p>We interpret these hyaloclastite rocks formations with carbonate inclusions as a result of lava flow effusion onto the shallow freshwater basin or boggy surface. Water and organic-rich sediments transferred with an explosion to steam and carbon dioxide gas, and this gas mixture was formed a hyaloclastite horizon at the basal part of a lava flow. We suppose that these sideromelane clasts with carbonate blobs are additional evidence of greenhouse gas generation during the early stage of the Siberian Traps lavas eruption.</p>

Petrology and Geochemistry of Gole Pillow Basalt in Penjween area Kurdistan Region- NE Iraq

The petrological, morphometric and geochemical analyses of pillow lava from Gole village (Penjween town) Sulaimani city Northeastern Iraq have been undertaken. The Gole Pillow basalt (GPB) extruded, in the form of pillow and sheet flow into the Qulqula radiolarite Formation. The basaltic intrusion restricted to a small area of about 100 m2 within Penjween- Walash zone in the Zagros Suture Zone (ZSZ) of Iraq. The investigated area divided into two sections GPB1 and GPB2. It is envisaged that the studied area distinct two episodes of submarine alkaline eruptions that produced pillowed lavas that differently interacted with seawater to produce different morphologies and geochemistries. The pillows of the GPB1 section well exposed all along the Shalair river near Gole village. Although the pillows of the GPB2 section altered due to low-grade metamorphism and late hydrothermal processes, their igneous textures are still preserved. GPB samples are mostly phyric in nature and show porphyritic or sub-ophitic textures. Petrographically, most of the GPB rock samples appeared as amygdaloidal and vesicular aphanitic basalt. Large phenocryst of hypersthene with schiller structure is present within a matrix of longer quenched plagioclase. Numerous small euhedral grains of opaque minerals like ilmenite and hematite are dispersed in the fine groundmass. Morphological features show that the GPB appeared as spheroidal and lobate to tubular individual pillows. Although some pillow extends 2 meters with a foreset distribution some others show cracked with irregularly jointed surface and larger vesicles partly filled with calcite and quartz. Geochemical investigation of GPB exhibit high TiO2 (3.42 – 3.84 wt.%), Fe2O3 (14.84–19.93 wt.%), and high Zr/Nb and Zr/Y ratios respectively (5.85 – 7.2) (7.10-11.40). The content of alkalies, with the Nb/Y ratio≥1.4, and silica, as well as many trace element discrimination diagrams, classify the GPB as alkaline basalts. The field, stratigraphic relationships, and geochemistry of the GPB and associated clastic and carbonate sediments suggest that the pillow lavas were emplaced in a shallow marine marginal within plate basin. The overall geochemistry of GPB resembles that of alkaline basalts generated in within-plate ocean island settings (OIB-type). http://dx.doi.org/10.25130/tjps.24.2019.131

Geology and geochemistry of pillow basalt in the Huilvshan region (west Junggar, China): implications for magma source and tectonic setting

Geological characteristics and geochemical analyses are reported for the early Carboniferous pillow basalt in the Huilvshan region (west Junggar, Northwest China), with the aim to indicate its petrogenesis, magma source characteristics, and tectonic implication. This pillow basalt consists of clinopyroxene and plagioclase with trace amounts of magnetite, apatite, and chromian spinel. It is tholeiitic in composition with low concentrations of Na2O + K2O (1.52–4.74 wt.%). Similar to the N-MORB, the samples of this pillow basalt have nearly flat chondrite-normalized REE patterns ((La/Yb)N = 0.87–1.47) with insignificant Eu anomalies (Eu/Eu* = 0.84–1.18), and show no obvious enrichments of LILEs and insignificant depletions in HFSEs. Petrology and geochemical characteristics suggest that this pillow basalt is the product of MORB-like magma derived from a depleted mantle corresponding to ≤4% partial melting of spinel lherzolite. SIMS analysis of the zircons separated from tuff interlayered with basalt gives a weighted average U–Pb age of 328 ± 3 Ma (MSWD = 1.4), which represents the magma eruption time in the Huilvshan region. From these observations, in combination with the previous work, we conclude that an extensional tectonic regime dominated the tectonic activity of west Junggar during early Carboniferous.

Lillooet Glacier basalts, southwestern British Columbia, Canada: products of Quaternary glaciovolcanism

The retreat of Lillooet Glacier (LG) has exposed a succession of pillow basalt and subordinate amounts of breccia and hyaloclastite. The lithofacies and physiographic setting suggest that the deposits have a glaciovolcanic origin and represent a partially dissected basaltic pillow-dominated tindar. Chemically, the LG volcanic rocks are basalt to basaltic andesite, and, as a group, they represent the highest-silica, Quaternary mafic products in the Garibaldi volcanic belt (GVB). Like other northern GVB (alkaline) basalts, they lack the Nb–Ta depletion signature typically associated with subduction-related products. Geochemical and petrologic analysis indicates that the LG basalts are comagmatic and that chemical variations within the suite are consistent with sorting of the observed phenocryst assemblage: olivine + plagioclase. Thermodynamic modeling establishes shallow, crustal, pre-eruptive storage conditions at <2 kbar (1 kbar = 100 MPa; or 7.5 km) and an H2O content of 0.5–1 wt.%. We estimate that the LG basalts were erupted at the peak of, or during the waning stages of, Fraser glaciation (17–13 ka). The eruption produced an englacial lake that was >150 m deep and that appears to have been sustained throughout the entire eruption (i.e., no discernible passage zone). Using hydrostatic constraints, we calculate a minimum overlying paleo-ice thickness of >645 m and a paleo-ice surface elevation of >1895 m above sea level.