Mount Morning Research Articles

Laser heating effect on Raman analysis of CO2 co-existing as liquid and vapor in olivine-hosted melt inclusion bubbles

Raman spectroscopy has become the tool of choice for analyzing fluid inclusions and melt inclusion (MI) vapor bubbles as it allows the density of CO2-rich fluids to be quantified. Measurements are often made at ambient temperature (Tamb ~18-25 °C), resulting in reported bulk densities between 0.2 and 0.7 g/mL despite that single-phase CO2 under these conditions is thermodynamically unstable and instead consists of a liquid (~0.7 g/mL), and a vapor phase (~0.2 g/mL). Here, we present results from experiments conducted at Tamb and 37 °C (above the CO2 critical temperature) on 14 natural CO2-rich MI bubbles from Mount Morning, Antarctica. Here, we show that at Tamb, laser power strongly affects the CO2 Raman spectrum of MI bubbles with bulk densities within the miscibility gap. High-power laser heating and low spectral resolution explain why published measurements have reported such bulk densities at Tamb even when using an instrument-specific calibration.

Eruptive history of Mason Spur, a Miocene—Pleistocene polygenetic volcanic complex in southern Victoria Land, West Antarctic Rift System, Antarctica

Mason Spur is a deeply eroded Middle Miocene to Pleistocene (c. 13 to 0.37 Ma) volcanic complex in southern Victoria Land, within the West Antarctic Rift System (WARS). The oldest rocks include a large volume of trachyte ignimbrites that provided abundant volcanic detritus recovered in McMurdo Sound drill cores. The ignimbrites together with early-formed intrusions were strongly deformed during a substantial caldera collapse at c. 13 Ma. Intense erosion modified the volcanic landscape, creating a paleo-relief of several hundred metres. Deep ravines were cut and filled by deposits of multiple lahars probably linked to gravitational collapses of trachyte dome(s). Small-volume trachytic magmas were also erupted, forming lavas and at least one tuff cone. The youngest trachytic activity comprises a lava dome and related block-and-ash-flow deposits, erupted at 6 Ma. Basanite erupted throughout the history of the complex and eruptions younger than 12 Ma are almost exclusively basanite, forming scoria cones, water-cooled lavas, and tuff cones. Three peripheral outcrops are composed of basanitic ‘a‘ā lava-fed deltas, probably erupted from vents on neighbouring volcanoes at Mount Discovery and Mount Morning. Abundant ignimbrite deposits at Mason Spur differentiate this volcanic complex from others in the WARS. Eruptions were triggered by rift extension initially, yielding the voluminous trachytes sourced from a magma chamber on the margin of the WARS. Later mafic eruptions were associated with deep crustal faults related to residual intraplate deformation. These results add important details to the eruptive history of the intracontinental WARS.

Chapter 5.2a Erebus Volcanic Province: volcanology

Abstract The Erebus Volcanic Province is the largest Neogene volcanic province in Antarctica, extending c. 450 km north–south and 170 km wide east–west. It is dominated by large central volcanoes, principally Mount Erebus, Mount Bird, Mount Terror, Mount Discovery and Mount Morning, which have sunk more than 2 km into underlying sedimentary strata. Small submarine volcanoes are also common, as islands and seamounts in the Ross Sea (Terror Rift), and there are many mafic scoria cones (Southern Local Suite) in the Royal Society Range foothills and Dry Valleys. The age of the volcanism ranges between c. 19 Ma and present but most of the volcanism is <5 Ma. It includes active volcanism at Mount Erebus, with its permanent phonolite lava lake. The volcanism is basanite–phonolite/trachyte in composition and there are several alkaline petrological lineages. Many of the volcanoes are pristine, predominantly formed of subaerially erupted products. Conversely, two volcanoes have been deeply eroded. That at Minna Hook is mainly glaciovolcanic, with a record of the ambient mid–late Miocene eruptive environmental conditions. By contrast, Mason Spur is largely composed of pyroclastic density current deposits, which accumulated in a large mid-Miocene caldera that is now partly exhumed.

Petrogenesis of the Rifted Southern Victoria Land Lithospheric Mantle, Antarctica, Inferred from Petrography, Geochemistry, Thermobarometry and Oxybarometry of Peridotite and Pyroxenite Xenoliths from the Mount Morning Eruptive Centre

The lithospheric mantle beneath West Antarctica has been characterized using petrology, whole- rock and mineral major element geochemistry, whole-rock trace element chemistry and Mossbauer spectroscopy data obtained on a suite of peridotite (lherzolite and harzburgite) and pyr- oxenite xenoliths from the Mount Morning eruptive centre, Southern Victoria Land. The timing of pyroxenite formation in Victoria Land overlaps with subduction of the Palaeo-Pacific plate beneath the Gondwana margin and pyroxenite is likely to have formed when fluids derived from, or modi- fied by, melting of the subducting, eclogitic, oceanic crustal plate percolated through peridotite of the lithospheric mantle. Subsequent melting of lithospheric pyroxenite veins similar to those repre- sented in the Mount Morning xenolith suite has contributed to the enriched trace element (and iso- tope) signatures seen in Cenozoic volcanic rocks from Mount Morning, elsewhere in Victoria Land and Zealandia. In general, the harzburgite xenoliths reflect between 20 and 30% melt depletion. Their depleted element budgets are consistent with Archaean cratonization ages and they have mantle-normalized trace element patterns comparable with typical subcontinental lithospheric mantle. The spinel lherzolite mineral data suggest a similar amount of depletion to that recorded in the harzburgites (20-30%), whereas plagioclase lherzolite mineral data suggest <15% melt deple- tion. The lherzolite (spinel and plagioclase) xenolith whole-rocks have compositions indicating <20% melt depletion, consistent with Proterozoic to Phanerozoic cratonization ages, and have mantle-normalized trace element patterns comparable with typical depleted mid-ocean ridge man- tle. All peridotite xenoliths have undergone a number of melt-rock reaction events. Melting took place mainly in the spinel peridotite stability field, but one plagioclase peridotite group containing high-sodium clinopyroxenes is best modelled by melting in the garnet field. Median oxygen fuga- city estimates based on Mossbauer spectroscopy measurements of spinel and pyroxene for spinel- facies conditions in the rifted Antarctic lithosphere are -0� 6 Dlog fO2 at Mount Morning and -1� 0 6 0� 1( 1r) Dlog fO2 for all of Victoria Land, relative to the fayalite-magnetite-quartz buffer.

Early Miocene Antarctic glacial history: new insights from heavy mineral analysis from ANDRILL AND-2A drill core sediments

The present study deals with heavy mineral analysis of late Early Miocene marine sediments recovered in the McMurdo Sound region (Ross Sea, Antarctica) during the ANDRILL—SMS Project in 2007. The main objective is to investigate how heavy mineral assemblages reflect different source rocks and hence different provenance areas. These data contribute to a better understanding of East Antarctica ice dynamics in the Ross Sea sector during the Early Miocene (17.6–20.2 Ma), a time of long-term global warming and sea level rise. The AND-2A drill core recovered several stratigraphic intervals that span from Early Miocene to Pleistocene and it collected a variety of terrigenous lithologies. The heavy mineral assemblages of the lower 650-m-thick sedimentary succession were analyzed through SEM observations and SEM–EDS microanalyses on heavy mineral grains. The heavy mineral analysis shows that the sediments are a mix of detritus dominated by McMurdo Volcanic Group sources most likely located in the present-day Mount Morning area (Proto-Mount Morning) with minor contribution from Transantarctic Mountains source rocks located west of the drill site. The heavy mineral assemblages in Interval 1 indicate that between 20.2 and 20.1 Ma, the grounding line of the ice sheet advanced to a position near the present-day Mount Morning volcanic center. During deposition of Interval 2 (20.1–19.3 Ma), the ice sheet most likely experienced a dynamic behavior with interval of ice advance alternating with periods of ice retreat, while Interval 3 (19.3–18.7 Ma) records further retreat to open water conditions. A dynamic behavior is noted in Interval 4 (18.7–17.6 Ma) with a decreasing contribution of materials derived from the basalts of the Mount Morning volcanic center located to the south of the drill site and a consequent increasing contribution of materials derived from the Transantarctic Mountains to the west of the drill site.

The petrology, geochronology and significance of Granite Harbour Intrusive Complex xenoliths and outcrop sampled in western McMurdo Sound, Southern Victoria Land, Antarctica

Granite Harbour Intrusive Complex xenoliths in McMurdo Volcanic Group rocks and in situ outcrops have been studied from Mount Morning, western McMurdo Sound, Antarctica. Calc-alkalic samples have whole rock signatures and normative compositions similar to the Dry Valleys 1b suite, and zircon grains in one specimen yield a 545.2 ± 4.4 Ma crystallisation age. This supports subduction-related magmatism initiating in Southern Victoria Land by 545 Ma. A second group of xenoliths is alkalic, with titanite grains in one xenolith from this group dated at 538 ± 8 Ma. Whole rock chemistry, normative compositions and geochronology of the alkalic group are comparable to the Koettlitz Glacier Alkaline Suite (KGAS). The position of a proposed lower crustal discontinuity that may form a significant basement suture in the McMurdo Sound region is newly constrained to the east of Mount Morning, perhaps along the trace of the Discovery Glacier. The boundary between East and West Antarctica may also pass along the trace of the Discovery Glacier if, as previously hypothesised, its location is controlled by the basement suture. A significant basement suture may also have provided the necessary egress for the (regionally) early and sustained magmatic activity observed at Mount Morning over the last 24 million years.

Petrogenesis of Cenozoic, alkalic volcanic lineages at Mount Morning, West Antarctica and their entrained lithospheric mantle xenoliths: Lithospheric versus asthenospheric mantle sources

Two volcanic lineages are identified at Mount Morning, a Cenozoic to recent, eruptive centre in the Ross Sea, West Antarctica, which is part of the McMurdo Volcanic Group. Both the older (at least 18.7–11.4Ma), mildly alkalic, nepheline- or quartz-normative Mason Spur Lineage, and the younger (at least 6–0.02Ma), nepheline normative, strongly alkalic Riviera Ridge Lineage evolved by fractional crystallization from nominally anhydrous (<0.5wt% H2O) parental magmas. Both lineages are analogous to other, relatively anhydrous lineages in the McMurdo Volcanic Group and distinctly different from those in which kaersutite is present on the liquid line of descent. Sub-continental lithospheric mantle (SCLM) xenoliths entrained in Riviera Ridge Lineage rocks show trace element and isotopic Sr–Nd–Pb variation that is consistent with four-component mixing whereby depleted mantle has been refertilised by enriched, HIMU-like and Nb-enriched (carbonatite) components. Refertilization may have occurred c. 530–490Ma ago when fluids derived from subduction associated with Gondwanaland amalgamation infiltrated the SCLM. Similar trace element and isotope variation (Sr–Nd–Pb) in Mount Morning basaltic rocks and entrained xenoliths suggests that the source for the basaltic magmas lies (at least in part) in the lithospheric mantle. It has long been recognized that Cenozoic volcanic rocks in Antarctica (Victoria Land – including Mount Morning – and Marie Byrd Land), Zealandia and eastern Australia share common chemical and isotopic source characteristics and they have been argued to collectively constitute a single diffuse alkaline magmatic province (DAMP). Source characteristic similarities suggest DAMP volcanic rocks inherit at least some of their trace element and isotopic characteristics from the lithospheric mantle. Super-chondritic Nb/Ta values measured in some SCLM xenoliths and volcanic rocks at Mount Morning, and in volcanic rocks across the DAMP, can be explained by addition of ⩽5wt% carbonatite to the source. The DAMP SCLM is a significant Nb reservoir that offers an explanation for the Nb paradox.

Volcanic activity and its link to glaciation cycles: Single-grain age and geochemistry of Early to Middle Miocene volcanic glass from ANDRILL AND-2A core, Antarctica

In the frame of the ANtarctic DRILLing Program, volcanic glass fragments were collected from the AND-2A core between ~354 and 765m below sea floor (mbsf) as accumulations (5–70vol.%) within sediments. Here, we present the physical characteristics, age and geochemistry of the glass, which enable us to reconstruct Early to Middle Miocene volcanic activity in southern McMurdo Sound and, for the first time, document the response of volcanism to climate change in Antarctica.Glass-rich sediments include muddy-to-fine sandstone and stratified diamictite. Glass varies in color, size, vesicularity, crystal content, angularity, and degree of alteration. The mostly fresh glass exhibits delicate cuspate forms indicating deposition as primary ash fall. 40Ar–39Ar age determinations on individual glass grains are in good agreement with the depositional age model of the sediments (ca. 15.6 to 18.6Ma), supporting for most of them a primary origin, however, some samples do contain older fragments that indicate glass recycling during times of enhanced glacial erosion.Most glasses are mafic (MgO=3 to 9wt.%) and vary from hypersthene to nepheline normative with a restricted range in SiO2 (45.2±0.8wt.%, 1σ) and trace element concentrations typical of the rift-related alkaline rocks in the Erebus Volcanic Province. The glass extends known composition of early phase Mount Morning activity (ca. 11–19Ma), the only known Early to Middle Miocene source, to a more mafic end, revealing a previously unknown explosive, strongly alkaline, basaltic phase and the most primitive forms of both strongly alkaline (basanite to phonolite) and moderately alkaline (alkali basalt to trachyte) magma associations.The glass-rich sediments occur in glacimarine sequences that record 56cycles of glacial advance and retreat. Volcanic response to glacial cyclicity is observed both physically and geochemically in AND-2A glass. Higher glass volumes in sediments correlate with ice minimum conditions between 300 and 800mbsf. Ratios of Ba to Hf, Nb, La and Zr in mafic glasses (≥5wt.% MgO) show a systematic increase in mean values during intervals of ice retreat and decreasing values with ice expansion, suggesting tapping of magmas with variable incompatible to compatible trace element ratios. This may be related to changes in the stress state of the crust in response to rapid ice volume fluctuations over the volcano, which may influence magma chemistry by varying the duration and depth of magma storage.

Geochronology of Mount Morning, Antarctica: two-phase evolution of a long-lived trachyte-basanite-phonolite eruptive center

Mount Morning is a Cenozoic, alkaline eruptive center in the south-west Ross Sea, Antarctica. New ages on 17 Mount Morning volcanic rocks (combined with 34 existing ages) allows division of Mount Morning volcanism into two phases, erupted between at least 18.7 Ma and 11.4 Ma, and 6.13 and 0.02 Ma. The position of Mount Morning on the active West Antarctic Rift System within the stationary Antarctic plate is a key factor in the eruptive center’s longevity. The earliest, mildly alkaline, Phase I volcanism comprises predominantly trachytic rocks produced by combined assimilation and fractional crystallization processes over 7.3 m.y. Strongly alkaline Phase II volcanism is dominated by a basanite – phonolite lineage, with the youngest (post last glacial maximum) activity dominated by small volume primitive basanite eruptions. The evolution from mildly to strongly alkaline chemistry between phases reflects magma residence time in the crust, the degree of mantle melting, or the degree of magma—country-rock interaction. Phase I magmatism occurred over a comparable area to the present-day, Phase II shield. The 5.2 m.y. volcanic hiatus separating Phase I and II coincides with a cycle of eruption and glacial erosion at the nearby Minna Bluff eruptive center. Mount Morning is the likely source of volcanic detritus in Cape Roberts drill-core (about 24.1 to 18.4 Ma) and in ANDRILL drill-hole 1B (about 13.6 Ma), located 170 km north and 105 km north-east respectively, of Mount Morning. Based upon the timing of eruptions and high heat-flow, Mount Morning should be considered a dormant volcano.

New criteria for systematic mapping and reliability assessment of monogenetic volcanic vent alignments and elongate volcanic vents for crustal stress analyses

Linear arrays of monogenetic volcanic vent alignments represent an important source of stress/strain data from volcanic regions of the Earth and other planets. Currently, however, there is no standard methodology for mapping vent alignments or for assessing alignment reliability, which are essential to defining a robust stress datum from vent alignments. Here we define a systematic method for defining monogenetic vent alignments by mapping the locations and shapes of vents. Elongation of vents into elliptical shapes is directly related to the trend of subsurface fissures that control alignments. Elongated vents therefore are critical for defining reliable regional vent alignments, and also provide an independent means for assessing stress directions. Our reliability assessment system (A > B > C > D) for vent alignments is based on the number of vents, the standard deviation of vent center points from a best-fit line, the numbers and types of elongate vents, the standard deviation of long axes of elliptical vents from a best-fit line, and, in cases where alignments lack elongate vents, by vent spacing distances. We quantified morphometric parameters of well-defined fissure-fed vent alignments from polygenetic volcanoes and platform volcanic fields to establish appropriate threshold values for reliability assessments. In this new method, the combined analysis of vent locations and shapes optimizes the process of alignment mapping and the assessment of the reliability of alignments to be incorporated in stress analyses. We provide quality-ranking schemes for stress data derived from reliability-assessed vent alignments and from elongate vents. We demonstrate the utility of this new mapping and assessment methodology by analyzing monogenetic cinder cone fields within a platform volcanic field (the San Francisco volcanic field in Arizona) and within a volcanic field on the flank of a polygenetic volcano (Mount Morning in Antarctica).

Structure and age of volcanic fissures on Mount Morning: A new constraint on Neogene to contemporary stress in the West Antarctic Rift, southern Victoria Land, Antarctica

Antarctica is characterized by a unique combination of active processes, including active crustal deformation, volcanism, and glacial loading and unloading, but little is known about the Neogene to contemporary geodynamic state of the Antarctic plate. This paper presents new data on the structure and timing of volcanism on the Mount Morning shield volcano, with the purpose of defining Pleistocene stress directions concomitant with volcanism and rifting in the southern portion of the Victoria Land rift basin. Elongate vents and vent alignments indicate parasitic volcanism has predominantly occurred along a primary set of NE fissures. Parasitic basaltic cinder cones yield 40 Ar- 39 Ar cooling ages, presented herein, that range from essentially zero to ca. 3.5 Ma, though mostly of Pleistocene age. The systematic NE trend of the fissures on Mount Morning records magmatically induced fracturing of the volcano flanks controlled by a regional N31°E maximum horizontal stress (S H ) that dominated the Mount Morning area during the Pleistocene and, probably, also the Pliocene. Minor volcanism occurred along shorter NW alignments that have no discernible age difference from the NE fissures. The Pleistocene age of the parasitic volcanism suggests that the stress direction documented at Mount Morning represents the contemporary differential stress field in the area. This NE S H direction differs from the N15°W S H direction measured in a borehole at Cape Roberts, 100 km to the north, and the S H orientations appear to track the changing trend of the segmented rift boundary. The exact cause for the variability in the S H directions is uncertain, but the change in S H could record different stress provinces within the rift system, or it could reflect stress reorientation along the major lithospheric boundary of the rift. The new contemporary stress datum at Mount Morning is consistent with a neotectonic normal-fault to strike-slip fault regime within the Terror Rift, which was active in Pliocene-Pleistocene times and could remain active today. This stress regime still dominates the contemporary geodynamic state of this sector of the West Antarctic Rift system.

Cenozoic basin evolution beneath the southern McMurdo Ice Shelf, Antarctica

Fifty-two kilometres of multi-channel seismic reflection data were acquired from the southern McMurdo Ice Shelf (SMIS) during potential drill site investigations for the Antarctic Drilling (ANDRILL) program. The survey was acquired atop 110 to 220 m of floating ice and extended across ablation and accumulation zones of the ice shelf. Seismic processing was tailored to the ice shelf environment, including: datum static corrections to account for changes in the thickness and average velocity of the near-surface firn layer, and changes in the surface elevation across the survey area; residual static corrections to account for near-surface ice shelf irregularities; and two-step predictive deconvolution to suppress ice and firn layer multiples. A model for the ice shelf thickness was also incorporated in the interval velocity model during depth conversion to ensure that the ice shelf structure did not impose non-static shifts on the seismic section. The depth converted CMP stacked sections reveal several N to NE trending normal faults, that offset reflective horizons by up to 150 m within the lower part of the section and form a broad east-dipping, half-graben structure. The seafloor possesses trough and arch morphology in parallel with the half-graben structure. These features are interpreted as the southern extension of the Terror Rift. The rift succession comprises a dislocated (?)early-Miocene synrift package and a relatively undeformed (?)late-Miocene post-rift package separated by an erosional unconformity. The post-rift package infills and onlaps the rift topography, and drapes over the graben system, reaching a maximum thickness of 400 m. Throughout the post-rift phase, the basin was also influenced by Neogene volcanism, evidenced by three small volcanic features within the seismic profiles, and associated successions of inferred volcanic material. An angular unconformity within the post-rift succession is interpreted as a flexural horizon related to the load of Mount Discovery and/or Mount Morning. Up to 150 m of flexural moat fill occurs above this surface at ~ 20 km from the load centres. The post-rift succession also includes several glacio-geomorphic features, the orientation and morphology of which indicate an approximately SW to NE ice flow direction during a mid-Miocene grounding event and a SE to NW ice flow direction during Quaternary ice sheet grounding events. The thickness and lower extent of the rift succession was not able to be determined because signal-to-noise ratio and vertical resolution were low at these depths. Strata from an earlier, Paleogene, rift episode may underlie the Terror Rift succession, or it may be directly underlain by acoustic basement. A Paleogene rift episode has previously been proposed based on the occurrence of Eocene fossiliferous erratics around the margin of the SMIS and the structural setting revealed by the SMIS seismic reflection profiles is consistent with this hypothesis.

Analysis of clast lithologies from CIROS-2 core, New Harbour, Antarctica — Implications for ice flow directions during Plio-Pleistocene time

This paper reports and discusses the distribution, petrography and mineral chemistry of granule- to boulder-size clasts in the Early Pliocene to Quaternary sedimentary succession recovered by the CIROS-2 drill hole, located near the mouth of the Ferrar Glacier (McMurdo Sound). In the Pliocene interval (166.47–99.27 mbsf), Early Paleozoic basement granitoids (monzogranites and granodiorites) are most common, apart from the basal 13-m-thick diamictite unit, which is dominated by basalt clasts from the late Cenozoic McMurdo Volcanics. In the Pleistocene interval (99.27–0 mbsf) basement granitoids are also the most common, but are largely tonalities. Gabbros and dolerites of the Jurassic Ferrar Supergroup are a minor persistent component throughout the core. In contrast, basement metamorphic rocks and Beacon Supergroup sandstones are present only within the lowest part of the core, the former disappearing above ca. 70.20 mbsf, and the latter above ca. 99.30 mbsf. During Pliocene time, the clast assemblage is consistent with the main source of the detritus from basement rocks to the west, transported by an ancestral Ferrar Glacier through the Transantarctic Mountains, the basal basalts suggesting an invasion of Ross Sea ice into Ferrar Fjord from the south (in the area of Mount Discovery and Mount Morning volcanoes). The dominance of tonalite in Pleistocene clasts also suggests derivation from the coastal Blue Glacier area immediately to the south. The decrease in volcanic clasts from Late Pliocene time may relate to the final construction of the Mount Morning–Mount Discovery peninsula, which acted as a barrier to the northern movement of a grounded Ross Ice Shelf, whereas the appearance of the tonalite clasts suggests periods of ice flow from its present day provenance, the Blue Glacier–Miers Valley area, northward along the coast and then into Ferrar Fjord from the east.

Geology and geochronology of McMurdo Volcanic Group rocks in the vicinity of Lake Morning, McMurdo Sound, Antarctica

Trachyandesite lava flows and trachytic dykes exposed at ‘Gandalf Ridge’ and near Lake Morning on the northern slopes of Mount Morning represent the oldest exposed volcanic rocks in the Erebus volcanic province of the McMurdo Volcanic Group. Conventional whole rock K-Ar age determinations show the rocks are mid-Miocene, ranging between 14.6 and 18.7 Ma. North–south trending faults, which parallel the Transantarctic Mountains, cut the dated dykes. The faults are probably part of a broad fault zone which bounds the uplifted Transantarctic Mountains and the down-dropped Ross Sea/Ross Ice Shelf embayment.