Magmatism at the globe-encircling mid-ocean ridges is responsible for 75% of Earth's basaltic vol... more Magmatism at the globe-encircling mid-ocean ridges is responsible for 75% of Earth's basaltic volcanism, covering 70% of the planet's surface. It has long been recognized that mid-ocean ridges are underlain by open magma chambers that experience regular cycles of replenishment, mixing, eruption and fractionation [1-3]. Existing models, which use major and incompatible trace elements to model these open systems, conclude the initial replenishment rate is high but declines during magmatic evolution [4, 5]. We report major and trace element abundances, emphasizing the highly compatible platinum-group elements, for glasses and whole rocks from the East Pacific Rise (EPR), Siqueiros transform zone and Mid-Atlantic Ridge (MAR). Following early sulfide saturation, mid-ocean ridge basalts (MORBs) show no evidence of further decline in Pd with decreasing MgO, which is attributed to the replenishment of primitive magma into the MOR magma chambers. We combine the highly compatible palladium abundances, with strongly incompatible elements (Th and La), to produce a replenishment model that successfully accounts for the variations of both classes of elements in the MORBs. We show that the sulfidesaturated MOR magma chambers experience frequent small replenishments between ~1% and 4%, rather than large initial inputs that systematically decrease in magnitude as the system evolves.
Major-element, trace-element, and mineralogic data from basalts drilled during Leg 64 indicate th... more Major-element, trace-element, and mineralogic data from basalts drilled during Leg 64 indicate that a wide spectrum of N-type MORB have been erupted in the Gulf of California. Leg 64 basalts have chemical and mineralogical characteristics broadly similar to those from the East Pacific Rise and Nazca Plate. They are not nearly so evolved as basaltic lavas recovered from the Galapagos Spreading Center. Trace-element data suggest that several N-type mantle sources or a spatially heterogeneous mantle were partially melted to generate the spectrum of basalts recovered during Leg 64. However, simple, closed-system crystal fractionation does not adequately explain all of the observed chemical and mineralogical features. Mixing of primitive magmas, with observed An-rich Plagioclase xenocrysts and fractionating magmatic liquids, is a plausible mechanism which can help to explain the evolution of basaltic magmas in the Gulf of California.
Over 60% of the Earth’s magma flux, > 21 km 3 /yr, takes place at mid-ocean ridges (MOR). Thes... more Over 60% of the Earth’s magma flux, > 21 km 3 /yr, takes place at mid-ocean ridges (MOR). These divergent plate boundaries are the loci of volcanism and plutonism that form the oceanic crust, which covers over 70% of Earth’s surface. Mid-ocean ridge magmas typically undergo less modification and differentiation from their original primary melt composition than magmas erupted in continental settings or at oceanic islands. With a less complicated history, these MOR lavas provide a clearer window into mantle melting and magma chamber processes. Much insight into many different magmatic rock suites can be gained by understanding the magmatic processes involved in the formation of mid-ocean ridge lavas and determining their petrogenetic histories. The major rock type recovered at MOR is basalt. In fact, because it is so common, basalt found at spreading ridges are called MORB, or mid-ocean ridge basalts. Other terms that have commonly been used to describe MORB include ocean ridge bas...
Abstract Increasingly, water and D/H ratios of silicic and basaltic glasses are used to investiga... more Abstract Increasingly, water and D/H ratios of silicic and basaltic glasses are used to investigate magmatic degassing and secondary hydration, as well as for study these parameters in the mantle and crustal magmas. The advent of the High Temperature Conversion Element Analyzer (TC/EA) continuous flow mass spectrometry made the determination of hydrogen isotopes relatively quick and precise (±0.04 wt% H2O and 1–3‰ δ2H). Many labs around the world have such systems, thus there is a need to develop both silicic and basaltic volcanic glass reference materials (RMs) that can be used for interlaboratory comparison by bulk and microanalytical methods. Here, we report results of such investigation run against solid RMs (USGS micas) and water RMs (including VSMOW) in three different labs and describe analytical protocols. We report on the effects of glass size fraction, the mass of aliquots measured, and yield dependency for two glasses: UOR (drill cutting of IDDP-1 rhyolite, Iceland) and UOB (an E-MORB basalt from the East Pacific Rise). Proposed RM values are: UOB rhyolitic glass (n = 31): H 2 O = 1.84 ± 0.06 wt % 1 s . d . , and δ 2 H = − 115.5 ± 2.6 ‰ 1 s . d . . UOB basaltic glass (n = 60): H 2 O = 0.37 ± 0.03 wt % 1 s . d . , and δ 2 H = − 82.1 ± 5.7 ‰ 1 s . d . . Glass reference materials are available in 100 mg quantities from the Stable Isotope Laboratory at the University of Oregon for a nominal fee.
Evaluating the roles of melt-rock interaction and partial degassing on the CO 2 /Ba ratios of MOR... more Evaluating the roles of melt-rock interaction and partial degassing on the CO 2 /Ba ratios of MORB: implications for the CO 2 budget in the Earth's depleted upper mantle, Geochimica et Cosmochimica Acta (2019), doi:
Near-axis seamounts provide a unique setting to investigate three-dimensional mantle processes as... more Near-axis seamounts provide a unique setting to investigate three-dimensional mantle processes associated with the formation of new oceanic crust and lithosphere. Here, we investigate the characteristics and evolution of the 8˚20’N Seamount Chain, a lineament of seamounts that extends ~ 175 km west of the East Pacific Rise (EPR) axis, just north of the fracture zone of the Siqueiros Transform Fault. Shipboard gravity, magnetic, and bathymetric data acquired in 2016 are utilized to constrain models of seamount emplacement and evolution. Geophysical observations indicate that these seamounts formed during four distinct episodes of volcanism coinciding with changes in regional plate motion that are also reflected in the development of intra-transform spreading centers (ITSCs) along the Siqueiros transform fault (Fornari et al. 1989; Pockalny et al. 1997). Although volcanism is divided into distinct segments, the magnetic data indicate continuous volcanic construction over long portions...
Magmatism at the globe-encircling mid-ocean ridges is responsible for 75% of Earth's basaltic vol... more Magmatism at the globe-encircling mid-ocean ridges is responsible for 75% of Earth's basaltic volcanism, covering 70% of the planet's surface. It has long been recognized that mid-ocean ridges are underlain by open magma chambers that experience regular cycles of replenishment, mixing, eruption and fractionation [1-3]. Existing models, which use major and incompatible trace elements to model these open systems, conclude the initial replenishment rate is high but declines during magmatic evolution [4, 5]. We report major and trace element abundances, emphasizing the highly compatible platinum-group elements, for glasses and whole rocks from the East Pacific Rise (EPR), Siqueiros transform zone and Mid-Atlantic Ridge (MAR). Following early sulfide saturation, mid-ocean ridge basalts (MORBs) show no evidence of further decline in Pd with decreasing MgO, which is attributed to the replenishment of primitive magma into the MOR magma chambers. We combine the highly compatible palladium abundances, with strongly incompatible elements (Th and La), to produce a replenishment model that successfully accounts for the variations of both classes of elements in the MORBs. We show that the sulfidesaturated MOR magma chambers experience frequent small replenishments between ~1% and 4%, rather than large initial inputs that systematically decrease in magnitude as the system evolves.
Major-element, trace-element, and mineralogic data from basalts drilled during Leg 64 indicate th... more Major-element, trace-element, and mineralogic data from basalts drilled during Leg 64 indicate that a wide spectrum of N-type MORB have been erupted in the Gulf of California. Leg 64 basalts have chemical and mineralogical characteristics broadly similar to those from the East Pacific Rise and Nazca Plate. They are not nearly so evolved as basaltic lavas recovered from the Galapagos Spreading Center. Trace-element data suggest that several N-type mantle sources or a spatially heterogeneous mantle were partially melted to generate the spectrum of basalts recovered during Leg 64. However, simple, closed-system crystal fractionation does not adequately explain all of the observed chemical and mineralogical features. Mixing of primitive magmas, with observed An-rich Plagioclase xenocrysts and fractionating magmatic liquids, is a plausible mechanism which can help to explain the evolution of basaltic magmas in the Gulf of California.
Over 60% of the Earth’s magma flux, > 21 km 3 /yr, takes place at mid-ocean ridges (MOR). Thes... more Over 60% of the Earth’s magma flux, > 21 km 3 /yr, takes place at mid-ocean ridges (MOR). These divergent plate boundaries are the loci of volcanism and plutonism that form the oceanic crust, which covers over 70% of Earth’s surface. Mid-ocean ridge magmas typically undergo less modification and differentiation from their original primary melt composition than magmas erupted in continental settings or at oceanic islands. With a less complicated history, these MOR lavas provide a clearer window into mantle melting and magma chamber processes. Much insight into many different magmatic rock suites can be gained by understanding the magmatic processes involved in the formation of mid-ocean ridge lavas and determining their petrogenetic histories. The major rock type recovered at MOR is basalt. In fact, because it is so common, basalt found at spreading ridges are called MORB, or mid-ocean ridge basalts. Other terms that have commonly been used to describe MORB include ocean ridge bas...
Abstract Increasingly, water and D/H ratios of silicic and basaltic glasses are used to investiga... more Abstract Increasingly, water and D/H ratios of silicic and basaltic glasses are used to investigate magmatic degassing and secondary hydration, as well as for study these parameters in the mantle and crustal magmas. The advent of the High Temperature Conversion Element Analyzer (TC/EA) continuous flow mass spectrometry made the determination of hydrogen isotopes relatively quick and precise (±0.04 wt% H2O and 1–3‰ δ2H). Many labs around the world have such systems, thus there is a need to develop both silicic and basaltic volcanic glass reference materials (RMs) that can be used for interlaboratory comparison by bulk and microanalytical methods. Here, we report results of such investigation run against solid RMs (USGS micas) and water RMs (including VSMOW) in three different labs and describe analytical protocols. We report on the effects of glass size fraction, the mass of aliquots measured, and yield dependency for two glasses: UOR (drill cutting of IDDP-1 rhyolite, Iceland) and UOB (an E-MORB basalt from the East Pacific Rise). Proposed RM values are: UOB rhyolitic glass (n = 31): H 2 O = 1.84 ± 0.06 wt % 1 s . d . , and δ 2 H = − 115.5 ± 2.6 ‰ 1 s . d . . UOB basaltic glass (n = 60): H 2 O = 0.37 ± 0.03 wt % 1 s . d . , and δ 2 H = − 82.1 ± 5.7 ‰ 1 s . d . . Glass reference materials are available in 100 mg quantities from the Stable Isotope Laboratory at the University of Oregon for a nominal fee.
Evaluating the roles of melt-rock interaction and partial degassing on the CO 2 /Ba ratios of MOR... more Evaluating the roles of melt-rock interaction and partial degassing on the CO 2 /Ba ratios of MORB: implications for the CO 2 budget in the Earth's depleted upper mantle, Geochimica et Cosmochimica Acta (2019), doi:
Near-axis seamounts provide a unique setting to investigate three-dimensional mantle processes as... more Near-axis seamounts provide a unique setting to investigate three-dimensional mantle processes associated with the formation of new oceanic crust and lithosphere. Here, we investigate the characteristics and evolution of the 8˚20’N Seamount Chain, a lineament of seamounts that extends ~ 175 km west of the East Pacific Rise (EPR) axis, just north of the fracture zone of the Siqueiros Transform Fault. Shipboard gravity, magnetic, and bathymetric data acquired in 2016 are utilized to constrain models of seamount emplacement and evolution. Geophysical observations indicate that these seamounts formed during four distinct episodes of volcanism coinciding with changes in regional plate motion that are also reflected in the development of intra-transform spreading centers (ITSCs) along the Siqueiros transform fault (Fornari et al. 1989; Pockalny et al. 1997). Although volcanism is divided into distinct segments, the magnetic data indicate continuous volcanic construction over long portions...
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Papers by Michael Perfit