Geothermal Anomalies and Helium Isotopes

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Questions and Answers

What do negative μ182W anomalies in ocean island basalt volcanoes suggest about their origin?

They may reflect contributions from Earth's core. (correct)

They are unrelated to mantle plume activity.

They originate exclusively from surface materials.

They are indicative of recent mantle activity.

Which of the following elements is identified as moderately siderophile during core formation?

Zinc

Iron

Tungsten (correct)

Uranium

How do the μ182W values in Earth's core compare to the terrestrial tungsten isotope standard?

They are identical at 0.

They are lower than the standard. (correct)

They are higher than the standard.

They fluctuate around the standard.

What is postulated about the high 3He/4He lavas associated with negative μ182W anomalies?

They reflect a deep primordial mantle signature. Signup and view all the answers

What does research suggest about the relation between recycled oceanic and continental material and μ182W anomalies?

A relationship emerges from certain data. Signup and view all the answers

What do long-lived 87Sr/86Sr signatures indicate in contrast to μ182W anomalies?

They have no relation to negative μ182W anomalies. Signup and view all the answers

Which phenomenon is suggested to be preserved within deeply sourced mantle plumes?

Core isotopic signatures. Signup and view all the answers

What is the significance of the grey band in the isotope systematics of plume volcanics?

It represents measurement uncertainties. Signup and view all the answers

What primarily distinguishes hotspot volcanism from other types of volcanism?

It is associated with narrow mantle upwellings. Signup and view all the answers

What is the approximate depth at which mantle plumes are thought to start?

2,900 km Signup and view all the answers

Which volcanic region is an example of an age-progressive volcanic chain?

Hawaii Signup and view all the answers

How much hotter are mantle plumes believed to be compared to the ambient mantle?

100–300 °C Signup and view all the answers

Which of the following statements about large igneous provinces (LIPs) is correct?

They have areal extents greater than 0.1 million km². Signup and view all the answers

What has been a key area of debate regarding mantle plumes since their conception?

The dynamics and shapes of plumes. Signup and view all the answers

What is required for mantle plumes to form hotspots?

They ascend to the base of the lithosphere. Signup and view all the answers

Which factor can affect the key characteristics of plume conduits?

Entrainment of chemical heterogeneity. Signup and view all the answers

What is the predicted ascent time for smaller plumes such as the Yellowstone plume?

80 million years or longer Signup and view all the answers

What is the estimated sinking speed of slabs in the mantle?

1-2 cm per year Signup and view all the answers

Which of the following is NOT a characteristic of thermochemical plume conduits?

They are typically narrower than thermal plumes. Signup and view all the answers

What correlates with the formation of Long Igneous Provinces (LIPs)?

Plume heads reaching the lithosphere Signup and view all the answers

How do hotspot tracks often correlate with flood basalts?

They correspond to thermal plumes extending into the mantle. Signup and view all the answers

What is one characteristic of plumes modeled in numerical simulations?

They do not generate lateral deflections in the mantle. Signup and view all the answers

For smaller plumes, what happens to the predicted tilts?

They are less marked in dynamically forming models. Signup and view all the answers

What is a likely duration for hotspot tracks after the formation of a LIP?

Last for 80 to 120 million years or longer Signup and view all the answers

What does the 208Pb/206Pb ratio measure in Hawaiian lavas?

The difference in isotopic ratios relative to meteorites Signup and view all the answers

Which two major volcanic centers are associated with the double-track volcanism in Hawaii?

Loa and Kea Signup and view all the answers

What aspect of volcanic activity does the model of double-track volcanism primarily investigate?

Plate motion changes Signup and view all the answers

What are the factors suggested by the text that could influence lava composition?

Thickness and lithology of the melting material Signup and view all the answers

What does the concentrically zoned plume model postulate about plume materials?

Plumes concentrate hotter and denser materials Signup and view all the answers

Which isotopic ratios measured in Hawaiian lavas provide insight into the chemical composition differences?

208Pb/204Pb and 206Pb/204Pb Signup and view all the answers

What is inferred to influence how different components in the plume are sampled?

Changes in plate motion Signup and view all the answers

How old are the chondritic meteorites that provide a baseline for comparison with Hawaiian lava compositions?

4.6 billion years Signup and view all the answers

What significant shift occurred in the Hawaiian plume according to the data?

The plume switched from Kea-only to a dual Loa-Kea component. Signup and view all the answers

What does the 40Ar/39Ar dating reveal about the Louisville and Rurutu hotspot tracks?

There is a consistent age progression indicating plate movement. Signup and view all the answers

What was the rate at which the Hawaiian hotspot moved between 63 and 52 Ma?

48 ± 8 mm per year Signup and view all the answers

What evidence supports a link between surface geochemical signatures and mantle geophysical domains?

The bilateral zoned plume model Signup and view all the answers

Which statement correctly describes the changes in plate motion around 6 Ma?

It may have affected the entrainment of the Loa component. Signup and view all the answers

Which of the following statements about other Pacific hotspots is true?

They exhibit slower movement than the Hawaiian hotspot. Signup and view all the answers

What is suggested by the observed bilateral trends within Pacific hotspots?

They likely share a common geological origin. Signup and view all the answers

What might explain the acute bends observed in the Louisville and Rurutu hotspot tracks?

Variations in tectonic plate motion. Signup and view all the answers

Study Notes

Negative μ182W Anomalies

High 3He/4He lavas in hotspots associated with negative μ182W anomalies may indicate samples from deep, primordial mantle sources.
Negative μ182W anomalies in ocean island basalts show no correlation with long-lived 87Sr/86Sr signatures.
An observation suggests that deep mantle plumes with negative μ182W anomalies inherit an isotopic signature from Earth's core, which maintains a low μ182W value.
Tungsten is moderately siderophile; during core formation, it became enriched in the core compared to its radioactive parent 182Hf that remained in the mantle.

Mantle Plumes

Mantle plumes are narrow upwellings essential to Earth's convection, contributing to volcanism away from plate boundaries, like in Hawaii.
These plumes may originate near the core-mantle boundary, approximately 2,900 km deep.
Plumes can exceed ambient mantle temperatures by 100–300 °C and take tens of millions of years to reach the lithosphere.
Predictions estimate that plume heads ascend more quickly than sinking slab rates, with plumes rising significantly faster than slab rates of 1–2 cm per year.

Large Igneous Provinces (LIPs)

LIPs involve significant volcanic rock accumulation covering areas over 0.1 million km², often leading to significant geological events within less than a million years.
Hotspot tracks linked with LIPs include flood basalts, indicating a potential relationship with thermal plumes.

Double-Track Volcanism

The Hawaiian Islands exhibit double-track volcanism, evident in Pb-isotopic ratios of lava flows correlated to distance from active volcanoes.
Differences in 208Pb*/206Pb* ratios can reveal chemical heterogeneities in the Hawaii plume, influenced by historical plate motion.

Plume Structure Models

The concentrically zoned plume model suggests plumes transport the hottest materials during ascent, affected by surrounding lithology and melting processes.
Changes in plate motion can impact how different plume components are sampled during volcanism, leading to complex zonation.

Temporal and Spatial Observations

The shift from a pure Kea component in the Hawaiian plume to dual Loa-Kea components occurred between 6.5 and 47 Ma, possibly linked to plate motion changes.
Geochemical signatures help correlate surface data with geophysical observations from the lowermost mantle, linking hotspots to ancient mantle structures.

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Description

This quiz explores the relationship between negative 182W anomalies and 3He/4He ratios in lavas, highlighting key hotspots that exhibit these geochemical features. Dive into the intriguing world of geoscience to better understand the implications of these isotopic compositions in the study of volcanic activity.