Episodic nature of continental arc activity since 750 Ma: A global compilation

Episodic nature of continental arc activity since 750 Ma: A global compilation

Wenrong Cao, Cin-Ty Lee, Jade Star Lackey

Earth and Planetary Science Letters (2017) 461:85-95

http://dx.doi.org/10.1016/j.epsl.2016.12.044

Continental arcs have been recently hypothesized to outflux large amounts of CO2 compared to island arcs so that global flare-ups in continental arc magmatism might drive long-term greenhouse events. Quantitative testing of this hypothesis, however, has been limited by the lack of detailed studies on the spatial distribution of continental arcs through time. Here, we compile a worldwide database of geological maps and associated literature to delineate the surface exposure of granitoid plutons, allowing reconstruction of how the surface area addition rate of granitoids and the length of continental arcs have varied since 750 Ma. These results were integrated into an ArcGIS framework and plate reconstruction models. We find that the spatial extent of continental arcs is episodic with time and broadly matches the detrital zircon age record. Most vigorous arc magmatism occurred during the 670–480 Ma and the 250–50 Ma when major greenhouse events are recognized. Low continental arc activity characterized most of the Cryogenian, middle–late Paleozoic, and Cenozoic when climate was cold. Our results indicate that plate tectonics is not steady, with fluctuations in the nature of subduction zones possibly related in time to the assembly and dispersal of continents. Our results corroborate the hypothesis that variations in continental arc activity may play a first order role in driving long-term climate change. The dataset presented here provides a quantitative basis for upscaling continental arc processes to explore their effects on mountain building, climate, and crustal growth on a global scale.

Dr. Albert Bally awarded a Doctor Honoris Causa from the University of Fribourg (Switzerland)

GCURS 2016 – Gulf Coast Undergraduate Research Symposium

Rice Earth Science was pleased to sponsor the ESCI section of the 2016 Gulf Coast Undergraduate Research Symposium (GCURS) on Saturday, October 22.  The department hosted 17 outstanding presenters from earth science departments across the country.  Enjoy some photos from this year’s event!

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EPSL: Critical porosity of melt segregation during crustal melting: Constraints from zonation of peritectic garnets in a dacite volcano

Critical porosity of melt segregation during crustal melting: Constraints from zonation of peritectic garnets in a dacite volcano

Xun Yu* and Cin-Ty Lee

*visiting student

Earth and Planetary Science Letters
Volume 449, 1 September 2016, Pages 127–134

 

The presence of leucogranitic dikes in orogenic belts suggests that partial melting may be an important process in the lower crust of active orogenies. Low seismic velocity and low electrical resistivity zones have been observed in the lower crust of active mountain belts and have been argued to reflect the presence of partial melt in the deep crust, but volcanoes are rare or absent above many of these inferred melt zones. Understanding whether these low velocity zones are melt-bearing, and if so, why they do not commonly erupt, is essential for understanding the thermal and rheologic structure of the crust and its dynamic evolution. Central to this problem is an understanding of how much melt can be stored before it can escape from the crust via compaction and eventually erupt. Experimental and theoretical studies predict trapped melt fractions anywhere from <5% to >30%. Here, we examine Mn growth-zoning in peritectic garnets in a Miocene dacite volcano from the ongoing Betic–Rif orogeny in southern Spain to estimate the melt fraction at the time of large-scale melt extraction that subsequently led to eruption. We show that the melt fraction at segregation, corresponding approximately to the critical melt porosity, was ∼30%, implying significant amounts of melt can be stored in the lower crust without draining or erupting. However, seismic velocities in the lower crust beneath active orogenic belts (southern Spain and Tibet) as well as beneath active magmatic zones (e.g., Yellowstone hotspot) correspond to average melt porosities of <10%, suggesting that melt porosities approaching critical values are short-lived or that high melt porosity regions are localized into heterogeneously distributed sills or dikes, which individually cannot be resolved by seismic studies.

 

NATURE GEOSCIENCE: Two step rise of atmospheric oxygen

Two-step rise of atmospheric oxygen linked to the growth of continents

Cin-Ty A. Lee, Laurence Y. Yeung, N. Ryan McKenzie, Yusuke Yokoyama, Kazumi Ozaki, & Adrian Lenardic

Nature Geoscience (2016) doi:10.1038/ngeo2707

Earth owes its oxygenated atmosphere to its unique claim on life, but how the atmosphere evolved from an initially oxygen-free state remains unresolved. The rise of atmospheric oxygen occurred in two stages: approximately 2.5 to 2.0 billion years ago during the Great Oxidation Event and roughly 2 billion years later during the Neoproterozoic Oxygenation Event. We propose that the formation of continents about 2.7 to 2.5 billion years ago, perhaps due to the initiation of plate tectonics, may have led to oxygenation by the following mechanisms. In the first stage, the change in composition of Earth’s crust from iron- and magnesium-rich mafic rocks to feldspar- and quartz-rich felsic rocks could have caused a decrease in the oxidative efficiency of the Earth’s surface, allowing atmospheric O2 to rise. Over the next billion years, as carbon steadily accumulated on the continents, metamorphic and magmatic reactions within this growing continental carbon reservoir facilitated a gradual increase in the total long-term input of CO2 to the ocean–atmosphere system. Given that O2 is produced during organic carbon burial, the increased CO2 input may have triggered a second rise in O2. A two-step rise in atmospheric O2 may therefore be a natural consequence of plate tectonics, continent formation and the growth of a crustal carbon reservoir.

 

Rice students win coveted Graduate Research Fellowships from the National Science Foundation

Every year, the National Science Foundation awards Graduate Research Fellowships to senior undergrads and beginning graduate students.  These prestigious awards provide full funding for graduate school in the fields of science, mathematics and engineering.  They are one of the most coveted awards for a young scientist.  This year, two of our current students and two very recent alumna received awards.  More information on how to apply for these scholarships can be found at http://www.nsfgrfp.org/.

Elli Ronay (BSc – 2016) for “Paleogroundwater Modeling from Cave Speleothem Drip Maps Surrounding the Colorado Plateau: Implications for Uplift History”.  Elli just completed a senior honor’s thesis with Cin-Ty Lee, entitled “Identifying Ash in the Cretaceous Eagle Ford Formation: Implications for Ash Source Identification and Ash Dissolution Properties”.  She will be starting a PhD at Vanderbilt University this fall.

Maya Stokes (BSc – 2015) for “Co-evolution of river networks and life”.  She is currently a PhD student at the Massachusetts Institute of Technology.  Maya says “I am finishing up my first year at MIT working with Dr. Taylor Perron.  I am interested in how fluvial bedrock river networks reorganize, specifically through divide migration and stream capture. My field area will be the central and southern Appalachians, where I hypothesize, the evolution of the river network has affected the evolution of and biogeography of aquatic species. I will use a combination of remote-sensing data and fieldwork to quantify the style and extent of reorganization of river networks, and landscape evolution models to better understand the mechanisms of stream capture. For my second project prior to my general exams at MIT, I am mapping paleoshorelines of lakes on the Chilean Altiplano with Dr. David Mcgee and graduate student Christine Chen to investigate the paleohydrology of the region.”  At Rice, she completed a senior honor’s thesis with Jeff Nittrouer entitled “Synsedimentary deformation in prodelta sedimentary deposits: the role of failures in shelf to deep-water sediment transport in the Western Irish Namurian Basin”

Rachel Marzen (BSc – 2015).  Rachel is currently a PhD student at Lamont Doherty Earth Observatory at Columbia University, New York.  While at Rice, she worked with Julia Morgan on a senior honor’s thesis entitled “Modeling Effects of Cohesion on Interactions between Erosion and Exhumation in a Bivergent Origenic Wedge”

Andrew Moodie is a current PhD student at Rice, working with Jeff Nittrouer.  His NSFGRP proposal was entitled “Evaluating limitless sustainability of deltas”. Andrew states, “The sustainability of deltas is far from certain, due to a multitude of natural and anthropogenic factors. My research seeks to evaluate the Huanghe (Yellow River) fluvial-deltaic system through numerical modeling and field survey, to identify best practices for promoting long-term deltaic sustainability.”

 

Congratulations Andrew, Elli, Maya, Rachel!

 

SCIENCE: Continental Arc Volcanism driving greenhouse-icehouse variability

Continental arc volcanism as the principal driver of icehouse-greenhouse variability

N. Ryan McKenzie, Brian K. Horton, Shannon E. Loomis, Daniel F. Stockli, Noah J. Planavsky,Cin-Ty A. Lee

Science  22 Apr 2016: Vol. 352, Issue 6284, pp. 444-447, DOI: 10.1126/science.aad5787
Variations in continental volcanic arc emissions have the potential to control atmospheric carbon dioxide (CO2) levels and climate change on multimillion-year time scales. Here we present a compilation of ~120,000 detrital zircon uranium-lead (U-Pb) ages from global sedimentary deposits as a proxy to track the spatial distribution of continental magmatic arc systems from the Cryogenian period to the present. These data demonstrate a direct relationship between global arc activity and major climate shifts: Widespread continental arcs correspond with prominent early Paleozoic and Mesozoic greenhouse climates, whereas reduced continental arc activity corresponds with icehouse climates of the Cryogenian, Late Ordovician, late Paleozoic, and Cenozoic. This persistent coupled behavior provides evidence that continental volcanic outgassing drove long-term shifts in atmospheric CO2 levels over the past ~720 million years.

April 16 – High Island birds and geology

When: April 16, 2016

Where: Birding at High Island and Bolivar Flats

What to expect: peak of bird migration, thousands of shorebirds, hundreds of colorful songbirds, and lunch on a salt dome rimmed by oil wells!

What to bring: binoculars (if you have them, but not absolutely necessary), hat, sunscreen, water, lunch, full gas tank.

Organizers: Cin-Ty Lee and Martha Lou Broussard

Itinerary

Meeting place: meet at the ferry parking lot on the BOLIVAR PENINSULA at 930 AM.  This means you should leave Rice at 8 AM, allowing for about 45 minutes to get down to Galveston and then about 30 minutes to cross the ferry (free of charge). The ferry parking lot is on hwy 87, just after you get off the ferry going from Galveston to Bolivar. MAP

Stop 1: Bolivar Flats Audubon Sanctuary. Go east on Hwy 87 from the ferry parking lot for about a mile. Turn right on 17th street and go to end and park.  We will walk out on the jetty.  The first part of the jetty is handicap accessible.  In addition to thousands of shorebirds, we will also get to see some barrier island geology and the effects of the jetty in modifying sediment transport. MAP

Stop 2: High Island Bird Sanctuary. Continue NE on 87 for about 20 miles. 87 will follow the coast and then turn inland.  After turning inland, you will reach High Island. Turn right on 5th street to the parking lot for Boy Scout Woods.  We anticipate arriving there around noon. Migrants typically pick up in the afternoon.  After Boy Scout Woods, we may move on to Smith Oaks, which is about a mile away. MAP

Optional Stop 3: Anahuac National Wildlife Refuge, which is on the way home. MAP

Contact Cin-Ty Lee or Martha Lou Broussard for more details, ride-sharing, etc. Please let us know if you are coming so that we don’t leave anyone behind at the meeting spot.

 

Cin-Ty Lee – 281 250 3606 (ctlee@rice.edu)

Martha Lou Broussard (mlbrou@rice.edu)

 

 

 

Role of arc magmatism and lower crustal foundering in controlling elevation history of the Nevadaplano and Colorado Plateau: A case study of pyroxenitic lower crust from central Arizona, USA

Monica Erdman, Cin-Ty Lee, Alan Levander, Hehe Jiang

PDF located here

Abstract

Garnet–pyroxenite xenoliths from a 25 Ma volcano on the southern edge of the Colorado Plateau in central Arizona (USA) are shown here to have crystallized as deep-seated cumulates from hydrous arc magmas, requiring the generation of a large complement of felsic magmas. U–Pb dating of primary titanite grains indicates that crystallization probably occurred around 60 Ma. These observations suggest that voluminous arc magmatism reached as far inland as the edge of the Colorado Plateau during the Laramide orogeny. Here, we employ a combination of petrology, petrophysics, and seismic imaging to show that the formation and subsequent removal of a thick, dense, cumulate root beneath the ancient North American Nevadaplano modified the buoyancy of the orogenic plateau, possibly resulting in two uplift events. A late Cretaceous–early Tertiary uplift event should have occurred in conjunction with thickening of the crust by felsic magmatism. Additional uplift is predicted if the pyroxenite root later foundered, but such uplift must have occurred after ∼25 Ma, the age of the xenolith host. We show that seismic velocity anomalies and seismic structures in the central part of the Colorado Plateau could represent pyroxenitic layers that still reside there. However, under the southern and western margins of the Colorado Plateau, the seismic signatures of a pyroxenite root are missing, despite xenolith records and geochemical evidence for their existence prior to 25 Ma. We suggest that these particular regions have undergone recent removal of the pyroxenite root, leading to late uplift of the plateau. In summary, our observations suggest that the Nevadaplano, west of the Colorado Plateau and now represented by the Basin and Range province, was underlain by high elevations in the late Cretaceous through early Tertiary due to magmatic thickening. This may have facilitated an east-directed drainage pattern at this time. Subsequent collapse of the Nevadaplano, culminating in Basin and Range extension and coupled with delamination-induced uplift of the margins of the Colorado Plateau in the late Cenozoic, may have reversed this drainage pattern, allowing rivers to flow west, as they do today.