439 Comer

61 Route 9W - PO Box 1000

Palisades

NY

10964-8000

US

Phone: 

(845) 365-8712

Fax: 

(845) 365-8155

class@ldeo.columbia.edu

As a student I became fascinated by the ability of geochemical tools to *look* into the otherwise inaccessible Earth's mantle and constrain its heterogeneity and temporal evolution as well as aspects of its convective regimes. Combined with the stunning beauty of volcanoes, which provide such *windows* into the Earth's interior, mantle geochemistry became my passion. In an attempt to understand the present and past geology of the mantle, I integrate a wide range of analytical techniques (major and trace elements, Sr-Nd-Pb-Hf-Os isotopic compositions and noble gases) to quantify geochemical processes wherever possible. My present research focuses on the following questions: (i) Constraints on the age and precursor materials of plume sources, (ii) Processes of plume-lithosphere interaction, identification of deep mantle plume components, and the composition of old oceanic lithospheric mantle, (iii) Processes of element transport from subducting slabs to the sub-arc mantle, (iv) The role of the continental lithospheric mantle in the formation of flood basalts, (v) The significance of detached continental lithosphere in the source regions of oceanic basalts and processes of detachment, and (vi) The origin of primordial 3He in oceanic basalts and its implications for mantle dynamics.

One aspect of my recent research is focused towards understanding the helium evolution of the Earth's mantle. Degassing of the Earth's mantle through magmatism results in the irreversible loss of helium to space. As virtually all of the 3He in the Earth is *primordial*, high 3He/4He ratios in ocean island basalts are generally taken as evidence for a primitive, unmelted reservoir in the deep Earth and makes helium a powerful tool for deciphering convective regimes in the mantle. Utilizing new and published geochemical data from ocean island basalts and mid-ocean ridge basalts from the global data now available from GEOROC and PetDB databases, it has been possible to demonstrate that the range in 3He/4He ratios in ocean island basalts reflects variable production rates of 4He as a function of (Th+U) in plume sources. Furthermore, this new global data compilation shows that ocean island basalts displaying the strongest primordial signal are chemically and isotopically most like mid-ocean ridge basalts, indicating a common melting history that resulted in continent and ocean crust formation. We show that a primordial reservoir in the mantle is not required in the deep Earth, and thereby reconcile a long-standing paradox in mantle dynamics.

My recent research also investigates the origin of unusual compositions of some oceanic basalts that have been attributed to their sources containing continental lithosphere detached during the breakup of Gondwana. However, the processes of how such continental lithospheric material is detached and transported into the ocean basin have not been constrained. The Walvis Ridge, where DSDP Site 525A has been argued to contain continental material, is identified in some of my ongoing research as a unique location to constrain these processes. The premise in this research is that tectonic detachment versus hotspot-related thermal erosion should sample spatially separated continental units of different age, in view of the regional tectonics. The diagnostic compositional characteristics of these continental units are constrained using new isotope measurements on mantle and lower crustal xenoliths from the region, combined with literature data. The new data clearly exclude tectonic detachment as a process and give strong support for a thermal erosion of the base of the Congo Craton by the Tristan mantle plume. A convective return flow is required to transport the thermally eroded cratonic lithospheric mantle to the site of plume activity some 50 Ma later and provides a unique constraint for the direction and velocity of mantle flow in the upper mantle between 80-130Ma.

Some of my projects include:

• Shona and Discovery Seamount Chains, South Atlantic (funded by Alfred Wegner Institut Germany and National Science Foundation)
• The Tristan-Gough plume source and constraints on the composition of recycled sediment (funded by the National Science Foundation)