Janet Hergt

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Janet Margaret Hergt
NationalityAustralian
Alma mater La Trobe University
Australian National University
OccupationGeochemist

Janet Margaret Hergt is an Australian geochemist. She is a Redmond Barry Distinguished Professor in the School of Geography, Earth and Atmospheric Sciences at the University of Melbourne, Victoria, Australia. [1] The main focus of her research has been in the chemical analysis of rocks and minerals to explore the exquisite record of Earth processes preserved within them. Hergt is best known for her geochemical investigations of magmatic rocks although she has employed similar techniques in interdisciplinary projects including areas of archaeological and biological science. [2]

Contents

Early life and education

Hergt's earliest years were spent living on dairy farms in rural Victoria before moving to Frankston where she attended Karingal Primary School, and later Karingal High School.[ citation needed ] Hergt completed her undergraduate degree (BScHons) at La Trobe University in Melbourne in 1983, where she was awarded the David Myers University Medal and Ian Carlyle Medal in Geology. She received an Australian Government scholarship to study at the Australian National University in Canberra where she completed her PhD under the joint supervision of Bruce Chappell and Ian McDougall. [1] Her project involved the analysis of compositionally unusual continental flood basalts (magmatism on a vast scale often occurring as a precursor to continental breakup) from the Ferrar Province and her thesis is entitled 'The Origin and Evolution of the Tasmanian Dolerites'. [2] It was during this time that she learned to appreciate the power of trace element and isotopic data retrieved from magmatic rocks.[ citation needed ]

Career and impact

Throughout her career, Hergt has retained a keen interest in extracting high quality geochemical data from rocks and minerals to solve problems in the geosciences. Her work on the Tasmanian Dolerites provided arguably the first dataset that combined major element, trace element, Sr-, Nd-, Pb- and oxygen isotope data on the same samples from a single suite of flood basalts. [3] The dataset for the Tasmanian Dolerites, together with the extreme compositions of these rocks, provided the first opportunity to test competing hypotheses about source processes and constrain the origin of these magmas. [4]

Hergt secured her first post-doctoral research position in the UK in 1988 working at the Open University with Chris Hawkesworth on a range of topics including further work on flood basalt magmatism (in Antarctica, Brazil [5] and Siberia) [6] with a number of Australian and international colleagues. It was at the Open University that she also began her studies into the geochemical expression of arc rupture and back-arc basin opening in the Lau Basin in the Southwest Pacific. Hergt participated on Integrated Ocean Drilling Program (IODP) Leg 135, identifying two mantle domains with geochemical characteristics of "Indian" or "Pacific" mid-ocean ridge basalts that has aided in understanding the mantle dynamics in this region. [7] Other work from the IODP expedition demonstrated that magmas erupted at the earliest stages of arc rupture had the ability to tap mantle sources as well as source rocks modified by the flux of elements released from the subducting slab. [8]

Following her move to the University of Melbourne in 1994, Hergt's contributions have involved a wide range of international collaborators and graduate students, and have included investigations of continental flood basalts, [9] arc magmas, [10] [11] granite formation, [12] [13] ore deposits, the origin of kimberlites [14] [15] [16] and processes preserved in mantle xenoliths. Hergt has also made important contributions in establishing innovative laboratory protocols [17] [18] [19] [20] [21] [22] and has supported the development of Iolite data visualisation software since its inception. [23] [24] Most recently, her work has extended to applications of geochemistry in the biosciences [25] and archaeological science. [26] [27] [28]

Hergt has held a variety of senior leadership roles at the University of Melbourne, including Deputy Head of the School of Earth Sciences (2001–2004), Associate Dean-Academic Programs in the Faculty of Science (2001–2003), Head of the School of Earth Sciences (2005–2013), Deputy Dean of the Faculty of Science (2011–2013 and 2014–2017), Acting Dean of the Faculty of Science (2013–2014), Deputy Vice President then Vice President and finally President of Academic Board (2018–2020). Hergt became a Vincent Fairfax Fellow in 2018 and was recognised as a Redmond Barry Distinguished Professor in 2019. [3]

Hergt has served on a range of advisory boards, senior committees, review panels, and the editorial boards of several international journals ( Chemical Geology 2008–2016; Geostandards and Geoanalytical Research 2000–2013; and the Journal of the Geological Society of London , 2002–2007). In 2021 the Geochemical Society (USA) and the European Association of Geochemistry awarded her the honorary title of Geochemistry Fellow for her contributions to the field of geochemistry. [3]

Related Research Articles

<span class="mw-page-title-main">Kimberlite</span> Igneous rock which sometimes contains diamonds

Kimberlite, an igneous rock and a rare variant of peridotite, is most commonly known to be the main host matrix for diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an 83.5-carat diamond called the Star of South Africa in 1869 spawned a diamond rush and led to the excavation of the open-pit mine called the Big Hole. Previously, the term kimberlite has been applied to olivine lamproites as Kimberlite II, however this has been in error.

<span class="mw-page-title-main">Xenolith</span> Rock inside a rock with a different composition

A xenolith is a rock fragment that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock entrained during magma ascent, emplacement and eruption. Xenoliths may be engulfed along the margins of a magma chamber, torn loose from the walls of an erupting lava conduit or explosive diatreme or picked up along the base of a flowing body of lava on the Earth's surface. A xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes. Xenoliths can be non-uniform within individual locations, even in areas which are spatially limited, e.g. rhyolite-dominated lava of Niijima volcano (Japan) contains two types of gabbroic xenoliths which are of different origin - they were formed in different temperature and pressure conditions.

<span class="mw-page-title-main">Peridotite</span> Coarse-grained ultramafic igneous rock type

Peridotite ( PERR-ih-doh-tyte, pə-RID-ə-) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high proportions of magnesium-rich olivine, with appreciable iron. Peridotite is derived from Earth's mantle, either as solid blocks and fragments, or as crystals accumulated from magmas that formed in the mantle. The compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole.

<span class="mw-page-title-main">Eclogite</span> Metamorphic rock formed under high pressure

Eclogite is a metamorphic rock containing garnet (almandine-pyrope) hosted in a matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, zoisite, dolomite, corundum and, rarely, diamond. The chemistry of primary and accessory minerals is used to classify three types of eclogite. The broad range of eclogitic compositions has led to a longstanding debate on the origin of eclogite xenoliths as subducted, altered oceanic crust.

<span class="mw-page-title-main">Komatiite</span> Magnesium-rich igneous rock

Komatiite is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava of at least 18 wt% magnesium oxide (MgO). It is classified as a 'picritic rock'. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene.

<span class="mw-page-title-main">Compatibility (geochemistry)</span> Partitioning of elements in a mineral

Compatibility is a term used by geochemists to describe how elements partition themselves in the solid and melt within Earth's mantle. In geochemistry, compatibility is a measure of how readily a particular trace element substitutes for a major element within a mineral.

<span class="mw-page-title-main">Adakite</span> Volcanic rock type

Adakites are volcanic rocks of intermediate to felsic composition that have geochemical characteristics of magma originally thought to have formed by partial melting of altered basalt that is subducted below volcanic arcs. Most magmas derived in subduction zones come from the mantle above the subducting plate when hydrous fluids are released from minerals that break down in the metamorphosed basalt, rise into the mantle, and initiate partial melting. However, Defant and Drummond recognized that when young oceanic crust is subducted, adakites are typically produced in the arc. They postulated that when young oceanic crust is subducted it is "warmer" than crust that is typically subducted. The warmer crust enables melting of the metamorphosed subducted basalt rather than the mantle above. Experimental work by several researchers has verified the geochemical characteristics of "slab melts" and the contention that melts can form from young and therefore warmer crust in subduction zones.

<span class="mw-page-title-main">Melt inclusion</span>

A melt inclusion is a small parcel or "blobs" of melt(s) that is entrapped by crystals growing in magma and eventually forming igneous rocks. In many respects it is analogous to a fluid inclusion within magmatic hydrothermal systems. Melt inclusions tend to be microscopic in size and can be analyzed for volatile contents that are used to interpret trapping pressures of the melt at depth.

Partial melting is the phenomenon that occurs when a rock is subjected to temperatures high enough to cause certain minerals to melt, but not all of them. Partial melting is an important part of the formation of all igneous rocks and some metamorphic rocks, as evidenced by a multitude of geochemical, geophysical and petrological studies.

<span class="mw-page-title-main">Geology of Cape Verde</span>

Cape Verde is a volcanic archipelago situated above an oceanic rise that puts the base of the islands 2 kilometers (1.2 mi) above the rest of the seafloor. Cape Verde has been identified as a hotspot and the majority of geoscientists have argued that the archipelago is underlain by a mantle plume and that this plume is responsible for the volcanic activity and associated geothermal anomalies.

<span class="mw-page-title-main">Crustal recycling</span> Tectonic recycling process

Crustal recycling is a tectonic process by which surface material from the lithosphere is recycled into the mantle by subduction erosion or delamination. The subducting slabs carry volatile compounds and water into the mantle, as well as crustal material with an isotopic signature different from that of primitive mantle. Identification of this crustal signature in mantle-derived rocks is proof of crustal recycling.

<span class="mw-page-title-main">Uruguayan dyke swarms</span> Large geological structure in Uruguay

The Uruguayan dyke swarms consist of three dyke swarms of Precambrian age that intrude Río de la Plata Craton and Brasiliano Cycle continental crust in Uruguay. The dykes – including the Florida dyke swarm, the Nico Perez dyke swarm, and the Treinta y Tres dyke swarm – are of mafic to intermediate composition and each group lies in a separate tectono-stratigraphic terrane. The rocks of the Florida dyke swarm have been quarried since the 1960s and are used in the construction industry as black dimension stone of very high quality, being marketed as "black granite".

A-type granite is a particular category of the S-I-A-M or 'alphabet' system which classifies granitoids and granitic rock by their photoliths or source. The 'A' stands for Anorogenic or Anhydrous, as these granites are characterized by low water content and a lack of orogenic or transitional tectonic fabric. Other SIAM categories are S, I, and M types.

<span class="mw-page-title-main">Noronha hotspot</span>

Noronha hotspot is a hypothesized hotspot in the Atlantic Ocean. It has been proposed as the candidate source for volcanism in the Fernando de Noronha archipelago of Brazil, as well as of other volcanoes also in Brazil and even the Bahamas and the Central Atlantic Magmatic Province.

<span class="mw-page-title-main">Tonalite–trondhjemite–granodiorite</span> Intrusive rocks with typical granitic composition

Tonalite–trondhjemite–granodiorite (TTG) rocks are intrusive rocks with typical granitic composition but containing only a small portion of potassium feldspar. Tonalite, trondhjemite, and granodiorite often occur together in geological records, indicating similar petrogenetic processes. Post Archean TTG rocks are present in arc-related batholiths, as well as in ophiolites, while Archean TTG rocks are major components of Archean cratons.

<span class="mw-page-title-main">North Arch volcanic field</span> Underwater volcanic field north of Oahu, Hawaii

North Arch volcanic field is an underwater volcanic field north of Oahu, Hawaii. It covers an area of about 25,000 square kilometres (9,700 sq mi) and consists of large expanses of alkali basalt, basanite and nephelinite that form extensive lava flows and volcanic cones. Some lava flows are longer than 100 kilometres (62 mi).

<span class="mw-page-title-main">South China Craton</span> Precambrian continental block located in China

The South China Craton or South China Block is one of the Precambrian continental blocks in China. It is traditionally divided into the Yangtze Block in the NW and the Cathaysia Block in the SE. The Jiangshan–Shaoxing Fault represents the suture boundary between the two sub-blocks. Recent study suggests that the South China Block possibly has one more sub-block which is named the Tolo Terrane. The oldest rocks in the South China Block occur within the Kongling Complex, which yields zircon U–Pb ages of 3.3–2.9 Ga.

Stanley Robert Hart is an American geologist, geochemist, leading international expert on mantle isotope geochemistry, and pioneer of chemical geodynamics.

<span class="mw-page-title-main">Peter H. Barry</span> American geochemist

Peter H. Barry is an American geochemist who is an associate scientist in the marine chemistry and geochemistry department at the Woods Hole Oceanographic Institution. He uses noble gases and stable isotopes to understand the volatile history and chemical evolution of Earth, including the dynamic processes of subduction, mantle convection and surface volcanism, which control the redistribution of chemical constituents between the crust and mantle reservoirs. Barry’s main research focus has been on high-temperature geochemistry, crust-mantle interactions and the behavior of volatile fluids in the lithosphere. He also studies crustal systems, the origin of high helium deposits, including hydrocarbon formation and transport mechanisms.

Catherine Chauvel is a geochemist at the Institut de Physique du Globe de Paris known for her research on the impact of volcanic activity on the chemistry of the mantle, continental crust, and island arc geochemistry.

References

  1. 1 2 "Janet Hergt – President of the Academic Board at University of Melbourne". THE ORG. Retrieved 30 March 2021.[ permanent dead link ]
  2. 1 2 "Janet Hergt". scholar.google.com.au. Retrieved 30 March 2021.
  3. 1 2 3 "Prof Janet Hergt". findanexpert.unimelb.edu.au. Retrieved 30 March 2021.
  4. ↑ HERGT, J. M.; CHAPPELL, B. W.; McCULLOCH, M. T.; McDOUGALL, I.; CHIVAS, A. R. (1 August 1989). "Geochemical and Isotopic Constraints on the Origin of the Jurassic Dolerites of Tasmania". Journal of Petrology. 30 (4): 841–883. doi:10.1093/petrology/30.4.841. ISSN   0022-3530.
  5. ↑ Hergt, J.M.; Peate, D.W.; Hawkesworth, C.J. (July 1991). "The petrogenesis of Mesozoic Gondwana low-Ti flood basalts". Earth and Planetary Science Letters. 105 (1–3): 134–148. Bibcode:1991E&PSL.105..134H. doi:10.1016/0012-821x(91)90126-3. ISSN   0012-821X.
  6. ↑ Lightfoot, P. C.; Hawkesworth, C. J.; Hergt, J.; Naldrett, A. J.; Gorbachev, N. S.; Fedorenko, V. A.; Doherty, W. (June 1993). "Remobilisation of the continental lithosphere by a mantle plume: major-, trace-element, and Sr-, Nd-, and Pb-isotope evidence from picritic and tholeiitic lavas of the Noril'sk District, Siberian Trap, Russia". Contributions to Mineralogy and Petrology. 114 (2): 171–188. Bibcode:1993CoMP..114..171L. doi:10.1007/bf00307754. ISSN   0010-7999. S2CID   128945624.
  7. ↑ Hergt, J.M.; Hawkesworth, C.J. (May 1994), "Pb-, Sr-, and Nd-Isotopic Evolution of the Lau Basin: Implications for Mantle Dynamics during Backarc Opening", Proceedings of the Ocean Drilling Program, 135 Scientific Results, Proceedings of the Ocean Drilling Program, vol. 135, Ocean Drilling Program, doi: 10.2973/odp.proc.sr.135.142.1994
  8. ↑ Hergt, J.M.; Farley, K.N. (May 1994), "Major Element, Trace Element, and Isotope (Pb, Sr, and Nd) Variations in Site 834 Basalts: Implications for the Initiation of Backarc Opening", Proceedings of the Ocean Drilling Program, 135 Scientific Results, Proceedings of the Ocean Drilling Program, vol. 135, Ocean Drilling Program, doi: 10.2973/odp.proc.sr.135.144.1994
  9. ↑ BRAUNS, C. M.; HERGT, J. M.; WOODHEAD, J. D.; MAAS, R. (1 July 2000). "Os Isotopes and the Origin of the Tasmanian Dolerites". Journal of Petrology. 41 (7): 905–918. doi: 10.1093/petrology/41.7.905 . ISSN   1460-2415.
  10. ↑ Hergt, Janet M.; Woodhead, Jon D. (October 2007). "A critical evaluation of recent models for Lau–Tonga arc–backarc basin magmatic evolution". Chemical Geology. 245 (1–2): 9–44. Bibcode:2007ChGeo.245....9H. doi:10.1016/j.chemgeo.2007.07.022. ISSN   0009-2541.
  11. ↑ Woodhead, J.D.; Hergt, J.M.; Davidson, J.P.; Eggins, S.M. (October 2001). "Hafnium isotope evidence for 'conservative' element mobility during subduction zone processes". Earth and Planetary Science Letters. 192 (3): 331–346. Bibcode:2001E&PSL.192..331W. doi:10.1016/s0012-821x(01)00453-8. ISSN   0012-821X.
  12. ↑ Hergt, J; Woodhead, J; Schofield, A (August 2007). "A-type magmatism in the Western Lachlan Fold Belt? A study of granites and rhyolites from the Grampians region, Western Victoria". Lithos. 97 (1–2): 122–139. Bibcode:2007Litho..97..122H. doi:10.1016/j.lithos.2006.12.008. ISSN   0024-4937.
  13. ↑ Iles, Kieran A.; Hergt, Janet M.; Woodhead, Jon D.; Ickert, Ryan B.; Williams, Ian S. (March 2020). "Petrogenesis of granitoids from the Lachlan Fold Belt, southeastern Australia: The role of disequilibrium melting". Gondwana Research. 79: 87–109. Bibcode:2020GondR..79...87I. doi:10.1016/j.gr.2019.08.011. ISSN   1342-937X. S2CID   210311456.
  14. ↑ Paton, Chad; Hergt, Janet M.; Woodhead, Jon D.; Phillips, David; Shee, Simon R. (November 2009). "Identifying the asthenospheric component of kimberlite magmas from the Dharwar Craton, India". Lithos. 112: 296–310. Bibcode:2009Litho.112..296P. doi:10.1016/j.lithos.2009.03.019. ISSN   0024-4937. S2CID   129645827.
  15. ↑ Woodhead, Jon; Hergt, Janet; Phillips, Dave; Paton, Chad (November 2009). "African kimberlites revisited: In situ Sr-isotope analysis of groundmass perovskite". Lithos. 112: 311–317. Bibcode:2009Litho.112..311W. doi:10.1016/j.lithos.2009.03.031. ISSN   0024-4937. S2CID   128679944.
  16. ↑ Dalton, Hayden; Giuliani, Andrea; O'Brien, Hugh; Phillips, David; Hergt, Janet (October 2020). "Corrigendum to "The role of lithospheric heterogeneity on the composition of kimberlite magmas from a single field: The case of Kaavi-Kuopio, Finland" [Lithos 354–355 (2020) 105333]". Lithos. 370–371: 105611. Bibcode:2020Litho.37005611D. doi:10.1016/j.lithos.2020.105611. ISSN   0024-4937.
  17. ↑ Chappell, Bruce W.; Hergt, Janet M. (December 1989). "The use of known Fe content as a flux monitor in neutron activation analysis". Chemical Geology. 78 (2): 151–158. Bibcode:1989ChGeo..78..151C. doi:10.1016/0009-2541(89)90113-7. ISSN   0009-2541.
  18. ↑ Woodhead, Jon D; Hergt, Janet M (June 1997). "Application of the 'double spike' technique to Pb-isotope geochronology". Chemical Geology. 138 (3–4): 311–321. Bibcode:1997ChGeo.138..311W. doi:10.1016/s0009-2541(97)00013-2. ISSN   0009-2541.
  19. ↑ Woodhead, Jon D.; Hergt, Janet M. (July 2005). "A Preliminary Appraisal of Seven Natural Zircon Reference Materials for In Situ Hf Isotope Determination". Geostandards and Geoanalytical Research. 29 (2): 183–195. doi:10.1111/j.1751-908x.2005.tb00891.x. ISSN   0150-5505. S2CID   98471188.
  20. ↑ Woodhead, Jon; Swearer, Stephen; Hergt, Janet; Maas, Roland (2005). "In situ Sr-isotope analysis of carbonates by LA-MC-ICP-MS: interference corrections, high spatial resolution and an example from otolith studies". Journal of Analytical Atomic Spectrometry. 20 (1): 22. doi:10.1039/b412730g. ISSN   0267-9477.
  21. ↑ Paton, Chad; Woodhead, Jon D.; Hergt, Janet M.; Phillips, David; Shee, Simon (16 November 2007). "Strontium Isotope Analysis of Kimberlitic Groundmass Perovskite via LA-MC-ICP-MS". Geostandards and Geoanalytical Research: 071117031212001––. doi:10.1111/j.1751-908x.2007.00131.x. ISSN   0150-5505. S2CID   95072741.
  22. ↑ Iles, Kieran A.; Hergt, Janet M.; Sircombe, Keith N.; Woodhead, Jon D.; Bodorkos, Simon; Williams, Ian S. (May 2015). "Portrait of a reference material: Zircon production in the Middledale Gabbroic Diorite, Australia, and its implications for the TEMORA standard". Chemical Geology. 402: 140–152. Bibcode:2015ChGeo.402..140I. doi:10.1016/j.chemgeo.2015.02.036. ISSN   0009-2541.
  23. ↑ Paton, Chad; Hellstrom, John; Paul, Bence; Woodhead, Jon; Hergt, Janet (2011). "Iolite: Freeware for the visualisation and processing of mass spectrometric data". Journal of Analytical Atomic Spectrometry. 26 (12): 2508. doi:10.1039/c1ja10172b. ISSN   0267-9477.
  24. ↑ Paul, Bence; Paton, Chad; Norris, Ashley; Woodhead, Jon; Hellstrom, John; Hergt, Janet; Greig, Alan (2012). "CellSpace: A module for creating spatially registered laser ablation images within the Iolite freeware environment". Journal of Analytical Atomic Spectrometry. 27 (4): 700. doi:10.1039/c2ja10383d. ISSN   0267-9477.
  25. ↑ Marillo-Sialer, Estephany; Black, Jay R.; Paul, Bence; Kysenius, Kai; Crouch, Peter J.; Hergt, Janet M.; Woodhead, Jon D.; Hare, Dominic J. (2020). "Construction of 3D native elemental maps for large biological specimens using LA-ICP-MS coupled with X-ray tomography". Journal of Analytical Atomic Spectrometry. 35 (4): 671–678. doi:10.1039/c9ja00423h. ISSN   0267-9477. S2CID   214102259.
  26. ↑ Finch, Damien; Gleadow, Andrew; Hergt, Janet; Levchenko, Vladimir A.; Fink, David (April 2019). "New developments in the radiocarbon dating of mud wasp nests". Quaternary Geochronology. 51: 140–154. doi:10.1016/j.quageo.2019.02.007. ISSN   1871-1014. S2CID   134230346.
  27. ↑ Finch, Damien; Gleadow, Andrew; Hergt, Janet; Levchenko, Vladimir A.; Heaney, Pauline; Veth, Peter; Harper, Sam; Ouzman, Sven; Myers, Cecilia; Green, Helen (February 2020). "12,000-Year-old Aboriginal rock art from the Kimberley region, Western Australia". Science Advances. 6 (6): eaay3922. Bibcode:2020SciA....6.3922F. doi: 10.1126/sciadv.aay3922 . ISSN   2375-2548. PMC   7002160 . PMID   32076647.
  28. ↑ Finch, Damien; Gleadow, Andrew; Hergt, Janet; Heaney, Pauline; Green, Helen; Myers, Cecilia; Veth, Peter; Harper, Sam; Ouzman, Sven; Levchenko, Vladimir A. (March 2021). "Ages for Australia's oldest rock paintings". Nature Human Behaviour. 5 (3): 310–318. doi:10.1038/s41562-020-01041-0. ISSN   2397-3374. PMID   33619375. S2CID   232020013.
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