Depth extent of cratons as inferred from tomographic studies

Research Article| March 01, 1995 Depth extent of cratons as inferred from tomographic studies J. Polet; J. Polet 1Seismological Laboratory, California Institute of Technology, Pasadena, California 91125 Search for other works by this author on: GSW Google Scholar Don L. Anderson Don L. Anderson 1Seismological Laboratory, California Institute of Technology, Pasadena, California 91125 Search for other works by this author on: GSW Google Scholar Author and Article Information J. Polet 1Seismological Laboratory, California Institute of Technology, Pasadena, California 91125 Don L. Anderson 1Seismological Laboratory, California Institute of Technology, Pasadena, California 91125 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1995) 23 (3): 205–208. https://doi.org/10.1130/0091-7613(1995)023<0205:DEOCAI>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation J. Polet, Don L. Anderson; Depth extent of cratons as inferred from tomographic studies. Geology 1995;; 23 (3): 205–208. doi: https://doi.org/10.1130/0091-7613(1995)023<0205:DEOCAI>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We address the question of the depth extent of mantle high-velocity zones under ancient cratons by using seismic velocity maps from recent mantle tomographic studies. We divided old continents into two age provinces: 800–1700 Ma (Middle Proterozoic) and older than 1700 Ma (Archean and Early Proterozoic). The areas included in these age provinces are cross-correlated with the tomography at different depths to quantify the global occurrence of high-velocity anomaly (HVA) extensions beneath cratons. Statistically significant HVAs underlie the oldest cratons to a depth of 250 km. There is no significant consistent correlation between tomography and younger cratons. The older cratons have correlated HVAs extending to depths varying from <100 to 450 km. There is no significant difference in the average velocity anomaly beneath the Early Proterozoic part and the Archean part of the Canadian Shield, whereas the Middle Proterozoic part does not contain any HVA. The mantle under Early Precambrian crust is distinctly different from mantle elsewhere. We propose two different hypotheses to explain these results: (1) cratons of Early Proterozoic age or older contain ancient and deep, physically attached roots, or (2) these cratons contain a small “permanent” physical root that induces cold downwellings beneath it. A root thickness of ∼200 km can be explained by an FeO-poor, olivine-rich mineralogy, whereas a requirement of high strength probably demands, in addition, a volatile-poor composition. Different root depths for cratons of similar age may be related to their location in the various supercontinents in which they were involved, and to their subsequent deformational history, or they may represent different snapshots in time of transient “roots,” such as thermal boundary layers. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.