Vol. 7, No. 1 January 1997 INSIDE • Presidential Address, p. 7 GSA TODAY • Southeastern Section Meeting, p. 22 A Publication of the Geological Society of America • Annual Meeting Recap, p. 36 Rodinia to Gondwana: The Geodynamic Map of Gondwana Supercontinent Assembly
Raphael Unrug Department of Geological Sciences, Wright State University, Dayton, OH 45435
ABSTRACT The new Geodynamic Map of Gond- wana Supercontinent Assembly provides insight into the Neoproterozoic breakup of the Rodinia supercontinent that existed from 1000 to 725 Ma, and the subsequent amalgamation of Gond- wanaland. Breakout of Laurentia from Rodinia at 725 Ma marks the reorganiza- tion of lithospheric plate motions that resulted in the Pan African–Brasiliano orogeny and assembly of Gondwana- land that lasted from 725 to 500 Ma.
INTRODUCTION The Geodynamic Map of Gondwana Supercontinent Assembly1 at a scale of 1:10 million was first presented at the 30th International Geological Congress, in Beijing, in August 1996. The map is a Figure 1. Reconstruction of Gondwanaland after 500 Ma and index map for Neoproterozoic mobile joint endeavor of International Geological belts of Gondwanaland. Mobile belts include collisional and transpressional orogens and aulacogens. Correlation Program Project 288 “Gond- Aulacogens are aborted rifts, undeformed to mildly deformed, terminating inside cratons. Gray = Archean- wanaland Sutures and Fold Belts” (data- Paleoproterozoic cratons (pre–1600 Ma); green = Mesoproterozoic (1600–100 Ma) mobile belts; Neo- base generation), the Council for Geo- proterozoic (1000–440 Ma) orogens in red, and aulacogens in white with red stipple; geodynamic provinces peripheral to Gondwanaland in shades of blue. Mobile belt index: 1—Mauretanides, 2— science, Pretoria, South Africa (Geographic Bassarides, 3—Rokelides, 4—Anti-Atlas, 5—Ougarta aulacogen, 6—Trans-Saharan, 7—Tibesti, 8—Gourma Information Systems [GIS] and digital car- aulacogen, 9—Dahomeides, 10—Nigeria-Cameroon, 11—Borborema, 12—Sergipe-Oubanguide, 13— tography), and the Bureau de Recherches East African, 14—Araguaia, 15—Goias, 16—Brasilia, 17—Paramirim aulacogen, 18—Araçuai, 19—West Géologiques et Minières, Orléans, France Congo, 20—Sangha aulacogen, 21—Tucavaca aulacogen, 22—Paraguay-Cordoba, 23—Pampean Ranges, (printing). It contains original contribu- 23a—Northern Patagonia, 24—Ribeira, 25—Rio Doce, 26—Dom Feliciano, 27—Kaoko, 28—Damara, 29— Lufilian, 30—Kundelungu aulacogen, 30a—Bukoban aulacogen, 31—Zambezi, 32—Gariep, 33—Saldania, tions by 67 coauthors from 11 countries. 34—Beardmore, 35—Pinjarra, 36—Adelaide, 37—Paterson-Peterman Ranges. GIS and digital cartography were managed by L. G. Wolmarans (CGS). The Editorial Committee included: C. Castaing (BRGM), J. L. Feybesse (BRGM), P. G. Gresse (CGS), tion of the mobile belts that suture the belts across modern oceans provided a C. McA. Powell (UWA), G. R. Sadowski cratons within Gondwanaland. means for reconstruction of superconti- (USP), L. Tack (MRAC), and R. Unrug nent assembly by geodynamic interpreta- (WSU) (see p. 5). GEODYNAMIC MAP SETUP AND tion of depositional, igneous, tectonic, Here I present the basis for construct- PHILOSOPHY and metamorphic events. Recognition of ing the geodynamic map from which the The objective of the Geodynamic Map the role played by Laurentia in the assem- index and summary maps, Figures 1–3, of Gondwana Supercontinent Assembly is to bly and breakup of Rodinia—the precursor were derived, and the synoptic insights present a synthesis of the accretion of supercontinent to Gondwanaland—and gleaned from the cartographic visualiza- Gondwanaland, which is composed of the application of lithotectonic terrane lithospheric plates that traveled large dis- concepts to the better studied Neoprotero- tances during the Neoproterozoic (1000 to zoic mobile belts added complexity to the 1R. Unrug, editor, 1996, scale 1:10 million, 545 Ma). Latitudinal movements of the geodynamic interpretation. four sheets, total dimensions 1,950 x 1,250 mm, 19 colors; published by Bureau de Recherches cratons that resided within Gondwana Chronostratigraphic limits for subdi- Géologiques et Minières, US$50. Order from: were determined from paleomagnetic vision of the Proterozoic period into Meso- Editions BRGM, Ave. Claude Guillemin, BP 6009, data, and their relative movements were proterozoic (1600 to 1000 Ma) and Neo- F-45060 Orléans Cedex 2, France, fax 33-2-38-64- inferred from events registered in mobile proterozoic (1000 Ma to the start of the 36-82, or Director, Council for Geoscience, Private Bag X112, Pretoria 0001, South Africa, Attn.: Infor- belts in the reconstituted supercontinent. mation Division, fax 27-12-841-1221. Intercontinental correlations of mobile Map continued on p. 2 IN THIS ISSUE January GSA TODAY Rodinia to Gondwana: GSA Bulletin Update ...... 20 Vol. 7, No. 1 1997 The Geodynamic Map of Gondwana GSA On The Web ...... 21 Supercontinent Assembly ...... 1 GSA TODAY (ISSN 1052-5173) is published Award Nomination Summary ...... 21 monthly by The Geological Society of America, Inc., Research Grant Alternates ...... 6 Southeastern Section Meeting ...... 22 with offices at 3300 Penrose Place, Boulder, Colorado. Why the Journals Are Late ...... 6 Mailing address: P.O. Box 9140, Boulder, CO 80301- Bulletin and Geology Contents ...... 28 9140, U.S.A. Periodicals postage paid at Boulder, Col- 1996 Presidential Address ...... 7 Congressional Science Fellowship ...... 29 orado, and at additional mailing offices. Postmaster: GSAF Update ...... 12 Send address changes to GSA Today, Membership Ser- In Memoriam ...... 29 vices, P.O. Box 9140, Boulder, CO 80301-9140. Officers and Councilors for 1997 ...... 14 Calendar ...... 30 Copyright © 1997, The Geological Society of America, Washington Report ...... 15 GSA Meetings ...... 31 Inc. (GSA). All rights reserved. Copyright not claimed on Congressional Science Fellow Report: content prepared wholly by U.S. Government employees The Bucks Start Here ...... 16 1997 GeoVentures ...... 32 within the scope of their employment. Permission is granted to individuals to photocopy freely all items other Division Officers for 1997 ...... 17 1996 Annual Meeting ...... 36 than the science articles to further science and educa- Environment Matters ...... 18 Classifieds ...... 38 tion. Individual scientists are hereby granted permission, without royalties or further requests, to make unlimited Wanted: Mentors in Applied Geology . . . 18 New Geology Co-Editor ...... 40 photocopies of the science articles for use in classrooms to further education and science, and to make up to five copies for distribution to associates in the furtherance of science; permission is granted to make more than five photocopies for other noncommercial, nonprofit pur- Map continued from p. 1 and anorogenic magmatic suites. Symbols poses furthering science and education upon payment for metamorphic rock units show foliation of the appropriate fee ($0.25 per page) directly to the Copyright Clearance Center, 27 Congress Street, Salem, Cambrian) periods follow the time scale trends, nature of protoliths, and metamor- Massachusetts 01970, phone (508) 744-3350 (when approved by the International Union of phic facies. Structural symbols indicate paying, reference GSA Today, ISSN 1052-5173). Written Geological Sciences (IUGS). The beginning plate margins, faults, structural trends of permission is required from GSA for all other forms of capture, reproduction, and/or distribution of any item in of the Cambrian Period is taken as ~545 folds and foliation, and tectonic transport this publication by any means. GSA provides this and Ma for correlation of chronometric and directions. other forums for the presentation of diverse opinions geologic time scales (Plumb, 1990; and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Brasier et al., 1994). GONDWANALAND QUESTIONS Opinions presented in this publication do not reflect offi- Archean to Paleoproterozoic (pre– Neoproterozoic organization of conti- cial positions of the Society. 1600 Ma) cratons that rode the moving nental crust into large supercontinents is lithospheric plates, but underwent no the subject of ongoing debate, and various SUBSCRIPTIONS for 1997 calendar year: Society Members: GSA Today is provided as part of member- deformation during Mesoproterozoic, models are evolving as new data become ship dues. Contact Membership Services at (800) 472- Neoproterozoic, and Paleozoic orogenies available (Powell, 1993; Dalziel, 1991; 1988 or (303) 447-2020 for membership information. are considered passive elements of the Trompette, 1994; Stern, 1994; Rogers et al., Nonmembers & Institutions: Free with paid sub- scription to both GSA Bulletin and Geology, otherwise Gondwanaland jigsaw puzzle. No struc- 1995b; Unrug, 1995; Yoshida, 1995). The $50 for U.S., Canada, and Mexico; $60 elsewhere. tural details are shown in these cratons, main questions are: Were there one or Contact Subscription Services. Single copies may be except for Mesoproterozoic and Neopro- more Neoproterozoic supercontinents, requested from Publication Sales. Also available on an annual CD-ROM, (with GSA Bulletin, Geology, GSA Data terozoic cover units, intracratonic basins, and when did they (it) form and break Repository, and an Electronic Retrospective Index to jour- and cratonic marginal foreland basins. up? How were the older cratons arranged nal articles from 1972). Members order from Member- Structural reactivation and rejuvenation within these supercontinents? Where are ship Services; others contact subscriptions coordinator. Claims: For nonreceipt or for damaged copies, mem- of cratonic basement near younger mobile the sutures marking closure of oceans? bers contact Membership Services; all others contact belts are indicated by special symbols. No Was there a collision between East and Subscription Services. Claims are honored for one year; geologic details are shown in post-Triassic West Gondwanaland? please allow sufficient delivery time for overseas copies, up to six months. cover postdating collisional and accre- The following discussion of the tionary events related to Gondwanaland events that resulted in the agglomeration STAFF: Prepared from contributions from the GSA assembly. of Gondwanaland presents a balanced staff and membership. The mobile belts are shown in as opinion, worked out during compilation Executive Director: Donald M. Davidson, Jr. much detail as practicable at the map of the Geodynamic Map, of the map Edito- Science Editor: Suzanne M. Kay Department of Geological Sciences, Cornell University, scale. Ages of rock units at supergroup, rial Committee. The map was compiled Ithaca, NY 14853 group, suite, and complex rank are shown from regional contributions by authors Forum Editor: Bruce F. Molnia in color and grouped in two-geon inter- currently or recently active in research in U.S. Geological Survey, MS 917, National Center, Reston, VA 22092 vals (200 Ma) for the Mesoproterozoic and the various parts of Gondwanaland. The Managing Editor: Faith Rogers one-geon (100 Ma) intervals for the Neo- availability of data along the individual Production & Marketing Manager: James R. Clark proterozoic and Paleozoic. Locations of mobile belts varies dramatically, with Production Editor and Coordinator: Joan E. Manly Graphics Production: Joan E. Manly, Adam S. McNally small igneous intrusions, ophiolitic some African belts having been studied sequences, eclogites, mafic to ultramafic in the most detail. In poorly understood ADVERTISING metamorphic tectonites, glaciogenic sedi- regions, relatively scarce reliable data Classifieds and display: contact Ann Crawford ments, and regions of thermal rejuvena- have been combined with results several (303) 447-2020; fax 303-447-1133 tion that are important for map interpreta- decades old. To simplify and focus descrip- Issues of this publication are available as electronic tion but too small for cartographic tions on major super-regional relation- Acrobat files for free download from GSA’s Web Site. They can be viewed and printed on various personal presentation are shown by special sym- ships, diachronous rifting and collisional computer operating systems: MSDOS, MSWindows, bols. Lithology of sedimentary rock units events along the margins of older cratons Macintosh, and Unix, using the appropriate Acrobat of supergroup and group rank and pro- have been grouped. The synthesis pre- reader. The readers are widely available, free, including from GSA at: http://www.geosociety.org/pubs/index.htm. toliths of metasedimentary rocks are sented here, founded on the database gen- shown with symbols indicating basin clas- erated by the map’s co-authors, is offered This publication is included on GSA’s annual CD-ROM, GSA Journals on Compact Disc. Call GSA Publication sification: rift, passive or active margin, to invigorate debate on important ques- Sales for details. oceanic, foreland, molasse, and aulacogen. tions of Neoproterozoic geodynamic Printed in U.S.A., using pure soy inks and recyclable Symbols for igneous rock units indicate evolution of continental crust. paper. rift-related, synorogenic, postorogenic,
2 GSA TODAY, January 1997 RODINIA BREAKUP AND THE begun by 830 Ma. Correlative sediments eastern margins of the West African, EARLY NEOPROTEROZOIC PAN- were deposited in central Australian basins Amazonian, and Rio de la Plata cratons THALASSAN OCEAN whose margins were later deformed in (Trompette, 1994). The Adamastor ocean Gondwanaland originated during an intracontinental mobile belt at 600 to opened between the Kalahari, Congo, the Neoproterozoic Pan-African–Brasiliano 550 Ma (Myers et al., 1994; Powell et al., Saõ Francisco, and Rio de la Plata cratons, orogeny that resulted in ocean closures 1994). In the Ross orogen of East Antarc- and a side branch extended between the and rearrangement, collision, and suturing tica, rifting starting at about 750 Ma Kalahari and Congo cratons. Rifting that of the older continental crustal fragments (Stump, 1995) led to deposition of a is dated at 900 to 800 Ma occurred along that constituted the Archean-Mesoprotero- passive margin sequence. the western margin of the Kalahari craton zoic cratons (Fig. 1). The latter were pro- Rifting is also documented in the (P. G. Gresse in Powell, 1993). duced by breakup of the precursor super- deformed corridor between the Kalahari Subduction also occurred during this continent Rodinia which has been and Congo cratons of Africa. In this period. Juvenile crust formed in early Neo- reconstructed according to the SWEAT region, transtensional and transpressive proterozoic magmatic arcs has been recog- (Southwest United States–East Antarctic events occurred successively as a series of nized in the East African orogenic belt in connection) hypothesis (Moores 1991; younging-to-the-east rift basins formed the Arabian-Nubian shield, in the Trans- Dalziel, 1991; Hoffman, 1991). The assem- between 1100 and 950 Ma (Unrug, 1995). Saharan belt, and at the margins of the bly of Rodinia occurred by amalgamation In the Lurio shear zone in the Mozam- South American Amazonian and Rio de la of Archean-Paleoproterozoic cratons in bique orogen, post-tectonic magmatism Plata cratons. A long history of Neopro- collisions that produced late Mesoprotero- lasted until 850 Ma (Pinna et al., 1993). terozoic magmatic-arc collisions and large- zoic (1300 to 1000 Ma) mobile belts (Fig. This shear zone extends into the Zambezi scale additions of juvenile crust is recorded 2). These pericratonic orogenic belts belt rift basin, which opened at 880 Ma in the northern East African orogenic belt formed a continuous system (Harris, 1995; and was deformed at 820 Ma (Barton et (Stern, 1994). The Trans-Saharan belt con- Sadowski and Bettencourt, 1996). Trunca- al., 1993; Wilson et al., 1993). tains Neoproterozoic calc-alkaline mag- tions of these Mesoproterozoic orogens Latest Mesoproterozoic–early Neopro- matic arcs with ages of 870 to 840 Ma along younger continental margins form terozoic events are also recognized in the (pre–Pan-African; see below), 750 to 665 the “piercing points” used to pinpoint southern segment of the East African oro- Ma, and 650 to 570 Ma that are related orogenic belt continuations and mark rela- gen. Separation of the Congo and the con- to east-dipping subduction zones (Black tive positions of older cratons in the tiguous East Sahara cratons from Rodinia et al., 1994). At the eastern margin of the Rodinia reconstruction (Dalziel, 1992). started at about 1200 Ma, as did the evolu- South American Rio de la Plata craton, The North American craton, Laurentia, tion of the sedimentary basin in Kenya. By polyphase magmatic activity in the Pelotas linked with Siberia (Condie and Rosen, 820 Ma, a passive margin was developing composite batholith started with arc mag- 1994) forms the central keystone of east of the Tanganyika shield of the Congo matism at 850 to 830 Ma (review in Rodinia. Locations of the North China craton, and migmatization, early collision, Trompette, 1994). In the Dom Feliciano and South China cratonic blocks are from ophiolite emplacement, and metamor- orogen on the eastern side of the Rio de la Li et al. (1995, 1996). phism were occurring in the Kenyan seg- Plata craton, the Villa Nova belt contains The reconstruction of Rodinia in Fig- ment of the East African orogen (Shackle- early Neoproterozoic juvenile crust (Babin- ure 2 accounts for all pre-Mesoproterozoic ton, 1986; Mosley, 1993). In the northern ski et al., 1996). In the South American continental crust and Mesoproterozoic East African orogen, bimodal rift-related Goias massif, southeast of the Amazonian orogens except for the small Archean magmatism has been dated at 870 to 840 craton, protoliths of orthogneisses have crustal blocks of Tarim, Lut, and central Ma in the Nubian shield and at 880 Ma in crystallization ages of 899 Ma and Iran. These blocks were presumably part the Arabian shield (review in Stern, 1994). metavolcanic rocks have ages of 929 of Rodinia, but their relative positions are In the Borborema tectonic province to 877 Ma and 764 Ma (Pimentel and unknown. Thus, Rodinia was a Pangean- of northeastern South America, wide- Fuck, 1992). size supercontinent, and the rest of Earth’s spread rifting at about 1000 Ma (Van surface was covered by a Panthalassan-size Schmus et al., 1995) affected a large region PAN-AFRICAN–BRASILIANO ocean. of crust. The affected crust contains some OROGENY AND GONDWANALAND Archean inliers, but was principally ASSEMBLY EARLY NEOPROTEROZOIC EVENTS formed during the Paleoproterozoic The Pan-African–Brasiliano orogenic AND THE BREAKUP OF RODINIA Amazonian and Eburnean orogenies. belts (red belts in Fig. 1; Fig. 3) mark the Events between 1000 and 720 Ma The continuity of South American Neo- collisional zones between the continental that postdated the assembly and predated proterozoic mobile belts across the pieces that reassembled to form the the breakup of Rodinia included wide- Atlantic and the rifting ages of 800 Ma in Gondwanaland supercontinent after the spread shearing and tectonic escape, post- the northern Cameroon region (Toteu et breakup of Rodinia. In the first stage of tectonic magmatism, extension, rifting, al., 1987) suggest that this general rifting this breakup, Laurentia separated from the and intracontinental mobile belt forma- was a long-lasting event. Some of the far- eastern Australia–East Antarctica rifted tion. The evolution of most western traveled terranes of the West African margin of the part of Rodinia that later Gondwanaland Neoproterozoic sedimen- Tuareg shield, whose positions in Rodinia became East Gondwanaland. As Laurentia tary basins can be traced to crustal exten- are unclear, have Archean or Eburnean drifted away, it pushed the cluster of Ama- sion and rifting predating the breakup of basement ages and early Neoproterozoic zonian–West African–Rio de la Plata cra- Rodinia. The breakaway of Laurentia from passive margin sequences (Black and Lié- tons (Fig. 2) away from East Gondwana- East Antarctica and Australia which began gois,. 1993) consistent with their having land. These cratons later collided, creating the disintegration of Rodinia by cutting rifted from Rodinia during this event. the Pan-African–Brasiliano orogenic belts the supercontinent in half (see Fig. 2) and Late Mesoproterozoic to early Neo- of West Gondwanaland (Fig. 3). creating the Pacific Ocean, is dated at 725 proterozoic rifting events reconfigured the Most of the Pan-African–Brasiliano Ma by paleomagnetic data (Powell et al., global oceanic realm. The large Arabian- orogenic belts were formed between 725 1994). Some of the important events pre- Nubian and Pharusian oceans opened (in Ma and 500 Ma by collisional events ceding this breakup are summarized below modern coordinates) east and west, respec- resulting from the convergence of litho- and their results shown in Figure 2. tively, of the Congo–East Sahara–Nile spheric microplates created by the breakup In Australia, formation of rift and sag craton cluster (Fig. 2). Passive margins basins in the Adelaide “geosyncline” had developed at about 1000 Ma along the Map continued on p. 4
GSA TODAY, January 1997 3 Map continued from p. 3 of Rodinia (Fig. 3). One of the principal belts, the East African orogen (13 in Fig. 1; see Fig. 3), contains the Arabian shield onto which several ensimatic and conti- nental terranes were accreted between 715 and 630 Ma (Stoeser and Camp, 1985). Accretion ages of terranes in Yemen (Windley et al., 1996) are probably similar. Farther south in Tanzania, granulite meta- morphism associated with crustal thicken- ing related to collision is dated at 715 to 652 Ma (review in Stern, 1994). In the Aïr region of the Trans-Saharan orogenic belt (6 in Fig. 1), collision related to a west-dip- ping subduction zone is indicated by mag- matic rocks with ages of 730 to 700 Ma (Liégeois et al., 1994). A collision of the West African craton with the terrane agglomeration of the Trans-Saharan belt (6 in Fig. 1) at 600 Ma has been recognized Figure 2. Reconstruction of Rodinia showing early Neoproterozoic events (1000 to 700 Ma). The mag- by Black et al. (1994). In the Bassarides matic arcs and microplates in the Arabian-Nubian and Pharusian oceans are schematic. Medium gray and Mauretanides mobile belts (1 and 2 in is East Gondwanaland. Green is Mesoproterozoic mobile belts suturing older cratons in Rodinia. Other Fig. 1) at the western margin of the West colors indicate ages of early Neoproterozoic mobile belts and basins. Abbreviations of cratonic names: African craton, collision is dated at 660 to BDK—Bundelkhand, G—Grunehogna, GA—Gawler, NA—North Australia, R—Rockall Plateau, SC—South China, SF—Saõ Francisco, WA—West Australia. 650 Ma. A younger collisional event in the Anti-Atlas (4 in Fig. 1) is dated at 620 to 600 Ma (Villeneuve et al., 1993). Mobile belts of South America and equatorial and western side of East Gondwanaland. East lier, extension-dominated Neoproterozoic southern Africa show diachronous colli- Gondwanaland, comprising Australia, East events related to the breakup of Rodinia. sions: 700 Ma in the Dom Feliciano belt Antarctica, India, and part of Madagascar The assembly of Gondwanaland was (26 in Fig. 1; Fernandes et al., 1992), 630 (compare Figs. 1 and 3), formed a stable complete by earliest Paleozoic time. There to 620 Ma in the Ribeira and Oubanguides Gondwanaland nucleus, which was sub- could have been a short time in the latest belt (12 and 24 in Fig. 1; Tassinari and jected only to intracratonic deformation. Neoproterozoic when Laurentia, still Campos Neto, 1988; Penaye et al., 1993), The authors of the map suggest that joined with Siberia and Baltica, was in 560 to 530 Ma in the Rio Doce belt (25 in the term “Pan-African–Brasiliano orogeny” contact with the Amazonian and Rio de la Fig. 1; Campos Neto and Figueredo, 1995), be applied only to the collisional events Plata cratons, which were already part of and 590 Ma in the Damara belt (28 in that led to the suturing of West Gond- West Gondwanaland. This combination Fig. 1; K. H. Hoffmann, 1992, personal wanaland. The term should not be for ear- would form the short-lived supercontinent commun.). Trompette (1994) drew attention to a second generation of West Gondwanaland mobile belts that originated as post- Rodinian break-up rifts after 650 Ma and underwent compressional or transpres- sional deformation at about 550 Ma. These belts include the Western Africa Rokelide belt (3 in Fig. 1), which formed by dextral shearing between the Amazo- nian and West African cratons, and the South American Araguaia(?)-Paraguay- Cordoba belts (14 and 22 in Fig. 1) where authors of the Geodynamic Map recognize oceanic crustal and metasedimentary sequences. The Paraguay-Cordoba belt contains a polyphase-deformed, cratonic marginal basin that was intruded by late- tectonic granites at 550 to 500 Ma. The concept of a single collision between East and West Gondwanaland in the Neoproterozoic appears to be an over- simplification. During the assembly of West Gondwanaland, several lithospheric plates carrying large cratons and a number of smaller lithotectonic terranes were tele- Figure 3. Map showing East Gonwanaland (medium gray), assembly of West Gondwanaland (light gray) from 700 to 500 Ma, and possible Pannotian supercontinent. Pan-African–Brasiliano mobile belts scoped (Fig. 3). This resulted in closures of within and on the margins of assembling West Gondwanaland. The Pannotia supercontinent could have intervening oceanic basins, and sequential existed briefly after the agglomeration of West Gondwanaland and the assembly of Gondwanaland, and docking of the terranes onto an evolving before Laurentia separated from the Baltica, Amazonia, and Rio de la Plata cratons. Symbols for geody- Neoproterozoic tectonic collage on the namic classification of belts and craton abbreviations as in Figure 2.
4 GSA TODAY, January 1997 called Pannotia (see Powell, 1955). Panno- margin, whereas rifting was occurring in Bartlett, J. M., Harris, N. W. B., Hawkesworth, C. J., and Santosh, M., 1995, New isotope constraints on the tia would have to have been destroyed by the Avalonian-Cadomian and Cimmerian crustal evolution of South India and Pan-African gran- about 540 Ma, when the Iapetus ocean provinces (Nance and Murphy, 1994; Met- ulite metamorphism, in Yoshida, M., and Santosh, M., formed as Laurentia separated from the calfe, 1993). The Ross-Delamerian mag- eds., India and Antarctica during the Precambrian: Geological Society of India Memoir 34, p. 391–397. Baltica, Amazonian, and Rio de la Plata matic arc was active along eastern Aus- Barton, C. M., Carney, J. N., Crow, M. J., Evans, J. A., cratons (Fig. 3). tralia and East Antarctica, and the and Simango, S., 1993, Geological and structural frame- Lachlan-Thomson accretionary-magmatic work of the Zambezi Belt, northeastern Zimbabwe, in LATE- TO POSTOROGENIC EVENTS arc assemblage was forming offshore Aus- Findlay, R. H., et al., eds., Gondwana eight: Assembly, evolution and dispersal: Rotterdam, Netherlands, Widespread late- to postorogenic tralia. West of the South American Rio de Balkema, p. 55–68. magmatism, shearing and lateral tectonic la Plata craton, a complex exchange of ter- Black, R., and Liégeois, J. P, 1993, Cratons, mobile belts, escape and major uplift resulting in deep ranes between the Amazonian craton and alkaline rocks and continental lithospheric mantle: The exhumation of mobile belts are salient fea- Laurentia resulted in the formation of the Pan African testimony: Geological Society of London tures in all of Gondwanaland including Famatinian collisional orogen and the Journal, v. 150, p. 89–98. the Himalayan basement of greater India. transfer of the Precordillera terrane from Black, R., Latouche, L., Liégeois, J. P., Caby, R., and Bertrand, J. M., 1994, Pan-African displaced terranes in These features are generally attributed to Laurentia to Gondwana (Dalla Salda et al., the Tuareg shield (central Sahara): Geology, v. 22, a major thermal event that lasted into the 1993). The Pampean exotic terrane and p. 641–644. Cambrian-Ordovician and led to wide- the Arequipa terrane were possibly Brasier, M., Cowie, J., and Taylor, M., 1994, Decision on spread resetting of isotopic ages. In the detached from the western margin of the the Precambrian-Cambrian stratotype: Episodes, v. 17, Antarctic shield, which apparently had Amazonian craton (Ramos, 1996), follow- p. 3–8. been stable since the Mesoproterozoic ing the late Neoproterozoic breakup of Campos Neto, M. C., and Figueredo, M. C. H., 1995, The Rio Doce orogeny, southeastern Brazil: Journal of consolidation of Rodinia, Stüwe and San- Laurentia and Amazonia. South American Earth Sciences, v. 8, p. 143–162. diford (1993) have attributed this thermal Condie, K. C., and Rosen, O. M., 1994, Laurentia-Siberia event to underplating by asthenospheric- ACKNOWLEDGMENTS connection revisited: Geology, v. 22, p. 168–170. 2 derived basaltic magmas and related heat I thank co-authors and members of Dalla Salda, L., Varela, R., and Cingolani, C., 1993, advection. In northern Africa, where wide the editorial committee for their contribu- Sobre la colisión de Laurentia-Sudamérica y el orogeno Neoproterozoic mobile belts developed in tions to the Geodynamic Map of Gondwana Famatinian: Congreso Geológico Argentino XII y Congreso de Exploración de Hidrocárburos II, Actas, the Tuareg and Arabian-Nubian shields Supercontinent Assembly. The Bureau de t. III, p. 358–366. and partial dismemberment of the inter- Recherches Géologiques et Minières Dalziel, I. W. D., 1991, Pacific margins of Laurentia vening East Saharan–Nile craton occurred (France), British Geological Survey, Coun- and East Antarctica–Australia as a conjugate rift pair: during the Pan-African orogeny (Schan- cil for Geosciences (South Africa), Instituto Evidence and implications for an Eocambrian supercon- delmeier et al., 1994), late- to postorogenic de Geociencias, Universidade de Saõ Paulo tinent: Geology, v. 19, p. 598–601. effects are attributed to lithospheric man- (Brazil), Museé Royal de l’Afrique Centrale Dalziel, I. W. D., 1992, On the organization of Ameri- can plates in the Neoproterozoic and the breakout of tle delamination following collision of (Belgium), and University of Western Aus- Laurentia: GSA Today, v. 2, p. 237, 240–241. lithospheric plates. This delamination is tralia provided essential help in many Fernandes, L. A. D., Tommasi, A., and Porcher, C. C., suggested to result in thinning or elimina- phases of the project. I thank R. J. Stern, 1992, Deformation patterns in the southern Brazilian tion of the lithospheric mechanical V. Ramos, and D. Rowley for reviews. branch of the Dom Feliciano belt: A reappraisal: Journal boundary layer, recycling of upper-mantle This is a contribution to IGCP Project 288. of South American Earth Sciences, v. 5, p. 77–96. material in the asthenosphere, and direct Harris, L. B., 1995, Correlation between the Albany, Fraser and Darling mobile belts of Western Australia contact of crust with upwelling astheno- REFERENCES CITED and Mirnyy to Windmill Islands in the east Antarctic Babinski, M., Chemale F., Jr., Hartmann, L. A., Van sphere (Black and Liégeois, 1993). shield: Implications for Proterozoic Gondwanaland Schmus, W. R., and da Silva, L. C., 1996, Juvenile A late Precambrian–early Paleozoic accretion at 750–700 Ma in southern Brazil: Geology, suture between East and West Gondwana- v. 24, p. 439–442. Map continued on p. 6 land that extended from East Africa into the Sør Rondane Mountains of East Antarctica has been suggested by Rogers et al. (1995a). This suggestion is based on 2 Co-authors: M. G. Abdel Salam (UTD), A. C. Ajibade (FUT), R. Baleeiro (USP), K. A. Bracchi (SMU), H. radiometric ages of 550 to 450 Ma for Bahlburg (UH), B. B. de Brito Neves (USP), R. Black (CNRS), J. M. Bertrand (CNRS), J. Bossi (UMU), R. Caby (CNRS), J. N. Carney (BGS), C. Castaing (BRGM), C. Cingolani (ULP), D. I. Cole (CFG), M. Costa (ACT), granulite formation and for mylonites that G. V. Dal Piaz (UP), L. Dalla Salda (ULP), I. W. D. Dalziel (UTA), G. De Kock (CFG), J. Delhal (MRAC), D. occur in a belt extending from the East Delvaux (MRAC), J. L. Feybesse (BRGM), J. W. Goodge (SMU), P. G. Gresse (CFG), P. B. Groenewald (UNP), African orogen into Madagascar, southern R. E. Hanson (TCU), I. W. Hälbich (US), L. B. Harris (UWA), R. J. Korsch (AGSO), I. Kusnir (CNART), India, Sri Lanka, and East Antarctica. This L. Latouche (CNRS), J. Lavreau (MRAC), J. P. Liégeois (MRAC), M. Litherland (BGS), R. Machado (USP), W. McCourt (BGS), P. Mosley (BGS), J. S. Myers (WADME), L. Ortiz (ULP), A. J. Parker (CA), C. McA. Powell suture is controversial; others argue that (UWA), D. Pérez (UBA), D. Piper (BGS), P. Pitfield (BGS), M. N. Rees (ULV), J. J. W. Rogers (UNC), G. R. Sad- Neoproterozoic to earliest Paleozoic struc- owski (USP), R. Sacchi (UT), H. Schandelmeier (TUB), R. D. Shaw (AGSO), J. Sheraton (AGSO), A. Pereira tural events in Dronning Maud Land in Sousa (USP), R. J. Stern (UTD), D. B. Stoeser (USGS), C. Stowe (UCT), M. Sultan (WU), L. Tack (MRAC), Antarctica are minor (Moyes et al., 1993), C. G. Tassinari (USP), W. Texeira (USP), K. Theunissen (MRAC), A. Thomas Filho (USP), R. J. Thomas (CGS), R. Tingey (AGSO), A. Uhlein (UFMG), R. Unrug (WSU), M. Villeneuve (CNRS), G. Vujovich (UBA), T. 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Trompette (UM). drous, high-temperature charnockites in Affiliations: ACT—Atwater Co., Torino, Italy; AGSO—Australian Geological Survey Organisation; BGS— southern India at about 500 Ma are better British Geological Survey; BRGM—Bureau de Recherches Géologiques et Minières, France; C—Consultant, Australia; CGS—Council for Geosciences, South Africa; CNRS—Centre National de Recherche Scientifique, attributed to a distensional or transcurrent France; CNART—Centre National d’Appui à la Recherche, Republique du Tchad; FUT—Federal University tectonic regime and lithospheric mantle of Technology, Minna, Nigeria; MRAC—Musée Royal de l’Afrique Centrale, Belgium; OSU—Ohio State Uni- delamination (Yoshida, 1995; Bartlett et versity; SMU—Southern Methodist University, Texas; TCU—Texas Christian University; TUB—Technische al., 1995). Universität, Berlin, Germany; UBA—Universidad de Buenos Aires, Argentina; UFMG—Universidade Federal de Minas Gerais, Ouro Preto, Brazil; UG—Universität Göttingen Germany; UH—Universität Heidelberg, Germany; ULP—Universidad de la Plata, Argentina; ULV—University of Nevada, Las Vegas; UM—Université PACIFIC MARGIN OF de Marseilles, France; UMU—Universidad de la República, Montevideo, Uruguay; UNC—University of GONDWANALAND North Carolina, Chapel Hill; UNP—University of Natal, Pietermaritzburg, South Africa; UP—Università By Paleozoic time, the locus of geody- degli Studi di Padova, Italy; US—University of Stellenbosch, South Africa; USGS—U.S. Geological Survey, Denver, Colorado; USP—Universidade de Saõ Paulo, Brazil; UT—Università degli Studi di Torino, Italy; namic activity had shifted to the margins UTA—University of Texas at Austin; UTC—University of Cape Town, South Africa; UTD—University of of Gondwanaland. Accretionary processes Texas at Dallas; UWA—University of Western Australia, Perth; WADME—Western Australia Dept. Minerals were dominant on the Pacific and Iapetus and Energy, Perth; WSU—Wright State University, Ohio; WU—Washington University, St. Louis, Missouri.
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Convention, 12th: Geological Society of Australia eastern Gondwana: Società Geologia Italiana, Memorie, Windley, B. F., Whitehouse, M. J., and Ba-Btatt, M. A. O., Abstracts, no. 37, p. 312. v. 31, p. 343–350. 1996, Early Precambrian gneiss terranes and Pan- Nance, R. D., and Murphy, J. B., 1994, Contrasting Stern, R. J., 1994, Arc assembly and continental African island arcs in Yemen: Crustal accretion of the basement isotopic signatures and the palinspastic collision in the Neoproterozoic East African orogen: eastern Arabian Shield: Geology, v. 24, p. 131–134. restoration of peripheral orogens: Example from the Implications for the consolidation of Gondwanaland: Yoshida, M., 1995, Assembly of East Gondwanaland Neoproterozoic Avalonian-Cadomian belt: Geology, Annual Review of Earth and Planetary Science, v. 22, during the Mesoproterozoic and its rejuvenation during v. 22, p. 617–620. p. 319–351. the Pan-African period, in Yoshida, M., and Santosh, Penaye, J., Toteu, S. F., Van Schmus, W. R., and Nzenti, Stoeser, D. B., and Camp, V. E., 1985, Pan-African M., eds., India and Antarctica during the Precambrian: J. P., 1993, U-Pb and Sm-Nd preliminary geochrono- microplate accretion of the Arabian Shield: Geological Geological Society of India Memoir 34, p. 25–45. logic data on the Yaundé series, Cameroon: Reinterpre- Society of America Bulletin, v. 96, p. 817–826. tation of the granulitic rocks as the suture of a collision Manuscript received September 10, 1996; revision received ■ in the “Centrafrican” belt: Académie des Sciences October 23, 1996; accepted November 11, 1996 (Paris), Comptes Rendus, sér. 2, v. 318, p. 789–794. Pimentel, M. M., and Fuck, R. A., 1992, Neoproterozoic crustal accretion in central Brazil: Geology, v. 20, p. 375–379. Each month, GSA Today features a short science article on current topics of general inter- Pinna, P., Jourde, G., Calvez, J. Y., Mroz, J. P., and Mar- est. For guidelines on submitting an article, contact GSA Today Science Editor S. M. Kay, ques, J. M., 1993, The Mozambique belt in northern Cornell University, (607)255-4701, fax 607-254-4780, E-mail: [email protected] Mozambique: Neoproterozoic (1100–850 Ma) crustal
Alternates Receive 1996 Student Why the Journals Research Grants Are Late Each year when the Committee on Research Grants selects student grant recipients, they Changes in the editorial-and-production also select an alternate group of recipients in the event that some of the grantees return processing of the GSA Bulletin have part or all of their funds because they have received funding elsewhere or have changed resulted in delayed publication time for their research plans. As the returned funds become available, they are re-awarded by the the journal. The Bulletin and Geology are Research Grants Administrator to the alternates named by the committee. grouped for mailing, to take advantage of significant savings on packaging, pro- In 1996 ten alternates received funding following the initial awarding of grants. They cessing, and postage rates; thus, both are: Daniel A. Cenderelli, Colorado State University; Ziqiang Chen, Florida State Univer- journals were mailed late for November, sity; Tina M. Dochat, University of Wisconsin—Madison; Ruifang He, University of Que- December, and January. We are working bec—Chicoutimi; Emmanuelle Javaux, Dalhousie University; Rynn M. Lamb, Western to get the Bulletin back on schedule, and Washington University; Richard Allyn Meyers, University of Calgary; James R. Ostdick, we hope to mail it, as well as Geology, on California State University—Bakersfield; Andrew John Willis, University of Toronto; and their regular dates (typically, within the Adam D. Woods, University of Southern California. first ten days of the month) in March.
6 GSA TODAY, January 1997