The ANDRILL McMurdo Ice Shelf (MIS) and Southern McMurdo Sound (SMS) Drilling Projects themed issue Early Miocene volcanic activity and paleoenvironment conditions recorded in tephra layers of the AND-2A core (southern McMurdo Sound, Antarctica) A. Di Roberto1, P. Del Carlo1, S. Rocchi2, and K.S. Panter3 1Istituto Nazionale di Geofi sica e Vulcanologia, Sezione di Pisa, via della Faggiola 32, I 56126 Pisa, Italy 2Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria, 53, I-56126 Pisa, Italy 3Department of Geology, Bowling Green State University, Bowling Green, Ohio 43403, USA ABSTRACT Victoria Land have come from archives of sedi- We also focus on some of the sedimentologi- ments recovered in cores drilled both onshore cal aspects of the tephra in order to infer their The ANtarctic geological DRILLing Pro- and offshore (Barrett et al., 1998, 2000; Ham- depositional history. The results provide con- gram (ANDRILL) successfully recovered brey and Barrett, 1993; Fielding and Thomson, straints on volcanic sources, eruptions styles, 1138.54 m of core from drill hole AND-2A in 1999; Naish et al., 2007; Harwood et al., 2008). and depositional paleoenvironments. the Ross Sea sediments (Antarctica). The core The ANtarctic geological DRILLing Program is composed of terrigenous claystones, silt- (ANDRILL) successfully recovered sediments EREBUS VOLCANIC PROVINCE stones, sandstones, conglomerates, breccias, and geophysical data from 1138.54 m of drill and diamictites with abundant volcanic mate- core in the second AND-2A drill hole (southern The Erebus volcanic province in southern rial. We present sedimentological, morpho- McMurdo Sound; Florindo et al., 2008). The Victoria Land represents the largest area of scopic, petrographic, and geochemical data on coring site is located in the Ross Sea, ~50 km exposed late Cenozoic volcanic rocks and the pyroclasts recovered from core AND-2A that northwest of Hut Point Peninsula on Ross Island most complete record of alkaline volcanism in provide insights on eruption styles, volcanic (77°45.488′S; 165°16.613′E; Fig. 1). Antarctica (Kyle and Cole, 1974; Kyle et al., sources, and environments of deposition. One The AND-2A core sampled an almost con- 1990; Di Vincenzo et al., 2010). The Erebus pyroclastic fall deposit, 12 resedimented vol- tinuous (98% recovery) sequence of sediments volcanic province comprises several large vol- caniclastic deposits and 14 volcanogenic sedi- composed of lithologies including terrigenous canic centers built on the western fl ank of the mentary deposits record a history of intense claystones, siltstones, sandstones, conglomer- intracontinental West Antarctic rift system in explosive volcanic activity in southern Victoria ates, breccias, and diamictites (Florindo et al., the McMurdo Sound region (Kyle et al., 1990) Land during the Early Miocene. Tephra were 2008; Panter et al., 2008); 14 lithostratigraphic that range in age from the Early Miocene ejected during Subplinian and Plinian erup- units were identifi ed on the basis of major (ca. 19 Ma) to the present day (Fig. 1). Ross tions fed by trachytic to rhyolitic magmas changes in lithology recognized during core Island is the largest volcanic complex in the and during Strombolian to Hawaiian erup- description (Fielding et al., 2011). Sediments area and is formed by the active Mount Ere- tions fed by basaltic to mugearitic magmas were interpreted to represent a wide and com- bus volcano, which is surrounded radially in submarine and/or subglacial to subaerial plex spectrum of depositional environments and by the Mount Terror, Mount Bird, and Hut environments. The long-lived Mount Morn- dynamic fl uctuations in the Antarctic ice sheet Point Peninsula eruptive centers. Mount Ere- ing eruptive center, located ~80 km south of recorded in numerous cycles of glacial advance bus is composed mostly of basanite and pho- the drill site, was recognized as the probable and retreat during the Early to Middle Miocene nolite deposits (Kyle, 1977, 1981; Kyle et volcanic source for these products on the basis (Fielding et al., 2011; Passchier et al., 2011). al., 1992) that date to 1.3 Ma (basanite dike of volcanological, geochemical, and age con- Results from 40Ar/39Ar radiometric dat- from Cape Barne; Esser et al., 2004). Mounts straints. The study of tephra in the AND-2A ing of primary to moderately reworked tephra Bird and Terror are basanitic shield volcanoes core provides important paleoenvironment layers (Di Vincenzo et al., 2010) range in age that were active from 4.6 to 3.8 Ma and 1.7– information by revealing that the deposition from Early Miocene to Pleistocene (ca. 20 to 1.3 Ma, respectively (Kyle et al., 1990; Kyle of primary and moderately reworked tephra ca. 0.08 Ma) and compose an expanded and and Muncy, 1989). Hut Point Peninsula is occurred in a proglacial setting under gener- almost continuous section of Early to Middle Pleistocene in age (ca. 1.3 Ma), formed by ally open-water marine conditions. Miocene sediments (ca. 20–11.5 Ma) that has alkaline volcanism, and is dominated by basa- not been previously recorded by drilling in this nitic-hawaiitic cinder cones and a phonolite INTRODUCTION region (Harwood et al., 2009). dome (Observation Hill) (Kyle, 1981). We present sedimentological, morpho- To the south of Ross Island, the Erebus vol- Over the past few decades signifi cant insights scopic, petrographic, and geochemical data canic province is represented by White Island, on paleoenvironmental conditions in southern from tephra recovered in the AND-2A core. a basanite to tephriphonolite shield volcano Geosphere; December 2012; v. 8; no. 6; p. 1342–1355; doi:10.1130/GES00754.1; 9 fi gures; 2 tables; 1 supplemental table; 1 supplemental fi gure. Received 20 September 2011 ♦ Revision received 6 September 2012 ♦ Accepted 9 September 2012 ♦ Published online 16 November 2012 1342 For permission to copy, contact [email protected] © 2012 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/8/6/1342/3345903/1342.pdf by guest on 01 October 2021 Volcanic activity and paleoenvironment conditions in tephra layers of the AND-2A core Erebus volcanic province and has been divided Beaufort Island into two phases of activity. Phase I (18.7– CRP 1,2,3 165°E 6.8 Ma 11.4 Ma) is dominated by mildly alkaline, ANTARCTICA mostly trachytic rocks, and phase II (6.13– 0.02 Ma) is composed of strongly alkaline Mt.Bird rocks belonging to the basanite-phonolite lin- 3.8-4.6 Ma 1000 km eage (Kyle and Muncy 1989; Wright-Grassham McMurdo 1987; Kyle et al., 1990; Paulsen and Wilson, 2009; Martin, 2009; Martin et al., 2010). Sound Ross Island Cape Crozier North of Ross Island, Franklin and Beaufort 0.8-1.3 Ma Islands represent remnants of alkaline volcanic Cape Royds edifi ces, with ages that range from Quaternary & Barne (90 ± 66 ka; date from a seamount 10 km north 77°30'S <1 Ma Mt. Erebus Mt.Terror of Franklin Island) to Late Miocene (6.80 ± <1.3-1.7 Ma Taylor Valley <1.3 Ma 0.05 Ma) (Rilling et al., 2009). In addition to 1.5-4 Ma AND-2A the large volcanic edifi ces, the Erebus volcanic province includes several small volcanic cen- Hut Point Peninsula ters and fi elds (Kyle and Cole, 1974; Kyle et <2 Ma al., 1990). Numerous volcanic ash deposits are Dailey found within the hyperarid Dry Valleys region Brown Islands of the Transantarctic Mountains, chiefl y in the Peninsula AND-1B <1 Ma Royal Society Range and the Wright and Tay- Range 2.1-2.7 Ma White Island lor Valleys. Most of these volcaniclastic depos- 7.65-0.17 Ma its were reported to be Miocene to Pliocene in ttlitz ier 40 39 oe c age with Ar/ Ar ages ranging from ca. 15.15 K <1-14 Ma Gla to ca. 4.33 Ma (Kyle and Cole, 1974; Kyle et al., 1990; Marchant et al., 1996; Lewis et al., Royal Society 2007). The Dailey Islands are ~10 km south Black Island 11.2-1.7 Ma Ross Ice Shelf of the Southern McMurdo Sound drill site and Mt.Discovery consist of heavily eroded remnants of basal- <1-5.5 Ma Minna Bluff tic cinder cones and lava deposits. Studies of 78°30'S 12-6 Ma Mt. Morning volcanic rocks from 2 of the 5 islands reveal 18.7-11.4 Ma paleomagnetic normal polarities and radiomet- 6.1-0.1 Ma ric ages of 0.78 ± 0.04 Ma (Mankinen and Cox, 1988; Tauxe et al., 2004; Del Carlo et al., 2009). Traces of the earliest activity within the Erebus Eruptive complex volcanic province come from volcaniclastic 050km AND-2A Coring site detritus and tephra recovered in the CIROS-1 (Cenozoic Investigations in the Western Ross Sea), MSSTS-1 (McMurdo Sound Sediment and Tectonic Study), Cape Roberts Project, Figure 1. Map of southern Victoria Land, Antarctica, showing the location of AND-2A and AND-2A drill cores, which extend the vol- Southern McMurdo Sound core site and relevant geological features of Erebus volcanic canic history of the province back to ca. 26 Ma province. Map also shows outcrops of volcanic rocks (in dark brown) belonging to the (Gamble et al., 1986; Barrett, 1987; McIntosh, McMurdo Volcanic Group with relative time span of activity according to K-Ar and 1998, 2000; Acton et al., 2008; Di Vincenzo et 40Ar-39Ar ages (Mercer, 1968; Kyle and Cole, 1974; Mayewski, 1975; Armstrong, 1978; al., 2010). Kyle, 1981, 1982; Kyle et al., 1990; Kyle and Muncy, 1989; Wilch et al., 1993, 2008; Marchant et al., 1996; Esser et al., 2004; Tauxe et al., 2004; Timms, 2006; Cooper et al., VOLCANIC ROCKS IN AND-2A CORE 2007; Lewis et al., 2007; Paulsen and Wilson, 2009; Martin et al., 2010).