Amphibole-Bearing Metamorphic Clasts in ANDRILL AND-2A Core: A
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The ANDRILL McMurdo Ice Shelf (MIS) and Southern McMurdo Sound (SMS) Drilling Projects themed issue Amphibole-bearing metamorphic clasts in ANDRILL AND-2A core: A provenance tool to unravel the Miocene glacial history in the Ross Embayment (western Ross Sea, Antarctica) Franco M. Talarico1, Donato Pace1, and Sonia Sandroni2 1Dipartimento di Scienze della Terra, Università degli Studi di Siena, Via Laterina 8, 53100 Siena, Italy 2Museo Nazionale dell’Antartide, Università degli Studi di Siena, Via Laterina 8, 53100 Siena, Italy ABSTRACT able, near-fi eld record of dynamic paleoenvi- cene to Pleistocene, which is punctuated by sev- ronmental history through the Miocene. eral disconformities, not clearly defi ned yet but A petrological investigation of amphibole- with an accumulative loss of 7–8 m.y. (Harwood bearing metamorphic clasts in the ANDRILL INTRODUCTION et al., 2008–2009; Acton et al., 2008–2009 with AND-2A core allows a detailed comparison modifi cations as in ANDRILL SMS Science with similar lithologies from potential source The ANDRILL Southern McMurdo Sound Team, 2010) (Fig. 2). The succession includes regions, leading to the identifi cation of three (SMS) project (Harwood et al., 2008–2009) is several intervals of massive and stratifi ed sandy distinct provenance areas in the present-day the last one of several scientifi c Antarctic drill- diamictites (lithofacies 8 and 7, respectively, segment of the Transantarctic Mountains ing projects (DSDP, DVDP, MSSTS-CIROS, as defi ned by Fielding et al., 2008–2009), with between the Byrd Glacier and the Blue Gla- CRP; Hambrey et al., 2002, and references variable local internal deformation, fossil con- cier (Mulock-Skelton glacier area, the Bri- therein; AND-1B, Naish et al., 2007) that recov- tent and bioturbation, and mainly interpreted tannia Range, and the Koettlitz-Blue glacier ered signifi cant sections of the latest Eocene to as glaciomarine sediments that accumulated at area in the Royal Society Range). A key role Pleistocene sedimentary succession deposited varying proximity to grounded ice, but almost in the comparison is played by the wide range in the Victoria Land Basin (Cooper and Davey, always at some distance. However, evidences of Ca-amphibole compositions, type of intra- 1985), a structural half-graben, ~350 km long, of few and short-lived grounding events are crystalline zoning, mineral assemblages, and bounded on its western side by the Transantarc- documented above 225 mbsf and below 650 fabrics, which refl ect different bulk rocks tic Mountains (TAM) front (Barrett, 1979; Wil- mbsf (Passchier et al., 2010). Other common and metamorphic conditions. Ca-amphibole son, 1999; Fig. 1). lithologies include sandstones (lithofacies 5), compositions and zonations also offer the The ANDRILL SMS project drilled the AND- interstratifi ed siltstone and sandstone (lithofa- opportunity for the application of geother- 2A drill hole from a site located in the south- cies 3), siltstone to very fi ne-grained sandstone mobarometry methods, which, consistent ern part of McMurdo Sound, ~30 km west of (lithofacies 2), and interbedded conglomerate with literature data, provide further evidence McMurdo Station (77°45.488′S; 165°16.613′E) and sandstone (lithofacies 9). that the three provenance regions corre- near the termination of Koettlitz and Blue gla- The AND-2A core represents the fi rst thick spond to distinct metamorphic terrains with ciers (Fig. 1). Regional seismic-refl ection sur- Miocene section recovered from an ice- proximal pervasive medium-pressure amphibolite- veys show that the penetrated succession is setting, and it provides a unique physical record grade conditions restricted to the Britannia composed of a series of clinoform sets produced for reconstructing the Antarctic paleoclimatic Range. The study contributes new insights by uplift and erosion as a result of renewed rift- evolution and the behavior of its ice sheets dur- into the depositional processes in a variety ing of the Terror Rift (Fielding et al., 2008). ing the critical climatic events of the late Ceno- of glacial environments ranging from open Accommodation for sediment was produced zoic. As demonstrated by several studies in other marine with icebergs to distal, proximal, and through fault- and fl exure-related subsidence Victoria Land Basin cored sedimentary sections subglacial settings. The results also highlight associated with rifting. The active rifting and (e.g., Talarico and Sandroni, 2009) and in gla- the record of two distinct glacial scenarios passive thermal subsidence during the early and cigenic successions of the Antarctic continental refl ecting either short-range (<100 km) fl uc- middle Miocene produced the accommodation margin elsewhere (e.g., Reinardy et al., 2009), tuations of paleoglaciers in the Royal Society for the accumulation of this Neogene succession compositional and distribution patterns of gravel Range with dominant fl ows from W to E, or (Fielding et al., 2008). fraction throughout the AND-2A core play a larger volume of ice sourced from southern- With a recovery of ~98%, the AND-2A core key role in the identifi cation of potential prov- more outlet glaciers from the Skelton-Byrd recovered an almost 1140-m-long succession enance regions and reconstruction of ice-fl ow glacier area with fl ow lines running N-S close including a thick and fairly continuous lower to patterns. Moreover, distribution patterns and to the Transantarctic Mountains front. Both middle Miocene lower part (~1140–225 mbsf textural analysis of the gravel fraction provide scenarios demonstrate the importance of the [meters below sea fl oor]) and an upper part relevant additional information to sedimento- AND-2A core to reveal a hitherto unavail- (above 225 mbsf), ranging in age from late Mio- logical models for subglacial and glacial-marine Geosphere; August 2011; v. 7; no. 4; p. 922–937; doi: 10.1130/GES00653.1; 6 fi gures; 3 tables; 1 supplemental table. 922 For permission to copy, contact [email protected] © 2011 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/4/922/3340417/922.pdf by guest on 01 October 2021 Amphibole-bearing metamorphic clasts in ANDRILL AND-2A core depositional settings and processes (e.g., Cowan tics of a distinctive group of metamorphic clasts in the Ross Embayment during Miocene time, et al., 2008; Reinardy et al., 2009). (i.e., Ca-amphibole–bearing metasedimentary which, as indicated by proxy records, includes In this paper, we especially concentrate on and metaigneous rocks) to track provenance several events of paleoenvironmental changes, the provenance history recorded in the clast- changes documented in the Miocene to Plio- such as the mid-Miocene climatic optimum rich diamictite units and, subordinately, in other cene AND-2A core section (between 150 and (ca. 17–14 Ma; Billups and Schrag, 2002; Hol- fi ner-grained lithofacies, and use the detailed 1140 mbsf). The results are signifi cant for their bourn et al., 2007; You et al., 2009) and the petrographical and mineralogical characteris- implications for the glacial evolution recorded Mi1a and Mi1b glaciations (Miller et al., 1996). A 65°S W 0° E Indian Ocean B Atlantic Ocean AN WEDDELL T ARCTAR SEA C T IICC PEN P PRYDZ LegLeg 178178 EN BAY E ANTARCTIC LegLeg 178118878 9 ICE SHEET 11 LegLeg 119 90° W ANTARCTICANTARCTIC 90° ICEICE SHEETSHEET Pacific Ocean 20002 0 0 100010 0 00 0 0 0 0 Fig.Fig. 1B1B 0 0 LegLeg 7878 20002 10001 DSDP/ODP drill holes ROSS SEA IODP Leg 318 Figure 1. (A) The Antarctic continent Transantarctic Mountains with present-day glacial fl ow lines Boundary between E & W Antarctic ice W 180° E 65°S Ice flow direction WILKESLAND (after Drewry, 1983; Barrett, 1999), location of McMurdo Sound (boxed), and of geological drill sites on land and on the Antarctic continental shelf. (B) Geological map (after War- ren, 1969a, 1969b; Craddock, 1970; Borg et al., 1987; Carosi et al., 2007). Also shown are the location of Cape Roberts Project drill hole CRP-1, ANDRILL drill holes AND-1B and AND-2A, and the location of samples with petrographical features closely matching those of the AND-2A core basement clasts. Present-day glacial fl ow lines of major outlet glaciers into the Ross Ice Shelf are after Fahne- stock et al. (2000) and Drewry (1983), and inferred catchments are based on elevation data from Drewry (1983). Abbreviations: BI—Black Island; CG—Carlyon Glacier; MM—Mount Morning; MiB—Minna Bluff; MD— Mount Discovery; RSR—Royal Soci- ety Range; TI—Teall Island; WI— White Island. McMurdo Volcanic Group Ross Orogen: metamorphic Beacon and Ferrar basement Supergroups Byrd Group Ross Orogen: Granite Horney Formation Harbour Intrusive Koettlitz Gp. & Skelton Gp. Complex with minor metamorphic rocks 100 km Geosphere, August 2011 923 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/7/4/922/3340417/922.pdf by guest on 01 October 2021 Talarico et al. GEOLOGICAL SETTING ney Formation (Carosi et al., 2007). Low-grade Ma Depth Clay Silt Sand Gravel metasediments, including extensive exposures of (m) The southern McMurdo Sound is surrounded metalimestone and metaconglomerates (Crad- with terrains characterized with a broad vari- dock, 1970; Goodge et al., 2004), are the domi- ety of rock types. Late Cenozoic (ca. 19 Ma to nant lithologies south of Byrd Glacier (Fig. 1). recent) alkali volcanic rocks, mainly basanites 100 >4.5 of the McMurdo Volcanic Group, form several MATERIALS AND METHODS volcanic centers exposed to the south and east of 169.20 the AND-2A drill site. The emplacement of Ross In the AND-2A core, a total number of 177.68 Island volcanoes resulted in signifi cant modifi ca- 103,759 clasts ranging in size from boulder 200 185.36 tion of the McMurdo Sound paleogeography and to granule class (>2 mm) were counted and, <7-8 14.20 fl exural loading with related basin subsidence for each clast, information such as occurrence 243.16 (Kyle, 1981, 1990).