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An asteroid impact in the Pacific respect, we go further proposing that such an may have triggered a cascade of impact may be the geologic equivalent to the tectonic events leading to formation falling domino principle: once the first piece is knocked over, the rest fall quickly. Thus, once of the mid Chilean Iron the meteorite impacted the mid Pacific, Belt subsequent and sequential plume emplacement, massive , plate El impacto de un meteorito en el Pacífico reorganization, increased plate stress along podría haber desatado una cascada de the Pacific margin, zone formation and eventos tectónicos que habría llevado a la emplacement of the Chilean Iron Belt (CIB) formación de la Faja Cretácica de would have taken place within a relatively Yacimientos de Hierro de short time span in mid Cretaceous time. Thus, we propose that formation of the CIB could be Jorge Oyarzún fully regarded as an integral part of the far Departamento de Ingeniería de Minas, Facultad de Ingeniería, reaching consequences derived form a large Universidad de La Serena, Casilla 554, La Serena, Chile meteoritic impact in the Pacific. Roberto Oyarzun Departamento de Cristalografía y Mineralogía, Facultad de Ciencias Geológicas, Universidad Complutense, 28040 Madrid, Spain Introduction

Javier Lillo “Coincidence is the word we use when we Escuela Superior de Ciencias Experimentales y Tecnología, Universidad Rey Juan Carlos, Tulipán s/n, 28933 Móstoles (Madrid), can't see the levers and pulleys” (Emma Bull; Spain in Zambetti 2006). In 2003 the authors of this

Jean Jacques Ménard note suggested a potential Iamgold Corporation Mali, B.P. 2699, Bamako, République du Mali scenario leading to formation of the mid Cretaceous Chilean Iron Belt (CIB) (Oyarzun et al. 2003). In that paper we indicated that a Abstract major change occurred in late Neocomian time, when superplume emplacement (Mid A cascade of tectonic and magmatic events Pacific Superplume) (Larson 1991; Vaughan that took place in the Pacific and northern 1995) and plate reorganization processes took Chile during mid Cretaceous led to formation place in the Pacific. The superplume event of one of the World‟s largest Kiruna-type iron resulted in major ridge-push force, belts with reserves of ~ 2000 Mt (60% Fe), a overwhelming slab-pull at subducting margins, unique case in the geological history of Chile. with the final result of increased coupling Geological evidence indicates that a major between the subducting and overriding plate change occurred in mid Cretaceous time, (Vaughan 1995) (Fig. 1A). In turn, these events when superplume emplacement and plate would have completely changed the tectonic reorganization processes took place in the setting of northern Chile, ending the Early Pacific. Although this scenario is well Cretaceous extensional period (aborted rifting documented, no proposals have been put in the back-arc basin), and increasing stress forward on the actual event that may have at a crustal scale (Fig. 1B). We went further, triggered the subsequent cascade effect. suggesting that overpressurized dioritic Unusual events require unusual perspectives were pushed up mainly along the for their analysis. We know that a large best possible structural path in northern Chile, meteoritic impact in the Pacific may have that is, the large Zone (AFZ) initiated massive volcanism leading to (Fig. 1B), eventually forming a +500 km long formation of the Ontong Java Plateau. In this belt of Kiruna-type iron deposits with reserves

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of ~ 2000 Mt (60% Fe), a unique case in source (90% probability) of the Chicxulub Chile's geological history (Ménard 1992; impactor. In this respect, our story has nothing Oyarzun et al. 2003) (Fig. 2). Although we to do with the famous K/T boundary but with keep supporting this tectonic scenario, we go events that took place some 50 Ma earlier, a step further suggesting that initiation of closer to another stratigraphic transition massive volcanism and plate reorganization in (Aptian-Albian: 112 Ma), and within a different the Pacific may have initiated after a large plate tectonics scenario (Pacific) (Fig. 1A, 3). meteorite impacted this realm. In this respect, impact cratering has been an ongoing and recurring geological process throughout the history of the planets (including Earth), that operates at many scales and has substantial geological, environmental, biological consequences, and can even force large geodynamic events (Head 2001; Glikson 2008). Besides, the linking of ore deposit formation to meteorite impacts is not new, and a remarkable example of this connection is provided by the giant crater, igneous complex, and nickel ore deposits of Sudbury in Ontario, Canada (e.g. Therriault et al. 2002; Mungall et al. 2004; among others). However, different from Sudbury, other, different links can be traced between impacts and ore deposit formation. As we argue in this paper, impact processes may not be directly involved in the actual formation of an ore deposit, but can trigger nonetheless an unstoppable chain of events in cascade that will ultimately lead to the development a full scale metallogenic scenario.

Basis for a speculative model Part of our proposal is based upon the observations and calculations made by Bottke Fig. 1: A) Configuration of continental and oceanic plates at 120 Ma, Mid et al. (2007), who studied the catastrophic Pacific Superplume and potential site for an asteroid impact. Plates: Aluk, disruption of the parent body of the asteroid Africa (AFR), Antartica (ANT), FAR (Farallon), Pacific (PAC), South America (SA). CIB: Chilean Iron Belt. Plate configuration after Baptistina. The asteroid broke up at about 160 Zonenshayn et al. (1984) and Turner et al. (1994). Mid Pacific Ma ago in the innermain asteroid belt, and Superplume after Larson (1991). B) Block diagram depicting the tectonomagmatic scheme for northern Chile in mid Cretaceous and the would have led to generation of large ascent of overpressurized magmas along a shear zone. Upper block fragments that have been slowly delivered by diagram and ascent based on Saint Blanquant et al. (1998). AFZ: Atacama Fault Zone. CIB: Chilean Iron belt. dynamical processes to orbits where they could strike the terrestrial planets. This is the Fig. 1: A) Configuración de las placas continentales y oceánicas hace 120 Ma y sitio potencial para el impacto de un asteroide. B) Bloque so-called Baptistina Asteroid Family (BAF). diagrama mostrando la situación tectonomagmática de la CIB hace 120 Bottke et al. (2007) went further, indicating Ma. that this asteroid shower was the most likely

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From our perspective, several elements are Superplume emplacement and subsequent crucial for the revisited CIB scenario. On one development of the OJP had far reaching side we have the Baptistina asteroids, hitting implications at the Pacific scale, including high terrestrial planets since the parent asteroid production of oceanic crust at mid ocean ridges broke up, on the other, seemingly (Larson 1991; Vaughan 1995), increased ridge- unconnected facts that can nevertheless be push force and coupling between the part of the same story. Major events to be subducting and overriding plates, and uplift, considered here are: 1) Superplume deformation, and metamorphism along the emplacement and development of the Ontong- Pacific margin (Vaughan 1995). As far as the Java Plateau (OJP) (the largest known flood northern Chilean realm is concerned, the basin basalt province on Earth) in the Pacific, was uplifted, and no more marine episodes beginning at ~ 120 Ma (Larson 1991; Vaughan were further recorded after this episode; 1995; Ingle and Coffin, 2004) (Fig. 1A); and 2) besides, volcanic activity along the arc formation of the large CIB at 128-100 Ma, with decreased dramatically, and the large Atacama a peak at 115-110 Ma (Oyarzun et al. 2003) Fault Zone began its development. It is (Fig. 1B, 2). precisely along this tectonic domain that the CIB formed (Fig. 1B) (Oyarzun et al. 2003). This period is also marked the onset of cooling and uplifting of the arc which eventually shifted to an eastward position by mid Cretaceous time (Scheuber et al. 1995). At a larger scale, it is also during this period that massive accretion of mafic-ultramafic complexes started in Colombia and Ecuador (e.g. Nivia 1996; Hughes and Pilatasig 2002).

The OJP and CIB revisited scenario A central part of our argument in the early paper (Oyarzun et al. 2003) was the link between the emplacement of a large plume in the mid Pacific and formation of the CIB during a major plate reorganization event. However, the main issue here is whether such Pacific superplume (Larson 1991) and therefore the OJP had a deep mantle (e.g. in the D” layer, sensu Schott and Yuen, 2004) or a shallow origin triggered by a meteorite impact. In this respect, there are arguments based on numerical simulations that rule out a

Fig. 2: The Cretaceous Chilean Iron belt (CIB) and the Atacama Fault firm relationship between asteroid impacts and Zone (AFZ). The five large iron deposits (28º-30º S) have reserves volcanism (Ivanov and Melosh 2003). (before mining) in the order of 200-400 Mt (60% Fe): Boquerón Chañar (BO), Los Colorados (CO), Algarrobo (AL), Cristales (CR), However, as also noted by Glikson (2003), and El Romeral (RO). The rest of the deposits are in the order of 100- there are crustal and petrologic factors that 20 Mt and even less. After Oyarzun et al. (2003). greatly increase the probability of impact- Fig. 2: La Faja Cretácica de Yacimientos de Hierro de Chile. triggered volcanism in geothermally active regions of oceanic basins. The latter is also

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supported by the more recent numerical grains) can be obtained in the field, a large analysis of Elkins-Tanton and Hager (2005), impact with subsequent massive volcanism on who indicate that large meteoritic impacts on oceanic lithosphere would leave few clues if thin lithosphere (as we can expect in ocean any. First, no quartz is to be found in oceanic basins) can indeed trigger the onset of large lithosphere, besides a huge volcanic plateau basaltic provinces. According to Ingle and such as Ontong Java would erase any Coffin (2004) there are sound arguments morphological signatures left by an impact: the ruling against a deep mantle model for the oceanic would fully blanket the area. As OJP plume: 1) the absence of a track; indicated by Elkins-Tanton and Hager (2005), 2) minor early crustal uplift associated with a most craters of the age and size seen on the super plume emplacement; and 3) minor late moon are obliterated on Earth through total subsidence compared with normal processes of plate tectonics and erosion, oceanic crust or other oceanic plateaus and whereas others would be obscured beneath submarine ridges. Instead, a meteorite impact the existing large basaltic igneous provinces. origin for both the plume and the OJP (Fig. In this respect, we are fully aware of the fact 1A) is favoured by: 1) high degrees of melting that we cannot prove beyond any reasonable at shallow upper mantle depths; 2) low water doubt that a large body impacted the Pacific contents of basalts; 3) enrichment of platinum by mid Cretaceous time. However, we also group elements in basalts; and last but not believe that it is likely that this may have least 4) because a ~300 km deep, seismically happened because of the following reasons. slow mantle root is much more consistent with On one hand the model of Bottke et al. (2007) the consequences derived from the impact of indicates that Earth was subjected to intense an asteroid colliding with the Pacific ocean bombardment of meteoritic bodies at ~ 30 to floor. Ingle and Coffin (2004) and Jones 60 Ma after BAF formation (at 160 Ma) (Fig. (2005) suggest that these events could have 3). been triggered by the impact of an asteroid ~20-30 km (diameter) on relatively young (~10-20 Ma) Pacific lithosphere. This would have resulted in large decompression melting in the upper mantle and initiation of massive volcanism at the OJP site. Although this may well explain massive volcanism at the OJP, the question regarding the mantle plume remains: how could an asteroid impact trigger such a plume? In this regard Jones et al. (2002) indicate that the withdrawal of a large volume of melt from the mantle (materials that ascend to feed the superficial volcanism) would lead to mass up-flow of the upper mantle into the vacated space, which in turn would lead to further melting. In this case, we would be dealing with impact-derived or simply, impact plumes (Jones et al. 2002). Fig.3: The Baptistina Asteroid Family (BAF) impact rate on Earth through time after its formation at 160 Ma (modified after Bottke et al. 2007). CIB: Different to impacts on continental crust where Chilean Iron Belt. D: Crater diameter. OJP: Ontong Java Plateau. morphological (e.g. crater rims) and Fig. 3: Tasas de impacto en la Tierra de la Familia de Asteroides mineralogical evidence (e.g. shattered quartz Baptistina.

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On the other, this time span perfectly matches ultramafic complexes along the Colombian the age range of the CIB: 128-100 Ma and and Ecuadorian Andes, and formation of the initiation of volcanism at the OJP (Fig. 3), CIB may in turn require unusual perspectives which in turn can be regarded as derived from for their analysis. If the OJP was indeed an impact plume (Jones et al. 2002). Besides, initiated by a large impact (Fig. 4), as sound it might not be a coincidence that it is precisely scientific arguments indicate, then it follows during this time span when a BAF derived that the cascade of tectonic, magmatic and body impacted the surface of the Moon, metallogenic events are related to that impact. forming the huge crater Tycho (109 Ma; Bottke et al. 2007) (Fig. 4). In this respect, multiple impact episodes (derived form fragmented asteroids or comets) are not be regarded as rare events (e.g. Spray et al. 1998; Keller et al. 2003), a phenomenon that is now well exemplified by the sequential impacts of the disrupted comet Shoemaker– Levy 9 with Jupiter in 1994 (Spray et al. 1998). Jupiter, a huge planetary body, is „a difficult to miss target‟, the Moon is not. Furthermore, if the idea of a mid Cretaceous large impact in the Pacific is correct, then it could also have far reaching implications, for example, as an additional explanation for the origin of the late Aptian-early Albian „cold snap‟, a time span Fig. 4: Above, formation of the Baptistina Asteroid Family (BAF); below characterized by global cooling as indicated left, impact of a BAF asteroid on the Moon forming the giant crater Tycho by sedimentological observations and oxygen (109 Ma); below right, according to this work: a coeval potential impact on the Pacific. Figure: from Southwest Research Institute. isotope data (Mutterlose et al. 2009). Fig. 4: Arriba, formación de la Familia Baptistina de Asteroides; izquierda abajo, impacto de un asteroide de la familia Baptistina en la Luna Final remarks formando el gran cráter Tycho (109 Ma); interpretación de acuerdo a este trabajo de un impacto contemporáneo en el Pacífico.

William Bragg said that the important thing in science was not so much to obtain new facts as As expressed above, these events would be to discover new ways of thinking about them the geologic equivalent to the „falling domino (Braga and Grepioni 2000). In this regard we principle‟: once the first piece is knocked over would like to think that this note opens new the rest fall quickly. Perhaps „quickly‟ is the ways for the understanding of the mid keyword here, because plume emplacement, Cretaceous Pacific scenario and therefore, for volcanism, plate reorganization, increased the CIB. We already related the origin of the belt plate stress along the Pacific margin, fault to superplume emplacement, increasing stress zone formation and emplacement of the at a crustal scale, and overpressurized dioritic Chilean Iron Belt all took place within a magmas pushed up along the best possible relatively short time span. If we are correct, structural path in northern Chile: the large then a large meteorite impact would have Atacama Fault Zone (Oyarzun et al. 2003). been that initial domino piece that made the Unusual, time-related combined events such others fell. We are not implying that everything as formation of the OJP, plate reorganization occurred overnight, but quick enough in in the Pacific, massive emplacement of mafic- geological terms to be regarded as a rather

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unique collection of chained events, that pétrologiques. C R Acad Sci Paris 315: 725- nonetheless would have started with a single, 731 Mungall JE, Ames DE, Hanley JJ (2004) Geochemical almost instantaneous massive release of evidence from the Sudbury structure for energy in the Pacific.Thus, formation of the crustal redistribution by large bolide impacts. CIB could be fully regarded as an integral part Nature 429:546−548 of the far reaching consequences derived form Mutterlose J, Bornemann A, Herrle J (2009) The Aptian a large meteoritic impact (Fig. 4). – Albian cold snap: Evidence for “mid” Cretaceous icehouse interludes. N Jb Geol Paläont Abh 252:217–225 Nivia A (1996) The Bolivar mafic-ultramafic complex, References SW Colombia: the base of an obducted oceanic plateau. J S Am Earth Sci 9:59–68 Bottke, WF, Vokrouhlicky D, Nesvorny D (2007) An Oyarzun R, Oyarzun J, Menard JJ, Lillo J (2003) The asteroid breakup 160 Myr ago as the Cretaceous iron belt of northern Chile: role of probable source of the K/T impactor. Nature oceanic plates, a superplume event, and a 449:48−53 major shear zone. Min Deposita 38:640–646 Braga D, Grepioni F (2000) Intermolecular interactions in Saint Blanquant M, Tikoff B, Teyssier C, Vigneresse JL nonorganic crystal engineering. Acc Chem Res (1998) Transpressional kinematics and 33:601−608 magmatic arcs. In: Holdsworth RE, Strachan Elkins-Tanton LT, Hager BH (2005) Giant meteoroid RA, Dewey JF (eds) Continental impacts can cause volcanism. Earth Plan Sci transpressional and transtensional tectonics. Lett 239:219–232 Geol Soc Spec Publ 135, London, pp 327–340 Glikson AY (2003) Impacts do not initiate volcanic Scheuber E, Reutter KJ (1992) Magmatic arc tectonic in eruptions: Eruptions close to the crater: the central Andes between 21º and 25ºS. Comment and Reply. Geology 31:e49 Tectonophysics 205: 127−140 Glikson AY (2008) Field evidence of Eros-scale Schott B, Yuen DA (2004) Influences of dissipation and asteroids and impact-forcing of Precambrian rheology on mantle plumes coming from the geodynamic episodes, Kaapvaal (South D”-layer. Phys Earth Planet In 146:139–145 Africa) and Pilbara (Western Australia) Spray JG, Kelley SP, Rowley DB (1998) Evidence for a . Earth Plan Sci Lett 267:558–570 late multiple impact event on Earth. Head JW (2001) Lunar and planetary perspectives on Nature 392:171−173 the geological history of the Earth. Earth Therriault AM, Fowler AD, Grieve RAF (2002) The Moon Planets 85–86:153–177 Sudbury Igneous Complex: a differentiated Hughes RA, Pilatasig LF (2002) Cretaceous and impact melt sheet. Econ Geol 97:1521−1540 Tertiary terrane accretion in the Cordillera Turner S, Regelous M, Kelley S, Hawkesworth C, Occidental of the Andes of Ecuador. Mantovani M (1994) Magmatism and Tectonophysics 345:29–48 continental break-up in the South Atlantic: Ingle S, Coffin MF (2004) Impact origin for the greater high precision 40Ar-39Ar geochronology. Earth Ontong Java Plateau? Earth Plan Sci Lett Plan Sci Lett 121: 333-348 218:123−134 Vaughan APM (1995) Circum-Pacific mid-Cretaceous Ivanov BA, Melosh HJ (2003) Impacts do not initiate deformation and uplift: a superplume-related volcanic eruptions: Eruptions close to the event? Geology 23:491−494 crater. Geology 31:869–872 Zambetti N (2006) Occasional coincidences: occasion- Jones AP (2005) Meteorite impacts as triggers to large making via meaningful coincidences with on- igneous provinces. Elements 1: 277−281 demand media. Interaction Design Institute Keller G, Stinnesbeck W, Adatte T, Stüben D (2003) Ivrea, Thesis Report, http://www.zambetti.com/ Multiple impacts across the Cretaceous– projects/occasionalcoincidences/documents/nz Tertiary boundary. Earth Sci Rev 62:327–363 ambetti_occasional_coincidences_2006.pdf Larson RL (1991) Latest pulse on Earth: evidence for a Zonenshayn LP, Savostin LA, Sedov AP (1984) Global mid-Cretaceous superplume. Geology 19: paleogeodynamic reconstructions for the last 547−550 160 Ma. Geotectonics 18: 181-195 Ménard JJ (1992) Comparaison entre les roches plutoniques associées à la Ceinture de Fer du Chili et aux porphyres cuprifères: arguments

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