Resume

• 2009

  The Central American forearc allows insight into the long-term evolution of the Middle American margin and possible shifts between accretionary and erosive periods of subduction. We present a revised tectonostratigraphic subdivision of the Azuero area based on new field observations and biochronologic data

  and a synthesis of previous age

  geochemical and stratigraphic data. The basement of the area is composed of an autochtonous oceanic plateau

  the early Central American arc and accreted seamounts

  which are unconformably overlain by forearc sediments. The nature and spatial arrangement of basement units combined with patterns of uplift and subsidence recorded in overlapping sediments allow reconstruction of the local evolution of subduction tectonics between the Upper Cretaceous and Miocene. Comparison of this evolution with that formerly proposed for the south Costa Rican margin based on a similar approach (Buchs et al.

  2010) provides an insight into temporal and along-strike changes of subduction tectonics along a ~ 500 km-long segment of the Middle American margin.We find that subduction erosion (or non-accretion)

  punctuated by seamount accretion

  was the dominant process along the margin between the late Campanian and Middle Eocene. In the Middle Eocene

  uplift of the Central American forearc

  initiation of a volcanic front retreat in Panama and a pulse of seamount accretion between south Costa Rica and west Panama are likely to relate to a reorganization of plate tectonics in the Pacific.A contrasted evolution occurred in south Costa Rica and Panama afterwards

  with continued subduction erosion in the Azuero area and net accretion of olistostromal and hemipelagic sediments in south Costa Rica at least until the Middle Miocene.Our results show that tectononstratigraphic observations in the forearc may represent a valuable complement to offshore drilling and geophysical studies to understand modern subduction tectonics along the Middle American margin.

  Late Cretaceous to Miocene tectono-stratigraphy of the Azuero area (west Panama) and the discontinuous accretion and subduction erosion along the Mid-American Margin

  Paulian Dumitrica

  Peter Oliver Baumgartner

  The study of the radiolarian ribbon chert is a key in determining the origins of associated Mesozoic oceanic terranes and may help to achieve a general agreement regarding the basic principles on the evolution of the Caribbean Plate. The Bermeja Complex of Puerto Rico

  which contains serpentinized peridotite

  altered basalt

  amphibolite

  and chert (Mariquita Chert Formation)

  is one of these crucial oceanic terranes. The radiolarian biochronology presented in this work is mainly based by correlation on the biozonations of Baumgartner et al. (1995) and O’Dogherty (1994) and indicates an early Middle Jurassic to early Late Cretaceous (late Bajocian–early Callovian to late early Albian–early middle Cenomanian) age. The illustrated assemblages contain about 120 species

  of which one is new (Pantanellium karinae)

  and belonging to about 50 genera. A review of the previous radiolarian published works on the Mariquita Chert Formation and the results of this study suggest that this formation ranges in age from Middle Jurassic to early Late Cretaceous (late Aalenian to early–middle Cenomanian) and also reveal a possible feature of the Bermeja Complex

  which is the younging of radiolarian cherts from north to south

  evoking a polarity of accretion. On the basis of a currently exhaustive inventory of the radiolarite facies s.s. on the Caribbean Plate

  a re-examination of the regional distribution of Middle Jurassic sediments associated with oceanic crust

  and a paleoceanographic argumentation on the water currents

  we come to the conclusion that the radiolarite and associated Mesozoic oceanic terranes of the Caribbean Plate are of Pacific origin. Eventually

  a discussion on the origin of the cherts of the Mariquita Formation illustrated by Middle Jurassic to middle Cretaceous geodynamic models of the Pacific and Caribbean realms bring up the possibility that the rocks of the Bermeja Complex are remnants of two different oceans.\n

  Aalenian to Cenomanian Radiolaria of the Bermeja Complex (Puerto Rico) and Pacific origin of radiolarites on the Caribbean Plate

  Mike Cosca

  Peter Oliver Baumgartner

  Sebastien Pilet

  Countless seamounts occur on Earth that can provide important constraints on intraplate volcanism and plate tectonics in the oceans

  yet their nature and origin remain poorly known due to difficulties in investigating the deep ocean. We present here new lithostratigraphic

  age and geochemical data from Lower/Middle Jurassic and Lower Cretaceous sequences in the Santa Rosa accretionary complex

  Costa Rica

  which offer a valuable opportunity to study a small-sized seamount from a subducted plate segment of the Pacific basin. The seamount is characterized by very unusual lithostratigraphic sequences with sills of potassic alkaline basalt emplaced within thick beds of radiolarite

  basaltic breccia and hyaloclastite. An integration of new geochemical

  biochronological and geochronological\ndata with lithostratigraphic observations suggests that the seamount formed ~175Ma ago on thick oceanic crust away from subduction zones and mid-ocean ridges. This seamount traveled ~65Ma in the Pacific before accretion. It resembles lithologically and compositionally “petit-spot” volcanoes found off Japan

  which form in response to plate flexure near subduction zones. Also

  the composition of the sills and lava flows in the accreted seamount closely resembles that of potassic alkaline basalts produced by lithosphere cracking along the Line Islands chain. We hypothesize based on these observations

  petrological constraints and formation of the accreted seamount coeval with the early stages of development of the Pacific plate that the seamount formed by extraction of small volumes ofmelt fromthe base of the lithosphere in response to propagating fractures at the scale of the Pacific basin.

  Low-volume intraplate volcanism in the Early/Middle Jurassic Pacific basin documented by accreted sequences in Costa Rica

  Abstract\nThe Santa Elena Ophiolite in Costa Rica is composed of a well-preserved fragment of the lithospheric mantle that formed along a paleo-spreading center. Within its exposed architecture

  this ophiolite records a deep section of the melt transport system of a slow/ultra-slow spreading environment

  featuring a well-developed melt-focusing system of coalescent diabase dikes that intrude the peridotite in a sub-vertical and sub-parallel arrangement. Here we present an integrated analysis of new structural data

  40Ar/39Ar geochronology

  major and trace element geochemistry and radiogenic isotope data from the diabase dikes in order to elucidate the tectonic setting of the Santa Elena Ophiolite. The dikes are basaltic and tholeiitic in composition. Petrological models of fractional crystallization suggest deep pressures of crystallization of > 0.4 GPa for most of the samples

  which is in good agreement with similar calculations from slow/ultra-slow spreading ridges and require a relatively hydrated (~ 0.5 wt.% H2O) MORB-like source composition. The diabase dikes share geochemical and isotope signatures with both slow/ultra-slow spreading ridges and back-arc basins and indicate mixing of a DMM source and an enriched mantle end-member like EMII. The 40Ar/39Ar geochronology yielded an age of ~ 131 Ma for a previous pegmatitic gabbroic magmatic event that intruded the peridotite when it was hot and plastic and an age of ~ 121 Ma for the diabase intrusions

  constraining the cooling from near asthenospheric conditions to lithospheric mantle conditions to ~ 10 Ma. Our findings suggest a complex interplay between oceanic basin and back-arc extension environments during the Santa Elena Ophiolite formation. We propose an alternative hypothesis for the origin of Santa Elena as an obducted fragment of an oceanic core complex (OCC).

  A melt-focusing zone in the lithospheric mantle preserved in the Santa Elena Ophiolite

  Costa Rica

  Percy Denyer

  Peter Oliver Baumgartner

  Detailed fi eld mapping and paleontological dating in the central and southeastern Nicoya Peninsula has\nrevealed Late Cretaceous and Paleogene radiolarian-bearing siliceous mudstones. These rocks belong to two terranes\n(Matambú and Manzanillo) that are partially contemporaneous with the Nicoya Complex

  but are genetically different.\nWhile the Nicoya Complex is formed exclusively by intraplate igneous rocks with associated radiolarites

  the studied sections\ninclude variable amounts of arc-derived volcanic and terrigenous materials. These fore-arc terranes include mafi c to\nintermediate volcaniclastics and associated pelagic and hemipelagic rocks rich in biogenic silica. Radiolarian preservation\nin these sediments is often enhanced by the presence of silica-saturated volcanic tuffs and debris. Seven out of 29 samples\nfrom different outcrops yielded relatively well-preserved radiolarian faunas. In total

  60 species belonging to 34 genera\nwere present in these faunas

  ranging in age from middle Turonian-Santonian to late Thanetian-Ypresian.

  Late Cretaceous and Paleogene Radiolaria from the Nicoya Peninsula

  Costa Rica: a tectonostratigraphic application

  GIS project based on ArcGIS platform dedicated to the reconstruction of the tectonic/geodynamic history of the Earth since the Cambrian times. It includes 2 geodatabases and 2 extensions of ArcGIS developed in .net and VB6.

  Eric Champod

  Thum Laurent

  Caroline WIlhem

  Flores

  American Museum of Natural History

  Brooklyn College

  Universidad de Costa Rica

  Columbia University

  American Museum of Natural History

  Brooklyn

  New York

  Structural Geology and Tectonics Assistant Professor at the Department of Earth and Environmental Sciences

  Assistant Professor

  Brooklyn College

  During these two semester I taught the following courses:\n- Introduction to Earth Science\n- Principles of geology\n- Earth Evolution and Geological Time

  Universidad de Costa Rica

  American Museum of Natural History

  New York

  New York

  Postdoctoral Fellow of the Swiss National Science Foundation and American Museum of Natural History working on Geochemistry and Geodynamics of the Guatemala Suture Zone. I also worked as a Science Educator for Young Initiatives programs of AMNH such as the NASA SRMP and Science Summer School teaching the Geodynamics and mentoring research projects on geochemistry of volcanic and metamorphic rocks

  Post Doc

  Palisades

  New York

  At the Lamont-Doherty Earth Observatory of Columbia University I carry out isotopic and geochronological analysis including Sr

  Nd

  Pb and Hf

  as well as Sm-Nd and Lu-Hf

  Associate Research Scientist

  Columbia University

  New York

  New York

  This position has two main tasks\n1- Research project on Geochemistry

  Geochronology and Geodynamics of metabasite blocks from subduction zone mélanges \n2- Co-teaching the Earth Enrichment and Earth systems

  Earth process courses for the Master on Arts of Teaching Earth Science program of the AMNH

  Faculty Research and Education Scholar

  American Museum of Natural History

• 2006

  PhD

  Geology

  Geochemistry & Geodynamics

  Université de Lausanne

• 2004

  English

  Spanish

  French

  DEA

  Science de la Terre

• 2002

  Licentiate degree

  Geology/Earth Science

  General

  Universidad de Costa Rica

• 1998

  Bachelor's degree

  Geology/Earth Science

  General

  Universidad de Costa Rica

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  kennet flores

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  Sedimentology

  Metamorphic history of riebeckite- and aegirine-augite-bearing high-pressure–low-temperature blocks within the Siuna Serpentinite Mélange

  northeastern Nicaragua

  Peter O. Baumgartner

  Dionisio Rodríguez

  Sussanne Skora

  The Siuna Serpentinite Mélange (SSM) is a subduction-zone-related complex that contains diverse blocks of igneous and sedimentary origin

  overprinted by various metamorphic conditions. The SSM is located at the southern border of the Chortís block and marks the boundary between continental and oceanic crusts in the western margin of the Caribbean Plate. The serpentinite matrix mainly consists of lizardite/chrysotile

  Cr-rich spinel

  and relict orthopyroxene that suggest a harzburgitic protolith and an upper mantle supra-subduction zone origin. Blocks within the southern and central regions range from Jurassic pelagic sediments to mafic/intermediate igneous rocks that are metamorphosed to various degrees

  ranging from prehnite-pumpellyite/greenschist to likely blueschist facies (e.g. riebeckite-bearing metashale) conditions. In contrast

  the northern section encloses almost exclusively epidote-amphibolite facies metabasite blocks

  and minor mica- and chlorite-rich rocks of metasomatic origin

  respectively. Some of the epidote-amphibolite blocks contain relic garnet-rich zones embedded in an amphibole-rich matrix. The garnets appear to record two generations of growth and contain mineral inclusions such as amphibole

  apatite

  titanite

  aegirine-augite

  and quartz. Thermobarometric estimates for the garnet-rich zones and epidote-amphibolite-rich matrix suggest a prograde blueschist facies at ~1.2 GPa and 400–450°C

  an eclogite facies metamorphic peak at 1.5–1.7 GPa and 565–614°C

  and a post-peak epidote-amphibolite facies metamorphism. These pressure and temperature estimates indicate a classical clockwise PT path that has been observed in many palaeo-subduction zone environments worldwide. Phengite Ar–Ar dating of mica-rich rock yields 140 Ma and suggests an Early Cretaceous exhumation along the southern edge of the continental Chortís block.

  Metamorphic history of riebeckite- and aegirine-augite-bearing high-pressure–low-temperature blocks within the Siuna Serpentinite Mélange

  northeastern Nicaragua

  Paulian Dumitrica

  Peter Oliver Baumgartner

  In the circum-Pacific ophiolitic belts; when no other biogenic constituents are found; radiolarians have the potential to provide significant biostratigraphic information. The Santa Rosa Accretionary Complex; which crops out in several half-windows (Carrizal; Sitio Santa Rosa; Bahia Nancite; Playa Naranjo) along the south shores of the Santa Elena Peninsula in northwestern Costa Rica; is one of these little-known ophiolitic mélanges. It contains various oceanic assemblages of alkaline basalt; radiolarite and polymictic breccias. The radiolarian biochronology presented in this work is mainly based by correlation on the biozonations of Carter et al. (2010); Baumgartner et al. (1995b); and O’Dogherty (1994) and indicate an Early Jurassic to early Late Cretaceous (early Pliensbachian to earliest Turonian) age for the sediments associated with oceanic basalts or recovered from blocks in breccias or megabreccias. The 19 illustrated assemblages from the Carrizal tectonic window and Sitio Santa Rosa contain in total 162 species belonging to 65 genera.

  Early Jurassic to early Late Cretaceous radiolarians of the Santa Rosa Accretionary Prism (north-western Costa Rica)

  Jadeite jade is sometimes referred to as hard jade and dominates the marketplace for gem material. However

  its usage rivals soft jade

  or nephrite

  in early cultures. Recent advances in the study of jadeite jade

  or jadeitite

  substantiates an origin in subduction channels through both hydrothermal vein crystallization and metasomatism. The hypotheses of origin are reviewed and studied occurrences enumerated

  with citations

  and a synopsis of the main jade varieties found among these deposits is provided. Finally

  guidelines for jadeite jade exploration

  based on lithological association and the tectonic framework

  are suggested.

  Jadeite jade: Origin

  Sources

  Varieties and Exploration

  Mordecai-Mark Mac Low

  Edmond Mathez

  Maritza Macdonald

  Rosamond J. Kinzler

  Jocelyn A. Sessa

  Ashley Pagnotta

  Nasser A. Zirakparvar

  Gokce Ustunisik

  Patricia A. Nadeau

  During the 2009–2010 school year

  40% of New York City (NYC) Earth science teachers were not certified to teach Earth science [New York State Education Department (NYSED)

  2011]. This highlights a longstanding shortage of certified teachers

  which persists today and prevents many schools from offering courses on the subject

  thus diminishing student opportunities to study or embark on careers in Earth science. More generally

  the paucity of qualified

  effective science teachers hinders student achievement in science

  technology

  engineering

  and mathematics (STEM)

  and research has consistently shown that improving the quality of teaching substantially increases achievement in STEM-related fields [National Science Board

  2007]. With only 36% of NYC 8th graders scoring at or above the basic level of proficiency in science and with even lower scores for African-American and Hispanic students [Livingston and Wirt

  2005]

  the need for more qualified science teachers is clear.

  Pilot Program for Teaching Earth Science in New York

  Daniel Cruz

  Peter Oliver Baumgartner

  We propose a new terrane subdivision of Nicaragua and Northern Costa Rica

  based on Upper Triassic to Upper Cretaceous radiolarian biochronology of\nribbon radiolarites

  the newly studied Siuna Serpentinite Mélange

  and published 40Ar/39Ar dating and geochemistry of mafic and ultramafic igneous rock\nunits of the area.\nThe new Mesquito Composite Oceanic Terrane (MCOT) comprises the southern half of the Chortis Block

  that was assumed to be a continental fragment\nof N-America. The MCOT is defined by 4 corner localities characterized by ultramafic and mafic oceanic rocks and radiolarites of Late Triassic

  Jurassic and\nEarly Cretaceous age: 1. The Siuna Serpentinite Mélange (NE-Nicaragua)

  2. The El Castillo Mélange (Nicaragua/Costa Rica border)

  3.The Santa Elena Ultramafics\n(N-Costa Rica) and

  4. DSDP Legs 67/84.\n1. The Siuna Serpentinite Mélange contains

  high pressure metamorphic mafics and Middle Jurassic (Bajocian-Bathonian) radiolarites in original

  sedimentary\ncontact with arc-metandesites. The Siuna Mélange also contains Upper Jurassic black detrital chert formed in a marginal (fore-arc?) basin shortly before\nsubduction. A phengite 40Ar/39Ar -cooling age dates the exhumation of the high pressure rocks as 139 Ma (earliest Cretaceous).\n2. The El Castillo Mélange comprises a radiolarite block tectonically embedded in serpentinite that yielded a diverse Rhaetian (latest Triassic) radiolarian assemblage

  \nthe oldest fossils recovered so far from S-Central America...

  Upper Triassic to Cretaceous Radiolaria from Nicaragua and Northern Costa Rica – the Mesquito Composite Oceanic Terrane

  Norman J. Pearson

  Hannes K. Brueckner

  Jadeitite is a rare rock type associated with high-pressure–low-temperature blocks within serpentinite matrix mélanges. Models of formation involve precipitation from subduction-zone aqueous fluids veining the overlying mantle wedge (P-type)

  or metasomatism of igneous and/or sedimentary protoliths previously emplaced into the mélange (R-type). Age determinations of mélange lithologies provide constraints on the timing of “peak metamorphism” and subsequent exhumation. The timing of jadeitite formation

  particularly in the rich source of the Guatemala Suture Zone (GSZ)

  is a controversial subject needing further attention.

  Jadeitite formed during subduction: In situ zircon geochronology constraints from two different tectonic events within the Guatemala Suture Zone

  The reconstructions show the break up of Gondwana with oceanisation between SouthAmerica (SAM) and Antarctica (ANT)

  together with the break off of ‘Andean’ geodynamical units (GDUs). We propose that oceanisation occurs also east and south of the Scotian GDUs. Andean GDUs collide with other GDUs crossing the Pacific. The west coast of SAM and ANT undergo a subsequent collision with all those GDUs between 103 Ma and 84 Ma

  and the Antarctic Peninsula also collides with Tierra del Fuego. The SAM–ANT plate boundary experienced a series of extension and shortening with large strike-slip component

  culminating with intra-oceanic subduction leading to the presence of the ‘V-’ and ‘T-’ anomalies in the Weddell Sea. From 84 Ma

  a transpressive collision takes place in the Scotia region

  with active margin to the east. As subduction propagates northwards into an old and dense oceanic crust

  slab roll-back initiates

  giving rise to the western Scotia Sea and the Powell Basin opening. The Drake Passage opens. As the Scotian GDUs migrate eastwards

  there is enough space for them to spread and allow a north–south divergence with a spreading axis acting simultaneously with the western Scotia ridge. Discovery Bank stops the migration of South Orkney and ‘collides with’ the SAM–ANT spreading axis

  while the northern Scotian GDUs are blocked against the Falkland Plateau and the North-East Georgia Rise. The western and central Scotia and the Powell Basin spreading axes must cease

  and the ridge jumps to create the South Sandwich Islands Sea. The Tierra del Fuego–Patagonia region has always experienced mid-oceanic ridge subduction since 84 Ma. Slab window location is also presented (57–0 Ma)

  because of its important implication for heat flux and magmatism.

  Geodynamic reconstructions of the South America – Antartica plate system

  Claudia Baumgartner-Mora

  Peter Oliver Baumgartner