Tectonic Analysis Ltd

Walnut Creek, CA, United States

Tectonic Analysis Ltd

Walnut Creek, CA, United States
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Boschman L.M.,University Utrecht | van Hinsbergen D.J.J.,University Utrecht | Torsvik T.H.,University of Oslo | Torsvik T.H.,Geological Survey of Norway | And 5 more authors.
Earth-Science Reviews | Year: 2014

The Caribbean oceanic crust was formed west of the North and South American continents, probably from Late Jurassic through Early Cretaceous time. Its subsequent evolution has resulted from a complex tectonic history governed by the interplay of the North American, South American and (Paleo-)Pacific plates. During its entire tectonic evolution, the Caribbean plate was largely surrounded by subduction and transform boundaries, and the oceanic crust has been overlain by the Caribbean Large Igneous Province (CLIP) since ~. 90. Ma. The consequent absence of passive margins and measurable marine magnetic anomalies hampers a quantitative integration into the global circuit of plate motions. Here, we present an updated, quantitatively described kinematic reconstruction of the Caribbean region back to 200. Ma, integrated into the global plate circuit, and implemented with GPlates free software. Our reconstruction includes description of the tectonic units in terms of Euler poles and finite rotation angles. Our analysis of Caribbean tectonic evolution incorporates an extensive literature review. To constrain the Caribbean plate motion between the American continents, we use a novel approach that takes structural geological observations rather than marine magnetic anomalies as prime input, and uses regionally extensive metamorphic and magmatic phenomena such as the Great Arc of the Caribbean, the CLIP and the Caribbean high-pressure belt as correlation markers. The resulting model restores the Caribbean plate back along the Cayman Trough and major strike-slip faults in Guatemala, offshore Nicaragua, offshore Belize and along the Northern Andes towards its position of origin, west of the North and South American continents in Early Cretaceous time. We provide the paleomagnetic reference frame for the Caribbean region by rotating the Global Apparent Polar Wander Path into coordinates of the Caribbean plate interior, Cuba, and the Chortis Block. We conclude that formation of the Caribbean plate, west of the North and South Americas, as a result of Panthalassa/Pacific spreading leads to a much simpler plate kinematic scenario than Proto-Caribbean/Atlantic spreading. Placing our reconstruction in the most recent mantle reference frames shows that the CLIP originated 2000-3000. km east of the modern Gala´pagos hotspot, and may not have been derived from the corresponding mantle plume. Finally, our reconstruction suggests that most if not all modern subduction zones surrounding the Caribbean plate initiated at transform faults, two of these (along the southern Mexican and NW South American margins) evolved diachronously as a result of migrating trench-trench-transform triple junctions. © 2014 Elsevier B.V.

Cochrane R.,University of Geneva | Spikings R.,University of Geneva | Gerdes A.,Goethe University Frankfurt | Gerdes A.,Stellenbosch University | And 5 more authors.
Lithos | Year: 2014

Crustal anatectites are frequently observed along ocean-continent active margins, although their origins are disputed with interpretations varying between rift-related and collisional. We report geochemical, isotopic and geochronological data that define an ~. 1500. km long belt of S-type meta-granites along the Andes of Colombia and Ecuador, which formed during 275-223. Ma. These are accompanied by amphibolitized tholeiitic basaltic dykes that yield concordant zircon U-Pb dates ranging between 240 and 223. Ma. A model is presented which places these rocks within a compressive Permian arc setting that existed during the amalgamation of westernmost Pangaea. Anatexis and mafic intrusion during 240-223. Ma are interpreted to have occurred during continental rifting, which culminated in the formation of oceanic crust and initiated the break-up of western Pangaea. Compression during 275-240. Ma generated small volumes of crustal melting. Rifting during 240-225. Ma was characterized by basaltic underplating, the intrusion of tholeiitic basalts and a peak in crustal melting. Tholeiitic intrusions during 225-216. Ma isotopically resemble depleted mantle and yield no evidence for contamination by continental crust, and we assign this period to the onset of continental drift. Dissected ophiolitic sequences in northern Colombia yield zircon U-Pb dates of 216. Ma. The Permo-Triassic margin of Ecuador and Colombia exhibits close temporal, faunal and geochemical similarities with various crustal blocks that form the basement to parts of Mexico, and thus these may represent the relict conjugate margin to NW Gondwana. The magmatic record of the early disassembly of Pangaea spans ~. 20. Ma (240-216. Ma), and the duration of rifting and rift-drift transition is similar to that documented in Cretaceous-Tertiary rift settings such as the West Iberia-Newfoundland conjugate margins, and the Taupo-Lau-Havre System, where rifting and continental disassembly also occurred over periods lasting ~. 20. Ma. © 2013 Elsevier B.V.

Solari L.A.,National Autonomous University of Mexico | Garcia-Casco A.,University of Granada | Martens U.,National Autonomous University of Mexico | Martens U.,Tectonic Analysis Ltd. | And 2 more authors.
Bulletin of the Geological Society of America | Year: 2013

The Rabinal Granite is a peraluminous S-type composite pluton formed upon partial melting of a metasedimentary source region that fringes the southernmost North America plate in central Guatemala. It is therefore considered, together with the intruded metasedimentary sequences, to be part of the continental basement of the Maya block. This leucocratic K-feldspar-plagioclase-quartz-muscovite ± biotite granite shows increasing deformation along its southern margin, where it is cut across by the dextral, Late Cretaceous, top-tothe-NE Baja Verapaz shear zone. Although it has been recently dated at 562-453 Ma (isotope dilution-thermal ionization mass spectrometry), the new data presented here, including laser ablation-inductively coupled plasma-mass spectrometry (LAICP-MS) U-Pb and 40Ar-39Ar geochronology and electron-probe mineral chemistry, allow us to more precisely establish the timing of intrusion and metamorphic overprinting of the Rabinal Granite. The zircons dated by LA-ICP-MS indicate a crystallization age of 471 +3/-5 Ma (Early Ordovician), as well as abundant inherited cores with Pan-African and Mesoproterozoic dates. Laser total fusion Ar-Ar analyses of magmatic low-silica muscovite (Si = 6.2-6.4 atoms per formula unit) indicate cooling following magmatic crystallization during the mid-late Paleozoic and variable extents of resetting of Ordovician micas during Cretaceous metamorphism and deformation. The pressure-temperature (P-T) conditions of the inferred Ordovician metamorphism that produced partial melting of the metasedimentary source of the Rabinal Granite and the ascent and crystallization of the granitic melt are uncertain, but a clockwise P-T-time path with maximum P and T of <8 kbar and 750 °C, respectively, is proposed. A second thermal event is recognized in recrystallized high-silica muscovite (Si up to = 6.8 atoms per formula unit) formed at peak P and T of ~8.5 kbar and ~300 °C, respectively. This second event, dated at 70.1 ± 0.6 Ma by means of laser total fusion 40Ar-39Ar analyses on high-Si muscovite grains, is interpreted to be the result of subduction and accretion of the basement of the Maya block during the latest Cretaceous, likely in a transpressional tectonic regime related to the lateral collision of the Maya block with the Pacific (Farallon)-derived Caribbean arc. This finding represents the first direct evidence for latest Cretaceous subduction of the metamorphic Paleozoic basement of the Maya block, north of the Baja Verapaz shear zone. © 2013 Geological Society of America.

Pindell J.,Rice University | Pindell J.,Tectonic Analysis Ltd. | Graham R.,Independent Consultant | Horn B.,ION Geophysical
Basin Research | Year: 2014

Interpretation of long-offset 2D depth-imaged seismic data suggests that outer continental margins collapse and tilt basinward rapidly as rifting yields to seafloor spreading and thermal subsidence of the margin. This collapse post-dates rifting and stretching of the crust, but occurs roughly ten times faster than thermal subsidence of young oceanic crust, and thus is tectonic and pre-dates the 'drift stage'. We term this middle stage of margin development 'outer margin collapse', and it accords with the exhumation stage of other authors. Outer continental margins, already thinned by rifting processes, become hanging walls of crustal-scale half grabens associated with landward-dipping shear zones and zones of low-shear strength magma at the base of the thinned crust. The footwalls of the shear zones comprise serpentinized sub-continental mantle that commonly becomes exhumed from beneath the embrittled continental margin. At magma-poor margins, outer continental margins collapse and tilt basinward to depths of about 3 km subsea at the continent-ocean transition, often deeper than the adjacent oceanic crust (accreted later between 2 and 3 km). We use the term 'collapse' because of the apparent rapidity of deepening (<3 Myr). Rapid salt deposition, clastic sedimentation (deltaic), or magmatism (magmatic margins) may accompany collapse, with salt thicknesses reaching 5 km and volcanic piles 1525 km. This mechanism of rapid salt deposition allows mega-salt basins to be deposited on end-rift unconformities at global sea level, as opposed to deep, air-filled sub-sea depressions. Outer marginal collapse is 'post-rift' from the perspective of faulting in the continental crust, but of tectonic, not of thermal, origin. Although this appears to be a global process, the Gulf of Mexico is an excellent example because regional stratigraphic and structural relations indicate that the pre-salt rift basin was filled to sea level by syn-rift strata, which helps to calibrate the rate and magnitude of collapse. We examine the role of outer marginal detachments in the formation of East India, southern Brazil and the Gulf of Mexico, and how outer marginal collapse can migrate diachronously along strike, much like the onset of seafloor spreading. We suggest that backstripping estimates of lithospheric thinning (beta factor) at outer continental margins may be excessive because they probably attribute marginal collapse to thermal subsidence. © 2014 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.

Estrada-Carmona J.,CICESE | Weber B.,CICESE | Martens U.,Tectonic Analysis Ltd | Martens U.,National Autonomous University of Mexico | Lopez-Martinez M.,CICESE
International Geology Review | Year: 2012

The recent discovery of Early Ordovician S-type granites in the southwest of the Chiapas Massif Complex adds a new perspective to the Palaeozoic history of the Maya block, inasmuch as no rocks of such age had previously been reported in this region. New geologic mapping west of Motozintla, Chiapas, revealed pelitic to psammitic metasedimentary successions (Jocote Unit) intruded by granitoids and metabasites. The Jocote Unit is unconformably underlain by the newly defined Candelaria Unit, which comprises deformed calc-silicate rocks and interlayered folded amphibolites. The Candelaria Unit is the oldest rock succession so far recognized in the southern Maya block. We used laser-ablation multicollector inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating to determine the ages of the rock, yielding Early Ordovician (ca. 470 Ma) and Late Ordovician (ca. 450 Ma) ages. Major and trace element geochemistry, as well as Nd and Sr isotope data, suggest that folded amphibolites of the Candelaria Unit are mantle-derived and are probably related to rifting. The Early Ordovician bimodal magmatism of the Jocote Unit is more strongly differentiated; it reflects crustal contamination and volcanic-arc chemical signatures. A granitic stock (Motozintla pluton) intruded the area in the Late Ordovician. Its geochemical composition indicates less crustal contamination and a mixed signature between volcanic-arc and within-plate settings. Magmatic rocks analogous in age and chemical character crop out in the Rabinal and the Altos Cuchumatanes areas of Guatemala, suggesting the existence of a semi-continuous Ordovician magmatic belt from Chiapas to central Guatemala. Similar but somewhat younger granites also occur in the Maya Mountains of Belize, suggesting that magmatism migrated in the Silurian from the Chiapas-Guatemala belt towards the Maya Mountains. © 2012 Taylor & Francis.

Reuber K.R.,University of Houston | Pindell J.,Tectonic Analysis Ltd. | Horn B.W.,ION GeoVentures
Interpretation | Year: 2016

The Demerara Rise is a prominent bathymetric feature that has been considered as a broad expression of shallow continental basement and used in conjunction with the Guinea Plateau as a pinning point for circum-Atlantic plate reconstructions. Previously, shallow-penetration, poorly imaged seismic data over the Demerara Rise were modeled with the lower sequences interpreted as continental crust at relatively shallow depths. However, new long-offset, deeply penetrating seismic data provide evidence that basement nearly or entirely comprises excessively thick volcanic strata (approximately 21 km). Seismic character and geometry, 2D gravity modeling, and volcanic margin analogs were used to identify unfaulted, convex-upward seaward dipping reflector (SDR) packages. These steeply dipping (approximately 20°) igneous successions are westwardly divergent, and occur as offlapping reflector sets in trains as long as 250 km. This rift-related volcanism now recognized at the Demerara Rise was probably conjugate to syn-rift volcanism in South Florida/Great Bahama Bank, and from this we have predicted a volcanic element for the Guinea Plateau. This volcanism could be linked to a Bahamas hot spot at the initial opening of the Central Atlantic. Six SDR packages have been interpreted below the Late Jurassic-Early Cretaceous carbonate section of the rise, indicating that the early volcanism produced a marine substrate upon which the subsequent carbonate bank section developed. We have inferred that this Early Cretaceous volcanic/carbonate margin continued into the Guinea Plateau of West Africa. The pre-Aptian section was inverted and peneplained with a strong angular unconformity prior to the Early Cretaceous opening of the Equatorial Atlantic seaway. The newly identified Central Atlantic volcanic margin of the Demerara Rise holds implications of a volcanic origin for its conjugate margins. We have confirmed a voluminous magma-rich opening of the southeastern Central Atlantic. © 2016 Society of Exploration Geophysicists and American Association of Petroleum Geologists.

Torres-De Leon R.,National Autonomous University of Mexico | Solari L.A.,National Autonomous University of Mexico | Ortega-Gutierrez F.,National Autonomous University of Mexico | Martens U.,Tectonic Analysis Ltd.
American Journal of Science | Year: 2012

The proposed connections between basement terranes of southwestern México and the Chortís Block of Central America are tested in this paper, which focuses on metamorphic units in northern Chortís that outcrop in southeastern Guatemala. Two chief units are recognized: the mid-to high-metamorphic grade Las Ovejas Complex made up of ortho-, para-gneisses, schists, amphibolites and marbles; and the tectonically juxtaposed, low-metamorphic grade San Diego Phyllite. U-Pb geochronology carried out by LA-ICPMS on zircons separated from both units reveal major differences between them. The high-grade metamorphism and deformation of Las Ovejas Complex is bracketed between ~27 and ~37 Ma, which correspond to the U-Pb zircon ages of the oldest cross-cutting dikes and youngest zircons in metasedimentary samples. Las Ovejas samples share xenocrystic and detrital zircon populations of Middle-Late Jurassic, Middle-Late Triassic and Permo-Carboniferous age. In contrast, the San Diego Phyllite contains zircons that overlap at ~830 to 870 and ~1150 to 1220 Ma, with the youngest concordant zircons yielding Cambrian age. The contrast in population ages supports the idea that Las Ovejas Complex and San Diego Phyllite are different lithotectonic units tectonically juxtaposed during or after their exhumation. When compared with available U-Pb zircon data for southern México, Las Ovejas Complex show similarities to samples of the Guerrero terrane, mainly the Arteaga Complex and Zihuatanejo subterrane, as well as to the southern and northern portions of the Cuicateco terrane. The San Diego Phyllite shows instead similarities with the Teloloapan subterrane of the Guerrero terrane, the Mexcala Formation, the low-grade units of the Cuicateco terrane and the Grenvillian ages of the Oaxacan Complex metaigneous samples, as well as some of the samples belonging to the Maya Block. We propose a tectonic model in which the Las Ovejas Complex was a portion of a fringing arc located in front of the Cuicateco terrane of southwestern México, removed during the Early Tertiary by docking of the Chortís Block represented by the San Diego Phyllite, and tentatively by similar units recognized elsewhere in the Chortís Block in Honduras and Nicaragua. Eocene-Oligocene metamorphism and deformation of the Las Ovejas Complex would be a result of its displacement off southern México, mainly characterized by sinistral stretching and tectonic Cenozoic transport.

Weber B.,CICESE | Scherer E.E.,University of Munster | Martens U.K.,Tectonic Analysis Inc. | Mezger K.,University of Bern
Chemical Geology | Year: 2012

Detrital zircon grains from Lower Paleozoic sedimentary rocks in the Yucatan Peninsula have an age distribution characterized by major probability peaks at ~. 1.0, ~. 1.2, and ~. 1.5. Ga (Martens et al., 2010). Here, we present new Lu-Hf data (MC-ICPMS) paired with U-Pb ages (ID-TIMS) for additional zircon grains from the same rocks. This analytical approach yields precise information about the time and geochemical environment of zircon growth, which in turn helps to distinguish between different crustal source regions that just happen to host zircon populations of similar age. In addition, single zircon grains from granitoids that intruded the sedimentary rocks were dated by U-Pb laser ablation MC-ICPMS and ID-TIMS, and their Hf-isotope compositions were determined by solution MC-ICPMS. The zircon data are complemented by Sm-Nd analyses of the sedimentary and igneous whole rocks. The Yucatan Peninsula, which forms part of the Maya block of Central America, includes lower Paleozoic rocks in the Maya Mountains of Belize. The pre-Mesozoic geologic history of the Maya block is related to the evolution of the mid-Proterozoic basement in Mexico (Oaxaquia), other Paleozoic peri-Gondwanan terranes, and the Pan-African-Brasiliano type basement of Florida. The initial 176Hf/ 177Hf values of ~1.0Ga detrital zircon grains lie on a crustal evolution trajectory similar to that defined by older, ~1.2 to ~1.5Ga grains. This trajectory is consistent with those that would be produced by crustal reservoirs that separated from the depleted mantle between 1.70 and 2.05Ga. However, some grains have significantly less radiogenic 176Hf/ 177Hf (t), indicating influence from even older cratonic crust. Zircon grains from granitoids that intruded the Early Paleozoic sedimentary rocks of the Yucatan Peninsula yielded Late Silurian to Early Devonian (~415-400Ma) crystallization ages. More radiogenic Hf isotope ratios indicate anatexis of a crustal reservoir that is distinct from that of the Early Paleozoic sedimentary rocks. The Sm-Nd systematics of whole rock samples further support the results from the Hf isotopes in zircon grains. The data suggest a more continental provenance for the sedimentary rocks from Yucatan as compared to typical ca. 1.3 to 1.0Ga outcrops in southern and central Mexico. The results indicate that sediments were shed either from mid-Proterozoic complexes of NW Amazonia or from similar continental sequences that were thrust over Oaxaquia during the Grenville orogeny and subsequently eroded in the early Paleozoic. Integrating the data into a new model for early Paleozoic times, the southern Maya block is inferred to have formed during the opening of the Rheic Ocean along the western margin of Amazonia adjacent to Oaxaquia. The paucity of Ediacaran (Pan African-Brasiliano) signatures implies that before the Silurian, the southern Maya block evolved geographically separated from NW Yucatan and Florida, where Pan African-Brasiliano crystalline rocks have been reported. © 2012 Elsevier B.V.

Estrada-Carmona J.,CICESE | Weber B.,CICESE | Scherer E.E.,University of Munster | Martens U.,Tectonic Analysis Inc. | Elias-Herrera M.,National Autonomous University of Mexico
Gondwana Research | Year: 2015

Since the first discovery of eclogite in the Acatlán Complex in southern México, the age of the high-pressure metamorphism has been a matter of debate. Several attempts to date high-pressure metamorphic rocks of the Acatlán Complex have been made using the U-Pb and 40Ar-39Ar methods. The resulting dates, however do not correspond unambiguously to the time of eclogite facies metamorphism. In this study, the age of high-pressure metamorphism in the Acatlán Complex has been determined by Lu-Hf garnet-whole rock geochronology. This paper presents four high precision, 4- to 7-point garnet-whole rock isochrons of amphibolitized eclogite from the Piaxtla Suite and the Asís Lithodeme, in the Acatlán Complex. The four dates agree within uncertainties, yielding a weighted mean of 352.5±1.6Ma, which we interpret to be the age of eclogite facies metamorphism in the Piaxtla Suite and the Asís Lithodeme, marking active subduction in the Acatlán Complex in the Carboniferous. Mississippian high-pressure metamorphism in turn, might be related to the closure of the Rheic Ocean and the assembly of Pangea. © 2015 International Association for Gondwana Research.

Pindell J.,Tectonic Analysis Ltd. | Pindell J.,University of Cardiff | Maresch W.V.,Ruhr University Bochum | Martens U.,Tectonic Analysis Ltd. | Stanek K.,TU Bergakademie Freiberg
International Geology Review | Year: 2012

We integrate known and suspected Meso-American plate motions with the geochronology of Caribbean arcs and Central American HP/LT belts to promote two primary concepts. The first is that the Greater Antillean Arc formed at about 135Ma by inception of SW-dipping subduction along a sinistral inter-American transform connecting the west-facing subduction zones of the North and South American Cordillera. Caribbean arc magmas date from 135Ma and Caribbean HP/LT complexes from 118Ma, and they were formed as the Caribbean lithosphere was engulfed between North and South America during westward drift of - and divergence between - the latter. Initial arc magmatism predates exhumation of HP/LT metamorphic rocks by 10-20 million years; that is, magmatism developed faster than refrigeration and recycling in the subduction zones. However, pre-130Ma HP/LT mélanges in Nicaragua (Siuna complex, 139Ma 40Ar/ 39Ar) and in Guatemala both north and south of the Motagua fault zone (140-130Ma Sm-Nd ages) require a different explanation. Therefore, our second concept is that these older rocks originated within a mature, west-facing Cordilleran subduction channel west of Mexico and/or the Chortis Block, and were subsequently dragged southeastward during sinistral subduction to a position along the NW portion of the inter-American transform. Upon initiation of SW-dipping subduction along this transform at 135Ma, these older HP/LT (and minor arc) rocks became entrained within the transpressive zone between the western end of the Caribbean Arc and the southeast-facing Proto-Caribbean passive margin of the Chortis and Maya blocks. They were obliquely and diachronously accreted along these margins in the Albian to Maastrichtian. Parts of these mélanges are now exposed on both the northern and the southern flanks of the Motagua Valley of central Guatemala, and we further develop earlier suggestions that the southern Motagua mélanges were emplaced there on Chortis basement units by mid-Tertiary south-vergent transpression along the Motagua Fault. © 2012 Copyright Taylor and Francis Group, LLC.

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