Rex Pilger

• PhD
• Geophysicist at Pilger G3

The importance of mantle hotspot traces to driving low-angle subduction beneath the Andes is strengthened by updated South American-Nazca plate reconstructions, including three oceanic hotspot traces, and a new isotopic date compilation. The Juan Fernandez hotspot trace, reconstructed from Pacific-hotspot models to the Nazca-Farallon plate, encount...

This version has been withdrawn. An entirely new version, with additional data and interpretations has been submitted. South American Andes: reconstructions of hotspot trace subduction, correlation with volcanic patterns from isotopic dates, calculated convergence rates, implications for Pacific hotspot reference frame.

A compilation of published radiometric dates for igneous, metamorphic, and sedimentary rocks from the South American Andes and adjacent parts of South America have been tabulated for access by researchers via GEOROC. The compilations exist as three distinct spreadsheets for access via MS Excel, Google Sheets, and other spreadsheet applications. Ini...

Compilation of published radiometric dates from the Andes and adjacent regions of South America: links to four Google Sheet sets (two igneous, plus one metamorphic and sedimentary).

This document provides links to the latest versions of the igneous, metamorphic, and sedimentary radiometric date workbooks. More dates have been added to the igneous workbook along with more of the references. Many duplicates, from other compilations, have been removed, reducing the size of the file. More such work needs to be done on the other tw...

Document provides links to distinct igneous and non-igneous data sets of radiometric dates from the South American Andes and adjacent areas. The data sets are updated regularly from published articles and supporting data.

Description (UPDATED September 27, 2018 - See Information tab) Radiometric dates from the South American Andes and adjacent areas: K/Ar, Ar/Ar, UPb, FT, 14C and others. Separate spreadsheets for igneous and non-igneous rocks. In Google Sheets - can be downloaded in Excel and other formats. Updated with corrections to corrupt items in non-igneous sp...

Radiometric dates from the South American Andes and adjacent areas: K/Ar, Ar/Ar, UPb, FT, 14C and others. Separate spreadsheets for igneous and non-igneous rocks. In Google Sheets - can be downloaded in Excel and other formats.

Data are abstracted from spreadsheet table posted May 19, 2018.

Updated Radiometric Data Compilation from Andes of Argentina, Bolivia, Chile, Ecuador, and Peru. Link to spreadsheet workbook. Links to KML (Google Earth) files to follow.

Incomplete compilation of radiometric ages of magmatic rocks from South American Andes - equivalent to Google Earth format of primary post. This compilation ended in 2011; additional data are in the process of being assembled for a larger database..

An incomplete compilation of radiometric dates of South American Andes magmatic sources (2011). An updated version with many more sources is in preparation. Other workers are invited to submit other published data, to include location (latitude & longitude preferred -- UTM if necessary can be transformed; geologic environment; rock type, dating met...

Two of the more actively applied mathematical objects, information entropy and fractals, are seldom found together in the same research project. Yet, as was first derived by Pastor-Satorras and Wagensburg, under certain conditions, mathematical fractal structures can be derived through the application of maximum entropy. The author applied the tech...

Information theory and fractal analysis are the basis of a novel fitting criterion for simultaneous plate tectonic reconstructions of magnetic isochrons and fracture zone crossings of a range of ages, rather than a single isochron age. Accretionary boundaries are modeled as two-dimensional fractal structures including both contemporary spreading bo...

Accretionary plate boundaries - spreading centers and associated transform faults - possess fractal structure like coastlines. Their apparent length demonstrates self-similarity over a range of scales, maximizing multiplicity (entropy) in a recursive chaotic process. Further, optimal, combined oceanic plate reconstructions, incorporating asymmetric...

Available isotopic age dates from the Foundation, Austral, Cook, Tokelau, and Gilbert island-seamount chains, combined with kinematic plate-hotspot modelling, indicate that the five chains originated from three distinct melting anomalies (or “hotspots”) well before the onset of postulated intraplate oblique extension. The kinematic pattern produces...

The origin of the bend in the Hawaiian-Emperor Island seamount chain is the prototypical problem at the heart of the ongoing hotspot debate: Does the bend represent a change in motion between the Pacific plate and underlying hotspot (plume?), or might it represent a change in the intraplate stress field? Reconstructions of continental plates relati...

To maximize the velocity of business value delivery Alistair Cockburn talks of having a process that is "barely sufficient". At Landmark Graphics we developed some guidelines as to what "barely sufficient" means for our various software projects. We examined over 60 projects and observed two primary attributes that influenced the type of process us...

In the ongoing debate concerning the origin of hot spots, and more generally, the nature of mantle convection and its relation to plate tectonics, it is important to recognize that viable models need to satisfy “all” of the data. Much of the recent literature has emphasized one or two subsets of geoscientific data (typically geochemical/petrologica...

A new concept unifies several diverse lines of evidence regarding the kinematics of lithospheric plates (``lithoplates'') and the underlying mesosphere. Three ``mesoplates''---shallow, kinematically rigid regions of the upper mesosphere of the Earth---are inferred to be the habitat of most hot spots, as well as the source region for the sea floor s...

There is a kind of frustration involved in interpolation of any numerical quantity, particularly if there are uncertainties involved in the input data. Uncertainties have been a passion for many plate tectonic workers; a number of important advances in the estimation of uncertainties in oceanic plate reconstructions and their composition into globa...

Check out the first one or two chapters of a good structural geology or seismology textbook and you’ll find the derivation of the elastic stress tensor. Read further and, while you might find some application of the total tensor; more typically the tensor is quickly reduced to principal stresses. Then, the principal stresses get reduced even more t...

Plate Tectonics has been almost completely developed by academic and government geoscientists. However, the largest proportion of geologists and geophysicists is employed in the oil and gas industry. Has Plate Tectonics played a significant role in hydrocarbon exploration over the past 30 years or so? For the most part the answer has to be negative...

One of the more challenging aspects of the doing of science is the apparent failure of communication. Does the paper reporting the results of an investigation get read? Is the paper understood?

Back-arc spreading was one of the big auxiliary surprises of second-generation plate tectonics. Tectonicists had visualized convergence of plates as resulting from converging convection cells with consequent compressive structures. As the geometric implications of plate tectonics began to be elaborated, the idea of convection cells tied to plate ge...

As Plate Tectonics matured, a number of workers began to consider philosophical implications of the science. Allan Cox (1973), in particular, found Thomas Kuhn’s “Structure of Scientific Revolutions”; published in the same year as Harry Hess’s “History of ocean basins — an essay in geopoetry”, to be directly applicable to the experience of earth sc...

Paleomagnetism, after morphology and geology, provided key evidence for the great precursor of plate tectonics — continental drift. One of the great hopes with plate tectonics was for paleomagnetism to provide additional kinematic constraints. Alas, the very processes apparently involved in generation of the geomagnetic field conspire against provi...

Part of the resistance to Plate Tectonics among earth scientists in the 1960s and 1970s involved the concept of rigidity. When advocates of the new global tectonics spoke of rigid plates, they encountered an intuitive misunderstanding of mechanical rigidity rather than kinematic rigidity. The idea of mesoplates as described below is likely to encou...

When Bernard Minster and Tom Jordan, together with Peter Molnar and Ian Haines, first published their inverse plate kinematic model in 1974 (Minster et al. 1974), the affect on the tectonics community was extraordinary. Jason Morgan had already published a global plate tectonics model parameterized in Cartesian vectors (Morgan 1972a), while Clement...

Data and patterns-so much of what we do in science reduces to that x versus y plot. Sometimes, it’s predicted and observed longitude and latitude (for example, reconstructed magnetic anomalies across a spreading center). When it comes to hotspot traces, it’s age versus distance (but there’s more to it than that). Despite what we may have learned in...

The typical approach to reading a scientific article is to skim the abstract, and, if it is of interest, skip to the last section or two and skim the discussion and conclusion. Since a monograph commonly lacks an abstract, this last chapter may well be where some readers begin.

In the early 1970s, a series of “second-generation” plate tectonics papers appeared in which the reconstruction techniques introduced by Bullard, Everett and Smith (1965) were progressively modified and applied to magnetic isochrons and paleofracture zones. McKenzie and Sclater (1971) attempted the first model of opening of the central Indian Ocean...

Since Morgan published the first hotspot motion model for the Pacific in 1972, the formal conversation among researchers evolved into a debate as to whether hotspots do indeed define a single, fixed, internal reference frame. However, discrepancies between Atlantic-Indian Ocean and Pacific Ocean sets became the primary focus of attention. In just t...

For those who entered the earth sciences in the mid-1960s or earlier, the advent of Plate Tectonics was either an extraordinarily upsetting encounter with a seemingly non-geological science or a marvelous revelation that rearranged a couple of centuries of field observations into a high degree of unanticipated coherence. Suddenly, a profound simpli...

Subsurface structures were interpreted from seismic images and well logs in the westernmost Mississippi Salt basin, Madison Parish, Louisiana. Structural and stratigraphic relations indicate that salt structures (Duckport, North Tallulah, South Coleman, Tallulah, and Walnut domes) have evolved through pillow, diapir, and postdiapir stages. Withdraw...

Tectonic thickening of the crust within the adjacent Brooks Range fold-thrust mountain belt has been suggested as a probable cause for rapid subsidence of the Colville basin in the Early Cretaceous. A simple mechanical model in which the response of the lithosphere to loading was approximated by a semi-infinite (broken) elastic plate overlying a we...

Seismic reflection and bottom hole temperature (BHT) data have been utilized for subsurface temperature investigatrons of two locatrons within the Gulf Coast Salt Basin in South Louisiana. A one-dimensional thermal model was constructed to analyze the subsurface temperature distributions. The model utilizes a relationship between seismic travel tim...

The variety of late Mesozoic through early Cenozoic tectonic elements and events in the Rocky Mountains region shows temporal and spatial correspondence with inferred variations in kinematics of plate interactions and geometries of subducted oceanic lithosphere. From this space and time correspondence and current understanding of subduction process...

A new palinspastic and tectonic model of the central Brooks Range, Alaska, has been completed, based on existing mapping, balanced cross sections, and isostatic constraints. A major thrust wedge, nor underlying the northern half of the range, developed early in the deformation. As much as 13 km or more of depression of the Schwatka-Doonerak terrane...

Several salt diapirs and pillows in southern and central north Louisiana have been studied using approximately 355 mi (570 km) of seismic reflection data and information from 57 deep well holes. Using seismic profiles with deep well-hole data is the most advantageous method to document regional salt tectonism through time. The following conclusions...

The subsidence history of the North Louisiana Salt Basin, determined from well data, indicates that the region underwent extension during rifting and has since passively subsided due to conductive cooling of the lithosphere. Timing of the rifting event is consistent with opening of the Gulf of Mexico during Late Triassic to Early Jurassic time. Cru...

Revised plate construction and enlarged isotopic age data sets strongly support three mechanisms for controlling the configuration and associated volcanism and tectonism of the Andean subduction zone. These include age of subducted plate, convergence rate and interaction with hot spot traces. From 50-25 m.y., the age of oceanic plate subducted in t...

Most variation in geometry and angle of inclination of subducted oceanic lithosphere is caused by four interdependent factors. Combinations of 1) rapid absolute upper-plate motion toward the trench and active overriding of the subducted plate, 2) rapid relative plate convergence, and 3) subduction of intraplate island-seamount chains, aseismic ridg...

Interpretation of available isotopic ages and of published geologic maps of igneous rocks in eastern Australia indicates a north-south time transgressive pattern of cessation of igneous activity along a curvilinear trace, beginning about 35 Ma at 20 °S and extending to the present, near 37 °S. However, volcanic activity began 70-60 Ma over the leng...

Computing smooth kinematics from cubic spline interpolation of reconstruction parameters

Separate abstracts were prepared for seven subprojects in this report.(MHR)

Low-angle-subduction segments beneath Peru and Chile are believed to represent interaction of the subduction zone with the aseismic Nazca and Juan Fernandez Ridges. On the basis of symmetric sea-floor-spreading models and plate-hotspot reconstructions, predicted continuations of the relatively buoyant ridges correspond well with the limits of the l...

Seismicity, magnetic anomaly, and bathymetric data are used to interpret the tectonic structure and history of the Easter plate. The Easter plate is a small oceanic plate in an area of locally anomalous seafloor spreading activity that internally disrupts the tectonic continuity of the Nazca-Pacific divergent plate boundary west of Easter Island. A...

Reconstructions of the Pacific and Nazca plates suggest that both the Nazca and Tuamotu Ridges originated from a melting anomaly which existed beneath the Pacific-Farallon Ridge during the time interval between anomalies 19 and 11, as would be predicted from the fixed-hotspot hypothesis. The hotspot hypothesis, interpreted according to morphology o...

Palinspastic and global plate tectonic reconstructions of the southwestern United States, combined with analysis of the distribution of Cenozoic igneous activity suggest that Neogene and younger volcanic rocks in the Continental Borderland and Coast, Transverse and Peninsular Ranges appear to reflect subduction of the Farallon plate south of the Me...

On the premise that calc-alkaline volcanism and plutonism are genetically related to subduction, a model is developed which serves as a basis for interpreting the dynamics and geometries of the plate interactions along the W margin of the USA that were responsible for the present distribution of Cainozoic magmatic complexes. The changing patterns a...

Anomalous subsidence of continental crust occurred during the Late Cretaceous in a region centred about Colorado, southern Wyoming and eastern Utah. The amount of subsidence is greater than can be explained by eustatic sea level rise and supracrustal loading by water and sediment. Analysis of thickness and distribution of Upper Cretaceous strata of...

As an alternative to trial-and-error methods, a least-squares technique for derivation of finite plate reconstructions has been developed. The method involves minimization of the summed distances squared separating data sets on corresponding former plate margin segments as a function of the reconstruction (rotation) parameters. Each data value cons...

A tighter reconstruction of Africa and South America implies initial north-south opening of the Gulf of Mexico with transform motion along the North Atlantic coast.

Volcanic record in the Andes corresponds with plate reconstructions of aseismic ridges which produce low-angle subduction with magmatic gaps.

The transition from subduction to transform boundary indicated by plate reconstructions and onshore igneous activity, western United States.

The Nazca and Juan Fernandez Ridges appear to control low-angle subduction beneath the Andes

Thesis (Ph. D.)--University of Southern California, 1976. Photocopy available from Micrographics Department, University of Southern California. Order number: 2515G. Includes bibliographical references (leaves 145-155).

Magmatic patterns in the Cordillera - relation to "absolute" plate motions

Space/time plots of radiometric age dates of talc-alkaline igneous rocks of silicic to intermediate composition reveal two major time-transgressive patterns of subduction related igneous activity in the western U.S. The oldest pattern is a southward migration of initiation of silicic igneous activity following a 20-25 my period of magmatic quiescen...