Maximum scope DR CHRISTINE SIDDOWAY A distinctive group of researchers on the EarthScope Bighorn Project are using innovative approaches in seismology and structural geology to study the formation of the Laramide Rocky Mountains. Dr Christine Siddoway, one of four female investigators in the team, explains their work Could you begin by introducing the Mountains? Have your studies provided any hypotheses that have been proposed to explain Earthscope Bighorn project and highlighting further insight into this phenomenon? the Bighorn Mountains intracratonic arch. the reasons for its establishment? The Laramide Orogeny occurred during plate How important has collaboration been to the The EarthScope Bighorn Project is an convergence between the Farallon and North project? integrated geological and geophysical American tectonic plates during the time investigation of the Bighorn Mountains in period 75-45 million years ago. Distinctive There is extraordinary harmony and cooperation Wyoming. The aim of the multi-institution aspects of the orogeny are: the involvement among the collaborative group, with strong interdisciplinary investigation, led by University of crystalline basement in the near-surface communication and collaboration between of Wyoming investigator Eric Erslev, is to faulting (‘thick-skinned’ deformation); the graduate and postdoctoral researchers identify the process of formation for some the migration of diffuse magmatism and at the various institutions. This makes for the of the ‘signature’ mountain ranges of the distributed deformation into the continental strongest possible interpretations of the 3D/4D North American West: the Laramide Rocky foreland, distant from the plate boundary architecture of the Bighorn arch that are derived Mountains. Unlike many active mountain zone; and the formation of large asymmetric from multiple independent methods belts (orogens) of the world such as the Andes, sedimentary basins between basement- Himalayas, New Zealand Alps or St Elias ranges involved uplifts. In the Rocky Mountains, Is it signifi cant that the project is led by – that developed upon plate tectonic boundaries, deformation produced an anastomosing and involves a high proportion of – women the vast mountains of the Laramide Rockies array of basement-cored arches separated participants? formed well within the continental portion of by lens-shaped foreland basins. Estimates of the North American tectonic plate, far from a the amount of shortening necessary to form I believe this is a really distinctive and unusual zone of plate convergence. the Bighorn arch ranges from 8-13 per cent. aspect of the Bighorn Project. Considering the Rather than fold-thrust style deformation, demographics of the Earth sciences community What is the signifi cance of using geology and the Laramide features large-scale anticlinal in the US, the rich collaboration among women geophysics to study the Rocky Mountains in structures that are either asymmetrical and researchers who have a leadership role as particular? bounded by thrust faults, or symmetrical, with Principle Investigators (PIs), and the number of smaller reverse faults on both limbs. women students who are contributing to the The Bighorn Mountains have a structural research is notable. Four of the six PIs and both architecture that is so well known to geologists Are there unanswered questions that the postdoctoral researchers on the project are worldwide that it serves as an archetype for Bighorn project seeks to address? women. In addition, the project has supported within-plate, intracratonic deformation. One two MSc and four undergraduate women thing that geologists perceive but that it is Paradoxically – in light of the scale of the researchers. For us participants, the experience perhaps diffi cult for the casual traveller to Bighorn range and the large number of geology has been exemplary as an affi rmation that appreciate is the phenomenal scale of the visitors – there is not a consensus about which capable and innovative female researchers are structure: there is a difference in elevation of of the multiple hypotheses proposed for the attaining leadership stature in Earth sciences, 10,000 m from the ‘basement’-cover contact formation of the prodigious arch best explains a fi eld that has historically been dominated by beneath the adjoining Bighorn Basin to its its form. The mechanism for shortening of strong men at the top levels. We feel a great optimism restored position over the top of the mountain Archean lithosphere has long been unresolved about the future prospects for infl uential range. due to lack of geophysical imaging. The Bighorn future contributions by female researchers who Project seeks to obtain a 3D seismic image of the received academic training and advanced their Are you able to provide a brief background integral structures that form the architecture of professional standing through participating in on the Laramide orogeny of the Bighorn the range, and thereby to test the four principal the Bighorn Project. WWW.RESEARCHMEDIA.EU 113 DR CHRISTINE SIDDOWAY Big discoveries in the Bighorns A group of EarthScope researchers are making important discoveries about the formation of intracratonic mountains, in an integrated geoscience project that has wide-reaching impacts THE STRIKING APPEARANCE of the Bighorn lithosphere-scale linkage of foreland arches to academic theses that are part of the Bighorn Mountains has long fascinated geologists and plate tectonics and regional fracture patterns Project tourists alike. The crystalline rocks and the in basement-involved orogens that commonly layered sedimentary rocks that cover them control oil and gas production”. The team of SEISMIC SOLUTIONS form an elongated, doubly-plunging arch, which Bighorn Project investigators hope to determine visitors can actually see when they observe the mechanisms that drive the formation of The fi rst of these encompasses the Bighorns that the sedimentary layers on the east side of basement-involved arches, like the Bighorns, Arch Seismic Experiment (BASE), which in the range slope down to the east, and those on which will greatly advance knowledge of intra- 2010 was successful in imaging the crust and the west dip to the west. On the outer fl anks continental deformation worldwide. In doing mantle below the Bighorn Arch by carrying of the range, geological faults cut through the so, this research deepens the understanding of out an active-source wide-angle refl ection rock creating abrupt changes in the angle of continental lithospheric rheology, one of the and refraction survey led by Kate Miller and the layers, as Dr Christine Siddoway, a Principal fundamental problems in plate tectonics. Steve Harder. This allowed project researchers Investigator for the EarthScope Bighorn Project, to measure crustal velocity and thickness, and explains: “The high, interior parts of the Bighorn identify large-scale structures: “Extraordinarily AN INTEGRATED PROJECT Mountains are underlain by crystalline-textured high-resolution images were obtained through granite and gneiss that have properties of great As an integrated Geoscience initiative, the use of 21 seismic shots recorded on 1,800 ‘Texan’ strength and resistance to erosion. The granites EarthScope Bighorn Project brings together an dataloggers, with 4.5 Hz vertical component and gneisses – often referred to as ‘basement’ innovative combination of approaches to its geophones,” Siddoway explains. The visionary rocks – have these characteristics partly because study of the range. Notably, these are: experiment produced 15,000 total travel times they are of great age, but also because they for inversion, obtaining the fi rst high-resolution formed at depth in the Earth’s crust during the • The use of a hybrid active/passive high- P-wave velocity models of the crust and upper Archean Eon, more than 2.5 billion years ago”. resolution seismic studies mantle of the Bighorn region. • The use of iterative retrodeformation The project employs passive seismic data, MECHANISMS OF FORMATION techniques that balance surface areas and 3D recorded principally from broadband The process of formation of the basement arch volumes to develop GIS-based geometric/ is the focus of the EarthScope Bighorn Project, kinematic models of the upper crust over which addresses not solely the Bighorns but also time-integrated steps seeks to increase understanding of the structures responsible for within-continent deformation, • The involvement of student participants as Siddoway outlines: “Our fi ndings apply who undertake individual research, to an array of global problems, ranging from through internship training and as FIGURE 1. Simplifi ed cross section of the Bighorns Arch, showing four contrasting Moho geometries for the four lithospheric models being tested. Scenarios one and four have been ruled out. DOCTORAL STUDENT WILL YECK AND INTERN AUSTIN ANDRUS AT WORK INSTALLING A BROADBAND SEISMOMETER 114 INTERNATIONAL INNOVATION INTELLIGENCE instruments, such as the EarthScope USArray BIGHORN PROJECT and BASE’s EarthScope FlexArray. Investigator Anne Sheehan conceived the innovative use FORMATION OF BASEMENT-INVOLVED of 850 of the Texan instruments as recorders FORELAND ARCHES: AN INTEGRATED for naturally occurring distant (teleseismic) EARTHSCOPE EXPERIMENT earthquakes. Siddoway elaborates: “Traditionally, OBJECTIVES the ‘Texan’ instruments are used solely as active sensors, so it is an innovation in our experiment The EarthScope Bighorn Project is an to extend their use to