Kevin P. Hefferan

Precambrian accretionary tectonics in the Bou Azzer-El Graara region, Anti-Atlas, Morocco

Ophiolites of the Anti-Atlas of Morocco occur as highly dismembered slivers of mafic and ultramafic rocks sandwiched between a Precambrian craton and a magmatic arc. Tectonic slices of accretionary melange, ophiolites, and forearc basins have been juxtaposed by oblique subduction and transpression in the forearc region of a Late Proterozoic subduction zone. Synkinematic to postkinematic calc-alkalic magmatism in these terranes indicates migration of the magmatic front over the deformed forearc terranes.

Anti-Atlas (Morocco) role in Neoproterozoic Western Gondwana reconstruction

Abstract Reconstruction of latest Neoproterozoic Gondwana hinges on the interpretation of the subduction and collision kinematics of Pan-African orogenic belts that rim the West African craton. The Anti-Atlas suture zone of southern Morocco has presented an enigma in this reconstruction as the inferred subduction zone polarity and age of suturing appear to be incongruous with better known West African orogens to the west (Mauretanian, Bassaride and Rokelide) and Transaharan orogens to the east (Ougarta, Tuareg, Gourma and Dahomeyan). Contrary to previous interpretations, new data from the Anti-Atlas indicate a history of late Neoproterozoic (∼750–600) north-dipping subduction culminating in the (∼600 Ma) collision of the Saghro magmatic arc to the north with the north-facing rifted margin of the West African craton. Thus, the Anti–Atlas suture links a ∼6000-km long chain of Pan-African suture zones that essentially encircle the West African craton. The suture zones demarcate the former position of subduction zones that in all cases dipped away from the West African craton. The Anti-Atlas suture links the western and eastern segments of the Pan-African orogenic belts associated with the amalgamation of Western Gondwana.

Proterozoic collisional basins in a Pan-African suture zone, Anti-Atlas Mountains, Morocco

Abstract The Anti-Atlas Mountains constitute a Late Proterozoic suture zone produced by northward subduction of oceanic lithosphere culminating in the Pan-African orogeny. Southward migration of thrust slices associated with the destruction of the forearc terrane resulted in the uplift and erosion of previously deposited basin sediments. These sediments were subsequently reincorporated into collisional basin deposits of the Tiddiline Formation. The Tiddiline Formation consists of coarsening-upwards sequences of maroon siltstones, sandstones and intraformational conglomerates. These rocks unconformably overlie metamorphosed volcaniclastic rocks of the relict forearc basin and accretionary terrane. Syn- and post-depostional deformation has resulted in folding about gently-plunging fold axes. Folds were subsequently cut by strike-slip faults that strike at a high angle to the basin axis. Deformation of the Tiddiline Formation is attributed to transpressional suturing of the relict forearc terrane to the West African Craton to the south. Collisional basins of the Anti-Atlas Mountains serve as ancient analogs for the destruction of forearc basins in an obliqueconvergent margin setting, such as those of the Western Pacific region.

Proterozoic blueschist-bearing mélange in the Anti-Atlas Mountains, Morocco

Abstract Blueschists from the Bou Azzer inlier provide compelling evidence for Late Proterozoic subduction in the Anti-Atlas Mountains of Morocco. High-pressure/low-temperature metabasites containing blue amphibole minerals crossite and magnesioriebeckite record pressures in excess of 5 kbar. Together with regional relationships, the geologic setting of the blueschists constrains the polarity of Pan African subduction in this region, which occurred from ∼750 to 600 Ma. Blueschist facies rocks crop out in a heterogeneous assemblage of variably deformed and metamorphosed tectonic slices of ophiolitic fragments enclosed in a schistose serpentinite matrix. The melange belt containing the blueschist facies rocks is intruded by a number of diorite plutons, one of which has yielded a U/Pb radiometric age of 650 Ma. Together with Transaharan Belt to the southeast, the Anti-Atlas suture zone exposed within the Bou Azzer inlier contains among the oldest known blueschist-bearing, ophiolitic melanges in the world.

Integrating Field Trips and Classroom Learning into a Capstone Undergraduate Research Experience

Abstract Interim semester field trips provide a unique opportunity for undergraduate students to collect field data in support of their capstone research experience. We encourage students to participate in collaborative research projects prior to the semester for which they enroll in the capstone course. Students select a research project based on a field trip itinerary, submit a research proposal to faculty, conduct preliminary research prior to departure and collect data in the field during a January “Winterim” course. During the spring semester, students continue laboratory research, incorporating data collected in the field to complete their research project and prepare scientific presentations. Field trips provide an inherent mentoring system whereby faculty interact with students, and underclass students collaborate on capstone research projects. This approach facilitates learning by emphasizing preparation and planning, collaborative learning and integration of classroom knowledge into field research.

Application of ASTER remote sensing data to geological mapping of basement domains in arid regions: a case study from the Central Anti-Atlas, Iguerda inlier, Morocco

Satellite remote sensing is shown to provide critical support for geological and structural mapping in semiarid and arid areas. In this work, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data were used to clarify the geological framework of the Precambrian basement of the Iguerda Proterozoic inlier in the Moroccan Central Anti-Atlas. In this study, the interpretation of the processed digital data has been ground truthed with geological field data collected during a reconnaissance-mapping program in the Central Anti-Atlas. The Iguerda inlier offers a deeply eroded Precambrian massif dominated by a Paleoproterozoic basement composed of supracrustal metasedimentary units intruded by various Eburnian granitoids. Impressive mafic dyke swarms mainly of Proterozoic age crosscut this basement. Eburnian basement rocks are unconformably overlain by Lower Ediacaran volcanosedimentary rocks of the Ouarzazate Group and Upper Ediacaran–Lower Cambrian carbonates. The applied ASTER analyses are particularly effective in the lithological differentiation and discrimination of geological units of the Iguerda inlier. The spectral information divergence (SID) classification algorithm coupled with spectral angle mapper and maximum likelihood classification effectively discriminates between metamorphic rocks, granitoid bodies, and carbonate cover. SID classification improves geologic map accuracy with respect to the spatial distribution of plutonic bodies and metamorphic units. In addition, Paleoproterozoic granitoids have been well discriminated into separate distinct suites of porphyritic granites, granodiorites, and peraluminous leucogranite suites. This discrimination was initially identified via remote sensing analysis and later ground truthed in the field. This methodology enhances geological mapping and illustrates the potential of ASTER data to serve as a vital tool in detailed geologic mapping and exploration of well-exposed basement of arid regions, such as the Proterozoic of the Anti-Atlas Mountains of Morocco.