Abstract Applying time-series analyses using Fourier transform and multi-taper methods to low-field, mass-specific magnetic susceptibility (χ) measurements on marine samples from well-studied shale and limestone outcrops of the Upper Ordovician (Edenian Stage; Upper Katian) Kope Formation, northern Kentucky, corroborates direct visual identification in outcrops of Milankovitch eccentricity (c. 405 and 100 ka), obliquity and precessional climate cycles. Because individual outcrops were too short and deposition too chaotic to yield significant time-series results, it was necessary to build a c. 50 m thick composite sequence from three well-correlated outcrops to quantify the cyclicity. Time-series analysis was then performed using χ measured for 1004 closely spaced samples covering the section. Milankovitch bands are recorded in the time-series data from the composite. We tested this result by comparison of these bands to cyclic packages in outcrop, which correspond to thicknesses represented in the time-series datasets. This is particularly well defined for the eccentricity and obliquity cycles, with precessional bands being evident but as less well-defined packages of beds.

The Carthage-Colton mylonite zone is a major geothermochronological discontinuity across the northwest Adirondack Mountains of New York, a southern extension of the Grenville Province. A large syenitic gneiss body, the Diana syenite, occurs along most of the southern Carthage-Colton mylonite zone. The present study examined petrofabrics and magnetofabrics of oriented cores and accurately oriented thin- sections to investigate the sources of anisotropy of magnetic susceptibility (AMS) within a central portion of the Diana syenite. Three petrographic foliations, a petrographic lineation, and a magnetic intersection lineation were clearly distinguished. Two of the foliations appear to represent axial planar foliations of the second- and third-phases of regional folding as defined by Wiener (1983). The youngest foliation and the magnetic intersection lineation have not been previously described. This research suggests that folding identified in the Adirondack Lowlands can be traced to at least the southwest margin of the Diana syenite with no obvious discontinuity. Significant implications of this research suggest that: (1) the Adirondack Lowlands deformation likely includes some folding events associated with Ottawan orogen compression, and (2) the kinematics and style of deformation within the Carthage-Colton mylonite zone remain cryptic and cannot conclusively be connected to the fabrics explored in this research.

Abstract Numerous geoscientists have proposed and evaluated many conceptually distinct models for the evolution of the Caribbean region since 1930 (Fig. 1). From these, seven predominant interpretations of Caribbean crustal generation and modification have emerged: (1) sea-floor spreading, involving mid-ocean rifting, tectonic convergence, subduction, and back-arc spreading (for examples, see Pindell and Barrett, this volume); (2) basification of continental crust (Skvor, 1969); (3) lateral shear and transverse extension with attenuation, a variation on plate-tectonic theory (Ball and Harrison, 1969); (4) in situ orthogeosynclinal crustal evolution (Khudoley and Meyerhoff, 1971; Meyerhoff and Meyerhoff, 1972), a process classically associated with the tectogene hypothesis; (5) magmatic crustal thickening, related to magmatic-arc emplacement near subduction zones, to "hot-spot" magmatism (Officer and others, 1957; Duncan and Hargraves, 1984), to basaltic intrusion (Burke and others, 1984), and to flood-plateau basaltic volcanism (Donnelly, 1973; Donnelly and others, this volume); (6) tectonic crustal thickening and crustal accretion: processes in which tectonites are formed, assembled, or reassembled at convergent plate margins into masses reaching continental thickness (MacDonald, 1972a, b); (7) another process, involving thermal contraction and attendant mantle surges, is described by Morris, Meyerhoff, and others in this volume. Most of these processes lead to three genetically distinct types of crust (Ewing and Press, 1955; this paper): (1) oceanic, (2) continental, and (3) accretionary. Physical and genetic aspects of these crustal types are discussed below. Crust that cannot be readily assigned to one of these classes is, temporarily at least, categorized as indeterminate. Knowledge of Caribbean crustal evolution has emerged

Abstract The principal objective of this chapter is to present a compilation of original sources of paleomagnetic data for the Caribbean region, as published to the end of 1985. Secondarily, trends in the data and explanations for them are summarized, with emphasis on post-Paleozoic structural-tectonic rotations and paleogeographic implications. Areal limits for this compilation coincide with the limits of the map of Case and Holcombe (1980): 05° to 24°N and 054° to 093°W (Fig. 1). A few studies overlap these boundaries. The focus is on paleomagnetic directional data; therefore, studies of regional continental and oceanic crustal magnetic anomaly trends have been excluded. Some theses and a few abstracts have been included, but works in preparation or in press have been omitted. As the objective of this chapter is to summarize paleomagnetic information, no attempt has been made to evaluate the numerous tectonic scenarios proposed by many authors for the Caribbean. It is hoped that researchers of diverse interests will find the appendix and citations of original data sources useful. The appendix identifies data sources by region: Greater Antilles; Lesser Antilles; Central America; northern South America; and the Caribbean area oceanic basins.

From the Sierra Nevada of Santa Marta at the northern terminus of the Andes, preliminary paleomagnetic results from ten sites in two formations characteristically have stable directions with northerly declinations and moderate positive inclinations. Most site mean directions are close in attitude to the present Earth's field and are not indicative of large tectonic rotations. An antipodally reversed direction is obtained at one site by thermal demagnetization, suggesting magnetization in an ancient paleofield nearly coaxial with the present field. Few cratonic Jurassic directions have been reported from South America, but at least one such study shows Jurassic paleofield directions close to the present field directions. In defining the Mesozoic polar wander path for South America, distinguishing Jurassic from present field directions will be a continuing challenge.

Attention is focused on the genesis and tectonic behavior of the crust, especially the continental crust. A distinction is made between the rigid upper mantle, or peridosphere, and the crust which overlies it. Crust and peridosphere together make up the lithosphere. Five major types of crust are recognized. Continental crust is distinguished especially by its great thickness and by the wide-spread distribution of Precambrian gneisses. Oceanic crust, overlying the Moho in the deep ocean basins, is thinner, younger, and more widespread over the Earth's surface. Undeformed crustal masses which contain great thicknesses of basaltic rocks overlying otherwise normal oceanic crust are called platillo crust. The undeformed crust of smaller ocean basins, being thicker than normal oceanic crust, is believed to represent a great thickness of sedimentary layers overlying normal oceanic crust. Such crust has been called transitional crust (Menard, 1967). Where Phanerozoic crustal rocks have accumulated into masses of tectonites of continental thickness, the crust is called tectonitic. A map of crustal types of the Caribbean area is presented as an illustration of classification. Basalt is assumed to be the primary ultimate source of the continental crustal materials. Many processes, especially tectonic ones, have built up the continental crust to a relatively uniform equilibrium thickness. That thickness is determined by the interplay of tectonics, erosion, and isostasy. Lateral additions probably dominate the process of continental growth. Sedimentary, igneous, and tectonic processes at the continental margins are important contributors. Away from the continental margins, some additions to the continental mass are possible by sedimentation on the surface, by limited intrusion near the surface, and perhaps by sill-like intrusions along the Moho. Intrusion of basic magma at the base of the continent is a mechanism which can explain epeirogenic uplift, the Conrad discontinuity, and the slight increase of density with depth in the continents. The disappearance of widespread granulite metamorphic facies terrains at the end of the Precambrian is interpreted to be the result of cooling in the crust. It is suggested that the 550° C isotherm descended to levels below the continental crust near the end of Precambrian time. This would simultaneously permit the formation of serpentinite along the Moho and increase the rigidity of the crust. The possibility of slip, or free sliding, of the continents along the Moho is thus increased in Phanerozoic time. Continental drift is seen to involve three possible processes: passive rafting, overriding, and free sliding. All three may operate simultaneously to produce the net effect known as drift.