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A study was conducted to determine the applicability of apatite fission track data on the study of the magnitude and timing of synorogenic and postorogenic denudation along folds and thrust belts. Results showed that the erosion of the orogen may have functioned as the main mechanism for the flexural isostatic unloading of the foreland crust. Mild reheating of the samples after the pre-Cretaceous cooling period was discovered.

Geochemical and isotopic studies of the Cretaceous (106 Ma) Prairie Creek olivine lamproites in southwestern Arkansas indicate that these diamond-bearing ultrapotassic magmas were derived from metasomatized Proterozoic subcontinental lithospheric mantle. Re-Os isotopic data yield a nonradiogenic initial [[Gamma].sub.Os] = -3.2 to -3.6 (percent deviation in 187Os/188Os from chondritic mantle) and mantle model ages ([T.sub.MA]) of 0.9 to 1.2 Ga. Sm-Nd isotopic data yield a nonradiogenic initial [[Epsilon].sub.Nd] = -10 and a depleted mantle model age ([T.sub.DM) of 1.2 Ga. These data are consistent with initial stabilization of low-density lithospheric mantle at [approximately] 1.2 Ga, followed closely in time by reenrichment in incompatible trace elements. This Middle Proterozoic lithospheric mantle source is younger than overlying Early Proterozoic crust of the southern U.S. midcontinent. Pre-Grenville subduction of oceanic lithosphere may have juxtaposed 1.2 Ga mantle beneath 1.6 to 2.0 Ga crust and imparted the necessary slab-derived chemical components for the growth of diamonds.

Observations of crystal growth in supersaturated KH2PO4 solutions indicate that it duplicates natural crystallization processes and formation of fluid inclusions in free liquids similar to vein formation or igneous systems. Continuous crystal growth by surface nucleation results in elongate fluid inclusions forming as hollow tubes within kinked growth steps. Large, flat fluid inclusions also form either by sealing of etch pits and other surface irregularities or along cracks propagated by crystal growth. Microscopic observation of real-time crystal growth documents the formation of fluid inclusions along a surface or within a plane, inclusions that would otherwise be identified as secondary. These primary fluid inclusions resemble pseudosecondary inclusions or secondary 'necked-down' inclusions commonly observed in geologic samples. Furthermore, these fluid inclusions, and many or most in natural samples, are not generated by spiral growth processes. This simple analogue experiment serves as a model for crystal growth and fluid-inclusion entrapment in hydrothermal and igneous systems.

Subduction followed by underthrusting of continental lithosphere, driven by Oligocene-Early Miocene spreading in the South China Sea marginal basin, account for the tectonic features of Sabah. Isostatic rebound then caused Late Miocene uplift of the Western Cordillera. The strata were buried under 4-8 km of overburden then rapidly exhumed and cooled at [is greater than] 10 [degrees] C [Ma.sup.-1]. A rate of exhumation of 0.5-0.7 mm [a.sup.-1] is deduced from thermochronology. The same order of uplift in the Labuk Highlands has exposed metamorphic rocks of the epidote-glaucophane facies. Rapid erosion of the Western Cordillera supplied abundant clastic sediments to the Miocene-Pliocene Baram Delta oil-bearing basin and to the Eastern Lowlands and Sulu Sea. The Eastern Lowlands were affected by Miocene rifting of the Sulu Sea marginal basin. In contrast to the Western Cordillera, the strata contain apatite crystals whose fission track ages pre-date the containing rocks, indicating burial by only about 2-3 km of overburden. The terrain has been isostatically stable. Some apatite and all zircon crystals, extracted from Tertiary strata, yield Cretaceous fission track provenance ages. Keywords: Sabah Malaysia, orogeny, isostasy, uplift, thermochronology.

The Late Cretaceous Epoch was characterized major global perturbations in the carbon cycle, the most prominent occurring near the Cenomanian-Turonian (CT) transition marked by Oceanic Anoxic Event/OAE-2 at 94.9-93.7 Ma. The Cretaceous Western Interior Seaway (KWIS) was one of several epicontinental seas in which a complex water-mass evolution was recorded in widespread sedimentary successions. This contribution integrates new data on the main components of organic matter, geochemistry, and stable isotopes along a North-South transect from the KWIS to the equatorial western Atlantic and Southern Ocean. In particular, cored sedimentary rocks from the Eagle Ford Group of West Texas (~ 90-98 Ma) demonstrate subtle temporal and spatial variations in paleoenvironmental conditions and provide an important geographic constraint for interpreting water-mass evolution. High latitude (boreal-austral), equatorial tethyan and locally sourced Western Interior Seaway water-masses are distinguished by distinct palynological assemblages and geochemical signatures. The northward migration of a tethyan water-mass into the KWIS occurred during the early-middle Cenomanian (98-95 Ma) followed by a major re-organization during the latest Cenomanian-Turonian (95-94 Ma) as a full connection with a northerly-boreal water-mass was established during peak transgression. This oceanographic change promoted de-stratification of the water column and improved oxygenation throughout the KWIS and as far south as the Demerara Rise off Suriname. In addition the recorded decline in redox-sensitive trace metals during the onset of OAE-2 likely reflects a genuine oxygenation event related to open water-mass exchange and may have been complicated by variable contribution of organic matter from different sources (e.g. refractory/terrigenous material), requiring further investigation. [ABSTRACT FROM AUTHOR]

Focuses on the regional erosion surface that provides constraints for interpreting apatite fission track (AFT) data obtained from structures of the Ouachita trend in the south central of the United States. Mechanisms for removing the orogenic load from the underlying foreland crust in foreland/thrust belt systems; Ouachita trend apatite fission track data summary.