87Rb-87Sr chronology of enstatite meteorites

摘要: A87Rb-87Sr analysis of some enstatite meteorites has been made. Whole rocks plot on an isochron age 4.508 ± 0.037b.y. and strontium initial ratio 0.69880 0.00044 (2σ errors; λ87Rb= 1.42 × 10−11yr−1) . If the Norton County results are joined, we get 4.516 0.029b.y. 0.69874 0.00022. This result is indistinguishable from whole rock for H chondrites. It interpreted as condensation solar nebula. The identity the87Sr/86Sr with ones Allende white inclusions shows that this was homogeneous in nebula, Rb-Sr fractionations observed between different chondrite groups appeared only shortly before or during accretion. Internal studies type-I chondrites Abee Indarch intermediate-type Saint Mark's Sauveur have done. Abee data scatter the87Rb-87Sr diagram. For Indarch, Sauveur, obtained well-defined straight lines “age” (T) “initial ratio” (I): Indarch,T = 4.393 0.043b.y.I 0.7005 0.0009; Mark's,T 4.335 0.050b.y.I 0.69979 0.00022; Sauveur,T 4.457 0.047b.y.I 0.6993 0.0014. Our agrees former Gopalan Wetherill [5]. A careful examination these neither due to leaching effects by heavy liquids, nor terrestrial weathering. “isochrons” can be mixing feldspar. terms cosmochemical secondary effects: shocked 60–200 m.y. after their formation. idea early generalized bombardment inner system; also indicates were rather situated outershells parent body might at origin I-Xe ages meteorites. Whole Bishopville, Cumberland Falls Mayo Belwa analysed. In three aubrites, system perturbed. Bishopsville sample not fresh makes significance our uncertain. probably suffered relatively recent shocks open-system redistribution Rb Sr.