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41.
B. K. Davis P. J. Pollard J. H. Lally N. J. McNaughton K. Blake P. J. Williams 《Australian Journal of Earth Sciences》2013,60(1):113-129
Plutons of the Naraku Batholith were emplaced into Proterozoic metasediments of the northern portion of the Eastern Fold Belt of the Mt Isa Inlier during two intrusive episodes approximately 200 million years apart. Structural relationships and geochronological data suggest that the older plutons (ca 1750 Ma) are contemporaneous with granites of the Wonga Batholith to the west. The Dipvale Granodiorite and the Levian Granite represent these older intrusive phases of the Naraku Batholith, and both contain an intense tectonic foliation, S1, which is interpreted to have formed during the north‐south shortening associated with D1 of the Isan Orogeny. The geometry of S1 form surfaces at the southern end of the Dipvale Granodiorite, and of the previously unrecognised sheeted contact, defines a macroscopic, steeply south‐southwest‐plunging antiform, which was produced by the regional D2 of the Isan Orogeny. S1 form surfaces in the Levian Granite define open F2 folds with wavelengths of several hundred metres. The structural age of emplacement of the Dipvale Granodiorite and the Levian Granite is interpreted to be pre‐ or syn‐ the regional D1. An intense foliation present in some of the younger (ca 1505 Ma) granites that comprise the bulk of the Naraku Batholith is interpreted to represent S3 of the Isan Orogeny. Foliations commonly have similar styles and orientations in both the pre‐D1 and younger plutons. This emphasises the simplicity with which regional fabrics can be, and probably have been, miscorrelated in the Eastern Fold Belt, and that the classification of granites in general on the basis of structural and geometric criteria alone is fraught with danger. 相似文献
42.
John N. Christensen Jane Selverstone John L. Rosenfeld Donald J. DePaolo 《Contributions to Mineralogy and Petrology》1994,118(1):1-12
In order to evaluate rates of tectonometamorphic processes, growth rates of garnets from metamorphic rocks of the Tauern Window, Eastern Alps were measured using Rb-Sr isotopes. The garnet growth rates were determined from Rb-Sr isotopic zonation of single garnet crystals and the Rb-Sr isotopic compositions of their associated rock matrices. Garnets were analyzed from the Upper Schieferhülle (USH) and Lower Schieferhülle, (LSH) within the Tauern Window. Two garnets from the USH grew at rates of 0.67
–0.13
+0.19
mm/million years and 0.88
–0.19
+0.34
mm/million years, respectively, indicating an average growth duration of 5.4±1.7 million years. The duration of growth coupled with the amount of rotation recorded by inclusion trails in the USH garnets yields an average shear-strain rate during garnet growth of 2.7
–0.7
+1.2
×10-14 s-1. Garnet growth in the sample from the USH occurred between 35.4±0.6 and 30±0.8 Ma. The garnet from the LSH grew at a rate of 0.23±0.015 mm/million years between 62±1.5 Ma and 30.2±1.5 Ma. Contemporaneous cessation of garnet growth in both units at 30 Ma is in accord with previous dating of the thermal peak of metamorphism in the Tauern Window. Correlation with previously published pressure-temperature paths for garnets from the USH and LSH yields approximate rates of burial, exhumation and heating during garnet growth. Assuming that theseP — T paths are applicable to the garnets in this study, the contemporaneous exhumation rates recorded by garnet in the USH and LSH were approximately 4
–2
+3
mm/year and 2±1 mm/year, respectively. 相似文献
43.
We have imaged several known molecular (CO) outflows in H2 v=1-0 S(1) and wide-band K in order to identify the molecular shocks associated with the acceleration of ambient gas by outflows from young stars. We detected H2 line emission in all the flows we observed: L 1157, VLA 1623, NGC 6334I, NGC 2264G, L 1641N and Haro 4-255. A comparison of the H2 data with CO outflow maps strongly suggests that prompt entrainment near the head of a collimated jet probably is the dominant mechanism for producing the CO outflows in these sources. 相似文献
44.
Levke Kp Kazuhide Nagashima Andrew M. Davis Alexander N. Krot 《Meteoritics & planetary science》2020,55(3):524-534
NASA's Genesis mission revealed that the Sun is enriched in 16O compared to the Earth and Mars (the Sun's Δ17O, defined as δ17O–0.52×δ18O, is –28.4 ± 3.6‰; McKeegan et al. 2011). Materials as 16O‐rich as the Sun are extremely rare in the meteorite record. Here, we describe a Ca‐Al‐rich inclusion (CAI) from a CM chondrite that is as 16O‐enriched as the Sun (Δ17O = –29.1 ± 0.7‰). This CAI also has large nucleosynthetic anomalies in 48Ca and 50Ti (δ‐values are –8.1 ± 3.3 and –11.7 ± 2.4‰, respectively) and shows no clear evidence for incorporation of live 26Al; (26Al/27Al)0 = (0.03 ± 0.11) × 10–5. Due to their anomalous isotopic characteristics, the rare CAIs consistent with the Genesis value could be among the first materials that formed in the solar system. In contrast to the CAI studied here, the majority of CAIs formed in or interacted with a reservoir characterized by a Δ17O value near –23.5‰. Combined with 26Al‐26Mg systematics, the oxygen isotopic compositions of FUN (fractionation and unidentified nuclear effects), UN, and normal CAIs suggest that nebular conditions were favorable for solids to inherit this value for an extended period of time. Many later‐formed materials, such as chondrules, planetesimals, and terrestrial planets, formed in reservoirs with Δ17O near 0‰. The distribution could be easier to explain if the common CAI value of –23.5‰, which is consistent with the Genesis value within 3σ, represented the average composition of the protoplanetary disk. 相似文献
45.
C. R. Purcell R. Balasubramanyam M. G. Burton A. J. Walsh V. Minier M. R. Hunt-Cunningham L. L. Kedziora-Chudczer S. N. Longmore T. Hill I. Bains P. J. Barnes A. L. Busfield P. Calisse N. H. M. Crighton S. J. Curran T. M. Davis J. T. Dempsey G. Derragopian B. Fulton M. G. Hidas M. G. Hoare J.-K. Lee E. F. Ladd S. L. Lumsden T. J. T. Moore M. T. Murphy R. D. Oudmaijer M. B. Pracy J. Rathborne S. Robertson A. S. B. Schultz J. Shobbrook P. A. Sparks J. Storey T. Travouillion 《Monthly notices of the Royal Astronomical Society》2006,367(2):553-576
46.
Patterns and controls of surface sediment distribution: west-central Florida inner shelf 总被引:2,自引:0,他引:2
Gregg R. Brooks Larry J. Doyle Richard A. Davis Nancy T. DeWitt Beau C. Suthard 《Marine Geology》2003,200(1-4):307-324
The west-central Florida inner shelf represents a transition between the quartz-dominated barrier-island system and the carbonate-dominated mid-outer shelf. Surface sediments exhibit a complex distribution pattern that can be attributed to multiple sediment sources and the ineffectiveness of physical processes for large-scale sediment redistribution. The west Florida shelf is the submerged extension of the Florida carbonate platform, consisting of a limestone karst surface veneered with a thin unconsolidated sediment cover. A total of 498 surface sediment samples were collected on the inner shelf and analyzed for texture and composition. Results show that sediment consists of a combination of fine quartz sand and coarse, biogenic carbonate sand and gravel, with variable but subordinate amounts of black, phosphorite-rich sand. The carbonate component consists primarily of molluskan fragments. The distribution is patchy and discontinuous with no discernible pattern, and the transition between sediment types is generally abrupt. Quartz-rich sediment dominates the inner 15 km north of the entrance into Tampa Bay, but south of the Bay is common only along the inner 3 km. Elsewhere, carbonate-rich sediment is the predominate sediment type, except where there is little sediment cover, in which cases black, phosphorite-rich sand dominates. Sediment sources are likely within, or around the periphery of the basin. Fine quartz sand is likely reworked from coastal units deposited during Pleistocene sea-level high stands. Carbonate sand and gravel is produced by marine organisms within the depositional basin. The black, phosphorite-rich sand likely originates from the bioerosion and reworking of the underlying strata that irregularly crop out within the study area. The distribution pattern contains elements of both storm- and tide-dominated siliciclastic shelves, but it is dictated primarily by the sediment source, similar to some carbonate systems. Other systems with similar sediment attributes include cool-water carbonate, sediment-starved, and mixed carbonate/siliciclastic systems. This study suggests a possible genetic link among the three systems. 相似文献
47.
48.
49.
50.
Emily I. Curtis John S. Richer Jane V. Buckle 《Monthly notices of the Royal Astronomical Society》2010,401(1):455-472
We present submillimetre observations of the J = 3 → 2 rotational transition of 12 CO, 13 CO and C18 O across over 600 arcmin2 of the Perseus molecular cloud, undertaken with the Heterodyne Array Receiver Programme (HARP), a new array spectrograph on the James Clerk Maxwell Telescope. The data encompass four regions of the cloud, containing the largest clusters of dust continuum condensations: NGC 1333, IC348, L1448 and L1455. A new procedure to remove striping artefacts from the raw HARP data is introduced. We compare the maps to those of the dust continuum emission mapped with the Submillimetre Common-User Bolometer Array (SCUBA; Hatchell et al.) and the positions of starless and protostellar cores (Hatchell et al.). No straightforward correlation is found between the masses of each region derived from the HARP CO and SCUBA data, underlining the care that must be exercised when comparing masses of the same object derived from different tracers. From the 13 CO/C18 O line ratio the relative abundance of the two species ([13 CO]/[C18 O]∼ 7) and their opacities (typically τ is 0.02–0.22 and 0.15–1.52 for the C18 O and 13 CO gas, respectively) are calculated. C18 O is optically thin nearly everywhere, increasing in opacity towards star-forming cores but not beyond τ18 ∼ 0.9 . Assuming the 12 CO gas is optically thick, we compute its excitation temperature, T ex (around 8–30 K), which has little correlation with estimates of the dust temperature. 相似文献