비만아 부모의 돌봄 경험: q 방법론

article i nfo The Lhasa Terrane in southern Tibet has long been accepted as the last geological block accreted to Eurasia before its collision with the northward drifting Indian continent in the Cenozoic, but its lithospheric architecture, drift and growth histories and the nature of its northern suture with Eurasia via the Qiangtang Terrane remain enigmatic. Using zircon in situ U-Pb and Lu-Hf isotopic and bulk-rock geochemical data of Mesozoic-Early Tertiary magmatic rocks sampled along four north-south traverses across the Lhasa Terrane, we show that the Lhasa Terrane has ancient basement rocks of Proterozoic and Archean ages (up to 2870 Ma) in its centre with younger and juvenile crust (Phanerozoic) accreted towards its both northern and southern edges. This finding proves that the central Lhasa subterrane was once a microcontinent. This continent has survived from its long journey across the Paleo-Tethyan Ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the Qiangtang Terrane to the north and with the Indian continent to the south. Zircon Hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks (e.g., ~50-90%, 0-70%, and 30-100% to the Mesozoic magmatism in the southern, central, and northern Lhasa subterranes, respectively). We suggest that much of the Mesozoic magmatism in the Lhasa Terrane may be associated with the southward Bangong-Nujiang Tethyan seafloor subduction beneath the Lhasa Terrane, which likely began in the Middle Permian (or earlier) and ceased in the late Early Cretaceous, and that the significant changes of zircon eHf(t) at ~113 and ~52 Ma record tectonomagmatic activities as a result of slab break-off and related mantle melting events following the Qiangtang-Lhasa amalgamation and India-Lhasa amalgamation, respectively. These results manifest the efficacy of zircons as a chronometer (U-Pb dating) and a geochemical tracer (Hf isotopes) in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics.

The Lhasa Terrane: Record of a microcontinent and its histories of drift and growth

Frequency-dependent crustal attenuation (1/ Q ) is determined for seven distinct physiographic/tectonic regions of the continental United States using high-quality Lg waveforms recorded on broadband stations in the frequency band 0.5 to 16 Hz. Lg attenuation is determined from time-domain amplitude measurements in one-octave frequency bands centered on the frequencies 0.75, 1.0, 3.0, 6.0, and 12.0 Hz. Modeling errors are determined using a delete-j jackknife resampling technique. The frequency-dependent quality factor is modeled in the form of Q = Q 0 f η. Regions were initially selected based on tectonic provinces but were eventually limited and adjusted to maximize ray path coverage in each area. Earthquake data was recorded on several different networks and constrained to events occurring within the crust ( m b 3.5 in size. A singular value decomposition inversion technique was applied to the data to simultaneously solve for source and receiver terms along with Q for each region at specific frequencies. The lowest crustal Q was observed in northern and southern California where Q is described by the functions Q = 152(±37) f 0.72(±0.16) and Q = 105(±26) f 0.67(±0.16) , respectively. The Basin and Range Province, Pacific Northwest, and Rocky Mountain states also display lower Q and a strong frequency dependence characterized by the functions Q = 200(±40) f 0.68(±0.12) , Q = 152(±49) f 0.76(±0.18) , and Q = 166(±37) f 0.61(±0.14) , respectively. In contrast, in the central and northeast United States Q functions are Q = 640(±225) f 0.344(±0.22) and Q = 650(±143) f 0.36(±0.14) , respectively, show a high crustal Q and a weaker frequency dependence. These results improve upon previous Lg modeling by subdividing the United States into smaller, distinct tectonic regions and using significantly more data that provide improved constraints on frequency-dependent attenuation and errors. A detailed attenuation map of the continental United States can provide significant input into hazard map mitigation. Both scattering and intrinsic attenuation mechanisms are likely to play a comparable role in the frequency range considered in the study.

Frequency Dependent Lg Q Within the Continental United States

Coda and Intrinsic Attenuations From Ultrasonic Measurements in Tight Siltstones

Zircon and monazite geochronology from the Rengali-Eastern Ghats Province: Implications for the tectonic evolution of the eastern Indian terrane

Seismic imaging of the deep crustal structure beneath Eastern Ghats Mobile Belt (India): Crustal growth in the context of assembly of Rodinia and Gondwana supercontinents

Lateral variation of crustal attenuation properties from southern Tibet to eastern Nepal Himalaya

Regional variations of coda wave attenuation (

${Q}_{c}^{-1}$
) have been analyzed for western Tibet using single isotropic scattering model A total of 628 local earthquakes, having a source-receiver distance less than 200 km recorded at the Y2 network of broadband stations during 2007–2011, are used for this analysis All the events are crustal having maximum hypocentral depth up to 40 km The estimation of 

${Q}_{c}^{-1}$
 is made at five different frequencies centered at 15, 3, 6, 12, and 18 Hz through lapse time windows from 30 to 70 s with an increment of 10 s starting at 12 times of secondary wave arrival time We find a strong frequency-dependent nature of 

${Q}_{c}^{-1}$
 in this region, which may demonstrate that the medium is highly heterogeneous and tectonically very active The regional variations of 

${Q}_{c}^{-1}$
 across the whole region have been performed, and we find a marked contrast across the Karakoram fault (KKF) at different frequencies and lapse time windows, which are consistent with the geotectonic diversity of the region 

${Q}_{0c}^{-1} ({Q}_{c}^{-1} \text {at 1 Hz})$
 and frequency-dependent parameter (nc) for each station are also estimated using the power law relation 

${Q}_{c}^{-1} = {Q}_{0c}^{-1} f^{-n_{c}}$
 There is a tendency to increase nc with increasing observed 

${Q}_{0c}^{-1}$
 values, and vice versa Variations of 

${Q}_{0c}^{-1}$
 at different lapse time windows and its corresponding apparent depths are also examined We have observed a certain rise in 

${Q}_{0c}^{-1}$
 values at a 60-s lapse time window which may be due to the change in velocities, temperature, rock composition variations, and strong heterogeneity in the lithospheric mantle The obtained values in this study are also found to be well compared with other results reported globally

An investigation of regional variations of coda wave attenuation in western Tibet

PgQ model for Nepal Himalaya

Relative role of intrinsic and scattering attenuation beneath the Andaman Islands, India and tectonic implications

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