Liu W.,Wuhan University |
Liu W.,Huazhong Tecnomechanical Research Center |
Zeng Z.X.,Wuhan University |
Zeng Z.X.,Huazhong Tecnomechanical Research Center |
And 9 more authors.
Acta Petrologica Sinica | Year: 2014
The Yangmingshan granite intrusions from Hunan are located at the junction area between the Yangtze block and Cathaysia block. They consist of Baiguoshi-Tuao biotite (muscovite) monzonitic granites, Yangmingshan two-mica monzonitic granites, Dajiangbei tourmaline muscovite monzonitic granites, Dayuanli biotite syenogranite granites, and LA-ICPMS zircon U-Pb dating show that 228. 6 ± 1. 4Ma and 205 ± 1. 8Ma, 229. 0 ± 2. OMa and 221. 8 ± 1. 3Ma, 218. 2 ± 2. OMa, 217. 8 ± 1. 6Ma, respectively. In conjuction with our field invest tigations, Yangmingshan granite inferred that there may be four-episode magma activities: ∼229Ma, ∼221Ma, ∼217Ma, ∼205Ma. The granites are characterized by high alkali (average 8. 55%), Al2O3 (average 14. 47%) and P2O5 (average 0. 25%) and low SiO2 (average 71. 74%), TFe2O3 (average 0. 92%), MgO (average 0. 19%). A/CNK varies from 0. 97% to 1. 30%, mostly > 1, belongs to high-K calc-alkaline and peraluminous series. They have LREE enrichments relative to HREE, and evidently Eu negative anomalies. In the spider diagram,they show enrichments in LILE (U, Th, K and Pb) and marked depletions in HFSE (Ti and Nb), Ba and Sr. These observations are characteristics of S-type granite and were regarded as a complex rock-mass resulted from repeated pulsating intrusion of magma from the same origin. Their zircons have negative εHf(t) values (-12 ∼ -5) and two-stages model ages (1. 28 ∼ 1. 60Ga), suggesting that the Yangmingshan granites were formed by partial melting of old crust. Combined zircon U-Pb dating and regional tectonic setting, we think that the Yangmingshan intrusions were formed by the decompression melting of Mesoproterozoic metamorphic mudstone in the environment of partial extension-thinning of the thicken lower crust, and the magma then suffered fractional, crystallization, when the Indosinian movement transformed from squeezing tectonic to extension tectonic. Their formation temperatures are 850 ∼ 875°C and pressures are 7 × 108 ∼ 10 × 108 Pa, corresponding at 26 ∼ 30km.
Zheng W.,Huazhong University of Science and Technology |
Zheng W.,Huazhong Tecnomechanical Research Center
Earth Science Frontiers | Year: 2013
In this paper, we use non-linear dynamic Finite Element Method (FEM)to obtain a simulation seismogram. Here, the dynamic FEM is a time-related simulation. Thus, dynanic FEM is quite different from the traditional FEM, and also different from the pseudo-dynamic simulation that is a set of static simulations at a series of time. Contrastingly, dynamic FEM takes every element's (node's) acceleration and its inertia into consideration. On the basis of theoretical seismogram, we proposed the concept of the simulation seismogram. Using non-linear dynamic FEM we got the simulated seismogram of a FEM model. With inversion steps and by comparing the simulation seismogram and the real seismogram, we approached the physics of the earth media and the physics of the focus of an earthquake. As an example, taking the Yanshan fault zone, Taihangshan Mountain Front fault zone, and Tan-Lu fault zone into consideration for the modeling, we built the FEM model for the crust of the north and middle of China. In addition, the model takes the coastline into consideration and the bottom of the crust is set to be the non-reflection boundary, which is equal to an infinitely continued media. When running the model, we applied an explosive load on the element where geographically matches to Tangshan City. As the model was running, we got three time-courses of stress at the elements matching to Lanzhou, Xi'an, and Shanghai Station, respectively. These time courses of stress are the simulated seismograms. By practicing the inversion methodology, we adjusted the physical parameters of the model. Compared to the theoretical seismogram, the simulation seismogram is more close to the physical reality.