| Paleomagnetism plays a key role in understanding of the Oroclinal arcs,however there exist a big difference among differenct researches in Lanping-Simao and Antarctic peninsula arcs.In this article,we combine the new paleomagnetic data and Isotopic Chronology,Rock Magnetism,magnetic fabric and Petrography to study the deformation behavior of these two areas.We first studied the Cretaceous,Paleogene,and Miocene sandstones in the Jinggu area of Simao Basin in western Yunnan,southwestern China to constrain the internal deformation of the Lanping-S imao Terrane.The primary magnetization components were isolated from samples obtained in the Jinggu area.The tilt corrected site-mean direction of the middle Cretaceous rocks in the Jinggu area was Ds=77.0°,Is=43.0°,ks=54 with ?95=2.9°.For the Miocene strata,the tilt-corrected site-mean direction for the HTC was Ds=13.9°,Is=35.5°,ks=50.7 with ?95=3.3°.The best-fit linear regression between the rotation degree and regional tectonic lines indicate a direct relationship between tectonic rotation and formation of the CLCMB.Paleomagnetic data confirm that about 70° of clockwise rotation has occurred in the Jinggu area since the late Eocene.The overall amount of rotation can be separated into three different parts.First,the Jinggu area experienced about 20° of clockwise rotation together with Indochina at 36-21 Ma.Then,accompanied by the aforementioned 20° clockwise rotation and extrusion of the Shan-Thai and Indochina Block along the JSRF,the Jinggu area experienced a further 35°(approximately)of clockwise rotation as part of the thrusting process from west-east thrust faults within the CLCMB between 27 and 15 Ma.The sinusoidal shape of the Lanping-Simao Arc also formed during the thrusting process.Lastly,after the middle Miocene,the Jinggu area experienced a small-scale internal rotation adjustment(ca.15°).Based on a comparison between the tectonic-metamorphic events and paleomagneticallydetermined rotation,we propose that there was a significant compression zone between the NBS and JSRF from about 40 Ma,which was associated with the indention of the Indian plate into Asia.The widespread west to east compressional stress together with the southeastward extrusion of the Baoshan Terrane and the Shan-Thai Block along the GLSZ,CSSZ,and JSRF since 36 Ma in southeast Tibet together formed the Lanping-Simao Arc.Secondly,consider the possibility influence of the Chuandian Fragment to the Simao Basin,we sampled the red sandstones from the Eocene Ninglang formation at Yongsheng area,the northwestern part of the Chuan Dian Fragment(CDF)of the Yangtze block.HTC and ITC were isolated from the Eocene rocks.The tilt corrected site-mean directions of HTC and ITC(Group A and B)are Ds=21.4°,Is=35.8°,ks=154.1 with ?95=6.2°(N=5;HTC);Ds=2.6°,Is=39.5°,ks=108.0 with ?95=2.7°(N=26;ITC of Group A)and Ds=22.0°,Is=42.7°,ks=179.2 with ?95=2.4°(N=21;ITC of Group B),with the positive fold tests indicating that the HTC and ITC were acquired before folding.ITC and HTC of Group A are.the CRMs and mostly acquired through carbonation process and the magnetic carriers are authigenic magnetite and authigenic(pigment)hematite.Paleomagnetic data confirm that about 19.5±4.9° of clockwise rotation has occurred in the CDF before?30Ma with the movement of the Ailaoshan-Red River Fault and Ziyun-Luodian Fault.Rotation degree(5.7°)calculated from bending of the Ailaoshan-Red River Fault is almost equally to the paleomagnetic determined rotation(8.3±3.2°)from the Miocene strata within the Simao Basin,which reveals the close relationship between tectonic rotation of Simao Basin and bending of the Ailaoshan-Red River Fault after the Miocene.In order to study the formation process of Antarctic Peninsula Arc,we made the detail studies of paleomagnetism,Isotopic Chronology,Rock Magnetism and magnetic fabric in Byers Peninsula,Livingston Island;Fildes Peninsula,King George Island and Coppermine Peninsula,Robert Island,South Shetland Island.We precisely measured the age of the Jasper Hill Formation-Long Hill Formation in Fildes Peninsula,King George Island;Hannah Point,Livingstone Island and Coppermine Peninsula,Robert Island by 40Ar/39Ar and Paleomagnetic method.We recalculate the paleopoles of Antarctic Peninsula of?110Ma,85Ma and 50Ma,after compare with the East Antarctic,we find no apparent difference between these two areas and the Antarctic Peninsula Arc in the north part at least formed before 110Ma.Combine with the South America plate,we reconstruct the relative position between the Antarctic Peninsula and South America plate.Paleomagnetic results show that the Antarctic Peninsula experienced a southward movement during 110-85Ma and clockwise/anticlockwise rotation during 85-54Ma/after 50Ma.The South America experienced a southward movement and clockwise rotation during 110-54Ma.Northward movement after about 50Ma led the separation between Antarctic Peninsula and South America plate.However,the magnetic anomalies reconstruction show the Antarctic Peninsula experienced clockwise rotation since 110Ma.Consider of the low relative certainty of magnetic seafloor anomalies,we prefer use the paleomagnetic data.In the future,more and more reliable and accurate paleomagnetic and magnetic seafloor anomalies data can help us to better constrain the paleo-position and internal deformation process of Antarctic Peninsula.In this thesis,we solved the controversy among different researches in Lanping-Simao basin by using the paleomagnetism,sedimentology,geochronology,rock magnetism,magnetic fabric and Petrography method,provide a perspective to study other oroclinal arcs around the world,however,because of the lack of paleomagnetic data in south Antarctic,we only proved that no relative rotation occured after 110Ma in the northern part of Orville Coast. |
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