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297     SON  ‘eae                    TN  Say   LN   =   43         gravity   g   he   :   sme   ae   fl   with   h   eis  (J),  cour  -  ee  . i : ce via   =  low   es   .   se   .   —   :   be   to   may   at  region


      Studies   5)  45°  North  Magnetic  Latitude(]  =  +45°*)   =i”   F,   @)  Magnetic South  Pole  (1  =  -90°)   wn?  dy  0      Bt      Fao f   nites      latitude,  the  At  each  d   es  sea   is a centr:   is   AF.   eos   the   than   a  Bo   to   ne   ek   ae   thus   can   the direction   studies   the   of

      Paleomagnetic                         q     ta    wed        é  latitudes.   ic   with   ly  the  anomaly   de), i  magnitude  magnetization  field  opposes  the  soi  30,000  nT  leads  to  low  amplitude   (ferromagnetic)   when hotter   according  increases   strong   their   most   for   magnetic   to   onerne   600°C.   about  information   Paleomagnetic   latitude   the







                             ~                                     the  same  body,  at  different  magnetic   i   For  the  ae   same.   (a  an   poles   high  induces   induced   strong   properties   temperature   lose   rocks   600°C   (~   bottom  shallow   magnetic   of   about   reach   records   lithified.   rock   suggest  perhaps
                        c¢)  Magnetic Equator  (1  =  0°)          magnetic  anomalies  from   i   the   is   (Ap)  body  of  density  contrast   and  south   north   i  magnetic   the   60,000  nT)   *   (F,,,,   field  magnetic  equator  (c),  the   the  magnetic  anomalies  (Fig.  9.11b);  Fy»  ~   AF.  intermediate  amplitude   exhibit   that  Minerals   (paramagnetic)  weaker   depth,  increasing   depth,   Curie   the   than  Deeper   temperature   Curie   the  beyond   a   hav













           a)  Magnetic  North  Pole  (1  «  +90°)   Fe   t+   ‘ene   o                      id   i   tie   tose   ine  Somat   varies.  At   i   AF)   i   ambient  tain  ee  es  =  magnetic  anomalies  (AF).  At  pe aie  body,  leading  to  negative   the  the  anomaly  is  asymmetric,  with   and  d)   Depth   Curie   have  temperatures   With  temperature.   gradient.   mal   up   heat   they   geothermal   high   colder   to  pared   the   map   to   PALEOMAGNETIC   remanent   Th








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           is   north   (The   is   cut-   lines,   is   air-   local   field   com-   esti-   and   the   of   in   in   of
           Fyn,»  AF   profile   field   airplane   Unlike   predictable)   an   direction,   the   fotal   coverage   distrib-   to   anomalies   given   a   Earth;   amplitude   remanent   If   effect may   materi-   those   Igneous   magnetization   opposite   rec-   are   Potential   high   and   and   anom-   results   com-   source   anomalies   because   and 8.31).  The   the pat-   areas


           to   magnetic   different.   magnetic   direction,   of  data.   behind   the   of   the   more   the   analogous   magnitude   at   the   on   and   that   field.   net   purposes.   mapping   with   bodies.   domes   density   gravity   magnetic   which   are   main   points,   studying   amplitudes,  short   in  9.14a);
           opposite   the   at   quite   of  the   south-north   induced   surface,  an   amounts   small,   towed   not   but   knowledge   determine   commonly   adequate   surveying.   interpret   in   the   magnetic   of   buried   anywhere   form   too,   ambient   their   modeling   for   contrast   intrusive   high   weak   field   material.   high   pronounced   subdued   content   rocks,   the   magnetic   8.28   by   (Fig.   9.14b).   (Fig.


           component   observed   thus   are   direction   in   a   would  parallel   the   on   large   relatively   can   be   (F),   with   to   are   dependence,   gravity   be   to   used   subsurface,   Changes   forms   anomaly,  mass   anomaly   vary   in   noted,   be   the   by   direction,   for   useful   tool   that   of   inducing   a   intrusions,  salt   velocity   9.13);   the   produce   and   dome.   mineral   basement   are   thus   gradients   for   observation



           a   9.11b)   running   undertaken   to  record   (or   no   magnitude   along   sufficient   anomalies   to   can   the   in   the   however,   should   induced   same   susceptibility   a   is   magnetizations   types   inducing   igneous   high   (Fig.   salt   ferromagnetic   deposits,   surface   for   magnetic   are
           has   anomalies   (Fig.   the   profiles   profile).   with   magnetometer   direction   data.   make   same   gravity   that   the   between   magnetite,   as   will   minimum   and   estimated,   shallow
           F,,4            and   the   is   compared   anomalies   (Ax)   It   in   Magnetics   behavior,   Like   features   low-susceptibility   Crystalline   the   examples   high   anomalies
      ‘    where   equator   because   profile   anomaly   are   areas   platform   measure   measurement,   (Fim)   magnetic   and   contrasts   gravity   however,   anomalies.  The   same   body,   9.12).   than   are   equivalent   of   9.8a).   experiments   intrusion   gravity   High   sedimentary   Amplitudes   from   be   with   Suggest
      Interpretation   areas   In   magnetic  body,   magnetic   complicated,   a  assumes   East-west  lines.   field   surveys  magnetic   large   require   a   precession   That   field  ambient   while   latitude   their   attain   to   magnetic   from  (Ap)   field,   the   the   same   (Fig.  latitude   stronger   magnetizations   an   Bodies   remanent   or   distinguishing   amounts   diamagnetic   (Fig.   refraction   two   the   igneous   a   to   low-density,   Basement





      Magnetic   positive.   the   same   the   and   more   9.11b   Fig.   field   different   total   some   cover   to   which   proton  aeromagnetic  surveys   magnetic field.   Earth’s   (AF).  Thus,   to   due   generally  easier   of  modeling   susceptibility   contrasts   ambient   than  gravity   essentially   anomalies  from   magnetic   often   much   induced   by  choosing   of  Magnetic   susceptibilities   rocks,  and   for   large   exhibits   field  ambient   seismic


          (AF)   is   For   9.11a)   even   induced   a   means   surveys,   standard   of   anomaly   interpret   magnetic   density   Earth’s   intuitive   produce   is   and   have   Salt   the   can   anomalies,   to   mafic   anomalies   the   is   and   basement
      9         is   important.   across   in   Although   a   Such   total   is   Forward   of   will   to   incorporated   Mapping   have   often   9.1).   to   from   magnetic  susceptibility   resulting   of   more   as   force   the   magnetic
      Chapter   anomaly   negative.   pole   (Fig.   problem   also   ting   resulting   an  effective   gravity   motions,   plane.   the   magnitude   magnetic   plex   to   area   of  an   of  ution   mating   direction   less   far   depth,   magnetic   according   magnetization   remanent   that   Surrounding   rocks   (Table   direction   ognized   studies   field   magnetic   alies   Depth   levels   monly   magnetic   decrease   magnetic   depth   to   of   wavelengths,   the


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