ListContourPlot table problems

I have a table of the form

xrange={0.1,1,0.05}
yrange={3000,15000,100}
tab1=Table[{x,y,z[x][y]},{x,xrange},{y,yrange}]

where z[x][y] comes from previous calculation and is a set of numerical values. I would like to do a contour plot, but using the code:

ListContourplot[tab1]

I obtain a white figure. Do you have any suggestions?

Thank you

z[x_][y_] = x + y
xrange = {0.1, 1, 0.05}
yrange = {3000, 15000, 100}
tab1 = Table[{x, y, z[x][y]}, {x, xrange}, {y, yrange}]
ListContourPlot[Flatten[tab1, 1]]