Updating z data on a surface_plot in Matplotlib animation

I am looking to create an animation in a surface plot. The animation has fixed x and y data (1 to 64 in each dimension), and reads through an np array for the z information. An outline of the code is like so:

import numpy as np
import matplotlib.pyplot as plt 
import matplotlib.animation as animation

def update_plot(frame_number, zarray, plot):
    #plot.set_3d_properties(zarray[:,:,frame_number])
    ax.collections.clear()
    plot = ax.plot_surface(x, y, zarray[:,:,frame_number], color='0.75')

fig = plt.figure()
ax = plt.add_subplot(111, projection='3d')

N = 64
x = np.arange(N+1)
y = np.arange(N+1)
x, y = np.meshgrid(x, y)
zarray = np.zeros((N+1, N+1, nmax+1))

for i in range(nmax):
  #Generate the data in array z
  #store data into zarray
  #zarray[:,:,i] = np.copy(z)

plot = ax.plot_surface(x, y, zarray[:,:,0], color='0.75')

animate = animation.FuncAnimation(fig, update_plot, 25, fargs=(zarray, plot))
plt.show()

So the code generates the z data and updates the plot in FuncAnimation. This is very slow however, I suspect it is due to the plot being redrawn every loop.

I tried the function

ax.set_3d_properties(zarray[:,:,frame_number])

but it comes up with an error

AttributeError: 'Axes3DSubplot' object has no attribute 'set_3d_properties'

How can I update the data in only the z direction without redrawing the whole plot? (Or otherwise increase the framerate of the graphing procedure)