MarginTotal:

The current allocated margin of all open trades of the strategy, calculated through MarginCost under the assumption of a constant margin requirement of open trades. This can be different in live trading when brokers adapt the margin requirement to the market situation or asset price. A margin call is simulated in test and training mode when Capital > 0 and Equity - MarginTotal reaches zero.

MarginVal:

The current allocated margin of the account. The account is threatened by a margin call when Equity - MarginVal approaches zero. In live trading, this parameter is updated from the broker API if available; in test and training it follows MarginTotal.

P.S. both definitions of the variables can be found in the Zorro manual